drell-yan perspectives at fair marco destefanis università degli studi di torino drell-yan...
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Drell-Yan PerspectivesDrell-Yan Perspectives
at FAIRat FAIR
Marco Destefanis Università degli Studi di Torino
Drell-Yan Scatteringand the Structure of Hadrons
Trento (Italy)May 21-25, 2012
for the PANDA Collaboration
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OverviewOverview
• Motivation
• Drell-Yan cross section and azimuthal asymmetries
• Experimental scenarios
• Drell-Yan process and background @ PANDA
A. Bianconi Drell-Yan generator
Cut studies
• Investigation of Drell-Yan asymmetries
• Towards antiproton polarized beams
• 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
1/2 1/2
L L
+1/2 1/2
R R
q(x) spin averaged
a
aaa xfxfxexxFxF )()()(2)( 212
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1/2 1/2
L L-
1/2 1/2
R R
Δq(x) helicity difference
Helicity Helicity basebase
Twist-2 PDFs: ),()(1 xuxf u ),()(1 xuxg u )()(1 xuxhu
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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 NLO• 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
1hL1hT1h
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
@ RHIC 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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Drell-Yan ProcessDrell-Yan Process
Gives access tochirally odd functions
Transversity
No convolution with FF
Chirally odd functions are not suppressed (as in DIS)
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DIS ProcessDIS Process
• RHIC energies: √s = 100 GeV -> τ ≤ 10-2 -> small x1 and/or x2
• Too small Soffer upper bound on ATT (percent level[1])
• ATT @ RHIC very small, smaller √s would help[2]
[1] Martin et al, Phys.Rev. D60 (1999) 117502.[2] Barone, Colarco and Drago, Phys.Rev. D56 (1997) 527.
a
aaaTT hhe
XppXpp
XppXppA 11
2
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DIS ProcessDIS Process
• RHIC energies: √s = 100 GeV -> τ ≤ 10-2 -> small x1 and/or x2
• Too small Soffer upper bound on ATT (percent level[1]):
• ATT @ RHIC very small, smaller √s would help[2]
[1] Martin et al, Phys.Rev. D60 (1999) 117502.[2] Barone, Colarco and Drago, Phys.Rev. D56 (1997) 527.
a
aaaTT hhe
XppXpp
XppXppA 11
2
2 20Q 0.23 GeV
2 2Q 25 GeV
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QCD higher order contributionsQCD higher order contributions
s=45 GeV2
s=210 GeV2
s=45 GeV2
s=210 GeV2
[1] Shimizu et al., hep-ph/0503270 .
• cross section affected• K-factors almost spin independent
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QCD contributions to AQCD contributions to ATTTT
• Contributions drop increasing the energy[1]
[1] Shimizu et al., hep-ph/0503270 .
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Perturbative CorrectionsPerturbative Corrections
• Smaller at higher energies[1]
2GeV 30s 2GeV 200s
[1]H. Shimizu et al., Phys. Rev. D71 (2005) 114007
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Double Spin Asymmetries @ s = 30, 45 GeVDouble Spin Asymmetries @ s = 30, 45 GeV22
• ATT small at large √s and M2
due to slow evolution of h1a(x,Q2)
• Large ATT expected[1] for √s and M2 not too large and τ not too small
[2]M. Anselmino et al., Phys. Lett. B594 (2004) 97.
2GeV 30s
2GeV 45s
220
20
201q
[2] GeV/c 23.0Q @ )Qx,(q)Qx,(h Assuming
[1] Shimizu et al., Phys.Rev.D 71 (2005) 114007.
[3] Efremov et al, Eur. Phys. J. C 35 (2004) 207.
Q2 = 5 GeV2
Q2 = 9 GeV2Q2 = 16 GeV2
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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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Expected polar Expected polar distributionsdistributions
E772 @ Fermilab
λ, μ, ν measured[1] in p N→μ+μ - X
Perfect agreement with pQCD exptectations!
