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Sparticle reconstruction at benchmark points

Sparticle reconstruction at benchmark points. Alessia Tricomi On behalf of ATLAS and CMS Collaboration Dipartimento di Fisica e Astronomia and INFN Catania. Outline. In the past years several inclusive studies done to understand the detector capabilities to discover SUSY

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Sparticle reconstruction at benchmark points

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  1. Sparticle reconstruction at benchmark points Alessia Tricomi On behalf of ATLAS and CMS Collaboration Dipartimento di Fisica e Astronomia and INFN Catania

  2. Outline • In the past years several inclusive studies done to understand the detector capabilities to discover SUSY • Counting excess of events over SM expectations • No explicit sparticle reconstruction done • Several different final states analysed • Etmiss + jets • No lepton + Etmiss + jets • 1 l + Etmiss + jets • 2 l OS + Etmiss + jets • 2 l SS + Etmiss + jets • 3 l + Etmiss + jets • Scan in mSUGRA (m0,m1/2) plane (also studies in p-MSSM scenario performed ) • Fast MC simulation used: ATLFAST, CMSJET • Today I will focus on recent studies to reconstruct strongly interacting SUSY particles S.Abdullin, F. Charles Nucl. Phys. B547 (1999) 60 S. Abdullin et al., J. Phys. G28 (2002) 469 M. Dzelalija et al., Mod. Phys. Lett. A15 (2000) 465 QCD and Hadronic Interactions, 28 March - 4 April 2004

  3. A0=0, tanb=35, m>0 Inclusive SUSY reach vs integrated luminosity Expected squark-gluino mass reach •  1.5 – 1.8 TeV with 10 fb-1 •  2.3 – 2.5 TeV with 100 fb-1 •  2.6 – 3.0 Tev with 300 fb-1 •  2.8 – 3.2 TeV with 1000 fb-1 • If Supersymmetry exists, LHC will probably observe it • Cosmologically interesting region covered with 10 fb-1 • Squark-gluino production dominates the total cross section at low mass scale • Squarks and Gluinos detectable up to 2 TeV mass with 100 fb-1 S.Abdullin, F. Charles Nucl. Phys. B547 (1999) 60 S. Abdullin et al., J. Phys. G28 (2002) 469 M. Dzelalija et al., Mod. Phys. Lett. A15 (2000) 465 QCD and Hadronic Interactions, 28 March - 4 April 2004

  4. But … It is not enough to observe the excess over the Standard Model… DISCOVERY SUSY SPECTROSCOPY This requires a different approach… Fix a set of points in the parameter space Get information on the spectrum (i.e. end-points) Reconstruct sparticles QCD and Hadronic Interactions, 28 March - 4 April 2004

  5. Decay chains Reconstruction of sbottoms, squarks and gluinos p b b p •  2 high pt isolated leptons OS (leptons = e,m) •  2 high pt non-b jets • missing Et •  2 high pt isolated leptons OS (leptons = e,m) •  2 high pt b jets • missing Et SM bkg: tt, Z+jet, W+jet, ZZ, WW, ZW, QCD jets QCD and Hadronic Interactions, 28 March - 4 April 2004

  6. Benchmark points Proposed Post-LEP Benchmarks for Supersymmetry, M. Battaglia et al. (hep-ph/0106204) • Rather low m0 and m1/2 values in order to have high SUSY cross section • Three differenttan bvalues (tanb= 10, 20, 35) since BR(c20 l+l-c10) depends on tan b QCD and Hadronic Interactions, 28 March - 4 April 2004

  7. g 595.1 tL 392.9 bL 496.0 tR 575.9 bR 524.0 c40 361.1 qL 559 c30 339.9 (17% bL, 10% bR) qR 520 c20 174.4 lL 196.5 c2± 361.6 (37 % bL, 25% bR) lR 136.2 c1± 173.8 (0.04 %) c10 = LSP 95.6 (16.4 %) (83.2 %) Point B spectra Point B Sbottom reconstruction • 2 isolated leptons, pT>15 GeV, |h|<2.4 •  2 b-jets, pT>20 GeV, |h|<2.4 QCD and Hadronic Interactions, 28 March - 4 April 2004

