Sijin QIAN On behalf of Peking University CMS Group 钱思进（北京大学物理学院）...

Sijin QIAN

On behalf of Peking University CMS Group

钱思进（北京大学物理学院）

第十届全国粒子物理学术会议，南京， 27-4-2008

To Measure Production Cross-section and

Polarization of Heavy Quarkonium in CMS on LHC

大型强子对撞机上 CMS 实验对重夸克偶素的产生截面和极化的测量

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钱思进 CMS 重夸克偶素的产生截面和极化

Outline• Introduction to Peking University (PKU) CMS group

• Motivation to study the heavy quarkonium production and polarization

• Color-Octet quarkonium generation

• Muon and di-muon reconstruction

• Production cross-section measurement

• Polarization extraction

• HLT trigger

• J/ cross-section plots for 10 or 5pb-1

• Summary and prospective

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PKU CMS group4 Professors: (1) Yanlin YE, (2) Yong BAN, (3) Yajun MAO and

(4) Sijin QIAN

1 Lecturer: Siguang WANG

6 Graduate Students: Haiyun TENG[2], Bo ZHU[3], Zongchang YANG[4], Lie LIU[4], Shuang GUO[4], Zhen HU[4]

Some engineers, technicians and undergraduate students.

• Hardware contribution to CMS: 144 (i.e. 1/3 of all) Endcap PRCs in CMS Muon system see Prof. BAN’s presentation in this afternoon

• Physics analysis topics planned:

(a) Heavy quarkonium and NRQCD this report

(b) Polarization of top quark and parity violation

(c) Large missing pT of charged leptons and invisible Higgs

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Heavy Quarkonium Study

• Suggested by Prof. Guangda ZHAO in 2003

• Have made the presentations in various CMS physics analysis meetings at CERN for 31 times since 2005/7 (21 times since 2007/3)

• Have published (or submitted) two CMS relevant Notes:– CMS Note 2007/017 "J/ Reconstruction in CMS" – CMS Analysis Note AN-2007/023

"Measurement of Heavy Quarkonium Production and Polarization in

CMS"

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Two CMS Publications

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Prompt charmonium production Bottomonium production

black dot: CDF experimentdashed line: color-singlet solid line : NRQCD COM fit

J/ ： PRL, 79 (1997) 572

： PRL, 88 (2001) 161802

Two motivations to study the heavy quarkonium production and polarization:1. Measure the cross section of J/psi at 14TeV.

• CSM (Color Singlet Model) : LO, NLO, NNLO• COM (Color Octet Mechanism) : NRQCDThe measured cross section in CDF experiment is much larger than the The measured cross section in CDF experiment is much larger than the

calculation from CSM, while COM can fit the curve.calculation from CSM, while COM can fit the curve.

Motivation (1)

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=+1: transversely polarized =1: longitudinally polarized

CDF run 1

J/ direction in lab frame

direction in J/ rest frame

PRL, 87 (2001) 022002

2. The polarization puzzle.

COM also predicts an increasingly transverse polarizations as pT increases. But both RUN I and II both didn’t show such a trend.

arXiv:0704.0638v1 (2007)

Motivation (2)NRQCD prediction

CDF run 2

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PRL, 87 (2001) 022002

New theoretical development at NNLO

From

Aafke Kraan

of Pisa

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Event generation (1)• Use PYTHIA6.4.09 and tune the parameters to fit with CDF data

CDF RUN I CDF RUN II

• Use the values of NRQCD matrix elements in hep-ph/0106120

• Use the DWT tunings in most of the CMS production

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Event generation (2)• Prediction of the differential cross-section of prompt J/ and B decayed

J/ at LHC, 14TeV

• Prompt J/: Use the tuned parameters and increase energy to 14TeV

• B decayed J/: MSEL=1, QCD processes

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MC simulation to fit Upsilon differential cross section at CDF

PT(GeV/c)

• NRQCD Parameters:– PARP(146)=9.28– PARP(147)=0.15– PARP(148)=0.02– PARP(149)=0.02– PARP(150)=0.09

• Reweight routine was performed

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Muon reconstruction

Bottom: Muon acceptance

Right: Muon reconstruction efficiency vs pT

and Eff vs pT

Eff vs

We required 2 muon’s pT>3GeV at generator level.

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J/ Mass Fit• To determine the number of J/ candidates, in each J/ pT bin, the di-

muon invariant mass distributions are fitted with a signal peak and a linear background.

