1. NIKHEF, January 2007 Dan Tovey 1 Construction Supersymmetry at ATLAS Dan Tovey University of Sheffield Dan Tovey University of Sheffield

2. NIKHEF, January 2007 Dan Tovey 2 Supersymmetry Supersymmetry (SUSY) fundamental continuous symmetry connecting fermions and bosons Q  |F> = |B>, Q  |B> = |F> {Q ,Q  }=-2    p   generators obey anti- commutation relations with 4-mom –Connection to space-time symmetry SUSY stabilises Higgs mass against loop corrections (gauge hierarchy/fine-tuning problem) –Leads to Higgs mass  135 GeV –Good agreement with LEP constraints from EW global fits SUSY modifies running of SM gauge couplings ‘just enough’ to give Grand Unification at single scale. LEPEWWG Winter 2006 m H <207 GeV (95%CL)

3. NIKHEF, January 2007 Dan Tovey 3   e H-dH-d ~ H+uH+u ~ H0dH0d ~ H0uH0u ~ 0404 ~ 0303 ~ 0202 ~ 0101 ~ SUSY Spectrum Expect SUSY partners to have same masses as SM states –Not observed (despite best efforts!) –SUSY must be a broken symmetry at low energy Higgs sector also expanded SUSY gives rise to partners of SM states with opposite spin-statistics but otherwise same Quantum Numbers. H±H± H0H0 A G   e bt sc du g W±W± Z  h W±W± Z  ~ ~~ g ~ G ~  ± 2 ~  ± 1 ~   e   e bt sc du ~~ ~ ~ ~~ ~~~ ~ ~ ~

4. NIKHEF, January 2007 Dan Tovey 4 SUSY & Dark Matter R-Parity R p = (-1) 3B+2S+L Conservation of R p (motivated e.g. by string models) attractive –e.g. protects proton from rapid decay via SUSY states Causes Lightest SUSY Particle (LSP) to be absolutely stable LSP neutral/weakly interacting to escape astroparticle bounds on anomalous heavy elements. Naturally provides solution to dark matter problem R-Parity violating models still possible  not covered here. Universe Over-Closed mSUGRA A 0 =0, tan(  ) = 10,  >0 Ellis et al. hep-ph/0303043 0101 0101 l l lRlR ~ ~ ~ 0101 11   /Z/h 11 ~ ~ ~ Disfavoured by BR (b  s  ) = (3.2  0.5)  10 -4 (CLEO, BELLE) 0.094    h 2  0.129 (WMAP-1year)

5. NIKHEF, January 2007 Dan Tovey 5 SUSY @ ATLAS Much preparatory work carried out historically by ATLAS –Summarised in Detector and Physics Performance TDR (1998/9). Work continuing to ensure ready to test new ideas with first data. Concentrate here on more recent work. LHC will be a 14 TeV proton-proton collider located inside the LEP tunnel at CERN. Luminosity goals: –10 fb -1 / year (first ~3 years) –100 fb -1 /year (subsequently). First data this year! Higgs & SUSY main goals.

6. NIKHEF, January 2007 Dan Tovey 6 Model Framework Minimal Supersymmetric Extension of the Standard Model (MSSM) contains > 105 free parameters, NMSSM etc. has more  difficult to map complete parameter space! Assume specific well-motivated model framework in which generic signatures can be studied. Often assume SUSY broken by gravitational interactions  mSUGRA/CMSSM framework : unified masses and couplings at the GUT scale  5 free parameters (m 0, m 1/2, A 0, tan(  ), sgn(  )). R-Parity assumed to be conserved. Exclusive studies use benchmark points in mSUGRA parameter space: LHCC Points 1-6; Post-LEP benchmarks (Battaglia et al.); Snowmass Points and Slopes (SPS); etc… LHCC mSUGRA Points 1 2 3 4 5

7. NIKHEF, January 2007 Dan Tovey 7 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. Heavier than sleptons, gauginos etc.  cascade decays to LSP. Long decay chains and large mass differences between SUSY states –Many high p T objects observed (leptons, jets, b-jets). If R-Parity conserved LSP (lightest neutralino in mSUGRA) stable and sparticles pair produced. –Large E T miss signature (c.f. W  l ). Closest equivalent SM signature t  Wb. l q q l g ~ q ~ l ~  ~  ~ p p

8. NIKHEF, January 2007 Dan Tovey 8 ATLAS 55 Use 'golden' Jets + n leptons + E T miss discovery channel. Map statistical discovery reach in mSUGRA m 0 -m 1/2 parameter space. Sensitivity only weakly dependent on A 0, tan(  ) and sign(  ). Syst.+ stat. reach harder to assess: focus of current & future work. Inclusive Searches ATLAS 55

