The dbar/ubar Ratio in Proton

1

HUGS 2009

Lingyan Zhu

2

What’s the expection with dbar and ubar?

Peng & Garvey, Prog.Part.Nucl.Phys.47(2001)203

K+[u+sbar]: 493.68 MeVK0[d+sbar]: 497.65 MeVπ+[u+dbar]: 139.57 MeV

SU(2) symmetry

3

Sea Asymmetry from DIS

0148.02

235.0*312

/][31][

1][]proton[uud

)(31)(

31/][

)(91)(

91)(

94/

)(91)(

91)(

94/

1

0 221

0

1

0

22

2

2

≠=−=−−

=−

=−= = >

+−+=−

+++++=

+++++=

∫∫

∫xdxFF

dxud

dxdu

dduuxFF

ssuuddxF

ssdduuxF

np

vv

np

n

p

NMC at CERN: PRL66(1991)2712;PRD50(1994)R1

Gottfried Integral SG=1/3?

4

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

Sea Asymmetry from Drell-Yan

5

Sea Asymmetry from ModelsProg.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

6

Flavor Decomposition in Semi-Inclusive DIS

2

2

((

( )(

))

)1

h

qqq

qq

q

q

f xed ep hXdz e x

D z

fσ

σ→ =

∑∑

: parton distribution function

: fragmentation functi( )

(

o

)

nq

hq

f

D z

x

νπ /Ez =

Favored fragmentation D+

Unfavored fragmentaion D-

)(or )( uddduu −+ →→ ππ

)(or )( dududu +− →→ ππ

7

Normally two jets: qh or qbarh

e+e-hX constrains D++D-

Fragmentation Functions

8

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

9

HERMES at DESYHERMES at DESY DESY-Hamburg: 27 GeV e+/− + 920 GeV p

10

Factorization Check at HERMES

11

Sea Asymmetry from HERMES

12

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+BigBiteHall B: large acceptance

spectrometerHall C: 2 spectrometers

13

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]

14

Sea Asymmetry Measurement at JLABL.Y.Zhu, J.P.Chen, X. Jiang and J.C. Peng, JLab Hall A PR04-114

15

Flavor Asymmetry in Kaons?

Is ( ) ( )?K KudD z D z

+ +

>

Is ( ) ( ) in ?sea sead 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

16

Unpolarized Kaon SIDIS

The semi-inclusive production of charged kaons from proton and neutron target

[ ][ ][ ][ ] 9/)(44

9/)(44

9/)(44

9/)(44

,

,

+++++−

++++++

+++++−

++++++

−+−+

+−+−

−+−+

+++++∝

+++++∝

+++++∝

+++++∝

===

==

==

Kd

Ks

Ku

Ks

Ku

Kn

Kd

Ks

Ku

Ks

Ku

Kn

Kd

Ks

Ku

Ks

Ku

Kp

Kd

Ks

Ku

Ks

Ku

Kp

Kd

Kd

Kd

Kd

Ks

Ks

Ku

Ku

Ks

Ks

Ku

Ku

DuusDDdDsdDY

DuusDDdDsdDY

DddsDDuDsuDY

DddsDDuDsuDY

DDDD

DDDD

DDDD

17

Kaon Fragmentation Function Ratio

Projection for JLab Hall A PR04-114

?1)()(

)()(4

2

][][

>+

++−+

+++−+

⋅==+

>

>

−+−+

−+−+

−+

−+

++

+

+

+

++

+

+

Kn

Kn

Kp

Kp

Kp

Kp

Kn

Kn

KKu

KKd

Ku

Ku

Kd

Ku

Kd

suKu

suKu

YYuuddYY

YYuuddYY

DD

DDD

DD

DD

If at large x ignoring strange quark contribution,

18

SIDIS Coverage With JLab Upgrade

Higher beam energy provide larger phase space.

27 G

eV

com

pass

herm

esJLab (upgraded)

JLab@6GeV

EIC

HERA

From Harut Avakian

Q2

19

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

20

Fermilab E866/NuSeaFermilab E866/NuSea(M. Leitch)

Data in 1996-1997 800 GeV proton beam

Fermilab E906Fermilab 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 sE789,PRD52(1995)1507

5050xx statistics!! statistics!!

Fixed Target

Beam lines

Tevatron 800 GeV

Main Injector

120 GeV

Fermilab E906 Drell-Yan timeline

21

2001: approved by Fermilab PAC2006: reaffirmed by Fermilab PACFunding request to DOE:~$2M primarily for the magnets.

2008

2007

2010 Publications

Expt. Funded

2009

Magnet Design ExperimentAnd construction Construction

Prop

osed

Jan.

200

7 ExperimentRuns

22

Drell-Yan & DIS Error Propagation

23

(anti-)neutrino cross section on hydrogen

Minerva experiment with hydrogen

24At x>0.3, (dbar+sbar)/(ubar+cbar) have similar slope as dbar/ubar.

W production with proton beam

25

W asymmetry

26

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

27

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

28

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

29

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Drell-Yan Cross Sections & Global PDFE866(J.C.Webb et al.), hep-ex/0302019.