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The dbar/ubar Ratio in Proton
1
HUGS 2009
Lingyan Zhu
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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
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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?
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4
Towell et al., Phys.Rev. D64 (2001) 052002
Sea Asymmetry from Drell-Yan
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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
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6
Flavor Decomposition in Semi-Inclusive DIS
2
2
((
( )(
))
)1
h
qqq
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
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7
Normally two jets: qh or qbarh
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 DESYHERMES at DESY DESY-Hamburg: 27 GeV e+/− + 920 GeV p
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10
Factorization Check at HERMES
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11
Sea Asymmetry from HERMES
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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
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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 JLABL.Y.Zhu, J.P.Chen, X. Jiang and J.C. Peng, JLab Hall A PR04-114
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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
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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
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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,
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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
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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
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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
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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
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Drell-Yan & DIS Error Propagation
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(anti-)neutrino cross section on hydrogen
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Minerva experiment with hydrogen
24At x>0.3, (dbar+sbar)/(ubar+cbar) have similar slope as dbar/ubar.
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W production with proton beam
25
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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
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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
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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.
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CTEQ inputs
29
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Drell-Yan Cross Sections & Global PDFE866(J.C.Webb et al.), hep-ex/0302019.