1. Concept of NA62 IRC based on PWO scintillation crystals A.Fedorov, M. Korjik, A. Lobko Institute for Nuclear Problems, Minsk, Belarus A. Kourilin JINR, Dubna CERN, July 14, 2010

2. INP, Minsk is on the way to collaborate with NA62 Prof. Augusto CECCUCCI visited Minsk in spring 2010. A. Lobko and M. Korjik had a meeting with Prof. A. CECCUCCI at CERN R. Fantechi provided Minsk team with technical requirements on IRC and results of Monte Carlo simulations

3. Some IRC technical requirements 1.IRC is a detector located around the beam pipe with an inner radius of 7 cm and an outer radius of 14.5 cm. The longitudinal space allocated to it is 50 cm. 2.The integrated photon rate on all the IRC is 3.2 MHz. 3. The expected muon rate on the IRC is expected to be 4.7 MHz with a maximum intensity of 16 KHz/cm 2 and a total muon dose of 8 Gy/year.

4. Monte Carlo simulations (R. Fantechi ) Energy distribution of photons at the IRC

5. Monte Carlo simulations (R. Fantechi ) X-Y distribution of the photons at the IRC

6. PWO scintillation crystal PbWO 4 (PWO) scintillation crystals introduced by INP team in 1994 are currently used by CMS, ALICE, PANDA collaborations in EM calorimeters, about 100000 crystals (10 m 3 ) in total is produced. PWO properties O.V.Buyanov, R.Chipaux, A.A.Fyodorov, V.A.Kachanov, V.Yu.Khodyrev, M.V.Korzhik, J.L.Faure, J.P.Peigneux, M.Poulet, Yu.D.Prokoshkin, P.Rebourgeard, V.V.Rykalin, P.M.Shagin, P.A.Semenov, A.V.Singovsky, V.L.Solovianov. A first electromagnetic calorimeter prototype of PbWO 4 crystals. Nucl. Instr. Meth. A349(1994)62-69. Density, g/cm 3 8.28 Effective atomic number Z eff. 76 Moliere radius Rm, cm2.0 Radiation Length X 0, cm0.89 Decay time, ns10 Emission maximum, nm420 Optical attenuation length, cm>100 Index of refraction2.28 Light Yield, photons per MeV100-200

7. Monte Carlo simulations (INP) Electomagnetic shower profile along the crystal, E e- =100GeV PWO 2.9x2.9x22 cm 3 ( 1.5R M x 1.5R M x 25X 0 )

8. IRC PWO crystal geometry 1.22.5X 0 length of the detector is enough to absorb more than 95% energy of 70 GeV gammas. 2.Detector radius to be at least one R M larger than radius of the photons distribution at the IRC. r1=7cm r2=14.5сm r3=14.5cm + Rm=16.5cm

9. IRC PWO crystal geometry (proposal) 8 rings of crystals 40 crystals in each ring Gap between crystals 0.2 mm => 320 PWO crystals, 43.35 cm 3 each.

10. IRC PWO detector barrel 8 rings, 40 crystals in each To avoid “dead” 0.2 mm gap along the barrel rings can be rotated at small angle respective to each other

11. IRC PWO detector assembly We propose to use alveolas made of carbon fiber. Such are used in CMS and PANDA and can be produced in Russia or France. For easy mounting on the beam pipe we propose to use carbon fiber alveola “Dees”, 16 in total for the whole detector.

12. IRC PWO detector readout Hamamatsu APD (5x5mm 2 ) of CMS design can be used for readout. CMS bought of about 1000 extra APD to construct Barrel. Most of them are still stored in different Institutes of CMS Collaboration. APDs may be passed from CMS to NA62 by appropriate Agreement between Collaborations. Most probably one APD per crystal is enough for a veto detector, however more precise simulation is required. Front-End electronics of CMS design including preamplifiers does not meet requirements of IRC detector. A possible solution is to take as a basic design the design of PANDA ECAL. Front-End IRC electronics may include analog optical fiber link based on laser diode transmitter similar to one used in CMS Tracker.

13. IRC PWO specification General properties –Crystals dimensions have to conform to the drawing. Tolerances are -0.01cm. Crystals have to be oriented with their front face to the seed part of ingot. –The appearances of crystals (color, visible spatial and surface defects) have to conform to the coordinated reference crystal. Experiment has to be provided with the reference crystal for evaluation of the appearance. –The polished surfaces are polished with Ra  0.02 μm. –The surface finish of chamfers should be made at a roughness of not more than 0.5 μm (lapping).

14. IRC PWO cpecification Optical properties –Longitudinal transmission (absolute values) ≥ 45% at 360nm ≥ 60 % at 420nm ≥ 70 % at 620nm –Light yield ≥ 16 pe - / MeV at 20°C (bialkali PMT) –Decay time: LY(100ns)/LY(1000ns) > 90% at 20°C. Radiation hardness – Radiation hardness is evaluated by the measurement of the induced optical absorption in crystal along its axis. Induced absorption of the crystal transmission damage k ≤ 1.5 m -1 at 420nm lateral 60 Co irradiation, dose 3 krad, dose rate 5-50 krad/h

15. Cost consideration Crystals Possible price range is formed by two values: 1. 5.45 euro/cc -cc price at the delivery of the last batch of EndCap type crystals to PANDA Collaboration (April 2009); 2. 6.5 euro/cc -cc price asked by Producer for the restart of crystal production for PANDA in October 2010 (7000 crystals). Combining of the crystal ingot production for PANDA and IRC allows to reach similar to PANDA price even if amount to be needed to construct IRC will be relatively small ( ~300 cells). It is supposed that 7000 crystals will be produced for PANDA in November 2010 -- May 2011. To obtain similar price IRC crystals have to be ordered not later than March 2011.

16. Cost consideration Avalanche Photo Diodes –Use of the part of the spare Hamamatsu 5x5 mm 2 APD designed for CMS ECAL. CMS has around 1000 APD stored in some Institutes of Collaboration. A special agreement between CMS and NA 62 to borrow and to use these APD is required. –Joint PANDA to buy from Hamamatsu LAAPD (1cm 2 ). PANDA plans to have a deal in December 2010, expected price per unit is 200-250 euro per unit. –Direct ordering of APD from Hamamatsu. Expected price per unit of LAAPD is 300-400 euro for the amount ~300 units. WHY NOT TO TRY TO GET APD FOR FREE FROM CMS AS A TECHNICAL ASSISTANCE?

17. Research Institute for Nuclear Problems Commitments Adaptation of certification equipment to certify 320 PWO crystals for NA62 Experiment. Final mechanical treatment of crystals. Certification of crystals and forming of the data list. Forming of the data list for the rest of APD (CMS type) in Institutes and their preselection. Design of the carbon Dees for the crystals mounting. Participation in the detector assembling.

18. Cost estimation and delivery Price per cc 5.45-6.5 euro Price per crystal- 236-282 euro. Amount of crystals- 320 Net price - 75600-90240 euro Shipment - DDU CERN

19. Conclusion Production and certification of 320 crystals in October- November 2010 at the earliest, May 2011 at the latest. Crystal dimensions (and number of crystals) to be defined soon. In other respects PANDA PWO specification is suitable for NA62 IRC including radiation hardness.