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Search for Exotic Physics with the ANTARES Detector

Search for Exotic Physics with the ANTARES Detector. Gabriela Pavalas and Nicolas Picot Clemente, on behalf of the ANTARES Collaboration ICRC 2009. 12 vertical lines with 884 Optical Modules (OM) deployed in the Mediterranean Sea, since May 2008

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Search for Exotic Physics with the ANTARES Detector

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  1. Search for Exotic Physics with the ANTARES Detector Gabriela Pavalas and Nicolas Picot Clemente, on behalf of the ANTARES Collaboration ICRC 2009

  2. 12 vertical lines with 884 Optical Modules (OM) deployed in the Mediterranean Sea, since May 2008 25 storeys on each line, PMTs arranged by triplet per storey Built gradually, stable configurations: 5-line (since Jan 2007), 12-line (since May 2008) ANTARES detector

  3. ANTARES acquisition • Data acquisition strategy: “all-data-to-shore” concept • Trigger logics operated up to now: - directional trigger: five local coincidences (L1 hits) causally connected, within a time window of 2.2 μs - cluster trigger: two T3-clusters (combination of two L1 hits in adjacent or next-to-adjacent storeys) within 2.2 μs • Local coincidence (L1 hit): two hits on two OMs of the same storey within 20 ns or a single hit with a large amplitude, typically 3 pe

  4. Introduction to magnetic monopoles (MM) MM initially introduced by Dirac in 1931. Make symmetric Maxwell’s equations. Imply the quantization of the electric charge. Magnetic charge given by . The smallest magnetic charge is the Dirac charge gD, where k=1.

  5. Introduction to magnetic monopoles (MM) MM initially introduced by Dirac in 1931. Make symmetric Maxwell’s equations. Imply the quantization of the electric charge. Magnetic charge given by . The smallest magnetic charge is the Dirac charge gD, where k=1. In 1974, ‘t Hooftand Polyakov found monopoles as solutions appearing in unified gauge theories, in which U(1)E.M. is embedded in a spontaneously broken semi-simple gauge group. Transition example with the minimal GUT group: MM appearwith charge g=gDat the first transition. In this typical case the monopole mass is about ~ 1016 GeV with a radius of the order ~ 10-28 cm.

  6. Introduction to magnetic monopoles (MM) MM initially introduced by Dirac in 1931. Make symmetric Maxwell’s equations. Imply the quantization of the electric charge. Magnetic charge given by . The smallest magnetic charge is the Dirac charge gD, where k=1. In 1974, ‘t Hooftand Polyakov found monopoles as solutions appearing in unified gauge theories, in which U(1)E.M. is embedded in a spontaneously broken semi-simple gauge group. Transition example with the minimal GUT group: MM appearwith charge g=gDat the first transition. In this typical case the monopole mass is about ~ 1016 GeV with a radius of the order ~ 10-28 cm. Intermediate mass magnetic monopoles could be produced after the GUT phase transitions, with a predicted mass range of ~105-1015 GeV Magnetic monopoles with masses up to ~1014 GeV could be relativistic, and some are expected to cross the Earth, making them detectable by ANTARES.

  7. Relativistic magnetic monopole signal in ANTARES Direct Cherenkov emission MM > 0.74: Direct Cherenkov g from MM with g=gD Number of photons emitted by a MM with the minimal charge gD ~ 68.5 e, is ~ 8500 times more than that of a muon. Cherenkov g from de (knock-on electrons). Cherenkov g from m. Indirect Cherenkov emission MM > 0.51: The energy transferred to electrons allows to pull out electrons (d-rays), which can emit Cherenkov light.

  8. Relativistic magnetic monopole signal in ANTARES Direct Cherenkov emission MM > 0.74: Direct Cherenkov g from MM with g=gD Number of photons emitted by a MM with the minimal charge gD ~ 68.5 e, is ~ 8500 times more than that of a muon. Cherenkov g from de (knock-on electrons). Cherenkov g from m. Indirect Cherenkov emission MM > 0.51: The energy transferred to electrons allows to pull out electrons (d-rays), which can emit Cherenkov light. Signature of a magnetic monopole in ANTARES: Large amount of light seen by the 12-line ANTARES photomultipliers. b ~ 0.90

