Endcap Disc DIRC for PANDA at FAIR Mustafa Schmidt, Klim Bigunenko, - - PowerPoint PPT Presentation
Endcap Disc DIRC for PANDA at FAIR Mustafa Schmidt, Klim Bigunenko, Michael D uren, Erik Etzelm uller, Klaus F ohl, Avetik Hayrapetyan, Oliver Merle, Julian Rieke on behalf of the PANDA Cherenkov Group FAIR 2015 - Novosibirsk, Russia
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Mustafa Schmidt, Klim Bigunenko, Michael D¨ uren, Erik Etzelm¨ uller, Klaus F¨
Julian Rieke
FAIR 2015 - Novosibirsk, Russia November, 2015
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Source: <http://www-panda.gsi.de> Mustafa Schmidt Disc DIRC 1 / 31
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Charged particles with speed higher than photon phase speed in medium emit Chrenkov light Equation of polar angle θC for Cherenkov light cone: cos θC = 1 n(λ)β with β =
0 /E 2
Cherenkov Angle θC: Number of photons per track length according to Frank-Tamm-Formula: dN dx = 2παz2
λ2
λ1
1
λ2 − 1 n2(λ)β2λ2
α ≈ 1/137 z: charge number of particle Refractive index n normally a function of wavelength λ (dispersion)
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Theoretical prediction for 100 π+ with momentum p = 4 GeV/c compared to simulated results with Geant4/PandaRoot Material thickness: ∆x = 2 cm
[nm] λ 300 400 500 600 700 800 ) [rad] λ (
C
θ 0.8 0.805 0.81 0.815 0.82 0.825 0.83 0.835 0.84 0.845 0.85
Cherenkov Angle
Simulated Results Theoretical Preditiction
Cherenkov Angle
[nm] λ 300 350 400 450 500 550 600 650 700 750 800 Entries 100 200 300 400 500 600
Number of photons
Simulated Results Theoretical Preditiction
Number of photons
Average photon amount per event: n = 1103 for λ = 300 . . . 800 nm
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Internal reflection of light inside radiator disk Cylindrical mirror on backside of focusing element for light focusing on readout plane Parallel photons focused on one spot Photons with different angles focused on different points
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Source: Merle, Oliver: Development, design and optimization of a novel Endcap DIRC for PANDA, Phd Thesis, JLU Giessen, 2015 Mustafa Schmidt Disc DIRC 6 / 31
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Collection efficiency approx. 30% (varying for different MCP-PMTs)
[nm] λ
300 400 500 600 700
#Efficiency [%]
5 10 15 20 25 MCP Efficiency
Product of quantum efficiency and collection efficiency equal to probability to detect photon (detection efficiency)
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integrated anode charge [mC/cm2]
2
10
3
10
4
10
quantum efficiency [%]
5 10 15 20 25
real PANDA time [a] 2 4 6 8 10
BINP #82 PHOTONIS XP85112 (9001223) BINP #1359 PHOTONIS XP85112 (9001332) BINP #3548
PHOTONIS XP85012 (9000296)
PHOTONIS XP85112 (9000897)
Source: Lehmann, A. et al.: Improved lifetime of microchannel-plate PMTs. Nucl. Instr. and Meth. A, (0):-, 2014. 127, 128, 129 Mustafa Schmidt Disc DIRC 8 / 31
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Separation power (π, K): ≥ 4σ Momentum coverage: 1.5 . . . 4 GeV/c Polar acceptance min/max: θx = 10◦, θy = 5◦ θx,y = 22◦ Detector lifetime: ≥ 10 years in duty cycles of 6 m/y Distance to intersection point: ≈ 194 cm in front of EM calorimeter Magnetic field: 0.5 . . . 1.3 T Energy deposit in radiator: ≈ 500 Gy for fused silica Energy deposit in optics: ≈ 10 Gy for fused silica Charged hadron flux: ≈ 100 Hz/cm2 (Ekin > 10 MeV)
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Calculation of required resolution for 4-σ-separation-power: σθC ≤ 1 4·
n
mπ
4 GeV
n
mK
4 GeV
2 3 4 5 6 7 8 9 10 π/K-separation [σ] 1 2 3 4 5 6 7 8 9 10 θ
c resolution per track [mrad]
2 G e V / c 3 G e V / c 4 G e V / c BaBar tracking error
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Photon trapping inside radiator due to internal reflection (approx. 70 % constant for θ > 10◦) Chromatic dispersion influencing photon resolution and time
tprop = s v = s c
dλ
I = I0 exp
−µ(λ)
roughness: I = I0 · RN with R = 1 − (4π cos θiRqn/λ)2 Losses in filter due to spin vector rotation in strong magnetic field (Faraday effect)
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Properties of chosen material: Large absorbtion length (less bulk losses) Small dispersion High radiation hardness Reasons for using fused silica: Already tested at BaBar DIRC High transmission for small wavelength Well understood technology Disadvantage: High production cost for polished radiator disk at large scale
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Cherenkov angle in fused silica:
1 2 3 4 5 6 p [GeV/c] 36 38 40 42 44 46 48 50 θ
c [◦]
e- pion kaon proton
