the old man and the sea

The Old Man and the Sea

Donald GeesamanAchievements and New Directions in Subatomic Physics

15 February 2010

2

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 GeV upgrade get built to study high x quarks

The glue dominates hadron structure at low x

New accelerators, like the electron-ion collider are planned to study the glue.

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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 MeV/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)

gq

q

u

u

It was then realized that some valence-like sea was needed.GRV, ZPC53, 127(92)

Then it was found that the sea was not flavor symmetric.

4

Most of the information on the sea came from deep-inelastic lepton scattering, especially charged current neutrino experimentsQ2 = (k-k’)2 = mass2 of the virtual boson

x= Q2/(2m) is the fractional momentum nucleon carried by the parton

= Ebeam- Escattered y = / Ebeam

)(xfdx

di

iql i

muon and electron scattering~ charge current scattering ~anti- c. c. scattering~ parity violating scattering, F3~parity violating anti- scattering~ )(2

)(2

))]()1([2

)]()1([2

])[9/1][9/4(2

2

2

sdcux

cusdx

sdycux

cuysdx

sdsdcucux

The high statistics experiments are all done on nuclear targets

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FNAL E866 Drell-Yan measurements on hydrogen and deuterium determined the x dependence of d-u

1

0

0)()( dxxuxd

Towell et al. Phys. Rev. D 64, 0522002 (2001)

Q2=54 GeV2Small but very important

Since this is a flavor non-singlet quantity

is true at all scales.

1

0

012.0118.0)()( dxxuxd

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The simplest explanation is the pion cloud

LA-LP-98-56

The proton spends part of its time as a neutron plus π+

|P> = α|uud> + β|udd> |uđ>

We know pion cloud effects are important in quark models.

7

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

)( udx

5/ ud

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pQCD - Gluon splitting? Meson Cloud? Chiral Solitons?

Instantons? Models describe well, but

not — pQCD becoming dominant????

LA-LP-98-56

Structure of the nucleon: What produces the nucleon sea?

Peng et al.

No one has come up with a physical mechanism to make

du

9

A key seems to be the spin carried by the non-singlet anti-quarks

E866

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. EPJC18, 719 (2001) gives similar result.

1

0

012.0118.0)()( dxxuxd

)()( udud

)](3/5[)( udud

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What are the correlations between the q and q pairs in the sea?

Gluon 1-, 3S1

Flavor neutral

Meson 0-, 1+

Vacuum 0+, 3P0

Flavor neutral

gq

q

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What do the data tell us ?

E866 - PR D64, 052002 (2001) Q2=54 GeV2

HERMES - PR D71, 012003 (2005)

COMPASS- arXiv:0909.3729v1 Q2=3 GeV2

de Florian et al - PRL 101, 072001 (2008) Q2=10 GeV2

1

0

012.0118.0)()( dxxuxd

3.0

023.0

028.057.0048.0)( dxud

3.0

004.0

013.035.0052.0)( dxud

1

0

036.0117.0)( dxud3 σ from zero2 σ from .197=Chiral soliton

To be compared with0, -1, -5/3 * flavor asymmetry

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COMPASS and HERMES Data

1

0

036.0117.0)( dxud

1

0

)( dxud

1

0

036.0117.0)( dxud

DNS 2005

DSSV 2008

-.03 to -.19

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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 toso I believe the prediction is small.

ud

14

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 semi-inclusive kaon multiplicities

)()()(

)()()()()(

)()()()(),()(

)(2)(5),()(

22

2

22

2

xsxsxS

xdxdxuxuxQ

dzzDxSdzzDxQQxdxdQ

xNd

xSxQQxdxdQ

xNd

KS

KQU

K

U

DIS

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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) Q2=2.5 GeV2

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How is this consistent with years of neutrino multi-muon data? ν + s → μ+ + c →μ-

NUTEV, PRD 64 112006(2001) CTEQ, JHEP 42, 89 (2007)

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NuTeV Data Suggest Small Strange vs Anti-strange AsymmetryPRL 99, 192001 (07)

