arXiv:hepex/0405035 v1 14 May 2004
AMANDA: STATUS AND LATEST RESULTS
Mathieu Ribordy
Universit´e de MonsHainaut, 19, av. Maistriau, B7000 Mons
for the AMANDA collaboration
M. Ackermann
4
, J. Ahrens
11
, H. Albrecht
4
, X. Bai
1
, R. Bay
9
, M. Bartelt
2
, S.W. Barwick
10
, T. Becka
11
,
K.H. Becker
2
, J.K. Becker
2
, E. Bernardini
4
, D. Bertrand
3
, D.J. Boersma
4
, S. B¨oser
4
, O. Botner
17
,
A. Bouchta
17
, O. Bouhali
3
, J. Braun
15
, C. Burgess
18
, T. Burgess
18
, T. Castermans
13
, D. Chirkin
9
,
B. Collin
8
, J. Conrad
17
, J. Cooley
15
, D.F. Cowen
8
, A. Davour
17
, C. De Clercq
19
, T. DeYoung
12
,
P. Desiati
15
, P. Ekstr¨om
18
, T. Feser
11
, T.K. Gaisser
1
, R. Ganugapati
15
, H. Geenen
2
, L. Gerhardt
10
,
A. Goldschmidt
7
, A. Groß
2
, A. Hallgren
17
, F. Halzen
15
, K. Hanson
15
, R. Hardtke
15
, T. Harenberg
2
,
T. Hauschildt
4
, K. Helbing
7
, M. Hellwig
11
, P. Herquet
13
, G.C. Hill
15
, J. Hodges
15
, D. Hubert
19
,
B. Hughey
15
, P.O. Hulth
18
, K. Hultqvist
18
, S. Hundertmark
18
, J. Jacobsen
7
, K.H. Kampert
2
A. Karle
15
,
J. Kelley
15
M. Kestel
8
, L. K¨opke
11
, M. Kowalski
4
, M. Krasberg
15
, K. Kuehn
10
, H. Leich
4
, M. Leuthold
4
,
I. Liubarsky
5
, J. Madsen
16
, K. Mandli
15
, P. Marciniewski
17
, H.S. Matis
7
, C.P. McParland
7
, T. Messarius
2
,
Y. Minaeva
18
, P. Mioˇcinovi´c
9
, R. Morse
15
, K. M¨unich
2
, R. Nahnhauer
4
, J.W. Nam
10
, T. Neunh¨offer
11
,
P. Niessen
19
, D.R. Nygren
7
, H.
¨
Ogelman
15
, Ph. Olbrechts
19
, C. P´erez de los Heros
17
, A.C. Pohl
6
,
R. Porrata
9
, P.B. Price
9
, G.T. Przybylski
7
, K. Rawlins
15
, E. Resconi
4
, W. Rhode
2
, M. Ribordy
13
,
S. Richter
15
, J. Rodr´ıguez Martino
18
, H.G. Sander
11
, K. Schinarakis
2
, S. Schlenstedt
4
, D. Schneider
15
,
R. Schwarz
15
, A. Silvestri
10
, M. Solarz
9
, G.M. Spiczak
16
, C. Spiering
4
, M. Stamatikos
15
, D. Steele
15
,
P. Steffen
4
, R.G. Stokstad
7
, K.H. Sulanke
4
, I. Taboada
14
, L. Thollander
18
, S. Tilav
1
, W. Wagner
2
,
C. Walck
18
, M. Walter
4
, Y.R. Wang
15
, C.H. Wiebusch
2
, R. Wischnewski
4
, H. Wissing
4
, K. Woschnagg
9
,
G. Yodh
10
(1)
Bartol Research Institute, University of Delaware, Newark, DE 19716;
(2)
Department of Physics, Bergische
Universit¨at Wuppertal, D42097 Wuppertal, Germany;
(3)
Universit´e Libre de Bruxelles, Science Faculty CP230,
Boulevard du Triomphe, B1050 Brussels, Belgium;
(4)
DESYZeuthen, D15735, Zeuthen, Germany;
(5)
Blackett
Laboratory, Imperial College, London SW7 2BW, UK;
(6)
Dept. of Technology, Kalmar University, S39182
Kalmar, Sweden;
(7)
Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA;
(8)
Dept. of Physics,
Pennsylvania State University, University Park, PA 16802,
USA;
(9)
Dept. of Physics, University of California,
Berkeley, CA 94720, USA;
(10)
Dept. of Physics and Astronomy, University of California, Irvine, CA 92697,
USA;
(11)
Institute of Physics, University of Mainz, Staudinger Weg 7, D55099 Mainz, Germany;
(12)
Dept. of
Physics, University of Maryland, College Park, MD 20742, USA;
(13)
University of MonsHainaut, 7000 Mons,
Belgium;
(14)
Departamento de F´ısica, Universidad Sim´on Bol´ıvar, Caracas, 1080, Venezuela;
(15)
Dept. of Physics,
University of Wisconsin, Madison, WI 53706, USA;
(16)
Physics Dept., University of Wisconsin, River Falls, WI
54022, USA;
(17)
Division of High Energy Physics, Uppsala University, S75121 Uppsala, Sweden;
(18)
Dept. of
Physics, Stockholm University, SE10691 Stockholm, Sweden;
(19)
Vrije Universiteit Brussel, Dienst ELEM, B
1050 Brussels, Belgium;
