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**Report of the**

**Jefferson Laboratory**

**Program Advisory Committee**

**PAC 28**

#### Meeting of August 23-26, 2005

**Letter from the Director**

September 1, 2005

Members of the Jefferson Lab User Group,

A great deal has happened to position Jefferson Lab and its unique
scientific programs for the future since the last PAC meeting, the most
notable of which is the DOE Independent Project Review of the 12 GeV
Upgrade Project in July. The Review had no findings and stated that the
project was ready for CD-1approval, the next milestone. This is a very
important step for the project team and for Jefferson Lab's users who
have been working toward the 12 Gev Upgrade for many years.

This Program Advisory Committee reviewed 15 proposals and 3 letters of
intent. Of these, 7 were approved, 2 were conditionally approved, 3 were
deferred with regret, and 3 were deferred. The PAC continues its
tradition of high standards for approved beam time and does its part to
ensure that Jefferson Lab remains focused on doing the very best
science. Peer review, such as that done by the PAC, is critically
important in establishing a research program of forefront, compelling
science. I want to commend the 28^th^ PAC particularly for their
"activist" engagement and useful voice on how to maximize scientific
return within our constrained circumstances.

Serving on the PAC is both an honor and a responsibility, and we are
fortunate that we have four new members, Barbara Badelek, Naomi Makins,
David Bowman and Gordon Cates, to replace those PAC members who have
completed their terms and are rotating off. I want to thank Nicola
Bianchi, T. William Donnelly, Eddy Jans, and Peter Kroll for their work
and dedication as part of the PAC and wish them continued success in
their research.

Sincerely,

![](media/image1.jpeg){width="2.3069444444444445in"
height="0.8013888888888889in"}

Christoph W. Leemann

Director, Jefferson Lab

**Letter from the PAC Chairman**

# 

# Introduction

> The Jefferson Laboratory Program Advisory Committee held its 28th
> meeting on August 23 - 26, 2005. The membership of the Committee is
> given in Appendix A. In response to the charge (Appendix B) from the
> JLab Director, Dr. Christoph Leemann, the Committee reviewed and made
> recommendations concerning the fifteen proposals and three letters of
> intent submitted by JLab users.
>
> **General Overview**
>
> The meeting was stimulating in terms of the discussions of new physics
> results which emerged from recent JLab measurements and the plans for
> new measurements proposed for the physics research program. Impressive
> new data were presented from all Halls. In Hall A, due to an
> appreciable improvement of the overall energy resolution, hypernuclei
> are produced, that will allow us to gain important information on the
> nuclear spin-orbit and spin-spin part of the Λ-N interaction. In Hall
> B two high statistics experiments yield no signals of pentaquarks in
> production channels in which signals were observed previously at JLab
> and abroad. It is remarkable that these experiments have been carried
> out, including data analysis, within 18 months after their approval by
> the PAC. The management demonstrated a high degree of flexibility in
> the process of the beam time scheduling. Studies of the transition
> form factor of the Roper resonance provide precise data that
> discriminate between various model calculations of the nucleon. By
> measuring the x~B~-dependence up to x~B~ = 2.8 for ^4^He, ^12^C and
> ^56^Fe, remarkable signals have been observed providing the first ever
> hints for three- nucleon short-range correlations in inclusive
> experiments. In Hall C the results of the G0 forward angle
> measurements were presented. They, certainly, provide interesting
> information in the quest to determine the strange quark contribution
> to the proton form factor.
>
> The PAC is also very pleased to see the progress made by the Lab
> toward the JLab 12 GeV-upgrade. CD-0 has been reached in March 2004
> and all CD-1 prerequisites were met with formal CD-1 expected in fall
> 2005.
>
> The overall JLab program continues to show solid growth; prior to PAC
> 28 it included 155 approved experiments. To date, 113 experiments have
> been completed at JLab, up by 3 over the last six months. 31 papers
> have been published or submitted to the Physical Review, Physical
> Review Letters and Physics Letters over the past year, in addition to
> over 56 papers published elsewhere. Archival papers dealing with the
> construction of the experimental facilities in the three halls have
> been published. The number of Ph.D. projects completed to date at JLab
> is 210 (up by 18 in the past six months), with an additional 193
> projects in progress.

Turning to accelerator operations, in the second-half year of FY05 there
were 22 weeks of operation with beam availability of 68.3 %. Hall
availability averaged 91% and the multiplicity (the average number of
halls scheduled to take data) was 2.25. The expectation of beam
delivered to experiments on an annual basis is \> 30 weeks.

The physics scope of the proposals presented to PAC28 was again broad.
Two themes, however, dominated the requests for beam time. Five
proposals are part of the program of deeply exclusive and semi-inclusive
experiments to study the nucleon's internal structure at a finer level
and three proposals intend to use parity violating (PV) electron
scattering to study, by elastic and quasielestic scattering, the strange
nucleon form factor and, by inelastic scattering, for the first time the
parity-violating inelastic response of the nucleon in the resonance
region.

Measurements of parity-violating electron scattering from hydrogen
(elastic, both forward and backward angles) and deuterium
(quasi-elastic, backward angles) provide information on the strangeness
content in the nucleon via the form factors G~Es~ and G~Ms~, as well as
on the neutral-current axial-vector form factor G~A~. At present, the
indications are that the strangeness form factors are not consistent
with zero and that G~A~ is modified from naïve expectations. Obtaining
more stringent constraints on these interesting quantities remains a
high-priority goal for studies of hadronic structure.

Experiments in PV inelastic electron scattering covering the resonance
region provide new insights into quark-hadron duality, nucleon
excitations via axial vector current and the modeling of neutrino cross
sections.

Polarized semi-inclusive deep-inelastic scattering (SIDIS) is a powerful
tool to determine the polarized parton distributions. Such experiments
address questions of the flavor asymmetry of the polarized light quark
sea and, indirectly, of the orbital angular momentum of quarks. Deeply
exclusive experiments constrain functions within the formalism of the
General Parton Distributions (GPD).

Three proposals address questions on nuclei via inelastic electron
scattering: First, the (e,e\`p) reaction on ^208^Pb, investigating
issues like spectroscopic factors, long-range correlations and dynamic
relativistic effects, second, a precision measurement of longitudinal
and transverse response functions of quasi-elastic electron scattering
and an extraction of the Coulomb sum rule from the data, and third, the
extension of studies of hypernuclei over a wide mass region.

The quest for a better understanding of the small wave function
components of ^3^He provides the motivation for an experiment
investigating the reaction ^3^He(e,e\`d).

A measurement of the Gerasimov-Drell-Hearn integral at low Q^2^ on the
neutron and the deuteron would extend the data set into the low Q^2^
region for the neutron.

The proposal, Measurement of R=σ~L~/σ~T~ on Deuterium in the Nucleon
Resonance Region, asks for the allocation of remaining beam time of an
ongoing experiment.

The proposal, Low Energy Deuteron Photodisintegration, asks for beam
time in a parasitic mode running concurrently with G0\`s low energy run.
This opens up an opportunity to measure polarization observables, so far
not yet measured.

**Recommendations**

Of the fifteen proposals received, nine experiments were approved, two
of them conditionally. The ratings for these nine proposals were one
with A, seven with A^-^, and one with B^+^. Three experiments have been
deferred with regret.

The PV scattering program on the proton at JLab reached an exciting as
well as a critical phase. Having seen the data from the forward
scattering runs of G0 and faced with a request for 140 days of beam time
in two proposals, the PAC was convinced that an opportunity appears to
have arisen where the JLab program in PV eN scattering can tighten the
constraints on G~Es~, G~Ms~ and G~A~. G0 at backward angles using
hydrogen and deuterium provide G~Ms~ and G~A~, and together with
forward-angle measurements including the tightest constraints from the
measurements proposed in PR05-109, can lead to a much better
determination of G~Es~ as well. However, this requires a coherent
approach from the two collaborations in the two proposals. Accordingly
the PAC recommends that an optimized physics strategy be developed by
the proposers of PR05-108 and PR05-109 for how to achieve these goals.
That common strategy should be reviewed by the PAC. Thus, PR05-108 and
PR05-109 have been approved conditionally.

The PAC approved four experiments in Hall A for a total of 85 days:
PR-05-102, Measurements of A~x~ and A~z~ Asymmetries in the
Quasi-elastic ![](media/image2.wmf)![](media/image3.wmf) Reaction, for
15 days; PR-05-103, Low Energy Deuteron Photodisintegration, for 14
days; PR-05-109, A Measurement of Nucleon Strange Form Factors at High
Q^2^, for 30 days; PR-05-103, which will run parasitically with G0's
low-energy run in summer 2006; and PR-05-110, Precision Measurement of
Longitudinal and Transverse Response Functions of Quasi-Elastic Electron
Scattering in the Momentum Transfer Range 0.55 GeV/c\<q\<0.9GeV/c, for
26 days.

Two experiments have been approved in Hall B for 120 days: PR-05-113,
Semi-Inclusive Pion Production with a Longitudinally Polarized Target at
6 GeV, for 60 days; and PR-05-114, Deeply Virtual Compton Scattering at
6 GeV with Polarized Target and Polarized Beam Using the CLAS Detector,
for 60 days. Both experiments can run concurrently.

