The Nature of the Quark- Anti-quark Sea of the Proton and Nuclei: FNAL E906

1. The Nature of the Quark- Anti-quark Sea of the Proton and Nuclei: FNAL E906 Don Geesaman 2 February 2009

2. Simple view of the quark/parton distributions Motivated by desire to link to constituent quark or bag models, the hope was that at some long wavelength, valence-like quark distributions plus glue would describe the proton, and the sea of quark-antiquark pairs and could be generated by gluon-radiation u g • QCD is Flavor symmetric • equal up and down quark-antiquark pairs u

3. xtarget xbeam Drell-Yan scattering: The laboratory for sea quarks p Use a proton beam: primarily u quarks at high 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. v target E906 Spect. Monte Carlo

4. FNAL E866 in 1996 mapped out the light antiquark flavor asymmetry: • Naïve Assumption: • E866/NuSea (Drell-Yan) • Knowledge of distributions is data driven • Sea quark distributions are difficult for Lattice QCD

5. LA-LP-98-56 This is a non-perturbative phenomenon.The simplest explanation is the pion cloud of the proton but there are other possible explanations The proton spends part of its time as a neutron plus π+ |P> = α|uud> + β|udd> |uđ> This can explain extra d anti-quarks in the proton. We know pion cloud effects are important in quark models.

6. Other implications New insight from strange quark distributions. ANL HERMES results show strange quark distributions are different than light quark distributions Close relation between anti-quark distributions and the spin distributions carried by the quarks

7. LA-LP-98-56 Structure of the nucleon: What produces the nucleon sea? • pQCD - Gluon splitting? • Meson Cloud? Chiral Solitons? Instantons? • Models describe well, but not — pQCD becoming dominant? Peng et al.

8. Alde et al (Fermilab E772) Phys. Rev. Lett. 64 2479 (1990) Parton Distributions in Nuclei • 1984 – Parton distributions in the nucleus are different EMC effect – nucleon carries smaller fraction of momentum or changes in proton structure Shadowing or parton-fusion • Expected large pion-cloud effects • 1990 – FNAL E772 Drell-Yan measurement showed there was little change in sea quarks for x~0.1-0.2 • But this is also the regime where the effects are small in deep inelastic scattering. • Most of our previous knowledge of antiquark distributions comes from neutrino scattering on nuclear targets.

9. average spacing at ρnm ~ 1.8 fm Radius of a nucleon ~ 0.8 fm average spacing at 3ρnm ~ 1.3 fm Our visual images of a nucleus OR “nucleons” held apart by short range repulsion but even in 208Pb, half the nucleons are in the surface

10. Main Injector 120 GeV Tevatron 800 GeV Advantages of 120 GeV Main Injector The future: Fermilab E906 • Data in 2010 • 1H, 2H, and nuclear targets • 120 GeV proton Beam The (very successful) past: Fermilab E866/NuSea • Data in 1996-1997 • 1H, 2H, and nuclear targets • 800 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 xLuminosity for same detector rate as 800 GeV beam 50 x statistics!! Fixed Target Beam lines

11. Typical statistical errors from E906 at 120 GeV The nucleus The proton

12. Parton Energy Loss • Colored parton moving in strongly interacting media. • Only initial state interactions are important—no final state strong interactions. • E866 data are consistent with no energy loss • Energy loss  1/s—larger at 120 GeV • Important to understand Relativistic Heavy Ion Collision data.

13. Where do we stand • We first proposed this experiment in 1999 • We received Scientific Approval in 2002 • Issues • Conflict with maximum collider and neutrino experiment intensity • Nuclear Physics funding for experiment • Resolution 2006-2009 • Scenario for running consistent with FNAL need for test beams • DOE Nuclear Physics funding secured • FNAL funding of installation in question? • Redesign of experiment to allow transfer ONP funding for FNAL M&S • Significant new groups have joined including 4 from Japan, 2 from Taiwan and 3 from US: U of Maryland, U of Michigan and JLAB. • Memorandum of Understanding and Phase II approval in December 2008 • Experiment will being running in 2010.

14. Fermilab E906/Drell-Yan Collaboration Abilene Christian University Donald Isenhower, Mike Sadler, Rusty Towell Academia Sinica Wen-Chen Chang, Yen-Chu Chen, Da-Shung Su 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, Dave Christian University of Illinois Naomi C.R Makins, Jen-Chieh Peng KEK Shin'ya Sawada Kyoto University KenIchi Imai, Tomo Nagae Ling-Tung University Ting-Hua Chang *Co-Spokespersons Los Alamos National Laboratory Gerry Garvey, Xiaodong Jaing, Mike Leitch, Pat McGaughey, Joel Moss University of Maryland Prabin Adhikari, Betsy Beise University of Michigan Wolfgang Lorenzon, Richard Raymond RIKEN Yuji Goto, Atsushi Taketani, Yoshinori Fukao, Manabu Togawa Rutgers University Ron Gilman, Charles Glashausser, Elena Kuchina, Ron Ransome, Elaine Schulte Texas A & M University Carl Gagliardi, Robert Tribble Thomas Jefferson National Accelerator Facility Dave Gaskell Tokyo Institute of Technology Toshi-Aki Shibata, Yoshiyuki Miyachi

15. Summary • The origin and structure of the sea is a central theme in the physics of the nucleon and nucleus • We need to push to higher quark fraction momentum values and FNAL E906 is especially well suited for this. • The new knowledge of antiquark distributions has implications on possible new physics at the LHC, for example, limits on new W bosons. • We expect to begin taking data in 2010.