We briefly review some of the recent AMANDA results emphasizing the all flavor capabilities
of the high energy neutrino telescope, important in the context of equal neutrino mixing from
distant sources at Earth. Together with a report on a preliminary UHE neutrino flux limit, the
course of our progress in the quest for point sources is described. Finally, a 1 year preliminary
limit of AMANDAII to neutralino cold dark matter (CDM) candidates, annihilating in the
center of the Sun, for various MSSM parameter choices is presented and discussed.
1 Motivations
Figure 1: Illustration of the underlying physics
performed with AMANDA, see text.
The observation of the neutrino sky may eventually
shed some light on the obscure origin of the charged
cosmic ray (CR) spectrum. The acceleration mecha
nisms at energies above the knee remain a mystery.
CRs are believed to be accelerated in the expanding
shocks of e.g. SNR, AGN or GRB
1
. Hadrons accel
erated in these objects collide with surrounding radia
tion or with background radiation between the source
and the Earth to produce pions, which further decay
into neutrinos and gamma rays. Although it seems
to be established that SNRs accelerate electrons up to
≈
100 TeV through the study of multiwavelength spec
tra in conventional astronomy, it has not yet been un
ambiguously demonstrated that they might also accel
erate hadrons. The nascent field of neutrino astronomy
may settle the controversy. The neutrino travels unab
sorbed, undeflected and escapes optically thick sources
and so offers an advantage over other astrophysical
messengers (neutrinos are nevertheless difficult to de
tect and require large detection volumes). CR direction
is randomized by magnetic fields. Gamma rays interact
with the CMBR and the IR background, which reduces
their mean free path above modest energies (10 GeV), consequently affecting the observed emis
sion spectra of astrophysical objects (the close AGN Mrk501 would be invisible at 100 TeV
2
).
The neutrino telescope AMANDA (Antarctic Muon And Neutrino Detector Array) is dedicated
to the exploration of the high energy (HE) universe and aims at detecting extraterrestrial HE
neutrinos, which may be produced by the powerful processes at work in cosmic accelerators.
2 The AMANDA detector
Figure 2: Left: the AMANDA telescope and the detection principle
of muon tracks. Right: ”cascades” allow for all flavor detection.
AMANDA is buried in the trans
parent ice of the South Pole ice
cap at depths between 1.5 and 2.2
km
3
, see Fig. 2, in order to es
cape a large fraction of the atmo
spheric muon flux. The remaining
events, misreconstructed below the
horizon, constitute a main source
of background. Atmospheric neu
trinos
4
represent another important
source of background in a astrophys
ical search. AMANDA is a 19 string
detector equipped with 677 PMTs
instrumenting a cylindrical volume
with an outer radius of 60 m. Events
are reconstructed by measuring the
arrival time of Cherenkov light emit
ted either by crossing relativistic (neutrinoinduced) muons or by EM/hadronic cascades, which
results from NC for all three flavors and
ν
e
, τ
CC interaction
5
. AMANDA is therefore an all
flavor detector, important in the context of neutrino oscillation, as all flavors are expected to be
equally populated at Earth after traveling cosmological distances (given
ν
e
:
ν
µ
:
ν
τ
=1:2:0 at the
source, this relies on the
U
e1
≈
0 and
U
µ
3
≈
U
τ
3
in the neutrino mixing matrix
6
). Muon tracks
are reconstructed with an incidence direction resolution ∆Ψ
≈
2
.
