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Supersymmetry at ATLAS

Construction. Supersymmetry at ATLAS. Dan Tovey University of Sheffield. Supersymmetry. Supersymmetry (SUSY) fundamental continuous symmetry connecting fermions and bosons Q a |F> = |B>, Q a |B> = |F> {Q a ,Q b }=-2 g m ab p m : generators obey anti-commutation relations with 4-mom

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Supersymmetry at ATLAS

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  1. Construction Supersymmetryat ATLAS Dan Tovey University of Sheffield 1

  2. Supersymmetry • Supersymmetry (SUSY) fundamental continuous symmetry connecting fermions and bosons Qa|F> = |B>, Qa|B> = |F> • {Qa,Qb}=-2gmabpm: 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 mH<207 GeV (95%CL) 2

  3. SUSY Spectrum ~ ~ ~ ~ A H0 H± H0u H0d H+u H-d ~ ~ ~ ~ u d e ne ~ ~ ~ ~ c s m nm ~ ~ ~ ~ t b t nt ~ ~ ~ g Z W± g Z W± ~ g g ~ ~ ~ ~ ~ ~ ~ G c02 c03 c ±1 c04 c01 c ±2 • SUSY gives rise to partners of SM states with opposite spin-statistics but otherwise same Quantum Numbers. h • 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 ne u d e c s m nm t b t nt G 3

  4. SUSY & Dark Matter mSUGRA A0=0, tan(b) = 10, m>0 Ellis et al. hep-ph/0303043 Disfavoured by BR (b  s) = (3.2  0.5)  10-4 (CLEO, BELLE) Universe Over-Closed ~ c01 t ~ c01 l ~ t1 ~ ~ t1 g/Z/h lR ~ c01 l 0.094    h2  0.129 (WMAP-1year) • R-Parity Rp = (-1)3B+2S+L • Conservation of Rp (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. 4

  5. SUSY @ ATLAS • 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. • 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. 5

  6. Model Framework LHCC mSUGRA Points 3 1 2 5 4 • Minimal Supersymmetric Extension of the Standard Model (MSSM) contains > 105 free parameters, NMSSM etc. has more g 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 g mSUGRA/CMSSM framework : unified masses and couplings at the GUT scale g 5 free parameters • (m0, m1/2, A0, tan(b), sgn(m)). • 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… 6

  7. SUSY Signatures p p ~ c01 ~ ~ ~ q ~ c02 l g q q l l • 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. g cascade decays to LSP. • Long decay chains and large mass differences between SUSY states • Many high pT objects observed (leptons, jets, b-jets). • If R-Parity conserved LSP (lightest neutralino in mSUGRA) stable and sparticles pair produced. • Large ETmiss signature (c.f. Wgln). • Closest equivalent SMsignature tgWb. 7

  8. Inclusive Searches • Use 'golden' Jets + n leptons + ETmiss discovery channel. • Map statistical discovery reach in mSUGRA m0-m1/2 parameter space. • Sensitivity only weakly dependent on A0, tan(b) and sign(m). • Syst.+ stat. reach harder to assess: focus of current & future work. 5s 5s ATLAS ATLAS 8

  9. Inclusive SUSY Jets + ETmiss + 0 leptons ATLAS • 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 ETmiss: Meff=S|pTi| + ETmiss. • 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 … 10 fb-1 9

  10. Exclusive Studies p p ~ c01 ~ ~ ~ ~ q c02 g lR q q l l • 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) g 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 (n mass from b decay spectrum, W (transverse) mass in Wgln). • Difference here is we don't know mass of neutral final state particles. 10

  11. Dilepton Edge Measurements ~ ~ c01 c02 ~ l l l • When kinematically accessible c02 canundergo sequential two-body decay to c01 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- + m+m- - e+m- - m+e- • Position of edge measured with precision ~ 0.5% (30 fb-1). ~ ~ • m0 = 100 GeV • m1/2 = 300 GeV • A0 = -300 GeV • tan(b) = 6 • sgn(m) = +1 e+e- + m+m- - e+m- - m+e- e+e- + m+m- Point 5 ATLAS ATLAS 30 fb-1 atlfast 5 fb-1 SU3 Physics TDR 11

