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Taylan Yetkin Cukurova University, Physics Department Thesis Defense

SEARCH FOR SUSY IN MISSING TRANSVERSE ENERGY PLUS MULTIJET TOPOLOGIES AT √s = 14 TeV AND GEANT4 SIMULATION OF THE CMS HADRONIC FORWARD CALORIMETER IN THE 2004 TEST BEAM. Taylan Yetkin Cukurova University, Physics Department Thesis Defense. Outline. Introduction

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Taylan Yetkin Cukurova University, Physics Department Thesis Defense

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  1. SEARCH FOR SUSY IN MISSING TRANSVERSE ENERGY PLUS MULTIJET TOPOLOGIES AT √s = 14 TeV AND GEANT4 SIMULATION OF THE CMS HADRONIC FORWARD CALORIMETER IN THE 2004 TEST BEAM Taylan Yetkin Cukurova University, Physics Department Thesis Defense Taylan Yetkin

  2. Outline • Introduction • Definitions of Jet and Missing Transverse Energy • Search for Supersymmetry in Missing Transverse Energy and Multijets Topologies • Geant4 Simulation of Hadronic Forward Calorimeter in CMS • Remarks and Conclusions • Appendix Taylan Yetkin

  3. Introduction The thesis is divided in two parts: In the first part a study entitled Search for SUSY in Missing Transverse Energy plus Multijet Topologies at √s = 14 TeV is presented where discovery potential of SUSY is shown by using a set of five parameters in mSUGRA model as well as discussion of the methods in the analysis. The study improves and develops the analysis tools that has been used in past experiments and can be used when we have data from CMS. In the second part a Geant4 Simulation study for Hadronic Forward Calorimeters in CMS is presented. The simulation results were used to confirm test beam results as well as updating shower library in OSCAR which is one of the CMS simulation software that based on Geant4. Taylan Yetkin

  4. Working in a Transverse Plane PT is conserved not P. The collisions does not occur in fixed z-coordinate value (there is boost in z-coordinate). Also, most of the time, in each collision only two partons will experience hard scatter. The others and some of the collision remnants will go through the beam pipes. As a result, measurement in z-coordinate is impossible and only transverse quantities can be used. Unfolded EcalPlusHcalTowers   Taylan Yetkin

  5. Phenomenology of Jets • pp collisions produce quarks/gluons • quarks/gluons fragments to hadrons • Hadrons interacts with calorimeter • Jets clustering algorithms adds towers inside cone • Fraction of energy is out-of-cone due to magnetic field • Underlying events contribute to signal q p p Taylan Yetkin

  6. Missing Transverse Energy The missing transverse energy vector is calculated by summing individual calorimeter towers having energy Ei , polar angle i, and azimuthal angle i, and negating this sum: The sources of missing transverse energy are particles that interacts weakly with the detector, mismeasured muons, cracks in the detector, beam halo particles, dead detector channels, cosmic rays, and everything that goes wrong in the detector. In any BSM theory there is additional source of missing transverse energy which is a neutral, weakly interacting stable particle. Taylan Yetkin

  7. Search for SUSY in Missing Transverse Energy plus MultijetTopologies at √s = 14 TeV Taylan Yetkin

  8. Purpose of the Analysis • If SUSY exist and the sparticle masses are in the range 100 GeV~ 1TeV, it will be discovered in LHC. Therefore • The goal is not just to show that we will be able to discover SUSY at 10 fb-1, because S/B is huge at this luminosity. • Develop analysis strategies and necessary tools for data handling. • Also make contribution to PTDR Vol. II (and to Vol. III). Taylan Yetkin

  9. Signal Characteristic In the mSUGRA model we study R-Parity conserved scenario. Hence, there are two LSPs in the final state of each SUSY decay and they will contribute to the missing transverse energy measurement. Also there are multijets because of the squark/gluino decays. Therefore Missing Transverse Energy plus Multijes (3 jets) are chosen for the signal characteristic. Taylan Yetkin

  10. Properties of mSUGRA LM1-I Taylan Yetkin

  11. Properties of mSUGRA LM1-II Taylan Yetkin

  12. Event 1 Event 2 Event 3 3 quark jets, 1 tau jet 2 quark jets 2 quark jets, 2 tau jets Example Events in mSUGRA LM1 Taylan Yetkin

