# Presentation: 580393

## Summary: Fixed Target Experiments (E5) Organizers:  K. Kumar, R. Ray, P. Reimer, M. Strovink

- Snowmass 2001
- 20 Jul 01
*Paul Reimer *(ANL)

- Facilities
- CP violation
- , K  , K 
- Spectroscopy
- Low-energy nucleon physics
- Structure Functions
- Parton distributions
- Spin structure functions
- Electroweak Standard Model
**-*e* conversion

- [Neutrino physics and experiments at the front end of a neutrino factory belong to Group E1]

## E5 working group participants

- M. Aoki, Ed Blucher, Tom Bowles, Stan Brodsky, Alak Chakravorty, Martin Cooper, Kees de Jager, Fritz de Jongh, Abhay Deshpande, Steven Dytman, Alex Dzierba, Gerald Gabrielse, Geoff Greene, Rajan Gupta, Rob Harr, Mike Hebert, Dan Kaplan, Peter Kasper, Peter Herczeg, Pervez Hoodbhoy, Gerry Jackson, Ed Kinney, Yury Kolomensky, Krishna Kumar, Y. Kuno, Alex Kushnirenko, Sasha Ledovskoy, Anatoli Lednev, GeiYoub Lim, Bill Marciano, Joe Mildenberger, Bill Molzon, Craig Moore, Bill Morse, K. Nagamine, Ken Nelson, Fred Olness, Jen-Chieh Peng, Rainer Pitthan, Stephen Pordes, Ron Ray, Paul Reimer, Lee Roberts, Thomas Roser, A. Sato, Bob Tschirhart, Shinya Sawada, Paul Souder, Marco Sozzi, Mark Strovink, Dietrich von Harrach, Dieter Walz, Mike Woods, K. Yoshimura, Albert Young

## New (or improved) hadron facilities

| Facility | Beam  Energy | Intensity | Notes |
| --- | --- | --- | --- |
| Japanese High Intensity Proton Accelerator (JHF) | 50 GeV protons | 1 MW 
(5MW upgrade)
16 A | Project is funded (phase 1) Completion in 2007
LOI’s solicited soon |
| Brookhaven AGS | 24 GeV protons | 0.14 MW
(1 MW upgrade 1014 at 2.5 Hz) | Available when RHIC runs
Upgrade requires 1.2 GeV linac |
| Fermilab Main Injector | 120 GeV protons | 0.2 MW
3x1013 at 0.3 Hz | Low intensity beams ~2002
CKM in 2007 |

- New (or improved) hadron facilities

- Low Energy AntiProtons
- Commercial (medical) applications

- Japanese High Intensity Proton Accelerator

*Sawada*

## New (or improved) lepton and photon facilities

- New (or improved) lepton and photon facilities

| Facility | Beam | Intensity | Notes |
| --- | --- | --- | --- |
| Jefferson Lab | 12 GeV polarized e | 50 A CW | New Hall D; 11 GeV Halls A, B, C
Physics ~2008 |
| SLAC 
End Station A | 10-50 GeV polarized e
polarized   | 10 A 
120 Hz | 

Coherent bremsstrahlung  |
| TESLA-N

ELFE@DESY | 250500 GeV polarized e
20-30 GeV e | 20 nA 5 Hz

30 A CW | Populate missing RF buckets

HERA ring used as stretcher |
| NLC | 250-500 GeV polarized e  | 27 A
120 Hz | Spent beam |

- TESLA-N

*Von Harrach*

## CP violation

- results are now consistent; lattice calculations at relevant precision are at least 5 years away.
- Direct CP violation is established, consistent with the CKM formalism of the SM.
- Are there other sources of CP violation?

*Sozzi, Blucher*

- Fixed target experiments offer unique opportunities to address this physics.

- Almost any extension to the SM includes new possibilities for CP violation.

