Effect of v drift tuning on reconstruction

1. Effect of vdrift tuning on reconstruction Filippo Pisano, Marco Terranova, N. Amapane, G. Cerminara

2. Introduction • Goal: Test the effect of vd correction on reconstruction • At the moment, vd = 54.3 mm/ns for all chambers/SL • Study vd on collision data in the different chambers • How much we gain in correcting for the average vd in each chamber? • We get vd from the 4-parameter segment fit by Anna M. • Fits “Dt0seg” and Dvd/vd together with segment parameters • Possible only for phi segments (>5 hits needed) • Standard CMSSW code • Card: performT0_vdriftSegCorrection = cms.bool(True) • Re-reco using corrected <vd> for each chamber • No attempt to look at e.g. the Z-dependence of vd in the chamber: such a dependence is not supported the present vdrift DB

3. Sample and Event Selection • Sample used: /MuOnia/Run2010A-CS_Onia-v6/RAW-RECO • Central skim of global/tracker di-muons with Mmm > 2 GeV • Includes RAW (necessary for re-reco) • Additional filters: good vertex, noscraping Note: New skim of golden Z + W candiates with RAW recently requested. Will be the ideal sample for this kind of studies. • Consider only events with one GlobalMuon or TrackerMuon with pT>5 GeV • Use only 4D segments with: • |f |<25 deg • at least 7 phi hits and 4theta hits

4. With vd fit activated: both t0seg and Dvd/vd computed: CMSSW Default: t0seg fit with fixed vd = 54.3 mm/ns Example: W0, MB1, all sectors Dt0seg = 1.5 ns Dt0seg = – 0.2 ns W0, MB1, all sectors Dt0seg (ns) Dt0seg (ns) <Dvd/vd> = –1.7% Dvd/vd 4-Parameter fit (Anna M.) • When we activate the computation of vd: • t0seg peak is shifted (as expected) • Vd and ttrig must be corrected together to keep residuals centered at 0 • Dvd/vd distribution is large • Still, we try to use average value for correction

5. + Data – Data (merged sectors) – MC 3.8.2 (Z→mm) vd (mm/ns) MB1 MB2 MB3 MB4 Current DB value: 54.3 mm/ns MC DB only: 52.3 mm/ns in W+-2 MB1 Result: Measured vd • Generally ~1.8% higher than the current DB value • Lower vd in MB1 W+– 2, as already observed in CRAFT • Nicely Z-symmetric. • Same code gives lower value on MC - but same behavior • Spread among sectors is small • Use the value obtained merging sectors in the following

6. Dt0seg = – 0.48 ns Example: W0, MB1, all sectors <Dvd/vd> = –0.05% Re-Reconstruction: Closure Test • Re-reconstruct segment with correction for both < Dvd/vd> and < Dt0seg>, for each chamber • Algorithm converges: negligible residual corrections • Example: W0 MB1

7. Improvement in Residuals (e.g.: W0 MB1) • Some improvement in residual widths (just one example here) • Flatter dependence vs distance from wire • Although the correction is modest if compared with non-linearity in the wire region… s = 285 mm CMSSW 3.8.2 default Corrected vd s = 276 mm

8. Effect on Track Fit Global muons with |h|<1.2, pT>10 GeV Global Standalone • Very small change (as expected) • No side effect observed – track reconstruction is not broken! • Tested on MC as well – Current vd – Corrected vd c2/DOF c2/DOF Global Standalone #DT hits in global fit #DT hits in STA fit

9. Conclusions • The 4-parameter fit seems to compute reliable vd values • Correction improves reconstruction quantities, although modestly • Resulting drift velocities are larger than the present DB value • Outlook: • Compare with vd from meantimer method • cf Silvia’s presentation in the Calibration session • MTs will have to be used for theta SLs • Look at of Z- and segment angle dependence • No mechanism is available to specify such dependencies in the vdrift DB • The ultimate resolution may be limited by non-linearities more than by the accuracy of the average vd determination • Tune the cell parametrization in the simulation with a scale factor to correct for the difference between vd in data and MC • Same for the parametrization available in reconstruction