The EEE project

The physics and the detector

F.Riggi, for the EEE Collaboration

Department of Physics and Astronomy and INFN, Catania

Lisboa, September 9, 2006

● To involve high school teams (students and teachers) in an advanced research work, to allow young fellows to learn about high energy physics, its methods and research tools

● Build and install in a large number of high schools, over an extended area (in the order of 106 km2) a network of cosmic ray telescopes to investigate Extreme Energy Cosmic Ray Events

● Carry out extensive measurements of the muon flux and possible correlations between different telescopes

The idea behind the EEE project

Physics topics to investigate/1

● Local measurements, with a single telescope, may give information on atmospheric and solar events

Muon flux

Atm. pressure

Corrected flux

Diurnal and long-term variations of atmospheric pressure are anticorrelated with muon flux

Diurnal variations may be analyzed through harmonic dial analysis

Time correlation analysis of the muon flux exhibit periodic variations

Physics topics to investigate/1

Solar flares may produce strong variations of the cosmic flux (Forbush events)

A Forbush event during November 2004 as seen from neutron monitor stations and muon detectors

Correlation between 2 distant neutron monitors

An educational experiment with a small Geiger during the same event (Nov.2004). Not enough statistics with the Geiger. However a large area muon telescope could see such events.

1013 eV 1014 eV 1015 eV 1016 eV

COSMOS Simulations of proton-induced air showers in Catania metropolitan area

Physics topics to investigate/2

● Correlation between telescopes not too far away (i.e. in the same town) may allow the detection of extended showers initiated by high energy primaries.

3 km

2 high schools in Catania presently involved in EEE

INFN & Phys.Dept

Physics topics to investigate/3

● Correlations between far telescopes (hundreds km) will allow for further studies which go beyond the physics of single showers

Different mechanisms have been discussed to explain possible long-distance correlations between two showers:

● Photodisintegration of heavy primaries in the photon solar field

● Interaction of primaries with cosmic dust grains

● Correlated emission from single sources

Such correlations are actively searched for, with no clear results at the moment

The GZ effect

l

EarthSun

P(l, )

P’

r

CR

Photodisintegration event

Original paper: Gerasimova & Zatsepin(1960)

Recent references:

Medina-Tanco & Watson (1999)

Epele et al. (1999)

A heavy primary may interact with ~eV photons from solar radiation, with a mean free path

]cos1)['()(d

dd

)(

1

0

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l

.

( = angle between cosmic and photon)

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1)TK/exp(102.7

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mb)T'()'(

)T'(A45.1)'()'(

2220

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GR eee

eee

Black body radiation from Sun

Photodisintegration cross section

mbe~1

expe~S8

1A)'(

e

e<30 MeV

e>150 MeV

Approximated by a large number of dipoles located in the equatorial plane

Each fragment is then deflected by the solar magnetic field

The GZ effect: results within EEE

The fragmentation probability vs orientation

Evaluation of the yearly event rate over the EEE geographical area depend on several factors:

● Mass composition of high energy primaries

● Detailed acceptance of the array

● Trigger conditions on single showers

…

Contour lines of the fragmentation probability (**106) for He, O and Fe nuclei @1019 eV

The EEE project: requirements and solution

● Need for an extended array (over a large area, ~106 km2)

● Large number of telescopes (in the order of 100)

● Reasonable cost

● Long term operation required

● Efficiency close to 100 %

● Reconstruction of muon orientation -> at least 3 planes (position sensitive) with good granularity

● Good time resolution

CHOICE:

Telescopes based on Multigap Resistive Plate Chambers

The MRPC telescopes

● Each telescope is made by 3 MRPC modules, approx. 160 x 80 cm

● Gas mixture of Freon+SF6

● Special FE cards for readout and trigger

● DC/DC converters for HV (±10 kV) to chambers

● GPS time-stamp of the collected events

● VME-based data acquisition

● Each module provides a two-dimensional position information

● Efficiency close to 100% and excellent time resolution

● Good reconstruction of the muon orientation

Chambers under test @ CERN

Carbon layerMylar

glass

glass

glass

glass

glass

glass

Mylar

Carbon layer

Pick-up electrode

Gas gaps ~ 300 m

Pick-up electrode

Anode 0 V

Cathode -10 kV

(-2 kV)

(-4 kV)

(-6 kV)

(-8 kV)

Multi-gap Resistive Plate ChambersThe basic working principles

Developed by the ALICE TOF group, to achieve excellent time resolution (40 ps) and efficiency

Each MRPC is a stack of resistive plates, transparent to the avalanches generated inside the gas gaps.

The induced signal on ext.electrodes is the sum over all the gaps

Gas gaps 300 μm

Cathode (resistive layer –HV)

Vetronite panel

Vetronite panel

Mylar

Mylar

15 mm honeycomb

15 mm honeycomb

Glass plates

(1.1mm)

readout pads

Anode (resistive layer +HV)

readout pads

MRPC for the EEE telescopes

Fishing line is used to create uniform small gaps (300 microns) between glasses

A mixture of Freon + SF6 (95% + 5%) is normally used, with continuous flow in the order of 40 cc/min

Preliminary tests point out that the chambers may be operated even in static mode for long periods, with no dramatic worsening of the performance

The final design of the gas mixing station

Gas flow in the chambers

Several gas mixtures have been tried by the TOF group for optimal performances, without the need for flammable components

Front-End electronics

An ultra-fast and low power front-end amplifier/discriminator ASIC specifically designed for the MRPC is being used.

