TWR_calibration

1. Calibration Files

Year	Baseline and Threshold	TWR Configuration	Time Offset	Amacalib	After pulse Probability	Example Usage
2003	TWR_threshold_baseline_2003.cnf	TWR.cnf_2003	T WR_dt_2003.txt	omdb2003.TWR.amacalib.txt	Afterpulse_Probability_2003.txt	Sigelinde / Icetray
2004	TWR_threshold_baseline_2004.cnf	TWR.cnf_2004	TWR_dt_2004.txt	omdb2004.TWR.amacalib.txt	Use 2003 File	Sigelinde / Icetray
2005	TWR_threshold_baseline_2005.cnf	TWR.cnf_2005	TWR_dt_2005.txt preliminary file*	omdb2005.TWR.amacalib.txt preliminary file*	Use 2003 File	Sigelinde / Icetray
2006		TWR.cnf_2006

* 2005 Time/Npe Calibration is preliminary because of two known bugs in the TWR raw data. Re-calibration should be followed after fixing the bugs.

2. Time Offset Calibration

This calibration is for correction for time offsets (dt) between TWR and MuDaq for each channels. These time offsets are caused by time delays in remo cables and internal electronics. We measure the dt by comparing the leading edge (LE) time distribution of two DAQs. In order to obtain accurate time offset, LE times for the TWR signals are determined by the fixed threshold method which is virtually same as the MuDaq. We apply the clock speed time of TDC for MuDaq LE time. Finally, the dt constants are measured by Gaussian fitting in the dt distribution. The resolution of the dt distribution depends on readout type (optical or electrical) and data taking seasons because TWR synchronization methods has been changed year by year. Typical time resolution is about 3-5 ns.

3. Npe Calibration
This calibration is a conversion for charge of signal pulse to number of photo electrons (Npe.) The conversion factor for an OM is corresponding to an inverse of the charge value for the single photo electron which is obtained by peak position in the charge distribution. Currently, we use a 0.25 pC of the charge unit for the Sieglinde. We may need a conversion for another preferred units such as pC or nC. All constants are listed in "A" lines of Amacalib files.

4. Time Slewing Calibration
The time slewing (Time walk) effect is an amplitude dependent timing error when the fixed threshold method is used to determine the LE time. Therefore, this calibration constant is for a case when people use that method. Only dt constants are relevant for amplitude independent methods such as a line fitting on early pulse of waveform and a pulse shape convolution fitting. Two constants (alpha and t0) are obtained by fitting distribution of LE - t_ref vs. 1/sqrt(Q). Here, the t_ref is reference time and Q is measured charge for each hit pulses. For 2003-2006 we use the amplitude corrected leading edge time of MuDaq.
The t0 which is a y intercept value in the fitting is added into the original T0 constant in the MuDaq calibration file. Since an additional amplitude error of MuDaq is involved in the t_ref measurement, time resolution of the dt distribution of the calibrated times of two Daq becomes a little worse. Typical time resolution of the calibrated time is about 4-5.5 ns.

5. After pulse Probability Calibration
The After pulse reconstruction method is developed in oder to extend dynamic range of Npe measurement up to a few thousands photoelectrons which is 2-3 magnitude higher than MuDaq. We estimate a primary charge by measuring charges of following after pulse. The After pulse probability constant is necessary when we convert the after pulse charge to the primary charge. Because the the probability varies depending on time delay (time difference between a primary and after pulse) of after pulse, we need time delay dependent constants for the reconstruction. The constants are obtained from time difference distribution of two hits. Assuming the after pulse characteristic is year independent, we have one calibration file based on Lisa Gerhardt's time difference histograms with 2002 MuDaq data.

6. TWR Configuration File
This file includes all hardware configuration information for the TWR system. This file is needed for STOP_DELAY time correction for timing measurement. Because TWR binary data file always includes this information in a header part, people don't need this configuration file when TWR binary file is used. Also, since 2005, the STOP_DELAY times have been corrected with TWR merger program in the South Pole. Therefore, these file are needed when they use 2003-2004 merged F2K file.

7. Baseline and Threshold File
This file is not for calibration constant, containing baseline values and threshold of MuDaq TDC. It is input parameter when we use the fixed threshold method.

8. Detailed Calibration Figures
2003: dt calibration, npe calibration, time slewing calibration
2004: dt calibration, npe calibration, time slewing calibration
2005: dt calibration, npe calibration, time slewing calibration
2006: dt calibration, npe calibration, time slewing calibration

9. Link for Old Page

Old TWR calibration page is found here.

Last Update April 7 2006
Jiwoo Nam