overview of unpolarized structure function measurements at high x roy j. holt jefferson lab 13...

Overview of unpolarized structure function

measurements at high x

Roy J. Holt

Jefferson Lab 13 October 2010

Argonne National Laboratory

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Outline

Introduction and Motivation New generation of experiments and tools

– The proton structure function– The neutron structure function– The strange quark distribution and Drell-Yan

Concluding statement

We are providing benchmark data for hadron structure.


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Wpu(x,k

T,r ) Wigner distributions

d2kT d3r

PDFs f1

u(x), .. h1u(x)

d2kT drzd3r

Form FactorsGE(Q2), GM(Q2)

dxd2kT drz & FT

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Four Pillars of Hadron Structure

GPDsTMD PDFs f1

u(x,kT), .. h1u(x,kT)

3 D

See X. Jiang, K. Hafidi,A. Accardi

See Z.-E. Meziani, J. Blumlein, J. Soffer


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Parton model

Quark charge

Prob. of q in proton

Structure function

leptonic hadronic

What is the internal landscape of the hadron? NSAC 2007

–Benchmark: Spatial, spin, flavor and gluonic structure

Partonic structure of the nucleon

fraction of the proton’s momentum carried by the struck quark


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Large x is essential for particle physics

Parton distributions at large x are important input into simulations of hadronic background at colliders, eg the LHC.

– High x at low Q2 evolves into low x at high Q2.

– Small uncertainties at high x are amplified.

HERA anomaly: (1996): excess of neutral and charged current events at Q2 > 10,000 GeV2

– Leptoquarks????– ~0.5% added to u(x) at x > 0.75 S. Kuhlmann et al, PLB 409 (1997)

Lake of GenevaLake of GenevaLarge Large HadronHadron Collider ColliderLarge Large HadronHadron Collider Collider

Airp

ort

CMSCMS

ATLASATLAS

LHCbLHCb

ALICEALICE


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W production at the LHC

W production at the LHC is sensitive to the d/u ratio

W’s and Z will be “standard candles” at the LHC

J.-L.Lai et al, hep-ph 14 Jul 2010


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Proton structure function

Plot credit: A. Accardi

(See J. Owens, S. Alekhin, A. Guffanti, D. Renner, V. Radescu)

DIS from proton gives good sensitivity to u, but not to d


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Why are proton structure function data still interesting?

New data at very high x can reveal information about:– Target mass corrections – High twist effects – Soft gluon resummation– Order in s

– Quark-hadron duality– Hadronic models

Recent data from JLab – more to follow after JLab 12 GeV Upgrade and Drell-Yan experiments

CTEQ6X, A. Accardi et al, PR D81 (2010)

(See J. Owens, S. Alkhin, T. Hobbs, M. Glatzmaier, S. Kulagin, A. Accardi, W. Melnitchouk, S. Malace, F. Steffens, S.-H. Lee, S. Liuti, E. Christy)


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Why is high x so difficult?

W > 2 GeVeg. if x =0.9, then Q2 = 27 GeV2

Practical limit at JLab12: x = 0.8


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The proton structure function

JLab E12-10-002, S. Malace et al Utilize resonance region Invoke duality

Upgraded JLab hasunique capability todefine the valence region

Plot credit: S. Malace, JLab PAC36

DOE milestone HP14 (2018)


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Proton structure function at an EIC

MEIC simulation Ee = 4 GeV, Ep = 60 GeV Luminosity ~ 3 x 1034

1 year of running (26 weeks)at 50% efficiency, or 230 fb-1

Alberto Accardi,Nuclear Chromodynamics with an EICArgonne, April 2010

With C. Keppel and R. Ent

An EIC is a powerful probe of the valence region.


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The Neutron Structure Function

Proton structure function:

Neutron structure function (isospin symmetry):

Ratio:

Nachtmann inequality:

Focus on high x:

Parton model ->


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Uncertainty in the d(x)/u(x) ratio

Q2 > 4 GeV2

W > 3.5 GeV x < 0.7


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Structure Function Ratio Problem

Convolution model

– Fermi motion and binding, covariant deuteron wave function, off-shell effects

Melnitchouk and Thomas (1996)

Nuclear density model:– EMC effect for deuteron scales with

nuclear density.

Frankfurt and Strikman

(1988)

Fermi smearing

Smearing + binding

Nuclear density model

(See I. Cloet)


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Models of the structure function

SU(6)-symmetric wave function of the proton in the quark model (spin up):

– u and d quarks identical, N and would be degenerate in mass.– In this model: d/u = 1/2, F2

n/F2p = 2/3.

SU(6) symmetry is broken: N- Mass Splitting– Mechanism produces mass splitting between S=1 and S=0 diquark spectator.– symmetric states are raised, antisymmetric states are lowered (~300 MeV). – S=1 suppressed => d/u = 0, F2

n/F2p = 1/4, for x -> 1

pQCD: helicity conservation (qp) => d/u =2/(9+1) = 1/5, F2n/F2

p = 3/7 for x -> 1

p 1

183u ud S0 u ud S1 2u ud S1 2d uu S1 2d uu S1

.


