Non-Simplified SUSY: Stau Coannihilation at LHC and...
Transcript of Non-Simplified SUSY: Stau Coannihilation at LHC and...
Non-Simplified SUSY: Stau Coannihilation
at LHC and ILC
M. Berggren, A. Cakir, D. Krücker, J. List, A. Lobanov, I.-A. Melzer-Pellmann
Linear Collider Forum
DESY 2013
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Outline
! Introduction ! LHC Analyses ! ILC Analyses ! Summary
Isabell-A. Melzer-Pellmann LC Forum – DESY 2013
Storyline
! What if LHC sees some kind of signal, but cannot distinguish between ! Is it SUSY or other BSM models? ! Is it more than one new particle? ! What are the masses and other properties of the new particles? ! Can LHC distinguish between different production processes? ! Do we see THE dark matter?
! Can ILC add information and see particles that LHC cannot see (or at least not distinguish)?
à LHC: discovery of colored states à ILC: precise measurement of EW states
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Storyline
! Choose a full model that is compatible with all recent observations, e.g.: ! Higgs @ 125 GeV ! Relic density ! Latest results of direct dark matter searches
! Full model chosen as example here: SUSY pMSSM model with small mass difference (10 GeV) between stau and LSP
• Four models with differing stop masses:
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Model name Mass parameter of right-handed top quark / GeV
Stop mass / GeV
STC4 400 293
STC5 500 416
STC6 600 527
STC8 800 736
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Full Spectrum STC4
! Low stop mass à large direct stop production cross section
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Full Spectrum STC5
! Relatively low stop mass à direct stop production cross section much smaller than in STC4
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Full Spectrum STC6
! EWkino production gains more weight
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Full Spectrum STC8
! EWkino production has largest cross section
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Lower part of STC8 Spectrum
! Many different decays at lower masses
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Cross sections for all models (LHC)
! Inclusive cross sections ! LO calculated with Pythia6 ! NLO calculated for most
sub-processes with Prospino2.1
! STC4 dominated by direct stop production
! EWkino cross sections quite dominating in the other scenarios
! 33 TeV cross section to be taken with some caveat – PDFs not known here…
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Sub-process cross sections for STC8
! NLO calculated where possible
! Gluino-gluino production ~0.2 fb à expect ~600 events at 3000 fb-1
! Direct production of first 2 generations ~20fb à 60.000 events à expect more sensitivity for these (e.g. search for high-energetic jets and MET, no b-tags)
! EWkino production dominates
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Where we are…
! Introduction ! LHC Analyses ! ILC Analyses ! Summary
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Figure 3: Expected and observed 95% C.L. exclusion limits in the mt̃1 −mχ̃01plane for ∆m = 5
GeV. The black, dashed line shows the expected limit if theoretical uncertainties on the signalare neglected. The yellow band shows the±1σ uncertainty on the expected limit. The red solidline shows the nominal observed limit, while the red dashed lines show its variation if theoryuncertainties on the signal are taken into account.
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Reach of current 8 TeV Analyses
! Full-hadronic analysis from ATLAS: ATLAS-CONF-2013-001 ! m_stop = 293 GeV and m_N1 = 95 GeV lies in excluded region, but…
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STC4
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Reach of current 8 TeV Analyses
! Full-hadronic analysis from ATLAS: ATLAS-CONF-2013-001
à No observation with current analysis expected
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Reach of current 8 TeV Analyses
! CMS EWkino Analysis PAS-SUS-12-022 ! Mass parameters outside excluded
region for case with stau mass in middle of C1 and N1 (even worse if stau closer to N1)
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LHC: Search for Stops (0 leptons)
! Simple cut-and-count analysis, inspired by ATLAS 8 TeV full-hadronic analysis: ! Lepton veto (no identified lepton with pT > 10 GeV) ! N_jets > 3
! Jet1: pT > 120 GeV ! Jet2: pT > 70 GeV ! Jet3: pT > 60 GeV
! N_btag >= 2 ! HT > 1000 GeV ! dΦ(MET, Jet1,2) > 0.5 ! MET/Meff > 0.2 ! MET > 750 GeV
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LHC: Search for Stops (0 leptons)
! Control plots before cut on MET, MET/Meff, Δφ(Jet1,2 and MET):
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LHC: Search for Stops (0 leptons)
! Discovery and exclusion sensitivity depends on systematic uncertainty
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LHC: Search for Stops (0 leptons)
! Full-hadronic search reaches 5σ discovery only for STC4 and systematic uncertainty of ~15%:
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LHC: Search for Stops (1 lepton)
! Simple cut-and-count analysis, inspired by ATLAS 8 TeV full-hadronic analysis: ! Exactly one e/µ with pT > 10 GeV, veto 2nd e/µ with pT > 10 GeV) ! N_jets > 3, with pT > 40 GeV ! N_btag = 1 or 2 ! dΦ(MET, Jet1,2) > 0.5 ! MET > 500 GeV ! HT > 500 GeV ! MT > 120 GeV
! MT2W > 250 GeV
or topness > 9.5, pT asymmetry (lepton, jet1) > -0.2
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topness: see arXiv:1212.4495
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LHC: Search for Stops (1 lepton)
! Control plots before cut on lepton and jet requirements: MT and lepton pT after the MT requirement
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LHC: Search for Stops (1 lepton)
! Discovery and exclusion sensitivity depends on systematic uncertainty
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LHC: Search for Stops
! Single-lepton search reaches 5σ discovery only for STC4 and STC5 and systematic uncertainty of ~15% with 300 fb-1, High Lumi LHC (3000 fb-1) needed for discovery of all four models:
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LHC: Search for EWkinos
! Search for same-sign leptons coming from: ! N2 C1 production, where
! N2à stau tau à tau tau N1 ! C1 à tau N1
! expect at least same-sign + additional lepton
! Rough comparison to same-sign analysis in PAS CMS-12-022 ! 8 TeV signal yields less than 10 Events for STC4 (where 11 are observed in
data and compatible with BG expectation)
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LHC: Search for EWkinos
! Need to reduce systematic uncertainties to exclude EWKinos, 5σ discovery hardly possible if uncertainty larger than 15%
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LHC Search – Conclusion
! High Lumi LHC will be able access all four models with 3000 fb-1, but:
! it will be difficult to identify the nature of the access ! EWkino sector will be difficult to see with more than 3σ ! staus very difficult for LHC ! will need ILC to further identify particle masses etc.
