Performance of the Spaghetti Performance of the Spaghetti calorimeter with individual fibercalorimeter with individual fiber--readoutreadout
T.Matsumura, T.Tojo, T.Shinkawa (N.D.A.)T.Yamanaka (Osaka Univ.)Y.Kato, T.Sawada, T.Hotta (RCNP)H.Watanabe (KEK)R.Ogata, S.Suzuki, T.Shimogawa (Saga Univ.)Y.Tajima (Yamagata Univ.)
01 November, 2006Joint Meeting of Pacific Region Particle Physics Community
Contents • Introduction
KL rare-decay experiment at J-PARCSpaghetti calorimeter for the pre-shower detector
• Performance of prototype detectorBeam test with photon beamShower tracking
e+e- conversion-pointAngular resolution
KL rare-decay experiment
Purpose:Purpose: Search for new physics beyond the S.M.Search for new physics beyond the S.M.by measuring the Kby measuring the KLL→→ππ00νννν decay decay
Br (KKL L →→ ππ00νννν) ~) ~ (3.0 (3.0 ±± 0.6)0.6)××1010--1111 (S.M.)(S.M.)
KEK E391a KEK E391a Feb. 2004 - Dec. 2005•• establishing the experimental method establishing the experimental method •• update the upper limitupdate the upper limit
JJ--PARC PARC -- KKL L •• first observation of the first observation of the KKL L →→ ππ00νννν decay decay
Br (KKL L →→ ππ00νννν) <) < 2.12.1××1010--77 (current upper limit: KEK(current upper limit: KEK--E391a 2006)E391a 2006)
Basic design of the experiment
~ 15m~ 15m
Veto counter
End
cap
CsIDecay Region γ
KL
γν
ν
prepre--shower detectorshower detector• Signal identification
2γ + nothing
• Main backgroundKL → π0π0 → 4γ
limited constraint
• 2γ missing• 1γ missing + 2γ fusion
• Pre-shower detector2γ separationphoton directionKL→π0νν decay
Candidate of the pre-shower detector
SpaghettiSpaghetti--type calorimeter (SPACAL)type calorimeter (SPACAL)
can be obtained with the spaghetti calorimeter.
ScitillatingScitillating fibers and lead radiator fibers and lead radiator
grooved lead plate and fibersfiber diameter 1 mmφfiber interval 1.35 mm
Photon energy, direction, position
report of the KLOE experiment
By measuring the fibers individually,
Feature of the SPACAL (1)
2 photons Eγ1 = Eγ2 = 0.3 GeVR12 = 65 mm
y(m
m)
x(m
m)
z (mm)
z (mm)
Fiber-hit distribution
X X
X XY Y
Y
γ1γ2
γ1γ2
End
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CsI
End
-cap
CsI70 mm
70 mm
MC Demonstration(simple XYXY configuration)
Conversion efficiency~ 90 % with 3.2 X0
=5 cm thickness Compact
Energy resolutionσE/E = 2 % for Eγ=1 GeV
( 1.5 % for CsI only )
Photon separation efficiency~100 % for >20 mm distance
Eγ >0.1 GeV
Eγ = 1.00 GeVEγ = 0.50 GeVEγ = 0.25 GeVEγ = 0.10 GeV
num
ber o
f fib
er-h
its /
even
ts
Energy deposit in a fiber (MeV)
MIP(150 keV)
No ADC is needed for energy measurement. Simplification of the readout electronics
The distribution of the energy deposit does not change so much among the all different energies.
Feature of the SPACAL (2)
Photon energy can be estimatedby just counting the number of fibers
Performance of the prototype detector
Prototype Detector10 x10 x 9.7 cm3
fibers(5,850)
fibers(5,850)• trigger timing
• energy deposit 75 cm• shower profile
light guide
~ 6 X0
IIT-1
IIT-2
CCD
γPMT
Image IntensifierImage Intensifier (2 stages)• IIT-1: image reduction (1/16)• IIT-2: amplification(x106), gate (100μs)
CCD cameraCCD camera• 768(H) x 494(V), 30 flames/sec
IIT+CCD system
Fiber bundleTotal: 5850 fibers
bundle unit( 3 x 25 fibers)
photon beam
Prototype detector
Pictures
Image Intensifier
PMT
Setup of the beam test
•• Photon beam @ SPringPhoton beam @ SPring--88– Eγ : 1.5 ~ 3.0 GeV tagged photons
•• CollimatorCollimator (1 mm2 hole)– avoiding the image overlap
CollimatorCollimator1x1 mm1x1 mm22
PMTPMT
IIT+CCDIIT+CCD
SPACALSPACALprototypeprototype
active collimatoractive collimator5 5 mmmmφφ
ACAC
γγ beambeam
scintillatorscintillator
10 kHz10 kHz
•• TriggerTrigger– self trigger (Eγ > 300 MeV)– rate: 16 Hz
TOP VIEW
γ beamrearrangement
top
bottom
3x25 fibers
9.7 cm (~6X0)
10 c
m
IIT effective area (10cmφ)
Detector (side view) IIT surface
Fiber rearrangementto maximize the number of readout-fibers
Fiber bundle
CCD image is not directly related to the fiber position in the detector.
