The most recent results which concern the heavy quark hadrons done in the CMS experiment are reported. The searching area spans over the heavy quark spectroscopy, production cross sections, beauty meson decay properties, rare decays, and CP violation

Fedi, G.

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Fedi, Giacomo

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Heavy quark physics in CMS

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DOI 10.1393/ncc/i2015-15129-7Colloquia: LaThuile15IL NUOVO CIMENTO 38 C (2015) 129Heavy quark physics in CMSG. Fedi on behalf of the CMS CollaborationINFN, Sezione di Pisa - Pisa, Italyreceived 2 October 2015Summary. — The most recent results which concern the heavy quark hadronsdone in the CMS experiment are reported. The searching area spans over the heavyquark spectroscopy, production cross sections, beauty meson decay properties, raredecays, and CP violation.PACS 14.40.Pq – Heavy quarkonia.1. – IntroductionRecent results regarding the heavy quark physics in CMS [1] can be divided in twomain categories: the indirect search for new physics beyond the Standard Model and thestudy of charm and beauty hadrons production and decay. In the former analysis categorya measurement which lead to a different results from the Standard Model expectation,gives the hint that new physics might be present in the measured processes, see sect. 2and 3. While in the latter category, the analyses aim is to do precise measurementswithin the Standard Model framework, or aim to test the theoretical approximations ofthe studied process, see sect. 4, 5, 6. 7, 8 and 9.2. – Search for B(s,d) → μμThe rare decays Bs → μμ and Bd → μμ were studied combining the CMS data col-lected at the center-of-mass energy of√s = 7 and 8TeV for a total integrated luminosityof 5 and 20 fb−1, respectively [2].The aim of the studies was to search for events of those two rare decays. In case of noevidence of signal were found new production upper limits would have been set. In theStandard Model of particle physics the B(s,d) → μμ decays are highly suppressed sincethey cannot decay through the tree-level diagrams. The flavour changing neutral-currentFCNC transitions are only possible via box or penguin diagrams, see fig. 1. Furthermorethe decays are Cabibbo and helicity suppressed. The Standard Model predictions forthe branching fraction are B(Bs → μμ) = (3.66 ± 0.23) · 10−9 and B(Bd → μμ) =(1.06± 0.10) · 10−10 [3]. Any measured deviation of the branching fractions with respectCreative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 G. FEDI on behalf of the CMS COLLABORATIONB0sW+W−Z0tbsμ+μ−B0sW+νW−tbs μ−μ+B0sX+W−X0tbsμ+μ−B0sX+νW−tbsμ+μ−Fig. 1. – Bs → μμ decay Feynman diagrams. From left to right: SM penguin diagram, SM boxdiagram, new physics penguin diagram, and new physics box diagram.to the Standard Model prediction might be a hint of New Physics particles present inbox or penguin diagrams, see fig. 1.With an unbinned maximum-likelihood fit to the dimuon invariant mass distributionthe branching fraction B(Bs → μμ) = (3.0+0.9−0.8(stat.)+0.6−0.4(syst.)) · 10−9 is measured. Anexcess of Bs → μμ events with respect to background is observed with a significance of4.3 standard deviations. In case of the decay branching ratio B(Bd → μμ) < 1.1 · 10−9,an upper limit is determined at 95% of confidence level. Both results are in agreementwith the expectations from the standard model. The two-dimensional likelihood scan ofthe fit is shown in fig. 2.3. – CP-violating phase φs using Bs →J/ψφ(1020) channelThe CP-violating weak phase φs and the decay width difference ΔΓs of Bs meson aremeasured by the CMS experiment at the LHC using a data sample of Bs →J/ψφ(1020)decays [4]. The analysed data sample corresponds to an integrated luminosity of 20 fb−1collected in pp collisions at√s = 8TeV.The weak phase φs of Bs arise from the interference between direct Bs meson decaysinto a CP eigenstate and decays through mixing to the same final state. It is predictedby the mean of a global fit of the SM parameters to be φs = 0.0363+0.0016−0.0015 rad [5].)