SUSY Searches with ZEUS Alessandro Montanari (DESY) on the behalf of the ZEUS Collaboration Overview Phyisical motivations Stop production (MSSM and mSUGRA) Gaugino production (MSSM) Gravitino production (GMSB) Summary and conclusions 04/04/2019 A. Montanari DIS2006 Tsukuba

A. Montanari DIS2006 Tsukuba SUSY at HERA New discrete, multiplicative, quantum number: R-parity R=(-1)3B+L+2S ( +1 SM particles, -1 sparticles) If R-parity is conserved: Sparticles produced only in pairs Lightest Supersymmetric Particle (LSP) candidate as dark matter The most general Lagrangian does not exclude R-parity violation Possibility to produce single sparticles The RPV superpotential: Lepton-Hadron Colliders At HERA interactions mediated by l´1jk coupling 04/04/2019 A. Montanari DIS2006 Tsukuba

A. Montanari DIS2006 Tsukuba Stop Search Stop produced as a resonance in the s channel via the l´131 coupling To simplify the decay phenomenology: only l´131 different by zero not considered decays with a top quark in the final state Three main decays cosidered: Direct decay via l´131 : e+-Jet Gauge decay: e+-Multiple-Jets, n-Multiple-Jets Two SUSY models considered: MSSM: GUT relation between M1, M2, M3 (100 GeV < M2 < 300 GeV), -300 GeV < m < 300 GeV, tanb=6, mass of other sfermions ~ TeV, heavy gluino. mSUGRA: only four parameters and one sign m0, m1/2, A, tanb and m s 04/04/2019 A. Montanari DIS2006 Tsukuba

Stop search: Preselection for e+ final state ZEUS: 65 pb-1 e+p One high energy positron qe>0.3: Pt > 8GeV qe<0.3: Pt > 20 GeV Q2DA > 1000 GeV2 0.2 < yDA < 0.98 45 GeV < E-Pz < 70 GeV MeX > 100 GeV Non ep events rejection (cosmic, halo-m, beamgas) Major source of background: NC DIS Good agreement data and SM prediction Red line: Mstop=220 GeV m=1000 GeV, M2=200 GeV, l´=0.1 04/04/2019 A. Montanari DIS2006 Tsukuba

Stop search: Preselection for n final state No positron Pt > 20 GeV 0.2 < yJB < 0.95 MnX> 100 GeV Non ep events rejection (cosmic, halo-m, beamgas) Major source of background: CC DIS Good agreement data with SM prediction Red line: Mstop=220 GeV m=1000 GeV, M2=200 GeV, l´=0.1 04/04/2019 A. Montanari DIS2006 Tsukuba

Stop search: final selections Invariant mass distributions For each decay channel, final selection to minimize the limits on the cross section e+-Jet Q2DA > 3000 GeV2 yDA > 0.8 - 0.002*MeX Pt,had/Et,had > 0.8 Efficiency ~0.2 – 0.55 e+-Multiple-Jets Pt,had/Et,had < 0.8 Efficiency ~0.25 – 0.5 n-Multiple-Jets E-Pz > 25 GeV Pt,had/Et,had < 0.4 Efficiency ~0.1-0.4 No evidence of resonances 04/04/2019 A. Montanari DIS2006 Tsukuba

Stop search: limits on l´131 on MSSM Limits calculated using a Bayesian approach Limits on l´131 are evaluated as a function of the stop mass and in a range of SUSY parameters: 100 GeV < M2 < 300 GeV -300 GeV < m < 300 GeV tanb=6 Yellow: exclusion at 95% CL Red: partially excluded by the SUSY parameters Limits are compared to APV results: tighｔer limits for masses up to 250 GeV For l’131 =0.3 scenarios with a stop of mass 270 GeV are ruled out 04/04/2019 A. Montanari DIS2006 Tsukuba

Stop search: limits on mSUGRA model Exclusion at 95% C.L. in (m0,m1/2): A=0, tanb=6, m<0 l´=0.3 Red: excluded at 95% C.L. Blue: theoretically not allowed (REWSB have no solution) Yellow: scenarios where neutralino (LSP) has mass lower than 30 GeV (already excluded by LEP) Dotted lines: curves of constant stop mass 250 GeV and 260 GeV Excluded scenarios with stop with mass less than 260 GeV NEW PRELIMINARY RESULTS! 04/04/2019 A. Montanari DIS2006 Tsukuba

