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

QCD and Hadronic Interactions, 28 March - 4 April 2004 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

Inclusive SUSY reach vs integrated luminosity A0=0, tanb=35, m>0 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 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 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

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

Decay chains p b b p SM bkg: tt, Z+jet, W+jet, ZZ, WW, ZW, QCD jets 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

QCD and Hadronic Interactions, 28 March - 4 April 2004 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 different tan b values (tan b = 10, 20, 35) since BR(c20  l+l- c10) depends on tan b QCD and Hadronic Interactions, 28 March - 4 April 2004

QCD and Hadronic Interactions, 28 March - 4 April 2004 Point B spectra 95.6 c10 = LSP 173.8 c1± 136.2 lR 361.6 c2± 196.5 lL 174.4 c20 520 qR 339.9 c30 559 qL 361.1 c40 524.0 bR 575.9 tR 496.0 bL 392.9 tL 595.1 g Point B (17% bL, 10% bR) (37 % bL, 25% bR) (0.04 %) (16.4 %) (83.2 %) 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

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

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

Second step: sbottom (squark) reconstruction At the end-point: 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 QCD and Hadronic Interactions, 28 March - 4 April 2004

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

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

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

Worse resolution, but model independent result 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

QCD and Hadronic Interactions, 28 March - 4 April 2004 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) 300 fb-1 60 fb-1 60 fb-1 300 fb-1 300 fb-1 60 fb-1 Sbottom Chain Squark Chain 10 fb-1 60 fb-1 300 fb-1 M(sbottom) 500±7 502±4 497±2 M(squark) 536±10 532±2 536±1 s(sbottom) 42±5 41±4 36±3 s(squark) 60±9 36±1 31±1 M(gluino) 594±7 592±4 591±3 592±7 595±2 590±2 s(gluino) 42±7 46±3 39±3 75±5 59±2 M(gl)-M(sb) 92±3 88±2 90±2 M(gl)-M(sq) 57±3 47±2 44±2 s(gl-sb) 17±4 20±2 23±2 s(gl-sq) 9±3 16±5 11±2 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

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 300 fb-1 10 fb-1 sbottom chain squark chain QCD and Hadronic Interactions, 28 March - 4 April 2004

QCD and Hadronic Interactions, 28 March - 4 April 2004 Results @ Point G sbottom gluino squark Sbottom Chain 300 fb-1 M(sbottom) 720±26 s(sbottom) 81±18 M(gluino) 851±40 s(gluino) 130±43 M(sb)-M(gl) 127±10 s(sb-gl) 48±11 Squark Chain M(squark) 774±9 s(squark) 84±9 853±11 126±11 M(sq)-M(gl) 82±3 s(sq-gl) 35±3 Repeating the same procedure as Point B: QCD and Hadronic Interactions, 28 March - 4 April 2004

Reconstruction @ point I G 300 fb-1 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 B Neutralino BR’s B G I BR(c20→ll) 16.44 2.26 0.25 BR(c20→tt) 83.22 75.88 98.13 QCD and Hadronic Interactions, 28 March - 4 April 2004

QCD and Hadronic Interactions, 28 March - 4 April 2004 Di-tau lepton edge _ As t l n n identification is not possible, must rely on hadronic decays – narrow, 1-prong jets (large QCD bkg though) Can typically achieve t/jet ~100 for et ~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, no e, m with pT > 20 GeV SM bkg 1 2- 4 Recent results – even more encouraging… QCD and Hadronic Interactions, 28 March - 4 April 2004

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

Why and how to measure the c10 mass… ~ qL c 2 q 1 R Long decay chains allow multiple measurements Use kinematics to measure end-points (in general both maximum and minimum value due to 2-body decays) Use dilepton signature to tag presence of c02 in event, then work back up decay chain constructing invariant mass distributions of combinations of leptons and jets c 2 ~ 1 h b - ATLAS Physics TDR 1% error (100 fb-1) Point 5 e+e- + m+m- 30 fb-1 atlfast Physics TDR ATLAS Point 5 Starting point : di-lepton OS SF mass edge Assume 2 hardest jets are from squarks, combine each of these with leptons to from : ATLAS Physics TDR 2% error (100 fb-1) Point 5 > < Mlq, Mlq ATLAS Physics TDR 1% error (100 fb-1) Point 5 Endpoints: Mllq Threshold : Tllq, requiring Mll > Mll / 2 max Also used endpoint from Mhq from h bb - 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 % QCD and Hadronic Interactions, 28 March - 4 April 2004

QCD and Hadronic Interactions, 28 March - 4 April 2004 Mass Reconstruction Combine measurements from edges from different jet/lepton combinations Numerical solution of simultaneous edge position equations c01 lR c02 qL Mass (GeV) ~ Allanach et al., 2001 ATLAS Point 5 Mllq High Mlq Low Mlq Mll Mhq Sparticle Expected precision (100 fb-1) qL  3% 02  6% lR  9% 01  12% ~ ATLAS Physics TDR Point 5 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

Lot of work before LHC start-up!!! 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 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 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… 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