Analysis of a Λ 0 b decay mode

Transcription

1 Analysis of a Λ 0 b decay mode María Magdalena Falla Solórzano Advisor Dr. Héctor Méndez Puerto Rico University HEP Group Master of Science in Physics Presentation May 2,

2 Outline 1. OBJECTIVES 2. INTRODUCTION 3. DATASETS 4. EVENT SELECTION 5. K 0 s π + π - AND B 0 CONTAMINATION 6. RELATIVE BRANCHING RATIO MEASUREMENTS AND UNCERTAINTIES 7. CONCLUSIONS 2

3 Objectives Measurement of the Λ 0 b Λ 0 ψ(2s) Branching Ratio with respect to the Λ 0 b Λ 0 ψ(1s) mode Λ 0 b (udb) Λ 0 (uds) + ψ(2s)(cc) - p(uud) π - (ud) - μ + μ - Normalizing mode Λ 0 b Λ 0 + ψ(1s), ψ(1s) μ + μ - It is the most copious charmed decay 3

4 Introduction a) Standard Model What are the ultimate constituents of matter? How are they categorized? How do they interact with each other? Recently Discovered at LHC 4th July 2012 M: ~125GeV/c 2 4

5 b) Large Hadron Collider (LHC) 5

6 c) Compact Muon Solenoid (CMS) Collaboration Approximately 3,600 people, representing 183 scientific institutes and 38 countries 6

7 d) CMS Experiment y x z 7

8 d) Compact Muon Solenoid (CMS) CMS Transverse View CMS Longitudinal View z y Towards Center of LHC x This analysis uses mainly the Tracking and the Muon System Pseudorapidity 8

9 2011 DataSet MuOnia L ~ TeV Recorded in may, august, september /MuOnia/Run2011A-May10ReReco-v1/AOD /MuOnia/Run2011A-PromptReco-v4/AOD /MuOnia/Run2011A-05Aug2011-v1/AOD RUN2011A ~2.5 /fb /MuOnia/Run2011A-PromptReco-v6/AOD /MuOnia/Run2011B-PromptReco-v1/AOD RUN2011B ~2.8 /fb 9

10 Event Selection: a) Topology of the decay Transverse momentum P µ+ DCA SV P Λ0 P µ- p σ PV Most active vertex (Highest Multiplicity) P Λ 0 b L Decay lenght p Impact par. I p 10

11 a) Topology of the decay Transverse momentum Pointing Angle α α prim-µµ recop Λ 0b SV P Λ 0 b p σ PV Most active vertex (Highest Multiplicity) p 11

12 a) Topology of the decay Transverse momentum P p+ recop Λ 0 α Λ 0 -µµ SV Pointing Angle α DCA P π- SV L P Λ 0 b p σ PV Most active vertex (Highest Multiplicity) p 12

13 b) µ + µ - Candidate Muons with opposite charge Both muons have to be inside η µ < 2.2 Common vtx Vtx CL μ+μ- vtx > 15% Distance closest approach dca µ+µ- < 1 cm Tight Cuts (Muon Id Tight Cuts followed POG recommendation) 1. recomu.isglobalmuon() 2. recomu.globaltrack() normalizedchi2() < 10 G muon track fit 3. recomu.globaltrack() hitpattern().numberofvalidmuonhits() > 0 Muon chamber hit 4. recomu.numberofmatchedstations() > 1 Muon segments in muon chambers 5. recomu.innertrack() hitpattern().numberofvalidpixelhits() > 0 intracker system hit 6. track() hitpattern().trackerlayerswithmeasurement() > 5 trackerlayers hits 13

14 b) Dimuon Trigger: High Level Trigger (HLT) Displaced low dimuon mass trigger (LMT) η p µµ T GeV/c L xy /σ Cos α xy m(µµ) GeV/c 2 p µ T CL (µµvtx) DCA xy (µµ) cm HLT_Dimuon6p5_LowMass_Displaced (240.0pb -1 ) < 2.5 > 6.5 > 3 > HLT_Dimuon7_LowMass _Displaced (999.5pb -1 ) < 2.2 > 6.9 > 3 > >3.0 > 5% > 0.5 HLT_DoubleMu4_LowMass_Displaced (437.3pb -1 ) < 2.2 > 6.9 > 3 > >4.0 > 15% > 0.5 HLT_DoubleMu4p5_LowMass_Displaced (721.7pb -1 ) < 2.2 > 6.9 > 3 > >4.5 > 15% > 0.5 HLT_DoubleMu5_LowMass_Displaced (2891.0pb -1 ) < 2.2 > 6.9 > 3 > >5.0 > 15% > 0.5 α xy 14