Mass distribution fit with linear background and signal peak of a simple Gaussian (left) or a double Gaussian (right).

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Dimuon (J/) reconstruction

Bottom: Dimuon pT and distribution

Right: Dimuon reconstruction efficiency vs pT and

Eff vs pT

Eff vs

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Performance of Upsilon reconstruction in CMS

Single Gaussian fit Double Gaussian fit

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Dimuon (Upsilon) reconstruction efficiency vs. pT and

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Measurement of Cross-section

( / ) (1 ')( / ) ( / ) sig

T trigger offreco T

N J AdJ Br J

dP Ldt A P

L1. : the integral luminosity

2. PT : the size of the pT bin.

3. Nsig: the number of reconstructed J/ signals

4. A, A’ : the acceptance and relative acceptance

5. trigger : trigger efficiency

6. offreco : off-line reconstruction efficiency

• The inclusive J/ cross-section is calculated by

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Acceptances and efficiencies

• To calculate the acceptances, we may combine the – Geometrical acceptance, – MC trigger efficiency and – MC offline reconstruction efficiency

as

• The trigger and offline efficiencies from data are considered as a correction factor.

)4.2|)/(|),/((

)4.2|)/(|),/((),(

JJPN

JJPNPA

Tgen

Trec

T

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Muon efficiency

• Muon efficiencies can be measured from data by Tag&probe method. It strongly depends on the cuts (pT & R).

• Tag&probe can be used both on MC events or real data. Thus the correction factor is:

( , )( , )

( , )MC T

Tdata T

pp

p

( , )Tp is ideal to be 1.

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J/ Efficiencies • The offline J/psi reconstruction efficiency is a function of J/’s pT, eta

and polarization angle.

Here:

P(pT,) is the probability density function of muons from J/ decays, can be extracted by Monte Carlo.

(pT,) is the correction factor of muon offline reconstruction efficiency.

/ / / // / / 2( , , ) ( , , )J J J JJ J Joffline T T vertexp p

/ //( , , ) ( , ) ( , )J JJT T T Tp P p p dp d

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B fraction (1)The B fraction can be extracted by fitting the pseudo-proper decay length distribution of the J/:

( / )

( / )xy

T

L M Jc

P J

is the J/psi transverse proper decay lengthxyL

1. Prompt J/ starts to decay immediately.

2. B-hadrons have some long lifetimes.

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B fraction (2)

),()( cRcFp )'(),'()( cccRcF mcB

Constrain the two Gaussian with the same mean value

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B fraction (3)

)()1()()( cFfcFfcF pBBBsig

mean_core = mean_tail

Prompt NonPrompt Combined

fra_tail 9.44831e-02 4.18656e-02 1.18763e-01

mean_core 8.05345e-06 -8.32907e-04 -3.10517e-05

mean_tail =mean_core =mean_core =mean_core

sigma_core 3.72622e-03 3.89145e-03 3.46209e-03

sigma_tail 2.55135e-02 5.44455e-02 2.21717e-02

frac_Bdecay 2.97188e-01

tau 4.17653e-02 4.14621e-02

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B fraction (4)

• B fraction from fit comparing to the MC truth.

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Polarization measurement

1 template 1 template(cos ) (1 )signalI I I

• CDF used a method called Template fit – to fit the data to a weighted sum of two MC templates: - transverse polarization template - longitudinal polarization template

2

21

21

3(cos ) (1 cos )

2( 3)

31: (1 cos )

83

1: (1 cos )4

I

I

I

J/ direction in lab frame

direction in J/ rest frame

1

3

= -1 generation

= +1 generation

=-1 reco template =+1reco template

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Methods to extract polarization parameter

1. Template fit– Find the cos() distribution of signal events– Produce templates by weighting MC events

with and – Fit the data to the combinations of

longitudinally and transversely polarized MC templates

2. Iterative fit

3. ANN (Artificial Neural Network)

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Method (2): Iterative method

TL

SDnorm NN

NNF

)1(

)0(00

• Iterative method is almost the same as the previous one . The difference is that we input a normalization parameter at the beginning by:

• Then fit a value 1, and use 1 to calculate Fnorm(=1). And then use Fnorm(=1) as input to fit 2…etc.