Gaugino and gravitino search If Msquark >> Mslepton: gaugino production in t channel via l´ijk Possible decay channels: Main contribution from up quark: only l´111 NC-like channel electron multiple jets CC-like channel neutrino Gravitino channel isolated photon missing transverse energy MSSM, mSUGRA Neutralino is LSP GMSB Gravitino is LSP 04/04/2019 A. Montanari DIS2006 Tsukuba

Gaugino production: limits No deviations from SM are observed in high discriminant region Limits in m-M2 plane (red zone) compared to LEP limits (green zone) Parameter scan: |m| < 500 GeV M2 < 250 GeV Mc± ≤103 GeV Modified frequentist method (T. Junk, NIM A434, p.435) Multi-variate discriminant method ALEPH/DELPHI limits from search of chargino pair production: (J.Abdallah et al. Eur. Phys. J. C37 (2004) 129-131) 04/04/2019 A. Montanari DIS2006 Tsukuba

A. Montanari DIS2006 Tsukuba Gravitino production Production mechanism c produced in t channel via eL exchange c (NLSP) decays into G (LSP) + g Event topology missing Pt (undetected G) isolated g at least one jet RPV coupling involved e+p: l´1j1, ,j=1,2 e-p: l´11k, ,j=1,2,3 Main SM background CC DIS events with g ~ ~ ~ ~ ~ ~ l’ 04/04/2019 A. Montanari DIS2006 Tsukuba

Gravitino production: event selection Selection cuts Q2JB > 700 GeV2, yJB>0.1 E-Pz < 65 GeV ≥ 1 jets (Pt > 6 GeV, -0.5 < hjet < 2.5) Non ep events veto Signal efficiency: 66-79% Good agreement data and SM expectation ZEUS: 65 pb-1 e+p 04/04/2019 A. Montanari DIS2006 Tsukuba

Gravitino: final selection ≥ 1 isolated g Eg > 4 GeV -2.8 < hg < 2.8 Signal efficiency: 59-71% Multi-variate discriminant method Signal: m(c0)= 100.4 GeV, Dm=40 GeV l´=1.0 Cut: D>0.7 04/04/2019 A. Montanari DIS2006 Tsukuba

Gravitino production: limits No deviation from the SM has been observed Limits in m(co)-Dm plane、obtained　using a frequentist approach (T.Junk,　Nucl., Inst., Meth. A 434, 435 (1999) ) Comparison vith H1 limits (H1 Collab., Phys. Lett. B616 (2005) 31-42): compatible results H1 results 04/04/2019 A. Montanari DIS2006 Tsukuba

Summary and conclusions Searches for SUSY particles (stop, gaugino and gravitino) have been performed by ZEUS using the HERA I data set. No deviations from the Standard Model have been found in the explored parameter spaces Limits have been set for: Stop search: l´ 131 as a function of stop mass (MSSM) and exclusion region in the plane (m0,m1/2) (mSUGRA) Gaugino search: improved the LEP limits in the m-M2 plane Gravitino search: exclusion limits for m(co)-Dm plane Taking new data from HERA II (expected 500 pb-1 at the end of HERA operation) → much more statistic HERA has still something to say before LHC 04/04/2019 A. Montanari DIS2006 Tsukuba

A. Montanari DIS2006 Tsukuba Backup slides 04/04/2019 A. Montanari DIS2006 Tsukuba

A. Montanari DIS2006 Tsukuba HERA and ZEUS Protons at 820/920 GeV e- / e+ at 27.5 GeV √s=300/318 GeV Equivalent to 50 TeV on fix target Luminosity: 1.8x1031cm-2s-1 H1(ep) ZEUS ZEUS: HEP multi-purpose detector tracking detectors calorimiter uranium muon chambers collected L=121 pb-1 during HERA I 04/04/2019 A. Montanari DIS2006 Tsukuba

Gaugino production: event selection ZEUS data 96-00:121 pb-1 Q2JB>100 GeV2, yJB > 0.4 45 GeV < E-Pz < 62 GeV Et > 75 GeV ≥ 2 jets (Et,jet> 10 GeV, -0.5 < hjet < 2.7) ≥ 1 e± candidate (Pt > 6 GeV, qe<90º) Signal efficiency x BR: ~30% Multi-variate discriminant method Cut D>0.7 Signal: Msquark=1 TeV, Msel=100 GeV l´=1, tanb=30 04/04/2019 A. Montanari DIS2006 Tsukuba