1 / 61

SU PER SY MMETRY @ LHC a Selection

SU PER SY MMETRY @ LHC a Selection. Ulrich Goerlach IPHC-IN2P3 CNRS ULP Strasbourg, France. Why SUSY SUSY at the LHC (Some examples) Strategy for (early) discovery Mass reconstructruction (Model parameters) Conclusions. Thanks to the many excellent talks

waterhouse
Download Presentation

SU PER SY MMETRY @ LHC a Selection

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. SUPERSYMMETRY @ LHC a Selection Ulrich Goerlach IPHC-IN2P3 CNRS ULP Strasbourg, France • Why SUSY • SUSY at the LHC • (Some examples) • Strategy for (early) discovery • Mass reconstructruction • (Model parameters) • Conclusions Thanks to the many excellent talks at recent conferences ! Apologies to everybody, whose work is not mentioned!

  2. Supersymmetry-Industry More than 7000 papers since 1990 "One day, all of these will be supersymmetric phenomenology papers."

  3. Why SUperSYmmetry (I) Since over 35 years (theoretical) physicists loveSUSY • SUSY is naturally implemented in string theories • SUSY is NOT a gauge symmetry, but the only and last extension of spacetime symmetry to be discovered • partners for all SM fields: Q|Boson, spin J> = |Fermion, spin J + ½> Q|Fermion, spin J> = |Boson, spin J - ½>

  4. Minimal Supersymmetric Standard Model SUSY Primer, S.P. Martin hep-ph/9709356

  5. loop correction (all fermions up to cutoff scale L ) + free mass loop correction (scalars) SUSY: ... + Perfect cancellation: Soft breaking: Why SUperSYmmetry (II) • stabilises Higgs mass against loop corrections from new physics (gauge hierarchy, naturalness or fine-tuning problem) • Leads to Higgs mass ≤ 135 GeV Planck scale 1028 eV, 10-35 m Electroweak scale 1011 eV, 10-18 m

  6. Top-Quark Mass at the Tevatron CDF & D0, hep-ex/0608032 Heinemeyer et al., hep-ph/0611373

  7. SUSY Why SUperSYmmetry (II) • SUSY modifies the running of the 3 coupling constants od the SM enough to assure unification of the four interactions at the GUT scale • SUSY scale is  1 TeV • SUSY is a broken Symmetry  many new heavy sparticles • If R-Parity = (-1)3(B-L)+2S is conserved: • sparticles are created in pairs • The LSP is stable  Best dark matter candidate SM

  8. SUperSYmmetry Breaking (SSB) • Standard Model19 free parameters • SUSY breaking is completely unconstrained • spontaneous SUSY breaking at high energy in hidden sector • Symmetry breaking has to be mediated to lower energy Effective Lagrangian (= ignorance w.r.t. SSB) at low energies, which is supersymmetric except for explicit soft SUSY-breaking terms • M.S.S.M. • unconstrained, many new parameters +105 (note: if RPV add + 48) • Constrained models (cMSSM): Spontanous symmetry breaking is "mediated" to the EW scale • mSUGRA (Supergravity, assuming universality at GUT scale) m0, m1/2, A0, tan β, sgn μ; +5 • G.M.S.B. (Gauge(EW) Mediated) λ, Mmes, N5, tan β, sgn μ, Cgrav +6 • A.M.S.B. (Anomaly mediated, SSB on different brane) m0, m3/2, tan β, sgn μ +4

  9. SUSY Breaking II mSUGRA • Supergravity (SUSY is local symmetry  Gravity • Universal scalar and gaugino mass at GUT scale • Gravity mediated from GUT- to EW-scale via RGE • R-Parity conserved • LSP is the neutralino, 10 • Constrained MSSM (1245 paramètres) • m0 : universal scalar mass • m1/2 : universal gaugino mass • A0 : tri-linear couplings • tanb : VeV- ratio of the two higgs doublets • sign(m) : sign of the Higgs mixing parameter • Gives "pricise predictions" and can easily be connected to cosmological dark matter constraints