  12. Measurements With Squarks ~ qL ~ ~ c02 ~ c01 q l l l ~ qL ~ ~ c02 c01 q h lq edge llq edge b b 1% error (100 fb-1) 1% error (100 fb-1) • 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. bbq edge llq threshold 1% error (100 fb-1) 2% error (100 fb-1) TDR, Point 5 TDR, Point 5 TDR, Point 5 TDR, Point 5 ATLAS ATLAS ATLAS ATLAS 12

  13. Full Simulation 4.20 fb-1 No cuts ll endpoint ATLAS • Full Geant4 simulation of signals + backgrounds now routine. • Invariant mass of dilepton+jet bounded by Mllqmin=271.8 GeV and Mllqmax =501 GeV. • Leptons combined with two jets with highest pT • Flavour subtraction & efficiency correction applied Preliminary SU3 Dilepton Edge = (100.3  0.4) GeV Larger of M(llq) • m0 = 100 GeV • m1/2 = 300 GeV • A0 = -300 GeV • tan(b) = 6 • sgn(m) = +1 Smaller of M(llq) Smaller of M(llq) Events ATLAS 4.20 fb-1 2j100+2l10 Preliminary 10 30 4.20 fb-1 2j100+2l10 ATLAS 0 Preliminary 0 0 200 400 600 M(qql) (GeV) 200 400 600 13

  14. ‘Model-Independent’ Masses Sparticle Expected precision (100 fb-1) qL 3% 02 6% lR 9% 01 12% ~ ~ ~ ~ ~ ~ c01 lR ATLAS ATLAS • Combine measurements from edges from different jet/lepton combinations to obtain ‘model-independent’ mass measurements. Mass (GeV) Mass (GeV) ~ ~ c02 qL ATLAS ATLAS LHCC Point 5 Mass (GeV) Mass (GeV) 14

  15. Sbottom/Gluino Mass p p ~ c01 ~ ~ ~ ~ b c02 g lR b b l l ~ ~ m(g)-0.99m(c01) = (500.0 ± 6.4) GeV 300 fb-1 ATLAS • 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 c01 mass remains g reconstruct difference of gluino and sbottom masses. • Allows separation of b1 and b2 with 300 fb-1. SPS1a ~ ~ ~ m(g)-m(b1) = (103.3 ± 1.8) GeV ATLAS ~ ~ ~ ~ m(g)-m(b2) = (70.6 ± 2.6) GeV 300 fb-1 SPS1a 15

  16. Stop Mass mtbmax= (443.2 ± 7.4stat) GeV Expected = 459 GeV ~ ~ ~ ~ ~ ~ 120 fb-1 • Look at edge in tb mass distribution. • Contains contributions from • gtt1tbc+1 • gbb1btc+1 • SUSY backgrounds • Measures weighted mean of end-points • Require m(jj) ~ m(W), m(jjb) ~ m(t) ATLAS LHCC Pt 5 (tan(b)=10) mtbmax= (510.6 ± 5.4stat) GeV Expected = 543 GeV • Subtract sidebands from m(jj) distribution • Can use similar approach with gtt1ttc0i • Di-top selection with sideband subtraction • Also use ‘standard’ bbll analyses (previous slide) 120 fb-1 ~ ~ ~ ATLAS LHCC Pt 5 (tan(b)=10) 16

