SUSY Search Strategies at Atlas and CMS

Transcription

1 1 SUSY Search Strategies at Atlas and CMS (Universität Hamburg) for the Atlas and CMS Collaborations All-hadronic SUSY search Leptonic Inclusive SUSY search Reach in the msugra plane supported by:

2 SUSY Production at LHC Large variety of BSM-theories Large variety of Search strategies: Signature SUSY Scenario briefly introduced in this talk msugra, AMSB, split-susy,... All-hadronic msugra, AMSB, split-susy, jets + 1 lepton LSCP, RPV,... jets + 2 lepton msugra, AMSB, GMSB ττ γγ GMSB, large tanβ GMSB SUSY cross section is domitated by squark and gluino pair-/associated production depends on their masses / parameter space 2

3 Generic Susy Signature Example diagram 3 R-parity conservation pair/associated SUSY production Stable LSP Cascade decay of primary produced SUSY particles missing ET, many jets, possibly leptons.

4 All-hadronic SUSY Search Atlas selection no lepton MET > 100 GeV 1st,2nd jet > 100 GeV 3rd,4th jet > 50 GeV MET / meff > 20% CMS selection indirect lepton veto MET > 200 GeV 1st jet > 180 GeV 2nd jet > 110 GeV 3rd jet > 30 GeV HT > 500 GeV Further MET clean-up and QCD rejection cuts are applied 4

5 Leptonic Inclusive Search 5 Atlas selection CMS selection same as all-hadronic (optimized for 10fb-1, using genetic algorithm) One additional lepton 1 muon pt > 20 GeV, OR 1 electron pt > 25 GeV 1 muon pt > 30 GeV MET > 130 GeV 1st, 2nd jet > 440 GeV 3rd jet > 50 GeV 0.95 < cos(met,1stjet)<0.3 cos(met,2ndjet) < fb-1 SUSY LM1 SM background

6 Same sign di-muons + jets + MET 6 Same electrical charge leptons are an excellent signature to search for deviations from the SM Only little SM background, e.g. di-boson production This signature occurs naturally in many extensions to the SM and occurs rather rarely in SM interactions Use muon triggers: expected to be robust at the LHC start-up A0=0, tan(β)=10, sign(µ)=+1 5σ reach Selection cuts: tan β = 10, μ>0, A0=0 Optimized cuts for 10 fb-1 luminosity More details in SUSY08 Talk by Yu. Pakhotin today Tevatron LEP

7 MET cleaning 7 MET is the discriminating variable for a discovery of SUSY. Essential to understand its scale and resolution! cut LM1 dead material / cracks j j pt EMF Cosmics CMS MET Event EM- jets 0.1 j p T Cleaning: Fraction 99.9% Beam halo jets Event ptt tracks Calorimeter Performance Charged jet CMS: =1.0 E T Fraction pt 91.3% Atlas: =0.5 E T Main SM-backgrounds: QCD: ν-contents, σ(jets) fake MET tt: semi-leptonic where lepton is lost Z νν MET [GeV]

8 QCD Background Estimation 8 Many methods to extract QCD-sample from the data: Leptonic: Invert/Loosen muon isolation or electron ID cuts All-Hadronic: variable 2 ABCD -method B A C D variable 1 If 'variable 1' and 'variable 2' are uncorrelated, then the following is true: C=D B A Avoid signal contamination in A, B, D! Smearing -method MET ν or σjet jet 2 smearing function: f pt =1 pt pt MET pt MET 2 jet 1 Either from data or MC-truth (ν pt) Use this function to smear data events in a control region, e.g. at MET<100 GeV.

9 QCD Cleanup 9 QCD suppression using topological cuts: R1,2 = 1,2 2,1 2 2 QCD with 1,2= j1, j2 MET cut R1,2 > 0.5 rad effective mass m = P Significance of MET eff MET = i i T MET MET ET MET in QCD originates from mismeasured jets SUSY

10 tt-background Estimation Semi-leptonic ttbar decays are dominant, methods to determine this background are: MC with lepton eff. corr. from the data Use reconstructed semi-lep. tt-events Combinatorial background estimation using mtop as uncorrelated variable to MET Reason why semi-leptonic tt events pass SUSY selection: hadronic τ decays out of acceptance pt > 10 GeV eta <2.4 too close to jets non-isolated misidentified 10

11 Z invisible Estimation 11 Z νν is a significant background for SUSY. There are different methods to determine the Z pt spectrum: Process Z μμ W lν γ Challenges: pros cons Standard Candle rather small x-sec large x-section No candle QCD γ-fake backgd Standard Candle Lepton ID efficiencies Controling Background Photon ID / fake-rate Trigger efficiencies Z jj μμ (tag) Z jj μμ Z jj νν --- data (pseudo) --- estimated Z ll Z νν ( data ) Z ll W lν ( data ) ETmiss (GeV) MET [GeV]]

12 Discovery Reach Comparison Atlas Reach vs n-jets CMS Reach vs channels All-hadronic search is most sensitive for both Exp. Leptonic searches are almost complementary! 12

13 Discovery Reach Comparison squark gluino mass plane m0 m1/2 msugra plane Exploration of a large SUSY parameter-space is possible already with 1 fb-1 of integrated luminosity 13

14 Summary Inclusive searches are very important parts of the LHC SUSY discovery strategy! Detailed Atlas and CMS studies show: Standard Model background and systematics can be controlled using data-driven methods Methods are permanently studied and improved If squark and gluino masses are below ~1 TeV SUSY can be discovered with ~1fb-1 of data! 14

15 Backup slides 15

16 The CMS Detector 16

17 The Atlas Detector 17

18 CMS SUSY benchmark points 18 All benchmark points are beyond Tevatron reach High mass points (HM) are near the ultimate LHC reach Atlas Point m0 m1/2 SU SU SU tan(β) sign(μ) A

19 Indirect Lepton Veto (ILV) 19 1 P T 15 GeV or P iso 0.10 slide: M. Tytgat