# Presentation: 468727

## E906:  Drell-Yan Measurements of Nucleon and Nuclear Structure with the Fermilab Main InjectorPhysics Goals

- Don Geesaman
- 11 December 2006

- What will we learn?
- d-bar/u-bar in the proton
- Nuclear effects in the sea quark distributions
- High-*x* valence distributions
- Partonic energy loss in cold nuclear matter
*What requirements does the science place on the experiment?*

## What is the distribution of sea quarks?

***What is the distribution of sea quarks?***

- In the nucleon:
- Sea and gluons are important:
- 98% of mass; 60% of momentum at Q2 = 2 GeV2

- Not just three valence quarks and QCD.  Shown by E866/NuSea d-bar/u-bar data
- Significant part of LHC and RHIC beams.
- What are the origins of the sea?

- CTEQ6m

- In nuclei:
- The nucleus is not just a sum of protons and neutrons
- What distinguishes this?
- Bound system
- Are there changes in the quark structure of hadrons in nuclei?

## What we learned from E866

***What we learned from E866***

- Naïve Assumption:

- NA51 (Drell-Yan)

- E866/NuSea (Drell-Yan)

- Knowledge of distributions is data driven
- Sea quark distributions are difficult for Lattice QCD
**E906 extends this knowledge**

- NMC (Gottfried Sum Rule)

## There is a gluon splitting component which is symmetric in
         and   

By looking at 
Symmetric sea via pair production from gluons subtracts off
Nonperturbative models are motivated by the observed difference

A proton with 3 valence quarks plus glue cannot be right at any scale!!

-          and
- By looking at
- Symmetric sea via pair production from gluons subtracts off
- Nonperturbative models are motivated by the observed difference
- A proton with 3 valence quarks plus glue **cannot** be right at any scale!!

***Proton Structure:  By what process Is the sea created?***

## Proton Structure:  By What Process Is the Sea Created?

***Proton Structure:  By What Process Is the Sea Created?***

- Meson Cloud in the nucleon
- Sullivan process in DIS
- |p> = |p0> +  |N> + |> + . . .
- Instantons

- Chiral Models
- Interaction between Goldstone Bosons and valence quarks
- |u>|d+> and |d>  |u->

## Something is missing

- All non-perturbative models predict large asymmetries at high x.
- Are there more gluons and therefore symmetric anti-quarks at higher x?
- Does some mechanism like instantons have an unexpected x dependence (what is the expected x dependence for instantons in the first place?) ?

## The models all have close relations between antiquark flavor asymmetry and spin

**  ****Statistical Parton Distributions **

## Structure of nucleonic matter: How do sea quark distributions differ in a nucleus?

- EMC:  Parton distributions of bound and free nucleons are different.
- Antishadowing not seen in Drell-Yan —Valence only effect?

- Intermediate-*x* *sea* PDF’s absolute magnitude set by -DIS on iron.
- Are nuclear effects the same for the sea as for valence?
- What can the sea parton distributions tell us about the effects of the nuclear medium?
- increased meson content
- changes in hadron parton distributions in nuclei

## Structure of nucleonic matter: Where are the nuclear pions?

- The binding of nucleons in a nucleus modifies the x dependence.
- Contemporary models still predict large effects to antiquark distributions as x increases.
- Models must explain both DIS-EMC effect and Drell-Yan

**Notes:**
George Bertsch in Science:  Where are the nuclear pions?  Answers in terms of Gluonic fields

Berger and Coester:  Standard nuclear convolution:  
		F_2^A = \int dy f_N^A(y) F_2^N(x/y) + \int dy f_\pi^A(y) F_2^\pi(x/y) 
	where the F_2’s are the DIS structure functions of the nucleus, nucleon and pion and f_N/\pi^A are the nucleon/pion distribution functions. Other baryons are added as well and all is subject to conservation rules on baryon number and small f’s have total momentum conservation rules

Jung and Miller:  Start with Berger and Coester, but uses different pionic distribution function in nucleus from Ericson and Thomas—points out that Berger and Coester should have used a light cone rather that instant-(time) form nuclear wave function.

