Cerenkov detector calibrations

There are two part of Cerenkov detector calibrations:

amplitude calibrations
time calibrations.

The goal of the amplitude calibrations is to link the measured amplitude in channels to the total number of photoelectrons detected in PMTs.

The goal of the time calibrations is to define for each channel the factor, linked the measured TDC in channels to the value in nsec, and to define the time delay constants, so that the measured time for electrons from the target to the Cherenkov detector will be the trajectory length divided by light velocity.

Amplitude calibrations

The amplitude in photoelectrons is calculated by

A_phe = (A_ch - A_pedest)/A_ope

where A_phe is a number of photoelectrons, A_ch is a measured amplitude in channels, A_pedest is a pedestal value, A_ope is a amplitude in channels for one-photoelectron peak. All values are specific for each PMT

So, to make calibrations, we need to define A_pedest and A_ope.

Pedestal calibrations

Pedestal calibration procedure is a part of pedestals calibrations for all detector groups, - CC, SC, EC and LAEC. There is a special pedestal run, it should be performed and analyzed at the beginning of every new run period, at the end of whole run period, and once per 1-2 weeks otherwise. Before starting this special run you need to check that HV is ON and HV settings are correct.

Name of the configuration : PEDS_ALL
Trigger file: calib/peds_all ? Ask Vardan !
Number of events needed and/or time : from 2000 to 10000 events are sufficient for pedestal measurements.

After this special run is performed, you need to analyze it, using program PEDMAN

To ana-Lise it, you have to

Login on some clon machine (i.e. clon00) as a clasrun.
type
> pedman
you COULD see the pedman GUI

Sometimes ( always) you have to enlarge right and left GUI windows to see the all. Be sure you can see all buttons and red points on CC,EC etc. buttons.
Click on the "File Select" button to select a file. IMPORTANT! For now the program works only with files in /raid/stage_in on clon cluster! Make sure, that /raid stage_in is visible.
Select CC only (other detectors should be De-selected). Define the event range. Usually you need ~100 events, so it can be from event 1100 to event 1200 for example.
Click on Process .
Click on the Change links .
Something about 500 nsec, - ask Vardan

One photoelectron amplitude definition.

To define the position of the one photoelectron peak, you need to proceed another special run. You need not any beam, but it will be best if you'll have the working magnetic field, standard HV setting must be ON. Single photoelectron amplitude calibration is a unique procedure, used for CC only. The idea is to use self-triggering of Cerenkov detector to see the noise function and to define the position of ONE photoelectron.

Before you shall start the Cerenkov calibration run you have to check Cerenkov HV, using CLAS EPICS screen. Status of all channels should be 1 , all channels should be enabled, PMT's current should be about 500 mA.
To start a run, you should use the configuration CC_CALIB. The configuration file is in directory calib and file name is cc_calib.cfg
The number of events needed is 18 M events, run will stop automatically after 18 M events. Such large number of events is necessary because different PMTs has different rate, some time by factor of 50. So , to have enough statistics in ALL PMT you need a lot of events.

To take a CC_CALIB run usually takes ~40 min with typical event rate about 10000/sec.

After the end of the run you'll have about 3 files on /raid/stage_in with names clas_cc_XXXXXX.A0Y, where XXXXX - run number, and Y = 0,1,2

To analyze this runs, you'll better copy them from /raid/stage_in to some work disk, say /work/clas/disk2. To measure the SPE positions we need simply to fill ADC distribution histograms for every PMT. It is possible to do that by any program, say RECSIS, but it takes a lot of time. Simplified code to do that was written and checked under cvs in the cc_cal directory.

First you'll have to check out the package : > cvs checkout cc_cal > cd cc_cal > make That should produce an executable named specal under your bin directory.
Before starting the run analysis you should copy file with pedestals cc.tped to your working directory. This file can be find on clon cluster in $CLON_PARMS/pedman/Tfiles/cc.tped, so that pedestals will be extracted correctly.
To start the run analysis, you type, for example: > ~/bin/SunOS/specal spe.ini
here spe.ini file is to specify the files you need to analyze
example of spe.ini file:
RunNumber=50200
;
DataFile=ff1,ff2,ff3
;

It said that 3 files should be analyzed , - ff1, ff2 and ff3. You can make a soft links ff1(2,3) to files you copied from /raid/stage_in directory.
After specal is finished, there is a hbook file with histograms, - cc_adc.rz
Then you can run paw and execute > exe spe
which will try to analyze the amplitude distributions and produce a file with OPE peak positions( spe.dat )

The (good) example of ADC distribution is shown here:

This peak can be fitted by simple Gaussian, and the position of this peak is One-Photoelectron position.

Unfortunately, there are some channels, where apart from Gaussian you see the noise , exponentially decreased with A, but visible. Those channels need to have some special fitting, using both functions to extract the OPE values. ( Ask Mauri ;-)

Time calibrations

There are two parts in the time calibration:

T1 is the parameter, which converts TDC in channels to nsec. Usually value of T1 was about 0.05 ( nsec/channel ). Now ( since summer,2005) old TDC hardware were substituted, and T1 values must be measured. The principle of calibration is that a pulser signal is send with different time delays to each TDC channel. Signals with definite time are repeated several times to increase the accuracy of the measurements. The TDC response is fitted by a linear function and T1 - is a slope parameter for the channel-time dependence.
This calibration procedure is the part of the forward carriage TDC calibration, and after every such run you need to add the entry into the database.
The other parameter - T0 represents the different delay factors for each PMT (cable length, electronics delay time etc.)