  17. RH Squark Mass ~ ~ c01 qR q ~ ~ ~ • Right handed squarks difficult as rarely decay via ‘standard’ c02 chain • Typically BR (qRgc01q) > 99%. • Instead search for events with 2 hard jets and lots of ETmiss. • Reconstruct mass using ‘stransverse mass’ (Allanach et al.): mT22 = min [max{mT2(pTj(1),qTc(1);mc),mT2(pTj(2),qTc(2);mc)}] • Needs c01 mass measurement as input. • Also works for sleptons. ~ qTc(1)+qTc(2)=ETmiss ATLAS ATLAS 30 fb-1 100 fb-1 30 fb-1 Right squark SPS1a ATLAS SPS1a SPS1a Right squark Left slepton Precision ~ 3% 17

  18. Heavy Gaugino Measurements ATLAS • 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). SPS1a ATLAS ATLAS ATLAS 100 fb-1 100 fb-1 100 fb-1 SPS1a 18

  19. Measuring Model Parameters Point m0 m1/2 A0 tan(b) sign(m) LHC Point 5 100 300 300 2 +1 SPS1a 100 250 -100 10 +1 Parameter Expected precision (300 fb-1) m0 2% m1/2 0.6% tan(b)  9% A0 16% • 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. 19

  20. SUSY Dark Matter • Can use parameter measurements for many purposes, e.g. estimate LSP Dark Matter properties (e.g. for 300 fb-1, SPS1a) • Wch2 = 0.1921  0.0053 • log10(scp/pb) = -8.17  0.04 Baer et al. hep-ph/0305191 LHC Point 5: >5s error (300 fb-1) SPS1a: >5s error (300 fb-1) scp=10-11 pb Micromegas 1.1 (Belanger et al.) + ISASUGRA 7.69 DarkSUSY 3.14.02 (Gondolo et al.) + ISASUGRA 7.69 scp=10-10 pb Wch2 scp scp=10-9 pb 300 fb-1 300 fb-1 No REWSB LEP 2 ATLAS ATLAS 20

  21. Complementarity D.R. Tovey et al., JHEP 0405 (2004) 071 No. MC Experiments scpsi Wch2 • Measurements at ATLAS complementary to direct and indirect astroparticle searches / measurements • Uncorrelated systematics • Measures different parameters EDELWEISS Wch2 log10 (scpsi / 1pb) CDMS scpsi (cm2) 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 Wch2, mc, scpsietc. CDMS-II ZEPLIN-I CRESST-II scpsi ZEPLIN-2 ZEPLIN-4 EDELWEISS 2 GENIUS XENON ZEPLIN-MAX mc Provides strongest possible test of Dark Matter model DM particle mass mc (GeV) 21

  22. SUSY Dark Matter 'Focus point' region: significant h component to LSP enhances annihilation to gauge bosons ~ ~ c01 t ~ c01 l ~ t1 ~ ~ t1 g/Z/h lR ~ c01 l mSUGRA A0=0, tan(b) = 10, m>0 Slepton Co-annihilation region: LSP ~ pure Bino. Small slepton-LSP mass difference makes measurements difficult. Ellis et al. hep-ph/0303043 • SUSY (e.g. mSUGRA) parameter space strongly constrained by cosmology (e.g. WMAP satellite) data. 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. Also 'rapid annihilation funnel' at Higgs pole at high tan(b), stop co-annihilation region at large A0 0.094    h2  0.129 (WMAP) 22

  23. Coannihilation Signatures • Small slepton-neutralino mass difference gives soft leptons • Low electron/muon/tau energy thresholds crucial. • Study point chosen within region: • m0=70 GeV; m1/2=350 GeV; A0=0; tanß=10 ; μ>0; • Same model used for DC2 study. • Decays of c02 to both lL and lR kinematically allowed. • Double dilepton invariant mass edge structure; • Edges expected at 57 / 101 GeV • Stau channels enhanced (tanb) • Soft tau signatures; • Edge expected at 79 GeV; • Less clear due to poor tau visible energy resolution. • ETmiss>300 GeV • 2 OSSF leptons PT>10 GeV • >1 jet with PT>150 GeV • OSSF-OSOF subtraction applied 100 fb-1 ATLAS Preliminary ~ ~ ~ • ETmiss>300 GeV • 1 tau PT>40 GeV;1 tau PT<25 GeV • >1 jet with PT>100 GeV • SS tau subtraction 100 fb-1 ATLAS Preliminary 23