5
◦
, cascades however have a
better energy resolution ∆log
E
≈
15%. The AMANDA analyses have to face various systemat
ical errors, which come from an imperfect knowledge of the ice properties, from uncertainties in
the absolute detector sensitivity and in the primary CR spectrum normalization and its exact
composition.
3 Diffuse flux analyses
This section discusses analyses aimed at finding global neutrino excess contributed to for example
by unresolved sources of a possible cosmogical origin. They exploit an expected harder extra
terrestrial spectrum (
d
Φ
/dE
∼
E
α
, α
≈
2) in comparison to the steeply falling atmospheric
neutrino background (
α
= 3
.
7). These analyses critically depend on the quality of the detector
simulation and can be performed in the two complementary muon and cascade channels.
3.1 Search for an UHE neutrino excess
Above
∼
1PeV, because of the rise of the neutrino cross section with increasing energy, the
Earth becomes gradually opaque and neutrino events concentrate near the horizon. An analysis
of the AMANDAB10 ’97 data was conducted focusing on PeV to EeV energies
7
. In this
range, a crossing muon illuminates the whole detector so different event selection techniques
had to be developed (Ref.
8
). Discriminant observables for this analysis used to distinguish
UHE neutrinoinduced muon from atmospheric muon bundles are: the fraction of hit channels
with exactly one hit, the number of hits, the number of hit channels, the averaged amplitude of
the hit channels and the reconstruction quality. At these energies, new sources of systematical
error caused by the uncertainties on the neutrino cross section and on the muon propagation
are taken into account. Given a
E
2
benchmark neutrino spectral shape, a preliminary limit
of
E
2
Φ
ν
(
E
)
<
1
.
5
·
10
6
GeV cm
2
s
1
sr
1
in the range 1 PeV
< E <
3 EeV is set, assuming
ν
e
:
ν
µ
:
ν
τ
=1:1:1 and
ν/
¯
ν
= 1.
3.2 Cascade analysis 2000
Figure 3: The experimentally reconstructed
energy distribution after the final selection
agrees with the expected background. The
corresponding response to an hypothetical sig
nal is also shown.
Strategies followed in this analysis are inspired by the
reconstruction and selection techniques originating in
a previous study
9
. These have now been further de
veloped. Neutrinos from each flavor were generated, as
well as a massive amount of atmospheric muon back
ground (2.5 yr). An optimized sequential selection
was applied to the experimental and to the simulated
data in order to reject the atmospheric muon back
ground, reduced by a factor better than 10
9
, while
preserving the efficiency on the signal, close to 3% for
ν
e
. The selection restricted the reconstructed thresh
old energy
E
rec
>
50 TeV and the reconstruction qual
ity
L
E
rec
(
E
), demanding the cascade to be contained.
Some of the restrained observables included among oth
ers: the smoothness (a measure of the equirepartition
of hits along the track), the number of hit channels, the
number of direct photons and the radial distance be
tween two independently reconstructed vertices (using two complementary sets of hit channels).
One event remained in the final sample of experimental data, with an energy
E
rec
≈
150 TeV.
This is shown in Fig. 3. Within the estimated systematical uncertainties, the energy distribu
Figure 4: The effective area w.r.t. the en
ergy allows to compute a limit for any model
(arbitrary spectrum and neutrino mixing).
Figure 5: Summary of the AMANDA and Icecube diffuse flux
limits in red (plain: published, dotted: ongoing analysis and
expected in the future). See also text.
tion is in agreement with the simulated background. Obtained sensitivities for all flavors are
comparable (Fig. 4), demonstrating the AMANDA detector as an all flavor neutrino telescope.
The upper limit reached in this analysis is
E
2
Φ
ν
(
E
)
<
8
.
6
·
10
7
GeV cm
2
s
1
sr
1
in the range
50 TeV
<E <
5 PeV, assuming
ν
e
:
ν
µ
:
ν
τ
=1:1:1 and a
E
2
neutrino spectrum. Some of the SDSS
models
10
,
11
are therefore discarded. A sensitivity at the same level is foreseen in an ongoing
analysis in the muon channel. Potential, preliminary and published limits are summarized in
Fig. 5, also indicating the level of the atmospheric neutrino flux (
ν
µ
and
ν
τ
)
12
, of the cosmo
genic flux
13
, the WB and MPR upper limits
14
,
15
and a specific flux prediction (MPR
15
).
4 Point source analyses
This section briefly illustrates analyses searching for a statistical excess originating in narrow
regions of the northern sky. These analyses exclusively rely on the muon channel, because of its
better pointing resolution. The sensitivities of these analyses are optimized by taking advantage
of the experimentally observed offsource detector response thus defining the background.
