1. Nuclearite search with the ANTARES neutrino telescope
Vlad Popa, for the ANTARES Collaboration
Institute for Space Sciences, Bucharest – Magurele, Romania

2. Nuclearites: basic properties E. Witten, Phys. Rev. D30 (1984) 272A
Nuclearites: basic properties E. Witten, Phys. Rev. D30 (1984) 272A. De Rujula, S. L. Glashow, Nature 312 (1984) 734
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
rN  3.5 x 1014 g cm-3
rnuclei  1014 g cm-3
A qualitative picture…
[black points are electrons]
R (fm)
M (GeV)
Produced in Early Universe or in strange star collisions (J. Madsen, PRD71 (2005) )
Candidates for cold Dark Matter! Searched for in CR reaching the Earth

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:

4. Arrival conditions to the depth of ANTARES
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

5. Intermediate mass nuclearites
M (GeV)
1022
Could traverse the Earth, but very low expected fluxes
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:
1014
s e d u
d s s e
M. Ambrosio et al., Eur.Phys. J. C13 (2000) 453; L. Patrizii, TAUP 2003
1010
Two low masses to reach ANTARES

6. A little more on dE/dx… 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  (lower bound)
(A. De Ruhula, S.L. Glashow, Nature 312 (1984) 734)

7. Velocities in ANTARES 2100 m 2274 m 2448 m
Example for vertical incidence

8. Light production / cm of path
 starts to increase
Example for vertical incidence

9. 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.
The basic info: the “hit”: time and charge information of a photon detected by a PMT

10. 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.

11. 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!

12. Nuclearite search in ANTARES,
2007 and 2008 data
Various detector configurations (5, 9, 10 and 12 lines)
Data recorded during ANTARES completion
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

13. 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.

14. Selection criterion: the duration of the events, dt = tlast trigg
Selection criterion: the duration of the events, dt = tlast trigg. – tfirst trigg.
Triggers optimized for relativistic particles → most simulated events produce multiple adjacent snapshots!
For single snapshot events we require dt > 2C1 (Cut “C2”)
“C1” cut

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

16. 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 e vent 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,