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