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Search for New Physics in the ME T Channel at D Ø

Search for New Physics in the ME T Channel at D Ø. Stelios Kesisoglou Alex Melnitchouk for the D Ø collaboration. APS-DPF 2003 Conference, Philadelphia. Gauge-Mediated SUSY.

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Search for New Physics in the ME T Channel at D Ø

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  1. Search for New Physics in the METChannel at DØ Stelios Kesisoglou Alex Melnitchouk for the DØ collaboration APS-DPF 2003 Conference, Philadelphia

  2. Gauge-Mediated SUSY • An alternative to gravity mediated SUSY: introduce new gauge fields (“messengers”) which propagate SUSY-breaking interactions and couple to ordinary and SUSY particles • Phenomenology: • Gravitino is very light (<<MeV) and is LSP • NLSP can be a neutralino or a slepton • NLSP lifetime is a free parameter • May yield non-prompt photons in the decay • In case of the neutralino NLSP: • Final state always has two photons • Do inclusive search for MET + X Stelios Kesisoglou, Alex Melnitchouk APS-DPF conference 2003

  3. Previous Searches CDF Run 1 LEP SUSY WG eeMET • CDF has found an intriguing event eeMET • In the GMSB framework CDF set lower limit on the neutralino mass at M(0) > 65 GeV DØ PRL(80) 1998 • DØ found no high ET diphoton+MET events andset lower limit on the neutralino mass at M(0) > 75 GeV • LEP2 recently set lower limit on 10 ~ 95 GeV Stelios Kesisoglou, Alex Melnitchouk APS-DPF conference 2003

  4. Data Selection • ~40 pb-1 (September 2002 - January 2003) • Trigger: • One EM object over the threshold OR • Two EM objects over the (lower) threshold • Off-line: events with two photons • Isolation • Shower shape consistent with photon • No matching tracks • || < 1.1 (since looking for heavy objects) • ET>20 GeV • to be above trigger turn-on: Trigger=0.98±0.02 • to be able to rely on EM ID efficiency from Z decays • MET is calculated summing all calorimeter cells and corrected for EM and jet energy scales EM ID = 0.85±0.06 Stelios Kesisoglou, Alex Melnitchouk APS-DPF conference 2003

  5. MET Resolution • Tails of MET distribution are most important (region of expected signal) • Can be caused by mis-measured jets  discard events in which ET is collinear with a jet Z+jet event: Both EM have tracks Mass consistent with Z MET has the same azimuthal angle as the jet! Red – EM energy Yellow – direction of MET Blue – hadronic energy Stelios Kesisoglou, Alex Melnitchouk APS-DPF conference 2003

  6. without true MET QCD: , +j, j+j (jet is “faking” ) Drell-Yan (lost tracks) with true MET (from) W e & Wj ej(lost track, fake ) Z  ee +X ( lost tracks ) tt  ee + X ( lost tracks ) WW, WZ, … Backgrounds if a jet ”fakes” an isolated EM object, it’s mainly because it’s fragmented into a leading 0 and therefore its energy resolution is similar to the EM energy resolution MET resolution is similar for , +jet, e+jet, ee, etc… Largest backgrounds   0 (leading particle) Quark or gluon hadrons Stelios Kesisoglou, Alex Melnitchouk APS-DPF conference 2003

  7. Predicting Backgrounds • QCD (, +j, j+j) • require at least one of the isolated EM clusters to fail the shower shape cut  “QCD Sample” • Assume that events in the  sample with small MET are dominated by QCD • use MET<20 GeV region for normalizing QCD sample • W e & Wj ej • require exactly one cluster to have a track match • subtract QCD contribution • multiply by (1-track)/track Stelios Kesisoglou, Alex Melnitchouk APS-DPF conference 2003

  8. Signal Efficiency  QCD / / / Snowmass Slope E: mGMSB() M=2; Nmess=1; tan=15; >0  = 55 TeV  = 45 TeV = 35 TeV ( ) MET, GeV Run 2 preliminary MET, GeV Stelios Kesisoglou, Alex Melnitchouk APS-DPF conference 2003

  9. Upper Limit Calculation • Bayesian approach • Cut on MET should depend on  - for now 30 GeV is conservative theory 95% CL 90% CL Stelios Kesisoglou, Alex Melnitchouk APS-DPF conference 2003

  10. Prospects for Diphotons R calo • Non-prompt decays: • Sensitivity drops as NLSP leaves the detector • In the limit of large lifetime we are back to jets+MET • Intermediate lifetime – ask for one photon plus jets plus MET J. Qian, hep-ph/9903548 Similar model to Snowmass Slope, but tg  = 2.5 • Prompt decays: • m(1+) discovery up to 300 GeV with 2 fb-1 Stelios Kesisoglou, Alex Melnitchouk APS-DPF conference 2003

  11. Conclusions • A search for the Gauge-Mediated SUSY signal was carried out in the inclusive MET + X channel • MET distribution is well understood and does not have significant non-Gaussian tails • Observed MET data are in good agreement with the Standard Model predictions • With 40 pb-1 neutralino mass limit has been set at 66 GeV (sensitivity approaches that in Run I) • More data are being accumulated • Search for non-prompt photons is underway • Stay tuned - new results will be coming soon Stelios Kesisoglou, Alex Melnitchouk APS-DPF conference 2003

  12. Photon Pointing Use calorimeter and preshower detectors to reconstruct displaced vertices in MET events Stelios Kesisoglou, Alex Melnitchouk APS-DPF conference 2003

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