Brown et al.: Brown, Rho rescaling—inside a nuclear environment masses of hadron composed of light quarks all decrease with density (at the same rate—see eqn 2.23).  The rescaling is based on a partial restoration of Chiral Symmetry.  This the also effects the coupling strengths.  Based on this, one obtains a modified pion density distribution and follows the convolution model of Berger and Coester.

Dieperink and Korpa: First, range of curves is for various Migdal parameters.  Looks at real and imaginary parts of particle-hole (nucleon-hole?) and \Delta-hole contributions.  Also look at the self-energy of the pion propagator.  The dressed pion propagator included nucleon and \Delta terms.  These affect the pion distribution function (f_pi)

## Does deuterium structure affect the results at higher x

## Drell-Yan Absolute Cross Sections:  xtarget

- Measures a convolution of beam and target PDF
- absolute magnitude of high-x valence beam distributions
- absolute magnitude of the sea in the target
*Currently determined by ****–Fe DIS*

## Drell-Yan Absolute Cross Sections:  xtarget

***Drell-Yan Absolute Cross Sections:  x******target***

- Reach high-x through *beam proton—*Large xF large x*beam*.
- High-x distributions poorly understood
- Nuclear corrections are large, even for deuterium
- Lack of proton data
- Proton-Proton—no nuclear corrections—*4u(x) + d(x)*

## Detector acceptance chooses xtarget and xbeam.
Fixed target  high xF = xbeam – xtarget 
Valence Beam quarks at high-x.
Sea Target quarks at low/intermediate-x.

- Detector acceptance chooses xtarget and xbeam.
- Fixed target  high xF = xbeam – xtarget
- Valence Beam quarks at high-x.
- Sea Target quarks at low/intermediate-x.

***Drell-Yan scattering:  ******A laboratory for sea quarks***

- E906 Spect.
- Monte Carlo

## Method to study flavor dependence of anti-quark distributions

***Method to study flavor dependence ******of anti-quark distributions***

**Assumptions**

**Use full parton distributions in analysis. The approximate sensitivity is**

## Advantages of 120 GeV Main Injector

- The (very successful) past:
- Fermilab E866/NuSea
- Data in 1996-1997
- 1H, 2H, and nuclear targets
- 800 GeV proton beam

- The future:
- Fermilab E906
- Data in 2009
- 1H, 2H, and nuclear targets
- 120 GeV proton Beam

- Cross section scales as 1/s
*7 **x** that of 800 GeV beam*
- Backgrounds, primarily from J/ decays  scale as s
*7 **x** **Luminosity for same detector rate as 800 GeV beam*
**50 ***x*** statistics!!**

- Fixed Target Beam lines

## Partonic Energy Loss

- An understanding of partonic energy loss in both cold and hot nuclear matter is paramount to elucidating RHIC data.
- Pre-interaction parton moves through cold nuclear matter and looses energy.
- Apparent (reconstructed) kinematic values (x1 or xF) is shifted
- Fit shift in x1 relative to deuterium

- Models:
- Galvin and Milana
- Brodsky and Hoyer
- Baier *et al.*

## Partonic Energy Loss

***Partonic Energy Loss***

- E866 data are consistent with NO partonic energy loss for all three models
- Caveat:  A correction must be made for shadowing because of x1—x2 correlations
- E866 used an empirical correction based on EKS fit do DIS and *Drell-Yan*.

- E866/NuSea

- Treatment of parton propagation length and shadowing are critical
- Johnson et al. find 2.2 GeV/fm from the same data with different shadowing correction
**Better data outside of shadowing region are necessary.**

## Parton Energy Loss

***Parton Energy Loss***

- Energy loss  1/s
- larger at 120 GeV
- Ability to distinguish between models
- Measurements rather than upper limits

***Energy loss upper limits based on E866 Drell-Yan measurement***

- LW10504*** ***

- E906 expected uncertainties
- Shadowing region removed

- E906 will have sufficient statistical precision to allow events within the shadowing region, x2 < 0.1, to be removed from the data sample

**Notes:**
Brodsky and Hoyer:  Gluon Bremsstrahlung process (A^1/3 / s)

Baier:  Build on Brodsky.  Energy loss depends on characteristic scattering length (A^1/3) and on squared p_T (A^1/3) giving a total A^2/3 / s effect.  Also make predictions for both hot and cold nuclear matter.

