Photons, Missing Energy and the Quest for Supersymmetry at the LHC

Transcription

1 Photons, Missing Energy and the Quest for Supersymmetry at the LHC Ulla Gebbert Thesis Defense

2 Motivation pp pp LHC: first pp-collisions in November 2009! Soon after: highest-energy particle accelerator on earth Susy Since March 2010: s = 7 TeV, L dt = ~5 fb-1 SM Higgs Boson Higgs 7 Searches for new physics 2

3 Outline 0. Introduction Standard Model Supersymmetry - and Photons? CMS Detector 1. Measuring the Missing Transverse Energy Reconstruction Corrections Large ET 2. Search for Supersymmetry in Events with Photons, Jets and ET Event Selection SM Backgrounds Results & Interpretation 3. Summary and Outlook 3

4 The Standard Model (SM) SM particles u c t g d s b γ νe νµ ντ W e µ τ Z γ Electromagnetic Force: Electric charge: q, e, µ, τ, W± ± H g - Strong Force: Colour: quarks & gluons quarks leptons Fermions Spin 1/2 Basic constituents of matter W±,Z0 - Weak Force: Weak isospin: left-handed fermions, W±,Z0 SU(2)L U(1)Y SU(3)C Bosons Spin 1 Spin 0 Mediators of forces Higgs: Accommodate massive gauge fields (MW/Z GeV) No experimental evidence hints at ~125 GeV? mh GeV (LEP), mh 127 GeV mh 600 GeV (CMS) 4

5 The Standard Model and beyond? Dark Matter? Unification of Forces? Origin unsolved within Standard Model Grand Unified Theories (GUTs) G SU(3) SU(2) U(1) SM SM? More fundamental theory? SUSY? Gravity? Naturalness of the SM? Number of free parameters? Number of generations? Masses of particles?... 5

6 The Standard Model and beyond? Dark Matter? Unification of Forces? Grand Unified Theories (GUTs) G SU(3) SU(2) U(1) SM Origin unsolved within Standard Model Lightest SUSY particle? SM? More fundamental Theory? SUSY SUSY? Gravity? SUSY? Naturalness of the SM? Number of free parameters? Number of generations? Masses of particles?

7 Supersymmetry Minimal Supersymmetric Standard Model (MSSM) u c t g d s b γ νe νµ ντ W± e µ τ Z quarks leptons Fermions ~ u ~ c ~t h0 H0 ~ d ~ s ~ b H± A 0 ν~e ν~µ ν~τ χ~10 ~ χ20 ~ χ30 ~ χ40 ~ e ~ µ ~τ ~ χ1± ~ χ2± Extension Bosons ~ g squarks sleptons Bosons Fermions Each SM particle linked to a supersymmetric particle (boson fermion) 7

8 Supersymmetry Minimal Supersymmetric Standard Model (MSSM) u c t g d s b γ νe νµ ντ W± e µ τ Z ~ u ~ c ~t h0 H0 ~ d ~ s ~ b H± A 0 ν~e ν~µ ν~τ χ~10 ~ χ20 ~ χ30 ~ χ40 ~ e ~ µ ~τ ~ χ1± ~ χ2± quarks leptons Fermions ~ g squarks sleptons Bosons Bosons Mass Eigenstates Fermions Each SM particle linked to a supersymmetric particle (Boson Fermion) 8

9 Supersymmetry Minimal Supersymmetric Standard Model (MSSM) u c t d s b νe νµ ντ e µ τ g 1 W W2 W3 B0 Hu0,Hd0, Hd,Hu+ quarks leptons Fermions ~ u ~ c ~t ~ d ~ s ~ b ν~e ν~µ ν~τ ~ e ~ µ ~τ ~ g Gauge Eigenstates ~ ~ B0,W0, ~ W± ~ ~ Hu+,Hd~ ~ Hu0,Hd0 squarks sleptons Bosons Bosons Mass Eigenstates Fermions Each SM particle linked to a supersymmetric particle (boson fermion) 9

10 Supersymmetry Minimal Supersymmetric Standard Model (MSSM) u c t g d s b γ νe νµ ντ W± e µ τ Z ~ u ~ c ~t h0 H0 ~ d ~ s ~ b H± A 0 ν~e ν~µ ν~τ χ~10 ~ χ20 ~ χ30 ~ χ40 ~ e ~ µ ~τ ~ χ1± ~ χ2± quarks leptons ~ g Gauge Eigenstates squarks sleptons Fermions Bosons PR=+1 Bosons Mass Eigenstates Fermions PR=-1 Each SM particle linked to a supersymmetric particle (boson fermion) Conservation of lepton/baryon number: R-Parity PR=(-1)3(B-L)+2S Pair production of SUSY particles at a collider Stable, lightest supersymmetric particle (LSP) Same colour, electrical charge, isospin and mass broken symmetry? 10

