Long-Lived stau Signature in the LHC

Transcription

1 Long-Lived stau Signature in the LHC Sho IWAMOTO The University of Tokyo, JAPAN DESY, Deutschland. Based on ATLAS collaboration Asai, Azuma, Endo, Hamaguchi, and Iwamoto. Theory group (Phenomenologists) Stau Kinks at the LHC. JHEP 1112 (2011) 077. [arxiv: ](hep-ph)

2 Talk Plan 1. SUSY SUSY search The LHC experiment 2. Long-lived stau signature stable stau signature stau kink signature SUSY Long-lived stau scenario stable stau stau kink 3. Stau Kink in detail Based on Asai, Azuma, Endo, Hamaguchi, and Iwamoto. Stau Kinks at the LHC. JHEP 1112 (2011) 077. [arxiv: ](hep-ph) <2>

3 CONCLUSION <3>

4 or THE MAIN MESSAGE <4>

5 Stau = Charged Long-lived stau a track in detectors ATLAS detectors (in the LHC) <5>

6 Stau = Charged Long-lived stau a track in detectors When decay inside track bends neutral charged Stau Kink Stau kink search is realistic & interesting. ATLAS detectors (in the LHC) <6>

7 1. SUSY and its Signature <7>

8 Standard Model Successful! Hierarchy problem supersymmetry MSSM [Minimal Supersymmetric Standard Model] Hierarchy solved. GUTs & Dark Matter? However <8>

9 Standard Model Successful! Hierarchy problem supersymmetry MSSM [Minimal Supersymmetric Standard Model] Hierarchy solved. GUTs & Dark Matter? However <9>

10 Standard Model Successful! Hierarchy problem supersymmetry MSSM [Minimal Supersymmetric Standard Model] Hierarchy solved. GUTs & Dark Matter? We want to discover SUSY. <10>

11 How to discover SUSY? What is characteristic in SUSY? Important one: R-parity If R-parity is conserved Proton decay problem avoided! LSP becomes stable! must be neutral. would be a Dark Matter candidate. <11>

12 How to discover SUSY? What is characteristic in SUSY? [Case 1] Signature from stable neutral particles Large missing energy = escaping (missing) particle; e.g. or. <12>

13 [Case 2] Signature from long-lived charged particles expected in several models. We will see in the next section. Then, where can we discover SUSY? of course, <13>

14 LHC <14>

15 LHC

16 We focus on LHC <16>

17 <17>

18 inner detectors (trackers) ele-mag calorimeters hadron muon spectrometer [m] [sectional (cut-away) view] <18>

19 inner detectors (trackers) ele-mag calorimeters hadron muon spectrometer hadron [m] Note immediately decays into leptons (35%) hadrons (65%) is observed. hadrons are observed. <19>

20 2. Long-lived Stau Signature Scenario with Long-lived stau Its Signature 1. Stable stau 2. Stau kink <20>

21 [Case 2] Signature from expected in several models: (We don t consider -case for simplicity.) long-lived charged particles (in GMSB framework) weakness of gravity tiny R-parity violation phase-space suppression Right: Jittoh et al., PRD [hep-ph/ ] <21>

22 [Case 2] Signature from long-lived charged particles signature depends on where stau decays. a) outside detectors b) inside a detector c) at the very center <22>

23 [Case 2] Signature from long-lived charged particles signature depends on where stau decays. a) outside detectors b) inside a detector c) at the very center Signature depends on the decay mode. (tau-rich or lepton-rich signature, etc ) <23>

24 [Case 2] Signature from long-lived charged particles signature depends on where stau decays. a) outside detectors b) inside a detector heavy μ-like track c) at the very center Signature depends on the decay mode. (tau-rich or lepton-rich signature, etc ) <24>

25 inner detectors (trackers) ele-mag calorimeters hadron muon spectrometer hadron quasi-stable [m] <25>

26 How to measure velocity? 1. Energy Deposit Bethe-Bloch formula A function of velocity! measured at an inner detector RED: material dependent BLUE: constants 2. Time of flight (TOF) at Tracker and MS 1ns resolution Simulation is distinguishable from. ATLAS coll., EPJ C62 (2009) 281 <26>

27 Current Bounds on STABLE LEP DELPHI [PLB478.65; hep-ex/ ] (direct production) OPAL [PLB572.8; hep-ex/ ] (direct production) LHC ATLAS (37pb -1 ) [PLB ; ] (assuming a GMSB model) (EW production = generic) CMS (1.1fb -1 ) [CMS-PAS-EXO ] (assuming a GMSB model) <27>

