[PPT] - B-physics results in CMS in Run2 Alessio Boletti on behalf of the PowerPoint Presentation

SLIDE 1

B-physics results in CMS in Run2

Alessio Boletti

n 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

SLIDE 2

Introduction

Large amount of collisions delivered by LHC in Run 2, about six times the luminosity of Run 1 Very efficient data collection by CMS detector, with improved and extremely competitive track momentum resolution Many B-physics analyses are statistically limited, benefit from increased statistics New challenges arise with increased luminosity:

Ingenious trigger algorithms developed, for efficient online event selection Sophisticated analysis techniques studied, to reduce background contamination

J u l ' 1 5 O c t ' 1 5 J a n ' 1 6 A p r ' 1 6 J u l ' 1 6 O c t ' 1 6 J a n ' 1 7 A p r ' 1 7 J u l ' 1 7 O c t ' 1 7 J a n ' 1 8 A p r ' 1 8 J u l ' 1 8 O c t ' 1 8

Date

20 40 60 80 100 120 140 160 180

Total Integrated Luminosity (fb¡1 )

Data included from 2015-06-03 08:41 to 2018-10-26 08:23 UTC LHC Delivered: 162.87 fb¡1 CMS Recorded: 150.28 fb¡1 20 40 60 80 100 120 140 160 180

CMS Integrated Luminosity, pp,

ps = 13 TeV

[CMS-DP-2018-036]

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 2 / 14

SLIDE 3

Introduction

Latest heavy-flavour analyses with Run 2 data

1. Observation of χb1(3P) and χb2(3P) states
2. Observation of B+

c (2S) and B+ ∗ c

(2S) states

3. Search for τ → µµµ decay
A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 3 / 14

SLIDE 4

χb1(3P) and χb2(3P) observation

Observation of χb1(3P) and χb2(3P) 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 χb(3P) states are interesting to study these forces in proximity of open-beauty threshold Unresolved χb(3P) state observed by ATLAS [1], D0 [2], and LHCb [3] Collaborations, through the χb(3P) → Υ(nS)γ decays [n = 1, 2, 3] In this CMS analysis the first observation of resolved χb1(3P) and χb2(3P) 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

SLIDE 5

χb1(3P) and χb2(3P) observation

Observation of χb1(3P) and χb2(3P) states

Phys. Rev. Lett. 121, 092002 (2018)

arXiv:1805.11192

Selection of Υ(nS) candidates

9 9.5 10 10.5 11 Dimuon mass (GeV) 20 40 60 80

3

10 ×

Events / 2.5 MeV Y(2S) Y(3S) Y(1S)

CMS

= 13 TeV s = 13 TeV

1

L = 80.0 fb y < 0.6 0.6 < y < 1.2

Trigger: two muons with mass in 8.5-11.5 GeV, and common vertex Upsilon candidate: pT > 14 GeV, |y| < 1.2 Mass resolution: 60-120 MeV pure samples of Υ(nS) obtained with tight mass windows

Selection of χb(nP) candidates

Photon reconstructed in γ → ee conversion

n beampipe and tracker material

Photon candidate: pT > 0.5 GeV, |y| < 1.2 Photon energy correction computed on sample

f χc1 → J/ψ(µµ)γ and applied event-by-event

Validated on masses of χb(1P) and χb(2P)

9.8 10.2 10.6 Y(nS) γ invariant mass (GeV) 200 400 600 800 1000 1200 Events / 3.5 MeV

= 13 TeV s = 13 TeV

1

L = 80.0 fb

CMS

(2P)

b

χ

(3P)

b

χ

(1P)

b

χ

Y(1S) + γ Y(2S) + γ Y(3S) + γ 9890 9895 10250 10255 → 1P 1S → 2P 1S → 2P 2S χ (nP) mass (MeV)

b1

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 5 / 14

SLIDE 6

χb1(3P) and χb2(3P) observation

Observation of χb1(3P) and χb2(3P) states

Phys. Rev. Lett. 121, 092002 (2018)

arXiv:1805.11192

Maximum likelihood fit to Υ(3S)γ mass

two signal peaks (double-sided Crystal Balls), background (exponential shape)