11 SUSY Breaking SUSY breaking in 'hidden' sector Different models exist, e.g: msugra: 'minimal supergravity' SM Gravity SUSY breaking 'hidden' sector GMSB: 'gauge mediated SUSY breaking' SM Messenger fields SU(3)C SU(2)L U(1)Y SUSY breaking 'hidden' sector Model independent framework: 'General Gauge Mediation' (GGM) Universal prediction: Gravitino LSP P. Meade, N. Seiberg, D. Shih, arxiv: v3 Lightest MSSM particle: NLSP 11

12 GGM Phenomenology at the LHC Typical production (LHC): squarks & gluinos R-parity conserved: two LSP's per event Neutralino NLSP mixture of Bino, Wino and Higgsino Y. Kats, et. al arxiv:

13 GGM Phenomenology at the LHC Typical production (LHC): squarks & gluinos R-parity conserved: two LSP's per event Neutralino NLSP mixture of Bino, Wino and Higgsino Final states with photons: γγ + ET +X J. Ruderman, D.Shih ArXiv: v1 Bino-like NLSP 13

14 GGM Phenomenology at the LHC Typical production (LHC): squarks & gluinos R-parity conserved: two LSP's per event Neutralino NLSP mixture of Bino, Wino and Higgsino Final states with photons: γγ + ET +X and γ + ET +X Wino-like NLSP J. Ruderman, D.Shih ArXiv: v1 14

15 GGM Phenomenology at the LHC Typical production (LHC): squarks & gluinos R-parity conserved: two LSP's per event Neutralino NLSP mixture of Bino, Wino and Higgsino Final states with photons: γγ + ET +X and γ + ET +X Wino-like NLSP J. Ruderman, D.Shih ArXiv: v1 15

16 GGM Phenomenology at the LHC Typical production (LHC): squarks & gluinos Wino-like NLSP R-parity conserved:two LSP's per event Neutralino NLSP mixture of Bino, Wino and Higgsino Final states with photons: γγ + ET and γ + ET (+jets/b-jets/leptons) Variety of other final states (without γ, non-prompt NLSP decay,...) Bino-like NLSP 16

17 GGM Phenomenology at the LHC Typical production (LHC): squarks & gluinos Wino-like NLSP R-parity conserved:two LSP's per event Neutralino NLSP mixture of Bino, Wino and Higgsino Final states with photons: γγ + ET and γ + ET (+jets/b-jets/leptons) Variety of other final states (without γ, non-prompt NLSP decay,...) Bino-like NLSP 17

18 CMS Detector Length:14.6m, 21.6 m, t 3.8 T solenoid enclosing calorimetry Tracker: good resolution & reconstruction efficiency H bb, SUSY with b/τ Electromagnetic calorimeter: excellent resolution (e,γ) H γγ, Z' ee, GGM Muon system: wide acceptance & charge measurement H ZZ µ+µ µ+µ,z' µ+µ Hadronic calorimeter Jets & ET: good hermetic coverage & resolution needed ET: needed for many SUSY & BSM searches technically challenging reconstruction 18

19 Outline 0. Introduction Standard Model Supersymmetry - and Photons? CMS Detector 1. Measuring the Missing Transverse Energy Reconstruction Corrections Large ET 2. Search for Supersymmetry in Events with Photons, Jets and ET Event Selection SM Backgrounds Results & Interpretation 3. Summary and Outlook 19

20 ET Reconstruction CMS 3 different algorithms commissioned hadronic calorimeter electromagnetic calorimeter Calo ET: Use only calorimetric energy deposits 20

21 ET Reconstruction CMS 3 different algorithms commissioned hadronic calorimeter electromagnetic calorimeter Calo ET: Use only calorimetric energy deposits tracker TC ET: Inclusion of the measured track momenta Correction of calorimeter only measurement 21

22 ET Reconstruction CMS 3 different algorithms commissioned hadronic calorimeter electromagnetic calorimeter Calo ET: Use only calorimetric energy deposits muon chambers tracker TC ET: Inclusion of the measured track momenta Correction of calorimeter only measurement PF ET: Use calibrated particles ( particle flow ) 22

23 Correction of the Measurement Non linear response HCAL Jet Energy Corrections (JEC) corrections needed Unclustered energy deposits in calorimeter below pt thresholds for other physics objects Derive correction from Z ee events: Use balance between Z boson momentum and recoil from: JINST 6 (2011) P11002 Type-I: Type-II: Correct ET for the difference between jets before/after JEC Correct ET for the difference between unclustered deposits before/after correction 23