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Where we are…
! Introduction ! LHC Analyses ! ILC Analyses ! Summary
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ILC: Precision Measurement
! At ILC (@ 500 GeV), all sleptons and bosinos can be produced with reasonable cross section (inclusive for both polarizations about 3pb)
! Full lines: P(e+e−) = (−0.3,+0.8) ! Dashed lines: P(e+e−) = (+0.3, −0.8)
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ILC: Stau_1 Measurement
! Very clean signal after few cleaning cuts ! Stau_1 can be measured with precision of 200 MeV
endpoint determination cross section determination using region between arrows
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ILC: Stau_2 Measurement
! Not only stau_1, but also stau_2 can be measured with high precision up to 5 GeV:
endpoint determination cross section determination using region between arrows
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ILC: Measurement of smuon
! Reconstruction of invariant di-muon mass à edge for smuon
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ILC: Measurement of smuon
! Reconstruction of invariant di-muon mass à edge for smuon
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/ ndf = 20.57 / 262χBackground(B) 2.93± 55.22 Edge (E) 0.0± 82.5 Width (S) 0.402± 1.747 Signal Amplitude (A) 5.8± 47.1 Signal Tail (T) 0.0785± 0.2713 Background Exp (BE) 0.0647± 0.9554 Background Slope (BS) 5.61± -79.82
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Background(B) 2.93± 55.22 Edge (E) 0.0± 82.5 Width (S) 0.402± 1.747 Signal Amplitude (A) 5.8± 47.1 Signal Tail (T) 0.0785± 0.2713 Background Exp (BE) 0.0647± 0.9554 Background Slope (BS) 5.61± -79.82
Standard Model BackgroundSUSY background
01χµµ → µµ∼ → 0
2χTotal signal
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ILC: Measurement of smuon
! Mu energy spectrum (smu_L)
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ILC: Measurement of smuon_L
! Mu energy spectrum (smuon_L)
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Amplitude(A) 2.94± 48.92 Edge (E) 0.04± 32.25 Slope (S) 1.10605± 0.03249 Background (B) 1.65± 38.21
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/ ndf = 8.39 / 142χAmplitude(A) 3.51± 43.97
Edge (E) 0.2± 151.5
Slope (S) 0.1233± 0.3775
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ILC: Measurement of Tau Helicity
! Tau polarization: depends on ! mixing angle θstau of the chiral eigenstates to mass eigenstates ! amount of Higgsino and gaugino eigenstates of N1 (gaugino and fermions:
conserving chirality; Higgsino: Yukawa coupling flips chirality)
! Ratio of pion over jet energy differs for different tau helicity both tau leptons opposite both tau leptons right-handed helicity left-handed
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c)
Figure 15: Distribution of R = Eπ/Ejet before (open histogram) and after event selection(grey (yellow) histogram). a): both τ leptons are right-handed. c): the τ leptons haveopposite helicity. r): both τ leptons are left-handed.
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Figure 16: The distribution of R = Eπ/Ejet in the selected sample. The line shows thefitted efficiency and background corrected model.
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Dark Matter
! Prediction of the relic density based on the assumption that the χ10 is the
only contribution to Dark Matter
! LHC alone can never reach precision as LHC+ILC ! ILC has high predictive power also for MSSM with 18 parameters
(compared to mSUGRA with 4 parameters)
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Where we are…
! Introduction ! LHC Analyses ! ILC Analyses ! Summary
Isabell-A. Melzer-Pellmann LC Forum – DESY 2013
Summary and Conclusion
! LHC capable to observe all four studied models due to discovery of the light third generation squarks
! Gluino measurement difficult due to low cross section ! Sensitivity to EW sector at LHC very low due to challenging stau decays –
sensitivity depends on control of systematic uncertainty à Need ILC for precision measurements of the EW sector
à At ILC all sleptons and bosinos with masses low enough to be produced with ILC energy have reasonable cross section to be measured, e.g.:
à Mass measurements of stau_1 and stau_2 à Mass measurements of smuons à Measurement of tau helicity
à ILC needed for Dark Matter question!
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Thank you for listening
Backup slides follow…