Klaus F öhl, PANDA Cerenkov workshop in Glasgow, 11 May 2006
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Transcript of Klaus F öhl, PANDA Cerenkov workshop in Glasgow, 11 May 2006
Klaus Föhl, PANDA Cerenkov workshop in Glasgow, 11 May 2006
Disc DIRC
• 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 ...
the current GSI
Gesellschaft für Schwerionenforschung
the new FAIR
SIS 100/300
Facility for Antiproton and Ion Research
planning as of 2004
Antiprotons at FAIR
SIS 100/300
Panda
HESR
1 GeV/c – 15 GeV/c
planning as of 2004
PANDA Side View
Pbar AND A AntiProton ANihilations at DArmstadt
Particle ID in PANDA
5 degrees
22 degrees
Particle ID in PANDA
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?
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
4-fold direction ambiguityangle and edges crucial
2-fold ambiguity in disc, lifted at readoutonly parallel surfaces required
DIRC: BaBar-type versus Disc
conservingangles andcircles
90 degrees
45
Solid Angle onto flat surface
conservingangles andcircles
90 degrees
45
Light transmitted in DISC
conservingangles andcircles
90 degrees
45
Colour fringes on rings
90 degrees
45
coordinates measured at rim
90 degrees
45
3-prong event in DISC
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
Location Changes
Location Changes
Location Changes
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)
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)
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
• further optimisation
• resolution scaling with pixels
• resolution not scaling with pixel size
(momentum resolution) ~ (pixel number * quantum efficiency)4
Yoke
Solenoid Housing
Solenoid and Yoke Environment
Photon Detectors
• phototubes
• APDs
• channel plate phototubes
• optical fibres and external phototubes
• HPDs with magnetic imaging
Position-sensitive Phototubes
H8500 H9500
R3292 10cm
B-field probably too strong
Yoke
Light guide or fibre readout?
determination
determination
HPD with magnetic imaging
Klaus Föhl 2-June-2004
fusedsilica
E
BSilicon Strip Detector
e-
photocathode
HPD readout possible?
fused silica
EB
photocathode
Silicon Strip Detector
e-
possibly higherquantum efficiencyin reflectivephotocathodegeometry
Temperature
• cold solenoid, cold EMC
• maybe coolde APDs
• SiO2, LiF different expansion coefficients
• dew, condensation on surfaces
Yoke
Radiation Countermeasures?
what radiation fields?
do we need radiation shielding?
will PB act:--as absorber-or as converter?
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
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
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
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
Conclusions?
Conclusions?
Material Test
Testing transmission and total internal reflectionof a fused silica sample (G. Schepers and C. Schwarz, GSI)
• 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
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
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
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
Photon Lines in space
target
particlevertices
point
Lensing
cylinder lense
N.B. to be comparedwith 10mm pixel height
spread over prism width
Chromatic Correction
higherdispersionglass
spread =300nm to 600nm
Lensing
cylinder lense
N.B. to be comparedwith 10mm pixel height
spread over prism width
Chromatic Correction
higherdispersionglass
spread =300nm to 600nm
Chromatic Correction
higherdispersionglass
effective pixel heightspread =300nm to 600nm
+
Cherenkov radiation
wavefrontPoyn
ting
vect
orc
Cherenkov radiationin a dispersive medium
wavefrontPoynt
ing
vect
orc
Cherenkov radiationin a dispersive medium
fused silica (aka quartz)
2%
6%
Momentum Thresholds
fused silica n=1.47
aerogel n=1.05
K
K p
p
total internal reflection limit
n=1.47
K p
tracks in Solenoid field
solenoid field taken to be homogenous
within the real field shape the particlesare better aligned with the field lines
fused silica
B. Morosov, P. Vlasov et al.December 2004
fused silica
LiF side view
front view
fused silica
LiF
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.
conservingangles andcircles
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
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)
briefly on Barrel-DIRC
time-of-propagation version
Klaus Föhl, FAIR-Panda-PID-meeting, 5/12/2005
Cherenkov radiationin a dispersive medium
=0.95
=1
incident particleat 45 degrees
fused silica slab3m long
=600nm=300nm correction1=300nm=300nm correction2
=0.99
Cherenkov radiationin a dispersive medium
fused silica (aka quartz)
2%
6%
reduce wavelength rangeto improve sensitivity
dispersion correction
correction needs to cover entire angular range of incident particles
dispersion correction
no correction improving over the entire angular range
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