1 / 50

Minimum bias studies etc….

Minimum bias studies etc…. Craig Buttar University of Glasgow. Outline. LHC start up Minimum bias events Why study them? What are they? Triggering minimum bias Minimum bias trigger scintilators (MBTS) Random trigger and track trigger Tracking Reconstructing low p T tracks

michi
Download Presentation

Minimum bias studies etc….

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Minimum bias studies etc…. Craig Buttar University of Glasgow Cosners House Forum on LHC startup April 07

  2. Outline • LHC start up • Minimum bias events • Why study them? • What are they? • Triggering minimum bias • Minimum bias trigger scintilators (MBTS) • Random trigger and track trigger • Tracking • Reconstructing low pT tracks • Vertex reconstruction • Using pixel tracklets • Underlying event • What is it and why measure it • Measurement with ATLAS • Summary Cosners House Forum on LHC startup April 07

  3. LHC Pilot run: 2007 Events/xing <<1 At L=1029, can get ~10M MB events in 1 day with 30% eff S. Myers Cosners House Forum on LHC startup April 07

  4. Possible Beam Parameter Evolution at 7TeV/beam S. Myers Cosners House Forum on LHC startup April 07

  5. Why measure min bias? Not exactly what the LHC was built for! But….. • Physics: measure dN/dh|h=0 • Compare to NSD data from SppS and Tevatron • MB samples for pile-up studies • Calorimeter • Physics analyses • Benchmark for sLHC • Overlap with underlying events • analyses eg VBF, Jets… • Demonstrate that ATLAS is operational • Inter-calibration of detector elements • Uniform events • Alignment • Baseline for heavy ions Cosners House Forum on LHC startup April 07

  6. What are minimum bias events? inelastic events Trigger bias: Typically select non-single diffractive (NSD) events Cosners House Forum on LHC startup April 07

  7. What are minimum bias events? • Minimum bias are inelastic collisions of two protons • Includes very rare high-pt scatters and very common low-pt scatters • Minimum bias is an experimental definition • Defined by experimental trigger and analysis • Relation between experiment and physics is: fi are acceptances for different physics processes determined by the trigger Cosners House Forum on LHC startup April 07

  8. Event characteristics • Event characteristics • Non-single diffractive~non-diffractive inelastic • Soft tracks pTpeak~250MeV • Approx flat distribution in h to |h|~3 and in f • Nch~30; |h|<2.5 • Trigger rates • s~70mb (NSD!) • R~700kHz @ L=1031cm-2s-1 M. Leyton Cosners House Forum on LHC startup April 07

  9. Triggering minimum bias • Use forward scintillators (MBTS) • Random trigger • inefficient where there are <<1 events/xing • Validate at L2/EF to reduce inefficiency • Other triggers: jet, lepton triggers • High pt thresholds  bias Cosners House Forum on LHC startup April 07

  10. η=2.0 interaction point η=3.8 +η pannel Beam-pipe MBTS MBTS • Trigger scintillation counters mounted on end of LAr calorimeter covering same radii as ID UA5 • To compare to UA5 and CDF data need to understand composition of the sample  trigger bias • Currently generate inelastic and diffractive parts using PYTHIA • Need to investigate other simulations-PHOJET Cosners House Forum on LHC startup April 07

  11. Noise and Accidental Suppression – Lab tests Eric Feng • Noise spectrum fits well to a Gaussian with σ=2.52pC • Beyond 9pC (almost 4σ), non-Gaussian behavior is possible Accidental rate must be suppressed to ~Hz, limited by EF output-rate of 100Hz suppression required of  10-6-10-7 at 900GeV and 14TeV Cosners House Forum on LHC startup April 07

  12. Trigger Efficiencies and Bias • Shown below for each coincidence logic:- Required counter threshold to suppress accidental rate to 1Hz- Corresponding trigger efficiency for each type of event Eric Feng Cosners House Forum on LHC startup April 07

  13. Track Trigger 13 MHz eventrate random trigger 1 kHz eventrate L2 track trigger to validate random trigger when <<1 events/xing LVL 1 pass-through LVL 2 reduction by a factor 10 Event-Filter 100 Hz eventrate R. Kwee storage Cosners House Forum on LHC startup April 07

  14. Selecting MinBias Events • At L2 can use • no. of spacepoints from pixel and SCT  little bias • no. of reconstructed tracks, needed to reject beamgas, halos  pt-track > ~1GeV  biased • Rejection of empty events, compare to cosmic runs noise spacepoints from ¼ sct-barrel from cosmics data simulation of noise in whole SCT <sct-spacepoints>=0 <sct-spacepoints>=3 R. Kwee Cosners House Forum on LHC startup April 07

  15. Rejecting beam-gas Diffractive Beamgas To reject beam gas  need track reconstruction R. Kwee Cosners House Forum on LHC startup April 07

  16. CMS MB trigger: Trigger Towers • Use Forward HCAL • Towers: N vs P • Strongly correlated • Trigger should cut on nTowers hit on “N” side and “P” side • e.g. N>10 and P>10 ORCA Simulation Cosners House Forum on LHC startup April 07