Global χb(3P) yield: 372 ± 36 Mass resolution: 2.18 ± 0.32 MeV Dominant source of systematic uncertainty: photon energy correction (0.16 MeV)

10.4 10.45 10.5 10.55 10.6 invariant mass (GeV) γ Y(3S) 20 40 60 80 100 Events / 3 MeV

Total fit (3P)

b1,2

χ Signal Background

= 13 TeV s

1

L = 80.0 fb

CMS

First observation of resolved χb1(3P) and χb2(3P) states M(χb1(3P)) = 10513.42 ± 0.41(stat) ± 0.18(syst) ± 0.5(Υ(3S)) MeV M(χb2(3P)) = 10524.02 ± 0.57(stat) ± 0.18(syst) ± 0.5(Υ(3S)) 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

SLIDE 7

B+ c (2S) and B∗+ c (2S) observation

Observation of two excited B+

c states

and measurement of the B+

c (2S) mass

Accepted by Phys. Rev. Lett. arXiv:1902.00571

Bc is the lowest-mass bound state of the b¯ c (¯ bc) family of mesons Its production cross section in pp collisions is ∼ 10−3 the one of other B meson families Low number of mesons produced makes more difficult to explore the set of its excited states With Run-1 data, ATLAS Collaboration observed an excited state B+

c (2S) decaying in B+ c π+π−

[Phys.

Rev. Lett. 113, 212004 (2014)]

Observation not confirmed with LHCb Run-1 data

[J. High Energ. Phys. (2018) 2018: 138]

2P 2S 1S

γ γ γ

B*

c

B

c + +

B* (2S)

c +

B (2S)

c +

ππ

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

SLIDE 8

B+ c (2S) and B∗+ c (2S) observation

Observation of two excited B+

c states

and measurement of the B+

c (2S) mass

Accepted by Phys. Rev. Lett. 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 pT > 4 GeV, track with pT > 3.5 GeV Common vertex with displacement > 100 µm B+

c transverse momentum > 15 GeV

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 8 / 14

SLIDE 9

B+ c (2S) and B∗+ c (2S) observation

Observation of two excited B+

c states

and measurement of the B+

c (2S) mass

Accepted by Phys. Rev. Lett. arXiv:1902.00571 6.0 6.1 6.2 6.3 6.4 6.5

) (GeV)

+

π ψ J/ ( M

500 1000 1500 2000

Events / 15 MeV

Data Fit result signal

+

π ψ J/ →

+ c

B

+

K ψ J/ →

+ c

B + X

+

π ψ J/ →

+ c

B

Comb. backg.

= 13 TeV s

1

L = 140 fb CMS

Selection of B+

c candidates

Trigger: two muons from J/ψ plus a track, with common vertex displaced from interaction point Muons with pT > 4 GeV, track with pT > 3.5 GeV Common vertex with displacement > 100 µm B+

c transverse momentum > 15 GeV

Maximum likelihood fit to B+

c invariant mass

Partially reconstructed background, from B+

c → J/ψ + π + X

Peaking background from B+

c → J/ψ + K decay,

studied on simulation and with contribution fixed to signal yield About 7500 B+

c candidates

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 8 / 14

SLIDE 10

B+ c (2S) and B∗+ c (2S) observation

Observation of two excited B+

c states

and measurement of the B+

c (2S) mass

Accepted by Phys. Rev. Lett. arXiv:1902.00571 6.0 6.1 6.2 6.3 6.4 6.5

) (GeV)

+

π ψ J/ ( M

500 1000 1500 2000

Events / 15 MeV

Data Fit result signal

+

π ψ J/ →

+ c

B

+

K ψ J/ →

+ c

B + X

+

π ψ J/ →

+ c

B

Comb. backg.