  10. SUSY-breaking III • Non constrained MSSM • Generalised mSUGRA (give up universality of masses at GUT scale) • GMSB • Messengers (new chiral supermultiplets) • EW gauge interactions  soft breaking terms in Lagrangian • Gravitino is LSP : • NLSP has finite lifetime ct  µm ..... km : • Λ = universal soft SUSY breaking scale • Mmes = messenger mass scale • N5 = messenger index (number of multiplets) • tan β, sgn μ, • Cgrav • Other SSB schemes • R-Parity Violation (RPV)

  11. 10 lepton slepton (NLSP) 10 lepton SUSY and dark Matter WMAP : 0.094 < Wm h2=nLSPmLSP< 0.129  rLSP = LSP mass LSP density LSP density ~ 1/ s(  ) s(  )  m2/ (m2  m2)2 ~ rLSP (m2  m2)2 / m  m3 ~ Patrick Janot - GDR SUSY,8 avril 2005

  12. 'Focus point' region: significant h component to LSP enhances annihilation to gauge bosons Slepton Co-annihilation region: LSP ~ pure Bino. Small slepton-LSP mass difference makes measurements difficult. ~ ~ c01 t ~ c01 l ~ t1 ~ ~ t1 g/Z/h lR ~ c01 l Also 'rapid annihilation funnel' at Higgs pole at high tan(b), stop co-annihilation region at large A0 SUSY Dark Matter mSUGRA A0=0, tan(b) = 10, m>0 • SUSY (e.g. mSUGRA) parameter space strongly constrained by cosmology (e.g. WMAP satellite) data. Ellis et al. hep-ph/0303043 Disfavoured by BR (b  s) = (3.2  0.5)  10-4 (CLEO, BELLE) 'Bulk' region: t-channel slepton exchange - LSP mostly Bino. 'Bread and Butter' region for LHC Expts. 0.094    h2  0.129 (WMAP) 0.094 < rLSP< 0.129

  13. 1 fb gluinos 1 fb squarks Some SUSY Phenomenology • Production cross sections: • squarks • gluinos • Decay modes depend on mass spectrum

  14. SPS1a tanb=10 LM2 35 LM5 10 LM1 10 LM9 (ATLAS) Benchmark points CMS • Low mass points for early LHC running but above Tevatron reach • High-mass points for ultimate LHC reach • Indirect WMAP constraintsexcept LM1, 2, 6, 9 (in favor of signatures) 21h 21Z

  15. Higgs at the limit of LEP reach light sleptons SPS1a point This point has been extensively studied by Atlas (fast simulation), favourable at LHC m0= 100 GeV, m1/2= 250 GeV, A0= -100 GeV, tan(β)=10 , μ>0 Moderately heavy gluinos and squarks Heavy and light gauginos

  16. proton proton SUSY Signatures Q: What do we expect SUSY events @ LHC to look like? A: Look at typical decay chain: • Strongly interacting sparticles (squarks, gluinos) dominate production. • Gauginos and quarks g cascade decays to LSP. • Event topology: • High pT jets (from squark/gluino decay) • Large ETmiss signature (from LSP) • High pT leptons, b-jets, t-jets • (depending on model parameters) • Closest equivalent SMsignature (Background) is tgWb. • Best strategy for mSUGRA is : • ETmiss + jets + n-leptons

  17. Selection of SUSY topics at LHC • Global selection of SUSY events • Inclusive analyses, discovery reach • MET and jets • Adding leptons • Single muons • same-sign dimuon • opposite-sign same flavor dielectron and dimuon • opposite-sign same flavor hadronic ditau • trileptons at high m0 • Z0 and Higgses • Top stop • Reconstruction of sparticle masses • Di-Leptons ee mm taus • Adding jets • (Spin determination) • (Model parameters)

