Transcript Slide 1

Nuclearite search with the ANTARES neutrino telescope
Vlad Popa, for the ANTARES Collaboration
Institute for Space Sciences, Bucharest – Magurele, Romania
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)
102
106
103
104
105
106
109
1012
1015
1018
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
•Typical galactic velocities   10-3
• Dominant interaction: elastic collisions with atoms in the medium
• Dominant energy losses:
dE
 rmed. v 2
dx
 3M / 4r 2 / 3
M  1.5ng (8.4 1014 GeV ) (e inside)
 
16
2



10
cm
M

1
.
5
ng
(
e
cloud)

• Phenomenological flux limit from the local density of DM:
  r DM v / 2 M 
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:


rmed. ( x )dx
M0
L
v( L)  v 0 e
ratm ( x )  a  e

Hx

b
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: rw  1 g cm-3
Intermediate mass nuclearites
M (GeV)
Could traverse the Earth, but very low expected fluxes
1022
1014
e
d e
u eu d s
s se u
d sds u
u
d
- 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:
  2  10 16 cm 2s 1sr 1
for
M  1014 GeV
M. Ambrosio et al., Eur.Phys. J. C13 (2000) 453; L. Patrizii, TAUP 2003
1010
Two low masses to reach ANTARES
A little more on dE/dx…
dE
 rmed. v 2
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  10-5 (lower bound)
(A. De Ruhula, S.L. Glashow, Nature 312 (1984) 734)
Velocities in ANTARES
Example for vertical incidence
2100 m
2274 m
2448 m
Light production / cm of path
Example for vertical incidence
 starts to increase
dN 
dE / dx

,
dx
E  visible
E
visible
 (eV)
General strategy in ANTARES: “all data to shore”.
If the charge (amplitude) is above a predefined 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
General strategy in ANTARES: “all data to shore”.
If the charge (amplitude) is above a predefined 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
Variations in the bioluminescence
background
Various detector configurations (5, 9, 10
and 12 lines)
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!
For single snapshot events we require dt > 2C1 (Cut “C2”)
“C1” cut
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 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,