Feasibility to Study the Bc Meson

Feasibility to Study the Bc Meson
at CMS Tao Junquan CMS Group Institute of High Energy Physics, Chinese Academy of Science 1st Chinese-French Workshop December, 2006

1st Chinese-French Workshop 14 December, 2006
Outline Introduction Process & results MC Production of Bc signal & backgrounds Event selection, by studying Bc signal & backgrounds Results Summary & Outlook (for real data) 1st Chinese-French Workshop December, 2006

Introduction 1st Chinese-French Workshop December, 2006

Bc Meson The Bc meson is the lowest-mass bound state of a charm quark and a bottom anti-quark. It is the latest such meson predicted by the Standard Model. Because Bc meson carry flavor, it provides a new window for studying heavy-quark dynamics for the two different heavy quarks, which is very different from the window provided by quarkonium. Its mass is predicted to be And its lifetime is predicted to be between 0.4 and 0.7 ps V.V.Kiselev, PACS number:13.20.Gd,13.25.Gv, Hx 1st Chinese-French Workshop December, 2006

TEVATRON: CDF (1998) 20 J/ψ lυ events, mass : 6.40±0.39±0.13 GeV life time : ps 1st Chinese-French Workshop December, 2006

Recent results of Bc Meson
Experimental observation (CDF & D0 , Tevatron) 1998 2004 2005 1st Chinese-French Workshop December, 2006

CMS Experiment Large Hadron Collider 2008 CMS 1st Chinese-French Workshop December, 2006

CMS Detector 1st Chinese-French Workshop December, 2006

Adavantages of study Bc at CMS
1. Higher Collide Energy LHC: PP collider 2. Larger detector region than CDF The CMS detector has the similar structure as CDF ,but it has larger detector region than CDF. CMS: eta~(-2.5,2.5) CDF: eta~(-1.0,1.0) (RUN I) eta~(-1.5,1.5) (RUN II) (Muon system) 3. A better identification ability to muons The CMS detector has a better identification ability to muons ,this is more useful for the channels which include muon/muons in the final state. 1st Chinese-French Workshop December, 2006

Goal & status The goal: to measure the mass and life time of Bc The first channel to look: Bc → J/ψ π (J/ψ → µµ) First publication at about 1 fb-1 1st Chinese-French Workshop December, 2006

Process & results 1st Chinese-French Workshop December, 2006

The CMS Analysis chain HEPEVT Ntuple MC generator ORCA OSCAR OSCAR 1)digitization 2)reconstruction 3)analysis SimReader RecReader RecReader Ntuple signal POOL SimHits/signal ROOT Tree POOL Digis DST Ntuple minbias POOL SimHits/minbias “data summary tape” User 1st Chinese-French Workshop December, 2006

The CMS Fast Simulation
HEPEVT Ntuple MC generator FAMOS Ntuple POOL Simulation, Digis, and DST ROOT Tree 1st Chinese-French Workshop December, 2006

Generator of Bc signal BCVEGPY IPT, Beijing, by Chang et al. Russian package IHEP, Protvino, by Berezhnoy et al. PYTHIA BCVEGPY is used: faster agrees well with PYTHIA 1st Chinese-French Workshop December, 2006

Bc signal About 30 1/fb Bc events were produced for efficiency study with both OSCAR/ORCA and FAMOS Particle Decay channels σ (pb) Generated (*104) Bc Bc→J/ψπ (J/ψ→µµ ) 1.781 5.2082 kine cut : Bc Pt≥10GeV |eta|≤2.0 Mu Pt≥4GeV |eta|≤2.2 Pion Pt≥2GeV |eta|≤2.4 Another independent 1/fb Bc were produced as data OSCAR_3_7_0 ORCA_8_7_3 FAMOS_1_3_2 1st Chinese-French Workshop December, 2006

Backgrounds 1. Other B hadrons’ decay include J/ψ 2. Prompt J/ψ 3. ccbar→μμx 4. bbbar →μμx 5. General QCD, W+jets, Z+jets 1st Chinese-French Workshop December, 2006

