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Tomas Hreus, Pascal Vanlaer Study of Strangeness Production in Underlying Event at 7 TeV 1QCD low pT meeting, 18/03/2011.

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Presentation on theme: "Tomas Hreus, Pascal Vanlaer Study of Strangeness Production in Underlying Event at 7 TeV 1QCD low pT meeting, 18/03/2011."— Presentation transcript:

1 Tomas Hreus, Pascal Vanlaer Study of Strangeness Production in Underlying Event at 7 TeV 1QCD low pT meeting, 18/03/2011

2 Event & Track-Jet Selection: - meant to be identical to UE QCD-10-010 analysis Trigger: HLT_MinBiasPixel_SingleTrack BSC Primary vertex: single single vertex (offlinePrimaryVertices) valid vertex (not fake, different from beam spot) dZ(vtx, beamspot) < 10cm ndof > 4 Leading Track-jet: tracks with pT > 0.5 GeV, |eta|<2.5 V0 Selection (K0s,  bar): |  daughters| < 2.5 |  V0| < 2.0 pT_K0s > 0.5 GeV ; pT_  bar > 1.0 GeV Transverse flight distance > 1 cm + kinematic fit 2 Data Sample and Selection Data Sample: /MinimumBias/Commissioning10- Jun14thReReco_v1/RECO Runs: 132440-137436 + JSON file (CMSSW_3_6_1_patch4) 60 o 120 o 0o0o QCD low pT meeting, 18/03/2011

3 3 Kinematic Fit: Principle V0s selected based on the chi2 probability of the kinematic fit. Kinematic fit: minimization of the   function with kinematic constraints: 3 constraints: -vertexing (daughter tracks cross secondary vertex) -fixed V0 mass to V0 PDG value -pointing (V0 point to primary vertex) Fitting 9 measured parameters:  = q / pt,  of two daughter tracks, sec. vertex (x,y,z), considering full 9x9 covariance matrix of measured parameters K0s mass [GeV]  mass [GeV] Talks on the fit presented at tracking PDG/POG and Alignment meetings K0s mass  mass https://indico.cern.ch/getFile.py/access?contr ibId=3&sessionId=2&resId=0&materialId=slide s&confId=82610 https://indico.cern.ch/getFile.py/access?contr ibId=4&sessionId=2&resId=0&materialId=slide s&confId=82616 https://indico.cern.ch/getFile.py/access?contr ibId=15&sessionId=1&resId=0&materialId=slid es&confId=120130 QCD low pT meeting, 18/03/2011

4 Cut:   probability > 0.05 Background to V0 sample estimated from MC: Background for K0s = 2.23 +- 0.02% Background for  = 6.64 +- 0.12% Background for  bar = 7.45 +- 0.14% Primary-matched within R  < 0.04 4 Kinematic Fit: Chi2 Probability & Background  K0s  bar   prob matched to primary not matched to primary

5 5 V0 Correction V0 Correction = 1 / ( acceptance x efficiency ) acceptance is restricted to kinematic range of sufficient V0 selection efficiency - small systematics expected efficiency is estimated with detailed MC MC Sample: /MinBias_TuneD6T_7TeV-pythia6/Summer10-START36_V10_SP10-v1/GEN-SIM-RECODEBUG (CMSSW_3_6_2) QCD low pT meeting, 18/03/2011

6 Acceptance definition: N_acc / N_gen N_gen = K0s generated inside: pT > 0.5 GeV |  | < 2.0 6 K0s Correction: Acceptance N_acc = fraction of N_gen which passed the acceptance cuts: pT_daughters > 0.3 GeV |  daughters| < 2.5 gen transv. flight dist. > 1 cm K0s  K0s pT [GeV] QCD low pT meeting, 18/03/2011

7 Efficiency definition: N_rec / N_acc N_rec = K0s passed all reco cuts: |  daughters| < 2.5 pT_daughters > 0.3 GeV |  K0| < 2.0 pT_K0s > 0.5 GeV Transverse flight distance > 1 cm 7 K0s Correction: Efficiency K0s  K0s pT [GeV] Efficiency is relatively high MC is describing efficiency correctly  lifetime test https://indico.cern.ch/getFile.py/access?contribId=0&resId =0&materialId=slides&confId=115969 (QCD meeting)  small systematic uncertainties expected on the rates.

8 8 V0 Correction: Acc x Eff  pT [GeV] Acc x Eff = 1/weight  pT [GeV]  K0s   bar

9 9 Cross-check: uncorr./corrected rates Shapes normalised to 1 Observed trend is not a feature of the correction QCD low pT meeting, 18/03/2011

10 10 1/  dN/d  QCD low pT meeting, 18/03/2011

11 11 Rates QCD low pT meeting, 18/03/2011

12 12 Scalar pT Sum QCD low pT meeting, 18/03/2011

13 13 Conclusion & Plans -very first look on the rates of the strange particles (K0s,  bar) in the underlying event -using kinematic fit to select relatively clean V0 sample -Similar trend with track-jet pT as for primary charged particles Plans -produce rates corrected for background -evaluate systematic uncertainties -V0 selection efficiency -V0 acceptance (different PYTHIA tunes) -background subtraction -trigger and event selection QCD low pT meeting, 18/03/2011

14 Backup Slides QCD low pT meeting, 18/03/201114

15 15 Cross-check: uncorr./corrected rates Leading-jet Shapes normalised to 1 Observed trend is not a feature of the correction QCD low pT meeting, 18/03/2011

16 16 pT Spectra (shape comparison) QCD low pT meeting, 18/03/2011

17 17 Rates More V0 activity in the toward region QCD low pT meeting, 18/03/2011

18 18 Scalar pT Sum QCD low pT meeting, 18/03/2011

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