SIDRA Fit

Introduction

This method is intended to improve the agreement between MC predictions and experimental data, in terms of muon momentum reconstruction. The method relies on the robustness of Z-boson mass theoretical predictions, and it is based on the comparison of the experimental reconstructed dimuon invariant-mass distribution with the predicted one by MC simulation. Correction terms on the reconstructed muon momentum are evaluated by fitting the MC distribution to the experimental one, by means of a binned log-likelihood method. Correction terms follow the same functional expressions as physical effects influencing momentum measurement. The feasibility to determine relevant terms affecting high transverse momentum muons, such as misalignment effects, is specially interesting. These correction terms can then be easily integrated into the MC to perform high-level physics predictions. The validity of this method has been evaluated for several experimental luminosity scenarios.

Description of the method

The method is described in CMS AN -2010/105. Presentation of the method for the MUON POG are available in the INDICO page.

MC sample

The MC sample used is the POWHEG DrellYan sample of Fall10, Winter10 and Summer11 productions:

/DYToMuMu_M-20_CT10_TuneZ2_7TeV-powheg-pythia/Fall10-START38_V12-v1/AODSIM

/DYToMuMu_M-10To20_CT10_TuneZ2_7TeV-powheg-pythia/Winter10-E7TeV_ProbDist_2010Data_BX156_START39_V8-v1/AODSIM

/DYJetsToLL_TuneZ2_M-50_7TeV-madgraph-tauola/Summer11-PU_S4_START42_V11-v1/AODSIM

Results for 2010 run

The results presented in this page correspond to the first 36 pb-1 of data. Muon pt of MC simulation is distorted the following way:

MC Fall10

For this MC we assume a parabolic shape in eta for shifs. Pt is distorted as:

ptINV = 1./pt + (A+B*eta*eta) * Gauss(0,1) /1000.+( A' + C'*qsin(phi+phi0)+ B'*eta*eta)/1000.

ptmod = 1/ptINV

where Gauss(0,1) is a gaussian random number with mean 0 and var 1, and the parameters A, B, A', C and B' are given in TeV-1.

The parameters after the fit are:

A = 0.236 (TeV-1)

B = -0.135 (TeV-1)

A' = 0.0156 (TeV-1)

B' = 0.0055 (TeV-1)

C = 0.282 (TeV-1)

phi0 = 1.337

zmass.jpg

MC Winter10

For Winter 10, a linear dependence in eta for shifts is observed. As a consequence we fit by distorting the muon pt as:

ptINV = 1./pt + (A+B*eta*eta) * Gauss(0,1) /1000.+( A' + C*qsin(phi+phi0)+ B'*q*eta)/1000.

ptmod = 1/ptINV

where Gauss(0,1) is a gaussian random number with mean 0 and var 1, and the parameters A, B, A', C and B' are given in TeV-1.

The parameters after the fit are:

Results for 2011 data (870 pb-1)

With data from 160404-167151 run interval we get (using VBTF standard Z selection) ~300k Zs. The corrections to apply are:

MC Summer11

For this MC we assume a linear shape in eta and sinusoidal shape in phi for scale shifts, and parabolic in eta for resolution. The correction is applied in two steps. First we correct scale shifts in phi on MC: pt = 1/pt; pt -= 0.0650687e-3 - 0.212987e-3*charge*sin(phi+1.53414); Then we distort MC to look like data

pt += (A+B*eta*eta) * Gauss(0,1) /1000. + (A' + C'*charge*sin(phi+phi0)+ B'*charge*eta)/1000.

ptmod = 1/pt

where Gauss(0,1) is a gaussian random number with mean 0 and var 1, and the parameters A, B, A', C and B' are given in TeV-1.

The parameters after the fit are:

A = 0.143812 (TeV-1)

B = 0.0404834 (TeV-1)

A' = 0.0995898 (TeV-1)

B' = -0.0692569 (TeV-1)

C = 0.0952174 (TeV-1)

phi0 = -1.08881

zmass_corrected.jpg

How to apply this corrections to your MC

If you want to make your MC resemble your data in terms of muon pt, you should apply the previous correction terms with the parameters coming from the fit.

Contacts

Review status

Reviewer/Editor and Date (copy from screen) Comments
Javier.Santaolalla - 16 Mar 2011 first version

Responsible: ResponsibleIndividual
Last reviewed by: Most recent reviewer

-- JavierSantaolalla - 08-Mar-2011

Topic attachments
I Attachment History Action Size Date Who Comment
JPEGjpg zmass.jpg r1 manage 24.1 K 2011-03-16 - 13:52 JavierSantaolalla Z mass distribution for Data (dots), reference MC (green) and MC after the fit (red)
JPEGjpg zmass_corrected.jpg r1 manage 28.9 K 2011-08-05 - 15:58 JavierSantaolalla  
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Topic revision: r8 - 2011-08-12 - JavierSantaolalla
 
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