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Comparison of ubar+dbar-s-sbar with dbar-ubar

)]()()()([ xsxsxdxux

Based on the HERMES result and assuming the strange quark distribution represents the gluon-splitting induced distribution, the shape of the non-perturbative

is similar to

)]()([ xuxdx vs 0.25 *HERMES

)]()([ xuxdx

)]()()()([ xsxsxdxux

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Nuclear corrections in charged lepton and neutrino scattering are different

Charged lepton Fe/D Neutrino Fe/D

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Parton Distributions in Nuclei

1984 – Parton distributions are differentEMC 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

Alde et al (F

ermilab E

772) Phys. R

ev. Lett. 64 2479 (1990)

My one publication with Tony6th on his citation list

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Our visual images of a nucleus

OR

“nucleons” held apart by short range repulsionbut even in 208Pb, half the nucleons are in the surface

average spacing at ρnm ~ 1.8 fmRadius of a nucleon ~ 0.8 fmaverage spacing at 3ρnm ~ 1.3 fm

Remember 1983 Thomas result favored a bag radius of 0.9 fm

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We want to describe a nucleus

Hadronic Description– 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– what are the clusters of quarks in a

nucleus?– know the parton distributions change

• 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?

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xtarget xbeam

Use a proton beam: primarily u quarks at high x. Detector acceptance chooses xtarget and xbeam.

Fixed target high xF = xbeam – xtarget Valence Beam quarks at high-x.

(e2 u)/(e2d) > 8 Dominated by u quarks Sea Target quarks at low/intermediate-x.

Drell-Yan scattering: A laboratory for sea quarks

E906

Spect

.

Mon

te C

arlo

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Advantages of 120 GeV Main InjectorThe (very successful) past:

Fermilab E866/NuSeaFermilab E866/NuSea Data in 1996-1997 1H, 2H, and nuclear targets 800 GeV proton beam

The future:

Fermilab E906Fermilab E906 Data taking 2010-2012 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 50 x statistics!! statistics!!

Fixed Target

Beam lines

Tevatron 800 GeV

Main Injector

120 GeV

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Fermilab E906/SeaQuest CollaborationAbilene Christian University

Donald Isenhower, Mike Sadler, Rusty Towell,Shon Watson

Academia SinicaWen-Chen Chang, Yen-Chu Chen, Da-Shung Su

Argonne National LaboratoryJohn Arrington, Don Geesaman*, Kawtar Hafidi,

Roy Holt, Harold Jackson, David Potterveld, Paul E. Reimer*, Josh Rubin, Patricia Solvignon

University of ColoradoEd Kinney

Fermi National Accelerator LaboratoryChuck Brown, Dave Christian

University of IllinoisNaomi C.R Makins, Jen-Chieh Peng

KEKShin'ya Sawada

Kyoto UniversityKenIchi Imai, Tomo Nagae

*Co-Spokespersons

Ling-Tung UniversityTing-Hua Chang

Los Alamos National LaboratoryGerry Garvey, Xiaodong Jaing, Mike Leitch,

Ming Liu, Pat McGaughey, Joel Moss

University of MarylandPrabin Adhikari, Betsy Beise, Kazutaka Nakahara

University of MichiganWolfgang Lorenzon, Richard Raymond

RIKENYuji Goto, Atsushi Taketani, Yoshinori Fukao,

Manabu Togawa

Rutgers UniversityLamiaa El Fassi, Ron Gilman, Elena Kuchina, Ron

Ransome, Elaine Schulte

Texas A & M UniversityCarl Gagliardi, Robert Tribble

Thomas Jefferson National Accelerator FacilityDave Gaskell

Tokyo Institute of TechnologyToshi-Aki Shibata, Yoshiyuki Miyachi

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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%

ud

27

Does deuterium structure affect the results at higher x

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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.

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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 E906/SeaQuest 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 GeV

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.

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

• Statistical Parton Distributions )()()()( xuxdxdxu