1. ALICE-V0A design, construction & proto beam-test Arturo Menchaca-Rocha for UNAM: Instituto de Fisica & Instituto de Ciencias Nucleares CINVESTAV: Mexico & Merida Valparaiso, Chile, 2006

2. Outline Aim of V0 Design and construction details Performance and proto test results Radiation hardness of the components Final V0A construction Current status Timetable

3. V0 detector tasks V0 has to : Give a fast minimum bias trigger (MB) for both pp and heavy ion collisions Provide a fast veto for beam gas interactions (BG) during the pp running mode Provide a fast rough centrality trigger based on forward multiplicities Provide a fast estimation of the luminosity in the pp and heavy ion scenarios Provide a fast wake-up signal for the TRD

4. V0 is a small-angle detector made of two independent arrays of fast scintillator counters, named V0A and V0C V0A is being built by Mexican Institutes (UNAM+CINVESTAV) V0C is built by a French group at Lyon Each counter is segmented in 4 rings and each ring has 8 independent modules The counters are read by WLS/clear fibers coupled to PMTs working inside the ALICE magnetic field Brief description

5. Position of the V0 arrays V0C V0A 3.40 m 3.33 m 90 cm

6. Segmentation and dimensions

7. ►The V0 arrays cover the following η ranges: Pseudorapidity coverage  V0AV0C Ring 15.1/4.5-3.7/-3.2 Ring 24.5/3.9-3.2/-2.7 Ring 33.9/3.4-2.7/-2.2 Ring 43.4/2.8-2.2/-1.7

8. The two arrays have different designs but use the same materials: ► Plastic scintillator BC404 Width: V0A, 2.5 cm; V0C, 2cm ► 1mm diameter WLS BC9929AMC ► 1.1 mm diameter clear fiber BCF98MC of a few meters ► H6153-70 PMT The design of the V0 arrays

9. V0 triggers The system can generate twelve level 0 triggers: 6 of class AND (V0A and V0C) and 6 of class OR (V0A or V0C): one minimum bias trigger (MB), two beam-gas triggers (BG) three centrality triggers (only 2 sent to the CTP) Recorded information when L2 is supplied: for the events of interest and the (+5, -5) events around: charge seen by all segments (integrated charge) time of all segments (leading and tailing edges) statement of all flags for all segments for data control and monitoring: various parameters (not yet fully defined) Signals delivered to other detectors: wake-up for the TRD eventually, centrality information for the EMCal

10. MB and BG interactions toto t V0C <t o t V0C >t o t V0A >t o BG t V0A <t o BG

11. The basic idea of MB and BG triggers Set four independent observation windows Two at the expected time of arrival of particles produced in beam gas interactions: BGA centered @ - 11.3 ns BGC centered @ - 3.0 ns Two at the expected time of arrival of particles produced in pp collisions BBA centered @ + 11.3 ns BBC centered @ + 3.0 ns The first hit produces the window sub trigger Form logical combinations with them

12. BG interactions at next bunch crossing Interactions of gas with beam particles in the next bunch and the current bunch crossing will arrive at V0A (if happening in the RB24 side) at 25-11.3 ns = 13.7 ns, Depending on the BBA window size they may mimic particles produced at the IP in the current bunch crossing At the start of LHC this will not be a problem: next bunch will be 100 ns later, not 25 ns. 25 ns 11.3 ns13.7 ns V0A

13. Efficiency of the MB trigger in % ProcessBBABBCBBA or BBCBBA and BBC q q  qq 96.294.599.791.0 q g  q g 99.699.710099.4 g g   qq 100 g g  g g 99.9 10099.9 Non diffractive99.198.799.997.8 pp  pY 73.245.174.643.8 pp  Xp 39.270.071.437.8 pp  XY 68.065.186.246.8 Diffractive61.260.678.443.3 MB87.687.293.481.4 Parameters used: 6ns windows, 0.6ns V0 resolution, 7.5 cm RMS of bunch in z

14. Dependence on the size of the BBA window (2/2) ProcessBBABBCBBA or BBCBBA and BBC q q  qq 96.2 89.694.599.7 99.291.0 85.0 q g  q g 99.6 98.999.7100 99.4 98.7 g g   qq 100 g g  g g 99.9 99.299.9100 99.9 99.2 Non diffractive99.1 97.198.799.9 99.897.8 96.0 pp  pY 73.2 66.045.174.6 70.843.8 40.4 pp  Xp 39.2 33.670.071.4 71.137.8 32.5 pp  XY 68.0 59.165.186.2 83.946.8 40.3 Diffractive61.2 53.860.678.4 76.343.3 38.1 MB87.6 84.087.293.4 92.781.4 78.5 Parameters used: 1ns BBA window and V0A at 3.33 m Only a few percent loss in efficiency: the first hit produces the trigger. Inefficiency from low multiplicity events

15. V0 requirements ~ 100% efficiency for charged particles Time resolution < 1 ns. Aim is 600 ps. Provide L0 trigger information with no dead- time. Work in the magnetic field ( 0.5 T)

16. V0A Megatile design

17. Prototypes Prototype 3 Prototype 4 V0A Sector 0

18. 6 mm  = 1 mm 4 mm 25 mm 10 mm

21. Machining the final detector

22. Baseline of Construction 25 mm BC404 scintillator. 4 Rings, 8 Sectors in two halves (vertical split). Megatile construction: elements glued to each other with Bicron white epoxy (TiO 2 ). Keyhole slots for WLS fibers  = 1 mm, fiber exits 5 mm into the next ring and this part is covered with white paint. For the last ring the fibers exit straight. The WLS fibers are covered with Thermofit tubing when they exit the scintillator up to the PMT connector. The front and back faces are covered with reflecting Teflon, and then with black tape.