Johnson et al.:  2.2 GeV/fm Different treatment of shadowing and parton propagation length

## Semi-Inclusive DIS—HERMES, JLab, JLab 12 GeV
Tag struck quark through leading hadron
Must understand fragmentation
HERMES will reduce statistical uncertainty but will still have significant systematic uncertainty
Dominated by systematic uncertainties

- Semi-Inclusive DIS—HERMES, JLab, JLab 12 GeV
- Tag struck quark through leading hadron
- Must understand fragmentation
- HERMES will reduce statistical uncertainty but will still have significant systematic uncertainty
_**Dominated by systematic uncertainties**_

***Other Possible Measurements of d-bar—u-bar  asymmetry***

- Drell-Yan—JPARC
- Initial phase of JPARC is 30 GeV—sufficient only for J/ studies, no Drell-Yan (no phase space for events above J/)
- JPARC Phase II—50 GeV
- great possibilities for polarized Drell-Yan
- Berger criteria for nuclear targets—insufficient energy for heavy A
- No partonic energy loss studies—xbeam-xtarget correlations
- Experimental issues:  pT acceptance, § decay in flight background
_**Physics Program cannot be reached by 30 GeV machine **_
_**(physics program strongly endorsed)**_

- There are no competing measurements

## Technical Requirements placed by the science

- Statistics – High rates, ~10 times E866
- Relative cross sections		E866	E906 Goal 1%
- relative beam intensity 		0.1%
- target thickness 			0.2%
- target composition		0.6%
- rate dependence			0.9%
- acceptance dependence		0.2%
- Absolute cross sections			E906 Goal 7%
- absolute beam intensity 		6.5%
- absolute target thickness 		0.2%
- target composition		0.6%
- rate dependence			0.9%
- acceptance 			3.0%
- radiative corrections		up to 1.0%

## Drell-Yan at Fermilab

***Drell-Yan at Fermilab***

**What is the structure of the nucleon?**
- What is d-bar/u-bar*?*
- What are the origins of the sea quarks?
- What is the high-x structure of the proton?

**Answers from Fermilab E906/Drell-Yan**
- Significant increase in physics reach over previous Drell-Yan experiments

**What is the structure of nucleonic matter?**
- Where are the nuclear pions?
- Is anti-shadowing a valence effect?
**Do colored partons lose energy in cold nuclear matter?**

## Fermilab E906/Drell-Yan Collaboration

- Abilene Christian University
- Donald Isenhower, Mike Sadler,
- Rusty Towell
- Argonne National Laboratory
- John Arrington, Don Geesaman*, Kawtar Hafidi, Roy Holt, Harold Jackson, David Potterveld
- Paul E. Reimer*,  Patricia Solvignon
- University of Colorado
- Ed Kinney
- Fermi National Accelerator Laboratory
- Chuck Brown
- University of Illinois
- Naiomi C.R Makins, Jen-Chieh Peng
- Los Alamos National Laboratory
- Gerry Garvey,  Mike Leitch,
- Pat McGaughey, Joel Moss
- *Co-Spokespersons

- University of Maryland
- Elizabeth Beise
- Rutgers University
- Ron Gilman, Charles Glashausser,
- Xiaodong Jaing, E. Kuchina, Ron Ransome, Elaine Schulte
- Texas A & M University
- Carl Gagliardi, Bob Tribble
- Thomas Jefferson National Accelerator Facility
- Dave Gaskell
- Valparaiso University
- Don Koetke, Jason Webb