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Structure Function Ratio

Reviews: N. Isgur, PRD 59 (1999), S Brodsky et al NP B441 (1995),W. Melnitchouk and A. Thomas PL B377 (1996) 11,R.J. Holt and C. D. Roberts, arXiv:1003.4666 [nucl-th],I. Cloet et al, Few Body Syst. 46 (2009) 1.

DOE milestone HP14 (2018)

SU(6) symmetry

pQCD

0+ qq only

DSE: 0+ & 1+ qq


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Extractions with modern deuteron wave functions

J. Arrington et al, J. Phys. G 36 (2009)

• Lorentz invariant convolution relation

• Light front with null plane kinematics

The ratio at high x has a strong dependence on deuteron structure.

A. Accardi, et al., arXiv:0911.2254More p/d data at JLab 12 GeVE12-10-008 - J. Arrington, A. Daniel, D. GaskellPAC 36: recommended approval

(See F. Olness, S. Kumano, A. Daniel, S. Kulagin, J. Arrington)


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Tagged Neutron in the Deuteron – BONUS + CLAS12

• PAC36: “recommended approval”• JLab E12-06-113, S. Bueltmann, H. Fenker,

M. Christy, C. Keppel et al

See S. Bueltmann, M. Sargsian, S. Kulagin


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Nuclear Physicists’ Approach to F2n

Problem:– The deuteron experiments present extraction

complications. Nuclear physicists’ solution: Add another nucleon. 3H/3He ratio: minimizes nuclear physics uncertainties

• I. Afnan et al., Phys. Lett. B493, 36 (2000); Phys. Rev. C68, 035201 (2003)• E. Pace, G Salme, S. Scopetta, A. Kievsky, Phys. Rev. C64, 055203 (2001)• M. Sargsian, S. Simula, M. Strikman, Phys. Rev. C66, 024001 (2002)

No DIS data exist for the triton!


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Tritium target at JLab??

Tritium Target Task Force

E. J. Beise (U. of Maryland) B. Brajuskovic (Argonne)

R. J. Holt (Argonne)W. Korsch (U. of Kentucky)

A. T. Katramatou (Kent State U.) D. Meekins (JLab)

T. O’Connor (Argonne)G. G. Petratos (Kent State U.)

R. Ransome (Rutgers U.) P. Solvignon (JLab)

B. Wojtsekhowski (JLab)

JLab Review: June 3, 2010-> “No show stopper”

E12-06-118 G. Petratos et alPAC 36: recommended conditional approval

See G. Petratos


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Parity Violating Deep Inelastic Scattering

• Proton target only• PAC35 “recommended approval”• Requires special spectrometer

• P. Souder – SoLID• JLab E12-10-007

(See P. Souder, T. Hobbs, M. Glatzmaier)


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Deep inelastic neutrino scattering from the proton Charge current neutrino/antineutrino scattering

MINOS high energy tune: 2 yearsLH2 target

MINERA: J. Morfin

MINOS@FNAL

dW+

uW-

(See J. Morfin, R. Petti)


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Deuteron structure function at an EIC

Ee = 8 GeV, EN = 30 GeV Luminosity ~ 3.5 x 1033

One year of running (26 wk)at 50% efficiency, or 35 fb-1

Detect ~30 GeV proton “Super BoNuS”

Alberto Accardi,Nuclear Chromodynamics with an EICArgonne, April 2010

With C. Keppel and R. Ent


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The strange quark distribution function

Strange quark distribution - HERMES

New data: COMPASS II at CERN, JLab with12 GeV, MINERA at FNAL

Far future: EIC-> also charm distribution, gluonic Sivers effect; LHeC -> beauty distribution

A. Airapetian et al, PLB 666 (2008) 446


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Projections for strange quarks

COMPASS-II

JLAB E09-007K. Hafidi et al.


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What about Drell-Yan experiments?

Pion structure function shape at very high x ??

Azimuthal asymmetry for the proton Boer-Mulders vs. pQCD?

High x distribution functions

4u + dsoft gluon resummation issues?

The kaon structure function should be measuredSee J.-C. Peng, P. Reimer

COMPASS-II, FNAL E906 SeaQuest, FAIR, J-PARC

Settled by soft gluon resummation – Aicher, Schaeffer, Vogelsang,hep-ph/1009.248


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Concluding statement

Understanding hadrons will be one of nuclear physics’ greatest contributions to science

New 21st century tools have positioned us well for the next decade: – JLab 12 GeV, CERN COMPASS-II, FNAL MINERA, FNAL E906,

RHIC, J-PARC, FAIR, petascale computing. Far future: EIC, exascale computing

– Continue to develop and assess the high x case for the EIC We are camped on one of the most interesting frontiers

in science


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Drell-Yan azimuthal asymmetry

2 21 31 cos sin 2 cos sin cos 2

4 2

d

d

R. J. Holt and C. D. Roberts, arXiv:1002.4666 [nucl-th]FNAL E906 SeaQuest


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overview of unpolarized structure function measurements at high x roy j. holt jefferson lab 13...

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