Analysis Lessons Learned (d2n)

What follows is a (partial) listing of analysis lessons learned from Transversity, which may be a useful guide for d2n. Much of this is culled from Transversity analysis meeting presentations, accessible through the Transversity ELOG (from experiment webpage [1]. I've given the student's name and the date of the relevant presentation, in italics, for each point. The Hall A Analysis Workshop 2009 is also a useful resource.

Beam Characteristics

• Calibrate phase difference between raster currents, BPM positions. (Vince, 2009.01.29)
• Transversity took an ARC measurement on Nov. 17. Do we have a d2n ARC measurement? (Vince, 2009.01.29)
• Raster x/y cables found to have been swapped (Jin at Analysis Workshop)

Target

• Extended target correction to account for <math>x_{tg} \neq 0</math> (Jin at Analysis Workshop)
  • THaExtTargCor class in analyzer

Optics

• Optics are calibrated with low-momentum data. Can we trust this calibration in a high-momentum regime? (Xin, 2009.03.06)

LHRS

General LHRS

• VDC T0 is calibration on which all others rest (Chiranjib, 2009.03.06)

S1, S2m

• Check ADC pedestal stability over time (Chiranjib, 2009.03.06)
• Timing calibration from s2m (Jin, Analysis Workshop, citing Chiranjib)
  • Two-bar-hit events, with tight ADC cut: rough offset alignment, get below 1 ns
  • With tight ADC cut and RF structure, use fits to extract matrix elements for flight path matrix (up to 2nd order corrections in x_{pf}, th_{pf})
  • Using RF structure, get fine bar offsets and time walk corrections

Gas Cerenkov

• Check stability of SPEs over run period (Chiranjib, 2009.03.06)

BigBite

General BigBite

• New BigBite class for Transversity experiment: THaBigBiteE06010 (Jin, 2009.03.04)

BigBite Shower/Preshower

• Shower sum #15 never reaches T1 trigger (was this fixed during d2n?) (Jin, 2009.03.04)
  • Can tell from lack of self-timing edge
• We want BB timing to be precise enough to identify beam bunches (Jin, 2009.04.09)
• Timing calibration done bar-by-bar (in comparison with neighbors) (Jin, 2009.04.09)
• Check ADC pedestal stability over time (Chiranjib, 2009.03.06)
• Radiation damage over time manifested as 5-15% gain drop (Chiranjib, Analysis Workshop)
  • Calibrate gain separately for several run periods

BigBite MWDC

• Xin found one cable mapping problem during a low-luminosity run -- do we have this fixed? (Xin, Analysis Workshop)
• Wires not always centered; cable lengths not always matched (Xin, Analysis Workshop)
• At "high" beam current (14 uA), we get lots of false tracks (Xin, Analysis Workshop)
  • Fix: additional cuts (optics, track quality, track-calorimeter match, PID, yield stability)
• MWDC sensitive to timewalk. T1, T6 times are very different. (Xin, 2009.03.06)
• MWDC calibration procedure (Xin, Analysis Workshop)
  • Chamber position, geometry, and cable mapping
  • Overall drift time calibration ($t_0$)
  • Conversion: Drift time $\rightarrow$ drift distance
  • Overall chamber position
  • t0 calibration: wire by wire
  • Position calibration: wire by wire
  • Iterate the wire-by-wire calibrations...

BigBite Tracking

• Don't use scintillators; about 10% of Transversity events fail to fire the scintillators (Jin, 2009.03.04)
• An error in trigger formation time leads to an error in electron drift time, which leads to an error in computed drift distance (Jin, 2009.03.04)
• Tracking inefficiencies (esp. from timing) may disproportionately affect some particle types (e.g. pions) (Jin, 2009.03.04)
• Additions to tracking software (Xin, Analysis Workshop)
  • New class: SpecialWirePlane for scintillator (not used in production?)
  • New method for converting drift time to drift distance: Pol2FitTTD
  • Road::CollectCoordinates(), Road::Fit() give slightly more tracks in exchange for slightly less speed

Triggers

• Since T3 arrives at the trigger supervisor before T5, it "steals" T5's timing. (Xin, 2009.03.06)
  • Can be corrected as a deadtime effect.
• Trigger timing can be checked via scintillator TOF (Jin, 2009.03.04)
• L1A problems caused difficulties with VDCs, other things (Chiranjib, Analysis Workshop)

Scalers

• Some gated scalers seemed to be unstable, or disagreed between LHRS and BigBite copies (Chiranjib, Analysis Workshop)
  • Fix: Ungated scalers were used in the analysis, and were gated in software during the skimming process.

Raw Asymmetries

• Basic cuts: (Jin, 2009.01.29)
  • beam trip
  • trigger type
  • vertex
  • quick PID
• Corrections to pairs (Jin, 2009.01.29)
  • angular reconstruction
  • polarization (target, beam)
  • dead-time

Skimmed Root Files

• Things removed by skimming process (Chiranjib, Analysis Workshop)
  • Beam trips
  • Chamber trips
  • Run periods with high deadtime
  • Run periods with trigger issues
• Things introduced by skimming process (Chiranjib, Analysis Workshop)
  • An "ss" scaler
  • Various kinematic variables computed offline
• Stages of the skimming process (Chiranjib, Analysis Workshop)
  • Shift scalers. Label beam trips.
  • Shift scalers. Label chamber trips, deadtime/trigger issues, etc.
  • Introduce kinematics variables, R-cut, BigBite acceptance cut.
  • Reduce root files to contain major variables (dramatic decrease in file size).

Data Quality Checks

• Stability check: Find mean/rms of some quantity during run, then plot this value run-by-run to check stability over experiment. (Chiranjib, Analysis Workshop)
  • Gas Cerenkov sum (after calibration, main peak was fitted with a Gaussian)
  • Aerogel A1 sum (after calibration, main peak was fitted with a Gaussian)
  • Pion peak in lead glass counters (after calibration, main peak was fitted with a Gaussian)
  • VDCs for T3, T5 after offset calibrations
  • Left S2m TDCs (right not considered, since self-timed)
  • Scalers: gated and ungated