## Publications of the Fermilab Drell-Yan Program

**E866/NuSea**
- E.A. Hawker *et al., **Measurement of the Light Antiquark Flavor Asymmetry in the Nucleon Sea**,* Phys. Rev. Lett. **80**, 3715 (1998).
- J.C. Peng *et al*., *d-bar/u-bar Asymmetry and the Origin of the Nucleon Sea**,* Phys. Rev. **D58**, 092004 (1998).
- M.A. Vasiliev *et al., Parton energy loss limits and shadowing in Drell-Yan dimuon production,* Phys. Rev. Lett. **83**, 2304 (1999).
- M.J. Leitch *et *al., *Measurement of Differences between J/**** and ****0** Suppression in p-A Collisions*, Phys. Rev. Lett. **84**, 3256 (2000).
- C.N. Brown *et al., **Observation of Polarization in Bottomonium Production at sqrt s = 38.8 GeV*, Phys. Rev. Lett. **86**, 2529 (2001).
- R.S. Towell *et al*.,  *Improved Measurement of the d-bar/u-bar Asymmetry in the Nucleon Sea**,* Phys. Rev. **D64**, 052002 (2001).
- T.H. Chang *et al., **J/**** polarization in 800-GeV p Cu interactions, *Phys. Rev. Lett. **91** 211801 (2003).
- L.Y. Zhu *et al.,* *Measurement of Angular Distributions of Drell-Yan Dimuons in p + d Interaction at 800-GeV/c**,* Submitted to Phys. Rev. Lett. arxiv:hep-ex/0609005.
**E789 Publications****:**
- M.S. Kowitt *et al.,*   *Production of J/**** at Large x**F** in 800 GeV/c p-Copper and p-Beryllium Collisions*, Phys. Rev. Lett. **72**, 1318 (1994).
- M.J. Leitch *et al.,*   *Nuclear Dependence of Neutral D Production by 800 GeV/c Protons,* Phys. Rev. Lett. **72**, 2542 (1994).
- C.S. Mishra et al.,   Search for the decay $D0 !*+****-*$, Phys. Rev. **D50**, 9 (1994).

## Publications of the Fermilab Drell-Yan Program

**E789 Publications (Cont.)****:**
- D.M. Jansen *et al.,*   *Measurement of the Bottom-Quark Production Cross Section in 800 GeV/c Proton-Gold Collisions*, Phys. Rev. Lett. **74**, 3118 (1995).
- M.H. Schub *et al.,*  *Measurement of J/**** and ****0** Production in 800 GeV/c Proton-Gold Collisions*, Phys.  Rev. **D52**, 1307 (1995); Phys. Rev. D53, 570 (1996).
- M.J. Leitch *et al.,*   *Nuclear Dependence of J/**** Production by 800 GeV/c Protons near x*F* = 0*, Phys. Rev. **D52**, 4251 (1995).
- C.N. Brown *et al.,*   *Nuclear Dependence of Single-Hadron and Dihadron Production in p-A Interactions at sqrt s = 38.8 GeV,* Phys. Rev. **C54**, 3195 (1996).
- D. Pripstein *et al.,*   *Search for flavor-changing neutral currents and lepton-family-number violation in two-body D*0* decays*, Phys. Rev. **D61**, 032005 (2000).
**E772 Publications:**
- D.M. Alde *et al*.,   *Nuclear Dependence of Dimuon Production at 800 GeV,* Phys. Rev. Lett. **64**, 2479 (1990).
- D.M. Alde *et al.,*   *A Dependence of J/**** and ****0** Production at 800 GeV/c*, Phys. Rev. Lett. **66**, 133 (1991).
-  D.M. Alde *et al.,*   *Nuclear Dependence of the Production of Upsilon Resonances at 800 GeV*, Phys. Rev. Lett. **66**, 2285 (1991).
- P.L. McGaughey *et al.,*   *Cross sections for the production of high-mass muon pairs from 800 GeV proton bombardment of *2*H*, Phys. Rev. **D50**, 3038 (1994).
- P.L. McGaughey *et al.,*   *Limit on the d-bar/u-bar asymmetry of the nucleon sea from Drell-Yan production*, Phys. Rev. Lett. **69**, 1726 (1992).