CMS Bc 模拟重建和分析
陈国明
CMS Experiment
2007年夏
Large Hadron Collider
CMS
At 1034
Bunch cross: every 25ns
23 inelastic events per bunch cross
Pile Up
16μm
77mm
At 1033 : 2.3 events /cross
Minimum bias events
the average charge multiplicity: 30
for |η|<2.5, pT>150MeV
CMS Experiment
CMS Experiment
η=2.5
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y
x
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高能所：
端盖μ子
探测器的
1/3
磁铁支架
地板
CMS
北大：
部分RPC
5M CHF 2500万人民币
ATLAS
高能所：
桶部和端盖交接
处的μ子探测器
部分桶部μ子探
测器
山东大学：
端盖μ子触发器的
1/6
中国科技大学：
端盖μ子触发电子
学
1.5M CHF 750万人民币
南京大学：
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+eBlind 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
Mass , life time and relative branching ratio
1. Bc→J/Ψlν(J/Ψ→l+l-)
2. Bc→J/Ψπ(J/Ψ→l+ l-)
Bc Meson (Experiment)
Experimental observation (CDF & D0 , Tevatron)
1998
2004
2005
Recent results on Bc meson
Production of Bc at LHC
LHC (14TeV)
p
p
CMS Experiment
Adavantage
• 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 Installation of CMS Software
The CMS software was downloaded and installed in our
home machine successfully.
ORCA_8_1_3
OSCAR_3_2_4
(2004,10)
ORCA_8_6_1
OSCAR_3_6_3
(2004,12)
ORCA_8_7_3
OSCAR_3_7_0
(2005,4)
The version of the CMS software are being used in our
home machines are
OSCAR_3_7_0
Newest:
OSCAR_3_9_8
ORCA_8_7_3
ORCA_8_13_1
need new framework .
Display of Bc events
Bc→J/ψµν (J/ψ→µµ)
Display of Bc events
Bc→J/ψµν (J/ψ→µµ)
The CMS Analysis chain
MC generator
HEPEVT
Ntuple
OSCAR
ORCA
OSCAR
1)digitization
2)reconstruction
SimReader
Ntuple
signal
Ntuple
minbias
RecReader
RecReader
POOL
SimHits/signal
POOL
SimHits/minbias
POOL
Digis
3)analysis
ROOT
Tree
“data summary tape”
User
DST
MC generator
bb  Bc  2 jets  J /l  2 jets
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)
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 require
in the generator level:
For µ : Pt >= 4.0GeV |Eta|<=2.2
For e : Pt >= 4.0GeV |Eta|<=2.2
Generator
Bc is generated with (pT≥10GeV,|eta|≤2)
The production cross section is
σ=10.6nb (including 11S0 ,13S0)
Generator Level Muon pT Cut Efficiency
Bc→J/ψµν (J/ψ→µµ)
|η|≤ 2.2
Generator
(Ntuple)
Simulation
(OSCAR)
Reconstruction
(ORCA)
Analysis
Results
Event Select
J/Ψ Selection
Bc→J/Ψ+ lν (or π)
J/Ψ→l+l-
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)
Bc→J/ψµν (J/ψ → µµ)
J/ψ µ Mass (GeV/c2)
Bc Signal Reconstructed Results
µ
from Bc directly
1/Ptrec – 1/Ptgene (GeV-1)
Bc→J/ψµν (J/ψ → µµ)
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
M(µ+µ-) (GeV/c2)
Bc→J/ψ π (J/ψ → µµ)
J/ψ π Mass (GeV/c2)
Bc Signal Reconstructed Results
π from Bc
1/Ptrec – 1/Ptgen (GeV-1)
Bc→J/ψπ (J/ψ → µµ)
Bc
1/Ptrec – 1/Ptgen (GeV-1)
Backgrounds Study
We don’t have enough computing power
A series of Datasets of backgrounds we need are stored in CERN, CNAF, etc.
CERN INFN
IHEP,BEIJING
LHC Computing Grid
__________
Backgrounds Study
The backgrounds which have been transmitted and studied by now
includes:
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
(udsg )
1.5 mb
0.64 mb
0.156 mb
0.021 mb
44999
89999
287747
433743
44999
89999
24000
223743
_
pt15_20
pt20_30
pt30_50
pt50_80
Backgrounds
Background
Channel
B0s →
J/ΨΦ(J/ψ→µµ)
_
B→
J/ΨX(J/ψ→µµ)
bb→µµX
QCD (udsg )
pt15_20
pt20_30
pt30_50
pt50_80
Study
Bc→J/ψµν Bc→J/ψeν Bc→J/ψ π
(J/ψ → µµ) (J/ψ →
(J/ψ → µµ)
µµ)
7 (59)
10 (84)
22 (185)
7
(21072)
5
(15051)
17
(51174)
0
0
1 (534)
0
0
0
Number of
Events in the
integrated
Luminosity
of 10 fb-1
Backgrounds
Study
Bc signal
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)
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. Preliminary Events Select
(for the search of Bc at the CMS experiment)
1. Bc→J/Ψlν(J/Ψ→l+l-)
1)
2)
3)
4)
5)
Pt (lepton) ≥ 4.0GeV.
3 leptons shared the same vertex.
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)|≤ 0.2GeV
For the uncertainty of the losing of neutrino, we take the range[3.0GeV,7.0GeV] as our
signal region of J/ψl.
For CMS HLT, required: Single µ: Pt≥ 19GeV
Double µ: Pt ≥ 7GeV
Single e: Pt≥ 29GeV
Double e: Pt ≥ 17GeV
2. Bc→J/Ψπ(J/Ψ→l+ l-)
1)
2)
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/ψ
Pion selection
The particle is not identified as a lepton
Pt ≥ 2.0GeV , shares the same vertex of J/ψ ΔR  ( )  ( )  0.2
Pion candidate is isolated in the cone
2
3) For CMS HLT.
2
Summary (II)
2. Number of Bc events available at the CMS experiment
Decay channel
(S-wave)
Number of events
Number of
at generator level 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→µ
µ)
6.2*105
562
2054
Bc→J/ψµν(J/ψ→e
e)
7.6*105
94
262
Bc→J/ψeν(J/ψ→e
e)
9.2*105
23
53
Bc→J/ψπ(J/ψ→µ
µ)
4.8*105
2426
1071
Bc→J/ψπ(J/ψ→ee)
4*105
28
19
total
9777
Summary (III)
3. Bc study in CMS
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.