drell-yan experiments for determining nucleon partonic structures wen-chen chang institute of...
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Drell-Yan Experiments for determining Nucleon Partonic Structures
Wen-Chen Chang Institute of Physics, Academia Sinica, Taiwan
The International Symposium on Physics of Unstable Nuclei 2014
ISPUN14Ho Chi Minh City, Vietnam, November 3-8, 2014
How to Probe the Structure of Nucleus / Nucleon?
2
probeddp
Shoot high-energy beam
Elastic Electron Scattering of Nuclei and Nucleons
3
Nuclear Form Factor Nucleon Form Factor
2 2max 0.16 GeVQ
Charge distributions of nuclei and protons.
2 2max 1.0 GeVQ
From Elastic Scattering to Deeply Inelastic Scattering (DIS)
4
Elastic scatteringInelastic scattering
resonance
• Very weak Q2-dependence, form factor1!
• Scattering off point-like objects?
2 2max 10.0 GeVQ
Quark-Parton Model (Feynman)
5
pquark = xPproton
0')( 222 quarkquark mpqxP
M
Q
Pq
QxqqxP
22 02
222
0 < x < 1Limiting case: x = 1,
elastic scattering
Bjorken-x: momentum fraction of struck parton
12 2 2 22 xp p pW M M Q M
6
“Elastic” Way
“Inelastic” Way
7
“Deeply Inelastic” Way
8
Structure Known
9
The Drell-Yan Process: Massive Di-lepton pairs from Hadron-Hadron Collisions
10
2
1 2
Qx x
s
p+U +X
PRL 25 (1970) 1523S.D. Drell and T.M. Yan, PRL 25 (1970) 316
Dimuon Invariant Mass Spectrum
11
Indium-Indium collisions at 158 GeV/nucleonNA60, PRL 99 (2007) 132302
Drell-Yan
p+U +X
PRL 25 (1970) 1523
J/
J/
Drell-Yan
Complementarity between DIS and Drell-Yan
12
Parton Distribution Functions (PDF) of Protons
13
Valance quarksSea quarks
x: momentum fraction of partons
14
Is in the Proton?
Gottfried Sum Rule
1
0
1 1
0 0
22[( ( ) ( )) / ]
1 2( ( ) ( )) ( ( )
( f ( )
( ))3 31
(3
))
G
v
n
v
pS x x x dx
u x d x dx u x d x dx
FF
i u x d x
=
22 , : Structure functions of proton and neutron from DISnp FF
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Experimental Measurement of Gottfried Sum
New Muon Collaboration (NMC), Phys. Rev. D50 (1994) R1
SG = 0.235 ± 0.026
( Significantly lower than 1/3 ! )
S. Kumano, Physics Reports, 303 (1998) 183
1
3
16
Naïve Assumption:NMC (Gottfried Sum
Rule):
NA51 (Drell-Yan, 1994):
Light Antiquark Flavor Asymmetry: Drell-Yan Experiments
NA 51 Drell-Yan confirms
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Naïve Assumption:NMC (Gottfried Sum
Rule):
NA51 (Drell-Yan, 1994):
E866/NuSea (Drell-Yan, 1998):
Light Antiquark Flavor Asymmetry: Drell-Yan Experiments
Origin of ?Pauli blocking of
valance quarks (Field and Feynman 1977)
Meson cloud in the nucleons (Thomas 1983, Kumano 1991): Sullivan process in DIS.
Chiral quark model (Eichten et al. 1992; Wakamatsu 1992): Goldstone bosons couple to valence quarks.
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“Flavor Structure of the Nucleon Sea”W.-C. Chang and J.-C. Peng, arXiv:1406.1260Prog. in Part. and Nucl. Phys. 79 (2014) 95.
