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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