Typical image
Accumulated image
Dead regionX (pixel)
Y (p
ixel
)A shower event
A cosmic-ray event
Reconstruction of the cosmic-ray track
CCD coordinate detector coordinate
251 pixels fired 107 fibers fired
x (pixel)
y (p
ixel
)
z (mm)
y (m
m)
Note: flip vertical
Shower tracking
Eγ = 2.1 GeV, real data
z (mm)
y (m
m)
1. Remove the isolated clusters by requiring cluster-size cut (Nsize)
2. Fit a straight line to the weighted mean of the fiber-hits in each layer
3. Select only shower core-regionby applying the Δ cut
4. Estimate the conversion point (z0)from the most upstream fiber in the selected region
γ
Angle of incident photons was estimated by using information of fiber hits in the core region.
Typical shower events
Δ
z0
Effect of shower-core selection
Eγ ~ 2.1 GeV, Nsize≧4
Δ (mm)
σ θ(r
ad)
MCdata
less shower fluctuation
• By selecting the shower-core region the angle resolution would be improved
• The dependence was not so significant, but improvement (~20 %) was seen in both data and MC.
Δ ~ 8 mm is sufficient
Conversion Point
Eγ (GeV)
z0 (mm)
Eγ ~ 2.1 GeVReal data
ε( |
z 0-z
true|
< 4
mm
) Reconstruction Efficiency
• Vertex resolution in y at the conversionpoint was independent of energies
~ 0.7 mm
• Reconstruction efficiency (<4mm ) is more than 95 % above 1 GeV photons
• Reconstructed z0 distribution shows an exponential curve as we expected
Tight Nsize cut results in the worse efficiencydue to the suppression of the small clusters near the conversion point.
Nsize≧2Nsize≧4Nsize≧6
limited by the position resolution of the fiber hits
MC
even
ts /
bin
Tracking length (Lz)
Eγ ~ 2.1 GeV, Nsize≧4, Δ = 8 mm
σ θ(r
ad)
Lz (X0)
X0 = 16 mm
MCdata
Lz
Large Lz→ Entire shower information
Small Lz→ Only the information of the early stage
of the shower development
z0
Deterioration at very small Lz regionswas due to the limitation by the position resolution of the fiber hits.
minimum at ~2.5 X0
Length from conversion point (z0)for straight line fitting.
• Good agreement between data and MC
Energy dependence
Eγ (GeV)
Nsize≧4, Δ = 8 mm, Lz = 2.5X0
σ θ(r
ad)
MCdata
Data point ranges 1.5 ~ 2.8 GeV( tagged photon energy)
37 mrad @ 2 GeV
• Angular resolution
Nfiber VS Energy deposit
ADC (PMT)
Nfib
er
dE ~ 150 MeV CCD
γ
PMT
Eγ ~ 2.1 GeV
Number of fiber-hits and the energy deposit measured by PMT
Linear correlation
Energy deposit can be measuredby just counting the number of fiber
~ 6 X0
Future plans• Improvement of the sampling ratio
Present setup with round fibers : 12 %
with 1 mm2 square fiber : ~ 30% is possible
Study of the basic performance ofthe M-APD samples (JINR, Russia)has been started.
1 mm
• Study of devices for the fiber readout
Square fibers(1x1 mm2)
Summary
• A pre-shower detector with spaghetti-type calorimeter was studied for– better 2γ separation– photon direction measurement
• Prototype detector of the Spaghetti-type calorimeter was constructed and tested with the photon beam.– angular resolution : 37 mrad @ 2 GeV– position resolution : 0.7 mm (independent of energies)
• For the future plan– Improvement of the photon detection inefficiency– Development of the readout device (M-APD)
Backup Slides
Energy resolutionσ E
/E (%
)
SPACAL thickness (mm)
Eγ = 0.1 GeV
Eγ = 1.0 GeV
Assumption:CsI Npe = 10p.e./MeVSPACAL Npe = 30p.e./MeV
50 1000
X (pixel)
Y (pixel)
1 mm @ IIT entrance → 4.7 pixel @ CCD
2.2 pixels @ CCD (0.47 mm @IIT entrance)
Trigger counterScintillating fiberKuraray SCSF-78IIT
90Sr
Gain 5.0, gate width 100μs
50 cmcollimator
CCD
• Monte-Carlo (MC) simulationGeant4 + pixel simulation was developed.
• Performance (evaluated by the 90Sr bench test)
Efficiency (1 pixel found)90 % for MIP energy (0.15 MeV)
1 fiber is covered by ~ 5x5 pixelsResolution
Performance of the IIT-CCD system
Position resolution of the fiber hits
• position resolution of the IIT-CCD is σ ~ 2.2 pixel (= 0.47mm)
X (pixel)
Y (pixel)
the pixel hits could leak intothe next fiber region
The position resolution of fiber hitswas estimated by MC
σy = 0.6 ~ 0.9 mmσz = 0.45 ~ 0.7 mm
depending on the bundle units
Position distribution @ z0
Eγ ~ 1.5 GeV Eγ ~ 2.1 GeV Eγ ~ 2.8 GeV
y (mm) y (mm) y (mm)
Position resolution for y direction at z0 is independent of energy.~ 0.7 mm
Image to fiber-hits
1. For all fired pixels, determine the fiber cell which the pixel belongs to
2. Summing up the number of pixels containing fibers
3. Fiber position in the detector coordinate is assigned according to the fiber position map.
3x25 fiber cellscell size ~ 5x5 pixels