1. 8th International Conference on Nuclear Physics at Storage Rings
Exploiting Di-Muon
Production at PANDA
Marco Destefanis Università degli Studi di Torino
Stori’11
8th International Conference on
Nuclear Physics at Storage Rings
Frascati (Italy)
October 9-14, 2011

2. Overview Experimental apparatus Drell-Yan process and background
A. Bianconi Drell-Yan generator
Cut studies
Investigation of Drell-Yan asymmetries
Strong and electromagnetic relative phase via J/ψ resonance scan
Simulated yelds
Energy choice method
Summary

3. The PANDA Detector
STT Detectors
Physics Performance Report for PANDA arXiv:

4. TDR for the PANDA Muon System, 2nd Draft (May 2011)
Muon Detector System
Iarocci Tubes working
in proportional mode
Ar+CO2 gas mixture
Prototype ready
FE electronics in production
JINR - Dubna
MDT layout
MDT cross section
TDR for the PANDA Muon System, 2nd Draft (May 2011)

5. Range System Prototype
JINR - Dubna
Muon Detector Layout
MDT’s
Wires
Strips
Barrel
2133
17064
49916
End Cap
618
4944
8911
Muon Filter
424
3392
6876
Forward Range System
576
4608
7128
Total
3751
30008
72831

6. Drell-Yan Process and Background
Drell-Yan: pp -> +-X
cross section   1 nb @ s = 30 GeV2
Background: pp -> +-X, 2+2-X,……
cross section   b
m = 105 MeV/c2; m 145 MeV/c2
average primary pion pairs:  1.5
Background studies: needed rejection factor of 107

7. Drell-Yan Asymmetries
UNPOLARISED
Collins-Soper frame
SINGLE-POLARISED .
U = N(cos2φ>0)
D = N(cos2φ<0)
Asymmetry

8. Distribution functions
TMD: KT-dependent Parton Distributions
Twist-2 PDFs
Transversity
Distribution functions
Chirality
even odd
Twist-2 U L T ,
h1,
Sivers
Boer-Mulders

9. Di-Lepton Production pp -> l+l-X CERN NA51 450 GeV/c
Fermilab E GeV/c
R.S. Towell et al., Phys. Rev. D 64, (2001)
A. Baldit et al., Phys. Lett. 332-B, 244 (1994)

10. Phase space for Drell-Yan processes
x1,2 = mom fraction
of parton1,2
 = x1 • x2
xF = x1 - x2
 = const: hyperbolae
xF = const: diagonal
1.5 GeV/c2 ≤ M ≤ 2.5 GeV/c2
HESR
symmetric HESR collider 1

11. A. 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:
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, (2005) & D72, (2005)
A. Bianconi, Nucl.Instrum.Meth. A593: , 2008

12. Background and Cuts Next Step: Kinematic refit Sources of background
Primary background: Primary  & Secondary  from Primary 
Secondary background: Secondary  & Secondary  from Secondary 
Cuts and their effect on signal
Rejection factor of 107
Iron
At least 1 hit in
the first 2 layers
qT > 0.75 GeV/c
Signal
Linear rejection depending on Fe
thickness
Reject 30% of
the signal
~ 35% of the signal is reconstructed
Primary
Background
Rejection ≈ 103
Rejection ≈ 104
Secondary
Almost no effect
Rejection >5•106
Next Step:
Kinematic refit

13. 500KEv included in asymmetries Acceptance corrections
DY Vertex
SINGLE-POLARISED
UNPOLARISED
1 < qT < 2 GeV/c
2 < qT < 3 GeV/c xP xP xP xP
500KEv included in asymmetries
Acceptance corrections
crucial! xP xP

14. J/ψ Strong and Electromagnetic Decay Amplitudes
Resonant contributions
Фp(GMp )~Фγ Ф3g = 0
Фγ: relative A3g - Ap
J/ψ → NN Фp = 89°±15° [1,2]
J/ψ → VP (1-0-) Фp = 106°±10° [3]
J/ψ → PP (0-0-) Фp =89.6°±9.9° [4]
J/ψ → VV (1-1-) Фp = 138°±37° [4]
NO INTERFERENCE!
Strong → A3g
hadrons
Electromagnetic → Aγ
hadrons
Non-resonant continuum
affects the measured BR [5]
affects Фp [5]
INTERFERENCE WITH A3g!
Non-resonant Continuum → AQED
hadrons
[1] R. Baldini, C. Bini, E. Luppi, Phys. Lett. B404, 362 (1997); R. Baldini et al., Phys. Lett. B444, 111 (1998)
[2] J.M. Bian, J/ψ -> ppbar and J/ψ -> nnbar measurement by BESIII, approved draft
[3] L. Kopke and N. Wermes, Phys. Rep. 174, 67 (1989); J. Jousset et al., Phys. Rev. D41,1389 (1990).
[4] M. Suzuki et al., Phys. Rev. D60, (1999).
[5] P. Wang, arXiv:hep-ph/ v2 and references therein.

15. J/ψ Strong and Electromagnetic Decay Amplitudes
IMAGINARY AMPLITUDES HARD TO BE EXPLAINED!
J/ψ perturbative regime (← ΓJ/ψ ~ 93KeV )
pQCD → real Aγ, A3g
QCD does not provide sizeable imaginary amplitudes (Фp 10° at most [1])
a J/ψ - V glueball mixing [2] may explain imaginary amplitudes; and ψ’?
determination of phases Фp rely on theoretical hypotheses
EXPERIMENTAL DATA
no interference term in the inclusive J/ψ and ψ’ production
expected evidence of an interf. term in e+e-→ J/ψ BESII [3]
no clear evidence of interf. or glueball in e+e-→ J/ψ → ρπ @ BESII [4]
[1] J. Bolz and P. Kroll, WU B
[2] S.J. Brodsky, G.P. Lepage, S.F. Tuan, Phys. Rev. Lett. 59, 621 (1987).
[3] J.Z. Bai et al., Phys. Lett. D 355, (1995).
[4] J.Z. Bai et al., Phys. Rev. D 54, 1221 (1996).

16. radiative corrections
Simulated Yields for e+e--> pp
Δφ = 0°
Δφ = 90°
Δφ = 180°
beam energy spread +
radiative corrections
continuum reference
σ ~ 11 pb
no corrections
beam energy spread

17. Simulated Yields for pp -> µ+µ-
Δφ = 0°
Δφ = 90°
Δφ = 180°
continuum reference
σ ~ 18 pb
no corrections
beam energy spread

18. Energy Points Choice Maximum interference: 0° What happens at 90°
Cross section simulated at 70°, 80°, 90°, 100°, 110°
Gradient
2 points at low W
fit the continuum
Student test
slope
Deep position
Beginning of Breit-Wigner
(σ90-σi)/σ90
i = 70
i = 80
i = 100
i = 110

19. Summary 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
Interest on J/ψ decay amplitudes
Simulation of different phases
Reasonable energy point choice
Optimization of the procedure