  8. SUSY events p b 10 fb-1 b p First step: c20 l+l- c10 QCD and Hadronic Interactions, 28 March - 4 April 2004

  9. SUSY Edge = 79  2 GeV Generated = 78.2 GeV ttbar Z+jets Bkg reduction SM bkg can be strongly reduced cutting on ETmiss QCD and Hadronic Interactions, 28 March - 4 April 2004

  10. p b b p Second step: sbottom (squark) reconstruction At the end-point: • Assuming M(c10) known • Selecting events “in edge” • Combining thec20 obtained from the two leptons with the most energetic b-jet in the event QCD and Hadronic Interactions, 28 March - 4 April 2004

  11. Squark mass peak Result of the fit: 1 fb-1 Generated values QCD and Hadronic Interactions, 28 March - 4 April 2004

  12. Result of the fit: Generated masses: Sbottom mass peak 10 fb-1 The peak should be considered as the superposition of two peaks QCD and Hadronic Interactions, 28 March - 4 April 2004

  13. p b 10 fb-1 10 fb-1 b p sbottom chain squark chain Gluino reconstruction Two separated gluino mass measurements, with two different samples Generated value: QCD and Hadronic Interactions, 28 March - 4 April 2004

  14. estimate The reconstruction is performed assuming M(c10) known but … The difference between the two masses is independent of M(c10) Result of the fit: Generated value: Worse resolution, but model independent result QCD and Hadronic Interactions, 28 March - 4 April 2004

  15. Results @ point B • Squark mass peak can be reconstructed in the first few weeks (resolution ~12%) • Sbottom and gluino in the first year (resolution ~6÷8%) • Two independent gluino mass measurements • The resolutions can be improved with larger statistics (~5÷6% at 300 fb-1) 60 fb-1 300 fb-1 60 fb-1 300 fb-1 300 fb-1 60 fb-1 • Errors are of the order of 1÷2 GeV (statistical) + 2÷3 GeV (energy scale of the calorimeters) • The main source of error is from the lack of knowledge on M(c10) • M(c10) assumed known for these reconstructions • No systematic errors evaluated QCD and Hadronic Interactions, 28 March - 4 April 2004

  16. 300 fb-1 10 fb-1 squark chain sbottom chain Reconstruction @ point G With respect to the Point B: • Lower total SUSY cross-section • Lower BR of useful decays • Higher BR’s of competitive decays • Lower BR of the last decay QCD and Hadronic Interactions, 28 March - 4 April 2004

  17. gluino gluino squark sbottom Results @ Point G Repeating the same procedure as Point B: QCD and Hadronic Interactions, 28 March - 4 April 2004

  18. B I 300 fb-1 G Reconstruction @ point I • Tau channel becomes predominant at large tan b • Tau-pair edge is not as sharp as in the e and m case, but could help to cover points in which the reconstruction is problematic • It could be exploited in regions with too low leptonic BR: work in progress both in ATLAS and in CMS QCD and Hadronic Interactions, 28 March - 4 April 2004

  19. Recent results – even more encouraging… Di-tau lepton edge _ Astln nidentification is not possible, must rely on hadronic decays – narrow, 1-prong jets (large QCD bkg though) Can typically achievet/jet ~100 foret ~50-60 % ATLAS Physics TDR study (full GEANT simulation) example (“Point 6”) : Narrow isolated jets selection : Rjet = 0.2, Risol = 0.4 30 fb-1 Real t from SUSY Require 0.8 GeV < Mjet < 3.6 GeV (biased against 1-prong, but improves di-tau mass resolution - less neutrino momentum) Fake t from SUSY Di-tau efficiency = 41 % Mvis = 0.66 Mtt visible expected Additional cuts : min. 4 jets : ET > 100 GeV, ET > 50 GeV missing ET > 100 GeV, noe, mwith pT > 20 GeV SM bkg 1 2- 4 QCD and Hadronic Interactions, 28 March - 4 April 2004