  18. ETmiss + jets candidate event display ETmiss =360 GeV, ET (1)=330 GeV, ET (2)=140 GeV, ET (3)=60 GeV

  19. Analysis Results(LM1) Selected SUSY and Standard Model background events for 1 fb-1. * (S) is ~13% with S/B ratio ~26. The 5 discovery can be reached by using ~6 pb-1 data collection (w/ sys+stat uncertainties in the significance estimation) CMS CMS Meff ETmiss *Due to limited Monte Carlo event generation the analysis path on QCD data is carried out without topological cuts and ILV. The estimate is conservative and based on the parameterization of the efficiency for cleanup and ILV requirements for ETmiss > 700 GeV

  20. But: Missing Transverse Energy Clean up cuts needed: cosmics, beam halo, dead channels, QCD

  21. QCD Data and Cleanup CMS • QCD jet production cross-section is very large at LHC. (j(2), (ETmiss)) > 20 deg QCD jets  2 + ETmiss > 93 GeV • Missing transverse energy in QCD jet production mostly due to jet mis-measurements and detector resolution. CMS CMS 3) SUSY LM1 QCD Effect of QCD Topological Reqs. (Acceptance Efficiency) min(j, (ETmiss)) > 0.3 rad Multi jets and large missing transverse energy data sample is dominated by QCD!

  22. MET Calibration Using Z-Candle Measure Z+jets with Z mm in data to normalize Z nn (invisible) contribution and calibrate MET spectrum With ~1fb-1 we will have enough Z+jets in the PT(Z)>200 GeV region of interest to normalize within 5% the invisible Z process as well as W+jets through the W/Z ratio and lepton universality dN/dPTmiss

  23. Discovering SUSYand Evaluating MSUSY RPC models signature: MET + several high-pT jets  Build discriminating variable Meff: where Coannihilation point Full sim 20.6fb−1 SUSY signal SM Bkg (Herwig)

  24. SUSY inclusive search Effective mass (after bkg. subtraction) Effective mass ATLAS Preliminary ATLAS Preliminary 0-lepton mode, L=1fb-1 0-lepton mode, L=1fb-1 Correct 30% over-estimate 30% under-estimate signal MSUSY~1TeV ATLAS Preliminary background Result with fast simulation. only scale is changed (slope is same). Important to understand background scale and slope.

  25. Inclusive MET + Jets + Muons Add lepton  clean trigger A0 = 0, tan(b) = 10, sign(m) = +1 Cuts optimized @LM1 • 1 isolated muon • pT > 30 GeV • MET > 130 GeV • 3 jets: • ET> 440, 440, and 50 GeV • ||< 1.9, 1.5, and 3 • Cuts on  between • jets and MET 30 fb-1 and 60 fb-1 : Re-optimised cuts for higher lumi m1/2 Optimised cuts for 10 fb-1 luminosity m0 Background (10 fb-1) 2.5 ev, systematic uncertainty ~20%

  26. LEP Tevatron Same-Sign Muon Reach A0 = 0, tan(b) = 10, sign(m) = +1 Even cleaner signature with low background due to same-sign requirement 100 fb-1 Optimized cuts for 10 fb-1 luminosity m1/2 Cuts optimized @LM1 • 2 SS isolated muons • pT > 10 GeV • MET > 200 GeV • 3 jets: • ET1>175 GeV • ET2>130 GeV • ET3>55 GeV 1 fb-1 m0 Background (10 fb-1) 1.5 ev, systematic uncertainty ~23%

  27. Inclusive MET + Top Catch stop decays to top Cuts optimized @LM1 Top is SM physics, SUSY -background and -signal Strong top analysis group (ex-D0) in Strasbourg (IPHC) • MET>150 GeV • Hadronic top selection and 2C fit • 1 b-jet + 2 non-b jets • Use the W and top mass constraints to fit top • and require good 2 LM1 signal LM1 ~200 pb-1 for 5 observation sys. uncertainty ~12%

