The Old Man and the Sea Donald Geesaman

The Old Man and the Sea Donald Geesaman Achievements and New Directions in Subatomic Physics

In the quark model and QCD, it seems like the valence quarks and glue get all the respect § Valence quarks determine the charge and flavor of hadrons § Seem to explain the magnetic moments. § We thought, until 1990, that the valence quarks carried the spin § New accelerators, like the JLAB 12 x quarks Ge. V upgrade get built to study high § The glue dominates hadron structure at low x § New accelerators, like the electron-ion collider are planned to study the glue. 2

Maybe the sea quarks will go away! Motivated by desire to link to constituent quark or bag models, the hope was that as some low scale, Q, of a few hundred Me. V/c, valence-like quark distributions plus glue would describe the nucleon, and the sea could be radiatively generated. Gluck, Godbole, and Reya (Z. Phys. C, 66 (1989) u It was then realized that some valence-like sea was needed. GRV, ZPC 53, 127(92) g u Then it was found that the sea was not flavor symmetric. 3

Most of the information on the sea came from deep-inelastic lepton scattering, especially charged current neutrino experiments Q 2 = (k-k’) 2 = mass 2 of the virtual boson x= Q 2/(2 m ) is the fractional momentum nucleon carried by the parton = E beam- E scattered y = / E beam muon and electron scattering~ charge current scattering ~ anti- c. c. scattering~ parity violating scattering, F 3~ parity violating anti- scattering~ The high statistics experiments are all done on nuclear targets 4

FNAL E 866 Drell-Yan measurements on hydrogen and deuterium determined the x dependence of d-u Towell et al. Phys. Rev. D 64, 0522002 (2001) Small but very important Q 2=54 Ge. V 2 Since this is a flavor nonsinglet quantity is true at all scales. 5

The simplest explanation is the pion cloud The proton spends part of its time as a neutron plus π+ LA-LP-9856 |P> = α|uud> + β|udd> |uđ> We know pion cloud effects are important in quark models. 6

Of course Tony Thomas and his collaborators knew all this. Indeed they invented much of it. § § 1972 Sullivan 1980 Cloudy Bag Model Pions have to be included to preserve chiral symmetry in bag or bag-like models § 1983 Tony used the calculated pionic content and measured DIS to conclude that the fraction of the momentum of the nucleon carried by pions was 5+/-1. 5% and was consistent with a bag radius of 0. 87 +/-0. 10 fm. Even today this is not such a bad representation of The problem is it also predicts the ratio as x goes to 1 from the charged and neutral pion Clebsch-Gordan coefficients 7

Structure of the nucleon: What produces the nucleon sea? § § § p. QCD - Gluon splitting? Meson Cloud? Chiral Solitons? Instantons? Models describe well, but not — p. QCD becoming dominant? ? LA-LP-9856 Peng et al. No one has come up with a physical mechanism to make 8

A key seems to be the spin carried by the nonsinglet anti-quarks E 866 Pion content – flavor non-singlet anti-quarks carry 0 net spin. Pions do affect the spin carried by the quarks through their interaction with the remnant baryon Statistical Model - Bourelly and Soffer Instanton Chiral quark- Soliton - Dresslar et al. EPJC 18, 719 (2001) gives similar result. 9

What are the correlations between the q and q pairs in the sea? § Gluon 1 - , 3 S g 1 Flavor neutral § Meson 0 - , 1+ § Vacuum 0 +, 3 P 0 Flavor neutral 10

What do the data tell us ? § E 866 - PR D 64, 052002 (2001) Q § HERMES - PR D 71, 012003 (2005) 2=54 2=3 Ge. V 2 § COMPASS- ar. Xiv: 0909. 3729 v 1 Q § de Florian et al - PRL 101, 072001 (2008) Q To be compared with 0, -1, -5/3 * flavor asymmetry Ge. V 2 2=10 Ge. V 2 3 σ from zero 2 σ from. 197=Chiral soliton 11

COMPASS and HERMES Data DNS 2005 -. 03 to -. 19 DSSV 2008 12

What does Tony say now? Myhrer-Thomas picture of proton spin § Relativistic valence quarks - orbital motion accounts for 35% § quark-quark hyperfine interaction § Pion cloud Only the hyper-fine interaction could contribute to so I believe the prediction is small. 13

HERMES has a new slant on the strange quark distributions. A. Airapetian et al Phys. Lett. B 666, 446 (2008) Usually s(x)+sbar(x ) ~ κ (ubar+ dbar) with κ ~ 0. 5 Best handle has been considered to be multi- muon events in neutrino scattering. HERMES looks at polarized DIS on deuterium and compares inclusive with semiinclusive kaon multiplicities 14

HERMES sees little strange quark content for x>0. 1 and s(x)+sbar(x) ~ ubar(x)+dbar(x) at x< 0. 03! A. Airapetian et al Phys. Lett. B 666, 446 (2008) Q 2=2. 5 Ge. V 2 15

How is this consistent with years of neutrino multi-muon data? ν + s → μ+ + c →μNUTEV, PRD 64 112006(2001) CTEQ, JHEP 42, 89 (2007) 16

Nu. Te. V Data Suggest Small Strange vs Anti-strange Asymmetry PRL 99, 192001 (07) 17

