1 / 52

Searches for Higgs and BSM physics with ATLAS

Searches for Higgs and BSM physics with ATLAS. Osamu Jinnouchi (Tokyo Institute of Technology) KIAS Pheno Workshop 2011/11/16-19 . contents. (1) The ATLAS experiment at LHC quick overview of the 2010/2011 data. (2) Search for the Standard Model Higgs boson  Analysis strategy

ishi
Download Presentation

Searches for Higgs and BSM physics with ATLAS

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. Searches for Higgs and BSM physics with ATLAS Osamu Jinnouchi (Tokyo Institute of Technology) KIAS Pheno Workshop 2011/11/16-19

  2. contents (1) The ATLAS experiment at LHC quick overview of the 2010/2011 data (2) Search for the Standard Model Higgs boson  Analysis strategy  Search channels  ATLAS Combined results (3) Search for physics beyond the Standard Model  Look for new particle resonances  Look for specific signatures based on supersymmetry  Look for exotic signatures (4) Conclusion ATLAS / JINNOUCHI

  3. in This Talk • Look into two major topics in the LHC physics i.e. • Mass and EW symmetry breaking (Higgs) • Hierarchy puzzles at TeV scale (BSM) • These are “Searches”, therefore they have to be based on the good control over the BG • heavily rely on • the trigger and detector performance • the large number of ATLAS SM measurements • MCs finely tuned with data • many analysis use the data-driven estimates of BG • measurement in the data control region, transfer it to the signal region with the help of MC ATLAS / JINNOUCHI

  4. LHC (pp) runs in 2010 and 2011 • In 2010 • First 7TeV pp collisions started • 48 pb-1 pp collisions delivered (45pb-1 recorded by ATLAS) • In 2011 (pp run finished at Oct 30.) • Peak luminosity 3.65 x 1033cm-2s-1 • ATLAS : 5.2(5.6) fb-1 data recorded(delivered) • ATLAS data taking efficiency : ~ 93.5% (over the year) • 1380 bunches, 50nsec spacing, 1.5E11 p/ bunch Log scale Linear scale 2010 2011 LHC will run in 2012 then long shutdown / willrestart at higher energy ATLAS / JINNOUCHI

  5. ATLAS detector • Gigantic general purpose detector with well balanced performance on resolutions and high hermetic acceptance • Emphasis on lepton measurements with excellent magnets • 2T central solenoid for inner tracker • Air core Toroid magnet (less MS + forward acceptance) for outer muon system • Accordion shape LAr EM calorimeters for fine lateral + longitudinal EM shower shape • Hadron Calorimeter is fully hermetic and thickness is ~ 30 X0  good jet/missing ET resolution Tracking  2 Silicon systems + Transition radiation tracker EM Calo  sampling LArcalo HAD Calo  plastiscintilator (barrel) + LAr (endcap) Muon  trigger chambers (RPC, TGC) + precision chambers (MDT, CSC) ATLAS / JINNOUCHI

  6. Trigger and data taking performance • Flexible trigger menu: • definition continuously updated along the luminosity evolvement through the year • primary unprescaled triggers in 2011 for 3x1033cm-2s-1 menu • electrons: pT>22GeV • muons: pT>20GeV • jets: pT>240GeV • etmiss: pT>60GeV • combinatory menu for low pT • Data taking and quality • efficiency ~ 93.5% • single detector operational fraction > 97% ATLAS / JINNOUCHI

  7. High luminosity = Pile up: the new challenge in 2011 • most of 2011 data, 50nsec bunch trains running at LHC • in-bunch & out-of-bunch pile-up effects need to be taken into account • MC superimposes reweighted MB events to reproduce data mean # collisions 6.3  11.6 (after reducing beam size) Z𝜇𝜇 with 20 reconstructed vertices ATLAS / JINNOUCHI

