# Presentation: 673524

## High-mass Dimuon Resonances in Pb-Pb Collisions at 5.5 TeV in CMS

**Dipanwita Dutta**
**BARC,  India**
**On behalf of the  CMS Collaboration**

## Outline

**Physics Motivation: **
**Dimuons from Quarkonia and Z****0**
**CMS Experimental Setup**
**Simulation for Dimuons**
**Results**
**Summary**

## Dimuons: From SPS, RHIC to LHC

**Dimuons: From SPS, RHIC to LHC**

**  ****LHC: Factor 30-45 increase in energy compared to RHIC**

**Heavy Ion Physics at LHC**
** ****Plasma ****Hotter, Bigger**** and**** Longer**** life time**
** ****Access to ****lower x**** and ****higher Q****2**
** ****Unprecedented gluon Density**
** ****Availability of ****new Probes (Y,Y****'****,Y****"****)**
** ****Z****0**** ****with**** large cross-section**

|  | SPS
17 GeV | RHIC
200 GeV | LHC
5.5 TeV |
| --- | --- | --- | --- |
| initial T  | ~ 200 MeV | ~ 300 MeV | > 600 MeV |
| volume | 103 fm3 | 104 fm3 | 105 fm3 |
| lifetime | < 2 fm/c | 2-4 fm/c | > 10 fm/c |

**High Mass Dimuon Resonances at LHC**
**                   ****J/********, Y,Y',Y", Z****0**

******20**

## Dimuons :Probe of Dense QCD Medium

**Dissociation of Q’nia (Debye Screening): ****Hot QCD Thermometer**

** ****Z****0**** : Weak production and decay-- No final state effect**
** ****Baseline for Quarkonium Suppression**

## Dimuons: Probe of Initial State

** ****state in a novel Bjorken-x range (****10****-3****-10****-5****):**
**nuclear shadowing**,
**high-density saturated gluon distribution**.

- 108
- 106
- 104
- 102
- 100

## }

**Muon system:**
**  ****Drift Tubes (DT) in central barrel region**
**  ****Cathode Strip Chambers (CSC) in endcap region**
**  ****Resistive Plate Chambers (RPC) in barrel and endcap**

** ****Excellent coverage:**
**~****5 units of rapidity**** and 2******
** ****Strongest magnetic field:**
**4 T****, ****2 T (return yoke)**** **
** ****Tag from muon stations,**
**momentum resolution from**
**Silicon tracker:**
** ****~****2%  of momentum **
**resolution for tracks with **
**p****T**** <100 GeV**
**   ****Ecal+Hcal+Coil –   absorbs hadrons **

- HCAL

- ECAL

- Tracker

- Coil

**CMS Detector for Heavy Ions**

**precise measurement of**
**position (momentum)**

**fast info for LVL-1 trigger**

## Signal Dimuon Resonances:

**Signal Dimuon Resonances****:**
** ****Quarkonia****: J/******** (BR: 5.9%), ******** (BR: 2.5%)**
** ****Z****0****: (BR: 3.4%)**

**Background Dimuons****:**
** ****Decays from open c and b**
** ****Decays  from ********, K**
** ****Decays from W**
** ****Mixed muon pairs**

## Simulation of Quarkonia

**b=0**

**5% c.c.**

**min.bias.**

**N(bb)    w/o shadowing**

**6**

**5.5**

**1.4**

**          **

**w/    shadowing**

**5**

**4.7**

**1.2**

**Simulation of Quarkonia**

|  | J/ | ' |  | ' | " |
| --- | --- | --- | --- | --- | --- |
|   Bprod | 48930 | 879 | 304 | 78.8 | 44.4 |

**Resonance cross-section (********b):**

**Marc Bedjidian, ****Olga Kodolova,**** ****CMS NOTE-2006/089**

** ****Signal (J/********,********):**** CEM, NLO-pp, **** (CTEQ5M+EKS98 PDF),T****AA**** scaled**
** ****Background Uncorrelated Muon Pairs from ********/K decays:**
**Two scenarios for the multiplicity of charged particles **
**                  ****dN****ch****/d******** = 2500 at ********=0**
**                  ****dN****ch****/d******** = 5000 at ********=0 **
- – **Only ******** and K**** ****are considered**** ****( 90% of charged particles multiplicity)**
- –** ****Kaon/pion = 11% (HIJING)**
- –** ****p****T ****and ******** distributions of pions and kaons  according to HIJING**
** ****Background Muons from Open Heavy Quark (b,c):**
**              ****NLO pp, CTEQ5M+EKS98 PDF****, ****T****AA**** scaled**

