CMS Bc 模拟重建和分析

CMS Bc 模拟重建和分析

陈 国 明

CMS Experiment

CMS

2007 年夏Large Hadron Collider

77m77mmm

1616μμmm

Bunch cross: every 25nsBunch cross: every 25ns23 inelastic events per bunch cross

Pile Up

At 10At 103333 : 2.3 events /cross : 2.3 events /cross

At 1034

Minimum bias events

the average charge multiplicity: the average charge multiplicity: 3030for |for |ηη|<2.5, p|<2.5, pTT>150MeV>150MeV

CMS Experiment

CMS Experiment

Cross-sectional view of CMS

η=2.5

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y

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Transverse slice through CMS detectorClick on a particle type to visualise that particle in CMS

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CMSCMS

5M CHF 25005M CHF 2500 万人民币万人民币

高能所：高能所：端盖端盖 μμ子子探测器的探测器的1/31/3

磁铁支架磁铁支架地板地板北大：北大： 部分部分RPC RPC

ATLAS

1.5M CHF 7501.5M CHF 750 万人民币万人民币

高能所：高能所： 桶部和端盖交接桶部和端盖交接处的处的 μμ 子探测器子探测器 部分桶部部分桶部 μμ 子探子探测器测器山东大学：山东大学：端盖端盖 μμ 子触发器子触发器的的 1/61/6

中国科技大学： 中国科技大学： 端盖端盖 μμ 子触发电子触发电子学子学南京大学：南京大学： 前后向吸收体前后向吸收体

取得了入场券 • 我国在硬件上的投了资 , 取得了数据分析的入场券。• 与投资多的国家有平等的机会，分析所有数据。

数据分析是挑战• 数据量大• 本底高• 探测器庞大 , 软件环境复杂• 竞争激烈： 30 多个国家， 200 多个大学和研究所， 2000 多科学家

国内 LHC 物理分析的现状 从 2000 年开始连续 3 次向基金委申请面上项目 , 用作 CMS

的 MC 研究 , 未批准 . 2004 年设立重点基金 , 并批准 135 万支持 CMS 和 ATLAS 的

MC 模拟 . 2005—2008 4 年 CMS 高能所 30 万 Bc HVV CMS 北大 35 万 大横动量 J/Ψ ATLAS 高能所 30 万 Htt ATLAS 山大 30 万 tt 公用 10 万

计算设施初步计划在高能所为 CMS 和 ATLAS 各建一个

Tier2计算设施， 需经费 2000 万 但还没有落实

IHEP CMS 物理分析设想 选取 2l+X sample 头三年 , 亮度≈ 1033, 轻子触发横动量 :

single electron >29GeV double electron >17GeV single muon >19GeV double muon >7GeV 合计 事例率 : 60Hz 每年 : RECO 75TB, AOD 25TB, 共 100TB往后 , 亮度 1034 , 轻子触发横动量提高

刻度 根据人力情况选做部分子探测器的刻度 :• MUCH μ+μ- 对 , J/Ψ, Z0 峰 , MUCH 径迹与 TRACKER 径迹的对比• TRACKER e+e- 对 , μ+μ- 对 , J/Ψ, Z0 峰 , MUCH 径迹与 TRACKER径迹的对比• ECAL e+e- 对 , J/Ψ, Z0 峰 , 能量动量对比

亮度测量通过 Drell-Yan e+e-,μ+μ- 的角分布测量亮度 目前，理论计算的误差 2%

物理研究• J/Ψ→μ+μ-,Υ→μ+μ- 横动量分布• Bc→J/Ψlν, J/Ψπ J/Ψ→μ+μ- ,e+e-

• Blind search e+e- , μ+μ- , e+ μ- , e- μ+ 共振态• Stau 寻找• HWW coupling l+l+ missing ET

• l-l- , l+l+ , without missing ET majorana ν• Higgs search H →ZZ →l+l- jj

CMS Bc goals and channels

1. Bc→J/Ψlν(J/Ψ→l+l-)

2. Bc→J/Ψπ(J/Ψ→l+ l-)

Mass , life time and relative branching ratio

Bc Meson (Experiment)

Experimental observation (CDF & D0 , Tevatron)

Recent results on Bc meson

1998

2004

2005

Production of Bc at LHC

pp pp

LHC LHC (14TeV)(14TeV)

CMS ExperimentAdavantage • LHC : PP Energy 14TeV The production cross section of Bc meson will be ~ 10

bigger than that at Tevatron.• The CMS detector has the similar structure as CDF, and

has larger detector cover region than CDF. CMS :eta~(-2.5,2.5) CDF:eta~(-1,1) (RUN I) eta~(-1.5,1.5) (RUN II) (Muon system)• The CMS detector has a better identified ability to

muons ,this is more useful for the channels which include muon/muons in the final state. And better vertexing.