Three experiments have been approved in Hall C for a total of 84 days:
PR-05-108, G0 Backward Angle Measurements, for running during the
special 12-week (\~50 PAC days) low-energy running period anticipated
for summer, 2006, PR-05-115, Spectroscopic Investigation of Λ
Hypernuclei in the Wide Mass Region using the (e,e'K^+^) Reaction, for
20 days and PR-05-101, Initial State Helicity Correlation in Wide Angle
Compton Scattering, for 14 days.

The laboratory guidelines provided for the approval of 54 days of beam
time in Hall A, 60 days of beam time in Hall B, and 9 days of beam time
in Hall C. Starting with PAC 24, the formula for these guidelines has
been modified, and is based on three components: 30/30/0 days of new
time to be made available in Halls A/B/C, plus 100%/100%/100% of the
time recovered from approved experiments now required to return to the
PAC due to the jeopardy process, and 0%/0%/50% of the days under target
in the halls. The PAC is allowed to exceed the laboratory guidelines if
it believes the physics has sufficiently high priority, that is at a
rating of A- or better, but the excess would then be deducted from the
allocation of the next PAC meeting.

The jeopardy process continues to evolve at JLab. At this meeting 24
days of approved time in two proposals were under jeopardy status, 15 in
Hall A and 9 in Hall C. The backlog in Hall A is now about 5,2 years,
while the backlog in Hall B is 2.6 years and that of Hall C 4.5 years.
The requests for beam time in Hall A and Hall C at this meeting were far
beyond the allocation. Given so many outstanding proposals the PAC
exceeded the laboratory guidelines in Hall A by 31 days and in Hall C by
25 days. The extra low energy running for G0 and PR-05-103 in summer
2006 has not been taken into account in those numbers.

The proposal reports and the PAC recommendations for the reviewed
proposals and the response to the letter of intent are given in
Appendices D and E. The tables on the following pages summarize the
status of the JLab commitments from PAC 4-PAC 28.

The PAC is very appreciative of the efforts of the Hall leaders and the
Laboratory staff in support of the PAC meeting and review process. The
TAC reports continue to be a very important ingredient in the process of
evaluation of proposals. The comments provided by the theory group help
greatly by putting the proposals in the context of ongoing theoretical
work.

The enthusiastic and thoughtful contributions of Karen Owens and Sue
Ewing were especially effective in making the PAC process proceed
gracefully and with high efficiency.

Berthold Schoch

Chairman, Jefferson Program Advisory Committee

**Tables**

Totals for PAC 4-28

+-------------------+---------------+------------------+-------------+
|                   | ## Experiment | ###              | ###         |
|                   | s Recommended | Experiments Reco |             |
|                   |  for Approval | mmended for Cond | ###         |
|                   |               | itional Approval |             |
|                   |               |                  | ### Totals  |
+-------------------+---------------+------------------+-------------+
| > Experiments     | > 166         | > 6              | > 172       |
+-------------------+---------------+------------------+-------------+
| > Authors         | > 1096        | > 36             | > 1132      |
+-------------------+---------------+------------------+-------------+
| > Institutions    | > 184         | > 3              | > 187       |
+-------------------+---------------+------------------+-------------+
| > Countries       | > 30          |                  | > 30        |
+-------------------+---------------+------------------+-------------+

# **Approved Experiments Totals by Physics Topics**

+----------------------+------------+----------+----------+-----------+
|                      |            |          |          |           |
+----------------------+------------+----------+----------+-----------+
| **Topic**            | #          | **       | **       | ####      |
|                      | ### Number | Hall A** | Hall B** | ## Hall C |
+----------------------+------------+----------+----------+-----------+
| Nucleon and Meson    | 30         | 12       | 6        | 12        |
| Form Factors & Sum   |            |          |          |           |
| Rules                |            |          |          |           |
+----------------------+------------+----------+----------+-----------+
| Few Body Nuclear     | 29         | 18       | 6        | 5         |
| Properties           |            |          |          |           |
+----------------------+------------+----------+----------+-----------+
| Properties of Nuclei | 30         | 8        | 11       | 11        |
+----------------------+------------+----------+----------+-----------+
| N\* and Meson        | 55         | 11       | 33       | 11        |
| Properties           |            |          |          |           |
+----------------------+------------+----------+----------+-----------+
| Strange Quarks       | 22         | 4        | 15       | 3         |
+----------------------+------------+----------+----------+-----------+
| ###### TOTAL         | 166        | 53       | 71       | 42        |
+----------------------+------------+----------+----------+-----------+

##### Approved Days and Conditionally Approved Experiments

<table style="width:100%;">
<colgroup>
<col style="width: 16%" />
<col style="width: 0%" />
<col style="width: 11%" />
<col style="width: 9%" />
<col style="width: 0%" />
<col style="width: 13%" />
<col style="width: 0%" />
<col style="width: 16%" />
<col style="width: 0%" />
<col style="width: 13%" />
<col style="width: 0%" />
<col style="width: 18%" />
</colgroup>
<tbody>
<tr class="odd">
<td></td>
<td colspan="9"><strong>Approved Experiments</strong></td>
<td colspan="2">Conditionally</td>
</tr>
<tr class="even">
<td>Hall</td>
<td colspan="3"><p># Expts</p>
<p>Completed<br />
(full/partial)</p></td>
<td colspan="2">Days Run</td>
<td colspan="2"><p>No. Exps</p>
<p>in Queue</p></td>
<td colspan="2"><p>Days to</p>
<p>be Run</p></td>
<td colspan="2"><p>Approved</p>
<p>Experiments</p></td>
</tr>
<tr class="odd">
<td colspan="2">A</td>
<td>34</td>
<td colspan="2">2</td>
<td colspan="2">623.5</td>
<td colspan="2">21</td>
<td colspan="2">301.4</td>
<td>3</td>
</tr>
<tr class="even">
<td colspan="2">B</td>
<td>55</td>
<td colspan="2">8</td>
<td colspan="2">570.0</td>
<td colspan="2">17</td>
<td colspan="2">248.8</td>
<td>1</td>
</tr>
<tr class="odd">
<td colspan="2">C</td>
<td>26</td>
<td colspan="2">5</td>
<td colspan="2">592.9</td>
<td colspan="2">15</td>
<td colspan="2">254.6</td>
<td>2</td>
</tr>
<tr class="even">
<td colspan="2">Total</td>
<td>113</td>
<td colspan="2">15</td>
<td colspan="2">1786.5</td>
<td colspan="2">53</td>
<td colspan="2">804.7</td>
<td>6</td>
</tr>
</tbody>
</table>

**APPENDICES**

A.  PAC 28 Membership

B.  Charge to PAC 28

C.  PAC 28 Recommendations

D.  PAC 28 Individual Proposal Reports

E.  PAC 28 Individual Letters-of-Intent Reports

F.  Approved Experiments, PACs 4-28, Grouped by Physics Category

> (To access Appendix F, go to
> <http://www.jlab.org/exp_prog/PACpage/pac.html> )

# **Appendix A**

**PAC 28 Membership**

+-----------------------------------+-----------------------------------+
| **BERTHOLD SCHOCH** (Chair)       | # **EDDY JANS**                   |
|                                   |                                   |
| Universitaet Bonn, Physikalisches | NIKHEF, P.O. Box 41882            |
| Institut                          |                                   |
|                                   | 1009 DB Amsterdam                 |
| Nussallee 12, Room 142            |                                   |
|                                   | The Netherlands                   |
| D 53115 Bonn, Germany             |                                   |
|                                   | Phone/Fax: 31 20 5922085/5155     |
| Phone/Fax: 49 228 73 2344/7869    |                                   |
|                                   | <eddy@nikhef.nl>                  |
| <schoch@physik.uni-bonn.de>       |                                   |
+-----------------------------------+-----------------------------------+
| **BARBARA BADELEK**               | # **FRITZ KLEIN**                 |
|                                   |                                   |
| Institute of Experimental Physics | Physikalisches Institut,          |
|                                   | Universität Bonn                  |
| Warsaw University                 |                                   |
|                                   | Nussallee 12                      |
| Hoza 69                           |                                   |
|                                   | 53115 Bonn, Germany               |
| PL-00681 Warsaw, Poland           |                                   |
|                                   | Phone/Fax: 49 228 73 2341/7869    |
| Phone/Fax: 48-22-62-14771/94309   |                                   |
|                                   | <klein@physik.uni-bonn.de>        |
| <badelek@cern.ch>                 |                                   |
+-----------------------------------+-----------------------------------+
| # **NICOLA BIANCHI**              | **SERGE KOX**                     |
|                                   |                                   |
| INFN LNF                          | Laboratoire de Physique           |
|                                   | Subatomique et                    |
| Via E. Fermi 40                   |                                   |
|                                   | De Cosmologie (IN2P3/CNRS-UJF)    |
| 00044-Frascati (Rome), Italy      |                                   |
|                                   | 53 Avenue Des Martyrs             |
| Phone/Fax: 39-06-94032320/2559    |                                   |
|                                   | 38026 Grenoble-Cedex, France      |
| <nicola.bianchi@lnf.infn.it>      |                                   |
|                                   | Phone/Fax: 33 4 76 28 41 55/4004  |
|                                   |                                   |
|                                   | <kox@in2p3.fr>                    |
+-----------------------------------+-----------------------------------+
| **J. DAVID BOWMAN**               | # **PETER KROLL**                 |
|                                   |                                   |
| Los Alamos National Laboratory    | Fachbereich Physik, Universitaet  |
|                                   | Wuppertal, Gaustrasse 20          |
| P.O. Box 1663                     |                                   |
|                                   | D-42097 Wuppertal, Germany        |
| Los Alamos, NM 87545              |                                   |
|                                   | Phone/Fax: +49 202 439 2620/3860  |
| Phone/Fax: 505-667-4363/665-4121  |                                   |
|                                   | <kroll@physik.uni-wuppertal.de>   |
| <bowman@lanl.gov>                 |                                   |
+-----------------------------------+-----------------------------------+
| **GORDON CATES**                  | **NAOMI MAKINS**                  |
|                                   |                                   |
| Department of Physics             | Department of Physics             |
|                                   |                                   |
| University of Virginia            | University of Illinois at         |
|                                   | Urbana-Champaign                  |
| Jesse Beam Laboratory             |                                   |
|                                   | 1110 West Green Street            |
| 382 McCormick Road                |                                   |
|                                   | Urbana, IL 61801                  |
| P.O. Box 400714                   |                                   |
|                                   | <makins@uiuc.edu>                 |
| Charlottesville, VA 22904         |                                   |
|                                   |                                   |
| Phone/Fax: 434-924-4792           |                                   |
|                                   |                                   |
| <gdc4k@virginia.edu>              |                                   |
+-----------------------------------+-----------------------------------+
| **T. WILLIAM DONNELLY**           | # **ZEIN-EDDINE MEZIANI**         |
|                                   |                                   |
| Massachusetts Institute of        | Temple University, Physics        |
| Technology                        | Department                        |
|                                   |                                   |
| Center for Theoretical Physics,   | Barton Hall                       |
| 60300                             |                                   |
|                                   | 1900 North 13^th^ Street          |
| 77 Massachusetts Avenue           |                                   |
|                                   | Philadelphia, PA 19122-6028       |
| Cambridge, MA 02139               |                                   |
|                                   | Phone/Fax:                        |
| Phone/Fax: (617)253-4847/8674     | (215)923-6416/(215)204-2569       |
|                                   |                                   |
| <Donnelly@lns.mit.edu>            | <meziani@temple.edu>              |
|                                   |                                   |
| #                                 |                                   |
+-----------------------------------+-----------------------------------+