9. NIKHEF, January 2007 Dan Tovey 9 Inclusive SUSY First SUSY parameter to be measured may be mass scale: –Defined as weighted mean of masses of initial sparticles. Calculate distribution of 'effective mass' variable defined as scalar sum of masses of all jets (or four hardest) and E T miss : M eff =  p T i | + E T miss. Distribution peaked at ~ twice SUSY mass scale for signal events. Pseudo 'model-independent' measurement. With PS typical measurement error (syst+stat) ~10% for mSUGRA models for 10 fb -1, errors much greater with ME calculation  an important lesson … Jets + ETmiss + 0 leptons ATLAS 10 fb -1

10. NIKHEF, January 2007 Dan Tovey 10 Exclusive Studies With more data will attempt to measure weak scale SUSY parameters (masses etc.) using exclusive channels. Different philosophy to TeV Run II (better S/B, longer decay chains)  aim to use model-independent measures. Two neutral LSPs escape from each event –Impossible to measure mass of each sparticle using one channel alone Use kinematic end-points to measure combinations of masses. Old technique used many times before ( mass from  decay spectrum, W (transverse) mass in W  l ). Difference here is we don't know mass of neutral final state particles. lq q l g ~ q ~ lRlR ~  ~  ~ pp

11. NIKHEF, January 2007 Dan Tovey 11 Dilepton Edge Measurements ~ ~ 0202 ~ 0101 ll l e + e - +  +  - ~ ~ 30 fb -1 atlfast Physics TDR Point 5 e + e - +  +  - - e +  - -  + e - 5 fb -1 SU3 ATLAS m 0 = 100 GeV m 1/2 = 300 GeV A 0 = -300 GeV tan(  ) = 6 sgn(  ) = +1 When kinematically accessible    can  undergo sequential two-body decay to    via a right-slepton (e.g. LHC Point 5). Results in sharp OS SF dilepton invariant mass edge sensitive to combination of masses of sparticles. Can perform SM & SUSY background subtraction using OF distribution e + e - +  +  - - e +  - -  + e - Position of edge measured with precision ~ 0.5% (30 fb -1 ).

12. NIKHEF, January 2007 Dan Tovey 12 Measurements With Squarks Dilepton edge starting point for reconstruction of decay chain. Make invariant mass combinations of leptons and jets. Gives multiple constraints on combinations of four masses. Sensitivity to individual sparticle masses. ~ ~  ~  ll l qLqL q ~ ~  ~  b h qLqL q ~ b llq edge 1% error (100 fb -1 ) lq edge 1% error (100 fb -1 ) llq threshold 2% error (100 fb -1 ) bbq edge TDR, Point 5 TDR, Point 5 TDR, Point 5 TDR, Point 5 ATLAS 1% error (100 fb -1 )

13. NIKHEF, January 2007 Dan Tovey 13 Full Geant4 simulation of signals + backgrounds now routine. Invariant mass of dilepton+jet bounded by M llq min =271.8 GeV and M llq max =501 GeV. Leptons combined with two jets with highest p T Flavour subtraction & efficiency correction applied Full Simulation Smaller of M(llq) Larger of M(llq) Smaller of M(llq) 4.20 fb -1 2j100+2l10 4.20 fb -1 2j100+2l10 M(qql) (GeV) 2004006000 400200 0 10 Events 0 30 ATLAS Preliminary ATLAS Preliminary 4.20 fb -1 No cuts Dilepton Edge = (100.3  0.4) GeV ll endpoint ATLAS Preliminary SU3 m 0 = 100 GeV m 1/2 = 300 GeV A 0 = -300 GeV tan(  ) = 6 sgn(  ) = +1

14. NIKHEF, January 2007 Dan Tovey 14 ‘Model-Independent’ Masses Combine measurements from edges from different jet/lepton combinations to obtain ‘model- independent’ mass measurements. 0101 lRlR 0202 qLqL Mass (GeV) ~ ~ ~ ~ ATLAS Sparticle Expected precision (100 fb -1 ) q L  3%  0 2  6% l R  9%  0 1  12% ~ ~ ~ ~ LHCC Point 5

15. NIKHEF, January 2007 Dan Tovey 15 Sbottom/Gluino Mass Following measurement of squark, slepton and neutralino masses move up decay chain and study alternative chains. One possibility: require b-tagged jet in addition to dileptons. Give sensitivity to sbottom mass (actually two peaks) and gluino mass. Problem with large error on input  0 1 mass remains  reconstruct difference of gluino and sbottom masses. Allows separation of b 1 and b 2 with 300 fb -1. lb b l g ~ b ~ lRlR ~  ~  ~ pp 300 fb -1 ~ ~ ~ m(g)-0.99m(  0 1 ) = (500.0 ± 6.4) GeV 300 fb -1 ATLAS SPS1a m(g)-m(b 1 ) = (103.3 ± 1.8) GeV m(g)-m(b 2 ) = (70.6 ± 2.6) GeV ~ ~ ~ ~ ~ ~