28 [Case 2] Signature from long-lived charged particles signature depends on where stau decays. a) outside detectors b) inside a detector c) at the very center heavy μ-like track Kink track etc. depends on the decay mode. (tau-rich or lepton-rich signature, etc ) <28>

29 Signature depends on Decay into WHAT? Complicated, determined by underlying model <29>

30 Long-lived stau scenarios 2-body hadron 4-body <30>

31 Long-lived stau scenarios 2-body (kink track) <31>

32 Kink track id. id. of stau track by a tracker id. of daughter track by a tracker <32>

33 Kink track id. id. of stau track by a tracker id. of daughter track by a tracker We have to do two id. in 1m <33>

34 Kink track id. id. of stau track by a tracker id. of daughter track by a tracker We have to do two id. in From ATLAS coll. [ ] <34>

35 Kink track id. id. of stau track by a tracker id. of daughter track by a tracker We have to do two id. in <35>

36 Kink track id. id. of stau track by a tracker id. of daughter track by a tracker We don t use end-cap for simplicity. <36>

37 Kink at TRT 1 st or 2 nd module can be observed. We don t use end-cap for simplicity. <37>

38 With this method, we can observe kinks. Sweet range (of stau) 300GeV stau can be observed. Some CMSSM-model is assumed. Efficiencies are considered. Background events are fairly suppressed. <38>

39 3. Stau Kinks in detail <39>

40 Stau kinks in detail Technical topics (experiment) trigger and efficiency track reconstructions and efficiency background events Monte Carlo simulation etc Physical topics (phenomenology) We can discriminate the models!! <40>

41 Long-lived stau scenarios (nearly massless) <41>

42 Kink type daughter signature Daughter lepton discrimination Ratio of the daughter leptons = Underlying models <42>

43 inner detectors (trackers) ele-mag calorimeters hadron muon spectrometer hadron had. decay Lep. decay Daughter lepton can be distinguished [m] <43>

44 (phenomenological) Conclusion Stau (slepton) in-flight-decay observable as kink events. decay length: Stau mass: (Much more luminosity allows us to go further.) This decay length corresponds to gravitino model: R-parity violation: Model discrimination is possible. <44>

45 Stau kinks in detail Technical topics (experiment) trigger and efficiency track reconstructions and efficiency background events Monte Carlo simulation etc Physical topics (phenomenology) We can discriminate the models!! <45>

46 Monte Carlo Simulation Method Benchmark Point: CMSSM model mass spectrum: event generation: fast detector sim.: SUSY-HIT Pythia6 PGS4 PGS4-based fast detector simulation [GeV] <46>

47 Monte Carlo Simulation Event selection <47>

48 Monte Carlo Simulation Event selection Trigger: 1jet(70) + MET(40) is stable (90% eff.) above this point. <48>

49 Monte Carlo Simulation Event selection TRT = information (know nothing about on z-direction.) TR azimuthal opening angle can be measured. TRT (1) (2) (3) <49>

50 Monte Carlo Simulation GOOD Event selection BAD Daughter must go through TRT (3). in order to the daughter reconstruction. <50>

51 Monte Carlo Simulation Event selection <51>

52 Possible Background Events Stable charged hadrons: Hit to detector material Few hadrons have Few hadrons interact with material. suppressed. In-flight-decay of hadrons suppressed. false tracks from noise We require two tracks (mother & daughter) ignorable. background events are ignorable! <52>

53 Numerical Results (again) Sweet range (of stau) 300GeV stau can be observed. Some CMSSM-model is assumed. Efficiencies are considered. Background events are fairly suppressed. <53>

54 Conclusion (again) Stau (slepton) in-flight-decay observable as kink events. decay length: Stau mass: (Much more luminosity allows us to go further.) This decay length corresponds to gravitino model: R-parity violation: Model discrimination is possible. <54>

55 <55>

56 <56>

57 <57>

58 7TeV, 5fb -1 <58>

59 8TeV, 5fb -1 <59>

60 14TeV, 10fb -1 <60>

61 Monte Carlo System <61>

62 SUSY spectrum generator SUSY-HIT Pythia6 Event generator others decay PGS4 Detector simulation (jet/met) Tauola C++ interface Decay of τ Pythia6 Decay of τ decay products Kink analysis Trigger analysis