**Appendix B**

**Charge to PAC 28**

**Jefferson Lab requests that PAC 28:**

1)  Review both new proposals\* and extensions^†^ or updates^‡^ to
    previously-approved proposals, and provide advice on their
    scientific merit, technical feasibility and resource requirements.

2)  Recommend one of four actions on each proposal, extension or update:

-   approval,

-   conditional approval status pending clarification of special issues,

-   deferral with regret,

-   deferral, or

-   rejection.

> (There are two types of conditional approval: conditional pending PAC
> review of open scientific questions; and conditional pending Jefferson
> Lab management review of open technical issues. In the later case, the
> PAC should recommend a beam time allocation.)

3)  Provide a scientific rating and recommended beam-time allocation for
    all proposals recommended for approval.

4)  Provide comments on letters-of-intent.

5)  Comment on the Hall running schedules.

\* Previously-approved proposals that have not, within 3 years of PAC
approval, been scheduled to run to completion are returned to the PAC
for a fresh scientific review. For the purposes of these reviews, the
"jeopardy" experiments are to be treated consistently with new
proposals.

^†^ Extension proposals are treated as new proposals, and the merits and
status of the original proposal are considered only to the extent that
they may bear on the relevance and merit of the extension proposal.

^‡^ In reviewing an experiment update, the PAC will treat the original
proposal and any request for changes taken together as a single new
proposal and treat the combination in a manner analogous to a
previously-approved proposal undergoing a jeopardy review.

**Appendix C**

**PAC 28 Recommendations**

**Class\*/Grade/Days**

+--------+-----------+---+-------------------------------------------------+
| A      | PR-05-101 |   | Initial State Helicity Correlation in Wide      |
| /A-/14 |           |   | Angle Compton Scattering                        |
+--------+-----------+---+-------------------------------------------------+
| A      | PR-05-102 |   | Measurement of Ax and Az Asymmetries in the     |
| /A-/15 |           |   | Quasi-elastic                                   |
|        |           |   |                                                 |
|        |           |   | 3He(e,e\'d) Reaction                            |
+--------+-----------+---+-------------------------------------------------+
| A\*    | PR-05-103 |   | Low Energy Deuteron Photodisintegration         |
| /B+/14 |           |   |                                                 |
+--------+-----------+---+-------------------------------------------------+
| D      | PR-05-104 |   | High Energy Neutral Pion Photoproduction        |
+--------+-----------+---+-------------------------------------------------+
| DR     | PR-05-105 |   | Impulse Approximation limitations to the        |
|        |           |   | (e,e\'p) reaction on 208Pb, identifying         |
|        |           |   | correlations and relativistic effects in the    |
|        |           |   | nuclear medium                                  |
+--------+-----------+---+-------------------------------------------------+
| DR     | PR-05-106 |   | Update Proposal for E02-109: Measurement of     |
|        |           |   | R=sigma_L/sigma_T on Deuterium in the Nucleon   |
|        |           |   | Resonance Region                                |
+--------+-----------+---+-------------------------------------------------+
| DR     | PR-05-107 |   | Parity Violating Electron Scattering in the     |
|        |           |   | Resonance Region (Res-Parity)                   |
+--------+-----------+---+-------------------------------------------------+
| A\*\*  | PR-05-108 |   | G0 Backward Angle Measurements                  |
+--------+-----------+---+-------------------------------------------------+
| A\*\*  | PR-05-109 |   | A Measurement of Nucleon Strange Form Factors   |
|        |           |   | at High Q2                                      |
+--------+-----------+---+-------------------------------------------------+
| A      | PR-05-110 |   | Precision Measurement of Longitudinal and       |
| /A-/26 |           |   | Transverse Response Functions of Quasi-Elastic  |
|        |           |   | Electron Scattering in the Momentum Transfer    |
|        |           |   | Range 0.55 GeV/c \< q\<.9 GeV/c                 |
+--------+-----------+---+-------------------------------------------------+
| D      | PR-05-111 |   | Measurement of the Gerasimov-Drell-Hearn        |
|        |           |   | Integral at low Q2 on the                       |
|        |           |   |                                                 |
|        |           |   | Neutron and Deuteron                            |
+--------+-----------+---+-------------------------------------------------+
| D      | PR-05-112 |   | The Delta-d Experiment: Constraining d-quark    |
|        |           |   | polarization through semi-inclusive spin        |
|        |           |   | asymmetry measurements on a polarized 3He       |
|        |           |   | target                                          |
+--------+-----------+---+-------------------------------------------------+
| A      | PR-05-113 |   | Semi-Inclusive Pion Production with a           |
| /A-/60 |           |   | Longitudinally Polarized Target at 6GeV         |
+--------+-----------+---+-------------------------------------------------+
| A/A/60 | PR-05-114 |   | Deeply Virtual Compton Scattering at 6GeV with  |
|        |           |   | polarized target and polarized beam using the   |
|        |           |   | CLAS detector                                   |
+--------+-----------+---+-------------------------------------------------+
| A      | PR-05-115 |   | Spectroscopic investigation of the hypernuclei  |
| /A-/20 |           |   | in the wide mass region using the (e,e\'k+)     |
|        |           |   | reaction                                        |
+--------+-----------+---+-------------------------------------------------+

-   A=Approve, C=Conditionally Approve, D=Defer, DR= Defer with Regret,
    R=Reject

\* Run Concurrently with G0

\*\* Conditionally Approve w/PAC Review

# **Appendix D**

## Individual Proposal Reports

**Proposal:** PR-05-101

**Scientific Rating:** A^-^

**Title:** Initial State Helicity Correlation in Wide Angle Compton
Scattering

**Spokespersons:** Donal Day and Bogdan Wojtsekhowski

**Motivation:** The aim of this experiment is a measurement of the
initial-state helicity correlation

A~LL~ for real Compton scattering off protons at wide angles (RCS),
thereby allowing for a further test of the dynamical interpretation of
RCS at JLab kinematics. This measurement is part of a series of
experiments on RCS. Experiment E99-114 has already measured the
polarization transfer observable K~LL~ at s=7 GeV^2^ and at a c.m.s.
scattering angle of 120^°^ and the differential cross section for this
energy and three others at a set of scattering angles. The approved
experiment E03-007 will extend the measurement of K~LL~ to other angles.
The comparison of data on A~LL~ with those on K~LL~ will provide
valuable information on the dynamics of RCS. In current dynamical
approaches to RCS differences between the two observables can be traced
back to quark helicity flip, and hence to quark masses. If these effects
are found to be small, as expected, the RCS data can provide unique
constraints on 1/*x*-weighted moments of the generalized parton
distributions.

**Measurement and Feasibility:** The proposed experiment uses circularly
polarized bremsstrahlung photons emitted by a longitudinally polarized
electron beam. The photons will be scattered off a longitudinally
polarized NH~3~ target and detected in the BigCal calorimeter. The
recoil protons will be detected in the HMS spectrometer. This large
installation experiment uses standard equipment and is judged to be
feasible. The background from Moeller electrons and from π°
photoproduction seems to be under control. The A~LL~ parameter will be
measured at s=9 GeV^2^ and two scattering angles (90° and 140°) with an
overall error less than ± 0.10. As a byproduct, A~LL~ will also be
measured for the photoproduction of neutral pions.