Backgrounds (1,2,3) generated by CMKIN & produced by FAMOS at local
1st Chinese-French Workshop December, 2006

Backgrounds (4,5) We don’t have enough computing ability. A series of Datasets of backgrounds we need are stored in CERN, CNAF, etc. IHEP,BEIJING CERN INFN CRAB LHC Computing Grid 1st Chinese-French Workshop December, 2006

bb→μμx background CMS official production with OSCAR/ORCA Dataset σ(mb) Nevents bt03_B0sCombBkg (bb→mumu+ X) 4.8*10-3 100,000 Kine cut: muon: Pt>2GeV |μ|<2.5 2 muons invariant mass : (2.5, 3.5) GeV 1st Chinese-French Workshop December, 2006

QCD CMS official production with OSCAR/ORCA Dataset σ(mb) No. of events getted using Grid jm03b_qcd_0_15 55.22 23999 jm03b_qcd_15_20 44999 jm03b_qcd_20_30 89999 jm03b_qcd_30_50 92997 jm03b_qcd_50_80 198993 jm03b_qcd_80_120 90000 jm03b_qcd_120_170 70000 jm03b_qcd_170_230 40000 jm03b_qcd_230_300 2.3855*10-5 50000 jm03b_qcd_300_380 *10-6 243983 jm03b_qcd_380_470 *10-6 5000 Total QCD events: 950,000 1st Chinese-French Workshop December, 2006

W+jets CMS official production with OSCAR/ORCA Dataset σ(mb) No. of events getted using Grid jm03b_Wjets_0_20 *10-4 150000 jm03b_Wjets_20_50 *10-5 200000 jm03b_Wjets_50_85 *10-5 jm03b_Wjets_85_150 *10-6 jm03b_Wjets_150_250 *10-6 100000 jm03b_Wjets_250_400 *10-7 30000 Total W+jets events: 880,000 1st Chinese-French Workshop December, 2006

Z+jets CMS official production with OSCAR/ORCA Dataset σ(mb) No. of events getted using Grid jm03b_Zjets_0_20 *10-5 200000 jm03b_Zjets_20_50 *10-6 jm03b_Zjets_50_85 *10-6 110000 jm03b_Zjets_85_150 *10-7 100000 jm03b_Zjets_150_250 *10-7 30000 jm03b_Zjets_250_400 *10-8 70000 Total Z+jets events: 710,000 1st Chinese-French Workshop December, 2006

Selection I J/Ψ candidates: 2 muons Pt ≥ 4.0 GeV , |η|<=2.2 2 muons share the same vertex 2 muons have different charge 2 muons’ invariant mass around the J/Ψ [3.0,3.2]GeV 1st Chinese-French Workshop December, 2006

Comparing of 2muon’s invariant mass of OSCAR/ORCA and FAMOS
_____ Full Simulation :3829 _____ Fast Simulation :3371 10/fb 10 fb-1 Normalized to 10 fb-1 , the number of reconstructed J/Ψ of the full simulation is about 12% more than that of fast simulation, the shape agrees well 1st Chinese-French Workshop December, 2006

Selection II Pion candidate: Be not identified as a lepton Pt ≥ 2 GeV |η|<=2.4 Share the same vertex with 2 muons (J/Ψ vertex) 1st Chinese-French Workshop December, 2006

Selection III Signal selection cuts: cos(thetasp)>0.8 thetasp: is the angle between the direction from the primary to the second vertex and the direction of the reconstructed Bc momentum PDLxy >60 μm PDLxy /σxy >2.5 1st Chinese-French Workshop December, 2006

1fb-1 1st Chinese-French Workshop December, 2006

Selection IV Bc mass window (6.25, 6.55) GeV 1st Chinese-French Workshop December, 2006

Cuts and Selections Cumulative Eff. Nevents Passed total: 52082 Dimu and J/ψ 32.88% 17127 Pion 15.07% 7851 Lxy/σxy >2.5 7.07% 3685 Cos(θsp)>0.8 7.04% 3666 PDL >60μm 6.98% 3637 Bc candidate in mass[6.25,6.55] 6.93% 3608 1st Chinese-French Workshop December, 2006

