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DETECTORS at HIGH LUMINOSITY e+e- STORAGE RINGS

DETECTORS at HIGH LUMINOSITY e+e- STORAGE RINGS. G. Eigen University of Bergen Snowmass July 14, 2001. OUTLINE. Introduction Silicon Vertex Detectors Drift Chambers DIRC Electromagnetic Calorimeters IFR Trigger Rates Examples of strawman detectors Conclusion.

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DETECTORS at HIGH LUMINOSITY e+e- STORAGE RINGS

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  1. DETECTORS at HIGH LUMINOSITY e+e- STORAGE RINGS G. Eigen University of Bergen Snowmass July 14, 2001 G. Eigen, University of Bergen

  2. OUTLINE • Introduction • Silicon Vertex Detectors • Drift Chambers • DIRC • Electromagnetic Calorimeters • IFR • Trigger Rates • Examples of strawman detectors • Conclusion G. Eigen, University of Bergen

  3. Introduction • For precision measurements of CP-violation asymmetries and rare B decays high luminosities are an important prerequisite • Recently, the design of an e+ e- storage ring s ~ 10GeV with luminosities of £peak = 1036 has become feasable • So how do present subsystems of multipurpose detectors cope with the increased background levels ? • The following results are my personal views based on BABAR studies: Report of the High-Luminosity Background Task force (C. Hast, W. Kozanecki (chair), A. Kulikov, T.I. Meyer, S. Petrak, T. Schietinger, S. Robertson,M. Sullivan, J. Va’vra, BaBar Note 522) • Results for £peak ≥ 1035 should be taken with a grain of salt:  Extrapolations are made over > 2 orders of magnitude (errors > factor 2) Extrapolations depend very much on IR layout G. Eigen, University of Bergen

  4. Background Issues • Acceptable levels of backgrounds are determined by  Radiation hardness of subdetectors  inefficiencies, destruction  Trigger rate  deadtime, loss of signal  Detector occupancies inefficiencies, worse resolution, worse S/B • Occupancy and trigger rate determine acceptable dynamic running conditions • Total integrated radiation dose determines lifetime of subdetectors  Dose is accumulated under normal running conditions, during injection, machine studies and beam-loss events  At PEP II dose accumulated during running dominates  At £peak = 1036machinethis is different, injection losses determine dose G. Eigen, University of Bergen

  5. Present Measures of BABAR Subsystems to Machine Backgrounds • Radiation Hardness of SVT detector modules is estimated at 2MRad Instantaneous dose rate in radiation protection diodes BW:MID & FE:MID are within factor of two representative of harshest radiation levels hitting SVT modules in horizontal plane • Total current drawn by drift chamber is limited to 1000 A by existing HV power supplies • Counting rate above 200-300 kHz in DIRC phototubes starts inducing significant dead time with present electronics • Fractional EMC crystal occupancy above a 1 MeV threshold and number of crystals above 10 MeV characterize potential degradation of calorimeter energy resolution, as well as number of fake neutral clusters • Level-1 (L1) trigger rate is currently limited to 2.0-2.5 kHz by DAQ bandwidth considerations

  6. Detector subsystems are subjected to different machine-related backgrounds Electrons:  lost particles backgrounds (beam-gas bremsstrahlung, Coulomb scattering) and synchrotron radiation Positrons:  lost particles backgrounds (beam-gas bremsstrahlung) 2 beams: no collision  single beam backgrounds above plus beam-gas cross term in collision  backgrounds from luminosity, beam-beam tails & above 3 Note that there is a difference in operation between PEP II at high £peak& an £peak = 1036 collider:  PEP II: inject & run (stable beams)  continuous injection (no stable beams) Present Sources of Machine Backgrounds G. Eigen, University of Bergen

  7. Backgrounds in PEP II & in an L=1036 Machine • Background estimates by W. Kozanecki based on J. Seeman’s design PEP II 1036 • Beam loss rates in PEP II and a 1036 machine differ by a factor of > 103 but only small fraction will contribute to detector backgrounds G. Eigen, University of Bergen

  8. Backgrounds in an L=1036 Machine • In PEP II LER lifetime is dominated by vacuum or Touschek effect, while HER lifetime is affected by beam-beam tune shift and then vacuum • Background sources in SVT, DCH and EMC result from beam-gas in the incoming straight section • Beam-beam tuneshifts, dynamic aperture and vacuum losses probably will contribute to vacuum-like backgrounds, since losses are transverse (like distant LER Coulomb scattering in PEP II) • Since quads need to be shielded transverse losses are produced at betatron collimators far from IP  combined transverselosses are main issue with LER backgrounds only 15%-20% of them, HER is minor problem • Effects of longitudinal losses at £peak = 1036are not known, since these have not been studied in PEP II • Since sum of longitudinal, all transverse and injection losses is so large, vacuum in IR will be less a problem, still need pressure of 10-9 within 50m of IP G. Eigen, University of Bergen