**Issues:** Merely due to lack of available beam time, the PAC
recommends that only the kinematic point in the backward hemisphere be
measured.

**Recommendation:** Approve for 14 days in Hall C

**Proposal:** PR-05-102

**Scientific Rating:** A^-^

**Title:** Measurements of A~x~ and A~z~ Asymmetries in the
Quasi-elastic ![](media/image4.wmf)![](media/image5.wmf) Reaction

**Spokespersons:** Shalev Gilad, Douglas Higinbotham, Wolfgang Korsch,
Blaine Norum, and

> Simon Širca

**Motivation:** The goal of the proposal is to study the small wave
function components of ^3^He, specifically the S′ and D states. Better
knowledge of these components is a prerequisite for the calculation of
the nuclear corrections that need to be applied to polarized ^3^He data
for the extraction of neutron properties. It is proposed to measure
simultaneously the doubly-polarized asymmetries A~x~ and A~z~ of ^3^He
for the ![](media/image6.wmf) and ![](media/image7.wmf) channels.
Predictions of A~x~ and A~z~ based on Faddeev calculations by the
Bochum/Krakow and Hannover groups show distinct differences for the
proton and deuteron channels as a function of the missing momentum,
p~m~, and the amount of S′ and D wave components in the bound state wave
function. At the same time a measurement of ![](media/image8.wmf) at
Q^2^=0.36 (GeV/c)^2^ will be performed with an accuracy of better than
0.0039.

**Measurement and Feasibility:** The Hall A polarized target is used
with HRSℓ for detection of the scattered electron in coincidence with
BigBite for the knocked out proton/deuteron. Particle identification in
BigBite is performed by means of ∆E/E in two successive scintillator
planes. The three-momentum and energy transfer amount to 620 MeV/c and
106 MeV, respectively, such that real pion production followed by
reabsorption is circumvented. The ![](media/image9.wmf) coincidences
will be measured between HRSℓ and a neutron detector behind BigBite. The
product of beam and target polarization is monitored with HRSr in which
A~elas~ will be measured continuously. The asymmetry data will be
grouped in parallel and perpendicular subsets that will cover the
p~m~-range (0, 200) and (-200,200) MeV/c, respectively. The projected
statistical precision will be sufficient to discriminate between the
presently available theoretical predictions.

**Issues:** Due to the addition of the proton channel and the data point
for ![](media/image10.wmf) the proposal has gained considerably in
potential since its original approval as E02-108 by PAC22. The two sets
of doubly-polarized asymmetries A~x~ and A~z~, as a function of p~m~,
would add significantly to the possibility to test the Faddeev methods
and ultimately reduce the uncertainty in nuclear corrections applied to
data of experiments that use polarized ^3^He as an effective neutron
target.

**Recommendation:** Approve for 15 days in Hall A

##  

## Proposal: P-05-103

**Scientific Rating:** B+

**Title:** Low Energy Deuteron Photodisintegration

**Spokespersons:** Ron Gilman, Adam Sarty, and Steffen Strauch

**Motivation:** It is proposed to study polarization observables in the
photodisintegration of the deuteron using photons at a single energy
that falls within the range of 360 to 500 MeV.

A plethora of data exists for deuteron photodisintegration for both
polarized and unpolarized observables. At 300 MeV, agreement with modern
state-of-the-art hadronic calculations is generally good, with perhaps
some inconclusive trouble with p~y~. The reasons for progress in this
area include improvement in the treatment of relativistic effects and
the use of modern high-precision NN potentials.

At higher energies, however, it is clear that existing calculations do
not describe the data well. The data at higher energies are also often
of fairly poor quality.

The impressive agreement of modern calculations, based on hadronic
degrees of freedom, with much of the existing data for
photodisintegration of the deuteron makes the proposed experiment all
that much more interesting. Obtaining high quality data on polarization
observables at an energy in the suggested range would be of great value
for better understanding the dynamics of the deuteron and the
NN-interaction.

**Measurement and feasibility:** The proposed experiment will use the
HRS with the focal plane polarimeter. The configuration will be nearly
identical to that used during E89-019 in which the same polarization
observables as proposed here were measured in the energy range of 0.5 --
2.4 GeV. Thus, in terms of the setup in Hall A, there is little doubt
that the experimental goals can be achieved. The proposed experiment can
run parasitically with G0's low-energy run, thus representing a
particularly attractive opportunity. Running two halls simultaneously at
such low energies, however, represents something of a challenge,
although the accelerator group appears both confident and willing.

**Recommendation:** Approve for 14 days in Hall A

**Proposal:** PR-05-104

**Scientific Rating:** N/A

**Title:** High Energy Neutral Pion Photoproduction

**Spokespersons:** Ronald Gilman and Bogdan Wojtsekhowski

**Motivation:** It is proposed to investigate the applicability of the
handbag mechanism in the photoproduction of neutral pions at photon
energies around 5 GeV and --t around several GeV^2^ through polarization
observables. Existing data comprise cross sections and recoil
polarization components up to 4 GeV, partially taken by the authors of
the proposal in previous experiments E94-012 and E99-114. In the π^0^
photoproduction background of their real Compton scattering data at 3.2
GeV they find compatibility of the observed polarization transfer K~LL~
to the proton with a calculated polarization transfer to a quark. On
this basis they argue that neutral photoproduction with its high cross
section might advantageously be used to investigate the onset of hard
scattering and to extract three well defined form factors as valuable
inputs for the determination of GPDs. As a side effect the polarization
data would allow a confrontation with the recoil polarization as
observed in K^+^Λ production of Hall B data.

**Measurement and Feasibility:** The experiment would be performed in
Hall A, using circularly polarized untagged photons hitting a 15 cm
liquid hydrogen target. The exclusive reaction would be identified by
coincident detection of both decay photons of the π^0^ in the newly
available BigCal Calorimeter, providing an acceptance of typically 50 %
as well as the proton in one of the HRS spectrometers. The differential
production cross section and all 3 components of the polarization of the
recoiling proton (p~y,~ K~LL~ and K~LS~ ), analyzed in the double layer
focal plane polarimeter (FPP) of HRS, would be measured. Based on
previous polarization experiments at lower energies, performed by the
authors with the detection of only one decay photon, the experiment
appears feasible as proposed.

**Issues:** While the study of photoproduction of neutral pions in the
proposed energy regime is considered interesting in itself as a tool to
explore and identify the active degrees of freedom, the PAC finds it
unlikely that the complicated behavior of the recoil polarization
observed below 3 GeV would rapidly turn over to a smooth shape
compatible with the handbag mechanism. More than for purely photonic
reactions, it is felt that for pion photoproduction stronger proofs are
required, particularly a successful description of the cross section in
the GPD framework. This could be attainable more convincingly at higher
photon energies and make the proposed pion production a more compelling
case.

**Recommendation:** Defer

## 

**Proposal:** PR05-105

**Scientific Rating:** N/A

**Title:** Impulse Approximation limitations to the (e,e′p) reaction on
^208^Pb, identifying

correlations and relativistic effects in the nuclear medium

**Spokespersons:** Arun Saha, Konrad Aniol, Bodo Reitz and Jose Udias

**Motivation:** Spectroscopic factors of ≈70% for valence orbits have
been extracted from (e,e′p) experiments at intermediate-energy
facilities on a variety of nuclei such as ^7^Li, ^12^C, ^16^O, ^40^Ca,
^90^Zr and ^208^Pb. However, the kinematical conditions at which these
experiments were performed were not ideal. With the presently available
equipment in Hall A the optimal experiment can be performed: in
(q,)-constant kinematics at a three-momentum transfer of 1 GeV/c and
*x*~B~=1. The contributions of the transitions to the low-lying states
in ^207^Tl will be separated by fitting the spectra as a function of
missing energy, E~m~, and missing momentum, p~m~, up to 500 MeV/c. These
results will be compared to non-relativistic and fully relativistic
distorted wave calculations and spectroscopic factors of the 3s~1/2~,
2d~3/2~, 1h~11/2~, 2d~5/2~ and 1g~7/2~ orbits will be determined. The
role of long-range correlations at high p~m~ will be addressed.
Moreover, it is proposed to extract the transverse-longitudinal
asymmetry, A~TL~, at p~m~=100, 200 and 300 MeV/c. This response is
predicted to be sensitive to dynamic relativistic effects that enter the
calculations via an enhancement of the lower components of the Dirac
spinors.

**Measurement and Feasibility:** The two high-resolution spectrometers
of Hall A will be used in their standard configuration. The cooled
target setup, developed and tested for E03-011, consists of a 0.2 mm
thick lead foil that is sandwiched between 2 diamond foils of 0.15 mm
each. Beam currents up to 100 A seem feasible. For the fitting
procedure, a dedicated (e,e′p) measurement will be performed on ^207^Bi
to determine the E~m~-spectrum of an isolated transition. Count rate
estimates and Monte Carlo simulations of the missing-energy resolution
indicate that it will be possible to separate the contributions of the 5
lowest states up to p~m~=300 MeV/c.

**Issues:** Extraction of the spectroscopic factors of the 5 valence
orbits of ^208^Pb from (e,e′p) data collected under optimal kinematical
conditions is a prerequisite for solving the longstanding issue in the
many-body physics of depletion. Since inevitably it is extremely
difficult at such high energies to separate completely the individual
states, procedures for fitting simultaneously the response as a function
of E~m~ and p~m~, should be further developed.