The detector is able to give 2-dimensional position information through individual (24) 2.5 cm strips with 7 mm spacing in one direction and right-left time comparison in the other direction.

90

cm

180 cm

This good space resolution can be achieved due to the low jitter electronics.No slewing corrections applied

FE cards (24 channels)

Tot. # of readout channels = 144

EventTime_1: Year, Day, s, ns EventTime_2: Year, Day, s, ns

GPS time stamping of events

Distant telescopes will be synchronized through GPS time stamping of individual events

Commercial GPS units are used for the first telescopes. Future installations could use integrated GPS cards

Trigger and data acquisition

VME Bridge

USB connection to PC

Trigger unit GPS Unit

144 channels TDC

VME crate

from FE cards

Acquisition and control software based on Labview is being exploited

Future developments will include integrated, low-cost electronics

MRPC Telescope

Data collection and distribution

GRID facilities will be used to distribute and share data and simulations

User-friendly Web interfaces will allow to search and retrieve data among different sites

Some of the involved sites will benefit from being a pole of the GRID network for LHC experiments

The acceptance depends on the assumed geometry (distance between chambers)

For typical distances in the order of 1 m

Acceptance

Frascati installation

Angular resolution: muon and shower reconstruction

Difference between generated and reconstructed muon zenithal angle (RMS ~0.3°)

Capability to reconstruct the shower axis direction with 3 non-aligned telescopes

~7°

~3°

A single muon

Average from 3 muons

The present status of the project:

installation of first telescopes and preliminary tests

Construction of chambers started in 2005 at CERN by teams including high-school teachers and students

More than 70 chambers built so far

First 7 telescopes sent out to italian sitesOn going installation and tests in progress

SC1

SC2

MRPC’s(CH1) AND (CH2) AND (CH3)

6-fold coincidence

(SC1) AND (SC2)

2-fold coincidence

(SC) AND (Chambers)

8-fold coincidence

Extensive tests of the chambers efficiency and response uniformity were carried out in several laboratories involving high school studentsCatania present

installation

Efficiency of the chambers

Efficiency vs HV

Sc

x

y

Probing the response uniformity

Catania set-up

0

10

20

30

40

50

60

70

80

90

100

14,0 15,0 16,0 17,0 18,0 19,0 20,0 21,0 22,0

HV (kV)

Eff

icie

ncy

(%

)

MRPC #15 MRPC #13 MRPC #19

without gas flow with gasMRPC#15 96,0% 96%

MRPC#13 94,4% 97%

MRPC#19 92,3% 96%

Tests carried out for about 3 weeks point out that chambers may be operated even without gas flow without large performance degrading

MRPC#15

0

10

20

30

40

50

60

70

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90

100

14 15 16 17 18 19 20 21 22

HV (KV)

Eff

icie

nc

y (

%)

gas off

gas on

Frascati set-up

About 1.7 % reduction in efficiency after ~ 3 days without gas flow

Catania set-up

Gas flow closed 70 hours later

Measure coordinate along strip by time difference from the two ends

With angle cut on the vertical orientations, extract position resolution:

(171 / 114)/√2 = 1.06 cm

Moving external trigger scintillators, extract time calibration: 114 ps/cm

Measurements and analysis carried out at CERN

GDG

Trigger UnitEVENT

InputGTS8000

Antenna GPS/A GPS/B

The GPS event time-stamp

Tests of the cross correlation between two independent GPS units

40 ns time resolution achieved in standard mode

Scatter plot of the geographical position over extended periods

Comparison between position information provided by 2 GPS

Checking fluctuations in position information over several days

A first physics measurement of the muon flux and atmospheric pressure

Muon count rate and atmospheric pressure monitored for a few days with one of the EEE telescopes in Catania (May 2006)

~ 7 x 107

events collected

Barometric coefficient ~ 0.13 %/mbar

Conclusions and outlook

Present status Preliminary set of EEE telescopes installed and tested

Time-scale: Before the end of 2006 EEE could start to collect first data Additional telescopes will be installed and tested

Technical developments: Upgrading of integrated electronics/acquisition Use of distributed computing for data access

Dissemination of results: Involvement of teams for measurements and analysis Remote access and distribution of data Physics results

Back-up slides

Background rejection in a single EEE telescope

MRPC background rate: 1-3 Hz/cm2 (13-40 KHz)

Spurious rate between 3 MRPC = 0.02 – 0.6 Hz

Expected muon count rate (1 m distance) = 30 Hz

Not negligible, but… 2 additional constraints:

-The 3 space points in the 3 MRPC must be aligned

- The time-of-flight between the chambers must fit muon speed and orientation

Background rejection between distant EEE telescopes

Single telescope rate: 36 Hz

Spurious rate between 2 telescopes ~ 1.3 x 10-3Δt (μs)

Time window Δt (μs)

Spurious rate between 3 telescopes (in 1 μs time window) = ~ 10-7 Hz (1 in 100 days)

Additional constraints on relative muon orientation (θrel <10°) reduce further ~2 orders of magnitudes

COSMOS Simulation Code

A Monte Carlo simulation code for the propagation of cosmic rays in the atmosphere and near Earth regions

COSMOS employs several nuclear interaction models