Measurement of the neutron detection efficiency of the KLOE calorimeter

1
Measurement of the neutron detection efficiency
of the KLOE calorimeter

• P.Gauzzi
• (Universita La Sapienza e INFN Roma)
• for the KLONE Group

M.Anelli, G.Battistoni, S.Bertolucci, C.Bini,
P.Branchini, C.Curceanu, G.De Zorzi, A.Di
Domenico, B.Di Micco, A.Ferrari, S.Fiore, P.G.,
S.Giovannella,F.Happacher, M.Iliescu, M.Martini,
S.Miscetti, F.Nguyen, A.Passeri, A.Prokofiev,
P.Sala, B.Sciascia, F.Sirghi
10th ICATPP Conference October 8-12, 2007 Como
2
The KLOE calorimeter

• Pb - scintillating fiber sampling calorimeter of
  the KLOE experiment at
• DA?NE (LNF)
• 1 mm diameter sci.-fi. (Kuraray SCSF-81 and
  Pol.Hi.Tech 0046)
• Core polystyrene, r 1.050 g/cm3, n1.6, ?peak
  460 nm
• 0.5 mm groved lead foils
  
• LeadFiberGlue volume ratio 424810
• X0 1.6 cm ?5.3 g/cm3
• Calorimeter thickness 23 cm
• Total scintillator thickness 10 cm

3
The KLOE calorimeter

• Operated from 1999 to 2006 with good performance
• and high efficiency for electron and photon
• detection, and also good capability of
• p/?/e separation
• Energy resolution
• ?E/E5.7/?E(GeV)

(??KSKL KS?pp- KL?2p0)
4?
(see KLOE Collaboration, NIM A482 (2002),364)
4
Why neutrons at KLOE ?

• Detection of n of few to few hundreds of MeV is
  traditionally performed with organic
  scintillators (elastic scattering of n on H atoms
  produces protons detected by the scintillator
  itself)
• ? efficiency scales with thickness ?
  1/cm
• Use of high-Z material improves the neutron
  efficiency
• (see C.Birattari et al., NIM A297 (1990)
  and NIM A338 (1994)
• and also T.Baumann et al., NIM B192
  (2002))
• Preliminary estimate with KLOE data (n produced
  by K? interactions in the apparatus) showed a
  high efficiency (?40) for neutrons with
• Enlt 20 MeV, confirmed by the KLOE MC
• n detection is relevant for the DA?NE-2 program
  at LNF two proposals
• search for deeply bounded kaonic nuclei
  (AMADEUS)
• measurement of the neutron time-like form
  factors (DANTE)
• A test has been performed with the neutron beam
  of the The Svedberg Laboratory of Uppsala
  (October 2006 and June 2007)

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The neutron beam _at_ TSL

• Neutrons produced in the reaction 7Li(p,n)7Be
• Proton beam energy from 180 MeV to ?20 MeV
• Neutron energy spectrum peaked at max energy
• (at 180 MeV ? fp42 of n in the peak)
• Tail down to termal neutrons

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Experimental setup

• 1. Old KLOE prototype
• total length ?60 cm
• 3?5 cells (4.2 cm ? 4.2 cm)
• read out at both ends by
• Hamamatsu/Burle PMTs
• 2. Beam Position Monitor
• array of 7 scintillating counters
• 1 cm thickness
• Reference counter
• NE110 5 cm thick 10?20 cm2 area
• (in June 2007 ? two other NE110 counters 2.5
  cm thick)
• All mounted on a rotating frame allowing for
  vertical (data taking with n beam)
• and horizontal (for calibration with cosmic rays)
  positions

(3)
(2)
(1)
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Trigger DAQ

• Trigger
• No beam extraction signal available
• Scintillator trigger Side 1 Side 2 overlap
  coincidence
• Calorimeter trigger analog sum of the signals of
  the
• first 12 cells (4 planes out of 5) ? ?A?B
  overlap coincidence
• Trigger signal is phase locked with the RF signal
  (45 - 54 ns)
• DAQ
• Simplified version of the KLOE experiment DAQ
  system (VME standard)
• Max DAQ rate 1.7 kHz - Typical run 106 events
• For each configuration/energy scans with
  different trigger thresholds
• Three data-sets
• Epeak 180 MeV -- October 2006 - two weeks
• Epeak 46.5 MeV -- June 2007
• Epeak 21.8 MeV --

4 days
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Efficiency measurement

• Global efficiency measurement integrated over
  all the energy spectrum
• flive fraction of DAQ live time
• ? acceptance
• (assuming the beam fully contained in the
• calorimeter surface ? ? ? 1)
• Sizeable beam halo at low peak energy
• ? Rate(trigger) must be corrected

En 180 MeV
flive
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Neutron rate

• Absolute flux of neutrons measured after the
  collimator
• 2 monitors of beam intensity (see
  A.Prokofiev et al., PoS (FNDA2006) 016)
• Ionization Chamber Monitor (7 cm ?) online
  monitor, not position sensitive
• Thin-Film Breakdown Counter (1 cm ?) offline
  monitor used to calibrate the ICM by measuring
  the neutron flux at the collimator exit
• Rate(n) Rate(ICM) ? K ? pr2 / fp
• r collimator radius (1 cm)
• K calibration factor (TFBC to ICM)
• fp fraction of neutrons in the peak
• ? accuracy 10 at higher peak energy
  (180 MeV)
• 20 at lower peak energy
  (20 50 MeV)

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Scintillator calibration

• Trigger threshold calibration in MeV eq.el.en.