  24. Full Simulation Two edges from: 20.6 fb-1 No cuts 20.6 fb-1 No cuts ATLAS Soft lepton Preliminary MC Truth, lL Hard lepton MC Truth, lR MC Data ATLAS Preliminary • m0 = 70 GeV • m1/2 = 350 GeV • A0 = 0 • tan(b) = 10 • sgn(m) = +1 Each slepton is close in mass to one of the neutralinos – one of the leptons is soft 24

  25. Focus Point Models ~ ~ ~ ~ c03 → c01 ll c02 → c01 ll Z0→ ll ATLAS 300 fb-1 Preliminary • Large m0 sfermions are heavy • Most useful signatures from heavy neutralino decay • Study point chosen within focus point region : • m0=3550 GeV; m1/2=300 GeV; A0=0; tanß=10 ; μ>0 • Direct three-body decaysc0n → c01 ll • Edges givem(c0n)-m(c01) : flavour subtraction applied ~ ~ ~ ~ M = mA+mB m = mA-mB 25

  26. SUSY Spin Measurement Measure Angle Point 5 Spin-0 Spin-½ Straightline distn Polarise (phase-space) Spin-½, mostly wino Spin-0 Spin-½, mostly bino • 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 c02 • relies on valence quark contribution to pdf of proton (C asymmetry) • shape of dilepton invariant mass spectrum measures slepton spin ~ Point 5 ATLAS 150 fb -1 mlq spin-0=flat 150 fb -1 ATLAS 26

  27. Preparations for 1st 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 s measurements at same Ös) • 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. 27

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

  29. W/Z+Jets Background (Zll) ATLAS • Z gnn + n jets, W g ln + n jets, W gtn + (n-1) jets (t fakes jet) • Estimate from Z g l+l- + n jets (e or m) • Tag leptonic Z and use to validate MC / estimate ETmiss from pT(Z) & pT(l) • Alternatively tag W g ln + n jets and replace lepton with n (0l): • higher stats • biased by presence of SUSY Preliminary (Wln) ATLAS Preliminary 29

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

  31. QCD Background jets MET • Work in Progress: several ideas under study • Step 1: Measure jet smearing function from data • Select events: ETmiss > 100 GeV, Df(ETmiss, jet) < 0.1 • Estimate pT of jet closest to EtMiss as pTtrue-est = pTjet + ETMiss • Step 2: Smear low ETmiss multijet events with measured smearing function fluctuating jet Njets >= 4, pT(j1,j2) >100GeV, pT(j3,j4) > 50GeV ATLAS ATLAS NB: error bars expected errors on background. Preliminary Preliminary ETmiss 31

  32. Top Background • Jets + ETmiss + 1 lepton: cut hard on mT(ETmiss, l) • Rejects bulk of ttbar (semi-leptonic decays), W g ln + n jets • Remaining background mostly fully leptonic top decays (ttbblnln, ttbbtnln, ttbbtntn) with one top missed (e.g. hadronic tau) ATLAS Preliminary Edge at W Mass 32

  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. ETmiss) • Perform standard SUSY analysis on merged event • Technique applicable to wide range of channels (not just SUSY) • Involves measurement of (top) pT: useful for exotic-top searches? 33

  34. Decay Resimulation Estimate 5201 m(lb) Zmm • Select seed events: • 2 leptons with pT>25GeV • 2 jets with pT>50GeV • ETmiss < <pT(l1),pT(l2)> (SUSY) • Both m(lb) < 155GeV • Solve 6 constraints for p(n) • Resimulate + merge with seed • Apply 1l SUSY cuts (but Njet >=2) cut ATLAS Preliminary GeV ETmiss Sample 5201, pT(top) > 200 GeV reco 11.0.4205, 450 pb-1 ATLAS Pull (top pT) Preliminary Estimate requires >=2 jets, Normalisation under study ATLAS Preliminary 34

