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

Massimiliano Chiorboli 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 27-09-2002 Massimiliano Chiorboli

Results with 10 fb-1

Massimiliano Chiorboli Point B I use the isajet 7.58 parameters as input parameters to pythia 6.152 95.6 c10 = LSP 173.8 c1± 136.2 lR 361.6 c2± 196.5 lL 174.4 c20 520 qR 339.9 c30 540 qL 361.1 c40 524.0 bR 575.9 tR 496.0 bL 392.9 tL 595.1 g ISAPYTHIA masses and BR’s (17% bL, 10% bR) (37 % bL, 25% bR) (0.04 %) PYTHIA (16.4%) (60%) (83.2%) (38%) 27-09-2002 Massimiliano Chiorboli

Sbottom and Gluino decay chain p b 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 27-09-2002 Massimiliano Chiorboli

Massimiliano Chiorboli First step: c20  l+l- c10 p b SUSY only SUSY + SM ttll, not only Z+jet E(ll) > 100 GeV ttbar 27-09-2002 Massimiliano Chiorboli

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 27-09-2002 Massimiliano Chiorboli

Sbottom reconstruction p b 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 b-tag: s>3 Etmiss > 150 GeV Eb-jet 1 > 250 GeV E(ll) > 100 GeV 10 fb-1 SM Generated values Result of the fit 27-09-2002 Massimiliano Chiorboli

Gluino reconstruction p b Next step: reconstruct gluinosbottom I associate the reconstructed sbottom to the b-jet closest in angle to it b-tag: s>3 Etmiss > 150 GeV Eb-jet 1 > 250 GeV E(ll) > 100 GeV 10 fb-1 Generated values Result of the fit SM We achieve a peak resolution better than 10% (still at CMSJET level!) 27-09-2002 Massimiliano Chiorboli

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 b c uds - g 27-09-2002 Massimiliano Chiorboli

Massimiliano Chiorboli 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 27-09-2002 Massimiliano Chiorboli

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 27-09-2002 Massimiliano Chiorboli

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) 27-09-2002 Massimiliano Chiorboli

Squark reconstruction Non-sbottom squarks: Process s(pb) n in 10 fb-1 0.5 5000 1.9 19000 7.0 70000 28.3 283000 1.8 18000 14.1 141000 0.4 4000 0.7 7000 The right component is almost negligible (16.4%) (22.4%) I have to select non b-jets: more combinatorial 27-09-2002 Massimiliano Chiorboli

Squark-gluino event topologies jet p jet p jet 27-09-2002 Massimiliano Chiorboli

Massimiliano Chiorboli 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) Process n in 10 fb-1 2 lepton b veto 2 non b-jet 2 SFOS lep 5378 1052 1041 36 27 18999 2278 2178 154 78 4767 865 476 258 130 69943 14533 4528 4185 1325 18880 2683 2422 1084 614 283199 40309 19847 17100 7198 18311 4819 1337 904 215 141609 12034 10513 7917 4355 3616 890 364 262 91 5153 2046 547 409 126 7063 2219 606 516 161 Main squark sources: 27-09-2002 Massimiliano Chiorboli

Massimiliano Chiorboli SM backgrounds s(pb) N 2 lep b-veto 2 non b-jets 2 SFOS isolate lep ttbar 621 6.21*106 (10 fb-1) 886809 336001 170182 14900 Z+jet (pthat > 60 GeV) 2870 3.9*106 172894 159479 17205 13138 W+jet 7500 2*106 4517 3869 738 2 QCD 50-100 2.86*107 1.9*106 460 270 78 100-200 1.64*106 3366 1658 965 200-300 6.67*104 11395 5349 4088 300-400 8.59*103 19892 9545 7954 1 400-500 1.83*103 28149 13961 11832 >500 8.20*102 39902 20343 17581 27-09-2002 Massimiliano Chiorboli

Dilepton edge Etmiss > 50 GeV Etmiss > 100 GeV I reproduce the same procedure as in the sbottom reconstruction method. I start from the dilepton invariant mass edge. E(ll) > 100 GeV SM 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 27-09-2002 Massimiliano Chiorboli

