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Prospects for sparticle reconstruction at new SUSY benchmark points

Prospects for sparticle reconstruction at new SUSY benchmark points. Massimiliano Chiorboli Universita’ and INFN Catania. Benchmark Points. Proposed Post-LEP Benchmarks for Supersymmetry (hep-ph/0106204). The goal is to try to reconstruct sparticles

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Prospects for sparticle reconstruction at new SUSY benchmark points

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  1. Prospects for sparticle reconstruction at new SUSY benchmark points Massimiliano Chiorboli Universita’ and INFN Catania

  2. Benchmark Points Proposed Post-LEP Benchmarks for Supersymmetry (hep-ph/0106204) The goal is to try to reconstruct sparticles Last time I showed gluino and sbottom at point B (isajet, 10 fb-1, 300 fb-1), and point G (pythia, 300 fb-1) In mSUGRA scenario, Pythia overestimates the BR of the decay chain to be selected Only ISAJET results in this talk Massimiliano Chiorboli

  3. Results with 10 fb-1

  4. g 595.1 tL 392.9 bL 496.0 tR 575.9 bR 524.0 c40 361.1 qL 540 c30 339.9 qR 520 c20 174.4 lL 196.5 c2± 361.6 lR 136.2 c1± 173.8 c10 = LSP 95.6 Point B I use the isajet 7.58 parameters as input parameters to pythia 6.152 ISAPYTHIA masses and BR’s (17% bL, 10% bR) (37 % bL, 25% bR) (0.04 %) PYTHIA (16.4%) (60%) (83.2%) (38%) Massimiliano Chiorboli

  5. p b b p Sbottom and Gluino decay chain • Event final state: •  2 high pt isolated leptons OS •  2 high pt b jets • missing Et 10 fb-1 of SUSY events at point B produced with the “ISAPYTHIA” generator Detector simulation: fast simulation (CMSJET 4.801) SM bkg: tt, Z+jet, W+jet, ZZ, WW, ZW • 2 SFOS isolated leptons, pT>15 GeV, |h|<2.4 •  2 b-jets, pT>20 GeV, |h|<2.4 B-tagging performed with the FATSIM package of CMSJET: A jet is a b-jet if it contains at least two tracks with a significance sip> sbcut Massimiliano Chiorboli

  6. p ttll, not only b b p First step: c20 l+l- c10 SUSY only SUSY + SM Z+jet E(ll) > 100 GeV ttbar Massimiliano Chiorboli

  7. Dilepton edge fit Etmiss > 150 GeV Cut on the EmissT to have a clean SUSY sample Subtract OFOS lepton pairs to eliminate combinatorial bkg Fit in good agreement with the MC value Massimiliano Chiorboli

  8. p b E(ll) > 100 GeV Etmiss > 150 GeV Eb-jet 1 > 250 GeV b-tag: s>3 SM b p Sbottom reconstruction • assuming M(c10) known • Selecting events “in edge” • Combining the c20 obtained from the two leptons with the most energetic b-jet in the event 10 fb-1 Generated values Result of the fit Massimiliano Chiorboli

  9. p b b p E(ll) > 100 GeV Etmiss > 150 GeV Eb-jet 1 > 250 GeV b-tag: s>3 SM Gluino reconstruction Next step: reconstruct gluinosbottom I associate the reconstructed sbottom to the b-jet closest in angle to it 10 fb-1 Generated values Result of the fit We achieve a peak resolution better than 10% (still at CMSJET level!) Massimiliano Chiorboli

  10. b c uds - g btag parameter optimization The b-tagging is a very important feature: With low purity the mass peaks are shifted to fake values With too high purity (few statistics) we cannot reconstruct the peaks at all This is a very simple algorithm. We would need a full simulation to properly evaluate this effect Massimiliano Chiorboli