Summary Bc 120±11 B+ 0.7±0.2 Bs 0.1 B0 0.9±0.3 Prompt J/ψ QCD 0.7±0.1 Λb ccbar 0.01 bbbar 1fb-1 Total 2.6±0.4 1st Chinese-French Workshop December, 2006

uncertainty of Bc number
source: LO only color singlet only (no color-octet available) Values of inputs mass of b quark, c quark ; parton distribution function (pdf). 1st Chinese-French Workshop December, 2006

Kinematic fitting Bc→J/ψπ, J/ψ→μμ Totally 3 tracks: 2 muon tracks: J/ψ mass constraint all the 3 tracks: share the same vertex 1st Chinese-French Workshop December, 2006

M(Bc): 6402.0±22.0 MeV Input:6400MeV cτ(Bc): 148.8±13.1 μm Input 150 μm 1st Chinese-French Workshop December, 2006

Systematic error source: Misalignment 1. muon momentum scale uncertainty 2. muon momentum resolution deterioration 3. vertex resolution deterioration Efficiency uncertainty Theoretical uncertainty Cuts sensitivity 1st Chinese-French Workshop December, 2006

Summary of systematic error
Bc mass (MeV) Bc cτ (μm) P scale 11 0.2 P smear 10 0.8 Vertex smear / 2.4 Cuts 0.1 Efficiency Theoretical 1.5 Total 14.9 3.0 1st Chinese-French Workshop December, 2006

Muon momentum resolution
CMS 1/fb: Mass: 22.0(fit) ±14.9(syst) MeV lifetime: 0.044(fit) ±0.010(syst) ps 1st Chinese-French Workshop December, 2006

Summary & Outlook 1st Chinese-French Workshop December, 2006

Summary With MC data, the feasibility for CMS to measure the mass and the lifetime of Bc meson was studied. The study focus on the decay channel Bc→J/ψπ. 120 events can be selected with the first 1 fb-1 data Mass resolution is estimated to be cτ resolution is corresponding to the lifetime error to be Uncertainty: effects of misalignment, theoretical uncertainty on the Bc Pt distribution, and limited Monte Carlo statistics. The results had been written into the CMS Note, and can be available from the website 1st Chinese-French Workshop December, 2006

Outlook (For the real data in 2008)
J/ψ+ 1 track will be selected as a control sample B+ → J/ψ+K+ will be used to estimate the Bc efficiency J/ψ peak side band will be used for the Bc background estimation 1st Chinese-French Workshop December, 2006

The End Thanks ! 1st Chinese-French Workshop December, 2006

Backup slides 1st Chinese-French Workshop December, 2006

Cross section comparison
Bc vs other B σ(other B) =1000 σ( Bc) LHC vs TEVATRON times larger H.C. Chang X.G. Wu Pt cut (GeV) 5 50 100 TEVATRON/LHC 6.3% 5.2% 1.0% 0.3% 1st Chinese-French Workshop December, 2006

Bc decay and interface with OSCAR: Force Bc to decay with the final states we need and interface with OSCAR (Implemented within SIMUB ) SIMUB is one of CMS Supported generator packages ,which is dedicated for simulation of B-meson production and decays G.M. Chen S.H. Zhang IHEP Beijing A.A. Belkov S. Shulga JINR Dubna (Russia) 1. Bc→J/Ψlν(J/Ψ→l+l-) Bc→J/ψµν(J/ψ→µµ) Bc→J/ψeν(J/ψ→µµ) Bc→J/ψµν(J/ψ→ee) Bc→J/ψeν(J/ψ→ee) 2. Bc→J/Ψπ(J/Ψ→l+ l-) Bc→J/ψπ(J/ψ→µµ) Bc→J/ψπ(J/ψ→ee) 1st Chinese-French Workshop December, 2006