by FNAL E906/SeaQuest
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Fixed Target
Beam lines
Tevatron 800 GeVMain
Injector 120 GeV
( ( ) / ( )) up to 0.45d x u x x
Fermilab E906 Physics data taking:
Feb, 2014 – Dec, 2015. 1H, 2H, and nuclear targets Unpolarized Drell-Yan using
120 GeV proton beam
KEK, RIKEN, Tokyo Tech, Yamagata, AS and U.S. institutes
x+x x-x
t
GPDs
P P’
Generalized Parton Distribution (GPD)
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( ,0,0) ( ) ( )
( ,0,0) ( ) ( )
f f f
f f f
H x q x q x
H x q x q x
1
1
1
1
2
1
1
1
1
1
( , , ) ( )
( , , ) ( )
( , , ) ( )
( , , ) ( )
ff
ff
f Af
f pf
dx H x t F t
dx E x t F t
dx H x t g t
dx E x t g t
)]0,,()0,,([2
1
2
1 1
1
xExHxdxLJ ffff
f
),,( txGPD
2)'( PPt
0t
5
( , , ) ( , , )
( , , ) ( , , )
f f
f f
no spin flip H x t H x t
spin flip E x t E x t
0t
Accessing GPD using Lepton Beam
21
Deeply Virtual Compton Scattering
2 0q 2 0q
Deeply Virtual Meson Production
JLAB, HERMES@DESY, COMPASS@CERN
Explored Regions of Generalized Parton Distribution (GPD)
22
Spacelike vs. Timelike ProcessesMuller et al., PRD 86 (2012) 031502
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Deeply Virtual Meson Production Exclusive Meson-induced Drell-Yan
2 0q 2 0q
channel crossings u
• Cross sections of exclusive DY process drop with an increase of beam energy. No sensitivity to parton d.o.f. if beam energy is small.
• The beam energy of pions at J-PARC at 10-20 GeV might be most ideal for studying this hard exclusive process.
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High-res., High-momentum Beam Line at J-PARC• High-intensity secondary Pion beam
• High-resolution beam: Dp/p~0.1%
Dispersive Focal Point (DFP)Dp/p~0.1%
Collimator
15kW Loss Target(SM)
Exp. Target (FF)
Pion BeamUp to 20 GeV/c
H. Noumi
See K. Tanaka’s talk
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High-res., High-momentum Beam Line• High-intensity secondary Pion beam
– >1.0 x 107 pions/sec @ 20GeV/c• High-resolution beam: Dp/p~0.1%
* Sanford-Wang:15 kW Loss on Pt, Acceptance :1.5 msr%, 133.2 m
Open a new platform for hadron physics
0 5 10 15 201.0E+03
1.0E+04
1.0E+05
1.0E+06
1.0E+07
1.0E+08
1.0E+09
[GeV/c]
Co
un
ts/s
ec
0 5 10 15 201.0E+03
1.0E+04
1.0E+05
1.0E+06
1.0E+07
1.0E+08
1.0E+09
[GeV/c]
Co
un
ts/s
ec
Prod. Angle = 0 deg. (Neg.)
p-
K-
pbar
p+
K+
Prod. Angle = 3.1 deg (Pos.)
H. Noumi
26
J-PARC E50 Spectrometer + MuID
p-
LH2-target
Ring ImageCherenkovCounter
Internal DC
FM magnet
ps-
K+
Fiber tracker
Beam GC
Internal TOF
Internal TOFDC
TOF wall
2m
Decay p(p+)
20 GeV/cBeam p-
Acceptance: ~ 60% for D*, ~80% for decay p+ Resolution: Dp/p~0.2% at ~5 GeV/c ( Rigidity : ~2.1 Tm)
||<60
Scintillator Muon trigger device
20-GeV N+-N MX In E-50 Spectrometer + MuID
27
Red: Exclusive DY ( 5 pb )Blue: Inclusive DY ( 500 pb )Green: random BG from meson decay
After 200-day data-taking
Assumption: Δp/p = 0.2 %
Missing Mass MX (GeV2)
Nev
ent The signal of exclusive
Drell-Yan processes can be clearly identified in the missing mass spectrum of dimuon pairs.
S. Sawada (KEK)S. Kumano (KEK)J.C. Peng (UIUC)T. Sawada (AS)W.C. Chang (AS)
Explored Regions of Generalized Parton Distribution (GPD)
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J-PARC (exclusive DY)
SummaryDrell-Yan process, based on the EM
annihilation of quarks and antiquarks from two hadrons, is a powerful experimental tool for exploring nucleon quark structures.
Unique information of the x-dependence of sea quark flavor asymmetry has been obtained with Drell-Yan experiments.
SeaQuest/E906 experiment at Fermilab will obtain at large-x regions.
The study of exclusive meson-induced Drell-Yan process at J-PARC will provide a valuable and complementary way of measuring the GPD structures of nucleons. 29
Backup
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Momentum Dependence of the Flavor Structure of the Nucleon Sea: NMC vs E866J.C. Peng et al., PLB 736 (2014) 411
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JR14 NMC
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Nucleon Partonic StructureWigner Distribution
Transverse Momentum Dependent PDF
Generalized Parton Distr.
d 2kt dzF.T.
d2k t
dx
Form Factors
GPD
Ji, PRL91,062001(2003)
( , , )TW r x k
f( , )Tx k
f( )x
H( , , t)x
1 2( ), ( )F t F t
d3 r