Transcript Document 7364459

Study of electron/hadron
discrimination with
the NEUCAL detector
M. Bongi (on behalf of R. D’Alessandro)
nTOF Collaboration Meeting – Athens
17th December 2009
The NEUCAL working group
O. Adriani1,2, L. Bonechi1,2, M. Bongi2, S. Bottai2,
M. Calamai4,2, G. Castellini3, R. D’Alessandro1,2,
M. Grandi2, P. Papini2,S. Ricciarini2,
G. Sguazzoni2, G. Sorichetti1, P. Sona1,2,
P. Spillantini1,2, E. Vannuccini2, A. Viciani2
1)
2)
3)
4)
University of Florence
INFN Section of Florence
IFAC – CNR, Florence
University of Siena
2
e/hadron discrimination in HEP
• Common requirement for HEP experiments
– particularly important for those devoted to Astroparticle Physics
• Electromagnetic calorimeters
– very good discrimination capability in a wide energy range
Two events detected by the PAMELA space experiment
SILICON
TRACKER
18 GeV/c
electron
36 GeV/c
proton
MAGNET
TRIG.
SCINTI.
E.M.
CALO
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The situation at high energy
• protons with energy beyond few hundreds GeV
interacting in the first layers of the calorimeter can
be tagged as electrons due to
– similar energy release
– similar shower development
• It is not possible, especially for space experiments,
to increase too much the calorimeter depth
– strong limitation in weight and power consumption
4
The use of a neutron counter in PAMELA
• Neutron production:
– Protons: hadronic interaction, nuclear excitation
– Electrons: only through the Giant Resonance
• Different yield in neutron production is expected for e.m. or
hadronic showers
• New idea in PAMELA: use a neutron counter as the final stage
of the apparatus (beyond calorimeter)
18 GeV/c
electron
36 GeV/c
proton
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Detection of neutrons produced inside the calorimeter:
the NEUCAL concept
PAMELA:
•
Moderation of neutrons by means of passive moderator (polyethylene layers)
•
3He
proportional tubes to absorb thermal neutrons and detect signals due to the
ionization of products inside gas:
n + 3He  3H + p (Q = 0.764 MeV)
New idea in NEUCAL:
• Study of the moderation phase using an active moderator
• Standard plastic scintillators are rich in hydrogen and thus suitable as
moderators (Eljen EJ-230  [CH2CH(C6H4CH3)]n )
• Detection of:
– signals due to neutron elastic/inelastic scattering
– signals due to absorption of neutrons
PMT or
3He (proportional tubes)
Si-PMT
n
SCINT
3He
tube
by
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Simulation of the detector
• First results based on FLUKA (now implementing GEANT4 simulation, too)
• Detector geometry has been dimensioned for application
together with a 30 X0 calorimeter (CALET experiment)
– NEUCAL is placed downstream a 30 X0 deep homogeneous BGO
calorimeter
11
scintillator
layers
BGO
tiles
30 X0
NEUCAL
3He
Tubes
(1 cm diam.)
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CALET FLUKA SIMULATION
1 TeV protons
400 GeV electrons
the average energy release of 1 TeV protons and 400 GeV electrons
in the calorimeter is almost the same
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Distribution of number of neutrons
1 TeV protons
400 GeV electrons
in case of hadronic showers the neutron yield is more than a factor 30 higher
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1 GeV
1 s
1 MeV
1 TeV protons
1 keV
Arrival time (Log(t(s)/1s)
arrival time vs neutron energy
100 ns
10 ns
Outgoing neutron energy Log (E(GeV)/1GeV)
 maximum in the MeV energy region (nuclear excitation)
 many neutrons undergo moderation before escaping, and their energy is degraded
 some neutrons are produced promptly in the hadronic interactions along the shower core
 the highest energy neutrons arrive close in time with respect to the charged component
of the shower, while the low energy component arrives with a delay which ranges from 10
to 1000 ns
10
11 cm of plastic scintillators
ENERGY RELEASE IN THE SCINTILLATORS
FLUKA based simulation,
Degree Thesis by
G. Sorichetti
Neutrons up to few
MeV kinetic energy
are
moderated
and detected with
high efficiency.
At 10 MeV 70% of
neutrons
gives
detectable signals.