  8. Mass and EW symmetry breaking HIGGS ATLAS / JINNOUCHI

  9. Theoretical and indirect exp. Higgs constraints Perturbativity and (meta) stability bounds versus the SM cut-off scale L • in the Standard Model, Higgs must be light • However in the BSM, Higgs can be heavy  must also search for a heavy Higgs boson EW fit not including direct Higgs searches J. Ellis et al., arXiv:0906.0954 http://cern.ch/gfitter theory  narrow venue if it is to survive up to Planck scale indirect meas.  prefer low mass 95% CL upper limit : 170GeV ATLAS / JINNOUCHI

  10. Higgs search strategy at LHC • multi-channel combined analysis is required • expected cross sections are in any case below “a few pb” • integrated luminosity and BG rej. are the two important factors • light Higgs • 𝛾𝛾 final state • 𝜏𝜏 final state • lepton final states via WW*,ZZ* • heavy Higgs • lepton final states via WW(*),ZZ(*) Dependence of the branching fractions on MH drives search strategy ATLAS / JINNOUCHI

  11. General search strategy Cut & Count based analysis • trigger • (changing along the luminosity evolution) • event Selection • Object definition (leptons, jets, missing ET, ...) • Specific event selection and acceptance definition • Collision event selection (common method) • background evaluation • Mostly data driven methods • count events in background enhanced control regions (CR) • extrapolation to signal region (SR) based on MC or data • for each value of MH, likelihood fit of data with one or more variablesConfidence Interval based on CLS method on 𝜇=𝜎/𝜎SM • finally, channel combination  Confidence Intervals for 𝜇 vs. MH ATLAS / JINNOUCHI

  12. (1) H𝛾𝛾 : the low mass “golden channel” • low cross-section (<0.1pb) but very clean signature with limited BG • photon identification based on calorimeter segmentation • narrow energy cluster |𝜂| • small leakage into HCal • cut on shower shape, discriminating 𝛾 from jets, 𝜋, 𝜂 • photon isolation energy criterion to reduce jet background • reduce fragmentation component • sum of transverse energy in ∆R cone (=0.4) around 𝛾 • corrections event by event • remove leakage from 𝛾 into cone • remove energy from pileup & UE S3 (“back”) S2 (“middle”) S1 (“strip”) pre-sampler 𝜸 𝝅0 P P P P ATLAS / JINNOUCHI

  13. (1) H𝛾𝛾 : the low mass “golden channel” • trigger : • 2 photons with ET>20GeV • selection: • two isolated “photons” ET1>40GeV, ET2>25GeV • di-photon inv. mass 100-160GeV • backgrounds: • di-photon (irreducible) 72% • photon + jet (rej.needed ~ 104) • di-jets (rej.needed ~ 107) • discriminant variable • m𝛾𝛾 (resolution ~ 1.7GeV) • fit with • BG: exponential • signal : CrystalBall function signal x 5 No signal found  set upper limits on 𝜇 for range 110<MH<150GeV ATLAS / JINNOUCHI

  14. (2) HWW(*)2𝓁(e,𝜇)+2𝜈 • Not clean but with large 𝜎 x Br : the best channel at intermediate mass • highest sensitivity for 130< MH<200GeV • signatures : • two leptons • W polarization : correlated lepton emission opening angle is a discriminant • missing Et : Higgs mass not reconstructed • count events in signal region heavily rely on the BG estimation • “limited“ jet activity Look into 0 and 1 jet channels • Backgrounds: • WW production (irreducible) • top pair production • single top • Z + jets ∂ ∂ ATLAS / JINNOUCHI

  15. (2) HWW(*)2𝓁(e,𝜇)+2𝜈 trigger : single lepton pT(e)> 20-22GeV or pT(𝜇)>18GeV • Selection: • 2 opposite sign isolated high-pT leptons (20,15)GeV • missing ET > 30 GeV • topological cuts on lepton system (mll, pTll, ∆𝜙ll) • transverse mass : 0.75xMH < mT < MH • different background composition in 0 and 1 jet channels jet : anti-kT R=0.4 pT>25GeV |𝜂|<4.5, b-tag veto 1-jet 0-jet entries / 10GeV no signal found  set upper limits on 𝜇 for range 150<MH<300GeV data/mc ATLAS / JINNOUCHI

