Testing of CMS Endcap RPCs and the Determination of Top Quark Mass Using High Pt Jets at LHC

1. Testing of CMS Endcap RPCs and the Determination of Top Quark Mass Using High Pt Jets at LHC Physics Department QAU Doctoral thesis IJAZ AHMED Supervisor: Prof. Hafeez R. Hoorani

2. PART 1Top Quark Mass Reconstruction Using High Pt Jets in Ttbar Semi-leptonic Channel at LHC(CMS DETECTOR SIMULATION) PART 2 Resistive Plate Chamber (CMS Trigger Detector)Beam test AND Cosmic test

3. OUTLINE (first part) • Motivations of Top Physics • Topology of Lepton + Jets • High Pt top basic idea • 3 methods for jets selection • Top quark mass reconstruction from jets • Jets clustering in detector • Clusters invariant masses Mtopclus • Underlying Event (UEclus) estimation and subtraction • Summary

4. Large Hadron Collider (LHC) Experiment Integrated luminosity=10fb-1

5. Compact Muon Solenoid Detector

6. Top Quark Properties, production and decays at the LHC Striking Features of top quark • Heaviest particle (spin ½, charge 2/3) • Origin of mass, EWSB, Higgs • Short life time (ttop =1/top, thad=1/LQCD) • No bound state • Yukawa coupling-unity 90% 10%  need to reconstruct and identify  muons  b-jets  light jets (u,d,c,s)  missing ET(neutrinos) ~66.5% ~29% ~4.5% NLO Cross-section for tt~ production at LHC is (tt)~830pb

7. High Pt Top Basic Idea • Highly boosted top quarks decay back-to-back, making two distinct hemispheres inside the detector. • When the top has a higher boost, one expects the opening angle between W and b (from top decay) to be smaller and as a consequence the decay products also have cone size smaller. • High Pt top quarks have decay angles close to the top flight direction and therefore the hadronic jets due to narrow cone size will have the probability of overlaping in space. • Calculate the invariant mass of the objects which are in larger cone around the top quark direction of flight and then is correlated with the real top mass. For this the top quark needs to have a larger Pt > 200 GeV.

8. Key elements of this analysis • This Topology reduces the combinatorial background as well as the backgrounds from other processes. • The systematic effects due to jet energy calibration and gluon effects will be different from an analysis with standard jets. • This technique has the potential to reduce the systematic errors, since it is less sensitive to the calibration of jets and to the intrinsic complexities of effects due to leakage outside the smaller cones, energy sharing between jets • ****************************************************** ****************************************************** • With mt being reconstructed from the three jets in the one hemisphere (mt= mjjb) • Then mt is reconstructed summing up the energies in the calorimeter clusters in a large cone around the top direction. Study of two different reconstruction methods

9. Kinematical variables • Invariant mass • Transverse momentum • Transverse mass • Transverse energy • Rapidity • Pseudo-rapidity • Jet cone radius • Missing Transverse Energy

10. Tools and Algorithms • Event generation (PYTHIA) • Simulation of the interaction of the generated particles with the detector (OSCAR, FAMOS) • Simulation of digitized phase (FAMOS, ORCA) • Local and global event reconstruction (FAMOS, ORCA) • Physics Analysis tools (PAW,ROOT) • Minimum Bias Events (Pile-up) • Triggering on isolated Muon • Clusters reconstruction • Jet reconstruction and Missing ET • B-tagging

11. Pre-selection cuts at Generator level FAMOS_1_4_0 samples • 165 Top mass point = 20K events • 175 Top mass point = 50K events • 185 Top mass point = 20K events • ORCA_8_7_3 sample (350K) • Pttop > 200 GeV, |h| < 3.0 • Ptanti-top > 200 GeV, |h| < 3.0 • Ptm> 30 GeV, |h| < 2.0 • Ptq > 20 GeV, |h| < 2.5 X-section approximately 1% of the total tT cross-section Pile-up events are included

12. Partonic Level Distributions Pttop MC htop DR(q,qbar) PtW DR(top, min W-quarks) DR(top, max W-quarks) DR(top,b-par) DR(top,W)

13. MET-> Missing Transverse Energy • MET > 30 GeV • At least 1 iso. muon, Pt>20 GeV, |h|<2.0 combined b-tag disc. > log (1.0) (60% b-tag efficiency) leptonic W reco mass combined b-tag discriminator

14. Leading jets and muons Pt distributions Muon Isolation Pt > 30 GeV SPttrks/Ptm) < 5% (DR=0.01-0.2) Efficiency > 92% Leading light jets Pt Ptjets > 20 GeV Leading b-jets Pt Ptb-jets > 20 GeV

15. Jet-Parton Matching (JPM) • 2 light jets + 2 quarks from W • 4 possible jet combinations  take best combination (J1,j2), (q1, q2) *************** (J1,q1), (j1,q2) (j2, q1), (j2,q2) DR(j1,q1) DR(j1,q2) DR(j2,q1) DR(j2,q2) I1=Max (DR(j1,q1),DR(j1,q2)) I2=Max (DR(j2,q1),DR(j2,q2)) Min(I1, I2)<0.4 worst of 2 quarks matching angles Correctly matched if DR < 0.4

16. Introducing 3 approaches • Three approaches to select events • + jet combination (for top direction) • Leading jets > = 2 b-tagged jets, > = 2 non b-tagged jets • Exactly 4 jets, =2 b-tagged jets, = 2 non b-tagged jets • > 2 leading b-jets, 2 light jets with mjj closest to W mass

