Search for New Physics at HERA

1. Search for New Physics at HERA On behalf of H1 & ZEUScollaborations Alessandro Montanari Lake Louise Winter Institute 2005

2. Contents of the talk • Introduction to HERA • Lepton Flavor Violation • Magnetic Monopole • Light Gravitino • Stop squark • Isolated Lepton with High Pt Missing • Conclusions and Outlook Many other BSM searches performed at HERA: • Quark Radius • Extra-dimensions • Excited fermions, • Leptoquark • SUSY New Papers • Single top limits • Multi-lepton events • Double-charged Higgs • General search Lake Louise Winter Institute 2005

3. The HERA Collider Q2: Virtuality of exchange boson Gated Luminosity HERA-I (1994 2000) • e+p (s=300 GeV): 40 pb-1 • e--p (s=318 GeV): 16 pb-1 • e+p (s=318 GeV): 66 pb-1 HERA-II (2002 to 2007) • Expected 0.75 fb-1 • Polarized lepton beams • e+p (s=318 GeV): 46 pb-1 • Nowe--p (s=318 GeV): 16 pb-1 Lake Louise Winter Institute 2005

4. Lepton Flavor Violation • The recent discovery of neutrino oscillation showed that the lepton flavor is not conserved at least in the neutral sector • Many extensions of SM (GUT and SUSY) predict lepton-flavor violation • Signature at HERA: a muon or tau instead of the electron in the final state • High efficiency and low background from SM, therefore HERA is an ideal place to look for LQ. • Coupling at the production leq • Coupling at decay lmq and ltq Lake Louise Winter Institute 2005

5. Lepton Flavor Violation II • Limits on λeq1√Blqj independent from final state quark generation (MLQ < √s) For leq1 = 0.3 and Blqj = 0.5, LQ masses up to 300 GeV are excluded. Lake Louise Winter Institute 2005

6. Magnetic Monopole (MM) Dirac predicted the existence of MM. String and GUT predict heavy primordial MM (1015 GeV) Recent theories (Klapdor,Zuber. ‘99) use different approach and estimate a mass of O(10) GeV MM has already been searched in pp and e+e- colliders. First search in ep collision at H1 experiment. MM produced stops in the beampipe (am ≈ 34 n2) Beampipe (’94-’97): aluminium radiated by 62±1 pb-1 Method of detection: search for the induction of a persistent current within a superconducting coil by the beam-pipe. Lake Louise Winter Institute 2005

7. Magnetic Monopole: Limits Signal Simulation • Efficiencies and exclusion limits based on two models: A Elastic e+p -> e+ MM p (MM spin 0) BInelastic e+p -> e+ MM X (MM spin ½) Lake Louise Winter Institute 2005

8. Light Gravitino Search • R-parity R=(1)(3B+L+2S) 1 SM particles -1 SUSY partners • If the R-parity is not conserved the t-channel exchange of a selectron can produce a neutralino. • For SUSY models in which gravitino (G) is the lightest supersymmetric particle (GMSB), the neutralino decays in g and G. ~ ~ Event signature: • Isolated photon • 1 jet • Missing transverse energy (undetected G) ~ Lake Louise Winter Institute 2005

9. Light Gravitino Search II • High Pt selection: • Pt miss > 25 GeV • Pt,g > 15 GeV Data 1 event (1.8 ±0.2 expected) • Limits are independent to the squark masses. • Scenarios in which M(Neutralino)<112GeV and M(selectron)<164GeV are excluded at 95% C.L. Lake Louise Winter Institute 2005

10. l’131 S-top in R-parity Violation • If R-parity violated: single sparticle production LSP unstable. • Single Stop Search on resonant production • Two different approaches: • Stop as lightest sfermion (H1&ZEUS) • Bosonic stop decay (H1) Gauge Stop Decay Bosonic Stop Decay Lake Louise Winter Institute 2005

11. Stop in R-parity Violation: Limits MSSM: Minimal Supersymmetric Standard Model, free variation of m, tan b • Bands shows stop mass vs l’131 changing with variation of SUSY parameters. • Stop excluded for masses up to 280 GeV and l’131=0.3 Lake Louise Winter Institute 2005

12. Jet Isolated lepton Missing Pt Isolated Lepton and High Pt-missing • A search for events containing isolated leptons and missing transverse momentum performed for HERA I data (H1&ZEUS) and HERA II data (H1). • Only contribution to this signal coming from SM is W production with leptonic decay s (ep -> e W± X) ~ 1 pb Lake Louise Winter Institute 2005

13. Isolated Lepton and High Pt-missing H1 observed 6 events with hadronic trans. Mom. > 40 GeV ZEUS: events agree with the SM but 2 tau candidate Are these processes due to new physics? Maybe HERA-II can give us the answer… Lake Louise Winter Institute 2005

14. Isolated Lepton and High Pt-missing • H1 updated the analysis using HERA-II data (L=53pb-1): still an excess • Combining HERA I+II H1 Preliminary L=171 pb-1 (1994-2005) Lake Louise Winter Institute 2005

15. Conclusions and Outlook • BSM scenarios have been investigated by HERA experiments • Exclusion limits have been set for LFV events, Magnetic Monopole production, RP-violating Stop and gravitino. • Interesting results on isolated lepton events observed also in L=56pb-1 from HERA-II data taking • The integrated luminosity provided in the middle of 2007 will help to resolve the HERA-I puzzles. Lake Louise Winter Institute 2005

16. LFV: Resonant Search • e p -> m + 1 jet • a muon and a jet back-to-back in the final state e p -> t + 1 jet • t -> e nent: missing transverse momentum in the same direction of the electron. • t -> m nm nt: same topology as for the electron channel. • t -> q q’ nt: two jets (one “pencil”-like) and missing transverse impulse in the same direction of tau-jet. tau-jet: narrow shape low radius ZEUS: Discriminant Method for tau-finder Lake Louise Winter Institute 2005

17. Stop in R-parity Violation II Comparison Data vs. Monte Carlo Standard Model: Agreement Excess in jet+m+missing Pt Gauge decay Bosonic and Direct Decay Lake Louise Winter Institute 2005