  16. (3) H ZZ(*)4𝓁 : the “golden” channel • very clean signature (4𝜇, 4e, 2𝜇2e) with good sensitivity in the full mass range • trigger : single lepton pT(e)>20-22GeV or pT(𝜇)>18GeV • selection : • 4 isolated leptons : 2 with pT > 20Gev, 2 with pT>7GeV • two pairs of same flavour opposite sign leptons • M12 within MZ±15GeV, 115GeV>M34> 15-60GeV (depends on M4l) • backgrounds : • ZZ (dominant irreducible) • Z + jets (electron channel), Zbb (muon channel) count the events after the selection and compare with the BG estimate no signal found  set upper limits on 𝜇 for range 110<MH<600GeV PLB705(2011)435 ATLAS / JINNOUCHI

  17. 4𝜇 candidate event with M4l =143.5GeV (M12=90.6GeV, M34=47.4GeV) ATLAS / JINNOUCHI

  18. Limits on ATLAS Higgs boson searches • Upper limits on the cross section divided by the SM Higgs boson production cross section (i.e. 𝜇) as a function of mH • 95% C.L. limit on 𝜇 for all channels (frequentist CLS method) • solid lines : observed limit (data) • dashed lines : expected limit (based on MC pseudo-experiments) • Observed Limit > Expected Limit  more data than SM prediction (vice versa) ATLAS / JINNOUCHI

  19. Limits on ATLAS Higgs boson searches (combined) • Upper limits on the cross section divided by the SM Higgs boson production cross section (i.e. 𝜇) as a function of mH • 95% C.L. limit on 𝜇 for all channels (frequentist CLS method) • solid lines : observed limit (data) • dashed lines : expected limit (based on MC pseudo-experiments) 2010 data (35pb-1) EPS results (July, 1-1.2 fb-1) Most recent results (August, 1-2.3 fb-1) Tevatron LEP ATLAS excludes SM higgs boson @ 95% C.L. in three mass region : 146<MH<232GeV, 256<MH<282GeV,296<MH<466GeV ATLAS / JINNOUCHI

  20. SM Higgs searches : conclusions • ATLAS has performed a Higgs search with 1~2.3 fb-1 pp data using various channels • Shown here only part of major search channels • No significant excess found so far in the mass range 110-600GeV • Exclusion limit at 95% C.L. set in the range • 146 < MH < 232 GeV • 256 < MH < 282 GeV • 296 < MH < 466 GeV • There will be an update of ATLAS-CMS combined results today presented at HCP (during this afternoon) • BSM Higgs not covered : Fermiophobic H𝜸𝜸, MSSM H𝞃𝞃, charged H+, H++ • Significant updates expected for winter conference with 5 fb-1 then definitive answer should be obtained by the end of 2012 with O(10fb-1) data ATLAS / JINNOUCHI

  21. Hierarchy puzzles at TeVscale Beyond the Standard Model ATLAS / JINNOUCHI

  22. Let’s start with .... summary of BSM searches • O(3000) authors  a huge number of interesting channels covered • limits go up to 0.5 ~ 1.5 TeV, progressing with larger data stats • exceeding Tevatron results in many places • the published data (up to summer 2011) found no “significant excess” yet so far Were our search strategies optimal? ATLAS / JINNOUCHI

  23. Two experimental approaches for “unknown” (1) Search for new particles / phenomena via model independent approach • Cross section (and many other observables) measurements of Standard Model processes, compared to theory prediction • Search the “peaks” or “excess”in mass distributions, or in many other kinetic observables (2) Search for specific signatures corresponding to well defined BSM physics models • Supersymmetry, Extra Dimensions, etc • search strategy should be model-independent as much as possible within the framework ATLAS / JINNOUCHI