• The fitting result converges quickly, and becomes stable after tens of step.

transversely polarized

longitudinally polarized

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Method (3): ArtificialNeuralNetwork

cos distributions can be normalized to be the pdfs (probability density function). ANN (Artificial Neural Network) can learn these pdfs and fit the data distribution function. Here only the shape of cos distribution is used.

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Compare the 3 methods1. These three methods all describe the right trend in transverse

and longitudinal samples.

2. The first two methods need a precise measurement of the J/psi efficiencies, while ANN doesn’t depends on the efficiencies.

3. ANN also has a disadvantage that it needs a large amount of events both in signals and templates.

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HLT trigger

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HLT J/ (or Upsilon) trigger

L2 muon reconstruction

L2 J/ Filter

L3 muon reconstruction

L3 J/ Filter

L1_DoubleMu3: trueMaxEta = 2.5 MinPt = 0MinQuality = -1MinN = 2

MaxEta = 2.5MinNhits = 0MaxDr = 100.MaxDz = 9999.ChargeOpt = 0MinPt = 3. MinInvMass = 1.0MaxInvMass = 5.0NSigmaPt = 0.

MaxEta = 2.5MinNhits = 0MaxDr = 0.02MaxDz = 9999. ChargeOpt = 0MinPt = 3. MinInvMass = 2.8MaxInvMass = 3.4NSigmaPt = 0.

L1 Filter

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J/psi L2 and L3 dimuonsL2 dimuons L3 dimuons

• These windows should be large enough since sideband events are very important in physics analysis

1 5 2.8 3.4

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Upsilon mass windows for L2 and L3

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L1 and HLT efficiencies• L1 and HLT trigger efficiencies of different HLT paths.

• The L1/HLT efficiency is that the efficiency of an offline reconstructed and selected J/psi passes L1/HLT trigger.

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Trigger efficiency from data

• The dimuon trigger efficiencies can be expressed as

• The L1/L2/L3 muon trigger efficiency is defined as the probability of an offline reconstructed muon to pass the L1/L2/L3 trigger criterias.

1 2/1 2( , )J

trigger trigger trigger

1 2( , ) corresponds to the dimuon correlation effects which is assumed to be 1. Then we use tag&probe method on the single muon trigger efficiencies.

1 2 3

( 1, | ) ( 1, , 2, | 1, ) ( 1, , 2, 3, | 1, 2, )

trigger L L L

P L offl offl P L L offl L offl P L L L offl L L offl

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Statistics• At an integral luminosity of 10pb-1, 100pb-1 or 1000pb-1, with HLT J/

or Upsilon triggers, we shall have:

• With 40pb-1 , CMS may have 572K prompt J/ which are as twice many as CDF had.

• With 70pb-1 , CMS may have 79K prompt Y(1s) which are about an order of magnitude higher than CDF had.

10pb-1 100pb-1 1000pb-1 CDF Statistics

J/psi

Prompt J/psi signals 143K 1.43M 14.3M 300K (40pb-1)

Nom-prompt signals 74K 740K 7.4M -

Backgrounds 33K 330K 3.3M -

Y(1s)Signals 11.3K 113K 1.13M 6K (70pb-1)

Backgrounds 10.4K 104K 1.04M -

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Misalignment• J/psi mass distribution in

different misalignment scenarios.• The efficiency is much lower at

10pb-1 misalignment. • The resolution improves with

long term alignment.

scenarios Mass resolution

10pb-1 34.4MeV100pb-1 31.2MeVLong term 30.9MeV

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For 10 pb-1 data

• In 10pb-1, the invariant mass peak of two global muons pass the HLT trigger and offline selection: dimuon pT>3GeV/c |eta|<2.4

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J/ Differential Cross Section

• For 5pb-1

Only statistic errors

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B-physics group summary in CMS physics plenary a week ago (1)

Among

total

21 pages,

6 pages

are related

with PKU

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P. 5

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P.11

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P.12

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P.13

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P.14

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P.21

PKU’s work

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Summary/Prespective• The solid ways to measure the heavy quarkonium

production and polarization have been developed in PKU.

• Our work has been well recognized and encouraged by CMS; hopefully it can lead to one of the first CMS physics publications after LHC’s proton collision.

• With more CMS data to come in next couple of years, we hope that this work can provide more clues for theorists to verify various models in NRQCD.

• To make more precise measurement, we have to understand the detector and CMSSW performances better; therefore, more hard works and challenges ahead us, we are delight to have this unusual opportunity and shall do our best for it.

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Thank you !

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