16. NIKHEF, January 2007 Dan Tovey 16 Stop Mass Look at edge in tb mass distribution. Contains contributions from –g  tt 1  tb  + 1 –g  bb 1  bt  + 1 –SUSY backgrounds Measures weighted mean of end-points Require m(jj) ~ m(W), m(jjb) ~ m(t) Subtract sidebands from m(jj) distribution Can use similar approach with g  tt 1  tt  0 i –Di-top selection with sideband subtraction Also use ‘standard’ bbll analyses (previous slide) ~ ~ ~ ~ ~ ~ 120 fb -1 ATLAS LHCC Pt 5 (tan(  )=10) 120 fb -1 ATLAS LHCC Pt 5 (tan(  )=10) m tb max = (443.2 ± 7.4 stat ) GeV Expected = 459 GeV m tb max = (510.6 ± 5.4 stat ) GeV Expected = 543 GeV ~ ~ ~

17. NIKHEF, January 2007 Dan Tovey 17 RH Squark Mass Right handed squarks difficult as rarely decay via ‘standard’  0 2 chain –Typically BR (q R   0 1 q) > 99%. Instead search for events with 2 hard jets and lots of E T miss. Reconstruct mass using ‘stransverse mass’ (Allanach et al.): m T2 2 = min [max{m T 2 (p T j(1),q T  (1) ;m  ),m T 2 (p T j(2),q T  (2) ;m  )}] Needs  0 1 mass measurement as input. Also works for sleptons. q T  (1) +q T  (2) =E T miss ~ ~ ~  qRqR q ~ ATLAS 30 fb -1 100 fb -1 Left slepton Right squark ~ ~ SPS1a Precision ~ 3%

18. NIKHEF, January 2007 Dan Tovey 18 Heavy Gaugino Measurements Also possible to identify dilepton edges from decays of heavy gauginos. Requires high stats. Crucial input to reconstruction of MSSM neutralino mass matrix (independent of SUSY breaking scenario). ATLAS 100 fb -1 ATLAS 100 fb -1 ATLAS 100 fb -1 ATLAS SPS1a

19. NIKHEF, January 2007 Dan Tovey 19 Measuring Model Parameters Alternative use for SUSY observables (invariant mass end-points, thresholds etc.). Here assume mSUGRA/CMSSM model and perform global fit of model parameters to observables –So far mostly private codes but e.g. SFITTER, FITTINO now on the market; –c.f. global EW fits at LEP, ZFITTER, TOPAZ0 etc. Point m 0 m 1/2 A 0 tan(  ) sign(  ) LHC Point 5 100 300 300 2 +1 SPS1a 100 250 -100 10 +1 Parameter Expected precision (300 fb -1 ) m 0  2% m 1/2  0.6% tan(  )  9% A 0  16%

20. NIKHEF, January 2007 Dan Tovey 20 SUSY Dark Matter Baer et al. hep-ph/0305191 LEP 2 No REWSB LHC Point 5: >5  error (300 fb -1 )   p =10 -11 pb   p =10 -10 pb   p =10 -9 pb Can use parameter measurements for many purposes, e.g. estimate LSP Dark Matter properties (e.g. for 300 fb -1, SPS1a) –   h 2 = 0.1921  0.0053 –log 10 (   p /pb) = -8.17  0.04 SPS1a: >5  error (300 fb -1 ) Micromegas 1.1 (Belanger et al.) + ISASUGRA 7.69 ATLAS 300 fb -1 pp ATLAS 300 fb -1 DarkSUSY 3.14.02 (Gondolo et al.) + ISASUGRA 7.69 h2h2

21. NIKHEF, January 2007 Dan Tovey 21 Complementarity   p si h2h2 ZEPLIN-MAX GENIUS XENON ZEPLIN-4 ZEPLIN-2 EDELWEISS 2 CRESST-II ZEPLIN-I EDELWEISS CDMS DAMA Aim to test compatibility of e.g. SUSY signal with DM hypothesis (data from astroparticle experiments) –Fit SUSY model parameters to ATLAS measurements –Use to calculate DM parameters   h 2, m ,   p si etc. Measurements at ATLAS complementary to direct and indirect astroparticle searches / measurements –Uncorrelated systematics –Measures different parameters   p si (cm 2 ) log 10 (   p si / 1pb) h2h2 No. MC Experiments DM particle mass m  (GeV) D.R. Tovey et al., JHEP 0405 (2004) 071 CDMS-II Provides strongest possible test of Dark Matter model   p si mm

22. NIKHEF, January 2007 Dan Tovey 22 SUSY Dark Matter SUSY (e.g. mSUGRA) parameter space strongly constrained by cosmology (e.g. WMAP satellite) data. mSUGRA A 0 =0, tan(  ) = 10,  >0 'Bulk' region: t- channel slepton exchange - LSP mostly Bino. 'Bread and Butter' region for LHC Expts. 'Focus point' region: significant h component to LSP enhances annihilation to gauge bosons ~ Ellis et al. hep-ph/0303043 0101 0101 l l lRlR ~ ~ ~ 0101 11   /Z/h 11 ~ ~ ~ Disfavoured by BR (b  s  ) = (3.2  0.5)  10 -4 (CLEO, BELLE) 0.094    h 2  0.129 (WMAP) Slepton Co- annihilation region: LSP ~ pure Bino. Small slepton-LSP mass difference makes measurements difficult. Also 'rapid annihilation funnel' at Higgs pole at high tan(  ), stop co-annihilation region at large A 0

