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Muon-based Calibration of Endcap Crystals
This page under construction. Direct questions to J. Ritchie
Bhabha calibration is not used for the inner three endcap rings (theta_index = 1,2,3). Instead, Bhabha-like constants are derived from muon energy deposition in single crystals. This calibration is done infrequently (e.g., once per year). The method is documented here.

Quick Link to
Muon Calibraion Results Page ( Table of Constants, Histgrams, etc.)

Purpose of Muon Calibartion
  • Muon-based calibration is developed for the inner three endcap ring as an alternative method to bhabha calibration.
  • Muons are a source of constant energy deposition (about 200 MeV).  As a result, they are a check on detector stability.
  • Muons deposit energy uniformly along their paths, so they maybe affected differently by radiation damage than photons and electrons if the damage is localized (e.g., near the front).
  • The precision of this method is limited to the few percent level by the uncertainty in muon peaks for individual crystals, but for rings 1-3, this is a substantial improvement. 
Method to calibrate inner three rings of endcap
  • Muon-based calibration for the endcap is based on the muon peaks found in the each crystal.  Muons "transfer" the calibration from good EMC regions into the inner three ring. (Go to Calorimeter Description and Drawings to check the geometry of EMC.)  
  • Use muons which hit only one crystals (Crystals = 1) selected from rawEnergy().  With this constraint, the muon peaks become narrower and cleaner.
  • Determine the central value for ring 4 using muon peaks.   Ring 4 is used as the normalization for the calibration since the radiation damage is similar and the momentum difference is negligible.
  • Calculate factors for each crystal in ring 1-3 to shift the peak for that crystal to the central value for ring 4.  Peaks are normalized and scaled to the Bhabha energy using source and bhabha constants.   
Procedure
   Data Selection:
  • Approximately 100 million events are needed to get enough statistic.  Use Bookkeeping User Tools to select desired datasets.  AllEvents are used for this analysis.  It is recommended to run smaller number of events (~2.5 million) and merge the resulted files.     
  • For Run4 data, BetaMiniApp is used to select events.  Modify MyMiniAnalysis.tcl to turn on BGFMuMu.  (Refer to the linked file for the example.)  Compile and link EmcMuonPeaks.cc and EmcMuonPeaks.hh.  This will give you a hbook with ntuple containing energy peaks along with theta and phi angles.
   Data Analysis:
  • Run muendc3p2.kumac on the ntuple.   The kumac file will plot energy peaks of theta 1 through 5 with gaussian fits.  At the end, the kumac will generates two files; one post script file (gzip) containing the plots of energy and vfactor, and a data file which contains columns of theta, phi, and vfactors.
  • In order to calibrate the vfactors, source and bhabha calibration constants are needed.  They can be found using  EmcCond.  Under the Analysis-21 directory, type
        >addpkg EmcCond V00-03-27
        >gmake EmcCond.FetchEmcCalChan     
  • Once the compiling is done, the executable called "FetchEmcCalChan" will be available.  By specifying the type and the date of calibration desired, this will return the columns of theta, phi and the constants.  This columns contains constants for all the angles but we are only interested in theta 1 through 3.  We can reformat the data file using calchan.kumac.
  • Three files containing columns of angles and constants are generated so far; vfactors, source and bhabha constants.  formatbhbh.kumac combines those 3 files to be used by mubhbh.kumac.  mubhbh.kumac rescales the vfactors and calculate the new bhabha-like constants and generates a plot and a data.
  • muanl.kumac is also helpful when comparing the difference between old and new sets of calibration constants
Talks on Muon Calibration
The progress of the muon calibration has been presented at EMC calibration meetings as "Muon Studies" by Jack Ritchie.

Links to Muon Studies (PDF files): July 17th, 2002, August 28th, 2002, September 25th, 2002 October 23rd, 2002,  March 12th, 2003, April 23rd, 2003, June 18th, 2003.


This page is: $BFROOT/www/Detector/Calorimeter/MuCalib/index.html
Page author: Natsumi Matsuda