CLAS12 FTOF at USC: Time Resolution Measurements

Transcription

1 CLAS1 FTOF at USC: Time Resolution Measurements Evan Phelps University of South Carolina Department of Physics and Astronomy November 4, 009 1

2 TOF1 Project at USC

3 TDC Differential Nonlinearity Random Start + Periodic Stop Uniform Distribution + DNL Fluctuations + Statistical Fluctuations 3

4 TDC Calibration and Resolution * 5ns cable delays 0.7 bins 5 t= ps 17.5 ps bin ns TDC Value.8 ns bin 4

5 ADC Calibration V79N testing: Single channel example sensitivity Adjustable pedestal range is insufficient to push system charge offset above the threshold. 5

6 Time Resolution Measurement Methods Coordinate method Reference counter methods One reference Two reference Three-bar cosmic ray method Independent position measurements High statistics. Requires multiple runs per counter. Energy deposit signature does not match CLAS experimental conditions. Independent position measurements. Energy deposit signature matches CLAS experimental conditions. Very to extremely low statistics. Requires multiple runs per counter. Energy deposit signature matches CLAS experimental conditions. High statistics. Requires only one data run for full bar. Does not incorporate independent position measurements. 6

7 Three-bar Method Concept B A t t t b t 1 t t 5 t 6 4tr t 3 t 4 t r t 1 t t 5 t 6 t 4 t 3 T= t m = = 4 4 t tl t tr t t= t ml t mr t m= t bl t br t b= t tl =t 1 t r t tr =t t r t ml =t 3 t r t mr =t 4 t r t bl =t 5 t r t br =t 6 t r t r =t 3 counter = pmt tb = 1= = 5 = 6 m = 3 = = tb m 4 T 1 counter = ref T 7

8 Reference Counter Resolution B A The middle counter is the one being evaluated; the top and bottom are reference counters of known resolution. 1 counter = ref T When all three counters are identical... counter = T 3 8

9 Three-bar Method Implementation 9

10 Base Resolution TDC resolution, between 30ps and 35ps, contributes to the resolution measurements. tdc=30.5 ps Total electronics resolution is measured, but does not contribute to the resolution measurements. electronics =57. ps 10

11 Three-bar System ADC Offset in-situ offset measurements σ = bins μ = bins 11

12 Full-width Trajectory Cuts via ADC Minimums Position Cuts via TDC Difference Position-specific Event Selection 1

13 Position-specific Timewalk Correction After cuts, tcorrected is distributed about a fixed value i 3 t corrected = TDC i TDC 3 ADC i ADC 3 σ TW parameters λi and λ3 are varied for each of tl, tr, bl, br, and mr to determine values leading to minimum tcorrected spreading. 13

14 Position-specific Timewalk Correction A paraboloid fit is sufficient to obtain the minimum value and corresponding TW parameters. (λ1,λ3) (1.7,1.7) 14

15 Position-dependent Resolution Left edge of scintillator The average position-restricted resolution, <σres>, Is approximately 40ps. Right edge of scintillator Resolution measurements are consistent, within statistical uncertainties, throughout the counter length. ( Scintillator edges are defined by FWHM of TDC Difference before cuts or TWC. ) 15

16 Position-dependent TW Parameters EXAMPLE Correction function for the time (t3) of the middle-left (ML) PMT 3= x x 16

17 Full-bar Resolution Event Selection Minimum ADC Cut only eliminates VERY Low ADC Values FWHM Cut on Reference Bars ADC, Arbitrary PMT 17

18 Full-bar Resolution without Vertical Cuts 86.6ps 4.6ps Timewalk Correction Functions 18

19 Recent Results 009 USC measurement of 13cm x 5cm x 5cm Panel-1A counter 1999 JLab measurement of 13cm x 5cm x 5cm Panel-1A counter 009 USC measurement (average positionspecific resolution) of 10cm x 6cm x 6cm Panel-1B prototype counter 19