CMS Data Analysis School 2013: Upsilon Analysis Exercises

[Under construction]

This page presents the Upsilon analysis using Heavy Ion methods for CMS DAS School, SINP, Kolkata, India.

CMS DAS School 7-11 November 2013 SINP, Kolkata, INDIA.


In this exercise we will measure the ratios of yields of Y(2S) and Y(1S) in pp and PbPb collisions.The motivation for such a measurement is to know the modification of the ratio of the yields in nuclear medium. Since the binding energies of the Upsilon states are different the medium is expected to act differently on different states.

The exercise is similar to the work presented in the paper arXiv with the corresponding analysis link HIN-11-011.

We will use latest pp data set measured in 2013 with integrated luminosity 5.4 pb-1. The PbPb data set measured in 2011 with luminosity 150 μb-1 will be used in the analysis.

First we will start will pp data obtain the yields of Y(2S) and Y(1S) and their ratio. We will then use MC to get the ratio of acceptances and efficiencies of Y(2S) and Y(1S).

The yields and ratios will be obtained in PbPb system for few centralities.The double ratio i.e. the ratio of ratio of two states in PbPb and pp systems will be obtained.

Analysis steps in real data:

1. Reconstructed data to dimuon skim.

2. Dimuon skim to event tree

3. Event tree to flat dimuon tree

4. Study different cuts with dimuon tree

5. Yield extractions of different states

Analysis steps in MC

1. Reconstructed MC to dimuon skim.

2. Dimuon skim to flat dimuon tree

3. Study different cuts

4. Efficiency calculations

Analysis Procedure

Setting up working area

Create working directory, set CMSSW release

cd scratch0
mkdir UpsilonAna
cd UpsilonAna
cmsrel CMSSW_5_3_8_patch3
cd CMSSW_5_3_8_patch3
cd src

Checkout and compile Heavy Ion modules:

cvs co -r V08-00-02 MuonAnalysis/TagAndProbe
cvs co -r V01-06-05 RecoVertex/PrimaryVertexProducer
cvs co -r pPbProd_v04 DataFormats/HeavyIonEvent
cvs co -r pPbProd_v10 RecoHI/HiCentralityAlgos
cvs co -r pPbProd_v09 HeavyIonsAnalysis/Configuration
cvs co -r HiForest _V02_02 -d Appeltel/RpPbAnalysis UserCode/Appeltel/RpPbAnalysis
cvs co -r branch_pA -d HiSkim/HiOnia2MuMu UserCode/tdahms/HiSkim/HiOnia2MuMu
cvs co -r branch_pA -d HiAnalysis/HiOnia UserCode/tdahms/HiAnalysis/HiOnia
scram build -j 4

Reconstrcuted data to dimuon skim

The aim of HiOnia2MuMu skimming is to make di-muon candidate objects starting from muons with some analysis level variables which would be tricky or tedious for everybody to compute by themselve.

Go to the directory


cmsRun > log &

tail -f log

It runs on a subset of data available here

Creating a dimuon event tree

The purpose of this exercise is to create a ROOT TTree with the Upsilon candidate information to be used for fitting the signal yield. The input is the skimmed data sample obtained in last step. The output TTree has to contain the basic information (e.g. mass, pt) of the Dimuon/Upsilon candidates, as well as the information of the daughter muons.

Go to the directory



Inspect the output file

root -l

Cuts used in the analysis

Dimuon candidates satisfy

Muon candidates satisfy

Submitting test crab jobs

Mass spectrum and signal yield

The number of upsilon events (signal yield) is determined from a fit to the dimuon invariant mass, in the range containing all three 1S, 2S and 3S states. The fitter uses the Roofit (Root) framework. With this one obtains the ratio of number of different Upsilon states in the data sample.

Efficiency ratios from MC

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