Effect of v drift tuning on reconstruction

Effect of vdrift tuning on reconstruction

Filippo Pisano, Marco Terranova, N. Amapane, G. Cerminara

Filippo Pisano Sep 28, 2010 2

Introduction

• Goal: Test the effect of vd correction on reconstruction

– At the moment, vd = 54.3 m/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 “t0seg” and vd/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


Sample and Event Selection

• Sample used: /MuOnia/Run2010A-CS_Onia-v6/RAW-RECO– Central skim of global/tracker di-muons with M > 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:– ||<25 deg– at least 7 phi hits and 4theta hits


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

• vd/vd distribution is large

– Still, we try to use average value for correction

CMSSW Default:t0seg fit with fixed vd = 54.3 m/ns

t0seg (ns) E

xam

ple

: W

0, M

B1,

all

sect

ors

t0seg = – 0.2 ns

With vd fit activated: both t0seg and vd/vd computed:

vd/vd

W0,

MB

1, a

ll se

cto

rs

<vd/vd> = –1.7%

t0seg (ns)

t0seg = 1.5 ns


• 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

Current DB value: 54.3 m/ns

v d (

m/n

s)

MB1 MB2 MB3 MB4

+ Data– Data (merged sectors)– MC 3.8.2 (Z→)

MC DB only:52.3 m/ns in W+-2 MB1

Result: Measured vd


Re-Reconstruction: Closure Test

• Re-reconstruct segment with correction for both < vd/vd> and < t0

seg>, for each chamber

• Algorithm converges: negligible residual corrections – Example: W0 MB1

Exa

mp

le:

W0,

MB

1, a

ll se

cto

rs

t0seg = – 0.48 ns

<vd/vd> = –0.05%


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…

= 285 mCMSSW 3.8.2 default

Corrected vd = 276 m


• Very small change (as expected) – No side effect observed – track reconstruction is not broken!– Tested on MC as well

Effect on Track Fit

2/DOF 2/DOF

#DT hits in STA fit#DT hits in global fit

Global muons with ||<1.2, pT>10 GeV

Global Standalone

Global Standalone

– Current vd

– Corrected vd


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

Effect of v drift tuning on reconstruction

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