  24. (1) search for new particles model independent approach ATLAS / JINNOUCHI

  25. Cross section measurements compared to SM predictions • compared to the predictions evaluated at NLO or more • good agreements over 4 orders of magnitude, indicating followings • No surprise observed ... • SM prediction is still applicable at 7TeV era • Detector performance extrapolated to high energy regime works fine σxBR(ZZ4l)~40fb Measuring cross-sections down to a few pb (~40fb including BR) ATLAS / JINNOUCHI

  26. Search for Z’ boson in di-leptons (ee or 𝜇𝜇) • simple/robust analysis : search a peak in a di-lepton invariant mass spectrum e+e- channel model independent upper limits on 𝜎 x Br as a function of the mass of the new vector boson 𝜇+𝜇- channel • model dependent lower limits on the Z’ mass: • SSM: m(Z’)> 1.83TeV @ 95% C.L. • RS graviton: m(G*)>1.64TeV @ 95% C.L. arXiv: 1108.1582 ATLAS / JINNOUCHI

  27. Search for W’ boson in lepton + neutrino (e𝜈 or 𝜇𝜈) • search for a “Jacobian” peak in a transverse mass spectrum e+𝜈 channel model independent upper limits on 𝜎 x Br as a function of the mass of the new vector boson 𝜇+𝜈 channel • model dependent lower limits on the W’ mass: • SSM: m(W’)> 2.15TeV @ 95% C.L. ATLAS / JINNOUCHI

  28. Di-jet mass and angular distributions • motivated by many models : excited quarks, contact interactions, axigluons, ... • search for jet-jet resonances in di-jet events, look for a peak in the Mjj spectrum 36fb-1 1.0fb-1 36fb-1 new way to express the difference to MC significance in Z instead of rel. difference with this variable 𝛘, one expects peak around 1 for heavy resonant particle (back to back jets) ATLAS / JINNOUCHI

  29. Di-jet mass and angular distributions • motivated by many models : excited quarks, contact interactions, axigluons, ... • search for jet-jet resonances in di-jet events, look for a peak in the Mjj spectrum 1.0fb-1 36fb-1 new way to express the difference to MC significance in Z instead of rel. difference model dependent mass lower limit (1fb-1): excited quarks : M(q*) > 2.99TeV axigluons: M(A) > 3.32TeV color octet scalar : M(S) > 1.92TeV ATLAS / JINNOUCHI

  30. (2) searching model specific signature SUSY ATLAS / JINNOUCHI

  31. Search for new physics in the context of SUSY • Typical event topology : cascade decay + stable LSP from R-parity  large ETmiss and multi-jet/leptons is used Control Region MC(Z/W/top)/Data(QCD) normalizedto data in the region sensitive to each BG examples of strong () productions incomplete event reconstruction  no peak & evidence will beat tail ofdistribution  understanding of backgrounds (top, W/Z+jets, QCD) is the highest priority from experiment believe MC shape to transfer from CR to SR Signal Region BG prediction ATLAS / JINNOUCHI

  32. Background estimate [1]: QCD multi-jets, Z+jets • QCD : huge cross section x high rejection at event selection + large theoretical uncertainty  data driven estimate necessary • CR is obtained by requiring ∆𝜙(jet, ETMiss)min < 0.4 • Pythia6 (+MRST2007LO*) is used QCD Z+jets • Z(𝜈𝜈)+jets : • CR is Z (ee/𝜇𝜇) + jets • P(ee/𝜇𝜇) is added to ETMisstoreproduce Meff • ALPGEN (+CTEQ6L1) is used ATLAS / JINNOUCHI

