1. Impact Parameter Resolution Measurements from 900 GeV LHC DATA Boris Mangano & Ryan Kelley (UCSD)

2. B.ManganoBTV POG meeting - 29/3/2010 Pag.2 Outline Samples and Event selection. Description of the method. Validation of the method on MC samples. Measurement of Transverse and Longitudinal Impact Parameter resolutions on 900 GeV DATA.

3. B.ManganoBTV POG meeting - 29/3/2010 Pag.3 Samples and Event Selection DATA: /MinimumBias/BeamCommissioning09-BSCNOBEAMHALO-Dec19thSkim_336p3_v1/RAW-RECO MC: /MinBias/Summer09-STARTUP3X_V8K_900GeV-v1/GEN-SIM-RECO Event Selection (see backup slides): - BSC trigger and BH Veto (already applied at the level of the central skim) - Tech.Trigger bit 0 - PhysicsDeclared bit - NoScrapingEvent filter - Only B=3.8 T runs - Only E=900 GeV runs

4. B.ManganoBTV POG meeting - 29/3/2010 Pag.4 Preliminary Remarks Different Components affecting the IP measurement Tk 1 is from decay-in-flight. Its d0 1, wrt the Primary Vertex, is genuinely ≠0. Tk 2 is a prompt track. Its d0 2 is exactly = 0. Tk 1 Tk 2 d0 1 PV Case 1) Exactly known trajectories and perfectly known collision point (SimTracks and SimVertex) Case 2) Exactly known trajectories, but measured collision point (SimTracks and reco PV) Both Tk 1 and Tk 2 have d0 different from their true values because of the “smearing” due to the vertex position resolution d0 = d0 true  “vertex smearing” Tk 1 Tk 2 true PV reco PV

5. B.ManganoBTV POG meeting - 29/3/2010 Pag.5 Preliminary Remarks Different Components affecting the IP measurement Case 3) Both trajectories and collision point are not exactly know because they are both measured = Real World Both Tk 1 and Tk 2 have d0 different from their true values because of the “smearing” due to the vertex position resolution and the smearing due to the finite resolution on the track parameters d0 meas = d0 true  “vertex smearing”  “track impact parameter resolution” Tk 1 Tk 2 reco PV reco Tk 1 reco Tk 2

6. B.ManganoBTV POG meeting - 29/3/2010 Pag.6 Preliminary Remarks Different Components affecting the IP measurement d0 meas = d0 true  “vertex smearing”  “track impact parameter resolution” The agreement between the resolutions of the primary vertex position measurements in DATA and MC has already been proved by Y.Gao, F.Fiori et al. https://twiki.cern.ch/twiki/bin/view/CMS/PrimaryVe rtexResolution In the rest of the talk, focusing on the effect of vertex resolution on the IP measurement: “vertex smearing” Final observable measured by this analysis

7. B.ManganoBTV POG meeting - 29/3/2010 Pag.7 Description of the method 1) Select only events with the primary vertex fitted from 10-16 tracks (see next). 2) For a given track with measurements on 8 Tracker layer (2 pixels), refit the primary vertex using all the other tracks in the event. 3) For the same track, evaluate d0 and dz w.r.t. the refitted vertex position. 4) Repeat 2-3 for all the other tracks in the event that pass the selection. 5) Save the previously evaluated d0 and dz values in bins of track’s p T and eta. 7) Repeat 2-5 for all the selected events.

8. B.ManganoBTV POG meeting - 29/3/2010 Pag.8 Description of the method (II) 8) Fit each p T and eta bin using the function F = VertexSmearingFunction  IP ResolutionFunction Measured d0 wrt recoPV [  m] Vertex “smearing” pdf [  m]Impact parameter resolution [  m] Measured from dataEstimated from MCExtracted from the Fit of the convolution function F

9. B.ManganoBTV POG meeting - 29/3/2010 Pag.9 The d0 and dz calculated in this way were put in separate histograms for distinct SimTrack’s p T and eta values. Vertex “smearing” pdf [  m] --- narrower gaussian --- wider gaussian --- 2 gaussian sum = VertexSmearing pdf --- narrower gaussian --- wider gaussian --- 2 gaussian sum = VertexSmearing pdf The d0 and dz of simulated SimTracks were evaluated with respect to the reconstructed PV position on the MC sample. Each bin is fitted by a 2-gaussian sum function. Tk 1 Tk 2 true PV reco PV Evaluation of the VertexSmearing function

10. B.ManganoBTV POG meeting - 29/3/2010 Pag.10 Evaluation of the VertexSmearing function Vertex smearing pdf  [  m] Vertex smearing for d0 as a function of the track’s p T Vertex smearing for d0 as a function of the track’s eta Vertex smearing for dz as a function of the track’s eta Track’s p T [GeV/c] Track’s eta Vertex smearing for dz as a function of the track’s p T

11. B.ManganoBTV POG meeting - 29/3/2010 Pag.11 Evaluation of the Impact Parameter Resolution Data are fit using the convolution function F, where only the parameters of the “IP ResolutionFunction” (a single gaussian) are unconstraint. Measured d0 wrt recoPV [  m] Vertex “smearing” pdf [  m] F = VertexSmearingFunction  IP ResolutionFunction The use of a single gaussian for modeling the resolution function is appropriate if: - The p T and eta of the tracks contributing to the same histogram are sufficiently “close”. - Only the core of the distribution is considered (2sigma fit)

12. B.ManganoBTV POG meeting - 29/3/2010 Pag.12 Validation of the method on MC Transverse Impact Parameter Resolution Additional Track cut: |eta| < 0.4 Additional Track cut: |eta| < 0.4 Good agreement between the “measured” resolutions (red) and the mc-truth-determined resolutions (black).

