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Neutron Detector: INFN plans

CLAS12 Central Detector Meeting - Saclay 2-3 December 2009

Patrizia Rossi for the INFN groups:Genova, Laboratori Nazionali di Frascati, Roma Tor Vergata

SimulationsTiming Tests

LEAD

FIBERSd=1mm

Detector SimulationsA Spaghetti Calorimeter option has been extensively studied by the

INFN group with Monte Carlo simulations in order to determine: 1) Neutron detection efficiency 2) TOF resolution (for n- separation in the momentum range of interest)3) Angular resolution (for the definition of the neutron direction)

• Simulation done with FLUKA (KLOE)• Parallelepiped shape (12.15 x 60 x 9.6) cm• Beam to the longer side, and to fibers• 20 cells (5 x 4), each 2.43 x 2.4 cm (x,z)• each cell contains 360 fibers

beam

60 cm

y

z

x

9.6 cm

12.1

5 cm

Compared to Scintillator Barrel : Neutron Efficiency: spaghetti calorimeter ~30-40% more efficientAngular resolution: the two options give comparable resultsTOF resolution: the two options give comparable results

But spaghetti calorimeter:1) Too efficient for 2) Energy loss localized in few fibers

limitation for signal read-out

Option discarded

Background Simulations_1

ELECTROMAGNETIC BACKGROUND

We want to understand:• the actual rates seen by the CND, their energy

distribution etc.• the probability of such background to be reconstructed

as a “good neutron” event

1 event @ L=1033cm-

2s-1

Results:• The background consists of photons • The overall rate is 2 GHz at luminosity of 1035 • The maximum rate on a single paddle is 22 MHz

(1.5 for Edep>100KeV) • This background can be reconstructed as a

neutron: - using a 5 MeV energy threshold the resulting rate is

few KHz - the of this “fake”neutrons is <0.1-0.2

Simulation of the background were done with gemc

We can handle it0 0,2 0,4 0,5 0,6 0,7 0,8

- the actual contamination depends on the hadronic rate in the forward part of CLAS12 (@ 1 KHz the rate of fake events is 0.4 Hz)

Background Simulations_2PHYSICS BACKGROUND

First estimate of hadronic background based on clasDIS event generator (pythia)

Background events that could mimic a DVCS event are defined as:

Q2>1 GeV2

W>2 GeV one energetic photon (E>1 GeV) in forward direction one photon in the central detector MM(e) < 1.1 GeV

Estimated rate at full luminosity (1035 cm-2 s-1) ~ 5 Hz (with one photon in CD)

All event rate

e missing mass

We need to finalize nDVCS event generator

to estimate neutron rates

Timing Tests TOF resolution required to separate from n for neutron

momentums up 1 GeV/c ~100-120 ps

Constraints on photodetectors:

- Light collection in high magnetic field

- Limited space for signal read-out No space for light guides due to the presence of the CTOF light guides

Timing tests wil be performed in 2010 by the INFN groups using

different setup

Timing Tests

Scintillator type Readout BC-408 PMT H2431-50

BC-408 •SiPM 1x1 mm2/ 3x3 mm2/matrix 12x12

Fermilab estruded scintillators +1 WLS

•SiPM 1x1 mm2/ 3x3 mm2/matrix 12x12

Fermilab estruded scintillators > 1 WLS

•SiPM 1x1 mm2/ 3x3 mm2/matrix 12x12

BC-408: =380 cm ; decay constant=2.1 ns PMT H2431-50: rise time = 0.7 ns; transit time spread = 0.37 ns Acquisition: Full electronic chain discriminator+TDC

Electronics, redout, scintillators in Genova

Estruded scintillator + WLS

Redout

Timing Tests

PMT1 PMT2

PMT3 PMT4

PMT6PMT5

Cosmic ray

X1

X3

X5

(t1-t2)=(2x1-L)/v+c1-c2 (t1+t2)=2*t01+L/v+c1+c2 (t3-t4)=(2x3-L)/v+c3-c4 (t3+t4)=2*t03+L/v+c3+c4 (t5-t6)=(2x5-L)/v+c5-c6 (t5+t6)=2*t05+L/v+c5+c6

taking into account that: (x1+x5)=2*x3 or (t01+t05)=2*t03

(t1-t2)+(t5-t6)-2(t3-t4)=costant(t1+t2)+(t5+t6)-2(t3+t4)=costante

t1=t0+x/v+c1 t2=t0+(L-x)/v+c2

Spread of these quantities is a measurement of the timing resolution

SiPMSiPM Fermilab estruded scintillator

Conclusions

INFN groups of Genova, Laboratori di Frascati, Roma Tor Vergata are involved in the development of the central neutron detector

Simulations have been done to determine its characteristics (neutron detection efficiency, angular resolution, timing resolution..) as well as the e.m. and physics background

Timing tests are planned for 2010 using different scintillators and redout systems