Chap 11: Online Analysis

There are a number of programs that can be run to look at the live data to make sure you're taking quality data. Typically these should be run on dblast13, on one of the two right-hand displays in the counting bay racks. Most of the sources are in /home/daq/blast/pro2003/etSpy/src . Many of them make use of libEtSpy.so to fetch the live data from the ET system, and Root to display histograms.

• onlineGui, a program to display appropriate raw histograms for the detectors (ADC and TDC for TOFs and neutron bars, hit wire numbers and drift time spectra for the wire chamber, etc.), as well as some calculated quantities (theta, z_target, etc.). The tabs on the various histogram panels are labeled according to the same convention used in the lrn n-tuple -- the first letter is the type of information (a for analog, t for time, n for number); the second letter is the type of detector (t for TOF, n for neutron, w for wire chamber); the third letter is the sector (l for left, r for right). onlineGui spies on the ET data stream. Histograms accumulate across runs unless the user explicitly clears them (by clicking the "Clear" button). Of course, ET must be up, and a run in progress, in order for the histograms to update. There is a "Pause" button to stop accumulating histograms, without clearing them. Usage:
  • dblast13> onlineGui and then press the "Start" button

  Histograms can be rebinned by clicking on Rebin at the top of the histogram display screen. This is especially useful for the wire chamber timing histograms.

• nsed, a single event display that shows hit detectors, wire chamber hits, and fitted tracks where possible. nsed operates from a data file rather than the ET data stream; best run from one of the spuds. Usage:
  • spudn> nsed xxx where xxx is a run number and n is a spud number (1-8)

• hits_vs_TOF_ONLINE, a root macro to display a histogram of hits versus TOF number for each sector. "Hit" is defined as good ADC and TDC information for that TOF for the event; counts are displayed in green. If a TOF has no hits, a message appears in red for that channel. This macro spies on the ET data stream. Usage:
  • dblast13> cd ~/pro2003/etSpy
  • dblast13> root -l hits_vs_TOF_ONLINE

Once a run is ended, there are several macros to run. For these macros, you should log in to one of the spuds; the sources are in /home/daq/blast/pro2003/analysis/macros and /home/daq/blast/pro2003/analysis/utils .

• spudn:xxx> cd ~/pro2003/analysis/CRUNCH/v3
• spudn:xxx> lrn mmm (mmm is the run number)
• spudn:xxx> root charge.C mmm
• spudn:xxx> root flrn.C mmm

lrn takes the raw data, finds and fits tracks, and writes out a standard ntuple to lr-mmm.root . charge.C integrates the charge (inhibited and total) for the run from the scaler events, sorted by beam and target helicity, and writes the result to charge-mmm.chg . flrn.C filters the lrn ntuple and writes to flr-mmm.root , selecting only events with good track information in both sectors (for an ep trigger), so the analysis will be faster. If you need to look at raw data, ntuple.C creates ntp-mmmm.root, where the ntp ntuple contains pulse heights and timing from each phototube. The charge results and the ntuples are put in $ANALDIR, currently /net/data/4/Analysis/pro2003 .

When a run has been deemed good, and crunched, note this in the /home/daq/blast/pro2003/analysis/RUNLIST text file. Eventually, runs will be crunched automatically based on information in the electronic logbook, but for now, keep records in the RUNLIST file also.

A simple script which plots elastic events normalized to beam charge can be run to compare rates across runs:

• spudn> .rate xxx (where xxx is the number of runs to look back over)

The script looks in the charge-mmm.chg files to find the elastic events and beam charge. The vertical limits for the plot are set in /home/daq/blast/.rate.plot .

Several Root macros use the lrn/flrn ntuple to form experimental observables. For example, /home/daq/blast/pro2003/analysis/macros/show_ep_asym.C forms beam and target asymmetries and the super ratio for each sector, and also forms false asymmetries. Cuts can be applied using a "-c arg" switch when running a macro, where "arg" is an entry in cuts.C . For example,

• spudn:xxx> root compare.C 300-306 -c padc -c coplaw

will run the macro which compares runs 300-306 to a simulation, cut on ADC values which indicate an electron on the right and proton on the left (or vice versa), and also cut on coplanarity.

You can also look at the data "by hand":

• spudn:xxx> root $ANALDIR/lr-1085.root (loads up the lr ntuple for run 1085)
• root [1] lr->Draw("ttl:atr","ntl==0&&ntr==14&&nwl>17");

will display a 2D plot of mean time for TOF left 0 versus pulse height for TOF right 14, for events with number of hits in WC left greater than 17. A list of names of ntuple elements (and their meanings) can be found in the macro that created the ntuple.