[1] McGaughey, Moss, JCP, Annu. Rev. Nucl. Part. Sci. 49 (1999) 217.
)cos1( 20
dd
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E537 @ Fermilab
Anassontzis et al., Phys. Rev. D38 (1988) 1377
vs coscos
d
d
p
pπ
π
vs coscos
d
d
Expected polar Expected polar distributionsdistributions
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Conway et al, Phys. Rev. D39 (1989) 92
E615 @ Fermilab
-N +-X @ 252 GeV/c
-0.6 < cos < 0.6
4 < M < 8.5 GeV/c2
Angular distribution in CS Angular distribution in CS frameframe
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Conway et al, Phys. Rev. D39 (1989) 92
30% asymmetry observed for -
E615 @ Fermilab -N +-X @ 252 GeV/c
Angular distribution in CS Angular distribution in CS frameframe
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NA10 coll., Z. Phys. C37 (1988) 545
NA10 @ CERN -N +-X @ 286 GeV/c
Deuterium
Tungsten
Nuclear Nuclear effects?effects?
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NA10 @ CERN[1]λ, μ, ν measured in π N→μ+μ – X
υ involves transverse spin effects at leading twist [2]
If unpolarised DY σ is kept differential on kT , cos2φ contribution to angular distribution provide:
2 21 2, 1 1h (x κ ) h (x ,κ )
[1] NA10 coll., Z. Phys. C37 (1988) 545
Violation of Lam-Tung sum Violation of Lam-Tung sum rulerule
[2] D. Boer et al., Phys. Rev. D60 (1999) 014012.
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[1] L. Zhu et al, PRL 99 (2007) 082301; [1] D. Boer, Phys. Rew. D60 (1999) 014012.
Boer-Mulders
T-odd Chiral-odd TMD
• ν > 0 → valence h 1 has same sign in π
and N
• ν(π-W→μ+μ-X) ~ h 1 (π)valence x h 1
(p)valence
• ν(pd→μ+μ-X) ~ h 1 (p)valence x h 1
(p)sea
• ν > 0 → valence and sea h 1 has same
sign, but sea h 1
should be significantly smaller
[1]
Drell-Yan Drell-Yan AsymmetriesAsymmetries
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Drell-Yan Drell-Yan AsymmetriesAsymmetries
λ 1, 0
Even unpolarised beam on polarised p, or polarised on unpolarised p
are powerful tools to investigate кT dependence of QDF
D. Boer et al., Phys. Rev. D60 (1999) 014012.
pp
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Transverse Single Spin Transverse Single Spin AsymmetriesAsymmetries
# of partons in polarized proton depends on
Sivers effect
p pS p k \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
PDFX
p\\\\\\\\\\\\\\p
pS\\\\\\\\\\\\\\
k
qp
X
p\\\\\\\\\\\\\\p
qS\\\\\\\\\\\\\\
k
qppartons’ polarisation in unpolarized proton depends on
Boer Mulders effect
q qS p k
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
FF
X
p\\\\\\\\\\\\\\q
S
\\\\\\\\\\\\\\
p̂
q
Polarising Fragmentation Function
qS p p \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
Hadrons’ polarisation coming from
unpolarised quarks depends on
X
p\\\\\\\\\\\\\\q
qS\\\\\\\\\\\\\\
p\\\\\\\\\\\\\\
qfragmentation of polarised quark depends on
Collins effect
q qS p p \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
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Transverse Single Spin Transverse Single Spin AsymmetriesAsymmetries
d d
d dNA
All those terms contribute to the Single Spin Asymmetry
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SINGLE-POLARISED
UNPOLARISED
.