4.1 Gamma ray burst analysis
The detection of a HE neutrino component (
E >
10
2
TeV) spatially and temporally coinciding
with GRBs would substantiate the hypothesis of hadronic acceleration occuring within the GRB
wind. The cumulative AMANDA data (’97’00), within a 10 minute time window around 317
BATSE reported triggered bursts
16
, were explored in search of a global excess
17
. The stability
of the detector was assessed by evaluating the noise rate within 1 hour from the trigger times,
leading to the exclusion of 5 BATSE triggers. A very low background analysis (due to the known
timestamp and direction of the burst) with a large muon effective area
A
eff
≈
50
?
000 m
2
(at
E
≈
PeV) was subsequently performed and no events were observed. An event upper limit of 1.45 was
derived. Assuming a WaxmanBahcall type spectrum, in the GRB fireball phenomenology
18
,
a 90% C.L. upper limit to its normalization constant is set to
4
.
8
·
10
8
GeV cm
2
s
1
sr
1
(
E
B
=100 TeV and =300).
4.2 Summary of the generic 2000 point source quest
An analysis searching for point sources in the 2000 data, developed by adopting the blindness
requirement, as described in Ref.
19
, follows an earlier analysis with 1997 data
20
and shows a
Figure 6: AMANDAII sensitivity w.r.t. the declina
tion. Not only a quantitative improvement in compar
ison to AMANDAB10 but also a qualitative improve
ment on the near horizon sensitivity is achieved.
sources
declination
1997
2000
SS433
5.0
◦
0.7
M87
12.4
◦
17.0
1.0
Cas. A
58.8
◦
9.8
1.2
Cyg. X3
41.0
◦
4.9
3.5
Mrk501
39.8
◦
9.5
1.8
Mrk421
38.2
◦
11.2
3.5
Crab
22.0
◦
weiss
24
), for
m
χ
>
500 GeV. Once a few years of data taking have been cumulated, the WIMP
sensitivity is expected to explore the MSSM parameter space beyond the reach of the current
direct CDM search experiment. It must be stressed that nuclear recoil and indirect CDM search
experiments are not equivalent. In the case of an unevenly distributed CDM halo throughout
the galaxy, the latter have a detection potential which remains intact. Moreover, solar spin
dependant scattering cross section could significantly enhance the trapping rate of neutralinos.
5 Conclusions and perspectives
AMANDA is a neutrino telescope with sensitivity to diffuse fluxes in all three flavor channels,
in an energy range extending over 7 orders of magnitude (
∼
(10
12
,
10
19
)eV). It was shown that
AMANDAII exhibits a declination averaged sensitivity of Φ
1yr
ν
<
2
.
3
·
10
8
cm
2
s
1
, greatly
improved near the horizon compared to a previous analysis
20
. A search for a response of
AMANDAII to neutralino annihilation in the Sun is currently being conducted. A preliminary
limit was presented, which remarkably suggests that regions of the MSSM parameter space not
yet probed will be covered once a few years of data taking have been cumulated. The upgraded
AMANDAII ground hardware of 2003 now has a full digital readout, which allows for single
photoelectron resolution and should improve the capabilities of reconstruction for UHE events.
During the next pole season, the first Icecube
25
strings will be installed. The construction of
this cubic km neutrino telescope should be completed in 2010. In the time being, the data will
be gradually combined with that of AMANDAII, enabling more sensitive analyses and probing
the neutrino sky to higher energy.
Acknowledgments
We acknowledge the support of the following agencies: National Science Foundation–Office of Polar Programs,
National Science Foundation–Physics Division, University of Wisconsin Alumni Research Foundation, Depart
ment of Energy, and National Energy Research Scientific Computing Center (supported by the Office of Energy
Research of the Department of Energy), UCIrvine AENEAS Supercomputer Facility, USA; Swedish Research
Council, Swedish Polar Research Secretariat, and Knut and Alice Wallenberg Foundation, Sweden; German Min
istry for Education and Research, Deutsche Forschungsgemeinschaft (DFG), Germany; Fund for Scientific Re
search (FNRSFWO), Flanders Institute to encourage scientific and technological research in industry (IWT), and
Belgian Federal Office for Scientific, Technical and Cultural affairs (OSTC), Belgium; Fundaci´on Venezolana de
Promoci´on al Investigador (FVPI), Venezuela; D.F.C. acknowledges the support of the NSF CAREER program.
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