  33. Background estimate [2]:W+jets, tt+jets W/tt control region (MT = 30 ~100GeV, ETMiss>130GeV)separate two components via b-tagging • b-tag veto : enhancing W+jets • with b-tag : enhancing tt + jets • ALPGEN (+CTEQ6L1) is used for W+jets • MC@NLO(+CTEQ6.6) is used for tt + jets • extremely important to understand the shape of large Meff W+jets tt+jets ATLAS / JINNOUCHI

  34. Meff search with no-lepton (1.04 fb-1) Jet energy scale (~4%) Theoretical error (depends on channel) dominates • Leading jet pT>130GeV, ETMiss>130GeV) • ∆𝜙(jet, ETMiss)min> 0.4 arXiv:1109.6572 • 4jet high-mass channel • 2-4 jets pT > 80GeV • ETMiss/Meff > 0.20 • Meff> 1100GeV • data = 18 • SM = 13.1±1.9±2.5 • (Z=3.3/W=2.1/tt=5.7/QCD=2.1) • 4jet channel • 2-4 jets pT > 40GeV • ETMiss/Meff > 0.25 • Meff> 1000GeV • data = 40 • SM = 33.9±2.9±6.2 • (Z=16.2/W=13.0/tt=4.0/QCD=0.7) consistent with SM, though there are some candidates events. hope to keep watching for high stats ATLAS / JINNOUCHI

  35. Meff search with 1-lepton (1.04 fb-1) Selections: • Electron (pT>25GeV) or Muon (pT>20GeV) • jet pT(1) > 60GeV, jet pT(2-4) >40GeV • ETMiss/Meff > 0.15, ETMiss>200GeV • Meff> 500GeV electron • Matrix method for QCD: • 1) define “loose” and “tight” leptons • 2) assess efficiency for real and fake leptons • 3) use data with “loose leptons” to estimate data with “tight” • Non QCD: • use MT to separate signal from background muon • Electron Channel • data = 9 • SM = 8.0±3.7 • (tt=4.5/W/Z=3.5/QCD=0.0) • Muon Channel • data = 7 • SM = 6.0±2.7 • (tt=4.7/W/Z=1.4/QCD=0.0) consistent with SM ATLAS / JINNOUCHI

  36. Interpretation 95% C.L. exclusion range in MSUGRA/CMSSM param. plane 0-lepton (4jet 1.04fb-1, 6jet 1.34fb-1) : 1-lepton case (1.04fb-1): 4-jet 800 GeV 800 GeV 600 GeV 700 GeV 800 GeV 900 GeV 1400 GeV 1000 GeV 6-jet as a result of several different assumptions/topologies studied we learnt that squarks and gluinos are not light ... or cannot be found with the simple model ATLAS / JINNOUCHI

  37. 𝛾𝛾 + missing ET channel • Sensitive to GMSB (or UED) models • Bino is NLSP, two high-pT photons in the final state, gravitinos create high Missing ET • Minimal Gauge Mediation (MGM) model, where one mass scale for the symmetry breaking and messenger mass determine the mass hierarchy (bench mark point : SPS8) • General Gauge Mediation (GGM) Recent analysis relaxes the constraint on mass hierarchy between gluinos and neutralinos • No excess observed yet (1.07fb-1), set the limit on gluino mass • GGM: Mgluino > 776GeV • MGM (SPS8): 𝛬>145TeV ATLAS / JINNOUCHI

  38. ATLAS looks for many directions other than ordinary strong production • EW gaugino production • 2 leptons + missing • multi-leptons + missing • 3rd generation light squarks • direct prodcution • from gluinodecays • RPV • resonant sneutrino • displaced vertex • special final status • disappearing (or kink) track • stable massive particle • .... etc, etc resonant sneutrino disappearing (or kink) track (2’) even more specific signatures SUSY

  39. No significant deviation from SM expectations RPV search • exactly 1 electron and 1 muon (opposite sign) • BG are SM processes with emu final state • Z/𝛾*𝞃𝞃 , ttbar, single top, WW, WZ, ZZ • also from instrumental backgrounds with fake leptons scalar tau neutrino search at 1 fb-1 experiments usually assume only and arXiv:1109.3089 look for D0 is competitive in low mass region excluded m𝜈<1.32 TeV (𝝀’311=0.10,λ312=0.05) ATLAS / JINNOUCHI

