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Search for Exotic Physics with the ANTARES Detector
Gabriela Pavalas and Nicolas Picot Clemente,on behalf of the ANTARES Collaboration
ICRC 2009
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ANTARES detector
► 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)
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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
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Introduction to magnetic monopoles (MM)MM initially introduced by Dirac in 1931.
Imply the quantization of the electric charge.
Make symmetric Maxwell’s equations.
Magnetic charge given by . The smallest magnetic charge is the Dirac charge gD, where k=1.
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Introduction to magnetic monopoles (MM)MM initially introduced by Dirac in 1931.
Transition example with the minimal GUT group:
MM appear with charge g=gD at the first transition.
Imply the quantization of the electric charge.
Make symmetric Maxwell’s equations.
Magnetic charge given by . The smallest magnetic charge is the Dirac charge gD, where k=1.
In 1974, ‘t Hooft and 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.
In this typical case the monopole mass is about ~ 1016 GeV with a radius of the order ~ 10-28 cm.
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Introduction to magnetic monopoles (MM)
MM initially introduced by Dirac in 1931.
Transition example with the minimal GUT group:
MM appear with charge g=gD at the first transition.
Imply the quantization of the electric charge.
Make symmetric Maxwell’s equations.
Magnetic charge given by . The smallest magnetic charge is the Dirac charge gD, where k=1.
In 1974, ‘t Hooft and 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.
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.
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Cherenkov from e
(knock-on electrons).
Direct Cherenkov from MM with g=gD
Cherenkov from .
Relativistic magnetic monopole signal in ANTARES
Number of photons emitted by a MM with the minimal charge gD ~ 68.5 e, is ~ 8500 times more than that of a muon.
Direct Cherenkov emission MM > 0.74:
Indirect Cherenkov emission MM > 0.51:
The energy transferred to electrons allows to pull out electrons (-rays), which can emit Cherenkov light.
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Cherenkov from e
(knock-on electrons).
Direct Cherenkov from MM with g=gD
Cherenkov from .
Relativistic magnetic monopole signal in ANTARES
Number of photons emitted by a MM with the minimal charge gD ~ 68.5 e, is ~ 8500 times more than that of a muon.
Direct Cherenkov emission MM > 0.74:
Indirect Cherenkov emission MM > 0.51:
The energy transferred to electrons allows to pull out electrons (-rays), which can emit Cherenkov light.
~ 0.90
Signature of a magnetic monopole in ANTARES:
Large amount of light seen by the 12-line ANTARES photomultipliers.
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Distribution of the number of cluster of hit floors T3 for atmospheric background events and for upgoing monopoles.
Analysis outlines
Atm. muonsAtm. neutrinos up.Atm. neutrinos do.
M.M. with M.M. with ~0.99
Search for fast ( > 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 (zen < 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 .
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Analysis outlines
For this fit quality cut, the best sensitivity is found for T3 > 170.
Example for Monopoles with and a cutfixed.
Optimisation of the Model Rejection Factor:
Discriminative variables : T3, the number of cluster of hit floors.
, the fit quality factor.
Optimisation of the sensitivity as a function of the T3, cuts applied for 0.80 < MM < 1.
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.
11~1.1 expected background events after one year of 12-line ANTARES data taking.
Preliminary expected 90% C.L. sensitivity with the 12-line ANTARES detector
PRELIMINARY
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Nuclearites
► 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
Monte Carlo simulation for 5-line detector configuration
Randomly generated: initial point on the hemisphere and particle direction
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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)
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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
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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
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L0-L1 distributions for data and simulated events
► A linear cut has been applied to separate the data/muon and nuclearite distributions
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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:
Nuclearite mass (GeV)
Triggered events
Percentage after linear cut
Percentage after multiple snapshot cut
3x1016 268 72.5% 16.3%
1x1017 1706 96.8% 89.1%
1x1018 319 98.7% 96.2%
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Sensitivity of the 5-line ANTARES detector
► A background value of 3 events has been considered in calculating the sensitivity
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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
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Backup
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Magnetic monopole acceleration in the Universe
Magnetic monopole’s masses: 105 to 1015 GeV (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).
M.M.
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.
B/μG ξ/Mpc gBξ/GeV
Normal galaxies 3 to 10 10-2 ~1012
Starburst galaxies 10 to 50 10-3 ~1011
AGN jets ~ 100 10-4 to 10-2 1011 to 1013
Galaxy clusters 5 to 30 10-4 to 1 109 to 1014
Extragalactic sheets 0.1 to 1.0 1 to 30 1013 to 1014
