Carla Distefano for the NEMO Collaboration

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Carla Distefanofor the NEMO Collaboration
VLVnT2 Catania 8 11 November 2005
Sensitivity and pointing accuracy of the NEMO km3
telescope
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Outline of the talk

• Simulation of the response of the NEMO-km3
  telescope to point-like sources
• Calculation of the detector sensitivity to
  point-like neutrino sources
• - Definition of the sensitivity
• - Background rejection and optimisation of event
  selection
• - Results.
• Simulation of the Moon shadow in the atmospheric
  muon flux
• - Measurement of the detector angular resolution
• - Check of the absolute pointing capability.

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Simulated NEMO-km3 detector

• Simulated Detector Geometry
• square array of 81 NEMO towers
• 140 m between each tower
• 18 stories for each tower
• vertical distance 40 m
• storey length 20 m
• 4 PMTs for each storey
• 5832 PMTs

D3500 m
CP site
- optical background 30 kHz - optical properties
of the NEMO site of Capo Passero - ANTARES s/w
tools used
PMT location and orientation
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Sensitivity to muon neutrino fluxes
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Detector sensitivity to neutrino fluxes

• Calculation of the sensitivity spectrum
• we simulate the expected background b (atm. ?
  and ?) and we estimate the 90 c.l. sensitivity
  in counts lt?90(b)gt (Feldman Cousins)
• we simulate a reference source spectrum
  (d??/d??)0 which produces ns counts
• we calculate the sensitivity spectrum as

- we apply an event selection in order to
minimize the sensitivity.
Feldman Cousins define the sensitivity as the
average upper limits for no true signal. It is
the maximum number of events that can be excluded
at a given confidence level.
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Event selection strategy

• quality cuts
• The used reconstruction algorithm is a robust
  track fitting procedure based on a maximization
  likelihood method. The reconstruction may give
  more than one possible solutions
• - ?gt ?cut ? ? - log(L)/NDOF0.1(Ncomp-1)
• log(L)/NDOF ? log-likelihood per degrees of
  freedom
• Ncomp ? total number of compatible solutions
  (within 1?)
• (see ANTARES documentation)
• energy cut
• - NfitgtNfitmin
  Nfit ? number of hits in the reconstructed event
• angular cut
• - rltrmin r ? angular distance from
  source position

The optimal values of ?cut, Nfitmin and rmin are
chosen minimizing the sensitivity spectrum.
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Generation of atmospheric muon events
The events are generated at the detector,
applying a weighted generation technique. We
simulate a broken power law spectrum (compromise
between the requirement of high statistics and
CPU time consumption)
Okada 1 year
X1 for E? lt 1 TeV Ngen 3107 events X3 for
E? gt 1 TeV Ngen 2.5107 events
Nrec ? 3.8106 reconstructed events tgen 3.65
days
Okada 1 year
The atmospheric muon events are weighted to the
Okada parameterization (Okada, 1994), taking into
account the depth of the NEMO Capo Passero site
and the flux variation inside the detector
sensitive height ( 900 m)
NOkada ? 4108 expected events/year
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Atmospheric muon background for a point-like
source
Distribution of equatorial coordinates of the
mis-reconstructed atmospheric muons. We can
project the sample of simulated events in a
single bin of RA centered in the source position.
Source declination ? - 60 our sample
corresponds to tgen ? 3 years
bin width 2
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Simulation of atmospheric neutrino background
We use the ANTARES event generation code
(weighted generation) We simulated a power law
interacting neutrino spectrum
X1 for 102 GeV lt E? lt 108 GeV Ngen 7109
interacting neutrinos 4? isotropic angular
distribution
Nrec ? 3.7105 reconstructed events
BartolRQPM 1 year
The atmospheric neutrino events are weighted to
the Bartol RQPM (highest prediction) flux
NBartolRQPM ? 4104 expected events/year
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Simulation of point-like neutrino sources
We use the ANTARES event generation code
(weighted generation) We simulated Ngen6108
interacting up-going neutrinos in the energy
range 102108 GeV with a generation spectral
index X1.
Source declination ? - 60 - 24 hours of
diurnal visibility - large up-going angular
range covered by the source (???24? 84?)
Nrec ? 2.5105 reconstructed events
Atm. bkg sample (1 deg) Neutrinos 842 Muons 13111
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Sensitivity to a point-like (? -60) neutrino
source
???(d??/d??)90 is expressed in GeV?-1/cm2 s
3 years of data taking
Search bin NEMO 0.3 IceCube 1
?2
IceCube sensitivity values from Ahrens et al.
Astrop. Phys. 20 (2004) 507
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Event detection for a point-like (? -60)
neutrino source
Energy spectra of reconstructed and selected
neutrino events (3 years) neutrino energy range
102-108 GeV
reconstruction selection
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Sensitivity to neutrinos from microquasars
Levinson and Waxman (2001) model predicts a E-2
neutrino flux in the energy range 1-100 TeV and a
total neutrino energy flux f?th We simulated
Ngen106 interacting up-going neutrinos in the
energy range 1-100 TeV with a generation spectral
index X1 We weighted the simulated events to
the theoretical flux f?th, counting N? 1yr events
in 1 year of data taking (in table N?exp refer to
?t days) We simulated 1 year atmospheric bkg b
and calculated the sensitivity as
Distefano et al., 2002.
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Sensitivity to neutrinos from microquasars (1
year)
Preliminary results
Average selection parameters ?cut -7.4
rmin0.5 deg

• Most ?QSO detectable in 1 year
• Expected improvement considering time correlation
  with source bursts.

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Detection of the Moon shadow
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Simulation of the Moon shadow
L. Ferrari, Diploma Thesis

• We simulated the lack of atmospheric muons in
  correspondence to the Moon disk
• Implemented the calculation of the Moon position
  in the atmospheric muon generation code (same as
  before).
• Restricted the muon generation in a circular
  window around the Moon position with radius R10
  (Ngen1.25 ?108).

Moon below the Horizon
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Observation of the Moon shadow
(1 year of data taking)
Event density
Event Selection Nhitmin 20 ?cut
-7.6 S1year5.5
k 659 8 deg-2 ? 0.19 0.02 deg
Minimum time needed for observation
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Study of the telescope absolute pointing
We introduce a rotation ? around the Z axis to
simulate a possible systematic error in the
absolute azimuthal orientation of tracks.
(1 year of data taking)

• for ? ? 0.2? (expected accuracy), the shadow is
  still observable at the Moon position
• for ? ? 0.2? (pessimistic case), systematic
  errors may be corrected
• the presence of possible systematic errors in
  the absolute zenithal orientation is still under
  analysis.

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Outlook
We simulated the proposed NEMO detector (9x9
array 5832 PMT and Capo Passero Site
environmental parameters) using the ANTARES
software tools. Detector Sensitivity to point
sources (3 years) NEMO (?2,102-108 GeV,
?-60) 1.710-9 E-2/(GeV cm2 s) search-bin 0.3
ICECUBE 2.410-9 search-bin 1 Most
?QSO detectable in 1 year 10-11 erg/(cm2
s) search-bin 0.5 ... This work is still under
development (higher atm. ?
statistics, improve selection criteria,
multi-muon events, time correlation with burst
events..) Diffuse fluxes is still under study
(higher statistics is required ) Pointing
Accuracy Detection of the Moon shadow in 100
days Estimated angular resolution 0.2
Absolute pointing can be recovered looking at the
Moon Shadow (multi-muon events,
improve analysis tools.)