1. 1 Rutherford Appleton Laboratory The 13th Annual International Conference on Supersymmetry and Unification of the Fundamental Interactions Durham, 2005 SUSY Discovery Potential at CMS using Two Same Sign Muons C. H. Shepherd-Themistocleous Rutherford Appleton Laboratory, UK

2. SUSY05, Durham, UK 2 Introduction  Generic search for SUSY  Determine CMS reach shortly after start up ( ∫ L dt up to 10 fb -1 )  Inclusive search within mSUGRA  Exploit clean signature –same sign di-muons plus jets Rejection of SM background High trigger efficiency Theoretical studies for Tevatron –hep-ph/9904282, "Supersymmetry Reach of the Tevatron via Trilepton, Like-Sign Dilepton and Dilepton plus Tau Jet Signatures", K.T.Matchev, D.M.Pierce

3. SUSY05, Durham, UK 3 mSUGRA old cosmological constraint 0.1 < < 0.3 WMAP cosmological constraint 0.094 < < 0.129 require that is the LSP excluded by favoured by at 2-σ level J.Ellis et al., hep-ph/0303043 Perform study within mSUGRA. Only 5 free parameters: m 0, m 1/2, tanβ, A 0, sign(μ)) Example of allowed regions. A 0 = 0, tanβ = 10, μ > 0

4. SUSY05, Durham, UK 4 SUSY points considered in this study - negligible σ Selected set of points with A 0 = 0, sign(  ) > 0. Updated post-WMAP benchmark point (hep-ph/0306219) [* - with modification] Additional points –(calculated by A.Birkedal (Cornell), K.Matchev (UF)) Six of the points (high mass) are found to have negligible cross-sections m 1/2 m 0 18 15 12 14 17 9 7 16 5 4,6,8,10,11,19,20 2 1 3 13

5. SUSY05, Durham, UK 5 Cross sections & simulation  SUSY coupling constants and cross sections determined at LO using ISAJET http://www.phy.bnl.gov/~isajet /  NLO corrections for SUSY processes determined using PROSPINO (v1) hep-ph/9611232  Cross sections for standard model processes determined using PYTHIA 6.220 and CompHEP 4.2 (Z/   b b, single top).  NLO corrections used for ( t t, ZZ, Z b b )  All hadronization done using PYTHIA 6.220  Full CMS detector simulation was used (CMSIM, ORCA)

6. SUSY05, Durham, UK 6 Standard Model Backgrounds Other potential background considered at generator level only (using CompHEP) - negligible contribution Full detector simulation for main backgrounds N1 – total number of expected events for integral luminosity of 10fb -1 N2 – number of events after pre-selection (two same sign muons with P T >10 GeV & |  |<2.5)

7. SUSY05, Durham, UK 7 SUSY cross sections  Notation: –N1 – total number of expected events for integral luminosity of 10fb -1 –N2 – number of events after pre-selection (two same sign muons, P T >10 GeV) –Significance, (S.I.Bityukov,N.V.Krasnikov) –S/B – ratio: - excluded points

8. SUSY05, Durham, UK 8 Signature Example signal Example Background  Variables for cuts: –Missing E T –Jets E T –Muon P T, Muon Impact Parameter –Plus: Muon Isolation, Muon η, Jet η, number of jets/muons, …

9. SUSY05, Durham, UK 9 Examples Distributions (1) mSUGRA point 11 m 0 =85 GeV, m 1/2 =400 GeV, tanβ = 10, A 0 = 0, signμ > 0 After preselection cuts: two same sign muons with P T >10 GeV & |  |<2.5

10. SUSY05, Durham, UK 10 Example Distributions (2) mSUGRA point 11 m 0 =85 GeV, m 1/2 =400 GeV, tanβ = 10, A 0 = 0, signμ > 0 After preselection cuts: two same sign muons with P T >10 GeV & |  |<2.5

11. SUSY05, Durham, UK 11 Example Distributions (3) mSUGRA point 3 m 0 =149 GeV, m 1/2 =700 GeV tanβ = 10 A 0 = 0 sign(μ) > 0