  28. proton proton Inclusive Higgs Search in SUSY events

  29. Inclusive Higgs Search LM5 1 fb-1 Consider Dominant squark decay chain in a significant domain of mSUGRA parameter space m(h)=116 GeV LM5 full simulation selection MET > 200 GeV ET (jet 1,2,3,4) > 200,150,50,30 GeV 2 tagged hi-quality b-jets in the same hemisphere closest in h-f-space Signal efficiency ~ 8%, main bkgd. – ttbar 5 s excess with 1.5 fb-1 m(h) = 112.9  6.6(stat.)  7.5(syst.) GeV

  30. Inclusive SUSY searches Search strategy based on different signatures Low mass SUSY(mgluino~500 GeV) shows excess in many channels for O(100) pb-1 Time for discovery determined by:  Time to understand the detector performance, Etmiss tails, jet scale,lepton id  Time collect SM control samples such as W+jets, Z+jets, top..

  31. Two leptons in a cascadeLM2 tanb=35 proton proton

  32. Di-Lepton Mass Edge Measure invariant mass distribution of same-flavor opposite-sign (SFOS) leptons as evidence for Endpoint in mass spectrum exhibits sharp edge dependent on sparticle masses Subtract different flavour leptons LM with 1 fb-1, fit result (expected 81 GeV):

  33. BF for :96% At large tanb, suppressed Cascade decays LM2 Point m0 = 185 GeV m1/2 = 350 GeV tan β = 35 A0 = 0; μ > 0 Dominique J. Mangeol Cascade decays at LM2 ___ tanb=10 ___tanb=35 At lower tanb One could measure tanb by the branching ratio !? UG SUSY is one of the main physics topics of the CMS group in Strasbourg (IPHC) hep-ph/0306219 LM2 compatible with WMAP result Probing this sector of SUSY essential BUT…

  34. Dominique J. Mangeol Always one very soft tau per event To reconstruct a full cascade we need to tag both tau's produced by neutralino2 and stau Experimentally difficult !!!!

  35. Dominique J. Mangeol Event selection • Selection: • Large Etmiss ( 2 LSP's) • 2 energetic jets (one for each cascade) • at least two hadronic tau's with DR(t,t)<2 2 t, DR(t,t)<2 Cut Etmiss>150GeV • Main backgrounds: • QCD multi-jet events (50%) • ttbar (39%) • W+jets (11%) Cut 2 jets avec Et>150GeV

  36. Dominique J. Mangeol Discovery potential of SUSY in di-tau final states Generalizing LM2 results to any m0,m1/2 values and for tanb=10 and 35 5s discovery contours systematics on background accounted for SUSY with di-tau final states could be discovered very early in LHC running

  37. Dominique J. Mangeol SUSY Mass Spectrum Measurement End-Point technique: With this cascade: 3 observables Hence: Fully resolved system of equations Position of end-point not changed by loss of neutrinos, but much more difficult to extract !!!

  38. 95±5 GeV Dominique J. Mangeol End-Point extraction (di-tau's) • Large Combinatorial background due to multiple candidates • Need to understand this background to extract end-points: • Fit the background distribution • Fit the distribution sum signal+background • For di-tau invariant mass: • Di-tau from have always opposite charge • Di-tau from combinatorics estimated with same charge di-tau Extract end-points from the fits Measure invariant masses at 40fb-1

  39. 559±11 GeV 596±12 GeV 780±20 GeV 298±7 GeV Dominique J. Mangeol Invariant mass distribution with tau's and jets extraction of end-points

  40. Dominique J. Mangeol From end-points to masses aFor one set of end-points several mass combinations are possible depending on sparticle mass hierarchy hypothesis In this analysis, 2 hypotheses returns a physical solution: Used for mass calculation

  41. Dominique J. Mangeol From End-point to masses E5 end-point is used to choose between the 2 solutions: E5 calculated using the 2 mass solution gives 765GeV in case (1) and 815 GeV in case (2) E5 extracted from the mass invariant gives 780±20GeV aIn better agreement with case 1 (LM2) CMS Note 2006/096