  13. Event 2 jet 1 jet 3 jet 2 Event Reconstruction Taylan Yetkin

  14. Data Samples for Analysis-I LM1: Generated by using PYTHIA 6.225 with ISAJET 7.69 interface, simulated with OSCAR 3_6_5 digitized and DSTed with ORCA_8_7_1 and analyzed with ORCA 8_7_4. The sample is digitized with low luminosity (2x1033 cm-2 s-2) pile-up conditions (with 5 on average pile-up events from the MU05b MBforPU dataset). ttbar: Generated by using PYTHIA 6.215, simulated with OSCAR 3_6_5 digitized and DSTed with ORCA_8_7_1 and analyzed with ORCA 8_7_4. The sample is digitized with low luminosity (2x1033 cm-2s-1) pile-up conditions (with 3.5 on average pile-up events from the MU05b MBforPU dataset). Single top: Generated by using PYTHIA 6.215, simulated with OSCAR 3_6_5 digitized and DSTed with ORCA_8_7_1 and analyzed with ORCA 8_7_4. The sample is digitized with low luminosity (2x1033 cm-2 s-1) pile-up conditions (with 5 on average pile-up events from the MU05b MBforPU dataset). Znunubar: Generated by using PYTHIA 6.215, simulated with OSCAR 3_6_5 digitized and DSTed with ORCA_8_7_1 and analyzed with ORCA 8_7_4. The sample is digitized with low luminosity (2x1033 cm-2s-1 ) pile-up conditions (with 5 on average pile-up events from the MU05b MBforPU dataset). Others: Generated by using PYTHIA 6.215, simulated with OSCAR 2_4_5 digitized and DSTed with ORCA 8_7_1 and analyzed with ORCA 8_7_4. The sample is digitized with low luminosity (2x1033 cm-2 s-1) pile-up conditions (with 3.5 on average pile-up events from the MU03b MBforPU dataset). Taylan Yetkin

  15. Data Samples for Analysis-II Transverse momentum pt hat is defined in the rest frame of the hard interaction for hard 22 processes, Taylan Yetkin

  16. Jets and MET • Jets: • We have adopted the Scheme A from the JetMET PRS group where different tower thresholds defined for different calorimeter components. • Jet algorithm is simple iterative cone algorithm with cone size 0.5. • SplittedEcalPlusHcalTowerInput is used (in “split tower” geometry the 100-towers are divided in two and tower 28/29 are further divided in  at = 2.825 to provide equal energy sharing in divisions.)is used. • EcalPlusHcalTowerCut is 0.5 GeV. • ConeSeedEtCut is 0.1. • JetEtCut is 3 GeV. • There is 30 GeV PT offline requirement on jets. • || < 3.0 is chosen for all jets. • Met: • The missing transverse energy is calculated from EcalPlusHcalTowerwithout any correction applied. Taylan Yetkin

  17. Trigger Taylan Yetkin

  18. Trigger-I Since we want to see missing transverse energy trigger efficiency it is proper to use a dataset of events that doesn’t have missing energy. Therefore, from the ttbar sample we form a pseudo dataset that we use as reference to measure the L1 jet+MET trigger efficiency The sample is designed based on the L1+HLT trigger path referred to as L1_2CJ_130 as follows: • require a primary vertex • require L1 bit 11 on (L1 two central jets, 130 GeV, L1_2CJ_130) • since no HLT dijet trigger exists we require offline 2 jets of uncorrected PT 130 GeV to confirm the L1 bit 11. We call this sample as JET130. Table: Pseudo JET130 data sample and L1 jetMET bit 28 test. Taylan Yetkin

  19. Trigger-II L1 Trigger Efficiency -Before -After In Jet130 dataset the events that pass the L1_CJ_88_MET_46 trigger (L1 bit 28 on) determine the L1 missing transverse energy trigger efficiency. The efficiency reach to 95% at about 100 GeV. Parameterized curve is used in the analysis. Taylan Yetkin

