Preliminary results on DT T0s in beam collisions

J. Santaolalla, J. Alcaraz

(+ help/suggestions from

C. Battilana, C. Fouz)

MOTIVATION

• Check/study DT timing with muons from collisions.

STRATEGY• Even if statistics will be poor, try to select a

rather pure sample, with minimal contamination from cosmics.

• Many of the ‘muons’ could be really punch-through (pions), MB1 dominated, but provided they are ‘in time’, it is OK.

12 Dec 2009 2

PROCEDURE• INPUT SAMPLE:

– /MinimumBias/BeamCommissioning09-SD_InterestingEvents-PromptSkimCommissioning_v2/RAW-RECO

• SAMPLE SELECTION:– HLT bits: "HLT_MinBiasBSC_OR” | "HLT_L1Mu” |

"HLT_L1MuOpen" (not critical)– At least 3 tracks in inner tracker with pt>0.5 GeV, impact

parameter<0.5 cm, and at least 1 valid hit in the pixel detector (good events+well in time)

• FOR THE SURVIVING SAMPLE:– Compute Meantimers, tboxes, …, to check DT timing.

12 Dec 2009 3

PROCEDURE

• We look for segments attached to StandAlone muons:– All segments having at least one hit attached

to the stand-alone muon are considered.– All hits in those segments are used (wether or

not they are actually included or used in fit).

• Some of the stand-alone muons have just one ‘station’ (stand-alone muon consider at least ‘two’, but the DT+RPC combination in one station counts as ‘two’)

12 Dec 2009 4

RESULTS• PHI segments (Tmean_avg = 21000 [m]/54.5[m/ns])• T0 used: exactly the same used in current reconstruction• All hits in plot (MB1+MB2+B3+MB4). Dominated by MB1. Chamber to

chamber things seem to change by <~10 ns (low statistics).• Tmean points to a 15+-6 ns global ‘T0’ shift’• It does not seem to be a wrong vDrift, according to Tbox.

Tmean – Tmean_avg (ns) Digi Time (ns)12 Dec 2009 5

expected width from intrinsic resolution ~ 6-7 ns

Station by station

Tmean – Tmean_avg (ns) Tmean – Tmean_avg (ns)

Tmean – Tmean_avg (ns) Tmean – Tmean_avg (ns)

MB1 MB2

MB3 MB4

12 Dec 2009 6

RESULTS using t0 from segment fit.

• PHI segments• segment->t0()~10 ns• 5 ns difference with respect MeanTimer estimate

• Difference wire propagation correction, … ?

Tmean – Tmean_avg (ns) Digi Time (ns)

After ev-by-ev t0 correction

12 Dec 2009 7

RESULTS using t0 from segment fit

• PHI segments: good correlation between meantimer and segment->t0() hit by hit

Tmean – Tmean_avg

T0

cor

Tmean – Tmean_avg (ns)

12 Dec 2009 8

RESULTS

• THETA segments: same shift?

Digi Time (ns)Tmean – Tmean_avg (ns)

12 Dec 2009 9

RESULTS using t0 from segment fit

• THETA segments

Digi Time (ns)Tmean – Tmean_avg (ns)

After ev-by-ev t0 correction

12 Dec 2009 10

Conclusions (preliminary)

• There seems to be a global T0 shift of 15+- 6 ns everywhere (with respect to ‘standard current’ reconstruction code).

• T0 determined by optimal segment fit gives a T0 shift of order 10 ns.

• Both Phi and Theta seem to ‘like’ this shift.• Remaining (systematic) T0 shifts from chamber to

chamber seem to be of order ~ 4-5 ns (systematic, i.e. on top of intrinsic statistical accuracy).

• T0 determined 12 Dec 2009 11

TO DO

• Look at things in more detail (what it is shown, it was done yesterday).

• Understand some ‘features’:– 5 ns difference between ‘meantimer shift’ and

“results from t0 segment fit”.– Some strange concentrations around t=350

ns in phi timebox plot, …

• Try to still increase statistics as much as possible.

12 Dec 2009 12