**b=0**

**5% c.c.**

**min.bias.**

**N(cc) w/o  shadowing**

**226**

**206**

**51**

**           **

**w/     shadowing**

**150**

**135**

**33**

## Dimuon reconstruction algorithm for Quarkonia 

**Dimuon reconstruction algorithm for Quarkonia**** **

## Dimuon High Level Trigger performance for Heavy Ions

**Two Different Level 1 Trigger:**** (single muon trigger)**
**                    ****L1:  optimised for High luminosity pp run**
**                    ****OL1: low quality muon candidates optimised for HI**
**L2 and L3  run on online farm:**** **
**Trigger Conditions:**** Two**** L1 ****or ****L2**** opposite sign+ ****L3 ****(cut on loose)**

**J/********trigger ****efficiency: **
**0.97% ****(OL1-L2 chain)                                                          ****0.44%****   (L1-L2  chain)**

******trigger ****efficiency: **
**21% ****(OL1-L2 chain)                                                          ****16.5****%****   (L1-L2  chain)**

## Dimuon efficiency & purity vs dNch/dy 

**“****realistic” LHC multiplicity range**

**Dimuon efficiency & purity vs ****dN****ch****/dy **

**Y is embedded in PbPb events**
**Efficiency:**
**Eff = Eff****trk-1**** x Eff****trk-2**** x Eff****vtx**
**   ****> 80% for all multiplicity (barrel)**
**   ****> 65% for all multiplicity**** **
**   ****(barrel+endcap)**
**Purity = [true Y reco]/[all vtx reco]**
**            ****> 90% (all multiplicities)**
**        **

##  J/ mass spectra (like-sign subtraction)

- J/ **= 35 MeV/c****2**** in (barrel+endcap), Both muons with |********|<2.4**

**S/B=1.2**

**S/B=0.6**

##   mass spectra (like-sign subtraction)

******Y**** = 54 MeV/c****2**** in (barrel)  and ************ =**** ****90 MeV/c****2**** in (barrel+endcap)**

** ******** ****mass spectra (like-sign subtraction)**

**Barrel+**
**endcap:**
**Both muons **
**with |********|<2.4**

**Barrel:**
**Both muons **
**with |********|<0.8**

_**Excellent Mass Resolution at LHC:**_

**S/B=0.97**

**S/B=0.12**

## pT and  reach of Quarkonia (1 Pb-Pb run)

**p****T **** of**** ****J/******** **

**p****T **** of**** **** ******** **

****** ****of**** ****J/******** **

****** ****of ******

**For 1 month LHC run, L ****int ****=0.5 nb****-1**

**p****T**** reach **
**~40 GeV**
**(without suppression)**

-  N(J/)~105

-  N()~104

**Very Large Statistics**

## Simulation for Z0+- : Gen. level

| Processes | Cross-section
pp(Z0) Pythia6.409
CTEQ5M | Cross-section
PbPb(Z0)=
TAA pp(Z0) BR
 0-10% cent. (MB)    | No. of Z0 for 0-10% cent. (MB) collisions
NPbPb=Lint PbPb(Z0)
Acc.(=0.55) |
| --- | --- | --- | --- |
|      Z0,Z0+jet
(MSUB=1,15,30) | 60 nb
 | 30.6 (77)b | 8.2103 (2.0104)
 |

**CMS Muon Acceptance :**
**p****T ****(********) > 3.5 GeV,  |********(********)|<2.4**
**Acceptance of Z****0****~55%**** **

**Expected No. for one month LHC run, L****int****=0.5 nb****-1**

**qq(bar)********Z****0****(Z****0****+jet)**

**Total**

**qg********(Z****0****+jet)**

**Dominant Contribution for Z****0**** prod:**
**qq(bar) annihilation********Study of Quark PDF Shadowing**

**BR in ****Z****0********+********-**** ~ 3.4%**

**D. Dutta et. al**

## Simulation for  Z0 +-

**Dimuons:**
-  **bb(bar) fragmentation**** **
**~ dominant contribution**
**Combinatorial background:**
**b and ********,K**** ~16%**
******,K and charm decay****: 5-6%**
**Signal from Z****0****: Clear peak**
**~11,000 events in **
**  ****M****Z****±10 GeV/c****2****, **
**Less than 5%  background**

**CMS Physics TDR: Addendum to High Density QCD with Heavy Ions,  J. Phys. G, Nucl. Part. Phys. 34 (2007) 2304**

**+DY**

## *- ,Z- jet tagging ‏

*******- ,Z- jet tagging ****‏**

-  **CMS can also calibrate jet-energy loss with back-to-back Z and/or virtual ******** (large cross-sections, good detection capabilities):**
-  **Dominant (heavy-Q) dimuon backgd.**
** “****removable” via secondary-vtx. cut**