  20. Trigger-III HLT Efficiency -Before -After In Jet130 dataset, after applying L1 Trigger, the events that pass the HLT_CJ_180_MET_123 trigger (one central jet with PT 180 GeV and missing transverse energy with 123 GeV) determine the HLT missing transverse energy trigger efficiency. Since there is not enough statistics, as can be seen from the top right figure, instead of using the efficiency curve we simply require 200 GeV missing transverse energy for each event after L1. Taylan Yetkin

  21. Data Cleanup and Pre-selections Taylan Yetkin

  22. Primitive Backgrounds in a PTmiss Trigger Data Cleanup-I • Beam Halo Particles • Data Acquisition problems • Detector problems (dead channels, cracks etc.) • Cosmic Rays • Everything that goes wrong in the detector. Taylan Yetkin

  23. Jet and Event EMF Data Cleanup-II • A jet is expected to have on average Electromagnetic/ETOT ratio • (EMF) between 0 and 1*. • • Cosmic bremsstrahlung depositions of energy in either the hadronic or • electromagnetic calorimeter when clustered as jets will have EMF close • to 0 or to 1. • • All-hadronic depositions of energy resulting from beam halo events will • have EMF close to 0 and have been studied at CMS in CMS-AN-2005- • 48. • • Electrons and photons that are also clustered as jets are expected to • have EMF closer to 1. • Given these properties, the electromagnetic fraction of a jet has been used as a “jet-quality” control variable and discriminator against backgrounds. • * Energy fraction is found from EcalPlusHcalTowers. Taylan Yetkin

  24. Leading Jet EMF Data Cleanup-III LM1 Taylan Yetkin

  25. Event EMF Data Cleanup-IV is defined to be the PT weighted jet EMF sum over the electromagnetic calorimeter acceptance, |d| < 3.0: where: • NJet is the number of IC jets of cone 0.5 with PT > 30 GeV and | d|<3.0 • PTj is the uncorrected PT of the jth jet • EMFj is the EMF of the jth jet Taylan Yetkin

  26. Event EMF in Beam Halo (CMS-AN-2005-48) Data Cleanup-V hadrons muons Taylan Yetkin

  27. Event EMF in Signal and Background Data Cleanup-VI LM1 We use EEMF0.1 as a clean-up requirement to retain the signal efficiency while eliminating backgrounds such as the beam halo background. Taylan Yetkin

  28. Jet and Event Charged Fraction Data Cleanup-VII • The charged to neutral tracks ratio of a hadronic jet is about 65%. • The jet charged fraction is defined as the ratio of the PT of the tracks associated with a jet over the total calorimetric jet PT . • Jets that are found in the tracker coverage region that have charged fraction close to 0 which are not associated with a photon, can be pathological and would indicate potential backgrounds. The overall Event Charged Fraction can be used to distinguish between real jets and such fake jets. N.B For analyses with photons in the final state the charged fraction might not be a proper clean-up variable. Taylan Yetkin

  29. Event Charged Fraction Data Cleanup-VIII The event charged fraction is calculated by finding all the tracks pointing to each jet within a cone of 0.75 of the - centroid of the jet. A jet enters into the event charged fraction variable if its absolute pseudorapidity is less than 1.7. Taylan Yetkin

  30. Event Charged Fraction in Signal and Background Data Cleanup-IX LM1 We use ECHF0.175 as a clean-up requirement to retain the signal efficiency while eliminating backgrounds such as the beam halo background. Taylan Yetkin

  31. Data Cleanup-X EEMF and ECHF for Good Hadronic Jet(Details are in CMS-IN 2006-010) Taylan Yetkin

  32. Indirect Lepton Veto (ILV) As a Pre-Selection Tool Taylan Yetkin

  33. ILV-I An “indirect lepton veto” method is studied as a strategy for eliminating W/Z+jets and ttbar backgrounds while retaining the efficiency to low mass mSUGRA-type signals where leptons from the decays of charginos and neutralinos are present. ILV combines tracker (Leading Track Isolation) and calorimeter (EMF of two most energetic jets) information and it is used as an indirect way to veto leptons (and/or fake jets from leptons) in the events. Taylan Yetkin

  34. ILV-II Jet EMF The two highest PT jets in the event are required not to be purely electromagnetic. The event is vetoed if: EMF (leading jet) > 0.9 or EMF (second jet) > 0.9 This requirement will mainly eliminate events with high PT electrons in the final state. W(e) +  2 jets First Jet Second Jet Taylan Yetkin

