1. Università degli Studi di Milano Bicocca A RICH with Aerogel Davide L. Perego Roma - October 19 th 2004 On behalf of the LHCb Collaboration 2004 IEEE NSS/MIC/SNPS and RTSD N21 - High Energy Physics Detectors (IV)

2. Roma – October 19 th 2004 Outlook Davide L. Perego  LHCb: physics motivations and layout of the detector  Silica aerogel, the Cherenkov radiator for low momenta particles  Optical characterisation of aerogel Ageing effects Beam Test results  Study of the uniformity of the refractive index within an aerogel monolith  Summary Presented also at the Poster Session I N16-101

3. Roma – October 19 th 2004 RICH Detectors of LHCb Davide L. Perego YZ view B0→K+K-B0→K+K- s To cover the wide momentum range (2-150 GeV/c) 2 RICH detectors with 3 radiators are foreseen RICH 2 RICH 1 Detector acceptance 300 mrad (H) and 250 mrad (V)

4. Roma – October 19 th 2004 Silica Aerogel Davide L. Perego  Silica aerogel: very fragile linked network of SiO 2 nanocrystals  Tunable density (  ~0.15 g/cm 3 ) → tunable refractive index n  Hygroscopic (production: Boreskov Institute of Catalysis)  Tested tiles with dimensions 100×100×40 mm 3 (200×200×50 mm 3 now available)  Transmittance T( ) measured to extract the parameter A and the clarity C  A~0.95 and C~0.0050  m 4 /cm; refractive index n~1.03 (@ =632 nm)  Rayleigh scattering

5. Roma – October 19 th 2004 Ageing Effects Davide L. Perego  The particle flux in the aerogel region in LHCb will be ~3.5×10 12 particles/cm 2 /year  Aerogel tiles have been exposed to  ( 60 Co), proton and neutron (CERN PS)  A worsening in its optical properties is expected if hygroscopic aerogel is exposed to humid air  T, C and n were monitored wrt the increasing dose and humidity absorbed  Irradiation: no significant degradation of aerogel for fluences comparable with the LHC lifetime  Humidity: the optical properties are not irreversibly degraded, but can be restored by baking the tiles at ~500°C

6. Roma – October 19 th 2004 Beam Test Davide L. Perego HPDs Aerogel Mirror  Aerogel photons has been read by three HPD  Beam tested: pure  - and mixed  + /p (CERN PS) Results  Good  +/p separation, up to ~20  (10GeV/c)  Photoelectron yield ~10 p.e./particle (full circle) in agreement with expectations (HPD: see G. A. Rinella’s talk)

7. Roma – October 19 th 2004 Uniformity Studies (I) Davide L. Perego  Local inhomogeneities of  lead to point-to-point variations of n (n(  )=1+0.21  )  Stringent requirements on the uniformity of n within tiles:  (n-1)/(n-1)≤1% Laser beam method Assuming parallel faces for the tile, the deviation angle  is proportional to the refractive index gradients

8. Roma – October 19 th 2004 Uniformity Studies (II) Davide L. Perego Laser Aerogel CCD camera  (n-1)/(n-1)~1.3%  Fast feed-back  One wavelength at a time can be monitored Y

9. Roma – October 19 th 2004 Uniformity Studies (III) Davide L. Perego  Alternative method: use of a charged particle beam to exploit the Cherenkov effect itself  500 MeV electron beam at the DA  NE Beam Test Facility (LNF – Frascati)  Black & White photographic films used as photodetectors Aerogel Photographic Analysis by CHerenkov Emission (BTF: see B. Buonomo’s talk)

10. Aerogel ring N 2 ring + beam Roma – October 19 th 2004 Apache I Davide L. Perego Aerogel ring N 2 ring + beam  (n-1)/(n-1)=1% corresponds to  (R)=0.4 mm Apache resolution:  R~0.25 mm  Configuration: proximity focusing geometry  Aerogel placed on a platform inside a dark room fluxed with nitrogen  0.1 mm D263 filter downstream the aerogel (UV photons)  Kodak ® 8”×10” B&W photographic films Data

11. Roma – October 19 th 2004 Apache I Davide L. Perego  Digitization of the images by a scanner  Subtraction of background due to the processing procedure  Search for the center of gravity, then integration of the light intensity  Fit of the aerogel peaks with a gaussian function convoluted with the appropriate threshold response of the film to multiple photon hits on the same grain  Comparison of the positions of peaks to extract variations of the refractive index n  (R)~0.37 mm

12. Roma – October 19 th 2004 Apache II Davide L. Perego  The thickness of the aerogel: most limiting parameter of APACHE I  New geometry with a tilted spherical mirror and film outside the acceptance  No aerogel thickness effects thanks to focusing  Distortions of the ring due to the spherical aberration Film Mirror Aerogel holder

13. Mirror Aerogel e - beam Film Roma – October 19 th 2004 Apache II Davide L. Perego Aerogel ring N 2 ring Aerogel ring N 2 ring  Cherenkov ring width dominated by chromaticity n=n( )   (n-1)/(n-1)=1% →  (  C )=1.17 mrad Data

14. Roma – October 19 th 2004 Apache II Davide L. Perego  Many entrance points checked  Hit-by-hit retracking algorithm to build the distribution of the reconstructed  C angle  Resolution: ~0.3 mrad, including systematics The very promising results from the APACHE runs show that large size aerogel tiles now available comply with the homogeneity requirements of LHCb  (  C )~1.14 mrad

15. Roma – October 19 th 2004 Summary Davide L. Perego  Silica aerogel with unprecedented optical quality and large transverse dimensions have been produced and tested for LHCb  The aerogel has been successfully tested against high radiation doses  Beam tests have demonstrated the potential of aerogel as Cherenkov radiator up to 10 GeV/c  Required uniformity of the refractive index has been proved with a new method

16. Roma – October 19 th 2004 Backup Slides Davide L. Perego

17. Roma – October 19 th 2004 Hybrid Photo Diodes Davide L. Perego  Vacuum tube, diameter 80mm, height 120mm  S20 multialkali photocathode on the inner surface of the entrance window, 22-27% QE  Cross-focusing electron optics (~20KV), demagnification factor ~5  Photoelectrons focused on the anode assembly (16×16mm 2 ), fully encapsulated in the vacuum enclosure (HPD: see G. A. Rinella’s talk)