B-physics results in CMS in Run2 Alessio Boletti on behalf of the CMS collaboration Universit` a degli Studi di Padova & INFN Moriond EW La Thuile, 21st March 2019 A. Boletti (Universit` a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 1 / 14
Introduction Introduction p s = 13 TeV CMS Integrated Luminosity, pp, Data included from 2015-06-03 08:41 to 2018-10-26 08:23 UTC Large amount of collisions delivered by LHC 180 180 Total Integrated Luminosity ( fb ¡ 1 ) LHC Delivered: 162.87 fb ¡ 1 160 CMS Recorded: 150.28 fb ¡ 1 160 in Run 2 , about six times the luminosity of Run 1 140 140 120 120 Very efficient data collection by CMS detector, 100 100 80 80 with improved and extremely competitive 60 60 track momentum resolution 40 40 20 20 0 0 Many B-physics analyses are statistically limited, 5 5 6 6 6 6 7 7 7 7 8 8 8 8 1 1 1 1 1 1 1 1 1 1 1 ' 1 1 1 ' ' ' ' ' ' ' ' ' ' ' ' ' u l c t n p r u l c t n p r u l c t n p r u l c t O a O a O a O J J A J J A J J A J benefit from increased statistics Date New challenges arise with increased luminosity: Ingenious trigger algorithms developed, for efficient online event selection Sophisticated analysis techniques studied, to reduce background contamination [CMS-DP-2018-036] A. Boletti (Universit` a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 2 / 14
Introduction Latest heavy-flavour analyses with Run 2 data 1. Observation of χ b 1 (3 P ) and χ b 2 (3 P ) states 2. Observation of B + c (2 S ) and B + ∗ (2 S ) states c 3. Search for τ → µµµ decay A. Boletti (Universit` a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 3 / 14
χ b 1(3 P ) and χ b 2(3 P ) observation Observation of χ b 1 (3 P ) and χ b 2 (3 P ) states Phys. Rev. Lett. 121, 092002 (2018) arXiv:1805.11192 Study of bottomonium ( b ¯ b ) family is very important to understand nonperturbative QCD in hadron binding χ b (3 P ) states are interesting to study these forces in proximity of open-beauty threshold Unresolved χ b (3 P ) state observed by ATLAS [1], D0 [2], and LHCb [3] Collaborations, through the χ b (3 P ) → Υ( nS ) γ decays [ n = 1 , 2 , 3] In this CMS analysis the first observation of resolved χ b 1 (3 P ) and χ b 2 (3 P ) states was obtained using data collected in 2015, 2016, and 2017, equivalent to 80 fb − 1 [1] Phys. Rev. Lett. 108 (2012) 152001 [2] Phys. Rev. D 86, 031103 [3] Eur. Phys. J. C74 (2014) 3092 A. Boletti (Universit` a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 4 / 14
χ b 1(3 P ) and χ b 2(3 P ) observation Observation of χ b 1 (3 P ) and χ b 2 (3 P ) states Phys. Rev. Lett. 121, 092002 (2018) arXiv:1805.11192 Selection of Υ( nS ) candidates Selection of χ b ( nP ) candidates 3 × 10 Photon reconstructed in γ → ee conversion s = 13 TeV = 13 TeV Y(1S) on beampipe and tracker material CMS -1 L = 80.0 fb 80 Photon candidate: p T > 0 . 5 GeV, | y | < 1 . 2 Events / 2.5 MeV y < 0.6 Photon energy correction computed on sample 60 of χ c 1 → J /ψ ( µµ ) γ and applied event-by-event 0.6 < y < 1.2 Validated on masses of χ b (1 P ) and χ b (2 P ) 40 Y(2S) 1P 1S → 1200 χ (1P) b Y(3S) χ (nP) mass (MeV) 9895 10255 CMS 20 1000 s = 13 TeV = 13 TeV 2P 1S → -1 L = 80.0 fb 9890 10250 Events / 3.5 MeV 2P 2S → b1 0 800 9 9.5 10 10.5 11 Dimuon mass (GeV) 600 Trigger: two muons with mass in Y(1S) + γ 8.5-11.5 GeV, and common vertex χ (2P) Y(2S) + γ b 400 Y(3S) + γ Upsilon candidate: p T > 14 GeV, χ (3P) b | y | < 1 . 2 200 Mass resolution: 60-120 MeV pure samples of Υ( nS ) obtained 0 9.8 10.2 10.6 with tight mass windows Y(nS) γ invariant mass (GeV) A. Boletti (Universit` a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 5 / 14
χ b 1(3 P ) and χ b 2(3 P ) observation Observation of χ b 1 (3 P ) and χ b 2 (3 P ) states Phys. Rev. Lett. 121, 092002 (2018) arXiv:1805.11192 CMS 100 s = 13 TeV Maximum likelihood fit to Υ(3 S ) γ mass -1 80 L = 80.0 fb two signal peaks (double-sided Crystal Balls), Events / 3 MeV background (exponential shape) Total fit 60 Signal χ (3P) Global χ b (3 P ) yield: 372 ± 36 b1,2 Background 40 Mass resolution: 2 . 18 ± 0 . 32 MeV 20 Dominant source of systematic uncertainty: photon energy correction (0.16 MeV) 10.4 10.45 10.5 10.55 10.6 Y(3S) γ invariant mass (GeV) First observation of resolved χ b 1 (3 P ) and χ b 2 (3 P ) states M ( χ b 1 (3 P )) = 10513 . 42 ± 0 . 41(stat) ± 0 . 18(syst) ± 0 . 5(Υ(3 S )) MeV M ( χ b 2 (3 P )) = 10524 . 02 ± 0 . 57(stat) ± 0 . 18(syst) ± 0 . 5(Υ(3 S )) MeV ∆ M = 10 . 60 ± 0 . 64(stat) ± 0 . 17(syst) MeV compatible with theoretical expectations A. Boletti (Universit` a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 6 / 14