**Recommendation:** Defer with regret

## 

**Proposal:** PR-05-106

**Scientific Rating:** N/A

**Title:** Measurement of ![](media/image11.wmf) on Deuterium in the
Nucleon Resonance Region (Update of E02-109)

**Spokespersons:** M.E. Christy, C. Keppel

**Motivation:** The transverse-longitudinal structure functions F~1~
(x,Q^2^) and F~L~ (x,Q^2^) would be extracted using the Rosenbluth
technique in the resonance region (1 \< W^2^ \< 4 GeV^2^) spanning the
Q^2^ range 2 \< Q^2^ \< 5 GeV^2^. This measurement adds unique
information on the deuteron and the neutron and is critical in several
aspects. It allows for the determination of the neutron singlet and
non-singlet (proton-neutron) combination of the moments of the F~L~
structure function. These moments are dominated by the large *x*
(resonance) data proposed in this experiment and provide a benchmark
test for Lattice QCD calculations at Q^2^ above 2 GeV^2^. Using duality,
which seems to work quite well on the proton, these precision data will
add information on the down quark parton distributions at large *x* and
moderate Q^2^. Furthermore, a precision measurement of R is needed for
the determination of the deuteron and neutron spin structure functions
g~1d~ and g~1n~ in the resonance region. These data are also relevant to
neutrino experiments like MINERVA and MINOS.

**Measurement and Feasibility:** This experiment would be performed in
Hall C using the HMS spectrometer to detect scattered electrons. Part of
this previously approved experiment has already been performed at Q^2^ =
0.5 and 2 GeV^2^. The collaboration has all the tools and expertise to
reach the quoted uncertainties on the ratio R. Similar precision has
been achieved in the proton measurement of experiment E94-110 by the
same collaboration. The quoted error bars in the extraction of F~L~ and
R in the deuteron are realistic.

**Recommendation:** Defer with regret

## 

**Proposal:** PR 05-107

**Scientific Rating:** N/A

**Title:** Parity Violating Electron Scattering in resonance Region
(Res-Parity)

**Spokespersons:** Peter Bosted, J. Arrington, V. Dharmawardane, H.
Mkrtchyan, X. Zheng

**Motivation:** The proposal is aimed at measuring Parity Violating
asymmetries on various targets, over the full resonance region (up to a
missing mass W = 2.1 GeV) in the Q^2^ domain 0.5 - 1.0 (GeV/c)^2^. The
physics addressed by this proposal ranges from quark-hadron duality and
EMC-type effects, inputs to key neutrino experiments and inputs
(background and radiative corrections) to PV measurements such as E-158
or DIS-Parity. This proposal was examined by PAC27 (PR05-005) and was
deferred with regrets.

**Measurement and Feasibility:** The experiment is proposed for Hall A
(versus Hall C for the proposal to PAC27) and requests 15 days in total
(including about 1 day contingency). It uses basically the same
equipment as that required by the approved E05-007 (DIS-Parity
experiment). The proposal has gained experienced collaborators and the
DIS- and Res-Parity collaborations are foreseen to work together on the
necessary developments (upgraded Compton polarimeter, Fast DAQ, ...).
The key elements of the experimental set-up are the 2 HRS spectrometers,
cryogenic target (25 cm long) for H and D, a polarized electron beam
with PV quality and a fast acquisition system allowing for a counting
method to reject pion background. Concerning the beam, the size of the
asymmetry to be measured is large (50-100 ppm) and the beam performances
achieved at JLab exceed the requirements of the proposal. The beam
energy and spectrometer settings have been optimized (no septum, energy
large enough to scan the missing mass region with adequate cross
sections) leading to the choice of a 4.8 GeV beam and a 12.5° detection
angle for the scattered electrons. Beam intensity requested is 85 μA,
with 80% polarization.

Concerning the recommendations and concerns expressed on PR05-005, PAC28
acknowledges the progress that has been made in the experimental device
and in the extension of the physics case presented in the new proposal,
in particular the importance of including the nuclear target. The last
adds the feature of providing information of value for neutrino
oscillation experiments and for a first glimpse at how the EMC effect
for PV may be manifested \-\-- these features in particular drew a
favorable response from the PAC.

**Issues:** Despite all of these improvements, the constraints in beam
time allocation did not allow the PAC to recommend approval of PR05-107
at this time. A future proposal containing clearer links with the
approved and deferred phases of the DIS-parity experiment would help in
making a convincing case for approval to explore the various features
proposed here in PR05-107.

**Recommendation:** Defer with regret

## 

**Proposal:** PR 05-108

**Scientific Rating:** A^-^

**Title:** G0 Backward Angle Measurements

**Spokespersons:** Douglas Beck

**Motivation:** Measurements of parity-violating electron scattering
from hydrogen (elastic, both forward and backward angles) and deuterium
(quasi-elastic, backward angles) provide information on the strangeness
content in the nucleon via the form factors G~Es~ and G~Ms~, as well as
on the neutral-current axial-vector form factor G~A~. At present, from
determinations of the PV asymmetry at JLab (G0 forward, HAPPEx forward),
MIT/Bates (SAMPLE, backward angles) and Mainz (PVA4 forward), the
indications are that the strangeness form factors are not consistent
with zero and that G~A~ is modified from naïve expectations. Obtaining
more stringent constraints on these interesting quantities remains a
high-priority goal for studies of hadronic structure.

Other on-going efforts at JLab (HAPPEx-H and HAPPEx-He) and at Mainz
with backward-angle running, together with the first phase of
backward-angle running with G0 (799 MeV, Q^2^ = 0.8 (GeV/c)^2^ scheduled
to begin running in March, 2006 and conclude in the fall of 2006) will
further tighten the constraints on the form factors. However, a strong
case is being made by the G0 collaboration in the present low-energy
proposal (see below) and by the Hall A HAPPEx collaboration in proposal
PR05-109 that an opportunity exists at JLab to have an even greater
impact in the attempts to determine G~Es~, G~Ms~ and G~A~.

The present proposal requests approval for the remaining time to
complete the G0 parity program at backward angles with beam energies of
360 MeV (Q^2^ = 0.23 (GeV/c)^2^) and 585 MeV (Q^2^ = 0.48 (GeV/c)^2^)
with hydrogen and possibly with deuterium as well. Specifically, the
collaboration requests scheduling for summer, 2006. For this period a
window of opportunity appears to have arisen in which, together with FEL
operation, it may be possible to have low-energy running with
parity-quality beam for the 40-50 days of summer operation. Normally the
accelerator would not be available at all for the nuclear physics
program.

**Measurement and Feasibility:** For running at backward angles the
collaboration has concluded that there are significant practical and
experimental advantages to running with a standard 499 MHz bunch
structure, rather than the 31 MHz structure used for the forward-angle
measurements. This will permit higher beam currents of 80 μA to be
employed, thereby reducing the statistical uncertainties in extracting
G~Es~, G~Ms~ and G~A~. A new set of scintillator detectors is needed to
separate elastic and inelastic events for ep scattering and a Cherenkov
detector to discriminate between pions and electrons when running with
deuterium. The TAC raised a number of concerns, some of which are
discussed below.

**Issues:** While very positive about the value of what is proposed
here, the PAC has concerns about several issues that (1) bear on the
overall strategy of the PV measurements proposed and their potential
impact on efforts to make definitive determinations of the form factors
and (2) relate to technical aspects of the experiment. These two items
are dealt with separately.

*Physics Strategy.* An opportunity appears to have arisen where the JLab
program in PV eN scattering can tighten the constraints on G~Es~, G~Ms~
and G~A~. G0 at backward angles using hydrogen and deuterium provide
G~Ms~ and G~A~, and together with forward-angle measurements including
the tightest constraints from the measurements proposed in PR05-109, can
lead to a much better determination of G~Es~ as well. However, this
requires a coherent approach from the two collaborations in the two
proposals. Accordingly the PAC recommends that an optimized physics
strategy be developed by the proposers of PR05-108 and PR05-109 for how
to achieve these goals. The PAC recommends that a single common value of
Q^2^ should be chosen. This choice will require discussions of
trade-offs in both low- and high-energy parts of the program. For
PR05-108 another important issue will be the choice of target: with only
hydrogen a full determination at the selected Q^2^ point will be
impossible and one will have to depend on G~A~ having a "reasonable"
Q^2^-dependence between 0.1 (GeV/c)^2^ and 0.8 (GeV/c)^2^ where it will
be known; with hydrogen and deuterium both G~Ms~ and G~A~ can be
determined, however with poorer precision given a fixed amount of
beamtime. An optimized, coherent strategy should be presented at PAC29
for final approval and should include a detailed analysis of the impact
of following alternative strategies on the ultimate error ellipses to be
expected in the determinations of G~Es~, G~Ms~ and G~A~. In summary, the
PAC recommends that the G0 collaboration work with the Laboratory and
the HAPPEx collaboration to choose an optimal common experimental
strategy based upon the additional information that is (or soon will be)
available for this important class of measurements.

*Technical Issues.* The TAC raised a number of technical issues
concerning installing, commissioning, and running the G0 low-energy
back-angle experiment. In order to address these issues, the
collaboration is asked to work with the Laboratory to develop:

1.  A well motivated table of beam requirements including halo,
    helicity-correlated modulations, intensity, and polarization.