## To search for new physics, the SM must be over-constrained and tested for consistency.
This requires control of experimental and theoretical errors.  The only processes promising both are:
B decays: BKs, Bs mixing
K decays: KL , K++

- To search for new physics, the SM must be over-constrained and tested for consistency.
- This requires control of experimental _and_ theoretical errors.  The only processes promising both are:
- B decays: BKs, Bs mixing
- K decays: KL , K++

- BR(KL )  |Vcb|4 (3.1 ± 1.3) x 10-11
- Theoretical error 1-2%

- Expected measurement precision for CKM parameters from K and B decays

- CP violation (cont’d)

- BR(K+ +)  |Vcb|4 |Vtd|2(0.9±0.3) x 10-10
- Theoretical error ~5%
- Experimental errors are dominated by Vcb, mc and mt .

*Ledovskoy*

## CP violation (cont’d)

- Together the two K  measurements can determine
- sin(2) without |Vcb| uncertainty.

- New physics could be manifested in different sin(2) measurements from the K and B systems.

- K  and BKs  are distinctly different processes that
- could be impacted by new physics in different ways:

- BKs includes tree level processes:

- CP violation (cont’d)

- KL 0 proceeds only through 2nd order loop diagrams:

- To fully explore the consistency of CP violation with the SM, all four well-controlled processes must be measured.

## BNL787:  Stopping experiment looking at K--e decay chain -- 1 clean event.
BNL949:   Upgrade to 787: expects 5-10 events at SM level.
CKM:             Newly approved Fermilab experiment -- decays in flight with velocity spectrometer -- expect 100 events with 10% background.

- BNL787:  Stopping experiment looking at K--e decay chain -- 1 clean event.
- BNL949:   Upgrade to 787: expects 5-10 events at SM level.
- CKM:             Newly approved Fermilab experiment -- decays in flight with velocity spectrometer -- expect 100 events with 10% background.

- CP violation (cont’d):  K+ +

*Kushnirenko*

- CKM detector

## KEK E791a:  1010 SES measurement to run in 2003 -- engineering run for eventual JHF experiment to collect 1000 events.  Backgrounds under evaluation.

- KOPIO:  Low energy method using micro-bunched beam, kinematics from timing and photon pointing, hermetic photon veto.  Experience
- from BNL787 measurement of K+ + directly applicable.  40 events/yr at SM sensitivity with S/B of 2.  Awaiting NSF construction funds.

- CP violation (cont’d):  K0 0

- KAMI:  High energy method proposed at Fermilab.  90 events/yr at SM sensitivity with S/B of 4.  Photon veto efficiency critical.

*Mildenberger*

*Lim*

*Ledovskoy*

## Hall D - Jefferson Lab

-  (L = qq angular momentum)

**exotic**
**nonets**

**0 ****– +**

**0 ****+ –**

**1 ****+ +**

**1 ****+ –**

**1****– +**

**1 ****– –**

**2 ****– +**

**2 ****+ –**

**2 ****+ +**

**0 ****– +**

**2 ****– +**

**0 ****+ +**

**Glueballs**

**Hybrids**

**1.0**

**1.5**

**2.0**

**2.5**

**qq Mesons **

**L = 0**

**1**

**2**

**3**

**4**

**Ground state ****nonets**

**Radial ****excitations**

**Gluonic Excitations**

- Expected
-  fJ(2220)

**Hall D - Jefferson Lab**

**CLEO-C plans to make complementary measurements of:**
- Glueballs (non-exotic QN)
- Charmed hybrids

- Focus on gluonic excitations leading to exotic QN. These are expected to be enhanced in photoproduction as opposed to pion beams owing to spin alignment of quarks in the probe.
-   Linear polarized photons for partial wave analysis
-   Upgrade of CEBAF to 12 GeV

- Spectroscopy

**CLEO-C**

*Dytman*

*Dzierba*

## Particle physics with ultracold neutrons

- Recent progress in superthermal UCN sources has demonstrated efficient production mechanisms
- This has spawned a new generation of neutron experiments: LANSCE, NIST, ILL, PSI, KEK, ...
- The Spallation Neutron Source           should provide beamlines for the following generation of neutron experiments ~2007

- World record UCN density at LANSCE

**ILL Density**

- n density (cm-3)

*Bowles*

*Greene*

- A permanent neutron electric dipole moment?
- Sensitive probe of new sources of CP violation
- Current limit: ~10-25 e-cm
- Standard Model prediction: ~10-31
- Many SUSY-GUT models predict values ranging from 10-27 to 10-25
- New  LANSCE experiment using Ultra-Cold Neutrons seeks to reach 10-28 sensitivity: feasibility experiments in progress; experiment launches ~2004

*Cooper*

## Vud from neutron beta decay

- When current data including** ft** measurements of super-allowed nuclear beta decay are used, the error on Vud dominates the unitarity test.

