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

2. Design Requirements Apollo Go, NCU Taiwan The luminosity monitor (LUM) is mainly for the quick feedback to the accelerator people for beam tuning. Requirements: 1.Precision: 3-5% 2.Enough statistics for fast feedback 3.Radiation tolerant: 5 Krad/year 4.Fit in the limited space around beam pipe, MDC and mini-  a)8cm height (max.); 1.5cm in the front due to MDC electronics. b)9cm deep; 2  coverage not possible due to beam pipe support at the last 3cm. MDC mini-  beam pipe

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

4. Design Considerations Apollo Go, NCU Taiwan Particularity of this luminosity monitor: 1.Limited space and location => measure the luminosity by counting small angle Bhabha events. 2.There is no a strong need for fine energy resolution, hadronic (mainly  background rejection does not require precise energy measurement => no need for expensive, homogeneous crystal calorimeter. 3.On the other hand, great rejection power can be achieved by selecting back-to-back events => Fine granularity (spatial resolution) detector. 4.Main uncertainty on luminosity measurement is in knowing well the acceptance, especially on the inner edge => need defining counter in front.

5. Base Design: Silicon-Tungsten Apollo Go, NCU Taiwan Two reasons for such geometry: 1.Not possible 2  coverage due to the beam pipe support on top. 2.Avoid horizontal plane where there is high synchrotron radiation. 3.4 modules makes debugging easier by comparing rates on each module. Preshower-like solution: Four 63x63mm 2 modules placed at the either side of the beam pipe: R=65-98mm Z=515-538mm  =  8-14 o

6. Silicon-Tungsten Preshower Apollo Go, NCU Taiwan X Silicon strips Y Silicon strips W W Each module consists of: 1.Two tungsten converters of 14 mm (4X 0 ) and 7mm (2X 0 ) thickness. 2.Two shower maximum sampling layers of silicon strip sensors, one in X and the other in Y direction. 3.Silicon sensor: 320  m thick, 32 strips of 1.9mm pitch, 63mm long. 4.Silicon are made by ERSO in Taiwan for CMS Preshower detector, in production. 5.A defining counter is place right before the converters. Same ERSO silicon is used. The size is known to few  m. 63mm 14mm 7 Defining Counter

7. e/  Separation, Silicon-Tungsten Apollo Go, NCU Taiwan 1.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. 2.  leaves much less energy, typically a MIP (0.11 MeV). From MC simulation (GEANT 3.21):

8. e/p separation, Silicon-Tungsten Apollo Go, NCU Taiwan By cutting on deposited energy on each layer: Good e acceptances and  rejection Additional MC results: 1.Excellent spatial resolution (<0.7mm), will give excellent Bhabha acceptance with back-to-back selection. 2.Bhabha event rate: 2.3KHz 3.3% (5%) luminosity measurement can be achieved with a mechanical precision of 0.5 (1)mm in the inner edge.

9. Front-End Electronics Apollo Go, NCU Taiwan Several possibilities exists: 1.Delta Chip: Preamp-Shaper, designed specifically for the CMS Silicon. 50 MIP full rage, 25ns shaping time, radiation hard, S/N>10. 2.Amplex-SiCal chip, used in ALEPH luminosity monitor, 1000 MIP full rage, S/N>10. 3.Charge & Post Amplifier from EMC. Signals are taken out for triggering and DAQ.

10. Back-up: Lead-Scintillating Fibers Apollo Go, NCU Taiwan Calorimeter-like solution: 1.4 modules, 2 on each side of the beam. Each module covers  /2 in  direction, 2.Z=472.5-562.5mm; R=65-107.5mm. 12.5 X 0 ; Moliere Radius~17.5mm. 3.17 layers of 2.5mm Pb with 16 layers of 1mm scintillating fibers every 3mm (2776 fibers). 4 readout layers, 136 channels. 4.defining counter: plastic scintillator with same fibers and APD readout

11. Lead-Scintillating Fibers, details Apollo Go, NCU Taiwan 1.At shower max (~6X 0 ), the transverse shower profile is around 1X 0 (~7.2mm), so we need a transverse granularity 1mm fiber, 2.5mm Pb. ~2800 photons on the hit APD. 2.Choice of Fiber: 1.Pol.Hi Tech’s 0046-100 (0044-100) has a peak response at 435nm (440nm), also rad hard specified to 1Mrad. 2.Bicron’s BCF-60 has peak response at 530nm and it is radiation tolerant (not specified how much) 3.Photodetector: ECAL APD is 5x5mm 2 area, high sensitivity and low noise. 80% QE 400-650nm. Small nuclear counter effect. Rad hard (500Krad). 4.Read out electronics can be placed outside.

12. Lead Scintillating Fibers, e/p separation Apollo Go, NCU Taiwan 1.An electron deposits 13 MeV in all fibers.  deposits less than 2 MeV, but with a long tail due to non- negligible nuclear interaction probability. 3.Worse  rejection power due to this nuclear interaction.

13. Trigger Apollo Go, NCU Taiwan Trigger: based on back-to-back event selection First level, on each module, fast 1.Hit on the defining counter 2.Energy deposited on each silicon layer over the threshold 32 Disc. Analog sum Disc.32 OR Disc. Analog sum AND 32 Defining Counter X layer Y layer Hit

14. Trigger & DAQ Apollo Go, NCU Taiwan Second level, coincidence on opposite modules, FPGA, slower 1.First level trigger on the two opposite modules. 2.A/D conversion of both silicon layers, both modules. 3.Calculate hit position (R-  ) using FPGA 4.Make coincidence decision (FPGA). 5.Count the rate, calculate the luminosity (FPGA). DAQ: Feed data into EMC data flow stream. 32 X layer Y layer Hit Position FPGA Hit Position FPGA Back-to- back Coinc. FPGA Rate & Luminosity FPGA R R   32 X layer Y layer Lum. Upstream Downstream ADC

15. Milestones and Conclusion Apollo Go, NCU Taiwan Schedule and Planning: 1.2002.09 - 2003.06: Detector R&D, full MC simulation study. 2.2003.06 - 2004.06: Prototype construction; test beam at CERN. 3.2004.06 - 2005.06: Final detector construction and installation. 4.2005.06 - 2006.06: Detector Commissioning. Conclusion: This is a relatively simple detector, we should be able to meet the target and build it on time!