13. B.ManganoBTV POG meeting - 29/3/2010 Pag.13 Track selection: 0.75 < |p T | < 0.85 (GeV) Track selection: 0.75 < |p T | < 0.85 (GeV) Track selection: 1.0 < |p T | < 1.4 (GeV) Track selection: 1.0 < |p T | < 1.4 (GeV) Validation of the method on MC Transverse Impact Parameter Resolution

14. B.ManganoBTV POG meeting - 29/3/2010 Pag.14 Track selection: 0.75 < |p T | < 0.85 (GeV) Track selection: 0.75 < |p T | < 0.85 (GeV) Track selection: 1.0 < |p T | < 1.4 (GeV) Track selection: 1.0 < |p T | < 1.4 (GeV) Validation of the method on MC Longitudinal Impact Parameter Resolution

15. B.ManganoBTV POG meeting - 29/3/2010 Pag.15 Results from 900 GeV DATA Track cut: |eta| < 0.4 Track cut: |eta| < 0.4

16. B.ManganoBTV POG meeting - 29/3/2010 Pag.16 Results from 900 GeV DATA Track selection: 0.75 < |p T | < 0.85 (GeV) Track selection: 0.75 < |p T | < 0.85 (GeV) Track selection: 1.0 < |p T | < 1.4 (GeV) Track selection: 1.0 < |p T | < 1.4 (GeV)

17. B.ManganoBTV POG meeting - 29/3/2010 Pag.17 Results from 900 GeV DATA Track cut: |eta| < 0.4 Track cut: |eta| < 0.4

18. B.ManganoBTV POG meeting - 29/3/2010 Pag.18 Results from 900 GeV DATA Track selection: 0.75 < |p T | < 0.85 (GeV) Track selection: 0.75 < |p T | < 0.85 (GeV) Track selection: 1.0 < |p T | < 1.4 (GeV) Track selection: 1.0 < |p T | < 1.4 (GeV)

19. B.ManganoBTV POG meeting - 29/3/2010 Pag.19 Conclusions Method to estimate the Track Impact Parameter Resolution from DATA has been implemented and described in this talk. The Method has been successfully validated on MC and used on 900 GeV DATA from December 2009 runs. Results based on 900 GeV DATA are very close to values expected from STARTUP MC. Impact Parameter resolutions are just slightly worse. Overall, the analysis will benefit from higher LHC energy events for which there are more high p T tracks from the collision and the uncertainty on the primary vertex position is smaller. TWIKI page and Analysis Note in preparation: https://twiki.cern.ch/twiki/bin/viewauth/CMS/ImpactParameterResolutionDec2009

20. B.ManganoBTV POG meeting - 29/3/2010 Pag.20 BACKUP SLIDES

21. B.ManganoBTV POG meeting - 29/3/2010 Pag.21 Event Selection for DATA (and that you don’t usually apply on a MC sample) 1)Require Tech.Trigger bit 0 (i.e. BPTX coincidence): it selects events in beam-beam bunch crossings. Discards single-beam BXs and empty BXs. 2)Require Tech.Trigger bit 40 or 41 (i.e. BSC triggers): selects events with activity compatible with a collision 3)Veto on Tech.Trigger bit 36-39 (BeamHalo triggers)

22. B.ManganoBTV POG meeting - 29/3/2010 Pag.22 Event Selection for DATA (II) (and that you don’t usually apply on a MC sample) 4)Discard events for which B!=3.8, e.g. events collected during the magnet ramping to its nominal value. 4’)For this study only, discard events from 2.36 TeV runs Discarded runs: 123967-123997, 124119,124120,124275 5)Require PhysicsDeclared bit: this bit is set to TRUE when all the CMS components are declared OK for data taking: e.g. all the HighVoltages of the Tracker sensors are ON.

23. B.ManganoBTV POG meeting - 29/3/2010 Pag.23 Event Selection for DATA (III) (and that you don’t usually apply on a MC sample) 6)Reject beam-background events (AKA pixel monster events, AKA scraping event). The NoScraping event filter has been used: it requires >25% of tracks in the event to be “highPurity” tracks.

24. B.ManganoBTV POG meeting - 29/3/2010 Pag.24 Track selection: |eta| < 0.4 Track selection: |eta| < 0.4 Validation of the method on MC Longitudinal Impact Parameter Resolution Some bins looks problematic

25. B.ManganoBTV POG meeting - 29/3/2010 Pag.25 Validation of the method on MC Longitudinal Impact Parameter Resolution After smoothing of the response function, the final fit is more stable There are less “problematic” bins

26. B.ManganoBTV POG meeting - 29/3/2010 Pag.26 Effect of the resolution on the Primary Vertex position 1) Are the reconstructed primary vertices of the MC (used to estimate the response function) consistent with DATA? From Y.Gao: https://twiki.cern.ch/twiki/bin/view/CMS/PrimaryV ertexResolution 2) Anyway, how much the Impact Parameter Resolution measurement is sensitive to the vertex smearing? See next slides..