15 c) Λ 0 p π - Candidate p and π with opposite charge Displaced vtx from prim. (L/σ) xy >5 I p /σ Ip > 0.5 P Tp P Tπ- > 1.5 GeV Displaced vtx from µ + µ - vtx (L/σ)>3 M pπ- - M PDG Λ 0 < 10 MeV P T Λ 0 > 1.0 GeV cos (α Λ 0 - µ+µ- )> 0.95 K 0 s π - π + Veto M pπ- - M PDG Ks > 20 MeV p assumed a π Yield: ~24 million M pπ- : 1116 MeV σ : 2.14MeV 15

16 d) Λ 0 b Candidates The best primary vtx is the closest one to the Λ b 0 trayectory (L/σ) Λ 0b >3 cos (α prim- Λ 0 µ+µ- )> 0.95 P T (Λ b 0 ) > 10 GeV M Λ 0 µ+µ- : GeV/c 2 16

17 e) Obtained Signal Signal Data Bck Λ 0 ψ(2s) Λ 0 ψ(1s) Monte Carlo Λ 0 ψ(2s) Λ 0 ψ(1s) Decay mode S (events) Signif.(S/ B) S MC (events) Λ b Λ 0 ψ(2s) ± σ ±12.60 Λ b Λ 0 ψ(1s) ± σ ±

18 e) MC Sample (Fall 2011) LambdaB To Psi MuMu Signal MC GEN-SIM-RECO */LambdaBToPsiMuMu_2MuPEtaFilter_Tight_7TeV-pythia6-evtgen/ Fall11-HLTBPh2011_START42_V14B-v2/GEN-SIM-RECO Λ 0 b Generated MC branching fraction: Mode ψ(2s) µ + µ - N gen Λb Λ0 ψ(2s) B(Λ b Λ 0 ψ(2s)) B(ψ(2s) µ + µ - ) f gen = = * = N gen Λb Λ0 ψ(1s) B(Λ b Λ 0 ψ(1s)) B(ψ(1s) µ + µ - ) 18

19 Contamination a) K 0 s π + π - Mode ψ(1s) Λ 0 pπ - K 0 s π + π - GeV/c 2 Excluded Mode ψ(2s) Λ 0 pπ - K 0 s π + π - GeV/c 2 19

20 b) B 0 K 0 s + [ψ(1s) or ψ(2s)] After Λ 0 quality Cuts M B 0 = 5.28±0.33 GeV/c2 M K 0 s + ψ(1s) GeV/c 2 M K 0 s + ψ(1s) GeV/c 2 M K 0 s + ψ(2s) GeV/c 2 Negligible Cross-feed ( not present in our MC sample)!! M K 0 s + ψ(2s) GeV/c 2 20

21 c) Λ 0 b Λ 0 + [ψ(1s) or ψ(2s)] in a B 0 MC sample Dataset: B0ToPsiMuMu, Tight_7TeV, Fall11-HLT, GEN-SIM-RECO B 0 K 0 s ψ(1s) B 0 K 0 s ψ(2s) GeV/c 2 GeV/c 2 Λ 0 b Λ 0 ψ(1s) Λ 0 b Λ 0 ψ(2s) GeV/c 2 GeV/c 2 Negligible Cross-feed (Λ 0 b not present in the B 0 MC sample)!! 21

22 Relative Branching Ration Measurement Absolute branching fraction: N Λ b Λ0 ψ(2s) B(Λ b Λ 0 ψ(2s)) = ϵ rec * ϵ trigger *L* B(ψ(2s) µ + µ - )* B(Λ 0 pπ - ) N Λ b Λ0 ψ(1s) B(Λ b Λ 0 ψ(1s)) = ϵ rec * ϵ trigger *L* B(ψ(1s) µ + µ - )* B(Λ 0 pπ - ) Dividing: Data Monte Carlo B(Λ b Λ 0 ψ(2s)) N Λb Λ0 ψ(2s) (ϵ Λb Λ0 ψ(1s)) rec = * f c B(Λ b Λ 0 ψ(1s)) N Λb Λ0 ψ(1s) (ϵ Λb Λ0 ψ(2s)) rec 22

