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UKHEP Forum, April 2004 Dan Tovey 1 Prospects for SUSY at ATLAS and CMS Dan Tovey University of Sheffield.

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Presentation on theme: "UKHEP Forum, April 2004 Dan Tovey 1 Prospects for SUSY at ATLAS and CMS Dan Tovey University of Sheffield."— Presentation transcript:

1 UKHEP Forum, April 2004 Dan Tovey 1 Prospects for SUSY at ATLAS and CMS Dan Tovey University of Sheffield

2 UKHEP Forum, April 2004 Dan Tovey 2 Introduction SUSY particularly well-motivated solution to gauge hierarchy problem, unification of couplings etc. etc. (see Weiglein talk). Also often provides natural solution to Dark Matter problem of astrophysics/cosmology. One of main motivations for building LHC and GPDs. Much work carried out historically by LHC experiments esp: –ATLAS Detector and Physics Performance TDR ( –CMS SUSY mega-note (J. Phys. G28 (2002) 469). Will concentrate in this talk on more recent studies and areas where new groups/people could get involved. DISCLAIMER: Will try to cover both CMS and ATLAS activities where relevant, however in places will focus more on ATLAS (personal bias due to familiarity). Will not cover non-SUSY exotica (ED, BH production etc.) PS: Spot a missing tilde and win a prize!

3 UKHEP Forum, April 2004 Dan Tovey 3 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

4 UKHEP Forum, April 2004 Dan Tovey 4 SUSY Signatures Q: What do we expect SUSY 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

5 UKHEP Forum, April 2004 Dan Tovey 5 Inclusive Searches One of first tasks of LHC experiments (SUSY cross-section large). Is LHC sensitive to all phenomenologically favoured models? Especially important given current interest in focus-point models with large mass scales. Use 'golden' Jets + n leptons + E T miss discovery channel. –Heavy strongly interacting sparticles produced in initial interaction –Cascade decay via jets and leptons –R-Parity conservation gives stable LSP (neutralino) at end of chain Map statistical discovery reach in mSUGRA m 0 -m 1/2 parameter space. Sensitivity only weakly dependent on A 0, tan( ) and sign( ). –Choose 'reasonable' values e.g.A 0 =0, tan( ) = 10, 35, sign( )=+/-1 Systematic + statistical discovery reach harder to assess –Focus of current and future work.

6 UKHEP Forum, April 2004 Dan Tovey 6 mSUGRA Reach ATLAS 5 5

7 UKHEP Forum, April 2004 Dan Tovey 7 SUSY Mass Scale First measured SUSY parameter likely to 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. Typical measurement error (syst+stat) ~10% for mSUGRA models for 10 fb -1. Jets + E T miss + 0 leptons ATLAS 10 fb -1

8 UKHEP Forum, April 2004 Dan Tovey 8 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

9 UKHEP Forum, April 2004 Dan Tovey 9 Dilepton Edge Measurements 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 ). ~ ~ 0 2 ~ 0 1 ll l e + e ~ ~ 30 fb -1 atlfast Physics TDR Point 5 e + e e e - 5 fb -1 FULL SIM Modified Point 5 (tan( ) = 6) ATLAS Preliminary

10 UKHEP Forum, April 2004 Dan Tovey 10 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 )

11 UKHEP Forum, April 2004 Dan Tovey 11 Model-Independent Masses Combine measurements from edges from different jet/lepton combinations to obtain model- independent mass measurements. 0 1 lRlR 0 2 qLqL Mass (GeV) ~ ~ ~ ~ ATLAS Sparticle Expected precision (100 fb -1 ) q L 3% 0 2 6% l R 9% % ~ ~ ~ ~

12 UKHEP Forum, April 2004 Dan Tovey 12 Sbottom 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 (but actually two peaks). lb b l g ~ b ~ lRlR ~ ~ ~ pp Post-LEP Point B: m 0 =100 GeV, m 1/2 = 250 GeV, tan( ) = 10, A 0 =0, >0 10 fb -1 CMS

13 UKHEP Forum, April 2004 Dan Tovey 13 Gluino Mass Can also move further up the decay chain to gain sensitivity to gluino mass. Can use either light squark decay or sbottom (as here). Problem with large error on input 0 1 mass remains solve by reconstructing difference of gluino and squark/sbottom masses. Allows separation of b 1 and b 2 with 300 fb fb -1 Sbottom ChainSquark Chain 10 fb fb fb fb fb fb -1 M(sbottom)500±7502±4497±2M(squark)536±10532±2536±1 (sbottom) 42±541±436±3 (squark) 60±936±131±1 M(gluino)594±7592±4591±3M(gluino)592±7595±2590±2 (gluino) 42±746±339±3 (gluino) 75±559±2 M(gl)-M(sb)92±388±290±2M(gl)-M(sq)57±347±244±2 (gl-sb) 17±420±223±2 (gl-sq) 9±316±511±2 Post-LEP Point B CMS Post-LEP Point B 300 fb -1 ~ ~ ~

14 UKHEP Forum, April 2004 Dan Tovey 14 Higgs Signatures Lightest Higgs particle produced copiously in 0 2 decays if kinematically allowed. Prominent peak in bb invariant mass distribution. Possible discovery channel. ~ CMS 100 fb -1 m 0 =500 GeV, m 1/2 = 500 GeV, tan( ) = 2, A 0 =0, <0

15 UKHEP Forum, April 2004 Dan Tovey 15 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 Preliminary Left slepton Right squark ~ ~ SPS1a Precision ~ 3%

