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

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

The PANDA Detector STT Detectors Physics Performance Report for PANDA arXiv:0903.3905

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)

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

Drell-Yan Process and Background 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 Background studies: needed rejection factor of 107

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

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

Di-Lepton Production pp -> l+l-X CERN NA51 450 GeV/c Fermilab E866 800 GeV/c R.S. Towell et al., Phys. Rev. D 64, 052002 (2001) A. Baldit et al., Phys. Lett. 332-B, 244 (1994)

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 PAX @ HESR symmetric HESR collider 1

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, 074014 (2005) & D72, 074013 (2005) A. Bianconi, Nucl.Instrum.Meth. A593: 562-571, 2008

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

500KEv included in asymmetries Acceptance corrections DY Asymmetries @ 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

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, 051501 (1999). [5] P. Wang, arXiv:hep-ph/0410028v2 and references therein.

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 →µ+µ- @ 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 95-35. [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, 374-380 (1995). [4] J.Z. Bai et al., Phys. Rev. D 54, 1221 (1996).

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

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

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

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