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Klaus Föhl, PANDA Cerenkov workshop in Glasgow, 11 May 2006
Disc DIRC
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• quick orientation for non-pandas• brief particle ID motivation• Cherenkov radiation flypast• lightguides and simulations• photo readout and B-field• Plexiglass?• Temperature!• ToP• Test Experiments ...
... the intended agenda ...
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the current GSI
Gesellschaft für Schwerionenforschung
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the new FAIR
SIS 100/300
Facility for Antiproton and Ion Research
planning as of 2004
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Antiprotons at FAIR
SIS 100/300
Panda
HESR
1 GeV/c – 15 GeV/c
planning as of 2004
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PANDA Side View
Pbar AND A AntiProton ANihilations at DArmstadt
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Particle ID in PANDA
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5 degrees
22 degrees
Particle ID in PANDA
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Particle ID & Kinematicspp KK T=5,10,15 GeV/c
pp DD D K T=6.6 GeV/c
pp i.e. charmonium production
need to measure two quantities:
dE/dxenergymomentumvelocitymomentum (tracking in magnetic field)velocity (Cherenkov Radiation)momentum (tracking in magnetic field)velocity (Cherenkov Radiation)
if mass known, particle identified
K K K
K evenor K
--
--
+ +
+ +
+ +
+ +
+ +
-
- +
+
distinguish and K (K and p) ...
D
For what channels do we not have this factor 2-3 reduction?
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Cerenkov Radiation
prism: correcting dispersionlens: turning angle into position
parallel light pathschromatic dispersion
=1
<1Cerenkov angle depends on particle speed the cone gives a ring image on a detector plane
material witha differentdispersion
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4-fold direction ambiguityangle and edges crucial
2-fold ambiguity in disc, lifted at readoutonly parallel surfaces required
DIRC: BaBar-type versus Disc
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conservingangles andcircles
90 degrees
45
Solid Angle onto flat surface
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conservingangles andcircles
90 degrees
45
Light transmitted in DISC
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conservingangles andcircles
90 degrees
45
Colour fringes on rings
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90 degrees
45
coordinates measured at rim
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90 degrees
45
3-prong event in DISC
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LiF
side view
front viewfused silica
LiF
polynomialcoefficients:c2= -3.0/(60^2)c3= -0.5/(60^3)c4= -0.1/(60^4)
focussing is better than 1mmover the entire linechosen as focal plane
side view
fused silica
completely within mediumall total reflectioncompact designall solid materialflat focal plane
DIRC Detector Idea
5cm
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Location Changes
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Location Changes
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Location Changes
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Lightguide-Designs
polynomialcoefficients:c2= -3.0/(60^2)c3= -0.5/(60^3)c4= -0.1/(60^4)
focussing is better than 1mmover the entire linechosen as focal plane
polynomialcoefficients:c2= -5.4/(60^2)c3= -0.9/(60^3)c4= -0.5/(60^4)
possibly difficult design requirements:1) vertical focal plane (normal to B-field)2) short focal plane (high dispersion deg/mm)
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Status of simple Disc Simulations– perfect surfaces– proper directions
• recent improvements– true 3D– analysis of pixel hits
• in the pipeline– angular straggling -important for (e,) and (,)– further optimising– include upstream tracking (necessary?)
• NOT:– no diffraction– no polarisation– no background (particles and photons)– no maximum likelihood analysis– not free of minor approximations (KISS)
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status of simulationsvertex providedposition providedall from DISC data
64 lightguides (no pixels) 128 (no pixels)
nondispersive materials
fluctuations numerical artefact- it’s on the “to do” list...
unpixelised focal planeno chromatic correction
REALLY
PRELIMIN
ARY
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• further optimisation
• resolution scaling with pixels
• resolution not scaling with pixel size
(momentum resolution) ~ (pixel number * quantum efficiency)4
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Yoke
Solenoid Housing
Solenoid and Yoke Environment
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Photon Detectors
• phototubes
• APDs
• channel plate phototubes
• optical fibres and external phototubes
• HPDs with magnetic imaging
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Position-sensitive Phototubes
H8500 H9500
R3292 10cm
B-field probably too strong
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Yoke
Light guide or fibre readout?
determination
determination
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HPD with magnetic imaging
Klaus Föhl 2-June-2004
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fusedsilica
E
BSilicon Strip Detector
e-
photocathode
HPD readout possible?
fused silica
EB
photocathode
Silicon Strip Detector
e-
possibly higherquantum efficiencyin reflectivephotocathodegeometry
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Temperature
• cold solenoid, cold EMC
• maybe coolde APDs
• SiO2, LiF different expansion coefficients
• dew, condensation on surfaces
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Yoke
Radiation Countermeasures?
what radiation fields?
do we need radiation shielding?
will PB act:--as absorber-or as converter?
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Plexiglass as Cerenkov radiator?
maybe not such a stupid idea
• transmission– SiO2 300-600nm N0/mm=14– plexi 400-600nm N0/mm= 7
• radiation hardness– BaBar “Spectrosil” proven– plexiglass “hamm wer doa” not proven
• but: radiation length X0 three times larger– 36cm versus 12cm (40.5g/cm2 vs 26g/cm2) more photons per X0
less chromatic dispersion no UV-grade material necessary (glass, glue, PMT)– focussing optics probably ok for thicker radiator– availability? time stability? radiation hardness?
higher lower dispersion
maybe not such a stupid idea
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Time-of-Propagationin a dispersive medium
fused silica (aka quartz)
2%
6%
Light propagation speed perpendicularto Cherenkov-light-emitting particle track:
=300nm photon is 6% slower than 600nm
larger Cherenkov angle – 2% shorter path
4% time difference (=600nm is “faster”) difference equivalent to =0.04
for 120cm radial distance ToP=8.3ns (400nm)
0.33 ns spread in arrival time
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ToP in DISC – some thoughs...