23. Gluing the sectors of the Megatile

24. Detector construction The two halves have been machined One of them is being tested with cosmics

25. Wavelength Shifting Fibers The WLS fibers have been polished and one end has been aluminized and covered with SiO 2.

27. Assembly of fibers in the detector

28. Mechanical support & PMT boxes The support boxes are half an Octagon of  = 1600 mm. Made out of 5 mm thick composite panels from Euro- composites. The inner hole is  =80 mm. The V0A counters are fixed to the panel that will be fixed to the support provided by the TC. The 8 boxes for the PMs will also be fixed to the same panel on the ribs along the perimeter that will serve to close the box. The lid will be screwed on the ribs and on the dead area of the V0A counters. The alignment to 1mm will be done on the feet of the support to the rails.

29. V0A array PM all fibres from a sector fibres gathered in 4 bundles fiber length 3 m

30. Front and lateral views

32. V0A support box Euro-Composites panels 3mm EC-PA 115G and EC-PA 119G EC-PA 119G Nomex® honeycomb core with epoxy/2S-UD-glass skins. Application: Aircraft flooring for under seat and aisle area, meeting the FAR 25853(a) requirements EC-PA 233 through EC-PA 238 Nomex® honeycomb core with different types and numbers of phenolic/glass skin layer. Application: Aircraft interiors where very stringent FST-requirements are obligatory. Above panel types meet ATS1000.001. EC-PA 323G to EC-PA 329G EC-PA 329G Nomex® honeycomb core with combined epoxy and phenolic skins, featuring the properties of both panel series EC-PA 1XX and EC-PA 2XX. These paneltypes excel in increased toughness combined with entire FST- properties

33. Beam tests The measurements were done using the Lyon Pad chamber and 4 scintillators in trigger using a blown up beam spot of 6 GeV/c negative hadrons from the PS T10 beam

34. Prototype 3 Amplitude Scan Top Amplitude nonuniformity of the order of +/- 5% both in vertical and horizontal The detector was moved with respect to the trigger counters to cover the top and bottom parts.

35. The amplitude nonuniformities are approximately the same in the top part Prototype 3 Amplitude Scan Bottom

36. Setup 3 Time distribution Top (Time ~0.6ns 0.54ns) Npe = 26  = 0.54 ns N pe = 26

37. Test Prototype 4 Tested at the PS 2 cm BC404 scintillator 1mm  WLS fibres BC9929A-MC 1.1 mm f 2 m long optical fibres BCF98-MC Hamamatsu H6153-70 PMT 500 – 600 ps MIP = 28 – 34 – 42 p.e.

38. First Test V0A Sector 0 with cosmics Ring 2

39. Time resolution corrected for trigger jitter 648 ps

40. Time resolution with 2m clear fibers

41. Test Ring0 with 75 cm WLS fibers only

42. Time distribution 75 cm WLS fibers only

43. Time resolution WLS only is 80% better

44. Radiation dose in 10 years of ALICE 20 100/200 50 10 60 20 6 10 V0C V0A Dose in krad

45. Irradiation of materials of the V0A A systematic measurement of the radiation effects on the materials of the V0A has been performed using the gamma cell of the ICN. –Detector prototype with scintillator and WLS fibers, characterized with a 90 Sr source and PMT. –WLS fibers only, characterized with a blue LED and a PIN-Diode measuring the produced and transmitted green light.

46. 46 Detector Prototype Results after Irradiation with 200 Krad. The signal after irradiation drops to 56% and recovers to 80 % Of the original in 350 hours.

47. WLS fiber irradiation The fiber: 30 cm long,1 mm Ø BCF9929A(double cladding) WLS fiber. Setup: On one extreme the fiber is excited from the side with a blue LED on the other a PIN-Diode measures the transmitted green light and the voltage is recorded with a precision electrometer. The reference is the average of 50 measurements of the voltage before irradiation, removing and re-inserting the fiber in the setup. The fiber was irradiated with a dose over 50 minutes of 50, 100, 200, 300 Krad of  ‘s from 60 Co source with 7 krad/min. The fiber is inserted in the measuring setup and the voltage is recorded every 30 min, 10 min after the irradiation ended.

48. white – 50 krad green – 100 krad red – 200 krad blue – 300 krad Relative amplitude referred to the corresponding mean value measured before irradiation All of the samples irradiated at the same dose rate: 7 krad/min

49. Consequences for V0A A maximal dose of 150 Krad in 10 years is calculated for Ring 0 of V0A. A loss of signal of < 20% can be expected, which can be recovered by a voltage increase. Just in case, 2 sets of fibers for Ring 0 will be prepared as spares and can easily be exchanged.

50. Current status V0A detector construction finished Will be tested with cosmics till March In April will be sent to CERN In May-June 2007 it’ll be calibrated with 7 GeV/c pions at CERN On 27 de June 2007 will be installed on ALICE On October 2007: data taking