24 Derivation of Type II Corrections Z ee if: no jets above JEC threshold 24

25 Derivation of Type II Corrections Measure <R> in dependence of qt: Calo ET 25

26 Derivation of Type II Corrections Measure <R> in dependence of qt: Calo ET 26

27 Derivation of Type II Corrections Measure <R> in dependence of qt: Calo ET Correction applicable to different event topologies! 27

28 Derivation of Type II Corrections Resulting correction: Z, rel= Calo ET Z p T U meas, Z pt Data-driven derivation Small (36/pb) dataset functional form from simulation Data/simulation agree within uncertainties PF ET: Similar results, smaller correction 28

29 Validation in Di jet Events Good performance in Z ee events test in other event topology (di jet) Di-jet Dominated by unclustered energy 29

30 ET scale in Di jet Events Calo ET published in: JINST 6 (2011) P09001 Type II reduces negative offset large effect for Calo ET: scale within 2 GeV down to lowest pt PF ET published in: JINST 6 (2011) P09001 Smaller, but similar effect for PF ET: already well adjusted (<2 GeV) Scale well adjusted after type II corrections for both ET algorithms 30

31 ET Resolution in Multi jet Events Calo ET Type-I Calo ET Type-II TC ET PF ET includes tracking information from: JINST 6 (2011) P09001 //AN Type-II correction improves Calo ET resolution Resolution improved clearly by inclusion of tracking information 31

32 SUSY: ET Tails sensitive to instrumental mismeasurement Anomalous calorimeter signals Non collision particles Non instrumented/non functioning detector regions... Additional contributions to tail of ET distribution crucial for analyses requiring high ET, e.g. SUSY searches from: JINST 6 (2011) P

33 Outline 0. Introduction Standard Model Supersymmetry - and Photons? CMS Detector 1. Measuring the Missing Transverse Energy Reconstruction Corrections Large ET 2. Search for Supersymmetry in Events with Photons, Jets and ET Event Selection SM Backgrounds Results & Interpretation 3. Summary and Outlook 33

34 Event Selection Final states with only one, jets + MET MET 366 GeV Jets (>=2) + MET + Photon Photon 96 GeV Lumi [fb 1] Trigger Photons Jets Photon-HT >=1, pt>80 GeV 2*,HT*>450 > 100 GeV 4.3 GeV pt > 30 GeV γ pt>70 GeV η <1.44 HT>400 GeV ET >=2 jets η <2.6 *scalar pt sum of jets (calorimeter jets, pt>40 GeV, η <3.0, cleaned from e,µ & leading γ) *particle flow jets, anti kt (R=0.5), cleaned from e,µ & leading γ 34

35 SM Background: γ/qcd Main background: γ/qcd Multi-jet: jet photon Photon-jet No intrinsic ET But: jet resolution, non-gaussian tails,... Data driven estimate: 1)Select γjet control sample γjet: similar to γ, looser isolation Orthogonal selection C Photon p T = Fake Photon Photon 35

36 SM Background: γ/qcd Main background: γ/qcd Multi-jet: jet photon Photon-jet No intrinsic ET But: jet resolution, non-gaussian tails,... Data driven estimate: 1)Select γjet control sample 2)Derive event weight w-1: Control region (ET<100 GeV) C Photon p T = 2 jets Fake Photon Photon >=3 jets 36

37 SM Background: γ/qcd Main background QCD: Multi-jet: jet photon Photon-jet No intrinsic ET But: jet resolution, non-gaussian tails,... Data driven estimate: 1)Select γjet control sample 2)Derive event weight w-1: Control region (ET<100 GeV) C Photon p T = Fake Photon Photon 3)Reweight γjet control sample Estimate for background Systematic uncertainties: Extrapolation from low to high ET < 5% Statistical uncertainty of w-1 Closure Test 37

38 SM Background: e γ (EWK) Minor background: e γ (EWK) tt+jets e γ, W+jets intrinsic ET from ν's Data driven estimate 1)Select γe (electron) control sample γe: same as γ, but require track 2)Z ee (ratio ee/eγ): derive fake rate γ pt > 80 GeV: C Photon p T = 3) Reweight γe control sample Estimate for background Fake Photon Photon Fit for γ>80 GeV taken from: AN (γγ) 38

39 Results: Observation & Expectation Signal region: 6 bins with ET > 100 GeV Data driven estimation for QCD & EWK Simulation for FSR/ISR No excess over the SM expectation observed 39