Squark reconstruction: selection of the first jet The jets coming from the squarks are harder than the others No angular correlation between this jet and ll 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) 27-09-2002 Massimiliano Chiorboli

Sbottom reconstruction Etmiss > 50 GeV Etmiss > 100 GeV Etmiss > 150 GeV SM 27-09-2002 Massimiliano Chiorboli

Massimiliano Chiorboli 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 27-09-2002 Massimiliano Chiorboli

Sources of combinatorial background Irreducible source: jets coming from other squarks Reducible source: jets coming from gluinos 27-09-2002 Massimiliano Chiorboli

Combinatorial suppression A cut on the energy of the selected jet can suppress the combinatorial Ejet>100 No Ejet cut Ejet>200 Ejet>300 27-09-2002 Massimiliano Chiorboli

Massimiliano Chiorboli Squark mass 10 fb-1 Result of the fit anti b-tag: s<2 Etmiss > 150 GeV Ejet 1 > 20 GeV b-veto SM Generated values 27-09-2002 Massimiliano Chiorboli

Gluino reconstruction Generator level cos(a) 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 27-09-2002 Massimiliano Chiorboli

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 27-09-2002 Massimiliano Chiorboli

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) 27-09-2002 Massimiliano Chiorboli

Gluino combinatorial suppression Ejet 2 < 80 GeV Ejet2<150 No Ejet2 cut Ejet2<120 Ejet2<100 Ejet2<80 all 27-09-2002 Massimiliano Chiorboli

Massimiliano Chiorboli Gluino mass peak 10 fb-1 Ejet 2 < 80 GeV anti b-tag: s<2 Etmiss > 150 GeV Ejet 1 > 20 GeV b-veto Result of the fit SM Generated value Worse resolution but better statistics than the gluino from the sbottom chain 27-09-2002 Massimiliano Chiorboli

M(gluino)-M(squark) The difference of masses is independent from the neutralino 1 mass 10 fb-1 Ejet 2 < 80 GeV anti b-tag: s<2 Etmiss > 150 GeV Ejet 1 > 20 GeV b-veto Result of the fit Generated value SM 27-09-2002 Massimiliano Chiorboli

Results with 300 fb-1

Point B: Sbottom and Gluino Result of the fit 300 fb-1 Generated values 300 fb-1 b-tag: s>3 Etmiss > 200 GeV Eb-jet 1 > 150 GeV cos f(b1-gluino) > 0.4 cos f(b1-sbottom) > 0.2 E(ll) > 100 GeV Result of the fit Generated value 27-09-2002 Massimiliano Chiorboli

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 27-09-2002 Massimiliano Chiorboli

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 27-09-2002 Massimiliano Chiorboli

Massimiliano Chiorboli 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 27-09-2002 Massimiliano Chiorboli

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 27-09-2002 Massimiliano Chiorboli

Point G

Point G: dilepton edge E(ll) > 100 GeV I ran point G again using ISAJET BR’s: (2.5%) (64%) E(ll) > 100 GeV 300 fb-1 ttll, not only 27-09-2002 Massimiliano Chiorboli

Massimiliano Chiorboli Point G: dilepton edge 300 fb-1 SM Etmiss >1 50 GeV Etmiss > 200 GeV Etmiss > 250 GeV 27-09-2002 Massimiliano Chiorboli

Point G: sbottom and gluino reconstruction SUSY only 300 fb-1 Eb-jet 1 > 150 GeV 27-09-2002 Massimiliano Chiorboli

Effect of the SM background Etmiss > 150 GeV Etmiss > 200 GeV 27-09-2002 Massimiliano Chiorboli

Point G: Sbottom and Gluino mass peaks Etmiss > 250 GeV 300 fb-1 Generated values Generated value 27-09-2002 Massimiliano Chiorboli

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 27-09-2002 Massimiliano Chiorboli

Point I

Point I: dilepton chain (0.25%) (98%) 300 fb-1 In this point it’s impossible to reconstruct the decay chain 27-09-2002 Massimiliano Chiorboli

Massimiliano Chiorboli 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 27-09-2002 Massimiliano Chiorboli