The dbar/ubar Ratio in Proton Lingyan Zhu HUGS 2009 1
What’s the expection with dbar and ubar? K + [u+sbar]: 493.68 MeV K 0 [d+sbar]: 497.65 MeV π + [u+dbar]: 139.57 MeV Peng & Garvey, Prog.Part.Nucl.Phys.47(2001)203 SU(2) symmetry 2
Sea Asymmetry from DIS 4 1 1 = + + + + + p F / x ( u u ) ( d d ) ( s s ) 2 9 9 9 4 1 1 = + + + + + n F / x ( d d ) ( u u ) ( s s ) 2 9 9 9 1 1 − = + − + p n [ F F ] / x ( u u ) ( d d ) 2 2 3 3 1 ∫ = = > − = proton[uud ] [ u d ] dx 1 v v 0 1 ∫ − − p n 1 3 [ F F ] / xdx − 1 3 * 0 . 235 1 2 2 ∫ − = = = ≠ 0 [ d u ] dx 0 . 148 0 2 2 0 Gottfried Integral S G =1/3? NMC at CERN: PRL66(1991)2712;PRD50(1994)R1 3
Sea Asymmetry from Drell-Yan Towell et al., Phys.Rev. D64 (2001) 052002 4
Sea Asymmetry from Models Prog.Part.Nucl.Phys.47(2001)203 Pion cloud models:Bare nucleon +pion cloud π N Chiral Models: Phys.Rev.D59(1999)014033 Constituent quarks + Goldstone Bosons More: Instanton Models, Lattice Gauge Approach, Chiral-Quark Soliton Model 5
Flavor Decomposition in Semi-Inclusive DIS ∑ 2 h e f ( x ) D ( z ) q q q σ 1 d q → = ( ep hX ) ∑ σ 2 dz e f ( ) x q q q f ( x ) : parton distribution function q h D ( ) z : fragmentation functi o n q z = ν E π / Unfavored fragmentaion D - → π − → π + u ( d u ) or d ( u d ) Favored fragmentation D + → π + → π − u ( u d ) or d ( d u ) 6
Fragmentation Functions Normally two jets: q h or qbar h e + e - hX constrains D + +D - 7
Semi-Inclusive DIS D. Boer , R. Jakob, and P.J. Mulders, NPB564, 471 (2000) [hep-ph/9907504]. Unpolarized Boer-Mulders Transversity/Collins Polarized target Sivers Polarized Long. Polarized PDF beam and target 8
HERMES at DESY HERMES at DESY DESY-Hamburg: 27 GeV e +/− + 920 GeV p +/ 9
Factorization Check at HERMES 10
Sea Asymmetry from HERMES 11
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 12
Factorization Check at JLab 1,2 H(e,e’π +/- ) from JLab E00108: PRL98(2007) 022001 [hep-ph/0608214] Data beyond Δ region are well described by LO SIDIS ansatz . 13
Sea Asymmetry Measurement at JLAB L.Y.Zhu, J.P.Chen, X. Jiang and J.C. Peng, JLab Hall A PR04-114 14
Flavor Asymmetry in Kaons? + = Is d ( ) x u ( ) in x K ? sea sea Difficult to measure sea quark distributions in K + ! Can the u / d flavor asymmetry be observed i n the kaon fragmentation functions? + + > K K Is D ( ) z D ( )? z u d 15
Unpolarized Kaon SIDIS The semi-inclusive production of charged kaons from proton and neutron target + − + − K = K K = K D D , D D u u s s − + − + = = K K K K D D , D D u u s s + − + − = = = K K K K D D D D d d d d [ ] + + + + + + ∝ + + + + + K K K K K K Y 4 uD s D 4 u D sD ( d d ) D / 9 p u s u s d [ ] − + + + + + ∝ + + + + + K K K K K K Y 4 uD s D 4 u D sD ( d d ) D / 9 p u s u s d [ ] + + + + + + ∝ + + + + + K K K K K K Y 4 dD s D 4 d D sD ( u u ) D / 9 n u s u s d [ ] 9 − + + + + + ∝ + + + + + K K K K K K Y 4 dD s D 4 d D sD ( u u ) D / n u s u s d 16
Kaon Fragmentation Function Ratio If at large x ignoring strange quark contribution, + + > K [ u s ] K [ u s ] D D u u + d d + − + − K + K − K + K ( Y Y ) ( Y Y ) + + + − K K + D 2 D K K D n n + p p u u > = = ⋅ > d d d 4 1 ? + + + + − + + d d K K + K K K D D D D + − + − + − + K K K K ( Y Y ) ( Y Y ) u u u u p p + n n u u Projection for JLab Hall A PR04-114 17
SIDIS Coverage With JLab Upgrade From Harut Avakian 27 GeV HERA Q 2 EIC s JLab ( upgraded ) s a p m s e o JLab@6GeV m c r e h Higher beam energy provide larger phase space. 18
Sea Asymmetry with JLAB Upgrade H. Gao, A.Bruell, H.Mkrchyan, J.P.Chen&L.Y.Zhu, JLab Proposal PR12-06-111 19
Sea Asymmetry with 120 GeV Proton Beam Fermilab E906 Fermilab E866/NuSea Fermilab E866/NuSea Fermilab E906 (M. Leitch) (D. Geesaman, P. E. Reimer) Data in 1996-1997 Data in 2009 800 GeV proton beam 120 GeV proton Beam t e g r a T s e d n e i l x i m F Cross section scales as 1/s a e B Backgrounds, primarily J/ ψ decays Tevatron drop with s 800 GeV E789,PRD52(1995)1507 Main Injector 50 x x statistics!! statistics!! 50 120 GeV 20
Fermilab E906 Drell-Yan timeline 2001: approved by Fermilab PAC 2006: reaffirmed by Fermilab PAC Funding request to DOE: ~$2M primarily for the magnets. Experiment Expt. Magnet Design Experiment Proposed Jan. 2007 Funded And construction Construction Runs 2007 2008 2009 2010 Publications 21
Drell-Yan & DIS Error Propagation 22
(anti-)neutrino cross section on hydrogen 23
Minerva experiment with hydrogen At x>0.3, (dbar+sbar)/(ubar+cbar) have similar slope as dbar/ubar. 24
W production with proton beam 25
W asymmetry Yang et al., arXiv:0905.3783 LHC: p+p RHIC: p+p center-of-mass energy at 14 TeV center-of-mass energy at 500 GeV 26
W asymmetry measurement at RHIC and LHC Yang et al., arXiv:0905.3783 LHC CMS: p+p RHIC PHENIC: p+p center-of-mass energy at 14 TeV center-of-mass energy at 500 GeV 27
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. 28
CTEQ inputs 29
Drell-Yan Cross Sections & Global PDF E866(J.C.Webb et al.), hep-ex/0302019. 30
Recommend
More recommend