- Vud from neutron beta decay

*Young*

- An alternative approach using UCN sources will allow more precise measurements of neutron lifetime and  -asymmetry.
- UCNA collaboration at LANSCE:
- Proposed error on -asymmetry ~ 0.3%
- Data taking planned ~2003

## Precise CPT test using antihydrogen

- Best CPT test with baryons:

- ATRAP collaboration goal:  extend the proton – antiproton CPT test by comparing laser spectroscopy of hydrogen and anti-hydrogen
- New facility: Antiproton Decelerator at CERN
- Plan: make cold anti-hydrogen from cold antiprotons and positrons
- Ultimate goal:  improve lepton and baryon CPT tests to same level as      system: ~10-18 accuracy

*Gabrielse*

## What happens to          as x grows?
How is the nucleon’s quark-antiquark sea generated?
Gluon splitting (                            ) cannot produce this asymmetry.
Fundamental to understanding of non-perturbative QCD.
Extract           from Drell-Yan cross section ratio.
Fermilab P906 being considered.
JHF proposal also expected (Sawada).

- How is the nucleon’s quark-antiquark sea generated?
- Gluon splitting (                            ) cannot produce this asymmetry.
- Fundamental to understanding of non-perturbative QCD.
- Extract           from **Drell-Yan** cross section ratio.
- Fermilab P906 being considered.
- JHF proposal also expected (*Sawada*).

- Unpolarized structure functions

- What would we like to know?
- Large-x proton structure is important.
- QCD evolution:
- (large x, low Q2)  (low x, high Q2)
- Intrinsic charm (bottom)?  Need  measurements near threshold.
- Nuclear corrections ? (*Olness, Hoodbhoy, de Jager*)
- Especially important at high x (JLab).

- E866/NuSea

## Spin structure functions

- The sea is implicated:                      gluons are likely polarized.

- What carries the spin ***S*** of the nucleon?

- Studied using spin-dependent deep-inelastic lepton-nucleon scattering.
- Data on polarized 1H, 2H, and 3He from CERN, DESY, and SLAC are well described by perturbative QCD.
- These data establish a nuclear spin deficit:

- The first direct measurements of gluon polarization will take place at DESY, RHIC, and SLAC over the next 5 years (*Kinney, Deshpande*).

- To cleanly establish gluon polarization and/or to discover a further spin deficit, precision measurements at new facilities would be required.

## Proton spin structure function g1p

**eRHIC:** 3-12 GeV e- on 50-250 GeV p

**TESLA-N: **250 GeV** **e- on fixed target

- Proton spin structure function g1p

- Ultra-precise measurements of spin dependent electron-proton DIS can be carried out either at a future linear collider or a polarized electron-hadron collider.

*Von Harrach*

*Deshpande*

**x**

## Neutron spin structure function g1n

- Neutron spin structure function g1n

- Ultra-precise measurements of spin dependent electron-neutron DIS require the full (“spent”) beam current envisioned for a future linear collider.

- fit to points

*Kolomensky*

- Precision neutron measurements are feasible with a dense gaseous polarized 3He target.
- 1014 e/sec are required.
- g1n can be measured precisely down to x ~ 103, establishing whether it is divergent.
- Requirements on polarized beam properties are modest.

- This is a clean experiment using the “spent” electron beam of a linear collider.

## Weak mixing angle from Møller scattering

- Why?

*Marciano*

- (natural relation at tree level)

- loop corrections

- Crucial consistency check if new scalars are discovered and identified
- Comparison of             at different energy scales probes new physics, e.g. new gauge bosons, extra dimensions, compositeness,...

