Simulation of X(3872) Resonance Scan Using the PandaRoot Framework 1

Transcription

1 Simulation of X(3872) Resonance Scan Using the PandaRoot Framework 1 XXXVIII. PANDA Collaboration Meeting, GSI Darmstadt Martin J. Galuska, Svende A. Braun, Wolfgang Kühn and Jens Sören Lange for the PANDA Collaboration II. Physikalisches Institut, JLU Gießen September, 5 th This work was supported in part by BMBF (06GI9107I) and HICforFAIR.

2 Outline Short Motivation Resonance Scan for X(3872) J/ψ π + π Study of X(3872) J/ψ γ

3 Motivation: X(3872) What is it? Belle, Phys. Rev. Lett.91(2003) CDF-II, Phys. Rev. Lett.93(2004) Discovered by Belle in X(3872) J/ψ π + π Confirmed by numerous experiments in the same decay channel Observed in several additional decay channels such as X(3872) J/ψ γ X(3872) D 0 D 0 X(3872) D 0 D0 π 0 BaBar, Phys. Rev. D71(2005) D0, Phys. Rev. Lett.93(2004) X(3872) is a well-established resonance, BUT

4 Motivation: X(3872) What is it?...many interpretations exist Loosely bound molecule of D 0 D 0 First excited state of conventional charmonium χ c1 (2P) QCD Exotica Tetraquark Hybrid charmonium S-wave threshold effect of D 0 D 0 Cusp effect Structure of X(3872) is still unclear To date only an upper limit for its width is known which was recently improved to Γ X(3872) 1.2 MeV at 90% C.L. [6] PANDA is well-suited for a measurement of Γ X(3872)

5 Prospects for PANDA J PC = 1 ++ favored, J PC = 2 + possible for X(3872) C = +1 prohibits direct formation of X(3872) in e + e collisions. PANDA will combine excellent PID capabilities with cooled antiproton beams of unprecedented momentum resolution Goal of this Work Detailed simulation of a resonance scan of X(3872) within the PandaRoot framework

6 Assumed Parameters for Simulation of X(3872) Resonance Scan at PANDA Resonance Scan Experiment PANDA (TPC option) Resonance X(3872) Decay Channel J/ψ π + π Subsequent Decay J/ψ e + e Number of scan points 20 Time Requirement 2 days per scan point Spacing Equidistant E cm interval [ MeV, MeV] HESR High resolution mode p beam distribution Gaussian, rms p beam /p beam = E cm distribution Gaussian, rms kev Accelerator duty factor 50% Integrated luminosity pb 1 /day

7 Assumed Parameters for Simulation of X(3872) Resonance Scan at PANDA X(3872) Mass m X(3872) GeV Width Γ X(3872) 100 kev Cross section model Breit-Wigner Production cross section in pp σ BW = 50 nb for E cm = m X(3872) Branching Ratio into J/ψ π + π 0.1 Decay model VVPiPi Subsequent J/ψ Decay Branching Ratio into e + e 0.06 Decay model VLL

8 Assumed Parameters for Simulation of X(3872) Resonance Scan at PANDA Background Processes Direct: pp J/ψ π + π All other σ = 1.2 nb for E cm m X(3872) Assumed to be suppressible with PID

9 Electron / Pion Discrimination Using E EMC /p Figure: Plots of E EMC /p for three different simulated decays are shown. A straightforward electron/ pion discrimination can be achieved with a cut on the value of E EMC /p. The muon/ pion discrimination can be significantly enhanced using dedicated µ-detectors. PID: Distinction between electrons and pions 0.8 E EMC /P 1.2 e +/ E EMC /P 0.8 π +/ µ-id to come

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13 The simulated results are fitted with a convolution of a Gaussian and a Breit-Wigner distribution plus a constant for the direct X(3872) J/ψ π + π background. The fit is only used to estimate the full width at half maximum W obs of the observed excitation function. This value allows to estimate the width of the X(3872). As described in [3], the width Γ X(3872) of the underlying Breit-Wigner distribution can be estimated with a maximum systematic error of 4% if the full width at half maximum W G of the Gaussian error distribution is known exactly using the following equation: Γ X(3872) W obs (1.02 W G) 2 W obs As an approximation, the FWHM of the center of mass energy distribution is assumed for W G. Setting W G to 79 kev and obtaining W obs kev from the fit yields the following estimate on Γ X(3872) : ( kev)2 Γ X(3872) kev kev kev. This straightforward procedure yields an acceptable result for the width of the X(3872) which is about 10% greater than the input width of 100 kev. The error of this estimate should be dominated by the estimation of W G and the statistical fluctuations of the observed signal counts and not by using the above approximation.

14 Reconstruction Procedure

15 Kinematics of X(3872) Forward half of CT gets 4 x as many hits as the rest ( ) p T is small ( 1 GeV/c) p z is high ( 10 GeV/c)

16 Comparison of X(3872) J/ψ γ and X(3872) J/ψ π + π 9 BR(X(3872) J/ψ γ) BR(X(3872) J/ψ π + π ) X(3872) J/ψ γ should yield: better efficiency: ε(j/ψ γ) (0.9) ε(j/ψ π + π ) (0.9) 4 better mass resolution: better signal-to-background-ratio: Due to the presence of the high energy photon, the background should be of electromagnetic nature and therefore be suppressed compared to hadronic background for X(3872) J/ψ π + π (α s 0.1 α em 1/137) X(3872) J/ψ γ might be favorable for PANDA

17 Boost into the X(3872) CMS Cut on monoenergetic γ possible

18 References [1] M. J. Galuska, Master Thesis (2011) [2] S. A. Braun, Bachelor Thesis (2011) [3] J. G. McEwen, G. J. Daniell: Nuclear Instruments and Methods 116 (1974) [4] G. Y. Chen, J. P. Ma, Phys. Rev. D77(2008) [5] Belle Collaboration, Phys. Rev. Lett. 91(2003) [6] Belle Collaboration, arxiv: [hep-ex] submitted to Phys. Rev. D [7] K. Nakamura et al. (Particle Data Group), J. Phys. G37(2010) [8] V. Flaminio et al., Compilation of Cross-Sections, Part 3, p and anti-p Induced Reactions, High-Energy Reactions Analysis Group, CERN-HERA-79-03, 1979 [9] J. S. Lange, M. J. Galuska, et al., arxiv: v2 [10] V. Uzhinsky, A. Galoyan, hep-ph/

19 Simulation of X(3872) Resonance Scan Using the PandaRoot Framework 2 Thank you very much for your attention! Martin J. Galuska, Svende A. Braun, Wolfgang Kühn and Jens Sören Lange for the PANDA Collaboration II. Physikalisches Institut, JLU Gießen September, 5 th This work was supported in part by BMBF (06GI9107I) and HICforFAIR.