This paper summarizes the first ATLAS results on inclusive J/ψ production cross section and the ratio between promptly and non-promptly produced J/ψ meson in pp collisions at √s = 7TeV

Orlando, N.

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DOI 10.1393/ncc/i2011-11058-9Colloquia: IFAE 2011IL NUOVO CIMENTO Vol. 34 C, N. 6 Novembre-Dicembre 2011J/ψ production cross section and non-prompt fractionmeasurement with the ATLAS detectorN. Orlando on behalf of the ATLAS CollaborationINFN Sezione di Lecce and Dipartimento di Fisica Universita` del Salento - Lecce, Italy(ricevuto il 29 Luglio 2011; pubblicato online il 6 Dicembre 2011)Summary. — This paper summarizes the first ATLAS results on inclusive J/ψ pro-duction cross section and the ratio between promptly and non-promptly producedJ/ψ meson in pp collisions at√s = 7TeV.PACS 13.85.-t – Hadron-induced high- and super-high-energy interactions.PACS 14.40.Pq – Heavy quarkonia.The early B-physics program [1] of the ATLAS experiment [2] starts with the studiesof charmonium states, the most abundantly produced of which is the J/ψ meson.The J/ψ production cross section and non-prompt ratio [3] exploits J/ψ observationthrough its decays in muon pairs because of the lower QCD background than in theelectron channel. Events are selected on-line with single muon triggers by applying pTthresholds increasing with the luminosity.The integrated luminosity of the collected data sample for inclusive cross sectionmeasurement is L = 2.27 pb−1; the non-prompt ratio can benefit by a slightly largerluminosity of 2.44 pb−1.In the off-line two reconstructed muons with invariant mass in the J/ψ mass windoware selected. Muon reconstruction generally requires a track in the inner tracking system(named Inner Detector), satisfying specific quality criteria, statistically compatible witha track reconstruction in the Muon Spectrometer. In order to increase the efficiency forlow-pT muons, one of the two muons is allowed to be reconstructed with loose criteria,i.e. by matching an Inner Detector track to a segment in the muon spectrometer. Thetwo muons are required to have opposite charge. For non-prompt fraction measurement,to avoid ambiguity in vertex association, it is also required that the two muons are bothassociated with the same primary vertex; this last requirement rejects less than 0.2% ofthe events. At least one of the two selected muons must be spatially close to the firedtrigger chamber. The cross section is given by the number of candidate J/ψ correctedfor the weight w−1 = A·M· ε2trk · εμ+(pT μ+ , ημ+) · εμ−(pT μ− , ημ−) · εtrig and normalizedto data luminosity. The single track inner reconstruction efficiency εtrk is evaluatedto be 99 ± 0.5% from simulations, trigger efficiency εtrig is measured by hybrid data-MC method [3] and the bin migration correction factor M that move the J/ψ transversec© CERN on behalf of the ATLAS Collaboration under CC BY-NC 3.0 260J/ψ PRODUCTION CROSS SECTION AND NON-PROMPT FRACTION MEASUREMENT ETC. 261 [GeV]TψJ/p5 6 7 8 910 20 30 40dy [nb/GeV]T/dpσ2)d- μ+ μ→ψBr(J/-310-210-110110210ATLAS-1L dt = 2.2 pb∫= 7 TeVs|<1.5ψJ/|y0.75 <ATLAS |<1.6ψJ/|y1.2   <CMS Spin-alignment envelopeInclusive cross-sectionFig. 1. – Inclusive J/ψ production cross section as function of pT (J/ψ) in the rapidity bin0.75 < |yJ/ψ| < 1.5.momentum distribution observed in data back to the truth distribution is evaluated fromsimulations. The charge dependent muon reconstruction efficiency εμ±(pT μ± , ημ±) ismeasured with the tag-and-probe method [4] separately for negative and positive chargedmuons. The acceptance correction A is evaluated inside the fiducial volume defined by|−→p ±| > 3GeV and |η±| < 2.5, to ensure that kinematic regions of very low trigger andreconstruction efficiency are rejected. As example in fig. 1 the results of the cross sectionmeasurement in the rapidity bin 0.75 < |yJ/ψ| < 1.5 as function of the J/ψ transversemomentum are shown; the yellow bars represent the spin-alignment envelope, i.e. thetheoretical uncertainty due to unknown polarization, and the CMS points [5] are alsosuperimposed. The non-prompt fraction fB is given by the fraction of J/ψ coming fromB-hadrons decays. The measurement of fB is performed by a likelihood fit to the 2-dimensional distribution given by pseudo-proper-time versus invariant mass [3] with alikelihood p.f.d. that includes a model for prompt and non-prompt component of thesignal and a model for the prompt and non-prompt component of the background aswell [3].In conclusion, the inclusive J/ψ cross sections and the non-prompt fraction are mea-sured with the ATLAS detector. Further studies on J/ψ polarization can be used in thefuture to improve the J/ψ cross section measurement.∗ ∗ ∗I thank the IFAE 2011 organizing committee for support this work. I also thank G.Chiodini and S. Spagnolo for reading and comment the first version of this manuscript.REFERENCES[1] Rossi E., these proceedings.[2] Aad G. et al. (ATLAS Collaboration), JINST, 3 (2008) S08003.[3] Aad G. et al. (ATLAS Collaboration), Nucl. Phys. B, 850 (2011) 387.[4] Aad G. et al. (ATLAS Collaboration), ATLAS-CONF-2011-021 (2011).[5] Khachatryan V. et al. (CMS Collaboration), Eur. Phys. J. C, 71 (2011) 1575.

J/ψ production cross section and non-prompt fraction

measurement with the ATLAS detector

http://eprints.bice.rm.cnr.it/17566/1/ncc10092.pdf

J/ψ production cross section and non-prompt fraction measurement with the ATLAS detector

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