Apollo Go, NCU Taiwan

1. BES III Luminosity Monitor Apollo Go National Central University, Taiwan September 16, 2002 Apollo Go, NCU Taiwan

2. Design Requirements • The luminosity monitor (LUM) is mainly for the quick feedback to the accelerator people for beam tuning. • Requirements: • Precision: 3-5% • Enough statistics for fast feedback • Radiation tolerant: 5 Krad/year • Fit in the limited space around • beam pipe, MDC and mini-b MDC • 8cm height (max.); 1.5cm in the front due to MDC electronics. • 9cm deep; 2p coverage not possible due to beam pipe support at the last 3cm. mini-b beam pipe Apollo Go, NCU Taiwan

3. Available Space MDC mini-b beam pipe Apollo Go, NCU Taiwan

4. Design Considerations • Particularity of this luminosity monitor: • Limited space and location => measure the luminosity by counting small angle Bhabha events. • There is no a strong need for fine energy resolution, hadronic (mainly p) background rejection does not require precise energy measurement => no need for expensive, homogeneous crystal calorimeter. • On the other hand, great rejection power can be achieved by selecting back-to-back events => Fine granularity (spatial resolution) detector. • Main uncertainty on luminosity measurement is in knowing well the acceptance, especially on the inner edge => need defining counter in front. Apollo Go, NCU Taiwan

5. Base Design: Silicon-Tungsten Preshower-like solution: Four 63x63mm2 modules placed at the either side of the beam pipe: R=65-98mm Z=515-538mm q=8-14o • Two reasons for such geometry: • Not possible 2p coverage due to the beam pipe support on top. • Avoid horizontal plane where there is high synchrotron radiation. • 4 modules makes debugging easier by comparing rates on each module. Apollo Go, NCU Taiwan

6. Silicon-Tungsten Preshower • Each module consists of: • Two tungsten converters of 14 mm (4X0) and 7mm (2X0) thickness. • Two shower maximum sampling layers of silicon strip sensors, one in X and the other in Y direction. • Silicon sensor: 320mm thick, 32 strips of 1.9mm pitch, 63mm long. • Silicon are made by ERSO in Taiwan for CMS Preshower detector, in production. • A defining counter is place right before the converters. Same ERSO silicon is used. The size is known to few mm. W W 7 14mm 63mm X Silicon strips Y Silicon strips Defining Counter Apollo Go, NCU Taiwan

7. e/p Separation, Silicon-Tungsten From MC simulation (GEANT 3.21): • A 1.55GeV electron gives, on the average, 16 MIPs (1.9 MeV) on first layer and 12 MIPs (1.4 MeV) on second layer. Per strip: 9 MIPs and 5 MIPs respectively. • p leaves much less energy, typically a MIP (0.11 MeV). Apollo Go, NCU Taiwan

8. e/p separation, Silicon-Tungsten • By cutting on deposited energy on each layer: • Good e acceptances and p rejection • Additional MC results: • Excellent spatial resolution (<0.7mm), will give excellent Bhabha acceptance with back-to-back selection. • Bhabha event rate: 2.3KHz • 3% (5%) luminosity measurement can be achieved with a mechanical precision of 0.5 (1)mm in the inner edge. Apollo Go, NCU Taiwan

9. Front-End Electronics • Several possibilities exists: • Delta Chip: Preamp-Shaper, designed specifically for the CMS Silicon. 50 MIP full rage, 25ns shaping time, radiation hard, S/N>10. • Amplex-SiCal chip, used in ALEPH luminosity monitor, 1000 MIP full rage, S/N>10. • Charge & Post Amplifier from EMC. Signals are taken out for triggering and DAQ. Apollo Go, NCU Taiwan

10. Back-up: Lead-Scintillating Fibers • Calorimeter-like solution: • 4 modules, 2 on each side of the beam. Each module covers p/2 in f direction, • Z=472.5-562.5mm; R=65-107.5mm. 12.5 X0; Moliere Radius~17.5mm. • 17 layers of 2.5mm Pb with 16 layers of 1mm scintillating fibers every 3mm (2776 fibers). 4 readout layers, 136 channels. • defining counter: plastic scintillator with same fibers and APD readout Apollo Go, NCU Taiwan

11. Lead-Scintillating Fibers, details • At shower max (~6X0), the transverse shower profile is around 1X0 (~7.2mm), so we need a transverse granularity <<7mm => 1mm fiber, 2.5mm Pb. ~2800 photons on the hit APD. • Choice of Fiber: • Pol.Hi Tech’s 0046-100 (0044-100) has a peak response at 435nm (440nm), also rad hard specified to 1Mrad. • Bicron’s BCF-60 has peak response at 530nm and it is radiation tolerant (not specified how much) • Photodetector: ECAL APD is 5x5mm2 area, high sensitivity and low noise. 80% QE 400-650nm. Small nuclear counter effect. Rad hard (500Krad). • Read out electronics can be placed outside. Apollo Go, NCU Taiwan

12. Lead Scintillating Fibers, e/p separation • An electron deposits 13 MeV in all fibers. • p deposits less than 2 MeV, but with a long tail due to non-negligible nuclear interaction probability. • Worse p rejection power due to this nuclear interaction. Apollo Go, NCU Taiwan

13. 32 Disc. Disc. 32 OR Disc. 32 32 32 32 Trigger • Trigger: based on back-to-back event selection • First level, on each module, fast • Hit on the defining counter • Energy deposited on each silicon layer over the threshold Defining Counter Analog sum X layer AND Hit Analog sum Y layer Apollo Go, NCU Taiwan

14. 32 32 32 32 Trigger & DAQ • Second level, coincidence on opposite modules, FPGA, slower • First level trigger on the two opposite modules. • A/D conversion of both silicon layers, both modules. • Calculate hit position (R-f) using FPGA • Make coincidence decision (FPGA). • Count the rate, calculate the luminosity (FPGA). • DAQ: • Feed data into EMC data flow stream. X layer ADC Hit Position Upstream R Y layer ADC f Back-to- back Coinc. FPGA Rate & Luminosity Lum. R ADC X layer Hit Position FPGA Downstream f FPGA Y layer ADC FPGA Apollo Go, NCU Taiwan

15. Milestones and Conclusion • Schedule and Planning: • 2002.09 - 2003.06:Detector R&D, full MC simulation study. • 2003.06 - 2004.06:Prototype construction; test beam at CERN. • 2004.06 - 2005.06:Final detector construction and installation. • 2005.06 - 2006.06:Detector Commissioning. Conclusion: This is a relatively simple detector, we should be able to meet the target and build it on time! Apollo Go, NCU Taiwan