1. Study of electron/hadron discrimination with the NEUCAL detector
M. Bongi (on behalf of R. D’Alessandro)
nTOF Collaboration Meeting – Athens
17th December 2009

2. 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
University of Florence
INFN Section of Florence
IFAC – CNR, Florence
University of Siena

3. 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
18 GeV/c
electron
36 GeV/c
proton
SILICON TRACKER
MAGNET
TRIG. SCINTI.
E.M. CALO 3

4. 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

5. 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 5

6. 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 = 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 by 3He (proportional tubes) n
PMT or
Si-PMT
SCINT
3He tube

7. 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.)

8. 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

9. Distribution of number of neutrons
400 GeV electrons
1 TeV protons
in case of hadronic showers the neutron yield is more than a factor 30 higher

10. arrival time vs neutron energy
1 TeV protons
1 keV
1 MeV
1 GeV
Arrival time (Log(t(s)/1s)
1 s
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

11. 11 cm of plastic scintillators
ENERGY RELEASE IN THE SCINTILLATORS
FLUKA based simulation,
Degree Thesis by
G. Sorichetti
1H(n,)2H
E = 2.2 MeV
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
1000 neutrons, E=1 MeV
1000 neutrons, E=10 MeV
1000 neutrons, E=100 MeV

12. Time distribution of signals in two scintillators
for 1000 neutrons, E=100 keV
radiative capture
of neutrons
+  emission
10 keV energy
threshold
100 ns
10 μs

13. 3He Tubes: time distribution of the signals
1000 neutrons, E=100 keV
1000 neutrons, E=1 MeV
1000 neutrons, E=10 MeV
100 μs

14. The prototype detector

15. Production of scintillators
Scintillator material:
Eljen Technology, type EJ (PVT, equivalent to BC-408)
Dimensions: 8.5 cm×25 cm×1 cm
Light guides: simple plexiglas
One side covered with aluminized tape

16. Production of prototype detecting modules
PMT
Hamamatsu R5946
Optical grease: Saint Gobain BC-630

17. Production of the first module
3He proportional counter tube: Canberra 12NH25/1
1 cm diameter

18. 3x3 matrix of scintillator modules + 5 3He proportional counter tubes
Prototype assembly
3x3 matrix of scintillator modules + 5 3He proportional counter tubes
1 cm diameter
3He tubes
PMT
light guide
scintillator

19. Test beam at CERN SPS (August 2009)

20. Integration of the NEUCAL prototype with a 16 X0 tungsten calorimeter (25 July 2009)

21. CALORIMETER

22. Beam test details CERN SPS, line H4 (one week test)
Beam type energy # of events:
Pions 350 GeV ( events)
electrons 100 GeV ( events)
electrons 150 GeV ( events)
muons 150 GeV ( 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…)

23. 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
beam
9 X0 Pb
2.25 X0
PbWO4`
30
Total thickness upstream NEUCAL: (16+13) X0

24. 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
Particle
signal ?
Scint. A
time
Prompt
signal
Particle
signal
Scint. B
time
t=0
t10ns
t=1ms

25. 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

26. Digitalization of one electron event
Trigger signals
UPSTREAM 1 2 3
All signals rise at t = 0
(prompt shower secondaries) 4 5
DOWNSTREAM
Scintillators
3He tubes

27. Digitalization of pion events (1)
Trigger signals
UPSTREAM 1 2 3
t ~34 s 4 5
t ~100 s
DOWNSTREAM
Scintillators
3He tubes

28. Digitalization of pion events (2)
Trigger signals
UPSTREAM 1 2 3
t ~46.8s
t ~28.5s 5 4
t ~250s
DOWNSTREAM
Scintillators
3He tubes

29. 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

30. Data/MC comparison: energy distribution in the scintillators
33000 ELECTRON events, E=100 GeV
GEANT4
PRELIMINARY
75000 PION events,
E=350 GeV
GEANT4
PRELIMINARY

31. Comparison data/MC: time distribution
33000 ELECTRON events, E=100 GeV
GEANT4
PRELIMINARY
75000 PION events,
E=350 GeV
GEANT4

32. Test at nTOF facility 2 weeks at end of October
Many thanks to the nTOF Collaboration!!!
Proton beam
Neutrons
Neucal
Target
~ 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

33. 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

34. Signals on scintillators

35. Signals on 3He

36. Thank you for your invitation!