Background of Bc→J/ψπ (J/ψ→µµ) from B0 Number decay channels Branch Ratio Nev σ(pb)after Kine cut 5110 B0 → JPsi + K0 0.08% 170000 16.040 5111 B0 → JPsi + K0* 0.14% 290000 28.288 5112 B0 → chi_c1 + K0 0.19% 120000 11.192 5113 B0 → chi_c1+ K0 * 0.25% 150000 14.808 channels Branch Ratio JPsi → mu+ mu- 5.88% chi_c1 → JPsi + γ 31.6% K0* → Random K- Pi+ K0 Pi0 K0 γ 66.5% 33.3% 0.2% Kinematic cuts at generator llevel Mu: pt ≥ 4.0GeV |eta| ≤ 2.4 K : pt ≥ 2.0GeV |eta| ≤ 2.7 More than 10 fb-1 bkg from B0 were produced 1st Chinese-French Workshop December, 2006

Background of Bc→J/ψπ (J/ψ→µµ) from B+ Number decay channels Branch Ratio Nev σ(pb) after kine cut 5210 B+ → JPsi + K+ 0.08% 170000 16.056 5211 B+ → JPsi + K+* 0.14% 290000 28.611 5212 B+ → chi_c1 + K+ 0.19% 120000 11.150 5213 B+ → chi_c1+ K+* 0.25% 150000 14.921 channels Branch Ratio JPsi → mu+ mu- 5.88% chi_c1 → JPsi + γ 31.6% K+* → Random K0 Pi+ K+ Pi0 K+ γ 66.6% 33.3% 0.1% Kine cut: Mu: pt ≥ 4.0GeV |eta| ≤ 2.4 K : pt ≥ 2.0GeV |eta| ≤ 2.7 More than 10 fb-1 bkg from B+ were produced 1st Chinese-French Workshop December, 2006

Background of Bc→J/ψπ (J/ψ→µµ) from Bs Number decay channels Branch Ratio Nev σ(pb) after kine cut 5310 Bs → JPsi + phi 0.14% 30000 2.215 5311 Bs → JPsi + eta 0.04% 40000 3.198 5312 Bs → JPsi + eta’ 2.968 5313 Bs → chi_c1+ eta 0.1% 2.064 5314 Bs → chi_c1+ eta’ 0.09% 20000 1.738 5315 Bs → chi_c1+ phi 0.25% 2.583 channels Branch Ratio JPsi → mu+ mu- 5.88% phi → K+ K- 48.9% chi_c1 → JPsi + γ 31.6% eta → Random 1 eta’ → Random Kine cut Mu: pt ≥ 4.0GeV |eta| ≤ 2.4 K : pt ≥ 2.0GeV |eta| ≤ 2.7 More than 10 fb-1 bkg from Bs were produced 1st Chinese-French Workshop December, 2006

Background of Bc→J/ψπ (J/ψ→µµ) from Λ0b Number decay channels Branch Ratio Nsel σ(pb) after kine cut 51220 Lambda_b0 → JPsi + Lambda0 0.22% 130000 12.797 51221 Lambda_b0 → chi_c1+ Lambda0 0.44% 70000 6.642 channels Branch Ratio JPsi → mu+ mu- 5.88% chi_c1 → JPsi + γ 31.6% Lambda0 → Random Kine cut Mu: pt ≥ 4.0GeV |eta| ≤ 2.4 More than 10 fb-1 bkg from Λb were produced 1st Chinese-French Workshop December, 2006

Background of Bc→J/ψπ (J/ψ→µµ) from prompt J/ψ Number decay channels Branch Ratio N(sel) σ(pb) after kine cut 4430 g (γ) + g (γ) → JPsi Chi_c0 Chi_c1 Chi_c2 5.88% 0.7% * 5.88% 31.6% * 5.88% 13.5% * 5.88% 10000 40000 180000 0.440 0.794 3.902 17.553 4431 g (q) + g (q) → c cbar + g (q) 260000 217.57 channels Branch Ratio JPsi → mu+ mu- 5.88% chi_c0 → JPsi + γ 0.7% chi_c1 → JPsi + γ 31.6% chi_c2 → JPsi + γ 13.5% Kine cut: Mu: pt ≥ 4.0GeV |eta| ≤ 2.4 More than 10 fb-1 bkg from 4430 were produced. Only 1 fb-1 events from Channel 4431 1st Chinese-French Workshop December, 2006