  40. Search for disappearing (kinked) tracks • AMSB: almost degenerate and • chargino long lived, decays inside tracking volume • pion is soft, looks like disappearing of the tracks • BG: interaction with TRT, mismeasured low pT tracks ATLAS / JINNOUCHI

  41. Concluding remarks • ATLAS has recorded/analyzed good amount of data(no excuse for “we just started...” phrase anymore) • keep updating the exclusion limits in many area • Search for the SM Higgs boson • large area unveiled, can expect for significant updates by winter conferences • Search for the beyond-SM phenomena • large number of analysis performed • exclusion reach updated in many channels • establishing analysis frameworks, better understanding on systematics  faster production on results(paper factory mode) • No big surprise yet  Let’s hope they are just around the corner ! !! good luck with 2011 & 2012 data !! ATLAS / JINNOUCHI

  42. EXTRA SLIDES ATLAS / JINNOUCHI

  43. ATLAS / JINNOUCHI

  44. Search for stable long lived and • new meta-stable particles features in many BSM scenarios • Sleptons would interact with detector as slow moving muons • or e-charged/neutral, color singlet bound state R-hadrons Pixel dE/dx Bethe-Bloch  𝛽 Tile HadCal timing  𝛽 ATLAS / JINNOUCHI

  45. ATLAS Data Quality as of 2011/10/05 Operational fractions very high (> 97%) high good quality data (>98% except LAr) luminosity weighted fraction of good quality data during LHC stable beam runs, L=2.33fb-1 (3/13-8/13) ATLAS / JINNOUCHI

  46. Upgrade & long shutdown (LS) plan (as of today) • LS1: 2013 – 2014 shutdown 24month physics-to-physics • Machine : mainly splices consolidation and repairs • ATLAS : IBL, Pixel new SQP, new LVPS for tile/lar, FTK, etc.... • RUN : 2015-2017 • √s ~ 13-14TeV, β*=0.55m, L~1x1034 ~50fb-1 • LS2: 2018 shutdown (Phase-I): ~1 year • Machine : injectors (LINAC4) and collimators • ATLAS : L1 trigger (topological, more granular), Muon Small Wheels, etc • RUN : 2018-2021 • L~2x1034  300fb-1 • LS3: 2022-2023 shutdown (Phase-II): ~2years • Machine : new inner triplets, crab cavities • ATLAS : new tracker, new calorimeter electronics,new FCAL, etc • RUN : 2024 - • L~5x1034  up to 3000fb-1 ATLAS / JINNOUCHI

  47. ATLAS Trigger performance • High level trigger menu : software based, continuous update with luminosity • 3x1033cm-2s-1 menu • Prescaled triggers • Electrons pT>22GeV • MuonspT>20GeV • Jets pT>240GeV • EtMiss > 60GeV • (Di)photons pT> 80(20)GeV • 5x1033cm-2s-1 menu • Even tighter menus planned electrons Muons Jets ATLAS / JINNOUCHI

  48. Data preparation and computing • Raw data are reconstructed at Tier-0 site (CERN) within 2days • Calibration and data quality performed for physics analysis • Data are ready for analysis on the grid within a week • Up to 800k jobs/day are processed on Tier-1 and Tier-2 sites • Analysis, Simulation, Reprocessing, various productions Full number of ATLAS jobs per day analysis simulation 2011.03 2011.07 ATLAS / JINNOUCHI

  49. kT and anti-kT Jet algorithms ATLAS / JINNOUCHI

  50. advanced b-taggings for QCD jet events: fraction of light jets incorrectly tagged as b-jets is substantially reduced with the advanced taggers ATLAS / JINNOUCHI

More Related