Monitoring SCT Efficiency and Noise SCT Monitoring Meeting 1st July 2008 Richard Batley (Cambridge) SCT efficiency : do we really need all those Tools ? SCT noise : can it really be measured with SpacePoints ? compare measured and true efficiency and noise in MC

SCT Hit Efficiency Algorithm For every SCT hit fitted to a reconstructed track : extrapolate track fit to opposite side of module (using simple intersection of a straight line with a plane) look for nearest cluster (if any) to extrapolated point declare opposite side to be “inefficient” if no cluster found within 1mm in local-x Note : no extrapolator tools, no track refitting, no HoleSearch the nearest opposite-side cluster will usually already be included in the track fit

Testing the efficiency algorithm Use single-muon and multihadron (ZZ→ttmm) MC : simulated with 13.0.10 (m) and 12.0.X (ZZ) digitised and reconstructed with 14.2.0 (SCT_Digitization-00-09-32-06) study SCT barrel only for now True MC inefficiency : default SCT digitisation has strip-level inefficiency of 1% (1% of strips above threshold are randomly rejected) cluster-level inefficiency may be different (due to multi-strip clusters, secondary particles, …) define “true inefficiency” as no cluster within 1mm of true track position

Distance to nearest cluster on opposite side In ZZ events : o/flow includes case where there is no cluster at all on the other side

Extrapolated track position for inefficient hits (no cluster on opposite side of module within 1mm of extrapolated track) (N.B. without track fit info, this could look like same-side noise)

Distance to nearest cluster on opposite side Require track extrap to be away from edges and bond-gap : o/flow includes case where there is no cluster at all on the other side

Measured and true inefficiencies: single muons SCT barrel (all track extrapolations) (track extrap within active region) (true inefficiency) measured efficiency consistent with true value

Measured and true inefficiencies: ZZ events SCT barrel (track extrap within active region) (true inefficiency, from single-m events) measured efficiency consistent with true value

Monitoring SCT Noise via Spacepoints SpacePoint algorithm (in SCT_Monitoring package) : estimates noise from rate of clusters not in SP’s doesn’t need reconstructed tracks etc. (just data from each SCT module alone) (aims to give approx. noise for monitoring purposes, not final best noise value) Study using single-m and ZZ→ttmm MC : compare SP estimate with true noise cluster rate true noise cluster : no contribution from any true particle in any strip of cluster default noise rate per strip in MC is only ~ 5 x 10-6 (same for all module types) (harder to measure noise in MC than in real data)

Width-improved Spacepoint algorithm Find SP alg doesn’t work for multihadron events : try to improve using cluster width information (nstrip >= 2 is a good signal for a track-induced, non-noise cluster) N.B. “noise” means random, uncorrelated, single-strip noise Combine width and SP info : extrapolate into nstrip = 1: normalise to nstrip = 2 : count nstrip = 1and nstrip = 2 clusters in and out of SP’s

Cluster and noise rates: single m events all clusters SP noise alg true noise clusters width-improved short middle barrel outer middle inner SP noise alg gives reasonable estimate of true noise Improved by width info for barrel

Cluster and noise rates: ZZ events all clusters SP noise alg true noise clusters width-improved short middle barrel outer middle inner

Cluster and noise rates: ZZ events Same plot as previous slide, with expanded vertical scale : SP noise alg barrel true noise clusters width-improved SP noise alg overestimates noise by large factor Width-improved SP alg gives big improvement in barrel

Summary SCT hit efficiency : can be reliably determined using a simple straight-line extrapolation to opposite side of module SCT noise : SP alg badly overestimates noise in busy events much improved (in barrel) using cluster width info

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