  42. Di-lepton Endpoint inVarious mSUGRA Scenarii Depending on point: different shape, number of edges, 2-body vs 3-body decay, … Focus Point Coannihilation ATLAS MC truth lL MC truth lR Full sim 6.9fb−1 signal Full Sim 20.6fb−1 • 2 edges for left and right slepton • m0 large,heavy scalars •  no sleptons in  decays • direct 3-body decay: • small BR • at least 1 lepton with • small pT S. Laplace, "Mass Reconstruction Methods"

  43. Sbottom and Gluino Masses:Near The l+l- Endpoint • Near l+l- endpoint: LSP and l+l- are at rest in frame, • thus can evaluate momentum (approximation): where and are known from endpoints b b • Add 1 or 2 b-jet to get sbottom and gluino masses: and SPS1a Fast sim 300 fb-1 Correlation between and =2.2 GeV Wrong associated b-jet SUSY bkg Spread from p(2)approximation is common to both masses Gluino – sbottom masses Gluino mass B.K. Gjelsten et al, ATL-PHYS-2004-007 S. Laplace, "Mass Reconstruction Methods"

  44. Obtaining the Fundamental Model Parameters LHC Measurements SUSY Model Ex: mSUGRA m0, m1/2, A0, tan, sgn() Spectrum Generator (Ex: SUSPECT, SoftSUSY, …) Ex: endpoints Fit: 2 Mes. Note: better to exploit edges than masses (correlations) S. Laplace, "Mass Reconstruction Methods" R. Lafaye, T. Plehn, D. Zerwas, hep-ph/0512028

  45. Sign(μ) fixed An Example List of measurements (300 fb-1) SFITTER program: mSUGRA Parameter determination R. Lafaye, T. Plehn, D. Zerwas, hep-ph/0512028 Note: m(ll) most powerful input (m0 driven by 1st and 2nd generation slepton sector)

  46. proton proton Conclusions • SUSY is the most likely extension of the Standard Model • SUSY can be discovered within the first (two?) years of data taking • If(!) we understand our detectors (ETmiss, Ejets) well • Complicated and long decay chains can be reconstructed • With 300 fb-1 a large fraction of the SUSY spectrum will be reconstructed at LHC ( and ILC) Let's get one !!! Thank you!!

  47. p p ~ c01 ~ ~ ~ q ~ c02 l g q q l l

  48. Interesting prospects in SUSY events Bulk region • Tau signatures important in much of the mSUGRA (minimal SuperGravity) parameter space, particularly at high tanβ (>10) • in mSUGRA R-parity conserved, all events contain 2 neutralinos escaping the detector -> one can measure kinematic endpoints in invariant mass distributions rather than mass peaks • At some points in the parameter space (e.g. funnel) can only observe kinematic endpoints in τ invariant mass distributions, • Mmax = fn (masses involved SUSY particles) • Only consider hadronic tau decays.No sharp edge because of ν, but end-point can still be measured. • Can use tau polarization measurement to further constrain the underlying SUSY model. MC truth 4.9 fb-1 Distr. from had. decay products (98.3 GeV) Can fit distorted distribution, and apply this MC fit to the reconstructed distribution 4.2 fb-1

  49. MET Reconstruction Sum of tr.momentum over calo towers QCD Minbias MET is a measure of imbalance Can be corrected for jets, muons MET resolution Measure from data: min.bias and prescaled jet triggers CMS stochastic term ~ 0.6-0.7 Jet calibration important to improve resolution and reduce systematic uncertainties, variety of techniques g-jet balancing, di-jet balancing W-mass constraint in hadronic decays of W in top-pair production CMS achieve 3% of JES uncertainty for ET > 50 GeV with 1-10 fb-1

  50. Discrimination between tau decays (1-prong) achieved by comparing the energy deposited in both Ecal and Hcal to the leading track momentum Reconstructing Tau's decaying hadronically Use main Tau decay property: narrow jet-like structure with 1 or 3 charged particles produced within a small opening angle Works well as long as Et>>Mt Problematic with low energy tau Allow to remove Tau leptonic decays (Even though) Tau selection used here optimized for low energy hadronic Tau's

More Related