B + c (2 S ) and B ∗ + (2 S ) observation c Observation of two excited B + c states and measurement of the B + Accepted by Phys. Rev. Lett. c (2 S ) mass arXiv:1902.00571 B* (2S) c (¯ + B c is the lowest-mass bound state of the b ¯ bc ) c 2S γ family of mesons B (2S) + c Its production cross section in pp collisions is 2P ∼ 10 − 3 the one of other B meson families Low number of mesons produced makes more ππ difficult to explore the set of its excited states γ With Run-1 data, ATLAS Collaboration observed an excited state B + c (2 S ) decaying in B + c π + π − [Phys. + B* Rev. Lett. 113, 212004 (2014)] c 1S γ Observation not confirmed with LHCb Run-1 data + B c [J. High Energ. Phys. (2018) 2018: 138] The CMS analysis presented here searches for excited states of the B + c meson, using data collected in full Run-2 period, corresponding to 140 fb − 1 A. Boletti (Universit` a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 7 / 14
B + c (2 S ) and B ∗ + (2 S ) observation c Observation of two excited B + c states and measurement of the B + Accepted by Phys. Rev. Lett. c (2 S ) mass arXiv:1902.00571 Selection of B + c candidates Trigger: two muons from J /ψ plus a track, with common vertex displaced from interaction point Muons with p T > 4 GeV, track with p T > 3 . 5 GeV Common vertex with displacement > 100 µ m B + c transverse momentum > 15 GeV A. Boletti (Universit` a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 8 / 14
B + c (2 S ) and B ∗ + (2 S ) observation c Observation of two excited B + c states and measurement of the B + Accepted by Phys. Rev. Lett. c (2 S ) mass arXiv:1902.00571 Selection of B + c candidates Trigger: two muons from J /ψ plus a track, with common vertex displaced from interaction point Muons with p T > 4 GeV, track with p T > 3 . 5 GeV Common vertex with displacement > 100 µ m B + c transverse momentum > 15 GeV Data CMS Maximum likelihood fit to B + 2000 -1 Fit result c invariant mass L = 140 fb + → ψ π + s = 13 TeV B J/ signal c + → ψ + B J/ K c Partially reconstructed background, Events / 15 MeV + → ψ π + B J/ + X 1500 c Comb. backg. from B + c → J /ψ + π + X 1000 Peaking background from B + c → J /ψ + K decay, studied on simulation and with contribution 500 fixed to signal yield About 7500 B + c candidates 6.0 6.1 6.2 6.3 6.4 6.5 ψ π + M ( J/ ) (GeV) A. Boletti (Universit` a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 8 / 14
B + c (2 S ) and B ∗ + (2 S ) observation c Observation of two excited B + c states and measurement of the B + Accepted by Phys. Rev. Lett. c (2 S ) mass arXiv:1902.00571 Selection of B + c (2 S ) candidates Addition of two tracks from primary vertex Data CMS B + 2000 c ππ common vertex -1 Fit result L = 140 fb + → ψ π + s = 13 TeV B J/ signal c + → ψ + B J/ K With multiple candidates in an event: c Events / 15 MeV + → ψ π + B J/ + X 1500 c Comb. backg. the one with largest p T retained 1000 500 6.0 6.1 6.2 6.3 6.4 6.5 ψ π + M ( J/ ) (GeV) A. Boletti (Universit` a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 8 / 14
B + c (2 S ) and B ∗ + (2 S ) observation c Observation of two excited B + c states and measurement of the B + Accepted by Phys. Rev. Lett. c (2 S ) mass arXiv:1902.00571 ML fit to mass of B + CMS Data c (2 S ) candidates: -1 Fit result L = 140 fb 60 Signal s = 13 TeV two signal components (Gaussian) + ψ + π π − B ( J/ K ) + c peaking bkg (Gaussian) Events / 10 MeV 50 Comb. backg. combinatorial bkg (3rd-order poly) B + c (2 S ) 40 Dominant systematic uncertainty: B + ∗ (2 S ) c 30 shape of signal peaks 20 Observation of two excited states Each has significance > 5 σ 10 Significance of two peaks instead of one 0 6.7 6.8 6.9 7.0 7.1 π π − + + larger than 6 σ M (B + ) M (B ) + m (GeV) - + B c c c Measured mass of B + c (2 S ): ∆ M 2 6871 . 0 ± 1 . 2(stat) ± 0 . 8(syst) ± 0 . 8( B + c ) MeV ∆ M := ∆ M 1 − ∆ M 2 = 29 . 0 ± 1 . 5(stat) ± 0 . 7(syst) MeV ∆ M 1 A. Boletti (Universit` a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 9 / 14
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