• chromatic time correction – do not see how (I see no space for red light to run extra length) (unless photon detector timing can be made colour-dependent)
• disc not self-timing “GPS altitude problem”• external time reference should be 100ps/sqrt(N)• if time reference from target vertex factor 2
betteroverall situation equivalent to 4.5 metres TOF • >>50*multiplicity pixels needed• multiple hits can be separated if spaced apart
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Towards Test Experiments
• Radiator slab (fused silica, plexiglass)
• Focussing lightguide– Edinburgh workshop:
• perspex: ok • quartz: we are happy to try (difficulties anticipated)
• photon readout
• DAQ
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Conclusions?
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Conclusions?
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Material Test
Testing transmission and total internal reflectionof a fused silica sample (G. Schepers and C. Schwarz, GSI)
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• FAIR international accelerator facility
• Particle ID – the physics requirements
• Cerenkov Radiation
• DIRC in PANDA
• Detector performance
• Conclusions and Outlook
Outline
working on Cerenkov detectors for PANDA:
Edinburgh, GSI, Erlangen, Gießen, Dubna, Jülich, Vienna, Cracow, Glasgow
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Pion-Kaon-Separation
K
K
K threshold
centrehole
figure of merit N = 152cmN(ideal) = N x 1cm x sin () = 82geometric transmittanceN(detected) = 82 x 0.61 = 50
02
-1
3
fused silica plate 10mm thickness(density 2.2g/cm thus 8% radiation length) detection efficiency 20% (=300-600nm)
0
64 segments in each with 48 rectangular pixels
overall 3072 pixels
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Conclusions
• optical properties of this design are good enough
• performance depends on number of pixels
• optical test bench
• phototubes + electronics
• operational detector slice
• testbeam experiments
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Side View
10mm fused silica plate (density 2.2g/cm , 8% radiation length)
plate radius 1500mm , detection plane radius 2000mmwavelength range 300-600nm, detection efficiency 20%figure of merit N = 152cmN(ideal) = N x 1cm x sin () = 82N(detected) = 82 x 0.61 = 50 geometry transmittance
0
02
-1
3
1500mm
2000mm
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Photon Lines in space
target
particlevertices
point
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Lensing
cylinder lense
N.B. to be comparedwith 10mm pixel height
spread over prism width
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Chromatic Correction
higherdispersionglass
spread =300nm to 600nm
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Lensing
cylinder lense
N.B. to be comparedwith 10mm pixel height
spread over prism width
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Chromatic Correction
higherdispersionglass
spread =300nm to 600nm
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Chromatic Correction
higherdispersionglass
effective pixel heightspread =300nm to 600nm
+
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Cherenkov radiation
wavefrontPoyn
ting
vect
orc
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Cherenkov radiationin a dispersive medium
wavefrontPoynt
ing
vect
orc
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Cherenkov radiationin a dispersive medium
fused silica (aka quartz)
2%
6%
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Momentum Thresholds
fused silica n=1.47
aerogel n=1.05
K
K p
p
total internal reflection limit
n=1.47
K p
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tracks in Solenoid field
solenoid field taken to be homogenous
within the real field shape the particlesare better aligned with the field lines
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fused silica
B. Morosov, P. Vlasov et al.December 2004
fused silica
LiF side view
front view
fused silica
LiF
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adjusting polynomial coefficients(c2 fixed, c3 and c4 so far used only)to find a mirror shape that providesoverall acceptable focussing alonga straight line (easier to instrument)
concurrent optimisation goals
minimise:• lensing errors• warping of focal plane
1.
2.
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conservingangles andcircles
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side view
fused silica polynomialcoefficients:c2= 1/1200c3= -0.5/(60^3)c4= -0.1/(60^4)
focussing is better than 1mmover the entire linechosen as focal plane
completely within mediumall total reflectioncompact designall solid materialflat focal plane
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Particle ID in PANDA
5 degrees
22 degrees
For particle ID, two quantities are required:dE/dxenergymomentum (tracking in magnetic field)velocity (Cherenkov Radiation)
If particle mass is known, the particle is identified.
For particle ID, two quantities are required:dE/dxenergymomentum (tracking in magnetic field)velocity (Cherenkov Radiation)
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briefly on Barrel-DIRC
time-of-propagation version
Klaus Föhl, FAIR-Panda-PID-meeting, 5/12/2005
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Cherenkov radiationin a dispersive medium
=0.95
=1
incident particleat 45 degrees
fused silica slab3m long
=600nm=300nm correction1=300nm=300nm correction2
=0.99
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Cherenkov radiationin a dispersive medium
fused silica (aka quartz)
2%
6%
reduce wavelength rangeto improve sensitivity
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dispersion correction
correction needs to cover entire angular range of incident particles
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dispersion correction
no correction improving over the entire angular range
![Page 67: Klaus Föhl, PANDA Cerenkov workshop in Glasgow, 11 May 2006 Disc DIRC](https://reader035.vdocuments.net/reader035/viewer/2022062409/5697bf8b1a28abf838c8b068/html5/thumbnails/67.jpg)
my conclusions Barrel-DIRC
• photon group velocity in dispersive medium
• photon detector number set by statistics
• dispersive correction not covering all relevant angles
• reference timing provided by first arriving photons
standard PMT timing is enoughconsider to cut out <400nm
photons/pixel << 1most stringent requirement
configuration angle-dependentuseless for the barrel
no external timing requiredto analyse barrel DIRC data