DOUBLE-POLARISED
Drell-Yan Cross SectionDrell-Yan Cross Section
R.D. Tangerman and P.J. Mulders, Phys. Rev. D51, 3357-3372 (1995)
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Azimuthal Azimuthal AsymmetriesAsymmetries
)2cos(
)sin(),sin(
2cos
21
22
SS
SS
• Unpolarized
• Single polarized
• Double polarized
U = N(cos2φ>0)
D = N(cos2φ<0) DUDU
A
Asymmetry
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Primary beams:• Proton• Heavy Ions• Factor 100-1000 over present in intensity
Future GSI andFuture GSI andFacility for Antiproton Facility for Antiproton
and Ion Researchand Ion Research
Secondary Beams:• Radioactive beams• Antiprotons 3 - 30 GeV 1-2 107 /s
Storage and Cooler Rings:
• Radioactive beams• e – A collider
• 1011 stored and cooled
0.8 - 14.5 GeV antiprotons
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High Energy Storage High Energy Storage RingRing
ElectroncoolerE<8 GeV
Injection
HESR
High res. mode: L = 1031 cm-2 s-1 p/p < 10-5
High lum. mode: L = 2·1032 cm-2 s-1 p/p < 10-4
Cooling: electron/stochastic
Pmax = 15 GeV/cLmax = 2·1032 cm-2 s-1
Ø < 100 mp/p < 10-5
internal target
Characteristics70 m
185
m
1011 stored and cooled 0.8-15 GeV/c antiprotons
Detector
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HESR: asymmetric collider layout
Asymmetric double-polarised collider mode proposed by PAX people:
• APR (Antiproton Polariser Ring): polarising antiprotons, p > 0.2 GeV/c• CSR (Cooled Synchrotron Ring): polarised antiprotons, p = 3.5 GeV/c• HESR: polarised protons, p = 15 GeV/c
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The PANDA DetectorThe PANDA Detector
STT Detectors
Physics Performance Report for PANDA arXiv:0903.3905
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Cherenkov
Polarized Antiproton eXperiments
Asymmetric collider (√s=15 GeV): polarized protons in HESR (p=15 GeV/c) polarized antiprotons in CSR (p=3.5 GeV/c)
The PAX DetectorThe PAX Detector
V. Barone et al., Technical Proposal for PAX, 2005
http://www2.fz-juelich.de/ikp/pax/portal/index.php?id=103
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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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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 -> +-X, 2+2-X,……
cross section 20-30 b
m = 105 MeV/c2; m 145 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
500KEv 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 500KEv generated
xP
)
)xP
xPPhysics Performance Report for PANDA arXiv:0903.3905
DY Asymmetries @ VertexDY Asymmetries @ Vertex
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The Road to The Road to
Polarized AntiprotonsPolarized Antiprotons
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How to polarize antiprotons?How to polarize antiprotons?
Intensity loss,
but it works
H. Ströher, PoS(STORI11) 030D. Oellers, PoS(STORI11) 008
Spin filtering
Λbar decay
Not feasible
Not enoughtintensity
Spin flip
Spin dependent reaction Under study
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Experimental setupExperimental setup
H. Ströher, PoS(STORI11) 030D. Oellers, PoS(STORI11) 008
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Beam PolarimenterBeam Polarimenter
• pd elastic scattering
detection in two (L-R) symmetric Silicon Tracking Telescopes
Deuteron separation
H. Ströher, PoS(STORI11) 030D. Oellers, PoS(STORI11) 008
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Results – Beam PolarizationResults – Beam Polarization
Measurements after a storing period of 5000 s
H. Ströher, PoS(STORI11) 030D. Oellers, PoS(STORI11) 008
• Polarization lifetime: τp > 105 s
• Spin-flip efficiency: 0.9887 ± 0.0001
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SummarySummary
New physics from unpolarized DY
Wide Single Spin Asymmetry program
Double Spin Asymmetries, if p can be polarized
• Interest on Drell-Yan studies• 1.5 < Mμμ < 2.5 GeV/c2
• Cuts for background rejection
Rejection factor achieved for secondary background: >
5 106
Kinematically constrained refit still to be investigated
• Few months of data taking are enough to: evaluate unpolarised and single-spin asymmetries with good accuracy investigate their dependence on qT,μμ
• Next step: Polarized Antiprotons