Our MC goals

• Studying the feasibility of research of Bc meson at the CMS

• Studying the events select strategy of the Bc reconstruction

• Estimating the number of Bc events available at the CMS

• Studying the system error

Preparing for the near future experiment!

List of CMS Software

The CMS software was downloaded and installed in our home machine successfully.

The version of the CMS software are being used in our home machines are

OSCAR_3_7_0 ORCA_8_7_3

The Installation of CMS Software

ORCA_8_1_3 OSCAR_3_2_4 (2004,10)ORCA_8_1_3 OSCAR_3_2_4 (2004,10)

ORCA_8_6_1 OSCAR_3_6_3 (2004,12)ORCA_8_6_1 OSCAR_3_6_3 (2004,12)

ORCA_8_7_3 OSCAR_3_7_0 (2005,4)ORCA_8_7_3 OSCAR_3_7_0 (2005,4)

Newest:Newest: OSCAR_3_9_8 ORCA_8_13_1 OSCAR_3_9_8 ORCA_8_13_1

need new framework .need new framework .

Bc→J/ψµν (J/ψ→µµ)

Display of Bc events

Display of Bc events

Bc→J/ψµν (J/ψ→µµ)

The CMS Analysis chainMC generator HEPEVT

Ntuple

OSCAR

OSCAR

Ntuplesignal

Ntupleminbias

POOLSimHits/signal

POOLSimHits/minbias

POOLDigis DST ROOT

Tree“ data summary tape”

User

SimReader RecReader RecReader

1)digitization 2)reconstruction 3)analysis

ORCA

MC generator

Bc production: C.H. Chang X.G. Wu ITP Beijing

Bc decay and interface with OSCAR: G.M. Chen S.H. Zhang IHEP Beijing A.A. Belkov S. Shulga JINR Dubna (Russia)

jetslJjetsBcbb 2/2

MC generator

comparision of Pt distributions of Bc meson

PYTHIA~ 1event/2 min. BCVEGPY~ 102 events/ min.

Single lepton reconstruction efficiency

The reconstructed efficiency of single muon/electron V.S. The Pt cut of the single muon/electron In order to get the reconstructed muon or electron as efficiency as enough,we requirein the generator level:

For µ : Pt >= 4.0GeV |Eta|<=2.2For e : Pt >= 4.0GeV |Eta|<=2.2

Bc is generated with (pT≥10GeV,|eta|≤2)

The production cross section is σ=10.6nb (including 11S0 ,13S0)

Generator

Bc→J/ψµν (J/ψ→µµ)|η|≤ 2.2

Generator Level Muon pT Cut Efficiency

Simulation (OSCAR)

Reconstruction (ORCA)

Analysis

Results

Generator (Ntuple)

Event SelectEvent Select

Bc→J/Ψ+ lν (or π) J/Ψ→l+l-

J/Ψ Selection

2 leptons Pt ≥ 4.0 GeV

2 leptons share the same vertex

2 leptons have different charge

2 leptons’ invariant mass around the J/Ψ

Selection of the Lepton from Bc

Bc→J/Ψ+ lν J/Ψ→l+l-

Be identified as a muon or a electron

Pt ≥ 4.0 GeV

come from the same vertex (J/Ψ vertex)

Bc Signal Reconstructed Results

M(µ+µ-) (GeV/c2) J/ψ µ Mass (GeV/c2)

Bc→J/ψµν (J/ψ → µµ)

Bc Signal Reconstructed Results

Bc→J/ψµν (J/ψ → µµ)

1/Ptrec – 1/Ptgene (GeV-1)

µ from Bc directly

Bc→J/ψπEvents Selection Study

(1). J/Ψ Selection is as before. (2). for pion, we required: Be not identified as a lepton

Pt ≥ 2 GeV Share the same vertex with 2 leptons (J/Ψ vertex)

Bc Signal Reconstructed Results

Bc→J/ψ π (J/ψ → µµ)

M(µ+µ-) (GeV/c2) J/ψ π Mass (GeV/c2)

Bc Signal Reconstructed Results

Bc→J/ψπ (J/ψ → µµ)

1/Ptrec – 1/Pt

gen (GeV-1)1/Ptrec – 1/Pt

gen (GeV-1)

π from Bc Bc

Backgrounds StudyWe don’t have enough computing power

LHC Computing Grid

IHEP,BEIJING

CERN INFN

A series of Datasets of backgrounds we need are stored in CERN, CNAF, etc.