  11. Eb1 cut • We can strongly suppress the combinatorial background in the sbottom reconstruction cutting on the energy of the most energetic jet • This cut suppresses b-jets coming from other sparticles Eb-jet 1 > 250 GeV Generator level CMSJET 1 jet 2 jet Massimiliano Chiorboli

  12. Eb1 cut optimization Also this cut has to be optimized not to deform peaks At point B, a cut of 150-250 GeV improves the signal to (combinatorial) bkg ratio without changing the mass values Massimiliano Chiorboli

  13. Mll window optimization A too broad window improves the statistics but gives untrue mass values (we go far from the ideal kinematic condition) A narrower mass window improves the width. Stable masses from Mll>70 GeV (we need more statistics) Massimiliano Chiorboli

  14. Non-sbottom squarks: (16.4%) (22.4%) Squark reconstruction The right component is almost negligible I have to select non b-jets: more combinatorial Massimiliano Chiorboli

  15. p jet p jet p jet jet p jet p jet jet jet p jet Squark-gluino event topologies Massimiliano Chiorboli

  16. Event selection • 2 SFOS isolated leptons, pT>15 GeV, |h|<2.4 •  2 jets (not b), pT>20 GeV, |h|<2.4 • b-jet veto (I reject events having 1 jet with s>3) Main squark sources: Massimiliano Chiorboli

  17. SM backgrounds Massimiliano Chiorboli

  18. SM Dilepton edge I reproduce the same procedure as in the sbottom reconstruction method. I start from the dilepton invariant mass edge. E(ll) > 100 GeV Etmiss > 50 GeV Etmiss > 100 GeV Etmiss > 150 GeV It looks much better than the b-jet case. Probably a better understanding of the SM bkg’s is needed Massimiliano Chiorboli

  19. Squark reconstruction: selection of the first jet No angular correlation between this jet and ll The jets coming from the squarks are harder than the others Generator level Generator level E parton (GeV) cos(a) CMSJET I select the most energetic jet and I associate it to the reconstructed chi2 E jet (GeV) Massimiliano Chiorboli

  20. SM Sbottom reconstruction Etmiss > 50 GeV Etmiss > 100 GeV Etmiss > 150 GeV Massimiliano Chiorboli

  21. Anti b-tagging Effect of the anti b-tagging parameter cut on the reconstructed sbottom peak s < 3 s < 2 s < 1 Effect of b-veto No b-veto b-veto Massimiliano Chiorboli

  22. Sources of combinatorial background Irreducible source: jets coming from other squarks Reducible source: jets coming from gluinos Massimiliano Chiorboli

  23. No Ejet cut Ejet>100 Ejet>200 Ejet>300 Combinatorial suppression A cut on the energy of the selected jet can suppress the combinatorial Massimiliano Chiorboli

  24. Etmiss > 150 GeV Ejet 1 > 20 GeV anti b-tag: s<2 b-veto SM Squark mass 10 fb-1 Result of the fit Generated values Massimiliano Chiorboli

  25. Generator level cos(a) Gluino reconstruction I try to reconstruct the gluino in squark decay chain with the same method. I associate the jet closest in angle to the reconstructed squark Etmiss > 50 GeV Etmiss > 100 GeV Etmiss > 150 GeV Massimiliano Chiorboli

  26. Combinatorial in gluino reconstruction The squark-squark events produce fake gluinos. Jets coming from squarks shift the peak to higher values and produce the tail on the right Massimiliano Chiorboli

  27. Gluino combinatorial suppression Generator level Un upper cut on the energy of the second jet can suppress jets coming from squarks E parton (GeV) 1 jet 2 jet CMSJET E jet (GeV) E jet (GeV) E jet (GeV) Massimiliano Chiorboli

  28. No Ejet2 cut Ejet2<150 Ejet2<120 Ejet2<100 Ejet2<80 Gluino combinatorial suppression Ejet 2 < 80 GeV all Massimiliano Chiorboli