= 13 TeV s

1

L = 140 fb CMS

Selection of B+

c (2S) candidates

Addition of two tracks from primary vertex B+

c ππ common vertex

With multiple candidates in an event: the one with largest pT retained

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 8 / 14

SLIDE 11

B+ c (2S) and B∗+ c (2S) observation

Observation of two excited B+

c states

and measurement of the B+

c (2S) mass

Accepted by Phys. Rev. Lett. arXiv:1902.00571

ML fit to mass of B+

c (2S) candidates:

two signal components (Gaussian) peaking bkg (Gaussian) combinatorial bkg (3rd-order poly)

Dominant systematic uncertainty: shape of signal peaks Observation of two excited states Each has significance > 5σ Significance of two peaks instead of one larger than 6σ

6.7 6.8 6.9 7.0 7.1

(GeV)

+ c

B

m ) +

+ c

(B M − )

π

+

π

+ c

(B M

10 20 30 40 50 60

Events / 10 MeV

Data Fit result Signal

−

π

+

π )

+

K ψ J/ (

+ c

B

Comb. backg.

= 13 TeV s

1

L = 140 fb CMS

Measured mass of B+

c (2S):

6871.0 ± 1.2(stat) ± 0.8(syst) ± 0.8(B+

c ) MeV

∆M := ∆M1 − ∆M2 = 29.0 ± 1.5(stat) ± 0.7(syst) MeV B+

c (2S)

B+ ∗

c

(2S) ∆M2 ∆M1

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 9 / 14

SLIDE 12

Search for τ → µµµ decay

Search for τ → 3µ decays using τ leptons produced in D and B meson decays

[CDS: CMS-PAS-BPH-17-004]

Charge-lepton flavour violating decay τ → µµµ Allowed by neutrino oscillation: predicted BF far smaller than experimentally accessible values Many New-Physics scenarios predict branching fraction enhancement Experimentally accessible and clean three-muon final state Search performed by Belle [1], BaBar [2], LHCb [3] and ATLAS [3], with no signal observed Most stringent limit (Belle): BF < 2.1 · 10−8 (90% CL) The CMS analysis presented here searches for the τ → 3µ decay in a sample of τ leptons produced in D and B hadron decays, using the data collected in 2016, corresponding to 33 fb−1

[1]Phys. Lett. B687 (2010) 139143 [2]Phys. Rev. D81 (2010) 111101 [3]JHEP 02 (2015) 121 [4]Eur. Phys. J. C (2016) 76:232

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 10 / 14

SLIDE 13

Search for τ → µµµ decay

Search for τ → 3µ decay

[CDS: CMS-PAS-BPH-17-004]

τ candidate selection Trigger: two muons and a track, with mass and vertex requirements Candidate: three vertexing muons with p(µ1,µ2)

T

> 3 GeV, p(µ3)

T

> 2 GeV Has charge ±1 and mass in 1.62 - 2.00 GeV Normalisation sample D±

s → φπ± → µ+µ−π± decays used as

normalisation channel Selected with signal trigger, and similar momentum requirements Fraction of Ds candidates from B meson decay from template fit to proper decay length

f = σ(pp → B)B(B → Ds + ...) σ(pp → Ds)

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 11 / 14

SLIDE 14

Search for τ → µµµ decay

Search for τ → 3µ decay

[CDS: CMS-PAS-BPH-17-004]

Categories by mass resolution Three-muon mass resolution computed event-by-event, varying from 0.4 to 1.5%, according to muon rapidity Sample divided in three categories, based on mass resolution

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 12 / 14

SLIDE 15

Search for τ → µµµ decay

Search for τ → 3µ decay

[CDS: CMS-PAS-BPH-17-004]

Categories by mass resolution Three-muon mass resolution computed event-by-event, varying from 0.4 to 1.5%, according to muon rapidity Sample divided in three categories, based on mass resolution Categories by BDT discriminator Boosted decision tree trained, using a set of vertex-quality variables and muon-quality ones Signal (from simulation) discriminated from background (from data sidebands) Output used to divide the sample in three categories, two used in the fit, one rejected

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 12 / 14

SLIDE 16

Search for τ → µµµ decay

Search for τ → 3µ decay

[CDS: CMS-PAS-BPH-17-004]

