The Nature of the Quark Anti quark Sea

The Nature of the Quark- Anti -quark Sea of the Proton and Nuclei: FNAL E 906 Don Geesaman 2 February 2009

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 u Don Geesaman QCD is Flavor symmetric Þequal up and down quark-antiquark pairs The Nature of the Sea 2

Drell-Yan scattering: The laboratory for sea quarks p v target Use a proton beam: primarily u quarks at high Detector acceptance chooses xtarget and xbeam. n Fixed target high x. F = xbeam – xtarget n Valence Beam quarks at high-x. n Sea Target quarks at low/intermediate-x. Don Geesaman The Nature of the Sea xbeam E M 906 on S te pe Ca ct rlo. xtarget 3

FNAL E 866 in 1996 mapped out the light antiquark flavor asymmetry: n Naïve Assumption: n E 866/Nu. Sea (Drell-Yan) n Knowledge of distributions is data driven – Sea quark distributions are difficult for Lattice QCD Don Geesaman The Nature of the Sea 4

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+ LA-LP-98 -56 |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. Don Geesaman The Nature of the Sea 5

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 Don Geesaman The Nature of the Sea 6

Structure of the nucleon: What produces the nucleon sea? LA-LP-9856 n p. QCD - Gluon splitting? n Meson Cloud? Chiral Solitons? Instantons? n Models describe well, but not — p. QCD becoming dominant? Peng et al. Don Geesaman The Nature of the Sea 7

Parton Distributions in Nuclei Don Geesaman The Nature of the Sea Alde et al (Fermilab E 772) Phys. Rev. Lett. 64 2479 (1990) n 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 n Expected large pion-cloud effects n 1990 – FNAL E 772 Drell-Yan measurement showed there was little change in sea quarks for x~0. 1 -0. 2 n But this is also the regime where the effects are small in deep inelastic scattering. n Most of our previous knowledge of antiquark distributions comes from neutrino scattering on nuclear targets. 8

Our visual images of a nucleus average spacing at ρnm Radius of a nucleon average spacing at 3ρnm ~ 1. 8 fm ~ 0. 8 fm ~ 1. 3 fm OR “nucleons” held apart by short range repulsion but even in 208 Pb, half the nucleons are in the surface Don Geesaman The Nature of the Sea 9

Advantages of 120 Ge. V Main Injector The (very successful) past: The future: Fermilab E 866/Nu. Sea Fermilab E 906 n Data in 1996 -1997 n 1 H, 2 H, and nuclear targets n 800 Ge. V proton beam n Cross section scales as 1/s – 7 x that of 800 Ge. V beam n Backgrounds, primarily from J/ decays scale as s – 7 x Luminosity for same detector rate as 800 Ge. V beam n Data in 2010 n 1 H, 2 H, and nuclear targets n 120 Ge. V proton Beam t rges a d T line e x Fi eam B Tevatron 800 Ge. V Main Injector 120 Ge. V 50 x statistics!! Don Geesaman The Nature of the Sea 10

Typical statistical errors from E 906 at 120 Ge. V The proton Don Geesaman The nucleus The Nature of the Sea 11

Parton Energy Loss n Colored parton moving in strongly interacting media. n Only initial state interactions are important—no final state strong interactions. n E 866 data are consistent with no energy loss n Energy loss 1/s—larger at 120 Ge. V n Important to understand Relativistic Heavy Ion Collision data. Don Geesaman The Nature of the Sea 12

Where do we stand n We first proposed this experiment in 1999 n We received Scientific Approval in 2002 n Issues – Conflict with maximum collider and neutrino experiment intensity – Nuclear Physics funding for experiment n 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 n Experiment will being running in 2010. Don Geesaman The Nature of the Sea 13

Fermilab E 906/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 Ken. Ichi Imai, Tomo Nagae Ling-Tung University Ting-Hua Chang Los Alamos National Laboratory Gerry Garvey, Xiaodong Jaing, Mike Leitch, Pat Mc. Gaughey, 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 *Co-Spokespersons Don Geesaman The Nature of the Sea 14

Summary n The origin and structure of the sea is a central theme in the physics of the nucleon and nucleus n We need to push to higher quark fraction momentum values and FNAL E 906 is especially well suited for this. n The new knowledge of antiquark distributions has implications on possible new physics at the LHC, for example, limits on new W bosons. n We expect to begin taking data in 2010. Don Geesaman The Nature of the Sea 15