23. NIKHEF, January 2007 Dan Tovey 23 Coannihilation Signatures E T miss >300 GeV 2 OSSF leptons P T >10 GeV >1 jet with P T >150 GeV OSSF-OSOF subtraction applied E T miss >300 GeV 1 tau P T >40 GeV;1 tau P T <25 GeV >1 jet with P T >100 GeV SS tau subtraction Small slepton-neutralino mass difference gives soft leptons –Low electron/muon/tau energy thresholds crucial. Study point chosen within region: –m 0 =70 GeV; m 1/2 =350 GeV; A 0 =0; tanß=10 ; μ>0; –Same model used for DC2 study. Decays of  0 2 to both l L and l R kinematically allowed. –Double dilepton invariant mass edge structure; –Edges expected at 57 / 101 GeV Stau channels enhanced (tan  ) –Soft tau signatures; –Edge expected at 79 GeV; –Less clear due to poor tau visible energy resolution. ATLAS Preliminary 100 fb -1 ~ ~ ~

24. NIKHEF, January 2007 Dan Tovey 24 Full Simulation Two edges from: Each slepton is close in mass to one of the neutralinos – one of the leptons is soft 20.6 fb -1 No cuts 20.6 fb -1 No cuts MC Truth, l L MC Truth, l R MC Data Hard lepton Soft lepton ATLAS Preliminary ATLAS Preliminary m 0 = 70 GeV m 1/2 = 350 GeV A 0 = 0 tan(  ) = 10 sgn(  ) = +1

25. NIKHEF, January 2007 Dan Tovey 25 Focus Point Models Large m 0  sfermions are heavy Most useful signatures from heavy neutralino decay Study point chosen within focus point region : –m 0 =3550 GeV; m 1/2 =300 GeV; A 0 =0; tanß=10 ; μ>0 Direct three-body decays  0 n →  0 1 ll Edges give m(  0 n )-m(  0 1 ) : flavour subtraction applied ~ ~ ~~ Z 0 → ll 300 fb -1    →    ll ~ ~    →    ll ~ ~ Preliminary ATLAS ParameterWithout cutsExp. value MM 68±92103.35 M 2 -M 1 57.7±1.057.03 M 3 -M 1 77.6±1.076.41 M = m A +m B  m A -m B

26. NIKHEF, January 2007 Dan Tovey 26 SUSY Spin Measurement Q: How do we know that a SUSY signal is really due to SUSY? –Other models (e.g. UED) can mimic SUSY mass spectrum A: Measure spin of new particles. One proposal – use ‘standard’ two-body slepton decay chain –charge asymmetry of lq pairs measures spin of  0 2 –relies on valence quark contribution to pdf of proton (C asymmetry) –shape of dilepton invariant mass spectrum measures slepton spin ~ 150 fb -1 spin-0=flat Point 5 ATLAS m lq Straight line dist n (phase-space) Point 5 Spin-½, mostly wino Spin-0 Spin-½ Spin-0 Spin-½, mostly bino Polarise Measure Angle ATLAS 150 fb -1

27. NIKHEF, January 2007 Dan Tovey 27 Preparations for 1 st Physics Preparations needed to ensure efficient/reliable searches for/measurements of SUSY particles in timely manner: –Initial calibrations (energy scales, resolutions, efficiencies etc.); –Minimisation of poorly estimated SM backgrounds; –Estimation of remaining SM backgrounds; –Development of useful tools. –Definition of prescale (calibration) trigger strategy Different situation to Run II (no previous  measurements at same  s) Will need convincing bckgrnd. estimate with little data as possible. Background estimation techniques will change depending on integrated lumi. Ditto optimum search channels & cuts. Aim to use combination of –Fast-sim; –Full-sim; –Estimations from data. Use comparison between different techniques to validate estimates and build confidence in (blind) analysis.