____________________

Backgrounds Study

Background Channel

Cross section Number of Simulated

Events

Number of Events we get from INFN and CERN using Grid

B0s→ J/ΨΦ(J/ψ→µµ) 167 pb 198275 198275

B→ J/ΨX (J/ψ→µµ) 51.4 nb 200750 200750

bb →µµX 4.8 nb 99736 99736

QCD pt15_20(udsg ) pt20_30 pt30_50 pt50_80

1.5 mb 0.64 mb 0.156 mb 0.021 mb

44999 89999 287747 433743

44999 89999 24000 223743

The backgrounds which have been transmitted and studied by now includes:

__

Background Channel

Bc→J/ψµν (J/ψ → µµ)

Bc→J/ψeν (J/ψ → µµ)

Bc→J/ψ π (J/ψ → µµ)

B0s →

J/ΨΦ(J/ψ→µµ) 7 (59) 10 (84) 22

(185)

B → J/ΨX(J/ψ→µµ)

7 (21072)

5 (15051)

17 (51174)

bb→µµX 0 0 1 (534)

QCD (udsg ) pt15_20pt20_30pt30_50 pt50_80

00 00 00

Backgrounds Study

Number of Events in the integrated Luminosity of 10 fb-1

__

Backgrounds Study

After event select and CMS HLT, the effect of background B0s→ J/ψΦ(J/ψ→µµ)

to the Bc channel Bc→J/ψπ(J/ψ→µµ)

Bc signal

Backgrounds Study

After event select and CMS HLT, in the integrated Luminosity of 10 fb-1 ,

the background B0s→ J/ψΦ(J/ψ→µµ) V.S. Bc signal Bc→J/ψπ(J/ψ→µµ)

Summary (I)

1. Bc→J/Ψlν(J/Ψ→l+l-)

2. Bc→J/Ψπ(J/Ψ→l+ l-)

1. Preliminary Events Select (for the search of Bc at the CMS experiment)

1) Pt (lepton) ≥ 4.0GeV.2) 3 leptons shared the same vertex.3) The invariant mass of a pair of leptons (l+l-) which have different charges is

around J/ψ. e.g. |M(µ+µ-) – M(J/ψ)|≤ 0.2GeV4) For the uncertainty of the losing of neutrino, we take the range[3.0GeV,7.0GeV]

as our signal region of J/ψl.5) For CMS HLT, required: Single µ: Pt≥ 19GeV Double µ: Pt ≥ 7GeV Single e: Pt≥ 29GeV Double e: Pt ≥ 17GeV

1) 2 leptons (from J/ψ) Pt (lepton) ≥4.0GeV ,share the same vertex, have different charge Invariant mass of the 2 leptons is around J/ψ2) Pion selection The particle is not identified as a lepton Pt ≥ 2.0GeV , shares the same vertex of J/ψ Pion candidate is isolated in the cone 3) For CMS HLT.

0.2ΔR 22 )()(

Summary (II)2. Number of Bc events available at the CMS experiment

Decay channel Number of events at generator level

Number of Reconstructed events (CMS HLT)

Number of Events at 10 fb-1 (CMS HLT)

Bc→J/ψµν(J/ψ→µµ)

1.18*106 3517 6318

Bc→J/ψeν(J/ψ→µµ)

6.2*105 562 2054

Bc→J/ψµν(J/ψ→ee)

7.6*105 94 262

Bc→J/ψeν(J/ψ→ee)

9.2*105 23 53

Bc→J/ψπ(J/ψ→µµ)

4.8*105 2426 1071

Bc→J/ψπ(J/ψ→ee)

4*105 28 19

total 9777

(S-wave)

3. Bc study in CMS

Summary (III)

After our analysis of Bc signals and background ,for the channels Bc→J/Ψlν(J/Ψ→l+l-) , it’s believed we can distinguish the signals from the backgrounds efficiently.

For the channels Bc→J/Ψπ(J/Ψ→l+ l-) ,we still need more detailed analysis of the properties of the π in order to distinguish the signals and backgrounds more efficiently.

In a word, It’s believe that studying the Bc meson at the CMS experiment is very optimistic.

To do list• More backgrounds research: prompt J/Ψ etc. for Bc→J/Ψπ(J/Ψ→l+ l-) ,the more important

background is B±→J/ΨK± ,now we have been starting to simulate this channel.

• Research the Bc signals and backgrounds carefully, find out a better selection to distinguish the Bc signals from backgrounds .

• Mass and lifetime fitting, error estimation.