16 UKHEP Forum, April 2004 Dan Tovey 16 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 Preliminary ATLAS 100 fb -1 Preliminary ATLAS 100 fb -1 ATLAS Preliminary SPS1a

17 UKHEP Forum, April 2004 Dan Tovey 17 Mass Relation Method Hot off the press: new idea for reconstructing SUSY masses! Impossible to measure mass of each sparticle using one channel alone (Page 8). –Should have added caveat: Only if done event-by-event! 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

18 UKHEP Forum, April 2004 Dan Tovey 18 Chargino Mass Measurement Mass of lightest chargino very difficult to measure as does not participate in standard dilepton SUSY decay chain. Decay process via +slepton gives too many extra degrees of freedom - concentrate instead on decay + 1 W 0 1. Require dilepton 0 2 decay chain on other leg of event and use kinematics to calculate chargino mass analytically. Using sideband subtraction technique obtain clear peak at true chargino mass (218 GeV). ~ 3 significance for 100 fb -1. PRELIMINARY lq q l g ~ q ~ lRlR ~ 0 2 ~ 0 1 ~ p p + 1 ~ ~ q q q q q 0 1 ~ W g ~ Modified LHCC Point 5: m 0 =100 GeV; m 1/2 =300 GeV; A 0 =300 GeV; tanß=6 ; μ>0 100 fb -1 ~ ~ ~

19 UKHEP Forum, April 2004 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 SPS1a Parameter Expected precision (300 fb -1 ) m 0 2% m 1/2 0.6% tan( ) 9% A 0 16%

20 UKHEP Forum, April 2004 Dan Tovey 20 SUSY Dark Matter Baer et al. hep-ph/ LEP 2 No REWSB LHC Point 5: >5 error (300 fb -1 ) p = pb p = 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 = –log 10 ( p /pb) = SPS1a: >5 error (300 fb -1 ) Micromegas 1.1 (Belanger et al.) + ISASUGRA 7.69 ATLAS 300 fb -1 Preliminary p ATLAS 300 fb -1 Preliminary DarkSUSY (Gondolo et al.) + ISASUGRA 7.69 h 2

21 UKHEP Forum, April 2004 Dan Tovey 21 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/ l l lRlR ~ ~ ~ 1 /Z/h 1 ~ ~ ~ Disfavoured by BR (b s ) = ( ) (CLEO, BELLE) Favoured by g -2 (E821) Assuming = (26 10) from SUSY ( 2 ) h (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(

22 UKHEP Forum, April 2004 Dan Tovey 22 Coannihilation Models Small slepton-neutralino mass difference gives soft leptons from decay –Low electron/muon/tau energy thresholds crucial. At high tan( ) stau decay channel dominates. –Need to be able to ID soft taus (good jet rejection). Study just started within ATLAS examining signatures of these models. Study point chosen within coannihilation region : –m 0 =70 GeV; m 1/2 =350 GeV; A 0 =0; tanß=10 ; μ>0 Same model to be used for ATLAS DC2 SUSY study (see later). lq q l g ~ q ~ lRlR ~ ~ ~ pp

23 UKHEP Forum, April 2004 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 Chosen model point has very rich phenomenology. Decays of 0 2 to both l L and l R kinematically allowed. –Double dilepton invariant mass edge structure; –Edges expected at 57 GeV and 101 GeV Stau decay channels enhanced –Soft tau signatures; –Edge expected at 79 GeV; –Less clear due to poor tau visible energy resolution. ATLAS Preliminary 100 fb -1 ~ ~ ~

24 UKHEP Forum, April 2004 Dan Tovey 24 Super-LHC Proposal to increase sqrt(s) to 28 TeV, luminosity to cm -2 s -1 after initial running (14 TeV, L max = cm -2 s -1 ). Significant impact on detector performance, esp. tracking, electronics etc. Increased luminosity improves discovery reach by ~ 300 GeV. Increased sqrt(s) (less easy technologically) more useful: 800 GeV improvement. Needs further study. CMS A 0 = 0; tan =10; >0

25 UKHEP Forum, April 2004 Dan Tovey 25 ATLAS: DC1 SUSY Challenge First attempt at large-scale simulation of SUSY signals in ATLAS ( events: ~5 fb -1 ) in early Tested Geant3 simulation and ATHENA (C++) reconstruction software framework thoroughly. UK sites contributed 40% of initial event sample. 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

26 UKHEP Forum, April 2004 Dan Tovey 26 ATLAS has just embarked on DC2 (main production over summer). SUSY Working Group goals: –To validate complete ATLAS simulation and reconstruction software chain using physics objects in SUSY events (jets, taus, leptons etc.); –To carry out sample physics analyses for well-motivated SUSY models using fully simulated data. Models to be studied include: –DC1 point (for validation of Geant4 sim. + new reconstruction tools); –New coannihilation point (rich in signatures). Activity just started (open call for volunteers + phone meeting so far). UK interest so far from Cambridge, RHUL and Sheffield. More volunteers very welcome! (please see me for details) Similar activity within CMS (DC04, PRS SUSY/BSM WG) – aim to scan parameter space and perform detailed studies with specific models in preparation for Physics TDR (late 2005). Contact Luc Pape if interested. Data Challenge Activities

27 UKHEP Forum, April 2004 Dan Tovey 27 Supersummary The LHC will be THE PLACE to search for, and hopefully study, SUSY from 2007 onwards. SUSY searches will commence on Day 1 of LHC operation. Big challenge for discovery will be understanding systematics. Many studies of exclusive channels already performed. Massive scope for further work! ATLAS and CMS currently focusing on Data Challenges. Significant UK involvement already. Please get involved – this is a great opportunity for the UK to exploit its hardware investment.

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