Mott Analysis

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Data Files

 CODA writes the data to this disk: /data/mott

Decode a run

You must log on to the idaq account of the opsmdaq0 machine, a la:

 [21] user_name@opsl01 > ssh -Y idaq@opsmdaq0 

To then decode a run (turn it from a .dat file to a .root file which is more useable), first go to the proper directory:

 [22] idaq@opsmdaq0 > cd /work/idaq/Mott/Analysis/decoder/


 [23] idaq@opsmdaq0 > ./fadc_decode_Source fullpath/filename [Option(s)]


 [23] idaq@opsmdaq0 > RunNumber [Option(s)]

Output ROOTfiles go to:


Usage = ./ RunNumber -Ped -Debug -Trig x -PedFile x -S1 -Farm -Del x -960Hz -LVoff file or run# -Outputs directory

                -Ped       : Pedestal subtraction active with default files
                -Debug     : Debugging mode, saves all channels to ntuple
                -Trig x    : x=1=Detector, x=2=nT_Settle 
                -PedFile x : Pedestal subtraction with a specific file
                -S1        : Inclusion of scaler S1 data
                -Farm      : Farm option, NO pedestal subtraction 
                -Del x     : x=0 No Delay, x=8 8-window delay 
                -960Hz     : Frequency set to 960Hz, default is 30Hz
                -LVoff     : PMT Low voltage OFF, set to ON by default
                -Outputs   : Set the output directory for the .root and .txt files

Analysis Scripts

The new Full Analysis script is used by the logging on to idaq@opsmdaq0, then following these steps:

[60] idaq@opsmdaq0 > cd /work/idaq/Mott/Analysis/macro/Full_Analysis/
[61] idaq@opsmdaq0 > ./FullAnalysis [RunNumber]

This will tell you useful things like the asymmetry and detector rates as well as make a bunch of plots that go to:


Additional information about the script can be found in the README file maintained in the same directory as the script.

Additional Analysis Tools

  • ROOT provides a utility that generates a skeleton class designed to loop over the entries of the tree:
 root [0] TFile *f = new TFile("Mott_Sample_7231_0.root");
 root [1] T->MakeClass("MyClass")
 Files: MyClass.h and MyClass.C generated from Tree: T
  • Simple plots of data from decoded rootfiles can be generated by:
 [21] idaq@opsmdaq0 > cd /work/idaq/Mott/Analysis/rootfiles/
 [22] idaq@opsmdaq0 > root -l Mott_Sample_[RunNumber]_[SegmentNumber].root
 root [1] T->Draw("Sample_CH1:Iteration$","","*l",10,100)
 root [2] T->Draw("RingScaler_CH4:Entry$","","*l",100,1000)
 root [3] T->Draw("TDC18-TDC17")
 root [4] T->Draw("RingScaler_CH4:Entry$","","*l")
  • There are several additional macros that may used for the analysis (with some modification). All are in opsmdaq1 in the directory:
  • For example, to plot the Mott FADC Pedestals:
 [102] idaq@opsmdaq1 > root
 root [0] .L FADC_Ped.C
 root [1] FADC_Ped t
 Enter Run Number: 
 root [2] t.Loop()
  • To calculate Mott Asymmetries:
 [102] idaq@opsmdaq1 > root
 root [0]  .L MottAsym.C
 root [1]  MottAsym t
 Enter Run Number: 
 root [2] t.Loop()

Cross-ratio Method - Advantages and False Asymmetries

This is the paper that is frequently referenced when discussing the cross-ratio method to calculate asymmetries: G. G. Ohlsen, Jr. and P. W. Keaton,, Nucl. Instrum. Meth. 109, 41 (1973) Media:Cross_ratio.pdf. On page 3, the advantages of the this method are listed.

In this cross-ratio method, the Mott asymmetry is independent (cancel to all orders) of relative detector efficiencies and solid angles, of relative integrated charge (charge asymmetry), and of target thickness variations. However, differences in the beam polarization for the two helicity states cancel to first order.

Dead time in the counting equipment may be either common to the two channels or not, depending on the equipment used. If it is not common, a correction is required. For the Mott, the dead time is caused by the slow DAQ, which is common to all our detectors - no correction is required. This is why even when we have large dead times, we still measure the same asymmetry as the old Mott DAQ.

Section 3.3 of the paper talks about misalignment errors and the effect of detectors having different scattering angle. The Mott Analysing Power depends on the scattering angle, so false asymmetries from misalignments may only cancel to first order - see paper for detailed discussion.

MSS and Farm

  • From jlabl2, do: ssh ifarm to access ifarm1101, the interactive front end for the CentOS 6.2 farm.
  • MSS: The archive location of the Stub Files is: /mss/accel/peppo/raw
 Old files (before May 2012, Run Number < 4,000): /mss/accel/positron/PEPPo or /mss/accel/positron/mott
  • To get files from MSS:
 jget /mss/accel/peppo/raw/Mott_Sample_7231.dat.0
 The file will be copied from tape to the cache area: /cache/mss/accel/peppo/raw
  • Work Disk: /work/accel/peppo
  • Erica Fanchini is keeping the latest decoder at: /work/accel/peppo/Analysis/decoder/
  • Scratch Disk: /scratch