Diapositiva 1

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Cerenkov Light Measurements for the EUSO
Experiment
Alba Cappa Universita and INFN Torino
Rencontres de Moriond Very High Energy
Phenomena in the Universe La Thuile, March 12-19,
2005
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CONTENTS

• the ULTRA experiment for EUSO
• the ULTRA detector
• simulated and collected data
• data analysis
• conclusions

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EUSO an UHECRs observatory
UHECRs spectrum
EUSO will provide to solve some problems of
Fundamental Physics and HE astrophysics

• do the GZK cut-off exist?

• investigation of the highest energy processes
  in the Universe through the detection and
  investigation of the Extreme Energy component of
  the cosmic radiation (EECRs / UHECRs with E gt
  51019 eV)
• arrival direction and small-scale clustering
  will provide informations on the origin of EECRs
  and magnetic fields
• HE neutrino astronomy will probe the boundaries
  of the extreme Universe and the nature and
  distribution of EECRs sources.

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The EUSO project
EUSO will look downwards to the Earth
atmosphere. It will see the fluorescent UV traces
isotropically produced by the charged secondary
particles along the EAS development. EUSO will
detect also the Cherenkov light emitted in a
narrow cone centered on the shower axis and
hitting the Earth surface, where its partially
diffused.
EUSO geometrical design
Cherenkov signal
image of a shower from a UHE primary on the EUSO
focal surface fluorescent and Cherenkov signals.
EUSO focal surface
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ULTRA facility in the EUSO framework
?
reflection/diffusion coefficient
ULTRA
UV Light Transmission and Reflection in the
Atmosphere
ULTRA goals measurement of the EAS
characteristics and associated Cherenkov light
diffused by various surfaces.
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ULTRA a supporting activity for the EUSO project
UVscope
UV optical unit for Cherenkov light detection
ULTRA hybrid system
ETscope
EAS telescope, scintillators array
UVscope and ETscope work in coincidence to detect
the EAS and the Cherenkov light generated and
reflected/diffused back by the Earth surface.
ETscope detector characterization of the
triggering EAS (shower size, arrival direction,
core position) and comparison with the results of
the simulations.
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The ULTRA setup

• 2003/2004 Experimental Setup
• 41 counting stations
• distance between modules 35/54 m
• standard NIM CAMAC electronics / ACQ by Labview
• 4-fold coincidence 150 ns
• threshold 0.3 VEM
• 2 couples of Belenos (Cherenkov light
  detectors) near to the central station, pointing
  to zenith and nadir.

ETscope _at_ LPSC Grenoble 216 m a.s.l. - 990 g/cm2
ETscope _at_ Mont Cenis 1970 m a.s.l. - 805 g/cm2
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The ETscope detector
Scintillator NE102A 80x80 cm2 x 4 cm Expected
Light Yield 40 p.e./m.i.p. 2 PMTs High/Low
Gain HG pmt Saturation 40 VEM / 0.64 m2 LG pmt
Saturation 400 VEM / 0.64 m2

• Procedures for the triggering events
• event by event for each station the following
  characteristics are known
• arrival time
• deposited energy in the scintillator (number of
  VEMs)
• position of the detectors

arrival direction (q,f) shower size Ne (Eo)
core position
RECONSTRUCTION
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SIMULATIONS (I)

• Procedures for the simulated events
• event by event for each station the following
  characteristics are known
• deposited energy in the scintillator (number of
  VEMs)
• position of the detectors
• true values for size and core position

shower size Ne (Eo) core position resolution in
the reco
RECONSTRUCTION of the internal events
very important also for the reconstruction of the
real data
the ones having the core inside the array
UVscope FOV is limited to the dimensions of
ETscope area
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SIMULATIONS (II)
EAS simulation CORSIKA simulations of EAS with
QGSJET hadronic interaction model

• primary particles type protons
• 2000 events for each energy and primary
  inclination
• two observation levels 0m asl, 2000m asl.

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SIMULATIONS (III)
detector simulation a Monte Carlo program
simulate the detector response to the showers
generated by CORSIKA, for different geometrical
configurations (the experimental conditions used
in the measurement campaigns _at_ Grenoble, _at_
Mont-Cenis, _at_ Capo Granitola) .
optimization of the detector
study of the effective area
calculation of the threshold energy
measurement of the expected counting rate
From the simulations we can predict the detector
side that is required to have the best
measurement conditions _at_ the observation level of
interest.
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SIMULATIONS (IV)
E(GeV)
E(GeV)

• Some results for
• effective area for internal events
• effective area
• convolution between the effective area and the
  CR spectrum

Aint(m2)
Aeff(m2)
Capo Granitola (spring-summer 2005 campaign)
Grenoble (winter 2004-05 campaign)
Mont-Cenis (2004 campaign)
AeffAE-?(m2)
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Cerenkov light measurement (I)
in this measurement campaign, we are interested
to the detect em component in coincidence with
diffused Cherenkov light. For this reason (and
due to high beckground in Grenoble), we used a
surface with a very high reflectivity coefficient.
2004 CAMPAIGN
top oriented unit
Tyvec Refecting-Diffusing Surface
22 optical units (Belenos-up down) located
near to the ETscope central station (1.5 cm Ø pmt
fresnel lens) / triggered by EAS events
FOV 30o
bottom oriented unit
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The ETscope data _at_ LPSC

• Measurement campaigns
• 2004 (Mont-Cenis, Grenoble)
• winter 2004-2005 (Grenoble)
• I will show the data analysis of the 2004
  campaign _at_ Grenoble

937 events collected in 38.4 hours TRIGGER
CONDITIONS Data selected requiring the
triggering of the central detector and the
Belenos-up or the Belenos-down. Requiring a
signal over threshold on the Belenos-up high
energy shower are selected, and even higher
requiring the Belenos-down.
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Cherenkov light measurement (II)
green trigger of central station
Belenos-up red trigger of Belenos-down
LPSC size spectrum
ltLog10Negt 5.250.02 5.650.04 6.260.20
LPSC zenith angle
lt ?() gt 23.10.4 11.60.7 16.73.2
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Cherenkov light measurement (III)
blue points Cherenkov l.d.f. obtained from
events with core located within 20 meters to
central station (absolute single-pe calibration
used) background level 3000 photons /(m2 ns
sr) (10 x Mont-Cenis background) green line
CORSIKA Simulation for 1016 eV proton, with
wavelength in 300-400 nm band.
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Cherenkov light measurement (IV)
The signal measured by the Belenos-up shows the
excellent correlation between the two detectors.
Yellow points are the twilight, well visible at
the end of two measurement nights.
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Reflection coefficient measurement

• Data May-June 2004, 6 events selected
• Due to low ADC gain and wrong ADC calibration in
  May only June data are available 2 surviving
  events in Dt17 h used to a very preliminary
  estimation on the reflected light.
• background level used
• top/bottom units relative normalization applied

compatible with tyvec reflectivity and detector
acceptance
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CONCLUSIONS

• 2004 campaigns (Mont-Cenis _at_ 1970m asl, Grenoble
  _at_ 200m asl), measured
• em component
• direct Cherenkov light
• 2 events of diffuse Cherenkov light
• background evaluation
• winter 2004-2005 (Grenoble)
• more statistics, analysis of the events is
  still in progress
• UVscope characterization
• spring/summer 2005 (Capo Granitola _at_ sea level-
  Sicily)
• final measurements with UVscope
• direct Cherenkov light detection.