Status of Projectile Spectator Detector

A.Ivashkin

INR , Moscow

I. Introduction to PSD.

II. Design and readout.

III. Estimation of radiation dose. IV. Results of beam test of PSD prototype.

V. Comparision with simulation.

VI. Summary.

Very Forward Hadron Calorimeter

for detection of projectile spectators

PSD in CBM setup.

PSD

Experimental intention:

1. Measurement of centrality: b~ A - Nspect , selection of centrality at trigger level; 2. Measurement of event-by-event fluctuations to exclude the fluctuation of participants;3. Reconstruction of the reaction plane; 4. Monitor of beam intensity by detecting the neutrons from electromagnetic dissociation .

Schematic view of PSD configuration.

Low beam intensity. Detection of fragments. (25 modules)

Beam hole

Full beam intensity. Minimum 107 modules.

spectator spots at Z=15m Eau=15 AGeV

X

Z

Optional

Design and readout

Conception

Light readout – WLS-fibers for uniform light collection.

Signal readout – Micropixel APD (MAPD) to avoid nuclear counter

effect, detection of a few photons signal, compactness, low cost. Longitudinal segmentation – for permanent calibration of scintillators in radiation hard conditions, rejection of secondary particles.

Modular design – transverse uniformity of resolution, flexible geometry, simplicity.

Modular Lead/Scintillator sandwich compensating calorimeter. Sampling ratio Pb:Scint=4:1.

Expectation: For thickness δPb=16 mm and δScint=4 mm σE/E ~ 50%/√E .

Structure of PSD module.

• 6 WLS-fiber/MAPD.

• 10 MAPDs/module.

• 10 Amplifiers with gain~40.

• 60 lead/scintillator sandwiches.

• 10 longitudinal sections.

MAPDs and amplifiers.

Properties of selected MAPDs working in Geiger mode (deep micro-well type).

Active area: 3x3 mm2.

Number of pixels: 104/mm2.

Photon detection efficiency:~20%.

Gain: 5-6 x104.

Working voltage: 130-140V.

Production: Dubna-Mikron Co. (Z.Sadygov).

Pixel density is crucial for the calorimetry!

Linearity of MAPD response.

)1( totalN

PDEphotonsN

eNN totalfired

pixels

Depends on number of pixels

3x3 mm2 MAPD with pixel density 104/mm2 has a linear

response up to (1-2)x104 ph.el.

Dependence of signal width (σ2) on signal amplitude Nph.el. (both

in photoelectrons).

analytical formula

(σ2 ~ Nph.el. in linear case )

New generation of micropixel APD is produced by Zecotec.com (Singapore).

Number of pixel up to 40000/mm2. Gain ~ few x 105 . Single electron noise ~ 1 MHz/mm2 . Voltage < 100 V. Active area up to 5x5 mm2. High stability.

Radiation dose map for PSD.

~5 MRad/(12 months of CBM run)

Beam holeMagnet ON. Proton and

neutron spots are separated.Assuming 3x1014 events/year the flux ~ 1011 neutrons/cm2/year is

expected.

(~200 times less of CMS ECAL Hamamatsu 5x5 mm2 APDs )

Neutron flux at MAPD position(rear side of calorimeter).

UrQMD generator +GEANT3 of 104 Au-Au events at 25 GeV

~2 times light yield drop. No changes in uniformity

and resolution.

Fluka simulation with fragmentation is highly desired!

Radiation hardness test of MAPDs with 28 MeV positrons and flux 8x1010 /cm2 (PSI test-2006)

No significant changes in gain and PDE were found. Dark counts (noise) increased strongly.

Dubna MAPDsPSI-2006 test.

New MAPDs from Zecotek.com with dark current ~1 MHz/mm2 survived after one order more dose (PSI-2007 beam test, private communication). Results will be published soon.

28 MeV positron flux is equivalent to 20 times less flux of 1 MeV neutrons. MAPDs survive after dose ~3x1010 neutrons/cm2 (a few months of CBM run). Much better performance is expected.

Module assembling at INR.

PSD supermodule beam test at NA61 beam line (Sept. 27 – October 1, 2007)

Program of measurements:

-modules calibration with muon beam;

-study of the response and energy resolution

of the PSD on hadron beams 20, 30, 40, 80, 158 GeV/c;

-study of the PSD compesation;

-study of APDs long term stability

Calibration of modules by 75 GeV muon beam (response of each section in module)

Run 5362 mod 1

l.y~2ph.e/MeV

Deposited energy in 9 modules: simulation and experiment

Performance of calorimeter.

Energy spectrum in first section of module for mixed 30 GeV beam of pions, positrons and muons.

PID and rejection of secondary particles are possible.

muons

hadrons positrons

Energy resolution of 3x3 prototype: stochastic term ~ 55% constant term ~ 3.7%

Lateral shower leakage 16% is

introduced in parameterization*:stochastic term ~ 54% constant term ~ 1.9%

*NIM A308(1991)481-508

Energy resolution for 9 (3 x 3 area) modules (MC simulation GEANT3+Geisha)

σ(E)/(E) = 51.6%/√E(GeV) +3.2%

σ(E)/(E) = 48.7%/√E(GeV) +1.4%

+16%/ 4√E(GeV)

Shower leak

Rather good agreement with experiment

How is important the constant term in energy

resolution of PSD? • The PSD has very specific task of measurement of

many particles with the same energy.• The constant term in energy resolution is essential only

for energy measurement of single particle.• It is not important in case of measurement of total

energy from many particles with the same energy.• The reason is dependence of energy resolution for N

spectators as (1/sqrt(N)x(resolution for single particle):

1

1

1

12 )(1)()()(

E

E

NNE

EN

E

E

E

E

N

ii

N

N

Summary.• The prototype of modular longitudinally segmented PSD calorimeter

was developed and assembled. The readout is done by micropixel APDs working in Geiger mode.

• The prototype of 9 modules was tested in hadron beam at CERN.

• The possibility of PSD calibration with modules was demonstrated.

• Energy resolution was measured for 5 beam energies and equals to 54% (stochastic term) with constant term ~ 1.9%.

• The test of larger size prototype of 5x5 modules is planed.

• The measurement of transverse uniformity of energy resolution is requested.

• Radiation hardness of PSD modules and MAPDs need to be determined.

• Long-term stability and reliability of MAPDs are to be studied.

Thank you!