  17. Tracking in MB events 1000 events dNch/d • Acceptance limited in rapidity and pt • Rapidity coverage • Tracking covers |h|<2.5 • pT problem • Need to extrapolate by ~x2 • Need to understand low pt charge track reconstruction h Black = Generated (Pythia6.2) Blue = TrkTrack: iPatRec Red = TrkTrack: xKalman dNch/dpT Reconstruct tracks with: 1) pT>500MeV 2) |d0| < 1mm 3) # B-layer hits >= 1 4) # precision hits >= 8 Cosners House Forum on LHC startup April 07 pT (MeV)

  18. Where is the Momentum Limit ? 50MeV • Tracker is in principle sensitive to soft tracks • Pt = 400 MeV - tracks reach end of TRT • Pt = 150 MeV - tracks reach last SCT layer • Pt = 50 MeV - tracks reach all Pixel layers A.Salzburger 400MeV 150MeV Cosners House Forum on LHC startup April 07

  19. Track reconstruction efficiencies • MC/Track cuts: • η < 2.5, z0 < 150 mm, d0 < 1 mm • Efficiency: fraction of MC tracks with > 50% matched hits Tracking efficiency >20-50% for pt>200MeV Pt=200MeV pT (MeV) M.Leyton Cosners House Forum on LHC startup April 07

  20. Track Reconstruction efficiencies by track insertion Dan Clemens efficiency by track insertion reconstruction with New Tracking • Insert a track into a minimum bias event by overlapping a simulated single track event. • Reconstruct merged event and look for inserted single track to determine efficiency. Plot by M.Leyton for comparison : truth matched Cosners House Forum on LHC startup April 07

  21. I. Dawson, K. Prokofiev X Vertex Residuasl Track multiplicity Minbias Vertex Reconstruction • How well can we reconstruct primary vertex position of a minbias event? • A good vertex reconstruction efficiency in multi-pp bunch crossings may allow measurement of σNSD. • Knowledge of primary vertex position can improve signal to noise, eg, H →γγ (UE to Higgs similar to MB) • Use VxBilloirTools package to fit vertex to minbias tracks. • Shown here are residuals (difference between reconstructed and truth) Typically ~250μm precision Cosners House Forum on LHC startup April 07

  22. η Each hit assigned η,Φ relative to primary vertex Φ Calculate Δη,ΔΦ for each pair Hits in Layer 1 “Tracklet” defined (now) as Δη<0.01,ΔΦ<0.15 Hits in B-layer Primary vertex(standard tracking) Peter Steinberg, BNL Tracklet Method Exploring methods with sensitivity at lower pT with even fewer pixel-hits Cosners House Forum on LHC startup April 07

  23. Φ η Peter Steinberg, BNL Single Event Hits in B-layer and L1. Black circles are Truth-primary charged hadrons. Clustered pairs of hits visible near truth hadrons. Cosners House Forum on LHC startup April 07

  24. Peter Steinberg, BNL “Momentum Reconstruction” pT = 0.011/ΔΦ → Poor person’s tracking code. spatial resolution kicks in above ~2 GeV Cosners House Forum on LHC startup April 07

  25. Peter Steinberg, BNL Momentum reconstruction Charged primary hadrons Reconstructed at low pT (down to 100 MeV) the recontructed and truth pT match well, at higher pT reconstruction gets distorted Cosners House Forum on LHC startup April 07

  26. Peter Steinberg, BNL Inclusive dNch/dη Charged primary hadrons Reconstructed Focus on |η|<1, look at multiplicity distributions linear response,good resolution Current parameters good for η~0, large backgrounds at |η|~2 Cosners House Forum on LHC startup April 07

  27. CMS Tracking Similar to ATLAS pixel tracklets Cosners House Forum on LHC startup April 07

  28. What is the underlying event • Hard and soft physics • ISR • beam remnants • central particle production • colour flow/string drawing High PT scatter Beam remnants ISR Cosners House Forum on LHC startup April 07

  29. Tagging jet W Z/W H Z/W W Tagging jet VBF Signal (HWWll) • forward tagging jets • correlated isolated leptons • low hadronic activity in central region • central Higgs production Important discovery channel For Higgs in mass range 120-200GeV Cosners House Forum on LHC startup April 07

  30. Uncertainty at the level of ~6% on CJV Pt>20GeV and ~3% on lepton Giving a total uncertaintly in the range ~8% Cosners House Forum on LHC startup April 07

  31. Describing the region transverse to the leading jet Averagemultiplicity of charged particles in the underlying event associated to a leading jet with Ptljet (GeV). AveragepTsum (GeV) of charged particles in the underlying event associated to a leading jet with Ptljet (GeV). Cosners House Forum on LHC startup April 07

  32. “Leading Jet” “Back-to-Back” Min-Max analysis • TransMAX and transMIN sensitive to radiation and soft UE respectively • Back-to-back sample suppresses radiation • difference between tranMAX region and transMIN in leading jet and b-2-b jet sample Cosners House Forum on LHC startup April 07