Comparison of ubar+dbar-s-sbar with dbar-ubar Based on the HERMES result and assuming the strange quark distribution represents the gluon -splitting induced distribution, the shape of the nonperturbative vs 0. 25 *HERMES is similar to 18

Nuclear corrections in charged lepton and neutrino scattering are different Charged lepton Fe/D Neutrino Fe/D 19

Parton Distributions in Nuclei Alde et al (Fermilab E 772) Phys. Rev. Lett. 64 2479 (1990) § 1984 – Parton distributions are different EMC effect – nucleon carries smaller fraction of momentum or changes structure Shadowing § Expected large pion-cloud effects § 1990 – little change in sea quarks for x>0, 1 My one publication with Tony 6 th on his citation list 20

Our visual images of a nucleus average spacing at ρnm ~ 1. 8 fm Radius of a nucleon ~ 0. 8 fm average spacing at 3ρnm ~ 1. 3 fm OR “nucleons” held apart by short range repulsion but even in 208 Pb, half the nucleons are in the surface Remember 1983 Thomas result favored a bag radius of 0. 9 fm 21

We want to describe a nucleus § Hadronic Description § – what are the clusters of quarks in a nucleus? – know the parton distributions change – exemplified by ab initio calculations with potentials • • § NN NNN + NNNN + Bare form factors Meson exchange currents Past two decades have shown this is remarkably successful Pure QCD Description • EMC effect • shadowing • x>1 § One problem is always whether our description of a bare proton is good enough. The second is how to actually calculate many body effects beyond mean field? 22

Drell-Yan scattering: A laboratory for sea quarks Use a proton beam: primarily u quarks at high x. Detector acceptance chooses x target and x beam. § Fixed target high x F = x beam – x target § Valence Beam quarks at high-x. (e 2 u)/(e 2 d) > 8 Dominated by u quarks § Sea Target quarks at low/intermediate-x. xbeam E M 906 on S te pe Ca ct rlo. xtarget 23

Advantages of 120 Ge. V Main Injector § § The (very successful) past: The future: Fermilab E 866/Nu. Sea Fermilab E 906 Data in 1996 -1997 1 H, 2 H, and nuclear targets 800 Ge. V proton beam Cross section scales as § § § Data taking 2010 -2012 1 H, 2 H, and nuclear targets 120 Ge. V proton Beam t rges a d T line e x Fi eam B Tevatron 800 Ge. V 1/s – 7 x that of 800 Ge. V beam § Backgrounds, primarily from J/ decays scale as s – 7 x Luminosity for same detector rate as 800 Ge. V beam 50 x statistics!! Main Injector 120 Ge. V 24

Fermilab E 906/Sea. Quest Collaboration Abilene Christian University Donald Isenhower, Mike Sadler, Rusty Towell, Shon Watson 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*, Josh Rubin, Patricia Solvignon University of Colorado Ed Kinney Fermi National Accelerator Laboratory Chuck Brown, Dave Christian Ling-Tung University Ting-Hua Chang Los Alamos National Laboratory Gerry Garvey, Xiaodong Jaing, Mike Leitch, Ming Liu, Pat Mc. Gaughey, Joel Moss University of Maryland Prabin Adhikari, Betsy Beise, Kazutaka Nakahara University of Michigan Wolfgang Lorenzon, Richard Raymond RIKEN Yuji Goto, Atsushi Taketani, Yoshinori Fukao, Manabu Togawa University of Illinois Naomi C. R Makins, Jen-Chieh Peng Rutgers University Lamiaa El Fassi, Ron Gilman, Elena Kuchina, Ron Ransome, Elaine Schulte KEK Shin'ya Sawada Texas A & M University Carl Gagliardi, Robert Tribble Kyoto University Ken. Ichi Imai, Tomo Nagae Thomas Jefferson National Accelerator Facility Dave Gaskell *Co-Spokespersons Tokyo Institute of Technology Toshi-Aki Shibata, Yoshiyuki Miyachi 25

Projected errors on ratios of D to H Errors on ratio ~ 1% until statistics become a factor. The absolute cross section on deuterium measures Errors limited by beam normalization and acceptance ~ 5% 26

Does deuterium structure affect the results at higher x 27

Structure of nucleonic matter: § Nucleon motion in the nucleus tends to reduce parton distributions – f(y) peaked below y=1. § Rescaling effects also reduce parton distribution for x>0. 15 § Antiquark enhancement expected from Nuclear Pions. § This data also constrains the maximum effects for deuterium. 28

Summary § The origin and structure of the sea remain critical themes in the physics of the nucleon and nucleus § We need to push to higher x values and E 906/Sea. Quest is especially well suited for this. We start this summer and run for two years. § The other really key measurement is improved precision in the spin carried by the sea quarks and the spin-correlations in the sea. – COMPASS, RHIC, J-PARC, JLAB 12 Ge. V § This is difficult and may require the next generation of polarized Drell-Yan experiments § Whatever we measure, Tony Thomas will have thought of it first and helped stimulate the experiments § And there is a chance, he may even have got it right. 29

The models all have close relations between antiquark flavor asymmetry and spin • Statistical Parton Distributions 30