ADC counts
Events
? 6 counts/mV
ADC counts
Thr. mV
? source to set the energy scale in MeV
90Sr ?- endpoint 0.56 MeV 90Y ?- endpoint
2.28 MeV 25 keV/ADC count
Events
ADC counts
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Scintillator efficiency

• Check of the method and of the beam monitor
  accuracy

• Agrees with the thumb rule
• (1/cm) at thresholds above
• 2.5 MeV el.eq.en.

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Calorimeter calibration

• Cell response equalized MIP peak at ? 550 ADC
  counts
• Trigger threshold calibration

ADC counts
Events
? 6 counts/mV
ADC counts
Thr. mV

• Energy scale calibration with the
• MIP/MeV conversion factor from
• KLOE ( 1 MIP in one calorimeter
• cell ? 35 MeV eq. en.)
• (see KLOE Collaboration, NIM A354 (1995),352)

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Calorimeter efficiency

• Epeak 180 MeV

• Stable for different run conditions
• Very high efficiency w.r.t.
• the naive expectation
• ( 10 _at_ 2 MeV thr.)

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Energy spectrum from TOF

• Energy spectrum can be reconstructed from TOF

• Rephasing is needed, since the trigger is phase
  locked with the
• RF (45 ns period)
• From TOF ? ? spectrum of the neutrons
• Assuming the neutron mass ? kinetic energy
  spectrum

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Efficiency vs energy

• Fast MC to test the sensitivity of the time
  distribution to the shape of the
• efficiency curve
• Better agreement with an efficiency decreasing
  with energy
• Some discrepancy in the low energy part of the
  spectrum

e()
e()
Ekin(MeV)
Ekin(MeV)

• Data

• Data

MC
MC
Tcell(ns)
Tcell(ns)
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Low energy data

• In June 2007 we took data at lower peak energies
  21.8 and 46.5 MeV
• Large errors
• big uncertainty in the beam halo evaluation
• worse accuracy of the beam monitors
• Correction factor for beam halo ? 0.9 ? 0.1

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Calorimeter efficiency

• Very high efficiency at low threshold
• Agreement with the high energy measurements
• Correct. factor for beam halo ? 0.8 ?0.1

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MC simulation

• A detailed simulation of the calorimeter
• structure and of the beamline (source,
• collimator and concrete shielding) has
• been carried out with the FLUKA Code

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Preliminary results of MC
Some discrepancy in the low energy part of the
spectrum
?()

• No cut in released energy
• No trigger simulation
• ? Upper limit on ?

En (MeV)
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Conclusions

• The first measurement of the detection efficiency
  for neutrons of 20 - 180 MeV of a high sampling
  Pb-sci.fi. calorimeter has been performed at the
  The Svedberg Laboratory in Uppsala.
• Measurement of the n efficiency of a NE110
  scintillator
• agrees with published results in the same
  energy range.
• The calorimeter efficiency, integrated over the
  whole neutron energy spectrum, ranges between
  30-50 at the lowest trigger threshold.
• Study of the efficiency as a function of n energy
  is in progress.
• Full simulation with FLUKA is in progress.
• Further test foreseen for beginning 2008 at
  Louvain-la-Neuve
• (En 10 70 MeV larger interbunch time)

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Spares
22
Time structure
2.4 ms
4.2 ms
? 5 ns FWHM
41 ns
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Preliminary results of MC

• Simulated neutron beam Ekin 180 MeV
• Each primary neutron has a high
• probability to have elastic/inelastic
• scattering in Pb
• In average 5.4 secondaries per
• primary neutron are generated,counting only
  neutrons above
• 19.6 MeV.

Secondaries created in interactions of low energy
neutrons (below 19.6 MeV) are - in average
- 97.7 particles per primary neutron.
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Preliminary results of MC

• The enhancement of the efficiency appears to be
  due to the large inelastic
• production of neutrons in Pb.
• These secondary neutrons - are produced
  isotropically - are associated with a non
  negligible fraction of e.m. energy and of
  protons,
• which can be detected in the nearby
  fibers - have low energy and then have a large
  probability to do new interactions in the
  calorimeter with neutron/proton/? production.

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Beam halo

• TSL beam experts measured a sizeable beam halo at
  low peak energy (21.8 and 46.5 MeV)
• TFBC scan of the area near the collimator
• ? integrated flux over the ICM area ? 5
  of the core flux
• 
  (with large uncertainty)
• ? halo shape also measured
• Confirmed by our background counters
• Our calorimeter is larger than the projection of
  ICM area
• By integrating over the calorimeter we obtain an
  estimate of the halo contribution to the trigger
  rate of (20 ? 10)
• Only 10 on the reference scintillator due to the
  smaller area

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KLOE vs others

• Comparison with other
• calorimeters
• KLOE 23 cm thick
• Crystall Ball NaI 40.7 cm thick
• (NIMA462(2001),463)
• GRAAL BGO 24 cm thick
• (NIMA562(2006),85)