28. NIKHEF, January 2007 Dan Tovey 28 Background Estimation Inclusive signature: jets + n leptons + E T miss Main backgrounds: –Z + n jets –W + n jets –QCD –ttbar Greatest discrimination power from E T miss (R-Parity conserving models) Generic approach to background estimation: –Select low E T miss background calibration samples; –Extrapolate into high E T miss signal region. Used by CDF / D0 Extrapolation is non-trivial. –Must find variables uncorrelated with E T miss Several approaches being developed. Jets + ETmiss + 0 leptons ATLAS 10 fb -1

29. NIKHEF, January 2007 Dan Tovey 29 W/Z+Jets Background Z  + n jets, W  l + n jets, W   + (n-1) jets (  fakes jet) Estimate from Z  l + l - + n jets (e or  ) Tag leptonic Z and use to validate MC / estimate E T miss from p T (Z) & p T (l) Alternatively tag W  l + n jets and replace lepton with  0l): –higher stats –biased by presence of SUSY ATLAS Preliminary ATLAS Preliminary (Z  ll) (W  l )

30. NIKHEF, January 2007 Dan Tovey 30 QCD Background Two main sources: –fake E T miss (gaps in acceptance, dead/hot cells, non-gaussian tails etc.) –real E T miss (neutrinos from b/c quark decays) Much harder : simulations require detailed understanding of detector performance (not easy with little data). Strategy: 1)Initially choose channels which minimise contribution until well understood (e.g. jets + E T miss + 1l) 2)Reject events where fake E T miss likely: beam-gas and machine background, bad primary vertex, hot cells, CR muons, E T miss phi correlations (jet fluctuations), jets pointing at regions of poor response … 3)Cut hard to minimise contribution to background (at expense of stats). 4)Estimate background using data Pythia dijets SUSY SU3

31. NIKHEF, January 2007 Dan Tovey 31 QCD Background Work in Progress: several ideas under study Step 1: Measure jet smearing function from data –Select events: E T miss > 100 GeV,  (E T miss, jet) < 0.1 –Estimate p T of jet closest to EtMiss as p T true-est = p T jet + E T Miss Step 2: Smear low E T miss multijet events with measured smearing function MET jets fluctuating jet Njets >= 4, p T (j1,j2) >100GeV, p T (j3,j4) > 50GeV ETmiss NB: error bars expected errors on background. ATLAS Preliminary ATLAS Preliminary

32. NIKHEF, January 2007 Dan Tovey 32 Top Background Jets + E T miss + 1 lepton: cut hard on m T (E T miss, l) Rejects bulk of ttbar (semi-leptonic decays), W  l + n jets Remaining background mostly fully leptonic top decays (tt  bbl l  tt  bb  l  tt  bb  ) with one top missed (e.g. hadronic tau) Edge at W Mass Type of Event Number of Events Electron-Electron 67 Muon-Muon 80 Tau-Tau 14 Electron-Muon 152 Electron-Tau 100 Muon-Tau 109 Electron-Hadron 77 Muon-Hadron 174 Tau-Hadron 7 ATLAS Preliminary

33. NIKHEF, January 2007 Dan Tovey 33 Decay Resimulation Work in progress: several approaches under study Goal is to model complex background events using samples of tagged SM events. Initially we will know: –a lot about decays of SM particles (e.g. W, top) –a reasonable amount about the (gaussian) performance of the detector. –rather little about PDFs, the hard process and UE. Philosophy –Tag ‘seed’ events containing W/top –Reconstruct 4-momentum of W/top (x2 if e.g. ttbar) –Decay/hadronise with e.g. Pythia –Simulate decay products with atlfast(here) or fullsim –Remove original decay products from seed event –Merge new decay products with seed event (inc. E T miss ) –Perform standard SUSY analysis on merged event Technique applicable to wide range of channels (not just SUSY) Involves measurement of (top) p T : useful for exotic-top searches?

34. NIKHEF, January 2007 Dan Tovey 34 Decay Resimulation Select seed events: –2 leptons with p T >25GeV –2 jets with p T >50GeV –E T miss (SUSY) –Both m(lb) < 155GeV Solve 6 constraints for p( ) Resimulate + merge with seed Apply 1l SUSY cuts (but Njet >=2) m(lb) cut Pull (top pT) Sample 5201, pT(top) > 200 GeV reco 11.0.4205, 450 pb-1 GeV Z   Estimate 5201 ETmiss Estimate requires >=2 jets, Normalisation under study ATLAS Preliminary ATLAS Preliminary ATLAS Preliminary

35. NIKHEF, January 2007 Dan Tovey 35 Supersummary The LHC will be THE PLACE to search for, and hopefully study, SUSY from 2007 onwards at colliders (at least until ILC). Complementary to direct/indirect astroparticle dark matter searches –ATLAS: evidence / limits on SUSY –Astroparticle: evidence / limits on DM SUSY searches will commence on Day 1 of LHC operation. Many studies of exclusive channels already performed. Lots of input from both theorists (new ideas) and experimentalists (new techniques). Big challenge for discovery will be understanding systematics. Big effort ramping up now to understand how to exploit first data in timely fashion

36. NIKHEF, January 2007 Dan Tovey 36 Supersymmetry

37. NIKHEF, January 2007 Dan Tovey 37 BACK-UP SLIDES

38. NIKHEF, January 2007 Dan Tovey 38 Reconstruct top mass in semi- leptonic top events Select events in peak and examine ETmiss distribution. Subtract combinatorial background with appropriately weighted (from MC) top sideband subtraction. Histogram – 1 lepton SUSY selection (no b-tag) Data points – background estimate ttbar ATLAS Preliminary SUSY ATLAS Preliminary Good agreement with top background distribution in SUSY selection. With this tuning does not select SUSY events (as required) With btag Top Background to SUSY