  35. ILV-III Leading Track Isolation-I Tracking isolation is used at CMS as a powerful criterion in  selection (PTDR-Vol1). We developed a tracking isolation strategy in order to reject electrons, muons and taus from W and Z decays while retaining the SUSY signal efficiency. The highest PT track is found among the tracks that are associated to primary vertex in each event where the tracks have the requirements: • PT > 1.2 GeV/c • Nhits 5 • transverse impact parameter |d0|  600 µm • |zPV − ztrk| < 1 mm • |trk| < 2.4 Taylan Yetkin

  36. ILV-V Leading Track Isolation-II If the leading track has PT > 15. GeV/c, a cone is cast around this track with a cone size dR = 0.35 where (dR)2 = (d)2 + (d)2. Then the PT of the other tracks inside the cone are summed up to construct an isolation parameter (Pisol) as follows: Leading Track If Pisol 10% we tag the leading track as isolated track and reject the event. The fraction above we refer to as “leading track isolation parameter”. The requirement of rejecting events with an isolated leading track is noted as Isotrk=0. Both the cone size and the value of the fraction is determined such that the maximum rejection of the background is achieved with the minimal loss of signal efficiency. Taylan Yetkin

  37. ILV-VI Summary and Results ILV works well for rejecting backgrounds from W/Z and also from ttbar when the final state has high energy electrons and muons. Table 1: Rejection efficiency of Indirect Lepton Veto in LM1. Table 2: Rejection efficiency of Indirect Lepton Veto in W/Z Samples Taylan Yetkin

  38. SM Candle Normalization with W/Z + Jets Taylan Yetkin

  39. SM Candle Norm. -I • In collider experiments W/Z bosons will be produced associated to hadronic jets. Here we study the methods for SM Candle Normalizations as a preparation. Z(ℓℓ) + jets can be used in data for various things: • W+jets sample can be estimated from the Z+jets data since Z+jets gives relatively clean signals. • In Z+ N jets sample, where N is the number of jets, the number of events each bin in N can be estimated since the cross-section is proportional to sN in lowest order. • In mSUGRA LM1 Z(invisible) +  3 jets will be a major background and neither kinematical nor topological cuts will remove it. But from Z(mumu) +  3 jets (or Z(ee) +  3 jets ) it can be estimated. Taylan Yetkin

  40. SM Candle Norm. -II Taylan Yetkin

  41. QCD Background and Cuts Taylan Yetkin

  42. QCD Background and Cuts-I • The cross-section for the production of QCD dijet events are very high and therefore rate of the such events at LHC will be very high. • The QCD jet production causes large missing energy because of the small • contents as well as jet mismeasurements and detector resolution. Three variables are used to suppress QCD background: • Angle between second highest PT jet and missing transverse energy • Correlation between first, second jet and missing transverse energy • Minimum of the angles between all jets and missing transverse energy Taylan Yetkin

  43. QCD Background and Cuts-II QCD_470_600 LM1 Taylan Yetkin

  44. QCD Background and Cuts-III QCD_470_600 LM1 R1 and R2 are chosen as 0.5 Taylan Yetkin

  45. QCD Background and Cuts-IV QCD_470_600 LM1 Taylan Yetkin

  46. Analysis Results Taylan Yetkin

  47. Analysis Results-I The number of events that pass all the pre-selection and analysis cuts for the 10 fb-1. QCD Taylan Yetkin

  48. Analysis Results-IV There are two variables used in the literature for SUSY searches: HT and Meff. The former is frequently used in the experiments as an experimental variable independent from any model while latter is used as and index for the SUSY mass scale. They are defined as follows: where PT,i are the PT of the jets. In general Meff is twice the SUSY mass MSUSY ≈ min(Mgluino , Msquark) in which Msquark is the mass of light squarks (e.g., sup,sdown). Taylan Yetkin

  49. Analysis Results-V HT and Meff : HT Meff The signal is well visible above background. Taylan Yetkin

  50. Analysis Results-VI Signal/Background Ratio: From the table in Analysis Results-I Signal Background Taylan Yetkin

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