  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 35

  36. Supersymmetry 36

  37. BACK-UP SLIDES 37

  38. Top Background to SUSY With btag ttbar ATLAS • 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. Preliminary SUSY • Good agreement with top background distribution in SUSY selection. • With this tuning does not select SUSY events (as required) ATLAS Preliminary Histogram – 1 lepton SUSY selection (no b-tag) Data points – background estimate With btag 38

  39. Top Background to SUSY Estimate SUSY selection (top) SUSY selection (total) Estimate SUSY selection Work in progress • Fully simulated data. • No btag used • Background estimates altered by increased sideband • Large excess at ETmiss > 500 GeV • With 10 fb-1 obtain following no. events passing ETmiss 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 ATLAS Preliminary T2 T2 + SU3 39

  40. Full Simulation 20.6 fb-1 No cuts qll edge ql(min) edge • m0 = 70 GeV • m1/2 = 350 GeV • A0 = 0 • tan(b) = 10 • sgn(m) = +1 ATLAS ATLAS Preliminary Preliminary ql(max) edge qll threshold ATLAS ATLAS Preliminary Preliminary 40

  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 ATLAS ATLAS Preliminary M(02) (GeV) Preliminary M(01) (GeV) M(01) (GeV) 41

  42. llq Edge ~ ~ ~ c02 ~ c01 qL l l l q • Dilepton edges provide starting point for other measurements. • Use dilepton signature to tag presence of c02 in event, then work back up decay chain constructing invariant mass distributions of combinations of leptons and jets. ~ • 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. e.g. LHC Point 5 ATLAS 1% error (100 fb-1) Physics TDR Point 5 42

  43. lq Edge ATLAS • 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 g Require one llq mass above edge and one below (reduces combinatorics). Point 5 Physics TDR ATLAS • Construct distribution of invariant masses of 'slepton' jet with each lepton. • 'Right' edge sensitive to slepton, squark and c02 masses ('wrong' edge not visible). 1% error (100 fb-1) Physics TDR ~ Point 5 43

  44. hq edge ~ qL ~ ~ c02 c01 q h b b ~ ~ • If tan(b) not too large can also observe two body decay of c02 to higgs and c01. • Reconstruct higgs mass (2 b-jets) and combine with hard jet. • Gives additional mass constraint. ATLAS Point 5 1% error (100 fb-1) Physics TDR 44

  45. llq Threshold ATLAS Physics TDR ~ • Two body kinematics of slepton-mediated decay chain also provides still further information (Point 5). • Consider case where c01 produced near rest in c02 frame. • Dilepton mass near maximal. • p(ll) determined by p(c02). ~ Point 5 ~ • 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. Physics TDR ATLAS Point 5 2% error (100 fb-1) 45

  46. Mass Reconstruction • Combine measurements from edges from different jet/lepton combinations. • Gives sensitivity to masses (rather than combinations). 46

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

  48. AMSB ~ ~ • Examined RPC model with tan(b) = 10, m3/2=36 TeV, m0=500 GeV, sign(m) = +1. • c+/-1 near degenerate with c01. • Search for c+/-1 gp+/-c01 (Dm = 631 MeV g soft pions). ~ ~ • Also displaced vertex due to phase space (ct=360 microns). • Measure mass difference between chargino and neutralino using mT2 variable (from mSUGRA analysis). 48

  49. GMSB ~ c02 ~ ~ ~ l G l c01 l g • 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: 49

  50. GMSB • Use dilepton edge as before (but different position in chain). • Use also lg, llg edges (c.f. lq and llq edges in mSUGRA). • Get two edges (bonus!) in lg as can now see edge from 'wrong' lepton (from c02 decay). Not possible at LHCC Pt5 due to masses. • Interpretation easier as can assume gravitino massless: 50

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