Possible solutions for band width reduction: Higher photon statistics Reduction of wavelength acceptance (optical filter) Correction of dispersion by achromatic optics Correction by means of photons time of flight
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Transmission losses of fused silica after radiation with γ-dose of 100 krad:
Source: Hoek, M.: Tailoring the radiation hard ness of fused silica. Nucl. Instr. and Meth. A, 639(1):227 – 230,
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Testbeam at CERN in May 2015 with 3 FELs and 2 MCPs:
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Pixel distribution with Monte-Carlo data (green) and testbeam measurements (black) for polar angles. . . θ = 6◦ θ = 7◦
Source: Etzelm¨ uller, Erik: DIRC 2015 Mustafa Schmidt Disc DIRC 18 / 31
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Source: Etzelm¨ uller, Erik: DIRC 2015 Mustafa Schmidt Disc DIRC 19 / 31
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Angle Definitions: particle φrel αFEL Radiator Disk FEL Particle θc ϕ tan ϕ′ = tan ϕ tan αFEL ϕ′
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Calculation of the Cherenkov angle: θc = arccos(sin θp cos φrel cos ϕ + cos θp sin ϕ) (1) θp: θ angle of particle φrel: angular difference between φ angle of particle and photon ϕ: Angle between total reflected photon and radiator disk surface Calculation of ϕ if θc is known: cos ϕ = A cos θc B ±
B +
A cos θc
B
with A = sin θp cos φrel and B = A2 + cos2 θp
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Correlation between pixel number and angle ϕ′:
Pixel # 10 20 30 40 50 60 70 80 90 100 [rad] ϕ Angle 0.9 0.95 1 1.05 1.1 1.15 1.2
Fit Parameters 1.68377e-05 ± m = 0.00347196 0.000888066 ± b = 0.852934
_(FEL) α Calibration
tan ϕ = tan ϕ′ · tan αFEL
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Test simulations with new Disc DIRC prototype in Geant4:
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Testbeam simulations with 55% π+, 30% p, 5% K Beam momentum: p = 2 GeV/c (diameter: 2 cm uniform)
hist4 Entries 10000 Mean 44.26 RMS 2.778 [deg]
c
θ Reconstructed Cherenkov Angle 40 41 42 43 44 45 46 47 48 Entries 20 40 60 80 100 120 140 160 180 200 220 hist4 Entries 10000 Mean 44.26 RMS 2.778
Cherenkov Angle Distribution
Reconstruction results without removing outliers
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Calculation of separation power for p = 3 GeV/c: nσ = ¯ θc,π − ¯ θc,k
1 2(σ¯ θc,π + σ¯ θc,k) = 2.9
Probability for misidentification: Pmisid(nσ) = 1 2
2 · √ 2
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Input parameters:
Particle momentum vector p Particle angle and position (θp, φp, x, y) Hit pattern (zi, ti, sensor id) Mass hypotheses (mπ, mK, mp)
Calculation of all possible photon paths Computation of theoretical hit pattern and time of propagation Removing unwanted bhits with |z − zpred| < zthresh Matching of arrival times and removing of outliers: |t − tpred| < tthres Assuming gaussian probability density function and calculating pseudo likelihood function for each hypothesis: ln L =
N
[ln L(zi|zpred,i; σz) + ln L(ti|tpred,i; σt)]
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Particle: π+, momentum p = 4 GeV/c, polar angle θ = 10◦, azimuth angle φ = 0◦
Focusing Element 2 4 6 8 10 12 14 Pixel 10 20 30 40 50 60 70 80 90 100 Time of Arrival [ns] 3.5 3.6 3.7 3.8 3.9 4 4.1 4.2 4.3 4.4 4.5
Theoretical Hit Pattern
Focusing Element 2 4 6 8 10 12 14 Pixel 10 20 30 40 50 60 70 80 90 100 Time of Arrival [ns] 3.5 3.6 3.7 3.8 3.9 4 4.1 4.2 4.3 4.4 4.5
Simulated Hit Pattern
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Simulation parameters for final detector with TOFPET readout system: Material: Fused silica (definition of refractive index, absorption length and reyleigh length) Mirror coating
Type: Dielectric metal Gaussian scatter angle: 0.6 mrad Reflectivity: 85%
Time resolution (RMS): 21 ps TDC binning (LSB): 50 ps Pixel line height: 0.5 mm Surface roughness: 1.0 nm Track position error σx,y: 1.0 mm Track angular error σθp,φp : 1 mrad
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RMS values Misidentificaion for π and K
Source: Merle, Oliver: Development, design and optimization of a novel Endcap DIRC for PANDA, Phd Thesis, JLU Giessen, 2015 Mustafa Schmidt Disc DIRC 29 / 31
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Full simulation (Geant4/PandaRoot), reconstruction and PID algorithm available Disc DIRC prototype with 15 FELs development in progress Possibilities for testing in cosmics test stand at University of Giessen and test beam facilities (DESY, J¨ ulich, CERN etc.) Influences of magnetic fields have to be studied further Photon yields of simulation and measurement must be analyzed
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