Performance of the b-tagging algorithms with an upgraded CMS detector
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Performance of the b-tagging algorithms with an upgraded CMS detector Eric Brownson Vanderbilt University (For the CMS Collaboration) DPF-APS Meeting, Aug. 9, 2011 Brown University, Providence, Rhode Island. Phase1 Tracker Upgrade.

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Performance of the b-tagging algorithms with an upgraded CMS detector

Eric Brownson

Vanderbilt University

(For the CMS Collaboration)

DPF-APS Meeting, Aug. 9, 2011

Brown University, Providence, Rhode Island

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Phase1 tracker upgrade
Phase1 Tracker Upgrade detector

4th Barrel layer, 3rd Forward disk, Altered cooling & electronics …

  • Restore current performance in PileUp scenarios above design luminosity

  • Redundancy to compensate for data loss

  • Take advantage of any other changes

    • Smaller beam pipe

      Must be backed up by studies

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


3 rd disk 4 th layer
3 detectorrd Disk & 4th Layer

Different shape to the disks

  • Larger coverage in h

    Different spacing between the Barrel layers

  • Closer to IP & TIB

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Material budget
Material Budget detector

Barrel + Forward

Forward only

More sensors in more layers

  • In general move material out and away from IP

  • CO2 cooling

  • Lower the material budget

    Less interaction with the pixel tracker

Current Geometry

Phase1 Geometry

Current Geometry

Phase1 Geometry

Rad length

Rad length

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


B tagging

B detectorDecay Products

Flight Length ~ few mm

Collision

Decay Vertex

Impact Parameter

b-tagging

Exploit the properties of b hadrons to distinguish b-jets from light (u,d,s,g) jets:

  • Large lifetime ~1.5 ps (large decay length: 20 GeV B-hadron decays after ~2 mm)

    • Search for tracks or vertexes displaced w.r.t. primary vertex

  • Large mass ~5 GeV

    • Search for leptons, from semileptonic b decays, with large transverse momentum w.r.t. jet axis

      Good tracking & Vertex reconstruction are needed

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


B tagging algorithm
b-tagging algorithm detector

  • Find jets in the Ecal & Hcal

  • Find High Quality Tracks with the Tracker

    • Calculate ImpactParameter

  • Match the Tracks to the jets

  • Build the discriminator

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Track finding at high pileup
Track Finding at High PileUp detector

High Luminosity  Read out inefficiencies & Fake Tracks

ttbar events at 2x1034cm-2s-1,

<PU>=50 @ 25ns

High quality tracks similar to the requirements that are used in b-tagging

http://home.fnal.gov/~cheung/tmp/plots4tp/TP_buildingPU50_btagtracks

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Vertexing
Vertexing detector

Longitudinal Impact Parameter for all vertices

  • Improve with higher PT

  • Does best in central h regions

  • Phase1 Tracker provides improvement in vertexing

    Same story for the Transverse Impact Parameter…

m–gun Sample

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Vertexing1
Vertexing detector

Transverse Impact Parameter for all Vertices

  • Slight improvement on Longitudinal

  • Phase1 provides most improvement for lower PT tracks

    The secondary vertices, together with other lifetime

    information obtained from the tracks you get …

m–gun Sample

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


B tagging1
b-tagging detector

  • CombinedSecondaryVertex tagger

  • Without PileUp the Phase1 tracker only provides gains w.r.t. the Current tracker

  • At 2E34 cm-2s-1 (2x Design Luminosity) the Phase1 shows some improvement on the Current tracker

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Restore tracking at high pu
Restore Tracking at High PU detector

High quality tracks similar to the requirements that are used in b-tagging

ttbar events at

PileUp=0 for Current Geometry &

2x1034cm-2s-1 for Phase1 Tracker

Restore current tracking ability

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Restore b tagging at high pu
Restore b-Tagging at High PU detector

Restore current performance at twice the design luminosity scenarios

Open 

PileUp=0 for Current Geometry

Filled

2x1034cm-2s-1 for Phase1 Tracker

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Conclusions
Conclusions detector

  • 2x design luminosity provides challenges for tracking

    • Increased fake track rates

    • Increased data loss

    • Reduced b-tagging

  • Plans are underway to compensate & restore our current level of performance

    • 4th Pixel Barrel Layer & 3rd Pixel Disk

      • Redundancy

    • Pixels both closer to and further from IP

      • Information from closer to IP & longer lever arms for fitting

    • Minimize material budget

      • Move as much as possible away from IP

    • More is under study

      • Better understand data loss, alter size & placement of pixels, develop algorithms for high PU and more…

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Backup Slides detector

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Reconstructed hits in the Phase1 Pixel Detector detector

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Current: Phase1 Tracker:

Half disk consists of one inner blade assembly and one outer blade assembly and they are assembled next to each other

View of the current Forward Pixel detector

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Data losses as a function of the L1 accept rate of the innermost layer of the current pixel detector. The instantaneous luminosity is 1E34 cm-2s -1 and the bunch spacing is 25 ns. CMS has been designed for maximum average L1 trigger rates of 100 kHz. The data points beyond this rate in the plot simply illustrate the linear nature of this data loss at this particular instantaneous luminosity with the PSI46v2 readout chip.

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Hit position resolution (RMS) as function of the track pseudorapidity for an unirradiated (blue lines) and irradiated detectors (red and green lines). Longitudinal (a) and transverse hit resolution (b) are shown separately. The solid lines correspond to hits with total charge Q below the average charge. Dashed lines correspond to hits with total charge 1 < Q/Qavg < 1.5.

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Effect of a 20% loss in efficiency of the TIB. The efficiency loss in track reconstruction is shown in (a) and (b) for low luminosities and 1E34 cm-2s-1. In (c) and (d), the ratios of efficiencies are shown. For the higher luminosities, this 20% loss in TIB efficiency would result in an overall relative reduction of 5% in the barrel region of the upgraded detector, but a 13% reduction in the current detector.

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


Vertex reconstruction
Vertex Reconstruction efficiency loss in track reconstruction is shown in (a) and (b) for low luminosities and 1E34 cm

  • 1.0 ± 0.1 GeV/c (circles), 3.0 ± 0.2 GeV/c (squares) & 8.0 ± 1.0 GeV/c (triangles)

  • Filled and open symbols correspond to results from data and simulation

  • CMS PAS TRK 10-005

Meeting of the Division of Particles & Fields of APS, Aug 9, 2011


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