Only 10% are fully
moderated to be
detectable by the
3He Tubes
1000 neutrons, E=100 keV
1H(n,)2H
E = 2.2 MeV
1000 neutrons, E=1 MeV
1000 neutrons, E=10 MeV
1000 neutrons, E=100 MeV
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Time distribution of signals in two scintillators
for 1000 neutrons, E=100 keV
radiative capture
of neutrons
+  emission
10 keV energy
threshold
10 μs
100 ns
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3He
Tubes: time distribution of the signals
1000 neutrons, E=100 keV
1000 neutrons, E=1 MeV
100 μs
1000 neutrons, E=10 MeV
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The prototype detector
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Production of scintillators
Scintillator material:
Dimensions: 8.5 cm×25 cm×1 cm
Eljen Technology, type EJ-230 (PVT, equivalent to BC-408)
Light guides: simple plexiglas
One side covered with aluminized tape
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Production of prototype detecting modules
PMT
Hamamatsu
R5946
Optical grease: Saint Gobain BC-630
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Production of the first module
3He
proportional counter tube: Canberra 12NH25/1
1 cm diameter
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Prototype assembly
3x3 matrix of scintillator modules + 5 3He proportional counter tubes
1 cm diameter
3He tubes
PMT
light guide
scintillator
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Test beam at CERN SPS (August 2009)
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Integration of the NEUCAL prototype with a 16 X0
tungsten calorimeter (25 July 2009)
CALORIMETER
NEUCAL
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CALORIMETER
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Beam test details
• CERN SPS, line H4 (one week test)
• Beam type - energy # of events:
–
–
–
–
Pions
electrons
electrons
muons
350 GeV
100 GeV
150 GeV
150 GeV
( 230000
( 240000
( 50000
(130000
events)
events)
events)
events)
• Data collected in different configurations
– scan of detector (beam impact point)
– different working parameters
• PMTs and tubes voltages
• Digitizer boards parameters (thresholds, data compression…)
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Detectors configuration
• Next slides report a comparison of data with GEANT4 simul. for
electron and pion events taken in the following configurations:
NEU
CAL
16 X0
W
CALO
ELECTRON
beam
Total thickness upstream NEUCAL: 16 X0
NEU
CAL
16 X0
W
CALO
PION
30
beam
Total thickness upstream NEUCAL: (16+13) X0
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How to find neutron signals?
• Digitalization of scint. output for a long time interval (1ms)
• Look for signals which are not in time with other signals on
other channels:
– Avoid the prompt signals due to charged particles coming directly from the shower
– Avoid single charged particles giving signals on more than one scintillator
Trigger
Prompt
signal
Scint.
Particle
signal
A
?
time
Particle
signal
Prompt
signal
Scint.
time
B
t=0
t10ns
t=1ms
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Digitalization of one muon event
Trigger signals
UPSTREAM
t ~700ns
1
2
3
t=0
4
5
Bounces are due to additional filters on
the digitizer inputs to solve a problem of
firmware (loss of fast signals)
DOWNSTREAM
Scintillators
3He tubes
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Digitalization of one electron event
Trigger signals
UPSTREAM
1
2
3
All signals rise at t = 0
(prompt shower secondaries)
4
DOWNSTREAM
Scintillators
5
3He tubes
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Digitalization of pion events (1)
Trigger signals
UPSTREAM
1
2
3
t ~34 s
4
5
t ~100 s
DOWNSTREAM
Scintillators
3He tubes
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Digitalization of pion events (2)
Trigger signals
UPSTREAM
1
2
t ~46.8s
t ~28.5s
4
3
5
t ~250s
DOWNSTREAM
Scintillators
3He tubes
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Digitalization of pion events (3)
Trigger signals
UPSTREAM
t ~14.6s
t ~170s
1
2
3
t ~250s
4
5
t ~12.6s
DOWNSTREAM
Scintillators
3He tubes
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Data/MC comparison: energy distribution in the scintillators
33000 ELECTRON events,
E=100 GeV
GEANT4
75000 PION events,
E=350 GeV
GEANT4
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Comparison data/MC: time distribution
33000 ELECTRON events,
E=100 GeV
GEANT4
75000 PION events,
E=350 GeV
GEANT4
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Test at nTOF facility
2 weeks at end of October
Many thanks to the nTOF Collaboration!!!
Proton beam
Neutrons
Target
Neucal
~ 200 meters
 Very intense p beam (20 GeV, 1012 p/spill)
 Neutrons are produced in the target with different energies
 Neutrons travel along the 200 m line
 The energy of the neutron is inferred from the arrival time on the Neucal detector
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Basic Idea
• Study the detector response to neutrons as a
function of the neutron energy
• By knowing the neutron spectrum (both in
shape and absolute normalization) we can
measure the neutron detection efficiency
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Signals on scintillators
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Signals on 3He
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Thank you for your invitation!
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