-μ+μ→s0BF(B0 1 2 3 4 5 6 7 8 9 10-910×)- μ+ μ→0BF(B00.20.40.60.811.21.41.61.82-910×σ1σ2 σ3 σ4CMSSMCMS -1=8 TeV, L=20 fbs-1=7 TeV, L=5 fbs)-μ+μ→s0BF(B0 1 2 3 4 5-910× lnLΔ202468101214161820σ1σ2σ3σ4-910×)-0.9+1.0        (3.0)=-μ+μ→s0BF(Bσ4.3SM)-μ+μ→0BF(B0 0.2 0.4 0.6 0.8 1-910× lnLΔ202468101214161820σ1σ2σ3σ4-1010×)-1.8+2.1        (3.5)=-μ+μ→0BF(Bσ2.0SMFig. 2. – Two-dimensional likelihood scan for B(Bs → μμ) and B(Bd → μμ). The red pointshows the SM prediction value.HEAVY QUARK PHYSICS IN CMS 3 [rad]sφ-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5]-1 [pssΓΔ00.020.040.060.080.10.120.140.160.180.2CMSCMS Preliminary-1=8 TeV  L=20 fbs68% C.L.90% C.L.95% C.L.Standard ModelFig. 3. – Two-dimensional scan of the likelihood function for φs and ΔΓs, the best fit valuesand the C.L. contours are shown in comparison with the SM prediction.Being the predicted φs with a good accuracy and close to zero, a significant deviationof the measured weak phase with respect to the prediction, might be the sign of NPparticles in the mixing decay of Bs.An angular analysis of the Bs decay based on three angles (θT , ψT , and φT ) is neededin order to disentangle the two CP states (odd and even). The differential decay rate ofBs is studied in terms of proper decay time and the angular variables. In order to increasethe sensitivity on φs, the flavour of Bs at production time (flavour tagging) is used as anobservable in the fit of data. The total tagging power of tagging is (0.97± 0.03)%.Assuming a polarisation-independent CP violation model and no direct CP violation,the values for the weak phase and the decay width difference between the Bs masseigenstates are measured to be:φs = −0.03± 0.11 (stat)± 0.03 (syst) rad,ΔΓs = 0.096± 0.014 (stat)± 0.007 (syst) ps−1.In fig. 3 the two-dimensional scan of the likelihood function for φs and ΔΓs is shown.The value of φs is in statistical agreement with the SM fit prediction. The ΔΓs isconfirmed to be non-zero.4. – B+ → ψ(2S)φK+ rare decayThe B+ → ψ(2S)φK+ invariant mass peak was detected by the CMS experimentusing 19.6 fb−1 integrated luminosity at√s = 8TeV of center-of-mass energy. Theunbinned maximum likelihood fit was performed on the invariant mass distribution toextract the peak characteristics. The likelihood function is composed by the signal PDF,which is parametrized as a double Gaussian. While the background PDF is parametrizedas a first-order Chebyshev polynomial. In fig. 4 the mass distribution and the best fitprojection is shown. The peak centroid is compatible with the B+ mass and the measuredresolution is about 3MeV. The obtained signal events might be used to measured theB+ → ψ(2S)φK+ decay branching fraction.4 G. FEDI on behalf of the CMS COLLABORATION (GeV)± Kφ(2S)ψm5.22 5.24 5.26 5.28 5.3 5.32Candidates / 0.002 GeV0204060 = ~ 3 MeV σMass resolution =8 TeV)s (-1L=19.6 fbCMS PreliminaryFig. 4. – B+ → ψ(2S)φK+ invariant mass distribution and relative best fit. The lines representthe signal-plus-background fit (solid) and the background-only component (dashed).5. – Bc decaysAt a center-of-mass energy√s = 7TeV in proton-proton collisions, the ratio of theproduction cross sections times branching fractions σ(B±c )×B(B±c → J/ψπ±)/σ(B±)×B(B± → J/ψK±) is studied [6]. The analysed data sample corresponds to an integratedluminosity of 5.1 fb−1. The ratio is determined to be (0.48 ± 0.05(stat) ± 0.03(syst) ±0.05(τBc))× 10−2 in the kinematic region that requires B±c and B±x mesons with trans-verse momentum pT > 15GeV and rapidity |y| < 1.6. A previous measurement of thesame ratio done by LHCb is in agreement with the present result taking into account forthe different kinematic regions used in the analyses.The ratio of the branching fractions R = B(B±c → J/ψπ±π±π∓)/B(B±c → J/ψπ±)is also measured. The efficiencies were assessed using a model-independent method.The measured ratio is R = 2.55 ± 0.80(stat) ± 0.33(syst)+0.04−0.01(τBc), consistent with theprevious LHCb result.In figs. 5 the invariant mass distributions for B±c → J/ψπ±π±π∓ (left) and B±c →J/ψπ± (right) are shown. invariant mass (GeV)-π+π+πψJ/6 6.1 6.2 6.3 6.4 6.5 6.6Events / 0.015 GeV020406080100) > 15 GeV+c(BTp)| < 1.6+c|y(B (7 TeV)-15.1 fbCMS invariant mass (GeV)+πψJ/5.8 5.9 6 6.1 6.2 6.3 6.4 6.5 6.6 6.7Events / 0.015 GeV102030405060) > 15 GeV+c(BTp)| < 1.6+c|y(B (7 TeV)-15.1 fbCMSFig. 5. – Invariant mass distributions for B±c → J/ψπ±π±π∓ (left) and B±c → J/ψπ±) (right).The fit function projections is also shown.HEAVY QUARK PHYSICS IN CMS 5 Invariant mass [GeV]ππψJ/5.15 5.2 5.25 5.3 5.35 5.4 5.45 5.5 5.55Events / 9 MeV050100150200250300350DataFitSignalCombinatorial backgroundPeaking backgroundCMS (7 TeV)-15.3 fb invariant mass [GeV]-π+πψJ/5.15 5.2 5.25 5.3 5.35 5.4 5.45 5.5 5.55Pull-2025.25 5.3 5.35 5.4 5.45Events / 4.5 MeV02004006008001000DataFitSignalCombinatorial backgroundCMS (7 TeV)-15.3 fb invariant mass [GeV]-K+KψJ/5.25 5.3 5.35 5.4 5.45Pull-4-202Fig. 6. – Invariant mass distributions for Bs → J/ψf0(980) (left) and Bs →J/ψφ(1020) (right).The fit function projections is also shown.6. – B(Bs → J/ψf0(980))/B(Bs →J/ψφ(1020)) ratioAt a centre-of-mass energy of√s = 7TeV in proton-proton collisions, the ratio ofbranching fractions Rf0/φ = B(Bs → J/ψf0(980))/B(Bs → J/ψφ(1020)) is measured [7].The analysed data sample corresponded to an integrated luminosity of 5.3 fb−1. Themeasured ratio is Rf0/φ = 0.140 ± 0.013(stat) ± 0.018(syst), where the first uncertaintyis statistical and the second is systematic. This result is consistent with theoreticalpredictions and previous measurements.In figs. 6 the invariant mass distributions for Bs → J/ψf0(980) (left) and Bs →J/ψφ(1020) (right) are shown.7. – J/ψ and ψ(2S) productionAt a centre-of-mass energy of√s = 7TeV in proton-proton collisions, the double-differential cross sections of promptly produced J/ψ and ψ(2S) mesons are measuredas a function of transverse momentum pT and absolute rapidity |y| [8]. The analysedJ/ψ and ψ(2S) data samples correspond to integrated luminosities of 4.55 and 4.90 fb−1,respectively. The differential cross section as a function of pT only, where the rapidityis integrated for values lower than 1.2, is also measured. With the present analysis thehighest-pT values in the context of the measured cross sections has been reached.In figs. 7 we show the differential cross sections as a function of pT times the dimuonbranching fractions for four rapidity bins and integrated over the range |y| < 1.2 (left)and the J/ψ and ψ(2S) differential cross sections integrated over rapidity (right).8. – Υ(nS) productionAt a centre-of-mass energy of√s = 7TeV in proton-proton collisions, the differentialcross sections as a function of transverse momentum pT for the production of Υ(nS) →μμ (n = 1, 2, 3) are presented [9]. The analysed data samples correspond to integratedluminosities of 4.9 fb−1. The Υ(nS) candidates are selected from those with dimuonrapidity |y| < 1.2 and transverse momentum 10 < pT < 100GeV.This measure extends the maximum pT range from 70 to 100GeV with respect theprevious results. The measurements show a transition from an exponential to a power-law6 G. FEDI on behalf of the CMS COLLABORATION [GeV]Tp0 20 40 60 80 100 120  [nb / GeV]Tpdy / d2σd-510-410-310-210-110110210ψJ/(2S)ψ = 7 TeVspp-1| < 1.2, 4.55 fb   (2.4%)yCMS, |-1| < 0.75, 2.3 pb   (3.5%)yATLAS, |-1| < 1.2, 4.90 fb   (10.6%)yCMS, |-1| < 0.75, 2.1 fb   (2.4%)yATLAS, || < 1.2yFKLSW, |Power-law fits [GeV]Tp0 20 40 60 80 100 120 [nb / GeV]y dTp / dσ d×B-610-510-410-310-210-1101 CMS-1 2)×| < 1.2 (y|| < 0.3y|| < 0.6y0.3 < || < 0.9y0.6 < || < 1.2y0.9 < |of 2.2% not includedLuminosity uncertaintyψJ/(2S)ψψ : L = 4.55 