alba cappa universita’ and infn torino

Alba CappaUniversita’ and INFN Torino

Čerenkov Light Measurements for

the EUSO Experiment

Rencontres de Moriond – Very High Energy Phenomena in the UniverseLa Thuile, March 12-19, 2005

13/03/2005 Alba Cappa - Very High Energy Phenomena in the Universe

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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:

• 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 > 5×1019 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.

• do the GZK cut-off exist?


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The EUSO project

EUSO geometrical design

EUSO focal surface

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 it’s partially diffused.

image of a shower from a UHE primary on the EUSO focal surface: fluorescent and Cherenkov

signals.

Cherenkov signal


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ULTRA facility in the EUSO framework

reflection/diffusion coefficient

?

ULTRAUV 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

ULTRA: hybrid system

UVscope

ETscope

UV optical unit for Cherenkov light detection

EAS telescope, scintillator’s array

ETscope detector: characterization of the triggering EAS (shower size, arrival direction, core position) and comparison with the results of the simulations.

UVscope and ETscope work in coincidence to detect the EAS and the Cherenkov light generated and reflected/diffused back by the Earth surface.


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ETscope @ Mont Cenis 1970 m a.s.l. - 805

g/cm2

ETscope @ LPSC Grenoble

216 m a.s.l. - 990 g/cm2

The ULTRA setup

2003/2004 Experimental Setup 4+1 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.

L=54 m

ST3 ST4

ST1

ST5

ST2

B-UP B-DW


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Scintillator NE102A 80x80 cm2 x 4 cm

Expected Light Yield ~40 p.e./m.i.p.

2 PMTs High/Low GainHG 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

RECONSTRUCTIONarrival direction

() shower size Ne (Eo)

core position

The ETscope detector


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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

RECONSTRUCTIONof the internal events

shower size Ne (Eo) core position

resolution in the reco

very important also for the reconstruction of

the real datathe ones having the core inside the array: UVscope FOV is limited to the

dimensions of ETscope area


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SIMULATIONS (II)

= 0o , energy (eV) = 20o , energy (eV)5*1013 5*1013

1*1014 1*1014

3*1014 3*1014

5*1014 5*1014

1*1015 1*1015

3*1015 3*1015

5*1015 5*1015

1*1016 1*1016

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

EAS simulation: CORSIKA simulations of EAS with QGSJET hadronic interaction model:


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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 @ Grenoble, @ Mont-Cenis, @ Capo Granitola) .

From the simulations we can predict the detector side that is required to have the best measurement conditions @ the observation level of interest.

study of the effective area

optimization of the detector:

calculation of the threshold

energy

measurement of the expected counting rate


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Grenoble (winter 2004-05

campaign):

Mont-Cenis(2004

campaign):

Capo Granitola (spring-summer

2005 campaign):

SIMULATIONS (IV)

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

E(GeV) E(GeV)

Aeff(m

2)

Ain

t(m

2)

AeffA

E-γ(m

2)


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Čerenkov light measurement (I)

Tyvec Refecting-Diffusing Surface

2+2 optical units (Belenos-up & down) located near to the ETscope central station (1.5 cm Ø pmt + fresnel lens) / triggered by EAS events

FOV = 30obottom oriented

unit

top oriented unit

2004 CAMPAIGN

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.


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The ETscope data @ LPSC

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.

Measurement campaigns:• 2004 (Mont-Cenis, Grenoble)• winter 2004-2005 (Grenoble)

I will show the data analysis of the 2004 campaign @ Grenoble


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<Log10Ne>

5.25±0.02 5.65±0.04 6.26±0.20

< θ(°) >

23.1±0.411.6±0.716.7±3.2

LPSC size spectrum

Cherenkov light measurement (II)

green: trigger of central station + Belenos-upred: trigger of Belenos-down

LPSC zenith angle


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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.

Cherenkov light measurement (III)


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UP Oriented Unit (1) vs Event Number

UP Oriented Unit (2) vs Event Number

Twilight

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 t=17 h used to a very preliminary estimation on the reflected light.

-background level used-top/bottom units relative normalization applied

run no. event no. Log(size) (°) reflectivity %

130 17 5.8 26 23

134 53 6.9 28 22

compatible with tyvec reflectivity and detector acceptance


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CONCLUSIONS

2004 campaigns (Mont-Cenis @ 1970m asl, Grenoble @ 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 @ sea level- Sicily):• final measurements with UVscope;• direct Cherenkov light detection.

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