  29. Etmiss > 150 GeV Ejet 1 > 20 GeV anti b-tag: s<2 b-veto Ejet 2 < 80 GeV SM Gluino mass peak 10 fb-1 Result of the fit Generated value Worse resolution but better statistics than the gluino from the sbottom chain Massimiliano Chiorboli

  30. Etmiss > 150 GeV Ejet 1 > 20 GeV anti b-tag: s<2 b-veto Ejet 2 < 80 GeV SM M(gluino)-M(squark) The difference of masses is independent from the neutralino 1 mass 10 fb-1 Result of the fit Generated value Massimiliano Chiorboli

  31. Results with 300 fb-1

  32. Etmiss > 200 GeV Eb-jet 1 > 150 GeV b-tag: s>3 E(ll) > 100 GeV cos f(b1-gluino) > 0.4 cos f(b1-sbottom) > 0.2 Point B: Sbottom and Gluino Result of the fit 300 fb-1 Generated values 300 fb-1 Result of the fit Generated value Massimiliano Chiorboli

  33. Effect of the pile-up on the sbottom and gluino reconstruction No pile-up 100 fb-1 Pile-up The background increases and the peaks are shifted on the left Massimiliano Chiorboli

  34. Separation of the two sbottoms Even at high integrated luminosities, it doesn’t seem possible to separate the two sbottoms I try to perform a double gaussian fit on the peak 300 fb-1 Both the mass values and the coefficient seem to be in agreement with the MC Massimiliano Chiorboli

  35. Sensitivity to M(c1) At 300 fb-1 we can perhaps have the M(c1) as input from a LC. To evaluate the effect the error on M(c1) on the sbottom and gluino mass measurements, I reconstruct the peaks changing the M(c1) Since we have a statistical error of 3 GeV at 300 fb-1, to have an uncertainty on the gluino and sbottom mass given by the M(c1) uncertainty smaller than this statistical error, we should know M(c1) with an error less than 3/1.6 = 1.9 GeV Massimiliano Chiorboli

  36. Squark and Gluino at 300 fb-1 Result of the fit 300 fb-1 Generated values 300 fb-1 Result of the fit Generated value Massimiliano Chiorboli

  37. Point G

  38. ttll, not only (2.5%) (64%) Point G: dilepton edge I ran point G again using ISAJET BR’s: E(ll) > 100 GeV 300 fb-1 Massimiliano Chiorboli

  39. SM Point G: dilepton edge 300 fb-1 Etmiss >1 50 GeV Etmiss > 200 GeV Etmiss > 250 GeV Massimiliano Chiorboli

  40. Point G: sbottom and gluino reconstruction SUSY only 300 fb-1 Eb-jet 1 > 150 GeV Massimiliano Chiorboli

  41. SM Effect of the SM background Etmiss > 150 GeV Etmiss > 200 GeV Massimiliano Chiorboli

  42. Point G: Sbottom and Gluino mass peaks Etmiss > 250 GeV 300 fb-1 Generated values Generated value Massimiliano Chiorboli

  43. Point B: squark and gluino reconstruction The squark channel seems more efficient than the sbottom one 300 fb-1 Etmiss > 250 GeV Eb-jet 1 > 250 GeV Etmiss > 250 GeV Eb-jet 1 > 250 GeV Eb-jet 2 < 100 GeV Massimiliano Chiorboli

  44. Point I

  45. (0.25%) (98%) Point I: dilepton chain 300 fb-1 In this point it’s impossible to reconstruct the decay chain Massimiliano Chiorboli

  46. Conclusions • At 10 fb-1: • Point B: • we can start the reconstruction of sbottom and gluino • Squark reconstruction seems possible, better than the sbottom chain, with resolution of 12% • At 300 fb-1: • Point B • Very good reconstruction of sbottom, squark and gluino • Possible double gaussian fit on the sbottom peak to evaluate the two sbottom masses • Point G: • Difficult reconstruction of sbottom and gluino • The squark reconstruction seems better • Point I • Any reconstruction is impossible Massimiliano Chiorboli

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