  33. Measuring the underlying event at ATLAS ETjet #1 = 1.63TeV ETjet #2 = 1.16TeV Cosners House Forum on LHC startup April 07 33

  34. First physics studies with the underlying event ATLAS - √s=900 GeV ATLAS - √s=14 TeV Reconstructed tracks √s=14TeV Multiplicity of charged particles with pT > 0.5 GeV and ||< 1 in region transverse to leading jet √s=900GeV ~ 15 days of data taking in 2007 enough to cover up to pT(leading jet) ~ 40 GeV • ~ 15 days of data taking in 2007 enough to cover up to pT(leading jet) ~ 40 GeV Cosners House Forum on LHC startup April 07 34

  35. Measuring the underlying event in TeV jets charged particles (generator level) J6 J6 J5 J5 J4 J4 J1 J2 J3 J1 J2 J3 Njets > 1, |ηjet| < 2.5, ETjet >10 GeV, |ηtrack | < 2.5, pTtrack > 1.0 GeV/c Selecting the underlying event: charged particles (generator level) Cosners House Forum on LHC startup April 07

  36. Ratio <NTrackReco>/<NTrackMC> Ratio <NTrackReco>/<NTrackMC> Leading jet ET (GeV) Leading jet ET (GeV) Njets > 1, |ηjet| < 2.5, ETjet >10 GeV, |ηtrack | < 2.5, pTtrack > 1.0 GeV/c Selecting the underlying event: Cosners House Forum on LHC startup April 07

  37. summary • Minimum bias and underlying event are uncertain at LHC energies • Energy extrapolation for SppS and CDF not known • dN/dh|h=0 measurement can be done in early running • Triggering • Both ATLAS and CMS are developing minimum bias triggers • Need to understand trigger bias to compare to UA5,CDF…. • Tracking • Low pt tracking is challenging but progress by both ATLAS+CMS • Underlying event can be measured with early data • Need to ensure overlap between jet and mb samples • Waiting for data Cosners House Forum on LHC startup April 07

  38. Extra slides Cosners House Forum on LHC startup April 07

  39. Day zero start-up looks promising! We are taking REAL DATA ! • SR1 cosmics test stand • Final TRT barrel • Final SCT barrel • 1 sector cabled for both Cosners House Forum on LHC startup April 07

  40. First Results • Offline reconstruction worked with little problems within hours • Debug cabling… • First results are very positive • See residuals and pulls • No alignment or detailed calibration yet ! • Reflects excellent mechanical precision… • More for Ringberg Workshop in 2 weeks • I am definitely very optimistic for first data taking having seen this ! • Detector is on a good way ! • Pixels are recovering from cooling problem delay • Finish 3 layer system in time Cosners House Forum on LHC startup April 07

  41. Tracking: Startup-Initial Alignment • Very first alignment will be based on: • Mechanical precision • Detailed survey data • Cosmics data (SR1/Pit) • Minimum bias events and inclusive bb • Studies indicate good efficiencies after initial alignment • Example taken from T.Golling • Precision will need Zs and resonances to fix energy scales, constrain twists, etc… M.Elsing Talk in SM meeting Cosners House Forum on LHC startup April 07

  42. Coincidences in MBTS PYTHIA charged-particle level Non-diffractive+SD+DD Diffractive events Non-diffractive only Cosners House Forum on LHC startup April 07

  43. Single and double diffractive inelastic events (sample 005002) Single diffractive events: energy is deposited on either side Double diffractive events MBTS response Non-diffractive inelastic events (sample 005001) Non-diffractive inelastic events: energy is deposited on both sides (typically) Cosners House Forum on LHC startup April 07 A.Moraes

  44. How many events? • For dN/dh require ~10k • For UE need ~20M MB events to get some with leading jets PT~30GeV • Need to overlap with jet triggers • Prescaled PT>25GeV • ~40M events gives ~10 hits/strip in barrel SCT • CMS quote ~18M to intercalibrate their calorimeter with MB Cosners House Forum on LHC startup April 07

  45. Performance goals Cosners House Forum on LHC startup April 07

  46. Machine considerations Cosners House Forum on LHC startup April 07

  47. LHC operational cycle Cosners House Forum on LHC startup April 07

  48. Cosners House Forum on LHC startup April 07

  49. 2 Physics inefficiencies • What fraction of primary particles reach the various detector layers, versus pT? • Charged particle component of MB events dominated by p+-, with ~10% K+-. First look at p- • Pixel system should provide 3 space points down to ~100MeV/c. • Down to ~150MeV/c, particles can traverse SCT magnetic field, but reduced efficiency below 300MeV/c due to inelastic interactions in ID material. Cosners House Forum on LHC startup April 07

  50. 3 Physics inefficiencies What about the charged kaons? • Much larger inefficiencies evident, due to increased material interactions and decays. • For pT=300MeV/c, ~10% of K+- do not reach final Pixel layer. • For pT=100MeV/c, K+- do not even make it into the Pixel system! • In the SCT system, 15% of 500MeV/c K+- do not reach last SCT layer. • Below 300MeV/c no spacepoints in outer SCT. Cosners House Forum on LHC startup April 07

More Related