Nuclearite search with the ANTARES neutrino telescope

Vlad Popa, for the ANTARES Collaboration

Institute for Space Sciences, Bucharest – Magurele, Romania

•Aggregates of u, d, s quarks + electrons , ne= 2/3 nu –1/3 nd –

1/3 ns

•Ground state of QCD; stable for 300 < A < 1057

Nuclearites: basic propertiesE. Witten, Phys. Rev. D30 (1984) 272A. De Rujula, S. L. Glashow, Nature 312 (1984) 734

Produced in Early Universe or in strange star collisions (J. Madsen, PRD71

(2005) 014026)

Candidates for cold Dark Matter! Searched for in CR reaching the

Earth

R (fm) 102 103 104 105 106

M (GeV) 106 109 1012 1015 1018

A qualitative picture…

[black points are electrons]

N 3.5 x 1014 g cm-3

nuclei 1014 g cm-3

•Typical galactic velocities 10-3

• Dominant interaction: elastic collisions with atoms in the medium• Dominant energy losses:

• Phenomenological flux limit from the local density of DM:

)(5.110

)()104.8(5.14/3216

143/2

cloudengMcm

insideeGeVngMM

2

.medv

dxdE

MDM 2/v

Arrival conditions to the depth of ANTARES

ev)L(v0

L

0

.meddx)x(

M

After a propagation path L in a medium, the velocity of a nuclearite of initial velocity v0 becomes:

in the atmosphere:

a = 1.2 10-3 g cm-3; b = 8.6 105 cm; H 50 km

(T. Shibata, Prog. Theor. Phys. 57 (1977) 882.)

in water: w 1 g cm-3

ea)x(atm

bxH

Intermediate mass nuclearitesM (GeV)

1014 s e

du

u uu

u

dd

d s

ds

s s

e ee

- Essentially neutral (most if not all e- inside)- “Simple” properties: galactic velocities, elastic collisions, energy losses…- Could reach ANTARES from above- Better flux limit from MACRO:

GeV10Mforsrscm102 1411216

M. Ambrosio et al., Eur.Phys. J. C13 (2000) 453; L. Patrizii, TAUP 2003

1010 Two low masses to reach ANTARES

1022 Could traverse the Earth, but very low expected fluxes

A little more on dE/dx…

2

.medv

dxdE For M 8.4 1014 GeV it depends only on v2

The passage of a nuclearite in matter produces heat along its path

In transparent media some of the energy dissipated could appear as visible light (black body radiation)

The “optical efficiency” = the fraction of dE/dx appearing as light in water estimated to be = 3 10-5 (lower bound) (A. De Ruhula, S.L. Glashow, Nature 312 (1984) 734)

Velocities in ANTARES

2100 m2274 m

2448 m

Example for vertical incidence

Light production / cm of path

starts to increase

)eV(E,E

dx/dEdx

dNvisible

visible

Example for vertical incidence

General strategy in ANTARES: “all data to shore”.

The basic info: the “hit”: time and charge information of a photon detected by a PMT

If the charge (amplitude) is above a pre-defined threshold, -> “L0” hit, buffered in a 2.2 s window.

General strategy in ANTARES: “all data to shore”.

If the charge (amplitude) is above a pre-defined threshold, -> “L0” hit, buffered in a 2.2 s window.

Local coincidence: “L1”. Two L0 hits in the same storey within 20 ns, or a single large amplitude hit (3 pe or more)

The “directional trigger” (DT): at least 5 L1 hits anywhere in the detector, within a 2.2 s window and causally connected.

“T3 cluster”: two “L1” hits in adjacent or next-to-adjacent storeys within 20 ns.

The “cluster trigger” (CT): at least two T3 within 2.2 s.

General strategy in ANTARES: “all data to shore”.

All PMT pulses in a 2.2 s window conserved in a buffer, as well as the previous window.

When a trigger occurs (DT or/and CT), all hits (above threshold) from the corresponding time window as well as the previous one are recorded for off-line analysis.

The shortest duration of an “event” (“snapshot”) is thus 4.4 s; as triggers could occur in the next time window, snapshots could be longer (adjacent events are merged).

Nuclearites are expected to be slowly moving: should be seen as anomalously long events, or as series of consequent snapshots. The typical crossing time about 1 ms!

Nuclearite search in ANTARES,2007 and 2008 data

Data recorded during ANTARES completion Various detector configurations (5, 9, 10 and 12 lines)

Variations in the bioluminescence background

Different threshold values

Each configuration treated separately!

Blind analysis: the search strategy defined trough Monte Carlo, validated using 15% of each data set, analysis on all data after unblinding maximized efficiency

Monte Carlo simulations

Nuclearites: Chose the mass and initial velocity, compute the velocity at the entry in the simulation hemisphere, propagate in the hemisphere with time resolution of 2 ns

Geometrical acceptance Events, mixed with background and processed by DT and CT triggers Efficiencies

Background:

-Atmospheric muons: MUPAGE (M. Bazzoti et al., Comput. Phys. Commun, 181 (2010) 835)- Bioluminiscence, K, etc, extracted from real runs.

Selection criterion: the duration of the events, dt = tlast trigg. – tfirst trigg.

Triggers optimized for relativistic particles → most simulated events produce multiple adjacent snapshots!

“C1” cut

For single snapshot events we require dt > 2C1 (Cut “C2”)

No event survived the C1 (+C2) cuts applied to 15% of the data collected during 2007 and 2008.Analysis sensitivities' obtained for all configurations.

After unblinding, data from 2007 and 2008 were analyzed.

Very few events survived the cuts. Each was carefuly analized:

- check of the Event Display

- study of the collected charge barycenter versus time. As the light emitted by the over-heated nuclearite path is isotropic, this should describe the event topology (a first step event reconstruction).

No event compatible with the down-going nuclearite predictions.

All events interpretable as bioluminescent phenomena. We could derive the 90% upper flux limit for down-going nuclearites,