Nsig(D) = N B(Ds → τ ν) B(Ds → φπ → µµπ) A3µ(D) A2µπ ǫ

3µ reco

ǫ

2µπ reco

ǫ

2µ trig,sig

ǫ

2µ trig(µµπ)

B(τ → 3µ) Nsig(B) = f B(B → τ + ...) B(B → Ds + ...)B(Ds → τ ν) A3µ(B) A3µ(D) Nsig(D)

Signal from Ds Signal from direct B meson decay

Normalisation channel yield Acceptance and efficiency correction from decay length fit

Maximum likelihood fit performed simultaneously on the six categories Weighted combination shown in the plot here Dominant systematic uncertainty: Ds normalisation (10%) No excess observed in the signal region Observed (expected) limits at 90% of CL: BF(τ → 3µ) < 8.8 (9.9) · 10−8

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 13 / 14

SLIDE 17

Summary

Analysis of χb(3P) states

Studied the decay χb(3P) → Υ(3S)γ with converted photon First observation of the resolved states χb1(3P) and χb2(3P) Measurement of their masses, and mass difference

Search for B+

c (2S) excited states

Studied the decay B+

c (2S) → B+ c ππ

First observation of two distinct states B+

c (2S) and B∗+ c

(2S) Measurement of their mass difference and B+

c (2S) mass

Search for τ → 3µ decay, in sample from B and D meson decays

Three-muon mass fit performed in six event categories No excess observed Upper limit set at 90% CL: BF(τ → 3µ) < 8.9 · 10−8

Many other B-physics results from CMS will come in the next months Stay tuned!

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 14 / 14

SLIDE 18

Backup slides

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 1 / 11

SLIDE 19

χb1(3P) and χb2(3P) observation (backup)

Selection criteria

Selection of Υ(nS) candidates Trigger: two muons with mass in 8.5-11.5 GeV, and common vertex Upsilon candidate with pT > 14 GeV, |y| < 1.2 Mass resolution σm varying with rapidity, 60-120 MeV: pure samples of Υ(nS) obtained with mass cut Selection of χb(nP) candidates Photons reconstructed through γ → ee conversion

n beampipe and tracker material

Photon candidate: pT > 0.5 GeV, |y| < 1.2 Vertex fit of Υ(nS) and photon candidates: χ2 probability > 1% Photon energy correction computed on sample of χc1 → J/ψ(µµ)γ decays, and applied event-by-event

A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 2 / 11

SLIDE 20

χb1(3P) and χb2(3P) observation (backup)

Photon energy correction

(GeV)

γ

E Photon energy scale

0.980 0.985 0.990 0.995 1.000 5 10 = 13 TeV s

CMS

2015+2016; L = 37.9 fb

c1

χ J/ψ γ

2017; L = 42.1 fb

1
1
A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 3 / 11

SLIDE 21

B+ c (2S) and B∗+ c (2S) observation (backup)

Selection criteria and fit shapes

Selection of B+

c candidates

Trigger: two muons from J/ψ plus a track, with common vertex displaced from interaction point Muons with pT > 4 GeV, track with pT > 3.5 GeV Common vertex: χ2 probability > 10%, displacement from primary vertex > 100 µm B+

c transverse momentum > 15 GeV

Maximum likelihood fit to B+

c invariant mass

Signal peak (double Gaussian shape) Combinatorial background (polynomial), partially reconstructed (ARGUS x Gaussian), peaking background (simulation-based shape) About 7500 B+

c candidates

Selection of B+

c (2S) candidates

B+

c candidates in range 6.2 - 6.355 GeV

Two tracks from primary vertex, with pT π2 > 0.8 GeV and pT π3 > 0.6 GeV B+

c ππ common vertex: χ2 probability > 10%

With multiple candidates in an event:

nly the one with largest pT retained
A. Boletti (Universit`

a & INFN Padova) Run2 CMS B-physics results MoriondEW, 21 Mar 2019 4 / 11

SLIDE 22