1. Preliminary results on DT T0s in beam collisions J. Santaolalla, J. Alcaraz (+ help/suggestions from C. Battilana, C. Fouz)

2. 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

3. 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

4. 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

5. 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

6. Station by station Tmean – Tmean_avg (ns) MB1MB2 MB3MB4 12 Dec 2009 6

7. 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

8. 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

9. RESULTS THETA segments: same shift? Digi Time (ns) Tmean – Tmean_avg (ns) 12 Dec 2009 9

10. 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

11. 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

12. 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