39. NIKHEF, January 2007 Dan Tovey 39 Top Background to SUSY Fully simulated data. No btag used Background estimates altered by increased sideband Large excess at E T miss > 500 GeV With 10 fb -1 obtain following no. events passing E T miss cut: –No SUSY: Observed: 50 ± 7 (stat), Estimate: 55 ± 17(stat) –With SUSY: Observed: 503 ± 22 (est. stat), Estimate: 7 ± 35 (est. stat) ATLAS Preliminary T2 + SU3 Estimate SUSY selection (top) SUSY selection (total) ATLAS Preliminary T2 Estimate SUSY selection Work in progress

40. NIKHEF, January 2007 Dan Tovey 40 qll edge qll threshold ql(min) edge ql(max) edge 20.6 fb -1 No cuts ATLAS Preliminary ATLAS Preliminary ATLAS Preliminary ATLAS Preliminary Full Simulation m 0 = 70 GeV m 1/2 = 350 GeV A 0 = 0 tan(  ) = 10 sgn(  ) = +1

41. NIKHEF, January 2007 Dan Tovey 41 Full Simulation: Mass Fit Fit to all distributions. Expected shape, acceptance corrections, detector resolution to be accounted for. Need to understand cuts to reject SM background Assume 1% error on lepton+jets endpoints 20.6 fb -1 No cuts M(  0 1 ) (GeV) M(  0 2 ) (GeV) ATLAS Preliminary ATLAS Preliminary

42. NIKHEF, January 2007 Dan Tovey 42 llq Edge Hardest jets in each event produced by RH or LH squark decays. Select smaller of two llq invariant masses from two hardest jets –Mass must be < edge position. Edge sensitive to LH squark mass. ~ ~  ~  ll l qLqL q ~ Dilepton edges provide starting point for other measurements. Use dilepton signature to tag presence of  0 2 in event, then work back up decay chain constructing invariant mass distributions of combinations of leptons and jets. ATLAS Physics TDR ~ e.g. LHC Point 5 1% error (100 fb -1 ) Point 5

43. NIKHEF, January 2007 Dan Tovey 43 lq Edge Complex decay chain at LHC Point 5 gives additional constraints on masses. Use lepton-jet combinations in addition to lepton-lepton combinations. Select events with only one dilepton-jet pairing consistent with slepton hypothesis  Require one llq mass above edge and one below (reduces combinatorics). Construct distribution of invariant masses of 'slepton' jet with each lepton. 'Right' edge sensitive to slepton, squark and  0 2 masses ('wrong' edge not visible). ~ ATLAS Physics TDR Physics TDR 1% error (100 fb -1 ) Point 5

44. NIKHEF, January 2007 Dan Tovey 44 hq edge If tan(  ) not too large can also observe two body decay of  0 2 to higgs and  0 1. Reconstruct higgs mass (2 b-jets) and combine with hard jet. Gives additional mass constraint. ~  ~  b h qLqL q ~ b Physics TDR Point 5 ~ ~ ATLAS 1% error (100 fb -1 )

45. NIKHEF, January 2007 Dan Tovey 45 llq Threshold Two body kinematics of slepton- mediated decay chain also provides still further information (Point 5). Consider case where  0 1 produced near rest in  0 2 frame. –  Dilepton mass near maximal. –  p(ll) determined by p(  0 2 ). Distribution of llq invariant masses distribution has maximum and minimum (when quark and dilepton parallel). llq threshold important as contains new dependence on mass of lightest neutralino. ~ ~ ~ ATLAS Physics TDR Physics TDR 2% error (100 fb -1 ) Point 5

46. NIKHEF, January 2007 Dan Tovey 46 Mass Reconstruction Combine measurements from edges from different jet/lepton combinations. Gives sensitivity to masses (rather than combinations).

47. NIKHEF, January 2007 Dan Tovey 47 High Mass mSUGRA ATLAS study of sensitivity to models with high mass scales E.g. CLIC Point K  Potentially observable … but hard! Characteristic double peak in signal M eff distribution (Point K). Squark and gluino production cross- section reduced due to high mass. Gaugino production significant ATLAS 1000 fb -1

48. NIKHEF, January 2007 Dan Tovey 48 AMSB Examined RPC model with tan(  ) = 10, m 3/2 =36 TeV, m 0 =500 GeV, sign(  ) = +1.  +/- 1 near degenerate with  0 1. Search for  +/- 1   +/-  0 1 (  m = 631 MeV  soft pions). Also displaced vertex due to phase space (c  =360 microns). Measure mass difference between chargino and neutralino using m T2 variable (from mSUGRA analysis). ~ ~ ~ ~

