1 / 27

Prospects for SUSY at ATLAS and CMS

Prospects for SUSY at ATLAS and CMS. Dan Tovey University of Sheffield. Introduction. SUSY particularly well-motivated solution to gauge hierarchy problem, unification of couplings etc. etc. (see Weiglein talk).

moyerr
Download Presentation

Prospects for SUSY at ATLAS and CMS

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. Prospects for SUSY at ATLAS and CMS Dan Tovey University of Sheffield 1

  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 (http://atlasinfo.cern.ch/Atlas/GROUPS/PHYSICS/TDR/access.html). • 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! 2

  3. 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… 3

  4. 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. 4

  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 + ETmiss 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 m0-m1/2 parameter space. • Sensitivity only weakly dependent on A0, tan(b) and sign(m). • Choose 'reasonable' values g e.g.A0=0, tan(b) = 10, 35, sign(m)=+/-1 • Systematic + statistical discovery reach harder to assess • Focus of current and future work. 5

  6. mSUGRA Reach 5s 5s ATLAS 6

  7. SUSY Mass Scale Jets + ETmiss + 0 leptons ATLAS • 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 ETmiss: Meff=S|pTi| + ETmiss. • 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. 10 fb-1 10 fb-1 ATLAS 7

  8. 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. 8

  9. 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). ~ ~ e+e- + m+m- - e+m- - m+e- e+e- + m+m- 5 fb-1 FULL SIM Point 5 ATLAS ATLAS 30 fb-1 atlfast Modified Point 5 (tan(b) = 6) Physics TDR Preliminary 9

  10. 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 10

  11. ‘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 Mass (GeV) Mass (GeV) 11

  12. Sbottom Mass p p ~ c01 ~ ~ ~ ~ b c02 g lR b b l l • 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). Post-LEP Point B: m0=100 GeV, m1/2 = 250 GeV, tan(b) = 10, A0=0, m>0 CMS 10 fb-1 12

  13. Gluino Mass 300 fb-1 • 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 c01 mass remains g solve by reconstructing difference of gluino and squark/sbottom masses. • Allows separation of b1 and b2 with 300 fb-1. Post-LEP Point B CMS ~ ~ ~ Post-LEP Point B 300 fb-1 CMS 13

  14. Higgs Signatures ~ • Lightest Higgs particle produced copiously in c02 decays if kinematically allowed. • Prominent peak in bb invariant mass distribution. • Possible discovery channel. m0=500 GeV, m1/2 = 500 GeV, tan(b) = 2, A0=0, m<0 CMS 100 fb-1 CMS 14

  15. 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 Preliminary Preliminary 30 fb-1 30 fb-1 30 fb-1 Right squark SPS1a ATLAS SPS1a SPS1a Right squark Left slepton Preliminary Precision ~ 3% 15

  16. Heavy Gaugino Measurements ATLAS Preliminary • 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). Preliminary Preliminary Preliminary SPS1a ATLAS ATLAS ATLAS 100 fb-1 100 fb-1 100 fb-1 SPS1a 16

  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 g ‘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 ATLAS SPS1a 17

  18. Chargino Mass Measurement ~ c+1 q ~ ~ q c01 ~ g p ~ W ~ c01 ~ c02 p q lR ~ q q g ~ q q q l l • Mass of lightest chargino very difficult to measure as does not participate in standard dilepton SUSY decay chain. • Decay process via n+slepton gives too many extra degrees of freedom - concentrate instead on decay c+1g W c01. • Require dilepton c02 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 s significance for 100 fb-1. PRELIMINARY ~ ~ Modified LHCC Point 5: m0=100 GeV; m1/2=300 GeV; A0=300 GeV; tanß=6 ; μ>0 ~ 100 fb-1 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 Preliminary Preliminary 20

  21. 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 Slepton Co-annihilation region: LSP ~ pure Bino. Small slepton-LSP mass difference makes measurements difficult. mSUGRA A0=0, tan(b) = 10, m>0 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) Favoured by g-2 (E821) Assuming  = (26  10)  10 -10 from SUSY ( 2 ) '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) 0.094    h2  0.129 (WMAP) 21

  22. Coannihilation Models p p ~ c01 ~ ~ ~ ~ q c02 g lR q q l l • Small slepton-neutralino mass difference gives soft leptons from decay • Low electron/muon/tau energy thresholds crucial. • At high tan(b) 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 : • m0=70 GeV; m1/2=350 GeV; A0=0; tanß=10 ; μ>0 • Same model to be used for ATLAS DC2 SUSY study (see later). 22

  23. Coannihilation Signatures • Chosen model point has very rich phenomenology. • Decays of c02 to both lL and lR 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. • 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. Super-LHC CMS • Proposal to increase sqrt(s) to 28 TeV, luminosity to 1035 cm-2 s-1 after initial running (14 TeV, Lmax= 1034 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. A0 = 0; tanb=10; m>0 24

  25. ATLAS: DC1 SUSY Challenge Modified LHCC Point 5: m0=100 GeV; m1/2=300 GeV; A0=300 GeV; tanß=6 ; μ>0 ATLAS Preliminary • 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. • UK sites contributed 40% of initial 50 000 event sample. SUSY Mass Scale ATLAS ll endpoint No b-tag With b-tag Dijet mT2 distribution ATLAS Preliminary Preliminary llj endpoint ATLAS Preliminary 25

  26. Data Challenge Activities • 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 <luc.pape@cern.ch> if interested. 26

  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. 27

More Related