fbJ/(2S) : L = 4.90 fbψ -1 = 7 TeVspp2Fig. 7. – Left: J/ψ and ψ(2S) the differential cross sections as function of pT times the dimuonbranching fractions for four rapidity bins and integrated over the range |y| < 1.2. Right: J/ψand ψ(2S) differential cross sections integrated over rapidity.behavior at pt 20GeV for the three Υ states. In figs. 8 we show: the μμ invariant massdistribution and the well definite Υ(nS) peaks (left) and the relative differential crosssections as a function of pT (right).9. – χbn productionAt a centre-of-mass energy of√s = 8TeV in proton-proton collisions, the productioncross section ratio σ(χb2)/σ(χb1) is presented [10]. The analysed data samples correspondto integrated luminosities of 20.7 fb−1.The prompt χb1(1P) and χb2(1P) are detected using the radiative decays χb1,2(1P)→Υ(1S)+γ. The emitted photons are reconstructed using the decay to electron pairswhile interacting with the tracker material (converted photons). That permitted theχb1,2(1P) peaks to be resolved. The selected χb1,2(1P) kinematic region is defined by thephoton pseudorapidity |η| < 1.0, the Υ(1S) rapidity |y| < 1.5, and the Υ(1S) transversemomentum 7 < pT < 40GeV.Events / 10 MeV01000200030004000|y| < 0.6 < 12 GeVT10 < p(a) (7 TeV)-14.9 fbCMS [GeV]μμM9 9.5 10 10.5 11Pull-4-2024 [GeV]Tp0 20 40 60 80 100) [pb/GeV]− μ+ μ Br(×T/dpσd-510-410-310-210-110110210310410 (7 TeV)-14.9 fbCMS(1S)Υ 0.1×(2S)Υ 0.01×(3S)Υ(a)CMS 2011 |y| < 1.2 0.5×CMS 2010 |y| < 2.4 NLO theoryFig. 8. – Left: μμ invariant mass distribution and best fit projections. Right: the Υ(nS)differential cross sections as a function of pT.HEAVY QUARK PHYSICS IN CMS 7 [GeV]γμμm9.7 9.75 9.8 9.85 9.9 9.95 10 10.05Events/5 MeV 20406080100120140160 < 11 GeVΥT7 < p (8 TeV)-120.7 fbCMS [GeV]YTp5 10 15 20 25 30 35 40)b1χ(σ) / b2χ(σ00.20.40.60.811.21.41.6 (8 TeV)-120.7 fbCMSBF uncertainty (9%) not included| < 1γη| < 1.5, |YCMS, |y| < 4.5χLHCb, 2.0 < |yarXiv:1409.0693CMS average)b1χ(σ) / b2χ(σ)b1χ(σ) / b2χ(σFig. 9. – Left: μμγ invariant mass distribution of the χb1,2(1P) peaks and fit function projectionsfor the first Υ rapidity bin. Right: cross sections ratio σ(χb2)/σ(χb1) as a function of theΥ(1S) pT.The cross section ratio is measured as function of Υ(1S) transverse momentum. Themeasured average value of the cross section is 0.85± 0.07(stat+ syst)± 0.08 (BF), wherethe first uncertainty is the combination of the statistical and systematic uncertaintiesand the second is due to the uncertainty of the branching fractions.In figs. 9 we show: the μμγ invariant mass distribution of the χb1,2(1P) peaks for thefirst Υ rapidity bin (left) and the relative cross sections ratio as a function of the Υ(1S)pT (right). The cross section ratio does not shows any significant dependence on theΥ(1S) transverse momentum.REFERENCES[1] CMS Collaboration, JINST, 3 (2008) S08004.[2] Chatrchyan S. et al. (CMS Collaboration), Phys. Rev. Lett., 111 (2013) 101804,arXiv:1307.5025 [hep-ex].[3] Bobeth C., Gorbahn M., Hermann T., Misiak M., Stamou E. and Steinhauser M.,Phys. Rev. Lett., 112 (2014) 101801, arXiv:1311.0903 [hep-ph].[4] CMS Collaboration, CMS-PAS-BPH-13-012.[5] Charles J., Deschamps O., Descotes-Genon S., Itoh R., Lacker H., Menzel A.,Monteil S. andNiess V. et al., Phys. Rev. D, 84 (2011) 033005, arXiv:1106.4041 [hep-ph].[6] Khachatryan V. et al. (CMS Collaboration), JHEP, 01 (2015) 063, arXiv:1410.5729[hep-ex].[7] (CMS Collaboration), submitted to Phys. Lett. B, arXiv:1501.06089 [hep-ph].[8] Khachatryan V. et al. (CMS Collaboration), Phys. Rev. Lett., 114 (2015) 191802,arXiv:1502.04155 [hep-ph].[9] Khachatryan V. et al. (CMS Collaboration), Phys. Lett. B, 749 (2015) 14,arXiv:1501.07750 [hep-ph].[10] Khachatryan V. et al. (CMS Collaboration), Phys. Lett. B, 743 (2015) 383,arXiv:1409.5761 [hep-ph].

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Heavy quark physics in CMS

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