2.  Detailing of detector and apparatus performance criteria.

3.  Discussions of background criteria including radiation levels at
    detectors.

4.  A run plan including

    a.  milestones and times for achieving 1, 2, and 3.

    b.  count rates and running times to achieve statistical
        uncertainties.

    c.  auxilary measurements and times to control systematic
        uncertainties.

**Recommendation:** Conditionally approve (C2) for running during the
special 12-week (\~50 PAC days) low-energy running period anticipated
for summer, 2006.

**Proposal:** PR 05-109

**Scientific Rating:** A-

**Title:** A Measurement of Nucleon Strange Form Factors at High Q^2^

**Spokespersons:** Kent Paschke, Paul Souder

**Motivation:** The proposal is aimed at measuring with high precision a
combination of electric and magnetic strange form factors at Q^2^ = 0.6
(GeV/c)^2^. The anticipated uncertainty would allow a 4-σ confirmation
of a non-zero strange contribution signal if observed at the level
reported by the G0 experiment. As discussed below, the high-precision
forward-angle measurement together with backward-angle measurements on
the H and D targets (proposed by G0) at a common Q^2^ would provide a
complete determination of G~Es~, G~Ms~, and G~A~ at that Q^2^.

**Measurement and Feasibility:** The experiment is proposed in Hall A
for 30 days total. The experimental set-up uses the one that was
previously successful for the HAPPEx I and II experiments. Most of the
concepts and equipment have been used and tested in the earlier data
taking. Most of the experimental specifications have been met in earlier
phase of HAPPEx, in fact in HAPPEx II they were exceeded by almost an
order of magnitude. The polarized electrons will be produced either by
the super-lattice or strained GaAs cathode (75-85% polarization). The
beam intensity required is 100 μA. . This proposal makes use of the 2
HRS spectrometers to detect the elastically scattered electrons on a
20-cm-long liquid hydrogen target. The dedicated detectors will be
placed in the focal plane of the HRS and the PMT signal will be. Key
elements and challenges of the set-up will be the polarization
measurement with the Hall A Compton polarimeter, which will need an
upgrade already planned for future high-precisions PV experiments. Also,
target boiling should be kept under control. The proponents are seeking
a precision (statistics [and]{.underline} systematic) about a factor 2-3
better than obtained earlier in the same momentum transfer region. This
is quite demanding concerning any kind of systematic or theoretical
uncertainties and this is where the difficulties reside. These
difficulties include form factor knowledge and the contribution of
2-photon exchange, polarization measurement with a 1 % precision, etc.

While very positive about the value of what is proposed here, the PAC
has concerns about the *Physics Strategy.* An opportunity appears to
have arisen where the JLab program in P-V eN scattering can tighten the
constraints on G~Es~, G~Ms~ and G~A~. G0 at backward angles using
hydrogen and deuterium provides G~Ms~ and G~A~ and together with
forward-angle measurements including the tightest constraints from the
measurements proposed in PR05-109, can lead to G~Es~ as well. However,
this requires a coherent approach from the two collaborations in the two
proposals. Accordingly the PAC recommends that the Laboratory and the
proponents of PR05-108 and PR05-109 develop a common strategy to achieve
these goals. A single common value of Q^2^ should be chosen. This choice
will require discussions of trade-offs in both low- and high-energy
parts of the program. For PR05-108 another important issue will be the
choice of target: with only hydrogen a full determination at the
selected Q^2^ point will be impossible and one will have to depend on
G~A~ having a "reasonable" Q^2^-dependence between 0.1 (GeV/c)^2^ and
0.8 (GeV/c)^2^ where it will be known; with hydrogen and deuterium both
G~Ms~ and G~A~ can be determined, however with poorer precision given a
fixed amount of beamtime. The common strategy should be reviewed by the
PAC.

**Recommendation:** Conditional approval (C2) for 30 days in Hall A

## 

**Proposal:** PR 05-110

**Scientific Rating:** A^-^

**Title:** Precision Measurement of Longitudinal and Transverse Response
Functions of Quasi-Elastic Electron Scattering in the Momentum Transfer
Range 0.55 GeV/c\<q\<0.9GeV/c

**Spokespersons:** Seonho Choi, Jian-Ping Chen and Zein-Eddine Meziani

**Motivation:** The goal of the proposed measurements is to extract the
longitudinal and transverse response functions for inclusive,
unpolarized, quasi-elastic scattering from a variety of targets (^4^He,
^12^C, ^56^Fe, ^208^Pb) at momentum transfers ranging from q = 0.55 to
0.9 GeV/c. Integration of the longitudinal part yields the Coulomb sum.
Previous determinations in all but very light nuclei suggest that
significant quenching occurs, although those results do not extend to
very high momentum transfers where effects from Pauli blocking and some
types of correlations are expected to be diminished. By extending the
previous separations to higher values of q, it is hoped that the
resulting longitudinal response and its accompanying Coulomb sum will
shed light on the issue of whether or not other effects are required to
reconcile the predictions of standard modeling with experiment.

**Measurement and Feasibility:** The earlier version of this proposal
came under jeopardy review at the time of PAC25 and was deferred for two
reasons: (1) concerns existed with respect to the lack of unanimity in
the theory community of how to handle Coulomb distortion effects for
quasi-elastic scattering and (2) the fact that simulations allowing one
to arrive at projections for the uncertainty expected in the Coulomb sum
were not available.

Both of these concerns have extensively been addressed by the proposers.
Firstly, two workshops have been organized, focusing on the issue of
inter-relating the various theoretical approaches to treating Coulomb
distortion effects, especially at intermediate energies and for heavy
nuclei. Much progress has been made; the theory community has become
quite active; and it appears that a consensus is within reach, likely at
roughly the 10% level or better. Secondly, the proposers have performed
simulations and produced realistic projections for the uncertainties to
be expected for the Coulomb sum, as requested.

**Issues:** Beyond the previous issues discussed above, which appear to
have been dealt with, the proposers were asked about potential
backgrounds and their impact on the L/T separation. Dedicated analysis
has shown that the major source of background originates at Q3 in the
HRS, which can be suppressed adequately. Moreover, additional
suppression will be obtained by means of information from a PbF~2~
calorimeter. Therefore it appears that the goals of the experiment can
be met.

**Recommendation:** Approve for 26 days in Hall A

## 

**Proposal:** PR 05-111

**Scientific Rating:** N/A

**Title:** Measurement of the Gerasimov-Drell-Hearn Integral at low Q^2^
on the Neutron and Deuteron

**Spokespersons:** Alexandre Deur, Gail Dodge and Karl Slifer

**Motivation:** The proposal aims at measuring the generalized (Q^2^≠0)
GDH integral for the deuteron at Q^2^ down to 0.01 (GeV/c)^2^ in a Hall
B experiment using the CLAS detector and a polarized deuterium target
(ND~3~). By combining the results with the approved experiment on the
proton target (NH~3~) in Hall B (E03-006), this proposal should allow
the determination of this integral and therefore a test of the GDH sum
rule on the neutron at Q^2^ close to 0. This will complement data of a
similar but less accurate experiment (EG1b) already performed in Hall B
at Q^2^ above 0.05 (GeV/c)^2^.

**Measurement and Feasibility:** The experiment is proposed in Hall B
for 30 days. The experimental set-up uses the CLAS detector with a new
Čerenkov counter for absolute normalization. The polarization of
electrons is assumed to be 80 % and a beam current of 1-4 nA is
required. This proposal relies on the operation of a polarized solid
target (ND~3~) with 40% deuteron polarization. The experimental
specifications appear to be reachable with CLAS, which will be used in
rather standard operation. The new Čerenkov counter is under
construction for E03-006 and will be available.

The determination of the sum rule for the deuteron will include the
disintegration channel which is large below pion threshold where the
elastic channel also contributes.

The extraction of the neutron GDH integral relies on nuclear corrections
which are not small in the case of a deuteron target. It will make use
of the combination of data from this proposal and from the proton data
(E03-006) which will cover about the same kinematics.

**Issues:** The beam and target polarizations used in the proposal might
be too high and safer values of 75% and 30% have been assumed
respectively. The PAC recognized the great importance of the measurement
of the GDH sum rule for the neutron at very low Q^2^ which will also
allow an extrapolation to the photon point. However, an experiment
(E97-110) has already collected data in Hall A with a polarized ^3^He
target which provides a cleaner source of polarized neutrons. The
present proposal offers no large improvement in accuracy and only a
moderate extension towards lower Q^2^ with respect to the projected
E97-110 results. Therefore it will be important to wait for the results
of E97-110 for a better judgment of the need for an additional
measurement with a nuclear target (ND~3~ instead of ^3^He).

**Recommendation:** Defer

## 

**Proposal:** PR 05-112

**Scientific Rating:** N/A

**Title:** The Δd Experiment: Constraining d-quark polarization through
semi-inclusive spin asymmetry measurements on a polarized 3He target

**Spokespersons:** Xiaodong Jiang

**Motivation:** Polarized semi-inclusive deep-inelastic-scattering
(SIDIS) is a powerful tool to determine the polarized parton
distributions. The present knowledge of the latter is by far less
accurate than that of the unpolarized ones. In particular the sea-quark
polarized distributions are poorly constrained by present SIDIS data and
by global analyses based on QCD fits; it is not clear whether or not the
polarized light-quark sea is flavor asymmetric, like the unpolarized
one, if true a fact with very important consequences. The goal of this
proposal is to measure the SIDIS asymmetry for charged pions (and kaons)
on a polarized 3He target which is mainly sensitive to the d-quark
polarization. A combined LO analysis of the results of this experiment
with the ones from the approved semi-SANE experiment will be needed for
the extraction of the polarized distributions, including
the![](media/image12.wmf)- ![](media/image13.wmf) difference.