- (world average ~0.0002)

## Weak mixing angle from Møller scattering (cont’d)

- Weak mixing angle from Møller scattering (cont’d)

*Souder*

- Several possibilities to achieve
- Giga-Z:  1 billion Z decays, with e**-** polarization
- Polarized e**-** e**-** collisions at high energy with 250 fb-1
- Fixed target parity violating e- e- scattering:

- 50 GeV experiment underway at SLAC (E158):  goal is
- probes chirality violating compositeness scale to ~15 TeV
- sensitive to Z’ from GUTS, extra dimensions ~ 0.8 - 2.5 TeV
- physics in 2002
- Figure of merit rises with Ebeam: 250-500 GeV experiment can potentially improve error by a factor of 10.

## Weak mixing angle from Møller scattering (cont’d)

- Possible experiment at a linear collider

|  | E158 | LC |
| --- | --- | --- |
| Energy (GeV) | 48 | 250-500 |
| Intensity/pulse | 3  1011 | 6  1011 |
| Pulse Rate (Hz) | 120 | 120 |
| Pe | 75% | 90% |
| Time (s) | 5  106 | 2  107 |
| ALR (ppm) | 0.18 | 1.8 |
| ALR (ppm) | 0.01 | 0.006 |
| sin2(W) | 0.0007 | 0.00007 |

- Compton Polarimetry (dominant systematic error)

*Pitthan*

*Woods*

## Searches for lepton flavor violation

*Molzon/Hebert*

- Experimental evidence supports near conservation of a family quantum number **G**.
- These laws are accidental -- no known gauge symmetry protects lepton flavor.
- Essentially all extensions to the SM allow lepton flavor violation, which in the charged sector would be clear evidence for physics beyond the SM.

##   -e conversion

*Marciano*

## -e conversion at BNL AGS: MECO

**-*e* conversion at BNL AGS: MECO

- Essential ingredients:
- Higher (1000) muon flux (idea from MELC at MMF):  high Z target; capture ’s in graded solenoidal field; transport ’s in curved solenoid.
- Pulsed beam (nsecs every sec) to eliminate prompt backgrounds, as at PSI.
- Detector with improved resolution, background rejection, and rate tolerance: immersed in graded solenoidal field; ~axially symmetric, high resolution elements.

*Molzon/Hebert*

## Ideas for -e conversion at JHF

- JHF muon beam would use an FFAG ring (model below) to coalesce momenta.

*Kuno*

## Ideas for -e conversion at JHF (cont’d)

- MECO is a fully designed, simulated, and costed proposal awaiting NSF construction funds.
- PRISM (**-*e* conversion at JHF) is exploring a conceptual design, and is not yet part of the Phase 1-2 JHF program.
- PRISM hopes to extend MECO’s  single-event-sensitivity by a factor 50-100 to ~2-4 x 10-19, based on two key elements:
- 1.  Higher proton current at JHF, leading to a 10-40x increase in muon rate.
- 2.  Muon *******p*** vs. *******t**** *phase rotation using a FFAG ring, collapsing the muon momentum spread, with two major benefits:
- Muons stop in a thinner target, allowing improved electron energy resolution.
- Pion, proton, and neutral backgrounds are suppressed.
- But the FFAG’s 1 kHz 100 kHz(?) pulse rate isn’t ideally matched to the muon lifetime: faster detectors would be required.

*Yoshimura*

## Closing thoughts

- Fixed target experimentation remains vigorous and important.

- In certain cases, the information that is sought...
- ...wouldn’t readily be obtained if other techniques were used, _and_
- ...could change our thinking about elementary physics.

- This workshop has reminded us of some examples:
- Well-controlled tests of the SM CP formalism in K decay
- Ultraprecise determination of the weak mixing angle and its evolution
- Lepton flavor violation tests at PeV scales in the charged sector

- As new facilities are planned, we should identify any unique opportunities that would be presented by fixed target experiments there, and, where it is practical, we should sieze those opportunities early on.