The dbar/ubar Ratio in Proton Lingyan Zhu HUGS 2009 1 Whats the - - PowerPoint PPT Presentation

The dbar/ubar Ratio in Proton

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HUGS 2009

Lingyan Zhu

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What’s the expection with dbar and ubar?

Peng & Garvey, Prog.Part.Nucl.Phys.47(2001)203 K+[u+sbar]: 493.68 MeV K0[d+sbar]: 497.65 MeV π+[u+dbar]: 139.57 MeV

SU(2) symmetry

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Sea Asymmetry from DIS

148 . 2 235 . * 3 1 2 / ] [ 3 1 ] [ 1 ] [ ] proton[uud ) ( 3 1 ) ( 3 1 / ] [ ) ( 9 1 ) ( 9 1 ) ( 9 4 / ) ( 9 1 ) ( 9 1 ) ( 9 4 /

1 2 2 1 1 2 2 2 2

≠ = − = − − = − = − = = > + − + = − + + + + + = + + + + + =

∫ ∫ ∫

xdx F F dx u d dx d u d d u u x F F s s u u d d x F s s d d u u x F

n p v v n p n p

NMC at CERN: PRL66(1991)2712;PRD50(1994)R1 Gottfried Integral SG=1/3?

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Towell et al., Phys.Rev. D64 (2001) 052002

Sea Asymmetry from Drell-Yan

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Sea Asymmetry from Models

Prog.Part.Nucl.Phys.47(2001)203

Pion cloud models:Bare nucleon +pion cloud Chiral Models: Constituent quarks + Goldstone Bosons

Phys.Rev.D59(1999)014033

More: Instanton Models, Lattice Gauge Approach, Chiral-Quark Soliton Model

π N

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Flavor Decomposition in Semi-Inclusive DIS

2 2

( ( ( ) ( ) ) ) 1

h q q q q q q q

f x e d ep hX dz e x D z f

σ σ → =

∑ ∑

: parton distribution function : fragmentation functi ( ) (

• )

n

q h q

f D z x

ν

π /

E z =

Favored fragmentation D+ Unfavored fragmentaion D-

) (

• r

) ( u d d d u u

− +

→ → π π

) (

• r

) ( d u d u d u

+ −

→ → π π

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Normally two jets: qh or qbarh e+e-hX constrains D++D-

Fragmentation Functions

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Semi-Inclusive DIS

Unpolarized Polarized target Polarized beam and target Sivers Transversity/Collins

• D. Boer,R. Jakob, and P.J. Mulders, NPB564, 471 (2000) [hep-ph/9907504].

Boer-Mulders

• Long. Polarized PDF

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HERMES at DESY HERMES at DESY

DESY-Hamburg:

27 GeV e

+/ +/− + 920 GeV p

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Factorization Check at HERMES

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Sea Asymmetry from HERMES

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Jefferson Lab (JLab)

6 GeV polarized CW electron beam (P = 85%, I = 180 mA) 3 halls for fixed target experiments Hall A: 2 high resolution spectrometers +BigBite Hall B: large acceptance spectrometer Hall C: 2 spectrometers

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Factorization Check at JLab

Data beyond Δ region are well described by LO SIDIS ansatz.

1,2H(e,e’π+/-) from JLab E00108: PRL98(2007) 022001 [hep-ph/0608214]

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Sea Asymmetry Measurement at JLAB

L.Y.Zhu, J.P.Chen, X. Jiang and J.C. Peng, JLab Hall A PR04-114

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Flavor Asymmetry in Kaons?

Is ( ) ( )?

K K u d

D z D z

+ +

>

Is ( ) ( ) in ?

sea sea

d x u x K

+

=

Difficult to measure sea quark distributions in K+ !