(1) PYTHIA 1st Chinese-French Workshop December, 2006

(2) PYTHIA 1st Chinese-French Workshop December, 2006

Backgound estimation None of the QCD, W+jets, Z+jets, ccbar and bbbar passed the selection. As the number of events produced is less than one 1/fb, the number of background events from these samples will be estimated step by step 1st Chinese-French Workshop December, 2006

QCD background estimation
selection efficiency two muons pT>4GeV, |η|< ε(2μ) J/ψreconctruction same vertex, mass(μμ) : (3.0,3.2) ε(rec) 3. Final cuts Lxy/σ>2.5, PDL>60μm cos(thesp)>0.8 mass(J/ψ,π): (6.25, 6.55) ε(prompt) The total efficiency is ε(2μ)*ε(rec)* ε(prompt) 1st Chinese-French Workshop December, 2006

Dataset σ(mb) No. of events getted using Grid No. of Single Mu (>= 1 Mu) Double Mu (>= 2Mu) jm03b_qcd_0_15 55.22 23999 10 jm03b_qcd_15_20 44999 122 1 jm03b_qcd_20_30 89999 461 4 jm03b_qcd_30_50 92997 933 12 jm03b_qcd_50_80 198993 4382 126 jm03b_qcd_80_120 90000 3408 147 jm03b_qcd_120_170 70000 3872 248 jm03b_qcd_170_230 40000 3130 247 jm03b_qcd_230_300 2.3855*10-5 50000 4963 453 jm03b_qcd_300_380 *10-6 243983 31873 3769 jm03b_qcd_380_470 *10-6 5000 744 111 Kine cut: Mu: pt ≥ 4.0GeV |eta| ≤ 2.2 ε(2μ) can be estimated from QCD samples 1st Chinese-French Workshop December, 2006

ε(rec) estimation Using ccbar→μμx sample total: 210,000 The number of events pass 2 muon selection: , reconstructed J/ψ: 192 ε(rec)= (1.3±0.1) × 10-3 1st Chinese-French Workshop December, 2006

ε(prompt) estimation Using prompt J/ψ sample The number of events pass the above selection is 434,566 Enlarge the mass window from (6.25,6.55) to (5.0,8.0), 27 events obtained assuming random distribution of the 27 events ε(prompt)=( )/(8-5)*27/434566= (6.2±1.2) ×10-6 1st Chinese-French Workshop December, 2006

Prompt J/ψ 1st Chinese-French Workshop December, 2006

QCD background contribution Dataset σ(mb) ε(2 mu) Total ε N1fb-1 jm03b_qcd_0_15 55.22 ( ± )e-7 ( ± )e-15 0.077 ±0.011 jm03b_qcd_15_20 ( ± )e-6 ( ± )e-14 0.089 ±0.004 jm03b_qcd_20_30 ( ± )e-5 ( ± )e-13 0.230 ±0.067 jm03b_qcd_30_50 ( ± )e-4 ( ± )e-12 0.162 ±0.020 jm03b_qcd_50_80 ( ± )e-4 ( ± )e-12 0.107 ±0.005 jm03b_qcd_80_120 ( ± )e-3 ( ± )e-11 0.039 ±0.002 ε(JPsi →Bkg) = (6.2±1.2 ) ×10-6 ε(2mu→JPsi) = (1.3±0.1) × 10-3 1st Chinese-French Workshop December, 2006