23 a) Measurement of B(Λ b Λ 0 ψ(2s)) (ϵ Λb Λ0 ψ(1s)) rec N rec Λb Λ0 ψ(1s) / N gen Λb Λ0 ψ(1s) N rec Λb Λ0 ψ(1s) = = *f gen (ϵ Λb Λ0 ψ(2s)) rec N rec Λb Λ0 ψ(2s) / N gen Λb Λ0 ψ(2s) N rec Λb Λ0 ψ(2s) Monte Carlo ± ±46.75 Data B(Λ b Λ 0 ψ(2s)) N Λb Λ0 ψ(2s) N rec Λb Λ0 ψ(1s) MC = * *f gen * f c B(Λ b Λ 0 ψ(1s)) N Λb Λ0 ψ(1s) N rec Λb Λ0 ψ(2s) ± ±12.60 MC Mode ψ(2s) µ + µ - N gen Λb Λ0 ψ(2s) B(Λ b Λ 0 ψ(2s)) B(ψ(2s) µ + µ - ) f gen = = * = N gen Λb Λ0 ψ(1s) B(Λ b Λ 0 ψ(1s)) B(ψ(1s) µ + µ - ) PDG(2012) Mode ψ(2s) µ + µ - B(ψ(1s) µ + µ - ) f c = = ±0.80 B(ψ(2s) µ + µ - ) 23

24 a) Measurement of B(Λ b Λ 0 ψ(2s)) B(Λ b Λ 0 ψ(2s)) = 0.66 ± 0.11 (stat) ± 0.07(syst) ± 0.07(PDG) B(Λ b Λ 0 ψ(1s)) Preliminary 24

25 b) Statistical Uncertainty B( (2s)) MC MC b 0 (2s) b 0 (1s) b 0 (1s) b 0 (2s) b 0 N N N N stat MC MC B( b 0 (1s)) N (2s) N (1s) N (1s) N (2s) b 0 b 0 b 0 b 0 stat

26 c) Systematic Uncertainty Systematic U. Sources Cut Variation with respect to the central value(%) * Tightening cos (α prim- Λ 0 µ+µ- ) > Loosing p t (Λ 0 b) > Loosing muonid Tight cuts Only at least 1G 9.57 Background shape P2 + Gauss 0.43 Total 10.02** Brcv Brn * Br cv *100, Br 0.66 **Using quadrature cv 0.66* ( sys) sys 26

27 Conclusions The obtained preliminary relative branching fraction is: B(Λ b Λ 0 ψ(2s)) = 0.66 ± 0.11 (stat) ± 0.07(syst) ± 0.07(PDG) B(Λ b Λ 0 ψ(1s)) where: ψ(2s) µ + µ -, Λ 0 pπ -, J/ψ µ + µ -. This measurement is statistically dominated and can be improve by adding more data: One way is including the analysis of another ψ(2s) decay mode as ψ(2s) J/ψ π + π - (In progress). Another way is analyzing more data. The group already started working with dataset from MuOnia 2012 with ~20/fb of luminosity, collected by the CMS experiment in pp collisions at centre of mass energy of 8 TeV. The contaminations from B 0 K 0 sψ(2s), B 0 K 0 s J/ψ and K 0 s are negligible. 27

28 Hypernews:BPH

29 PDG 2012 Λ b Λ 0 ψ(2s) 29

30 30

31 Charmonium (meson cc) - Term Sym. n 2S + 1 L J Particle mass (GeV/c 2 ) 1 3 S 1 J/ψ(1S) 3.096± S 1 ψ(2s) 3.686± D 1 ψ(1d) 3.772± D 2 ψ 2 (1D) 1 3 D 3 ψ 3 (1D) 31

32 b - Baryons Particle name Symbol Quark content Rest. Mass (GeV/c 2 ) Mean lifetime (s) Lambda Λ 0 uds 1.115± ± bottom Lambda Λ 0 b udb 5.620± Commonly Decays p + + π or n 0 + π 0 32

33 Uncertainties 17/05/2013 Maria M. Falla S. (UPRM) B(Λ b Λ 0 ψ(2s)) 33

34 Looking for Λ 0 b Λ 0 + [ψ(1s) or ψ(2s)] in a B 0 MC sample M K 0 s + ψ(1s) M Λ 0 s + ψ(1s) M K 0 s + ψ(2s) M Λ 0 s + ψ(2s) Negligible Cross-feed, not present in B 0 MC sample!! 34