49. NIKHEF, January 2007 Dan Tovey 49 GMSB Kinematic edges also useful for GMSB models when neutral LSP or very long-lived NLSP escapes detector. Kinematic techniques using invariant masses of combinations of leptons, jets and photons similar. Interpretation different though. E.g. LHC Point G1a (neutralino NLSP with prompt decay to gravitino) with decay chain: ~ ~  ~  l l l ~ G 

50. NIKHEF, January 2007 Dan Tovey 50 GMSB Use dilepton edge as before (but different position in chain). Use also l , ll  edges (c.f. lq and llq edges in mSUGRA). Get two edges (bonus!) in l  as can now see edge from 'wrong' lepton (from  0 2 decay). Not possible at LHCC Pt5 due to masses. Interpretation easier as can assume gravitino massless:

51. NIKHEF, January 2007 Dan Tovey 51 R-Parity Violation Use modified effective mass variable taking into account p T of leptons and jets in event Missing E T for events at SUGRA point 5 with and without R-parity violation RPV removes the classic SUSY missing E T signature

52. NIKHEF, January 2007 Dan Tovey 52 R-Parity Violation Baryon-Parity violating case hardest to identify (no leptons). –Worst case: " 212 - no heavy-quark jets Test model studied with decay chain: Lightest neutralino decays via BPV coupling: Reconstruct neutralino mass from 3-jet combinations (but large combinatorics : require > 8 jets!) Phase space sample 8j +2l

53. NIKHEF, January 2007 Dan Tovey 53 R-Parity Violation Test point Decay via allowed where m( ) > m( ) Use extra information from leptons to decrease background. Sequential decay of to through and producing Opposite Sign, Same Family (OSSF) leptons

54. NIKHEF, January 2007 Dan Tovey 54 R-Parity Violation Gaussian fit: = 118.9  3 GeV, (116.7 GeV) = 218.5  3 GeV (211.9 GeV) Jet energy scale uncertainty  3%  3 GeV systematic No peak in phase space sample Perform simultaneous (2D) fit to 3jet and 3jet + 2lepton combination (measures mass of  0 2 ). Can also measure squark and slepton masses. ~

55. NIKHEF, January 2007 Dan Tovey 55 R-Parity Violation Different ” ijk RPV couplings cause LSP decays to different quarks: Identifying the dominant ” gives insight into flavour structure of model. Use vertexing and non-isolated muons to statistically separate c- and b- from light quark jets. Remaining ambiguity from d s Dominant coupling could be identified at > 3.5 

56. NIKHEF, January 2007 Dan Tovey 56 Mass Relation Method New(ish) idea for reconstructing SUSY masses! ‘Impossible to measure mass of each sparticle using one channel alone’ (Slide 10). –Should have added caveat: Only if done event-by-event! Assume in each decay chain 5 inv. mass constraints for 6 unknowns (4  0 1 momenta + gluino mass + sbottom mass). Remove ambiguities by combining different events analytically  ‘mass relation method’ (Nojiri et al.). Also allows all events to be used, not just those passing hard cuts (useful if background small, buts stats limited – e.g. high scale SUSY). Preliminary ATLAS SPS1a ~

57. NIKHEF, January 2007 Dan Tovey 57 DC1 SUSY Challenge First attempt at large-scale simulation of SUSY signals in ATLAS (100 000 events: ~5 fb -1 ) in early 2003. Tested Geant3 simulation and ATHENA (C++) reconstruction software framework thoroughly. No b-tag With b-tag llj endpoint ATLAS SUSY Mass Scale Dijet m T2 distribution ll endpoint Modified LHCC Point 5: m 0 =100 GeV; m 1/2 =300 GeV; A 0 =-300 GeV; tanß=6 ; μ>0 Preliminary

58. NIKHEF, January 2007 Dan Tovey 58 DC2 SUSY Challenge DC2 tested new G4 simulation and reconstruction. Points studied: –DC1 bulk region point (test G4) –Stau coannihilation point (rich in signatures - test reconstruction) 400k events fully simulated ATLAS ll endpoint Preliminary  +  - endpoint ATLAS Preliminary ATLAS Preliminary ll endpoint  +  - endpoint DC1 Point Coannihilation Point DC1 Point Coannihilation Point

59. NIKHEF, January 2007 Dan Tovey 59 Rome SUSY Studies Concentrate on signatures from WMAP-compatible points accessible with 10 fb -1 for Rome Physics Workshop (last week). Several points studied with full simulation (~100k events/point): –SU1: Stau Coannihilation Region (m 0 =70 GeV, m 1/2 = 350 GeV, A 0 = 0, tan(  ) = 10,  >0) –SU2: Focus Point Region (m 0 =3550 GeV, m 1/2 = 300 GeV, A 0 = 0, tan(  ) = 10,  >0) –SU3: Bulk Region (m 0 =100 GeV, m 1/2 = 300 GeV, A 0 = -300 GeV, tan(  ) = 10,  >0) –SU4: Low mass region (m 0 =200 GeV, m 1/2 = 160 GeV, A 0 = -400 GeV, tan(  ) = 10,  >0) –SU5.x: Scan (mostly m 1/2 = 600 GeV): Inclusive studies –SU6: Funnel Region (m 0 =320 GeV, m 1/2 = 375 GeV, A 0 = 0, tan(  ) = 50,  >0) Results hot off the press (1 week old) More to be shown by I Aracena at SUSY2005 next month!