W+Jets has none Dataset σ(mb) ε(2 mu) Total ε N1fb-1 jm03b_Wjets_0_20 *10-4 ( ±0.5850)e-4 ( ± )e-12 (4.5997 ±0.2541)e-4 jm03b_Wjets_20_50 *10-5 (1.4350 ± )e-3 ( ± )e-11 (3.1618 ±0.1446)e-4 jm03b_Wjets_50_85 *10-5 (2.880 ±0.120)e-3 ( ± )e-11 ( ±0.1030)e-4 jm03b_Wjets_85_150 *10-6 (4.4650 ± )e-3 ( ± )e-11 (2.2732 ±0.0986)e-4 jm03b_Wjets_150_250 *10-6 (7.740 ± )e-3 ( ± )e-11 (7.5131 ±0.3271)e-5 jm03b_Wjets_250_400 *10-7 ( ± )e-2 (9.0679 ± )e-11 (2.3871 ±0.1072)e-5 ε(JPsi →Bkg) = ( ± ) ×10-6 ε(2mu→JPsi) = ( ± ) × 10-3 1st Chinese-French Workshop December, 2006

Dataset σ(mb) ε(2 mu) Total ε N1fb-1 jm03b_qcd_120_170 ( ± )e-3 ( ± )e-11 0.014 ±0.001 jm03b_qcd_170_230 (6.1750 ± )e-3 ( ± )e-11 0.005 ±0.000 jm03b_qcd_230_300 2.3855*10-5 (9.060 ± )e-3 ( ± )e-11 0.002 jm03b_qcd_300_380 *10-6 ( ± )e-2 ( ± )e-10 0.001 jm03b_qcd_380_470 *10-6 (2.220 ± )e-2 ( ± )e-10 0.000 Total QCD Bkgs: 0.7 ±0.1 1st Chinese-French Workshop December, 2006

Z+jets background estimation
The probability for Z+jets to have fake prompt J/ψ: ( )/(10-0)*10/640,000=3.1*10-7 The probability for prompt J/ψ to fake Bc: (6.2±1.2) *10-6 The total cross section: 38.2nb The number of background at one 1/fb: 7.4*10-5 1st Chinese-French Workshop December, 2006

ccbar→μμx backgound estimation σ(mb) Events n fb-1 Dimuon selection J/ψselection (ccbar→mumu+ X) 1.69*10-6 210000 12.426% 147778 192 σ(mb) ε(rec) Total ε N1fb-1 (ccbar→mumu+ X) 1.69*10-6 ( ± ) × 10-4 ( ± ) × 10-9 0.010± 0.001 ε(JPsi →Bkg) = (6.2±1.2) ×10-6 1st Chinese-French Workshop December, 2006

bbbar→μμx backgound estimation Dataset σ(mb) ε(rec) Total ε N1fb-1 bt03_B0sCombBkg (bb→mumu+ X) 4.8*10-6 (4.2±0.6) 10-4 (2.6±0.6) 10-9 0.012± 0.003 2% fb-1 bb→μμx produced, totally 100,000 events, 42 events passed the dimuon and J/ψ selection 1st Chinese-French Workshop December, 2006

Zjets (pt 0_250) total events: 640,000 1st Chinese-French Workshop December, 2006

Muon momentum scale uncertainty
Δ(1/pT)=0.0005/GeV (Albert De Roeck) Bc mass changes by 11 MeV cτ changes by μm 1st Chinese-French Workshop December, 2006

Muon momentum resolution I. Belotelov et al CMS note 2006/017 Muon momentum were smeared according to This result Mass: 11 MeV Ctau: 0.8μm 1st Chinese-French Workshop December, 2006

Vertex resolution P. Vanlaer et al, CMS note 2006/029 Primary Vertex : x, y: smear 5.7μm, z:3.7μm Second Vertex: x, y: smear 12.4 μ m , z: 11.4μm cτ: 2.4 μ m 1st Chinese-French Workshop December, 2006

Cuts sensitivity Momentum cuts changed by one σ Other cuts changed by 10% mass: 0.1 MeV cτ : μm 1st Chinese-French Workshop December, 2006

Efficiency uncertainty
To estimate the efficiency uncertainty sqrt(N) events subtracted , efficiency recalculated cτ: μm 1st Chinese-French Workshop December, 2006

Theoretical uncertainty
Bc events were reweighted according the their Bc pT, so that the Bc pT distribution agrees with Gouz’s distribution cτ: 2.4μm 1st Chinese-French Workshop December, 2006

Feasibility to Study the Bc Meson

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