**Measurement and Feasibility:** The proposed measurement would use a 6
GeV polarized beam on a longitudinally polarized 3He target. The
scattered electrons would be detected with the BigBite spectrometer
positioned at 30^o^. The electro-produced hadrons will be measured by
the left-HRS located at 6^o^ with its septum magnet in front. Pions and
kaons of both charges will be identified. The semi-inclusive asymmetries
will be measured in the *x* region 0.12 - 0.41 and at Q2 =1.2 -- 3.1
GeV2. This measurement appears feasible.

**Issues:** The PAC recognizes the compelling case for the determination
of the polarized parton densities at large-x and in particular the
investigation of the flavor asymmetry of the sea-quarks. The present
experiment is aiming to provide statistically precise data in this
field. However, the statistical accuracy may be spoiled by the
uncertainties in the systematic errors which may originate from
different sources, namely, combining two data sets from two different
experiments, assuming the exact LO factorization and rigorous isospin
symmetry and charge conjugation in the fragmentation process. The two
latter assumptions may not be completely valid in the kinematic region
of this proposal and, therefore, the accurate determination of the small
asymmetry of the sea-quark at large x may not be possible. Since the
Semi-SANE experiment has already been approved, it will be important to
see the outcome of that measurement before demanding a very high
statistical accuracy as suggested in the present proposal.

**Recommendation:** Defer

## 

**Proposal**: PR-05-113

**Scientific Rating**: A-

**Title**: Semi-Inclusive Pion Production with a Longitudinally
Polarized Target at 6 GeV.

**Spokespersons**: H. Avakian, P. Bosted, D. Crabb, K. Griffioen.

**Motivation**: A measurement of the single- and double spin azimuthal
asymmetries in semi-inclusive electroproduction of pions using the 6 GeV
polarized electron beam on a longitudinally polarized proton target with
the CLAS detector equipped with the Inner Calorimeter is proposed. Spin
dependent parton distributions and in particular the transverse momentum
dependent ones will be studied in SIDIS at *Q*^2^ \> 1 GeV^2^. Both the
sin2φ and the sinφ azimuthal moments of the target spin-dependent cross
section will be determined. They will probe the Collins fragmentation
function and higher twist effects in single spin asymmetries.
Indirectly, information about orbital angular momentum of quarks will
also be provided.

**Measurement and Feasibility**: The study involves a simultaneous scan
of several observables (*x*, *Q^2^*, *z*, *p~T\ ~* and φ), possible with
the large acceptance of CLAS. A twenty-fold increase of statistics as
compared to the existing Eg1 data for the π^0^ asymmetries will be
achieved with the new IC. This is particularly important because much
smaller systematic uncertainties are expected for the neutral pion
production as compared to the charged ones since the former are less
affected by exclusive ρ meson production. Charged pions asymmetries will
be measured as well. A significant sample of two-pion events will be
accumulated also and will contribute to better understand the SIDIS as
well as the background due to ρ production. The existing CLAS Eg1 data
and simulations show that the planned measurements are feasible. No
technical problems are foreseen. The experiment will run concurrently
with PR05-114 which has the same apparatus and trigger requirements.

**Issues**: The PAC recognizes the importance of the proposed experiment
in view of the intensively developing theory of SIDIS and of the
extensive effort towards understanding the transverse aspects of the
spin structure of the nucleon (both parton distributions and
fragmentation) which will be carried out in other laboratories: CERN
(COMPASS), DESY (HERMES) and KEK (BELLE).

**Recommendation**: Approve for 60 days in Hall B

## 

**Proposal:** PR-05-114

**Scientific Rating:** A

**Title:** Deeply Virtual Compton Scattering at 6 GeV with Polarized
Target and Polarized Beam Using the CLAS Detector

**Spokespersons:** Latifa Elouadrhiri, Angela Biselli, Kyongseon Joo,
Silvia Niccolai

**Motivation:** The principal goal of this experiment is a precise
measurement of the single-spin asymmetry *A~UL~* in Deeply Virtual
Compton Scattering (DVCS) from a longitudinally-polarized hydrogen
target. Previous measurements of several DVCS asymmetries by both the
CLAS and HERMES collaborations, at similar kinematics to those of the
proposed experiment, have been well described by the "handbag diagram"
and the Generalized Parton Distribution (GPD) formalism. In this
formalism, the substructure of the nucleon is described by two
helicity-conserving functions ![](media/image14.wmf) and
![](media/image15.wmf) and two helicity-flip functions
![](media/image16.wmf) and ![](media/image17.wmf) (the index *q*
indicates quark flavor). The measurement of hard-exclusive processes,
such as DVCS, is the key to constraining these functions at off-forward
kinematics. For example, the DVCS beam-spin asymmetry *A~LU~* measured
by CLAS and HERMES provides information on the GPD *H* along the
off-forward kinematic line *x* = ±*ξ* .

This experiment will focus instead on the DVCS target-spin asymmetry.
Specifically, the exclusive process *ep* → *epγ* at hard scales (*Q*^2^
\> 1 GeV^2^) will be measured, with all three final-state particles
detected, and the distribution of the final-state photons in the
azimuthal angle φ (relative to the lepton scattering plane) will be
mapped out in both target spin states. The resulting asymmetry
*A~UL~*(φ) will be fitted to the functional form (*A* sin(φ) + *B*
sin(2φ))/(1 + *C* cos(φ)). In the GPD formalism, the sin(φ) moment "*A*"
arises from an interference between the DVCS and Bethe-Heitler
processes, and is sensitive to a roughly-equal mixture of the GPDs
![](media/image18.wmf)and ![](media/image19.wmf) (summed over quark
flavors) along the kinematic line *x* = ±*ξ*. (The moment also contains
a small, \< 10%, admixture of the GPD *E*, while the contribution from
![](media/image20.wmf) is much further suppressed.) When coupled with
the previously measured ![](media/image21.wmf) data (sensitive to *H*
alone, along the same *x* = ±*ξ* lines), the data will provide valuable
new constraints on ![](media/image22.wmf).

**Measurement and Feasibility:** *A~UL~* for DVCS has already been
measured, by both CLAS and HERMES, but the proposed experiment offers
much higher statistical precision than either data set. Compared with
the previous CLAS result, this experiment will collect about 25 times
more data: the requested running time of 60 days is more than an order
of magnitude larger than the duration of the previous data set, and the
recent addition of the Inner Calorimeter (IC) offers an acceptance gain
of roughly a factor of 2. This statistical gain will permit an
exploration of the *kinematic-dependence* of the ![](media/image23.wmf)
moment on *x* (0.12 -- 0.48), --*t* (0.1 -- 0.6 GeV^2^), and *Q*^2^ (1
-- 4 GeV^2^), with 5 bins in each variable. The ability to measure the
*Q*^2^ dependence is particularly important, as it will help to
establish whether or not the scaling region has been reached, and to
constrain the size of power corrections. It is also important to note
that HERMES will not collect any further data with
longitudinally-polarized target, and that the experiment will
additionally measure the SSA moment ![](media/image24.wmf) (sensitive to
higher-twist effects) and the double-spin asymmetry moment
![](media/image25.wmf) (sensitive to a principal-value integral over *x*
of ![](media/image26.wmf)and ![](media/image27.wmf)).

The CLAS collaboration has already published several results on DVCS
azimuthal asymmetries, and no particular new challenges are foreseen
with the proposed experiment. The only instrumental change is the IC,
but its successful operation has already been demonstrated. The
principal experimental issue for this measurement is the successful
treatment of non-exclusive background. Four sources of such background
may be identified:

1.  *ep* → *epγγ*, where the second photon arises from QED radiation

2.  *ep* → *epπ*^0^ with the *π*^0^ decaying to two photons

3.  scattering from the nucleons of the weakly-polarized ^14^N component
    of the ^14^NH~3~ target

4.  electrons or positrons misidentified as photons in the IC (which
    cannot differentiate)

The proposal presents two powerful cuts to eliminate these backgrounds,
both based on the fact that all three final-state particles will be
detected: the scattered beam-electron and target-proton in CLAS, and the
photon in either CLAS or the new IC. The most powerful
background-reduction cut arises from restricting the angle of the
detected final-state photon to within a 1° cone around its calculated
position for an exclusive event, given the electron and proton momenta
determined by CLAS tracking. The ability to evaluate and subtract this
background was clearly demonstrated in the first three cases, and the
projected systematic error includes any associated uncertainty. The
fourth case has not yet been evaluated, but it is highly unlikely that
it is a significant source of background compared with the other three.

