Mott Analysis

Data Files

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

Analyze a run

 In the directory: /work/idaq/Mott/Analysis/decoder/
 Type: ./fadc_decode_Source fullpath/filename [Option(s)]
 Or: decode.pl RunNumber [Option(s)]
 Output ROOTfiles go to: /work/idaq/Mott/Analysis/rootfiles/

Usage = ./decode.pl 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 Macros

Simple commands to plot data:
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")

There are several macros to be used for the analysis. All are in opsmdaq1 in the directory:

 /work/idaq/Mott/Analysis/macro/

To plot the Mott FADC Pedestals:
[102] idaq@opsmdaq1 > root
root [0] .L FADC_Ped.C
root [1] FADC_Ped t
Enter Run Number: 
7154
root [2] t.Loop()

To calculate Mott Asymmetries:
[102] idaq@opsmdaq1 > root
root [0]  .L MottAsym.C
root [1]  MottAsym t
Enter Run Number: 
7154
root [2] t.Loop()

Analysis Help

• 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

• Mott Summary (April 2012) Media:Mott_Summary_April2012.pdf Media:Mott_Summary_April2012.ppt
• PEPPo Electron Mott Results (July 2013) Media:PEPPo_Mott_Talk.pdf Media:PEPPo_Mott_Talk.pptx

Cross-ratio Method

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