1 Optical Properties of Cherenkov Radiators for the PANDA Barrel DIRC Roland Hohler, Klaus Peters, Georg Schepers, Carsten Schwarz, Jochen Schwiening GSI, Darmstadt Goethe Universität Frankfurt DPG spring meeting in Münster March 2011 Grzegorz Kalicy HK 27.2

2 PANDA antiProton ANihilations at DArmstadt Barrel DIRC Disc DIRC RICH ● Requirements : Good Particle Identification (PID) Excellent energy and angular resolution Nearly full solid angle coverage High rate capability (~20 MHz) Efficient event selection ● Particle Identification coverage of the ● both DIRC detectors: Endcap Disk DIRC (5 o – 22 o ) Barrel DIRC (22 o –140 o ) Grzegorz Kalicy, DPG Münster, March 2011 PANDA Detector at FAIR facility, GSI Darmstadt 2

3 DIRC Concept ● Detection of Internally Reflected Cherenkov ● light ● Charged particle traversing radiator (with ● refractive index n) with velocity: ● emits Cherenkov photons on cone with ● half opening angle: ● Magnitude of Cherenkov angle conserved during ● internal reflections. ● Photon detector array measures x, y and time of ● photons that exit radiator and defines θ c, φ c and ● time of propagation of individual Cherenkov ● photons. Detector Surface Fused Silica Radiator Particle Track Cherenkov Photon Trajectories Focusing Optics Grzegorz Kalicy, DPG Münster, March

4 Barrel DIRC fast focusing DIRC ● Inspired by BABAR-DIRC with important ● improvements ● Focusing optics: ● doublet lens system - remove bar size ● contribution from Cherenkov angle resolution term. ● New compact photon detectors: ● array of MCP-PMT - smaller expansion region, ● less sensitive to background. ● Fast photon detection: ● fast sensors and electronics – better time ● resolution, correction of chromatic dispersion (n(λ)). ● Still considering several design options ● (see talk HK 27.4) Radiator bars Photon detectors and electronics Focusing optics Barrel radius ~50 cm. 80 radiator bars, synthetic fused silica 17mm (T), 32mm (W), 2500mm (L). 30 cm depth oil-filled expansion volume. 10, ,000 channels of MCP-PMTs. Grzegorz Kalicy, DPG Münster, March

5 Radiator Quality Test Motivation ● Assumption: ● reflections, photons in UV range, single reflection ● probability of 99.9% needed to get transmission of 90% of ● photons (roughness: σ ≈ 10 – 15 Å). ● ● Mechanical tolerances: ● flatness, squareness, parallelism, optical finish, and sharp ● corners. ● Production: ● large pieces of fused silica, complicated processes. ● Bars used in BABAR-DIRC: ● polished to 5 Å rms, non-squareness < 0.25 mrad. ● PANDA DIRC shorter photon paths: ● can relax some of the specs. ● Test prototype bars from several vendors using different ● production methods. ● Perform quality assurance for full production. Grzegorz Kalicy, DPG Münster, March

6 Radiator Quality Test Motion-controlled scanning setup 1) Laser (405, 532, 635 nm) 2) Polarizer 3) Beam splitter 4) Diaphragm 5) Brewster mirror 6) Bar on x, y stage 7) Value Diode 8) Reference Diode Grzegorz Kalicy, DPG Münster, March

α a b ● Measurements at multiple laser ● wavelengths of transmitted intensity T ● (Normalization by reference intensity). ● Determine attenuation length Λ by ● aiming laser down length of bar. Radiator Quality Test Procedure 7 1) Laser (405, 532, 635 nm) 2) Polarizer 3) Beam splitter 4) Diaphragm 5) Brewster mirror 6) Bar on x, y stage 7) Value Diode 8) Reference Diode

8 bar ● Determine coefficient of total internal reflection R ● by bouncing laser off bar surfaces at Brewster angle. ● ● For 80 cm long bar 30/31 internal reflections ● from bar faces or 14/15 from bar sides. ● For 30 cm long bar 12 internal reflections ● from bar faces or 6 from bar sides. ● Calculate R from mean transmitted intensity T: ● Grzegorz Kalicy, DPG Münster, March 2011 Radiator Quality Test Procedure 8 Transmitted intensity T

9 ● Calculate surface roughness σ from R using ● scalar theory of scattering: ● Few Å uncertainty for bars with good surface finish. Systematics dominated by bar uniformity, mirror rotation, laser halo, diode uniformity. Proper cleaning important for results. Grzegorz Kalicy, DPG Münster, March 2011 bar 9 Radiator Quality Test Procedure

10 Radiator Quality Test Results Schott Lithotec, 80cm bar: Lytkarino LZOS, 30cm bar: Heraeus bar Grzegorz Kalicy, DPG Münster, March ● Results for Lithotec & ● Lytkarino bars consistent ● with the specifications. ● Pitch polishing - similar to ● method used in BABAR, is ● able to produce bars with ● very good surface polish. ● Heraeus extrusion method ● cannot reach requirements ● for optical properties of ● radiators (bar shape, ● surface roughness) ●

11 Summary & Outlook ● Motion-controlled setup to study optical ● properties of Cherenkov radiators for the ● PANDA Barrel DIRC and determine quality ● of surface finish with few Å accuracy. ● Tested prototype bars from several ● manufacturers. ● Measured internal reflection coefficients ● with multiple wavelengths → consistent ● with the scalar theory. ● Measured surface roughness in ● agreement with the specification. ● Improve automation and stability of the setup. ● Expand wavelength range using a UV-laser (266 nm). ● Testing bars from additional vendors (Zeiss, InSync Inc., etc). Grzegorz Kalicy, DPG Münster, March

12 Backu p Grzegorz Kalicy, DPG Münster, March

13 Grzegorz Kalicy, DPG Münster, March 2011 Antiprotons production FAIR Facility for Antiproton and Ion Research ● FAIR - Accelerator complex providing intense pulsed antiproton and ion beams ● HESR - High Energy Storage Ring ● High Resolution Mode: High Luminosity Mode: Stochastic & Electron Beam Cooling ● PANDA - Study of QCD with Antiprotons Charmonium Spectroscopy Search for Exotics Hadrons in Medium Nucleon Structure Hypernuclear Physics... and more 13

14 PANDA Physics Topics ● Charmonium Spectroscopy: Precision Spectroscopy Study of Confinement Potential Access to all these puzzling X, Y and Z ● Search for Exotics: Look for Glueballs and Hybrids Gluon rich environment → high discovery potential Disentangle Mixing via PWA ● Hadrons in Medium: Study in-medium modification of Hadrons ● Nucleon Structure: Generalized Parton Distribution Timelike Form Factor of the Proton Drell-Yan Process ● Hypernuclear Physics... and more Grzegorz Kalicy, DPG Münster, March