**Dimuon trigger**

**Associated Hadrons**

**q/g**

**Z****0****  ****/****  ***********

**Away side**

**D. Dutta, C.Mironov et al.**

**N****Z-jet****~10****3**

**p****T ****>25 GeV/c**

- r=50 m
- =20 m

- 3 vtx. cut

## Summary

**J/********,******** and Z****0****:**  Prominent probe of  QCD media in Pb+Pb collisions
**Stepwise melting– ****Thermometer of QGP**
**Quarkonia production via gg fusion:**** **
**probe of low x QCD**
**Z****0 **production via **qqbar** annihilation:
**Probe of Nuclear shadowing of quark PDF**
**Simulation Studies** **of J/********,********:**
**Acceptance :****J/********~15%**** ****(at high p****T****) and ********~26%**
**Dimuon ****Efficiency ~80%** and **purity 90%**
**Mass Resolutions at LHC:**
**    ****σ****=~1% M****QQ**** ****(barrel+endcap), ****σ****J/********=35 MeV/c****2**** ****(barrel+endcap)**
**           ****σ********=54 MeV/c****2**** ****(barrel alone)**
**Signal/Background**: ~5(1), ~1(0.1) for J/, in barrel (+endcaps)
**High rate expected (per year):**
**             ****J/******** ~ 180 kevents, Y ~ 25 kevents, Y’ ~ 7 kevents, Y’’ ~ 4 kevents**
**High p****T**** reach~ ****40 GeV**
**Generator Studies of Z****0****:**
**Aceeptance: Z****0****~55%**
**       ****No. of Z****0****: ~10****3****(10****4****)**** for 10% ****central (Minbias)**** within CMS acceptance**

**Thank you**

## Back Up Slides

## Quarkonia production: kinematical spectra

**J/******

**J/******

**Y**

**Y**

**Quarkonia production: kinematical spectra**

**p****T**** and ******** according to Yellow Report, CERN-2004-009, hep-ph/0311048**

## Heavy quark pairs production: kinematical spectra

**ccbar**

**bbbar**

**Heavy quark pairs production: kinematical spectra**

**p****T**** and ******** according to Yellow Report, CERN-2004-009, hep-ph/0311048**

## L1 Trigger: single muon trigger with no momentum cuts 

**                    ****optimized for HI run conditions**
**L2 and L3:  run on online farm**
**L2 trigger condition:**
**      ****either  opposite(like) sign  dimuon candidate at L1 trigger or**
**       ****opposite(like) sign  dimuon candidate at L2 trigger **
**L3 includes regional track finder starting from the muon stations, **
**     ****primary vertex finder with pixel detectors and dimuon vertex **
**     ****constraints**

**J/******** and Y trigger strategy**

## Dissociation (Color Screening): Hot QCD Thermometer 

**Dissociation (Color Screening): ****Hot QCD Thermometer**

##  Quarkonia rates and S/B ratio at CMS

** ****Quarkonia rates and S/B ratio at CMS**

**Signal-to-background ratio and expected quarkonia yields in one**
**month of PbPb running (0.5 nb****-1**** integrated luminosity) for two**
**multiplicity scenarios and two ******** windows**

**No of J/******** ~10****5**** and  ****No. of  ******** ~ 10****4**** ****in**** Minbias Event**

| dNch/d=0,  | S/B | N(J/) | S/B | N() | N(‘) | N(“) |
| --- | --- | --- | --- | --- | --- | --- |
| 2500, <2.4 | 1.2 | 184000 | 0.12 | 26000 | 7300 | 4400 |
| 2500, <0.8
 | 4.5 | 11600 | 0.97 | 6400 | 2000 | 1200 |
| 5000, <2.4
 | 0.6 | 146000 | 0.07 | 20,300 | 5900 | 3500 |
| 5000, <2.4 | 2.8 | 12600 | 0.52 | 6000 | 1800 | 1100 |

## Dimuon Sources at LHC : Signal and Background

**Signal Dimuon Resonances****:**
** ****Quarkonia****: J/******** (BR: 5.9%), ******** (BR: 2.5%)**
** ****Z****0****: (BR: 3.4%)**

**Background Dimuons****:**
** ****Decays from open c and b**
** ****Decays  from ********, K**
** ****Decays from W**
** ****Mixed muon pairs**

## Cross-sections for Z0

| Processes | Cross-section
pp(Z0) Pythia6.409
CTEQ5M | Cross-section
PbPb(Z0)=
TAA pp(Z0) BR
 0-10% cent. (MB)    | No. of Z0 for 0-10% cent. (MB)l collisions
NPbPb=Lint PbPb(Z0)
Acc.(=0.55) | No. of Z0  0-10% Cent. (MB) MRST HO PDF, with shadowing
[R. Vogt PRC64, 044901(2001)] |
| --- | --- | --- | --- | --- |
|      Z0,Z0+jet
(MSUB=1,15,30) | 60 nb
 | 30.6 (77)b | 8.2103 (2.0104)
 | 3.8103
(9.6103)
(using 15 nb with CMS acc.) |
| (mZ-5)GeV
≤M≤(mZ+5)GeV | 25.4 nb | 12.9 (32.7) b | 3.5103 (8.8 103) |  |