40 Interpretation Limit calculation: Use 6 bins with ET>100 GeV CLs, frequentist approach based on RooStats Systematic uncertainties (signal): Experimental: Photon efficiency in data/mc: 4% Jet energy scale 2% Luminosity 4.5% PDF uncert. on the acceptance ~ % Theoretical: PDF uncert. on cross section (10-70%) Renormalisation scale (10-30%) Three different GGM scenarios studied: Bino-like NLSP Wino-like NLSP 40

41 Interpretation Bino, ~ q vs. ~ g Typical acceptance: ET>100 GeV ~ 75% ET>350 GeV ~ 12% mgluino>msquark: more (high pt) jets Acceptance drops: Mass Neutralino Mass Gluino/Squark 41

42 Interpretation Bino, ~ q vs. ~ g Typical acceptance: ET>100 GeV ~ 75% ET>350 GeV ~ 12% Observed cross section limit, 95% CL ~0.01 pb Exclude: Mgluino < 960 GeV Msquark < 1040 GeV 42

43 ~ ~ Interpretation Bino, χ10 vs. g Typical acceptance: ET>100 GeV ~ 60-80% ET>350 GeV ~ 10-15% Observed cross section limit, 95% CL ~ pb Exclude: Mgluino < GeV, if Mχ < 800 GeV 43

44 ~ ~ Interpretation Bino, χ10 vs. g Typical acceptance: ET>100 GeV ~ 60-80% ET>350 GeV ~ 10-15% Observed cross section limit, 95% CL ~ pb Exclude: Mgluino < GeV, if Mχ < 800 GeV CMS γγ (4.7/fb) ATLAS γγ (1/fb) 44

45 ~ vs. g ~ Interpretation Wino, q Typical acceptance: ET>100 GeV ~ 8% ET>350 GeV ~ 1% Observed cross section limit, 95% CL ~0.1 pb Exclude: Mgluino < 730 GeV Msquark < 780 GeV 45

46 ~ vs. g ~ Interpretation Wino, q Typical acceptance: ET>100 GeV ~ 8% ET>350 GeV ~ 1% Observed cross section limit, 95% CL ~0.1 pb Exclude: Mgluino < 730 GeV Msquark < 780 GeV Most stringent limit on wino-like neutralino to date CMS γ+l (36/pb) ~ 450 GeV γγ : no published limits, much lower acceptances ( 6-10) 46

47 Results: γ + jets + ET Extend previous CMS GMSB SUSY searches: single photon, jets & ET Data driven estimates for main backgrounds (QCD,EWK) Further background (ISR/FSR TTBar, V+Jets) from simulation No excess in data observed Limits calculated for wino- and bino-like neutralino 4.3/fb results made public in PAS-SUS Luminosity 4.3 fb-1 +/- 4.5% Acceptance times efficiency Upper Limit cross section Msquark > Mgluino > Bino-like: ~ 80 % ~ 0.01 pb-1 ~ 960 GeV ~ 1040 GeV Similar (slightly lower) sensitivity than CMS γγ (SUS ) presented at Moriond 2012 paper in preparation Wino-like: ~8 % ~0.1 pb-1 ~780 GeV ~730 GeV Most stringent limit to date 47

48 Outline 0. Introduction Standard Model Supersymmetry - and Photons? CMS Detector 1. Measuring the Missing Transverse Energy Reconstruction Corrections Large ET 2. Search for Supersymmetry in Events with Photons, Jets and ET Event Selection SM Backgrounds Results & Interpretation 3. Summary and Outlook 48

49 Summary (1/2) ET: key ingredient to many SUSY & other BSM searches (not only GMSB) High ET : sensitive to misreconstruction non linear response of the calorimeter scale can be adjusted with type I/II corrections Inclusion of tracking: significantly lower resolution CMS has 3 different, well tested ET algorithms commissioned JINST 6 (2011) P09001 Several complementary measurements show excellent performance of ET Eur. Phys. J. C72 (2012) Measuring the Missing Transverse Energy JINST 6 (2011) P

50 Summary (2/2) Final states with photons expected in GGM SUSY scenarios Variety of possible final states including γ + ET + jets Branching ratios to photon & W,Z,H depend on neutralino mixture CMS has performed several analyses covering many of the possible final states Final states with photons: JHEP 1106 (2011), 36/pb γ + E + lepton T γ + ET + >=2 jets γγ + ET + >=1 jet presented here SUS , /fb Most stringent limits on GGM gluino/squark production to date Msquark Mgluino Bino-like: > ~ 1000 GeV > ~ 1100 GeV 1. Measuring the Missing Transverse Energy Wino-like: ~800 GeV ~700 GeV 50

