In the proceeding are reported precision measurement of differ ent b-hadrons lifetimes in the exclusive decays B+ -> J / psi K+ , B-0 -> j / psi K-*0 B-s(0) -> J / psi A, using 1 fb(-1) of data collected in 2011 with the LHCb detector at a centre-of-mass energy of 7 TeV

Dordei, F.

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Dordei, F

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$b-hadrons$ lifetime measurements using exclusive $b\rightarrow J/\Psi(\mu^{+}\mu^-)X$ decays at LHCb

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DOI 10.1393/ncc/i2014-11710-xColloquia: IFAE 2013IL NUOVO CIMENTO Vol. 37 C, N. 1 Gennaio-Febbraio 2014b-hadrons lifetime measurements using exclusive b → J/Ψ(μ+μ−) Xdecays at LHCbF. DordeiHeidelberg University, Physikalisches Institut - Heidelberg, Germanyricevuto l’1 Ottobre 2013Summary. — In this proceedings are reported precision measurements of differ-ent b-hadrons lifetimes in the exclusive decays B+ → J/ψK+, B0 → J/ψK∗0,B0 → J/ψK0s , B0s → J/ψφ, and Λ0b → J/ψΛ, using 1 fb−1 of data collected in 2011with the LHCb detector at a centre-of-mass energy of 7TeV.PACS 14.40.Nd – Bottom mesons (|B| > 0).PACS 14.20.Mr – Bottom baryons (|B| > 0).PACS 12.39.Hg – Heavy quark effective theory.1. – IntroductionPrecision measurements of b-flavoured hadron lifetimes are an important test ofthe theoretical approach to determine b-hadron observables, known as Heavy QuarkExpansion (HQE) [1]. This model is based on the operator product expansion in inversepowers of the heavy b-quark mass; it is used, for example, to extract |Vub| and |Vcb| frommeasurements of inclusive semileptonic B meson decays. In the free quark model thelifetimes of all b-hadrons are equal, because the decay width is determined by the b quarklifetime. Different corrections alter the lifetime at approximately 10% level. In the caseof the ratio of lifetimes of the Λ0b to the B0, differences of only a few percent are expected.However, different LEP measurements indicated that the corrections were significantlybigger [2], suggesting a small value of the ratio. Recent measurements have shownindications that a higher value is possible [3], although the uncertainties are still large.The B0s meson lifetime is measured using a single exponential to model the proper timedistribution, i.e., ignoring the non-zero decay-width difference between mass eigenstates(ΔΓs) of the B0s system. Measurements of the effective lifetimes in B0s -meson decaysallow to probe the width difference ΔΓs and the CP -violating phase φs of B0s − B0smixing box-diagram [4], with the advantage that only an untagged analysis is needed.Finally, the precision reached in these lifetime measurements demonstrates the excel-lent understanding of the LHCb detector and of the reconstruction system.2. – Lifetime determinationThe exclusive b-hadrons lifetimes presented here have been measured through thedecay channels B+ → J/ψK+, B0 → J/ψK∗0, B0 → J/ψK0s , B0s → J/ψφ and Λ0b →c© CERN on behalf of the LHCb CollaborationCreative Commons Attribution 3.0 License (http://creativecommons.org/licenses/by/3.0) 285286 F. DORDEITable I. – Results of the b-hadrons lifetime measurements. First uncertainty is statistical andthe second systematic. The value is blinded.Channel τ ± σstat ± σsys [ps]B+ → J/ΨK+ 1.xxx ± 0.004 ± 0.004B0 → J/ΨK∗0 1.xxx ± 0.006 ± 0.004B0 → J/ΨK0s 1.xxx ± 0.012 ± 0.008B0s → J/Ψφ 1.xxx ± 0.012 ± 0.005Λ0b → J/ΨΛ 1.xxx ± 0.024 ± 0.008J/ψΛ (charge conjugate modes are implied throughout), using 1.0 fb−1 of data collectedin pp collisions at√s = 7TeV with the LHCb detector [5]. At LHCb, b-hadrons areproduced with an average momentum of around 100GeV/c and have decay verticesdisplaced from the primary interaction vertex (around 1-2 cm), whereas combinatorialbackground candidates are produced by the random combination of tracks, which tendto originate from the primary vertex. So conventional selections exploit these featuresto select b-hadrons by requiring that their decay products are energetic and significantlydisplaced from the primary interaction point. However, this introduces a time-dependentacceptance which needs to be taken into account in the analysis and, making use of alimited unbiased sample, a data driven correction has been developed for it. Moreover,there are also implicit biases (∼ 20 fs), for example due to geometrical and reconstructionacceptances. Experimentally it is challenging to correct for these biases. In this analysiswe have established in great details the origin of this decay time acceptance. The maincontribution is due to a drop in the reconstruction efficiency at large decay time in theVertex Locator for tracks with large impact parameter relative to the z-beam axis. Wedeveloped a data-driven method to derive this inefficiency and to re-weight each eventin order to compensate for this effect. Further biases are instead reduced significantly,e.g., implementing a new method to reconstruct the primary vertex. All these methodshave been validated on large statistics samples of fully simulated events for each channel.Making use of a 2-dimensional unbinned maximum likelihood fit in the mass and in thedecay time distribution of the b-hadron it is possible to determine the B+, B0 and Λ0blifetime and the B0s effective lifetime.The b-hadrons lifetime measurements are listed in table I, where first uncertainty isstatistical and the second systematic, while the value is still blinded. All the measure-ments are the most precise measurements to date and are still statistically limited.∗ ∗ ∗The author acknowledges the support received from the ERC under FP7 and thesupport received from the International Max Planck Research School for Precision Testsof Fundamental Symmetries.REFERENCES[1] Lenz A., Nucl. Phys. Proc. Suppl., 177 (2008) 81.[2] Tarantino C., Eur. Phys. J. C, 33 (2004) S895.[3] ATLAS Collaboration, Phys. Rev. D, 87 (2013) 032002.[4] Fleischer R. and Knegjens R., Eur. Phys. J. C, 71 (2011) 1789.[5] LHCb Collaboration, Alves A. A. jr. et al., JINST, 3 (2008) S08005.

b-hadrons lifetime measurements using exclusive b -> J/psi(mu(+) mu(-)) X decays at LHCb

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b-hadrons lifetime measurements using exclusive b -> J/psi(mu(+) mu(-)) X decays at LHCb

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