**Recommendation:** Approve for 60 days in Hall B

**Proposal:** PR-05-115

**Scientific Rating:** A-

**Title:** Spectroscopic Investigation of ![](media/image28.wmf)
Hypernuclei in the Wide Mass Region using the ![](media/image29.wmf)
Reaction

**Spokespersons:** O. Hashimoto, S.N. Nakamura, J. Reinhold, L. Tang

**Motivation:** For the past three decades ![](media/image30.wmf)
hypernuclei have provided a special laboratory to investigate the
![](media/image31.wmf)-nucleus shell model potential with emphasis on
the determination of the ![](media/image32.wmf)N spin-orbit and the
![](media/image33.wmf)N hyperfine interaction. However, the
investigation of the ![](media/image34.wmf)N interaction using hadronic
probes has long been limited by a poor missing mass resolution and low
statistics. This situation has recently changed with a set of
experiments performed at Jefferson Lab, especially with E01-011 in Hall
C. Taking advantage of the newly achieved technical improvements these
important questions can be addressed in a comprehensive manner. With the
presently achievable resolutions the ![](media/image35.wmf) coupling can
also be probed by using neutron rich light nuclei.

**Measurement and Feasibility:** As an extension of E01-011 it is
proposed to measure the ![](media/image36.wmf) reaction in
![](media/image37.wmf) and ![](media/image38.wmf)to produce medium-heavy
hypernuclei, namely ![](media/image39.wmf)and ![](media/image40.wmf).
Furthermore, it is proposed to investigate hypernuclear structure of
neutron rich ![](media/image41.wmf) hypernuclei in the following
reactions![](media/image42.wmf) and ![](media/image43.wmf). In all
reactions, the kaons will be detected in the HKS spectrometer in
coincidence with the scattered electrons in the Enge or HES spectrometer
(under construction). Preliminary results of E01-011 show that the
achieved HKS spectrometer resolution is consistent with the design
specifications and that the tilt of the Enge spectrometer, implemented
to reduce bremsstrahlung and Moeller induced events, has been
successful. The presently achieved signal over accidental rates allows
for a high luminosity running consistent with acceptable production
rates. The ultimate goal of a missing mass resolution of 300 keV,
although not yet demonstrated, appears to be achievable with the present
understanding of the Enge spectrometer and its detector package.

**Issues:** While the Enge spectrometer can be used to perform part of
this experiment, the HES spectrometer combined with a new splitter
magnet would be a better alternative. Due to its larger central momentum
range the HES will give needed flexibility to run this experiment in
Hall C in parallel with activities in the other Halls. Furthermore the
required resolution for the exploration of the heavy nuclei must reach
the stated 320 keV goal so that the signal over background is much
improved and thus the required statistics can be better optimized for
the available beam time. The collaboration is encouraged to build and
test the HES in combination with the new splitting magnet in order to
take advantage of the various available beam energies in Hall C and
projected improved missing mass resolution.

**Recommendation:** Approve for 20 days in Hall C

## 

**Appendix E**

## 

## Individual Letter of Intent Reports

**Letter of Intent:** LOI-05-101

**Title:** Charged Electroproduction Ratios at High p~T~

**Spokespersons:** Garth Huber

**Motivation:** It is planned to measure exclusive charged pion
electroproduction at large Q^2^ and large momentum transfer t, while
keeping --t \> Q^2^. There are no data in this kinematical region yet.
The theoretical interest in such measurements is to learn about a
reaction with two (moderately) large scales, Q^2^ and t, and see the
eventual onset of the hard scattering regime. The measurement may
possibly provide a test of the handbag approach for hard wide-angle
reactions from which predictions on the π^-^/π^+^ cross section ratios
for either longitudinally or transversally polarized photons are
available. A strong dependence of the cross sections on the photon
polarization is expected theoretically. For the ratio of transverse
cross sections there also exists a prediction by Nachtmann which holds
for small t and large photon virtuality.

**Measurement and Feasibility:** It is planned to measure the cross
sections for ep → e´π^+^n, ed → e´π ^+^nn and ed → e´π^-^pp at Q^2^ = 2
GeV^2^, W\>2 GeV and for six c.m.s. scattering angles, including 90^°^.
The various cross sections allow for an extraction of the one for γ\* n
→ π^-^ p. The experiment is similar to the pion form factor measurement
E93-011. Preliminary data from the latter for scattering angles smaller
than 75° and at W = 2 GeV, Q^2^ = 2.5 GeV^2^ indicate the feasibility of
the planned experiment.

**Issues:** Separation of the longitudinal and transverse cross sections
is important for a comparison with theory. Two values of ε in the
planned experiment will allow a partial separation of the two cross
sections. The limited azimuthal coverage, on the other hand, will not
allow a separation of the two interference cross sections, σ~LT~ and
σ~TT~ from the longitudinal one. Therefore, in a full proposal, the
authors should demonstrate the quality of the longitudinal/transverse
separation.

**Recommendation:** The PAC considered this letter of intent with
interest and found the planned experiment compelling. It feels, however,
that the theoretical understanding of exclusive meson electroproduction
for the chosen kinematics is not yet sufficiently well developed. This
may prevent an interpretation of the obtained data. The planned
experiment seems to fit more into the forthcoming JLab 12 GeV upgrade
program.

## 

**Letter of Intent:** LOI-05-102

**Title:** Search for Light η-mesic nuclei via recoilless A(e,e´p )

**Spokesperson:** Liping Gan

**Motivation:** Here the authors propose to search for nuclei containing
a bound η using the reaction γ^\*^ + A → p + ~η~(A -- 1 ) with ^4^He and
^12^C as targets. At present, any experimental evidence for η-mesic
nuclei is inconclusive. If the authors succeeded in producing η-mesic
nuclei, this would be a nice discovery. The unambiguous identification
of such nuclei would provide our first real understanding of the η N
interaction, and would undoubtedly stimulate a great deal of theoretical
work.

**Measurement and Feasibility:** The authors propose an experimental
setup closely related to that currently being used by the hypernuclear
physics collaboration. The scattered electron would act as a tag for the
virtual photon, and would be detected by the HES. The knock-out proton
would be detected by the HKS. The authors state that the kinematics are
chosen such that the resulting eta/nuclear system is close to
recoilless. The π^-^ and p from the decay of the eta would be detected
by a two-arm scintillator telescope oriented perpendicular to the beam
in order to reduce background.

It is not at all clear that the suggested kinematics are optimal, and in
an eventual proposal, this issue should be addressed in detail. For
instance, plots illustrating event rates and background as a function of
energy would be quite useful. Furthermore, at least naively, the high
resolution of the HKS and HES would seem fairly irrelevant to their
search. It is quite possible that it would be advantageous to sacrifice
resolution for larger acceptance in the experimental design. Finally,
there is a danger that the elements of the scintillator telescope, which
are in close proximity to the target, may experience very high.rates or
even damage. This issue needs to be looked at carefully, including the
possibility that an absorber such as a few millimeters of Pb might be
required.

In summary there is a long history of interest in identifying η - mesic
nuclei, and indeed, their discovery would be quite valuable. Given the
challenge that this has represented to experimenters it is important in
an eventual proposal to make a convincing *quantitative* argument
explaining why this experiment would succeed where others have failed.

**Recommendation:** N/A

##  

**Letter of Intent:** LOI-05-103

**Title:** The search for non-nucleonic degrees of freedom in the
deuteron.

**Spokespersons:** Dipangkar Dutta, Haiyan Gao, and Roy Holt

**Motivation:** The authors propose to measure the cross section for
dual ∆ photo-production in the reaction γd → ∆^++^ ∆^-^ . In particular,
they propose to look for a sharp increase in the production cross
section for this reaction at short distances due to the onset of QCD
effects. At sufficiently short distances, QCD predicts that the six
quarks in the deuteron can reorganize and mix into a six-quark color
singlet. There are five such states, only one of which is nucleonic in
nature. The remaining states are referred to as having hidden color.
Thus, if the nucleons are sufficiently close, based on symmetry alone,
one would expect a five-fold increase in the cross section for dual ∆
photo-production, an effect that would be a striking smoking gun for the
emergence of the dominance of quark degrees of freedom. The literature,
on the other hand, contains other references suggesting that the ∆∆
component of the deuteron wave function could be far smaller than the
suggested 80%. Work by such authors as H. Arenhövel, E. Lomon and F.
Khanna are not cited in the LOI's Reference 4b, where the 80% number is
suggested. In an eventual full proposal, the relationship between
observing dual ∆s and the large "hidden color" component of the deuteron
wave function should be discussed, and the assumptions upon which this
prediction is based should be elaborated further.

**Measurement and Feasibility:** The authors envision performing the
experiment in Hall C using the SOS and HMS spectrometers. The authors
have chosen to consider kinematics such that both the π^+^ and the
proton would be detected by the SOS spectrometer. The ∆^-^ will decay
into a π^-^ and a neutron, of which the pion will be detected by the
HMS. The only background that was identified as an issue is the process
γ + d → π^+^ π^−^ p n, for which there is apparently only one
measurement that does not provide sufficient information on cross
section. For this reason, to estimate their rates, the authors analyzed
existing data from Hall B and looked at π^+^ π^-^ p events. By plotting
the invariant mass of the π^+^ p system versus the missing mass of the
same system, the authors state that they have identified a set of events
containing dual ∆ production, and fit the apparent background. The event
and background rates based on these studies suggest that the measurement
is feasible. In an eventual proposal, the studies resulting in this
conclusion should be more fully discussed There might be an issue with
the Coulomb interaction between the proton and the positive pion which
will be detected in the small solid angle detector SOS.

**Recommandation:** N/A

**Appendix F**

**Jefferson Lab Experiments, PAC 4-28,**

**Grouped by Category**

> (To access Appendix F, go to
> <http://www.jlab.org/exp_prog/PACpage/pac.html> )

#