51 Outlook (1/4) LHC results: challenging large parts of the SUSY parameter space msugra parameter space: CMS-PAS-SUS Measuring the Missing Transverse Energy ATLAS-CONF

52 Outlook (2/4) LHC results: challenging SUSY reach further! 1) Optimize analyses e.g. γ+jets+et (wino-like): High masses: EWK production less stringent jet selection? leptons? More exotic, less inclusive: additional b-jets (higgsino-like NLSP)? 1. Measuring the Missing Transverse Energy 52

53 Outlook (3/4) LHC results: challenging SUSY reach further! 1) Optimize analyses e.g. γ+jets+et (wino-like): High masses: EWK production less stringent jet selection? leptons? More exotic, less inclusive: additional b-jets (higgsino-like NLSP)? Taken from: L. Hill, LBNL SUSY Workshop ) New searches EWK production Low ET 3rd generation, e.g. stop Intermediate (via gluino): mg< 800 GeV Direct production: no LHC result ~ mstop < GeV 1. Measuring the Missing Transverse Energy Reinterpretation of LHC results Taken from: M. Papucci, et. al. arxiv: v1 53

54 Outlook LHC 2012 (4/4) Higher beam energies (8 TeV), higher luminosity +400 % +30% Taken from: Chamonix '12 Summary, CERN Find or exclude (SM?) Higgs SUSY? Other BSM? Measuring the Missing Transverse Energy 54

55 Backup 55

56 Analysis: γ+jets+met 56

57 Trigger efficiencies 57

58 Systematic uncertainties 58

59 >=3 jets 59

60 60

61 Sample Limit Calculation pb obs. upper limit Total number of signal events 61

62 Contributions from individual bins 62

63 Signal Contamination 63

64 Theor. Uncert. on cross section 64

65 GGM model parameter 65

66 Higgsino-like NLSP higgsino-like NLSP 66

67 SM Background: ISR/FSR Further background: ISR/FSR tt+jets initial/final state radiation of γ, W/Z+jets intrinsic E from ν's T Use MC simulation to estimate contribution Madgraph + Pythia no events with electrons on generator level (estimated already by fe->y) Assign conservative systematic uncertainty: 100% C Photon p T = Fake Photon Photon 67

68 SM Background: QCD 68

69 SM Background: e γ (EWK) Closure Test 69

70 Number of jet dependency 70

71 Theoretical uncertainties 71

72 2 vs 3 jet selection 72

73 Eventdisplays MET tail Punch-through? Masked ECAL? 73

74 Photon/Electron ID Object definitions very similar to di-photon, but No additional IsoVL cuts applied (needed due to trigger requirements for di-photon Higher upper cut on fake-photon isolation to ensure statistics PU correction derived with same methods, but for the slightly different photon Id Details: Photon ID (isolation cone 0.3):!hasPixelSeed() R9()<1 CombinedIsolation*<6 GeV σiηiη<0.011 H/E<0.05 Combined isolation = ecaliso() *rho + hcaliso() *rho +trackiso() < 6 GeV Fake Photon ID (jet FO) (isolation cone 0.3) Same as photon, but: CombinedIsolation> 6 σiηiη>0.011 CombinedIsolation* < min(30,0.3*pt) *CombinedIsolation=ecalIso**+hcalIso**+trackIso **PU correction for ecal/hcal iso applied: EcalIso=ecalIso() *rho(eta<2.5) HcalIso=hcalIso() *rho(eta<2.5) Electron ID: like photon but with pixel seed 74

75 Analysis: MET 75

76 Pf Corrections 76

77 Data driven results: all data points 77

78 Performance in Z ee 78

79 Performance in Z ee 79

80 Systematic uncertainties Quark-gluon- composition:1.5-6 % UT vs U: ~4 GeV negligible effect on scale compared to other uncert. 80

81 Minimum Bias 81

82 Punchthrough & masked ECAL Mask ECAL cells in simulation (only the ones masked in the real detector) 82

83 Z ee event selection pt>20 GeV 60 GeV< Minv<120 GeV 83

84 Higgs searches 84

85 Higgs 85

86 Higgs 86

87 SUSY & Higgs 87

88 CMS 88

89 UED CMS-PAS-SUS

90 Long lived NLSP CMS-PAS-EXO

91 JES From: JINST 6 (2011) P

92 CMS material thickness 92

93 CMS detector photons EB edge η =1.479 leptons ME edge η =2.1 jets HF edge η =2.6 beam line Interaction point 93

94 Event reconstruction 94

95 ATLAS Exotica Summary 95

96 ATLAS Summary 96