  20. 10-3 10-4 10-5 10-6 Allanach et al., 2001 • Using mass of lightest neutralino and RH sleptons can discriminate between SUSY models differing only in slepton mass. DAMA • SUSY Dark Matter • Lightest Neutralino LSP excellent Dark Matter candidate. • Test of compatibility between LHC observations and signal observed in Dark Matter experiments. Why and how to measure the c10 mass… • Use as starting point for other sparticle mass measurements (sbottom, gluino, squark…) QCD and Hadronic Interactions, 28 March - 4 April 2004

  21. Long decay chains allow multiple measurements Use kinematics to measure end-points (in general both maximum and minimum value due to 2-body decays) ~ c 0 ~ Starting point : di-lepton OS SF mass edge c 0 1 2 ~ ~ qL Use dilepton signature to tag presence ofc02 in event, then work back up decay chain constructing invariant mass distributions of combinations of leptons and jets R e+e- + m+m- q Point 5 ~ c 0 ATLAS Assume 2 hardest jets are from squarks, combine each of these with leptons to from : 1 ATLAS 30 fb-1 atlfast - ~ c 0 2 b 1% error (100 fb-1) < Physics TDR > ATLAS h Endpoints: Mlq, Mlq ATLAS Physics TDR b Point 5 max Physics TDR 2% error (100 fb-1) Threshold : Tllq, requiring Mll > Mll / 2 1% error (100 fb-1) - Also used endpoint from Mhq from h bb Point 5 Physics TDR Turns out to have enough constraints to determine all masses involved (!) Can measure mass relations to ~1% as a function of LSP mass, determined to ~10 % Point 5 Why and how to measure the c10 mass… Mllq QCD and Hadronic Interactions, 28 March - 4 April 2004

  22. Allanach et al., 2001 Mllq High Mlq Mll ~ ~ c01 lR Sparticle Expected precision (100 fb-1) qL 3% 02 6% lR 9% 01 12% ~ Point 5 Point 5 ~ ATLAS ATLAS ~ ~ Mllq Low Mlq Mhq Mass (GeV) Mass (GeV) ~ ~ c02 qL Point 5 Point 5 ATLAS ATLAS Mass (GeV) Mass (GeV) ATLAS Physics TDR Point 5 Mass Reconstruction Combine measurements from edges from different jet/lepton combinations • Numerical solution of simultaneous edge position equations • Systematic uncertainties not evaluated • Main sources: • Th: theoretical distributions of edges • Ex: detector resolution (i.e. energy resolution, b/t-tagging efficiency, bias due to cuts applied… Same order precision also @ point SPS1A (similar to “CMS” point B) Gives sensitivity to masses Gjelsten et al., ATLAS-PHYS-2004-07 QCD and Hadronic Interactions, 28 March - 4 April 2004

  23. Conclusions • LHC experiments are expected to explore SUSY in a decisive way. • The plausible part of mSUGRA-MSSM parameter space will be explored in a number of characteristic signatures • Strongly interacting SUSY particles can be accessed up to 2TeV for 100 fb-1 • Information on the SUSY spectrum achievable, with favourable SUSY parameters, already after the first months of data taking • Intermediate tan b (i.e. point G): • first year: • dilepton edge hardly visible • no reconstruction possible in e,m channel • high integrated luminosity: • reconstruction of squarks, sbottom (~11%) and gluino (~15%) • High tan b (i.e point I): • no reconstruction possible in the e-m channel even with high accumulated statistics • Reconstruction in the tau channel exploited. Work is going on… • Low tan b region (like point B, SPS1A, point 5): • first few weeks of LHC running period: • reconstruction of squark (resolution ~12%) • first year: • reconstruction of sbottom and gluino (resolutions ~6÷8%) • reconstruction of gluino in the squark chain (independent channel) • high integrated luminosity: • improvement on the resolutions • double fit of the sbottom peak • New analyses are going on: • New benchmark points to be analyzed • Full reconstruction studies in first priority • Multi-edge technique to be fully exploited • Deeper insight to the tau-tau channel • Systematic uncertainties to be evaluated Lot of work before LHC start-up!!! QCD and Hadronic Interactions, 28 March - 4 April 2004

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