Spin Studies via Drell-Yan Process at PANDA
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Spin Studies viaSpin Studies via
Drell-Yan ProcessDrell-Yan Process
at PANDAat PANDAMarco Destefanis Università degli Studi di Torino
MENU 201313th Conference on Meson-Nucleon Physics and the Structure of the Nucleon
Roma (Italy)September 30 – October 04, 2013
for the PANDA Collaboration
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OverviewOverview
pp -> µ+µ-X
• Drell-Yan process and background @ PANDA
A. Bianconi Drell-Yan generator
• Investigation of Drell-Yan
asymmetries
Summary
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MotivationMotivation
Complete description of the nucleonic structure
requires:
➠ Parton Distribution Functions (PDF)
➠ Fragmentation Functions (FF)
Including kT dependence
➠ Transverse Momentum Dependent (TMD) PDF and
FF
➠ Test of Universality
SIDISf
TDYf
T ff || 11
J. C. Collins and D. E. Soper, Nucl. Phys. B 194, 445 (1982)
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Helicity Helicity basebase
Twist-2 PDFs: ),()(1 xuxf u ),()(1 xuxg u )()(1 xuxhu
-
δq(x) helicity flip
off diagonal in the helicity base
LR
LR
uuu
uuu
2
12
1
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TransversiTransversityty
δq(x): a chirally-odd, helicity flip distribution function
δg(x): no gluon transversity distribution; transversely polarised nucleon shows transverse gluon effects at twist-3 (g2) only
SOFFER INEQUALITYSOFFER INEQUALITY
An upper limit:
• can be violated by factorisation at NNLO• inequality preserved under evolution to larger scales only
1 1 1
1( ) ( ) ( )
2h x f x g x
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TMD: KTMD: KTT-dependent Parton Distributions-dependent Parton Distributions
Twist-2 PDFs )k,x(fkd)x(f T1T2
1
Distribution functions
Chirality
even odd
Twist-2
U
L
T
, h1,
Transversity
Boer-Mulders
Sivers
1hL1h
T1h
Tf1 Tg1
1f
1g
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TMD PDF InvestigationTMD PDF Investigation
➠ Process SIDIS → convolution with FF
Drell-Yan → PDF only
pp annihilations: each valence quark can
contribute to the diagram
➠ Energies
@ FAIR unique energy range up to s~30 GeV2 with PANDA up to s~200 GeV2 with PAX
@ much higher energies → big contribution from sea-quarks
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Drell-Yan ProcessDrell-Yan Process
• Drell-Yan: pp -> +-X
Collins-Soper frameCollins-Soper frame
Kinematics
x1,2 = mom fraction
of parton1,2
= x1 • x2 =
M2/s
xF = x1 - x2
Collins-Soper frame: Phys. Rev. D16 (1977) 2219.
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NLO pQCD: λ 1, 0, υ 0
Lam-Tung sum rule: 1- λ = 2ν
• reflects the spin-½ nature of the quarks
• insensitive top QCD-corrections
Experimental data [1]: υ 30 %
[1] J.S.Conway et al., Phys. Rev. D39 (1989) 92.
Di-Lepton Rest Frame
Drell-Yan Drell-Yan AsymmetriesAsymmetries
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SINGLE-POLARISED
UNPOLARISED
.
Drell-Yan Cross SectionDrell-Yan Cross Section
R.D. Tangerman and P.J. Mulders, Phys. Rev. D51, 3357-3372 (1995)
U = N(cos2φ>0)
D = N(cos2φ<0) DUDU
A
Angular
Asymmetry
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CERN NA51 450 GeV/c
Fermilab E866 800
GeV/c
Di-Lepton ProductionDi-Lepton Production
pppp -> -> ll++ll--XX
A. Baldit et al., Phys. Lett. 332-B, 244 (1994)
R.S. Towell et al., Phys. Rev. D 64, 052002 (2001)
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Phase space for Drell-Yan processesPhase space for Drell-Yan processes
x1,2 = mom fraction of parton1,2
= x1 • x2
xF = x1 - x2
= const: hyperbolaexF = const: diagonal
PAX @ HESR
symmetric HESR collider
1
1.5 GeV/c2 ≤ M ≤ 2.5 GeV/c2
PANDA
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The PANDA The PANDA SpectrometerSpectrometer
STT Detectors
Physics Performance Report for PANDA arXiv:0903.3905
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Drell-Yan Process and BackgroundDrell-Yan Process and Background
• Background studies: needed rejection factor of 107
• Drell-Yan: pp -> +-X
cross section 1 nb @ s = 30 GeV2
• Background: pp -> N(+-)X
cross section 20-30 b
m = 105 MeV/c2; m = 140 MeV/c2
average primary pion pairs: 1.5
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A. Bianconi Drell-Yan Generator for ppA. Bianconi Drell-Yan Generator for pp• Antiproton beam
• Polarized/Unpolarized beam and target
• Drell-Yan cross section from experimental data
• Selects event depending on the variables:
x1, x2, PT, , , S
from a flat distribution
• Cross section: ST
T
,,AP'Sx,xSS
K
ddPdxdx
d
2121
A. Bianconi, Monte Carlo Event Generator DY_AB4 for Drell-Yan Events with Dimuon Production in Antiproton and Negative Pion Collisions with Molecular Targets,
internal note (PANDA collaboration)
A. Bianconi, M. Radici, Phys. Rev. D71, 074014 (2005) & D72, 074013 (2005)
A. Bianconi, Nucl.Instrum.Meth. A593: 562-571, 2008
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DY @ 15 GeV/c — pp->DY @ 15 GeV/c — pp->++--XX
• layout studies for muon id with ABDYG (1.5 MEv)
A. Bianconi Drell-Yan Generator
[1]A. Bianconi and M. Radici, Phys. Rev. D71 (2005) 074014
[1]
5.5s GeVDilepton Mass Distribution
Mdilepton [GeV/c2]
Focus on one single M range
1.5 MEv in 1.5 < M< 2.5 (GeV/c2)
σ04≤M≤9 ~ 0.4 pb
σ01.5≤M≤2.5 ~ 0.8
nbxP
xPx2
x1
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DY Asymmetries @ VertexDY Asymmetries @ VertexUNPOLARISED SINGLE-POLARISED
5·105 events included in asymmetries
Acceptance
corrections crucial!
1 < qT < 2 GeV/c
2 < qT < 3 GeV/c
xP xP
xP
xP
xPxP
Physics Performance Report for PANDA arXiv:0903.3905
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R = L·σ·ɛ
= 2·1032cm-2s-1 × x 0.8·10-33cm2× 0.33
= 0.05 s-1 ~ 130
Kev/month
Statistical errors for 5·105 generated events
xP
)
)xP
xPPhysics Performance Report for PANDA arXiv:0903.3905
DY Asymmetries @ VertexDY Asymmetries @ Vertex
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SummarySummary
DY studies feasable at PANDA
New physics from unpolarized DY
Wide Single Spin Asymmetry program
Investigation of TMD PDFs and nucleon structure
Few months of data taking in High Luminosity mode
are enough to: evaluate unpolarised and single-spin asymmetries with good accuracy investigate their dependence on qT,μμ