60. NIKHEF, January 2007 Dan Tovey 60 Methodology Possible approach: –Select semi-leptonic top candidates (standard cuts – what btag available?); –Fully reconstruct top and W momenta using E T miss and W mass constraint  reject (SUSY) background via reconstructed m(top); –Estimate background at high E T miss with events in top mass peak –Normalise to data at low E T miss. Study with Rome background (T1, T2, A7) and SUSY signal (SU3) samples. Used SusyPlot and AODs throughout (negative weights included). Simplified 1 lepton SUSY selection (softer cuts to accept events / no m T cut applied): –E T miss > 20 GeV (we will extrapolate to large E T miss later) –At least 4 jets with p T > 40 GeV –Exactly 1 lepton with p T > 20 GeV Similar to top selection cuts but without b-tag requirement (assume not available initially). Note: nothing has been tuned excessively (no time!)  almost ‘blind’.

61. NIKHEF, January 2007 Dan Tovey 61 Cannot use hadronic top as W reconstruction efficiency poor at high p T (W) (jets become collinear) Reconstruct semi-leptonic top mass from lepton + E T miss and W mass constraint –quadratic ambiguity –select solution nearest to top mass (only place m(top) used) Reconstruct top from combination of W with one hard jet –Reduce combinatorics by selecting highest p T top candidate. Top Mass Reconstruction ATLAS Preliminary

62. NIKHEF, January 2007 Dan Tovey 62 E T miss Estimation M(top) reasonably uncorrelated with E T miss. Select events at low E T miss and examine top mass distribution Define –signal band (140 – 200 GeV) –sideband (200-260 GeV) Scale sideband by 1.57 (from W+jets MC distribution  combinatorics + use of m(top)) Assume this factor will be known with negligible stat. error from MC in practice (not the case here  16% err.) Assumes same factor for ‘bad’ top / SUSY ATLAS Preliminary ATLAS Preliminary T2 A7 T1 E T miss : 100 GeV - 200 GeV E T miss : 100 GeV - 200 GeV

63. NIKHEF, January 2007 Dan Tovey 63 Normalising the Estimate Will use signal band – sideband (scaled) E T miss distribution as background estimate. Still need to normalise to SUSY selection (accounts for relative efficiency of top selection). Normalise to low E T miss region (100 GeV – 200 GeV) where SUSY signal expected to be small –Use T1 sample and assume low stats (0.5 fb -1 ) Scaling factor 4.13 ± 0.27 ATLAS Preliminary T1 Estimate SUSY selection

64. NIKHEF, January 2007 Dan Tovey 64 Use T2 sample (p T >500 GeV) to estimate precision. Count events with E T miss > 500 GeV in SUSY selection and background estimate. With 10 fb -1 obtain: –SUSY: 50 ± 7 (stat) –Estimate: 55 ± 17(stat)  30% Background Estimates With 44 fb -1 (full T2 sample) obtain: –SUSY: 174 ± 13 (stat) –Estimate: 198 ± 38(stat)  20% Errors in estimates mainly from sideband stats (poor top selection efficiency) Contribution from statistical error in normalistion (even with 0.5 fb -1 ) negligible. ATLAS Preliminary ATLAS Preliminary T2 Estimate SUSY selection Estimate SUSY selection

65. NIKHEF, January 2007 Dan Tovey 65 SUSY So what happens when a SUSY signal is present? Study by adding in SUSY sample SU3 (appropriately normalised). Repeat previous steps. Normalisation procedure OK for SU3 and 100 – 200 GeV window Normalisation factor 4.16 ± 0.27 Sideband subtraction appears to work ATLAS Preliminary ATLAS Preliminary T1 + SU3 SU3 Estimate SUSY selection Estimate SUSY selection (top) SUSY selection (total)

66. NIKHEF, January 2007 Dan Tovey 66 Background estimates affected by increased sideband Large excess at E T miss > 500 GeV With 10 fb -1 obtain: –SUSY: 503 ± 22 (stat - estimate) –Estimate: 7 ± 35 (stat - estimate) Actual stat error on estimate: ± 49 Clear excess (~13  ) Estimates with Signal With 44 fb -1 (full T2 sample) obtain: –SUSY: 2156 ± 46 (stat - estimate) –Estimate: -15 ± 75(stat - estimate) Actual staterror on estimate: ± 204 Expected errors on estimate increase due to dilution of top in signal band by SUSY (high E T miss ). ATLAS Preliminary ATLAS Preliminary T1 + SU3 Estimate SUSY selection (top) SUSY selection (total)