17. Top quark selection from leading jets mWnom = 65.24 (gaussian fitted correctly jet-parton matching)

18. Nominal mass—fitted mass ~ 65 GeV Same  mWnominal used in all selections (JPM)

19. Top quark mass measurment from leading jets Reco W-boson purity with 2 quarks matched = 18.17% Reco W-boson purity with 1 quark matched = 42.7% b-jet with biggest angle wr.t muon called Hadronic b-jets

20. Top quark selection from four jets topology

21. Reco W-boson purity with 2 quarks matched = 20.98% Reco W-boson purity with 1 quark matched = 43.26% Di-jet with associated b-jet invariant mass dist. from four jets selection Di-jet invariant mass dist from four jets selection

22. Top quark selection from jjW

23. W mass reconstruction jj---W Reco W-boson purity with 2 quarks matched = 20.76 % Reco W-boson purity with 1 quark matched = 40.6 % All jets combinations Before b-jet selection After full selection

24. Top quark mass reconstruction from jjW

25. Pt top dependence (leading jets approach) Wrong Right combinations

26. Mjjb plots for all selections after calibration

27. Comments on mjjb • Study based on shape of distributions for top direction determination • Explored three types of selection criteria for hadronic top mass reconstruction • Four jets selection results low efficiency with higher W purity • Jets with invariant mass close to W have higher efficiency with intermediate purity of W • Leading jets selection gives sharp and narrow dist. shape with less long tail behaviour and reasonable selection efficiency

28. Cluster Reco Method • Once top direction determined,and Pt(jjb)= 200 GeV • Invariant mass of all calorimeters clusters DhxDj around top direction • Ei represents total energy of the ith cluster • nDR runs over all clusters within selected cone size • Pi its 3-momenta vector • We know only E,h, j about clusters • Assumptions: • considering particles masseless

29. Mjjb(PTtop>200 GeV)

30. Reco clusters pseudo-rapidy Calorimeters identifications

31. Et Behaviour on jet cone size

32. Opening angle between reco. top and calorimeter clusters

33. Top mass reconstruction from calorimeter clusters

34. Underlying Event Estimation Excluded DR > 0.7, Jet Isolation cut, excluding high Pt events

35. UE Estimation Method LAYER # 01 (ECAL)

36. UE Estimation Method LAYER # 02 (HCAL)

37. Top mass Mclustop and UEclus subtraction Before UE Subtraction After UE Subtraction With 50,000 events which corresponds to 7.2 fb-1, one can expect a statistical uncertainty about dm=1-1.5 GeV on top mass.

38. Summary • Analysis based (Pttop > 200GeV) with Full and Fast Simulation of CMS detector is performed. • An alternate method for top mass reconstruction in CMS is presented, strongly depends on Calorimeter. • A new method for Underlying event (UE) is developed • Statistical error 1-1.5 GeV on top mass is determined. • CMS IN-2007/023 -- Top Quark mass measurement in the lepton plus jets channel using large calorimeter clusters cone at LHC • Authors: Ijaz Ahmed, Hafeez R. Hoorani, Martijin Mulders • 2. CMS IN-2006/046 -- Study of High Pt Top Anti-Top Production at LHC • Authors: Ijaz Ahmed, Hafeez R. Hoorani, Martijn Mulders

39. PART 2

40. Top Wide Top Narrow Bottom B D A C The Resistive Plate Chamber (RPC) Bakelite resistivity 10 9- 10 10cm Coated with linseed oil • Gap width: 2 mm • HV electrodes : 100 m graphite • PVC Spacers (tolerance ± 200 m) • Graphite coating • Gas pressure : ~ 1 Atm • Gas mixture: 96% Freon, 3.5% iso-Butane, 0.5% SF6 Df =5/16, Dh =0.1

41. Avalanche Mode RPC Raether condition RPC schematic diagram ref: CMS NOTE 1997/004

42. Ramo’s theorem

43. GIF (Gamma Irradiation Facility) Prototyping of RPC RPC Beam Test Set-up

44. At GIF SPS (CERN)-2003

45. Environment for the Beam test Muon Beam • Momentum : 200 GeV/c (450 GeV max) • Flux : ~104 per SPS cycle (2.38sec) • Repetition peroid 14.4 sec • Area : 10 × 10 cm2 • Gas Mixture • C2H2F4 96% + Iso-C4H10 3.5% + SF6 0.5% • Radiation Source • At 4m, Flux 0.86*105cm-2s-1 • 740 GBq(20Ci) 137Cs gamma ray (661keV) • Electronics • LeCroy 2277 TDC (1 nsec/bit, multi-hit, common stop/start) • 32-ch FEB, co-axial cables + Flate cables

46. RPC Test Beam Results

47. Beam Test Results Time Resolution Dark current Power consumption = (10.5kV*280 mA)/1.169 m2 = 2.5W/m2 Correction is of the order of 1% HVeff = HV - RI

48. Beam Test Results Efficiency Mean arrival time

49. Beam Test Results Rate capability Cluster size Voltage drop = Vd = 2 <Qe> r s r <Qe>=1pC, r = 1000Hz/cm2, r =1010W.cm, s = 0.2cm

50. RPC Cosmic Test Facility at NCP NCP experimental test facility for RPC