12. SUSY05, Durham, UK 12 Analysis Cuts  Simple 1d cuts based analysis  Variables considered –Missing E T, E T jet 1, E T jet 3, P T μ 1, P T μ 2, d 0 (μ min ), d 0 (μ max )  Range of values of cuts for each variable considered Missing E T : 0 - 500 GeV E T jet 1 : 0 - 400 GeV E T jet 3 : 0 - 250 GeV P T μ 1 : 10 - 150 GeV/c P T μ 2 : 10 - 80 GeV/c d 0 (μ min ) : 0.005 - 0.0005 cm and no cut d 0 (μ max ) : 0.1 - 0.005 cm and no cut  Set of cuts optimized at each SUSY point ~ 176k sets of cuts considered  Values of significance, S/B and N tot for 10fb -1 determined

13. SUSY05, Durham, UK 13 Selection of set of cuts

14. SUSY05, Durham, UK 14 Final analysis cuts  Two sets of cuts chosen which have high significance and S/B for all SUSY points –Set #1: Missing E T > 200 GeV, E T jet 3 > 170 GeV, P T μ 1 > 20 GeV –Set #2: Missing E T > 100 GeV, E T jet 1 > 300 GeV, E T jet 3 > 100 GeV  These cuts are applied in addition to the preselection cuts: –2 same sign muons, both with P T > 10 GeV &   Results were obtained for all SUSY points for each of the above sets of cuts Trigger cuts  L1: single  with P t > 14 GeV di-  with P t > 3 GeV  HLT: di-  with P t > 7 GeV

15. SUSY05, Durham, UK 15 Results for 2 nd set of cuts  Monte Carlo statistical errors shown for number of events after all cuts (N final)

16. SUSY05, Durham, UK 16 Results: Significance  Total number of points out of reach (Significance < 5) for 10 fb -1 –9 for cut set #1 –10 for cut set #2  Remainder are potential "discovery points" for 10 fb -1 of integrated luminosity –Significance > 5 –S/B > 0.4 (excess of 40% or more over expected number of SM events)

17. SUSY05, Durham, UK 17 Results: Reach for 10fb -1 m 1/2 m 0 18 15 12 14 17 9 7 16 5 4,6,8,10,11,19,20 2 1 3 13 4 6 8 10 11 1920  Many points will be visible for ∫L<<10 fb -1  Significance for many points >> 5 for ∫L=10 fb -1

18. SUSY05, Durham, UK 18 A First Estimate of Systematic Effects  To estimate the stability of the results, the effect of varying the cuts and the number of SM and SUSY events was investigated: –Uncertainty in signal acceptance and background variation 30% decrease in no. of SUSY events + 30% increase in no. of SM events –Energy and momentum scale uncertainty shift of all cuts by + or – 20% simultaneously  Only one "SUSY discovery" point (#13) goes out of reach  Above probably pessimistic scenario –Only one background process survives after all cuts: –Precision to which cross-section is expected to be known for this process (including theoretical systematics) is about 10%

19. SUSY05, Durham, UK 19 Summary  Study performed based on the mSUGRA model  tanβ=10,20,35, sign(μ)>0, A 0 =0  Full detailed simulation, trigger emulation and reconstruction was used  Excess of mSUGRA events over SM processes is statistically significant for many benchmark points for ∫L<<10fb -1  up to 600 GeV in m 1/2 and at least up to 1600 GeV in m 0  Results are optimistic for SUSY discovery

20. SUSY05, Durham, UK 20 Backup slides

21. SUSY05, Durham, UK 21 Location in parameter space  Variety of SUSY decay chains possible  Mix depends on where one is in SUSY parameter space. –e.g. for point 5, 42% of decay chains (PYTHIA) follow the form of the previous diagram.  Where m 0 < m 1/2 m(sleptons) < m (        two body decays to lepton final states open up.

22. SUSY05, Durham, UK 22 Previous CMS study Fast detector simulation only Integrated Lumi 100 fb -1