T1 calibrations

First of all you need to start a special run, using usual DAQ procedure. Configuration you need to load : TDC\_CALIB . No trigger configuration is needed for this run.
Number of events needed and/or time : This calibration run usually takes about 40 min, and it requires ~40000 events.
The result of that run will be the file in /raid/stage_in directory with name looks like : tdc_calib_* : i.e. tdc_calib_051313.A00 Here 051313 - is the run number. As any other file, it will be stored on SILO, and you can restore this file and make changes in the database some other time.
! But ! It is better to analyze the run ASAP to check that the file is OK.

Program to analyze the run is in CLAS standard place under cvs in the utilities/TDC_cal directory. So you need :

Somewhere in your directory you type: > setup_clas > cvs checkout include > cvs checkout utilities/TDC_cal Then you'll have all code in your directory. setup_clas needed to set up correct environment variables.
> cd utilities/TDC_cal
> make Hopefully you'll have executable to work with this kind of runs after that command. The name of the executable program is TDCcal . \end{itemize}
If you type
> TDCcal -h, you'll see brief instruction for it's using:
***** TDCcalibrate 5.0 *****
The program TDCcalibrate analyzes the raw banks (RCxx) of a data file for a TDC calibration run. A TDC calibration run consists of M sets of N events (N=20 typical) with a fixed delay T to the TDC for each of the M sets. T[i+1]=T[i] + dT for each successive run i. Each group of N events is fit, and the resulting mean values are fit to a 2nd order polynomial. The constants of this polynomial are then put in the MAP and written to a file.
USAGE HINTS (OLD FILES): If you get many 'data jump' errors, the data may be too noisy. In such a case you may want to check the data sequence using '-spy 13.8.0' (or any other channel). Then count by how many channels the trigger is off. I.e. the peak number goes up one for # channels before the TDC value jumps up. You then use the -skew # to correct the trigger point. (and check again.) If the data was taken with the scalers on, or if you expect there may be missing events, you can ask the code to attempt to correct these problems with -autojump. This tries to detect a premature jump in the time delay by spying on the TDC values and detecting a jump larger than 30 channels. This does not work with noisy data !
DATABASE: Use the -commit flag to commit new results into the database.
This code will put the values in the CALDB database through the MAP compatibility routines. Control over which database host etc can be set with environment variables. See the caldb/Map routines for more detail. setenv CLAS_CALDB_HOST mydbhost.myuni.edu # sets the DB host machine. setenv CLAS_CALDB_PASSWORD myspecialdbpass # sets DB password. Note that the DB password is NOT your login password (should not!) and that the USER environment variable is used for DB user also.
MAP: The only way to write to old MAP files is to compile with the MAP=yes argument to make. The executable will then be TDC_Cal_MAP.
USAGE: /home/vlassov/bin/LinuxRHEL3/TDC_cal
OPTIONS SUMMARY:

-quiet Become progressively more quiet.
-l # Start processing at event number #
-m # Process until event number #
-skew # 'Skew' the trigger, move the trigger point up (down) by #.
-commit Commit the new results to the DATABASE (equivalent to -map)
-map Put entry in MAP (or DB) for this run.
-mapfile Use mapfile instead of $CLAS_PARMS/Maps/ (MAP version only)
-hist Create a histogram output file. If ROOT is enabled, a root file, else an ascii hvplot file
-hist_old If ROOT is enabled, make an ascii hvplot file also.
-noint If ROOT is enables, do not go interactive, dump the file.
-noTT Do not use Translation Tables.
-uTT Use Translation Table from
-faults # Tolerate # number of errors reading crates. (10)
-ncoeff # Fit the TDCs up to order # (default is 2)
-nocompare Do not compare new values against the old ones.
-autojump Automatically jump the trigger when code detects a jump in TDC values.
-notdc Do not write the TDC_RCxx files.
-noascii Do not write the ascii tables.
-paddle Show progress with a paddle wheel.
-skip # Skip processing of crate # (can be repeated.)
-only # Only process for crate #.
-debug Become progressively more verbose.
-spy cr.sl.ch spy on crate.slot.channel
-backup Make a backup of the map before writing a new one.(default)
-nobackup DO NOT make a backup of the map before writing a new one.
-old Force compatibility with files taken before Oct 13 1999 (run 21086)
-help -h Print this help.
For more information: http://improv.unh.edu/Maurik/TDC_cal.shtml or email to
Jörn Langheinrich

T0 calibrations

Recently the CC package was rewrote in order to use the time information from CC properly.

There are no standard procedure under cvs for T0 calibrations. ( Under way )

Here are the steps needed to make this kind of calibrations:

To calibrate CC time cooked BOS-file (or ntuple) needed. It is important that SC was calibrated, at least that RF-time was defined properly.
The BOS - banks (NTUPLE blocks) needed:
HEVT,DCPB, CCPB, CC
First you'll have to select electrons, using all information you have.
Next step is for every PMT, which ADC is, say, more than 4 photoelectrons, to plot the value:
s = TDCCC(i)*T1(i) - tr_time - cc_r(i)/v_light
where TDCCC(i) - is a measured TDC for the electron;
T1(i) is the factor, defined before, to switch from channels to nanoseconds;
tr_time is a trigger time;
cc_r(i) is a length of the trajectory from the target to CC; V-light is a light velocity.
Mean value of this variable (s) gives you additive constant ( in nsec) for every PMT.

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