  9. Analysis outlines Search for fast (b > 0.74) upgoing magnetic monopoles: Use of the muon reconstruction algorithm. Selection criteria to remove background events (atmospheric neutrinos and muons): Upgoing magnetic monopoles Selection of only upgoing reconstructed events (qzen < 90°). Large amount of light Selection applied on the number of cluster of hit floors (T3). Remove most of misreconstructed events with the fit quality factor L. Distribution of the number of cluster of hit floors T3 for atmospheric background events and for upgoing monopoles. Atm. muons Atm. neutrinos up. Atm. neutrinos do. M.M. withb~0.75 M.M. withb~0.99

  10. Analysis outlines Optimisation of the Model Rejection Factor: Discriminative variables : T3, the number of cluster of hit floors. L, the fit quality factor. Optimisation of the sensitivity as a function of the T3, L cuts applied for 0.80 < bMM< 1. Example for Monopoles with and a L cutfixed. For this fit qualitycut, the best sensitivityisfound for T3 > 170. Blinding policy: A sample of 10 days of data are taken to compare distributions with Monte Carlo simulations to validate the study before the unblinding of data.

  11. Preliminary expected 90% C.L. sensitivity with the 12-line ANTARES detector PRELIMINARY ~1.1 expected background eventsafter one year of 12-line ANTARES data taking.

  12. Hypothetical stable particles composed of strange quark matter Origin: supernovae, collapsing binary strange stars, … Down-going nuclearites could reach the ANTARES depth with velocities ~ 300 km/s Black-body radiation emitted by the expanding shock wave produced in the traversed medium Main background in ANTARES: down-going atmospheric muons Nuclearites Monte Carlo simulation for 5-line detector configuration Randomly generated: initial point on the hemisphere and particle direction

  13. Comparison between simulated events and data • Simulated nuclearite events for masses: 3x1016 GeV, 1017 GeV and 1018 GeV • - lower mass limit detectable with the directional trigger: 3x1016 GeV • MUPAGE atmospheric muon events (20 GeV-500 TeV) • Monte Carlo events processed with directional trigger • Experimental data taken with 5-line ANTARES detector (5 hours run from October 2007) • Parameters used for comparison: • - number of L1 hits • - number of single hits (L0 hits, with threshold > 0.3 pe) • - duration of snapshot (time difference between the last and first L1 • triggered hit of the event) • A snapshot contains all information related to a muon triggered event (~ 4 μs)

  14. Snapshot distribution for simulated nuclearite events • The trigger selects from all the hits produced by a nuclearite only those that comply with the signal of a relativistic muon • For a nuclearite event, the hits can be contained in multiple snapshots

  15. Duration of snapshot and L0 hits distributions • A typical nuclearite event would cross the detector in an interval from hundreds of μs up to 1 ms • Good agreement between data and simulated muon events

  16. L0-L1 distributions for data and simulated events • A linear cut has been applied to separate the data/muon and nuclearite distributions

  17. Selection cuts • Data sample: 84 days of data taken with 5-line detector, from June to November 2007 • First cut: linear cut • Second cut : multiple snapshot cut (multiple snapshots in a time window of 1 ms) Data: - the first cut reduces the data by 99.99% - the second cut selects 3 “events” with a double snapshot Signal:

  18. Sensitivity of the 5-line ANTARES detector • A background value of 3 events has been considered in calculating the sensitivity

  19. Conclusions • Search strategies for exotic particles like magnetic monopoles and nuclearites are being developed • Preliminary expected sensitivity of the ANTARES detector in 12-line configuration for magnetic monopoles is better than existing upper limits for the monopole flux • Preliminary analysis for nuclearites shows a sensitivity of the ANTARES detector in 5-line configuration competitive to best existing limits • Further studies to implement in the data acquisition program a trigger dedicated to slowly moving particles

  20. Backup

  21. Magnetic monopole acceleration in the Universe Magneticmonopole’s masses: 105 to 1015GeV (depending on the mass scale of unification). Energy gain in a magnetic coherent field: Magnetic monopoles with masses below 1014 GeV should be relativistic (with extragalactic sheets expecting to dominate the spectrum). Estimated energy loss when crossing the Earth of ~ 1011 GeV. M.M. with masses up to about 1014 GeV are expected to cross the Earth and to be relativistic. M.M.

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