Can the / flavor asymmetry be observed i n the kaon fragmentation functions? u d

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Unpolarized Kaon SIDIS

• The semi-inclusive production of charged kaons from

proton and neutron target

[ ] [ ] [ ] [ ] 9

/ ) ( 4 4 9 / ) ( 4 4 9 / ) ( 4 4 9 / ) ( 4 4 , ,

+ + + + + − + + + + + + + + + + + − + + + + + + − + − + + − + − − + − +

+ + + + + ∝ + + + + + ∝ + + + + + ∝ + + + + + ∝ = = = = = = =

K d K s K u K s K u K n K d K s K u K s K u K n K d K s K u K s K u K p K d K s K u K s K u K p K d K d K d K d K s K s K u K u K s K s K u K u

D u u sD D d D s dD Y D u u sD D d D s dD Y D d d sD D u D s uD Y D d d sD D u D s uD Y D D D D D D D D D D D D

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Kaon Fragmentation Function Ratio

Projection for JLab Hall A PR04-114

? 1 ) ( ) ( ) ( ) ( 4 2

] [ ] [

> + + + − + + + + − + ⋅ = = + > >

− + − + − + − + − + − + + + + + + + +

+ +

K n K n K p K p K p K p K n K n K K u K K d K u K u K d K u K d s u K u s u K u

Y Y u u d d Y Y Y Y u u d d Y Y D D D D D D D D D

• If at large x ignoring strange quark contribution,

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SIDIS Coverage With JLab Upgrade

Higher beam energy provide larger phase space.

27 GeV

c

• m

p a s s h e r m e s JLab (upgraded)

JLab@6GeV

EIC

HERA

From Harut Avakian Q2

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Sea Asymmetry with JLAB Upgrade

• H. Gao, A.Bruell, H.Mkrchyan, J.P.Chen&L.Y.Zhu, JLab Proposal PR12-06-111

Sea Asymmetry with 120 GeV Proton Beam

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Fermilab E866/NuSea Fermilab E866/NuSea (M. Leitch)  Data in 1996-1997  800 GeV proton beam Fermilab E906 Fermilab E906 (D. Geesaman, P. E. Reimer)  Data in 2009  120 GeV proton Beam  Cross section scales as 1/s  Backgrounds, primarily J/ψ decays drop with s

E789,PRD52(1995)1507

50 50x x statistics!! statistics!!

F i x e d T a r g e t B e a m l i n e s Tevatron 800 GeV Main Injector 120 GeV

Fermilab E906 Drell-Yan timeline

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2001: approved by Fermilab PAC 2006: reaffirmed by Fermilab PAC Funding request to DOE: ~$2M primarily for the magnets.

2008 2007 2010

Publications

Expt. Funded 2009 Magnet Design Experiment And construction Construction

Proposed

• Jan. 2007

Experiment Runs

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Drell-Yan & DIS Error Propagation

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(anti-)neutrino cross section on hydrogen

Minerva experiment with hydrogen

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At x>0.3, (dbar+sbar)/(ubar+cbar) have similar slope as dbar/ubar.

W production with proton beam

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W asymmetry

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Yang et al., arXiv:0905.3783 RHIC: p+p

center-of-mass energy at 500 GeV LHC: p+p center-of-mass energy at 14 TeV

W asymmetry measurement at RHIC and LHC

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Yang et al., arXiv:0905.3783 RHIC PHENIC: p+p

center-of-mass energy at 500 GeV LHC CMS: p+p center-of-mass energy at 14 TeV

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Summary

The ubar and dbar asymmetry is large in the proton sea, with dbar/ubar around 2 at x=0.2. No model can explain the drop of this ratio at higher x observed in Drell-Yan process. Recent data has shown the LO factorization in Semi-inclusive DIS in HERMES and even JLab. The SIDIS was used to check the ubar and dbar sea asymmetry in proton, but the uncertainties can be greatly reduced at JLab especially with the energy upgrde. SIDIS can be also used to probe other parton distribution functions and fragmentation functions including theTransverse-Momentum- Dependent parton distribution functions. (Anti-)neutrino DIS on hydrogen target or W production with p+p collision may provide a way to measure the sea asymmetry without any nuclear correction and any charge symmetry assumption.

CTEQ inputs

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Drell-Yan Cross Sections & Global PDF

E866(J.C.Webb et al.), hep-ex/0302019.