  9. Dependence of backgrounds on beam currents • Touschek: Dependence is not known, expect no effect for a while (low ILER, long Touschek lifetime, negligible secondary particles) At some point it will take off  need simulation with Turtle • Beam-beam tune shift: very non-linear and very tune sensitive • Dynamic Aperture: linear (?) • Vacuum: quadratic in ILER (the base pressure will be well-controlled, the dynamic pressure will dominate) • Luminosity: linear in beam currents G. Eigen, University of Bergen

  10. Estimates of backgrounds due to beam losses • Touschek: Need Turtle-like simulation of energy spectrum • Tranverse losses: Scale distant Coulomb prediction by the ratio of loss rates with measured distant LER-only contributions (DCH,DIRC) • Injection losses: Take clean injection day from PEP II and scale by injection currents • Secondary particles: Due to multistage injection, betatron collimation and momentum collimation secondary particles are big issue realistic simulation is a major task • Radiative Bhabha: Debris in the detector from radiative Bhabhas eventually will become large, it is sensitive to beam line geometry & IR layout • Caution: In extrapolations below none of above effects is included G. Eigen, University of Bergen

  11. Multipurpose Detector for e+e-Collisions at 10GeV

  12. Luminosity Considerations • For luminosities shown in blue extrapolations have been taken from the report of the High-Luminosity Background Task force, while for luminosities shown in green results are my extrapolations using the algorithms given by the High-Luminosity Background Task force G. Eigen, University of Bergen

  13. Silicon Vertex Trackers G. Eigen, University of Bergen

  14. Dose accumulated in BABAR SVT G. Eigen, University of Bergen

  15. SVT Radiation Dose in Middle Plane 21033 10345 1035 5 1036 SVT dose rate [krad/y] FE MID BW MID time • SVT dose rate: FE MID [kRad/y] =128 ILER + 16 I2LER BW MID [kRad/y] =246 IHER + 9.1 I2HER • In top & bottom planes dose rate is ~ factor of 10 lower than in middle plane G. Eigen, University of Bergen

  16. Silicon Vertex Detector Occupancy G. Eigen, University of Bergen

  17. Conclusion on Silicon Vertex Detectors • Radiation levels depend very strongly on IR layout, (KEKB < PEP II) • In BABAR silicon detectors are expected to survive a total dose of 2MRad  With replacements of detectors in the MID plane BABAR SVT is expected to survive luminosities of 1.5-31034 • LHC R&D demonstrated that Si detectors can survive high irradiation H. Yamamoto bonded 150 thick pixels (55   55 ) (CMOS) • At £peak ~ 11036 occupancy is an issue for Si strip detectors close to IR  pixels in first two layers • So for£peak ~ 1-101035appropriate silicon detectors probably work G. Eigen, University of Bergen

  18. Drift Chambers G. Eigen, University of Bergen

  19. Drift Chambers • Machine backgrounds affect operation of Drift Chamber in 3 ways: • Total current IDCH in Drift Chamber drawn by wires is dominated by charge of beam-related showers IDCH is limited by high-voltage system,  above limit chamber becomes non operational!  high currents also contribute to aging of chamber!  maximum Qmax:0.1-1.0 Cb/cm of wire • Occupancy in Drift Chamber due to backgrounds (hits, tracks) can hamper reconstruction of physics events • Ionization radiation can permanently damage read-out electronics & digitizing electronics G. Eigen, University of Bergen

  20. Drift Chamber Currents • Single beam and collision measurements taken June/ July at HV=1900V • For HV=1960V scale current byfactor 1.67 • IDCH [A]= 35.3 ILER +23.5 I2LER + 77.2 IHER +46.3 I2HER + 41.9 £ -14 with currents in [A] and luminosity in units of [1033 cm-1 s-1] G. Eigen, University of Bergen

  21. Measured Drift Chamber Currents & Models • Single-beam measurements (LER) taken with BABAR DCH in June and July 2000 at HV=1900V G. Eigen, University of Bergen

  22. Drift Chamber Backgrounds 21033 10345 1035 5 1036 • Extrapolation for HV=1900V • At HV=1960 background levels are expecetd to be 65% higher total DCH current [A] Luminosity ILER IHER time G. Eigen, University of Bergen

  23. Drift Chamber Occupancy • At HV=1900V (Jan-July): NDCH = 158+0.27 IDCH (<350A) • At HV=1960 V(July-now): NDCH = 203+0.18 IDCH (>200A) • Large spread  extrapolation difficult data points at ~ same £ • NDCH= 0.044+0.191 ILER +0.0402 I2LER + 1.03 IHER +0.113 I2HER + 0.147 £ with occupancy in [%], currents in [A], luminosity in units of [1033 cm-1 s-1] at 1900V G. Eigen, University of Bergen

  24. Drift Chamber Occupancy 21033 10345 1035 5 1036 Luminosity ILER IHER • Extrapolation for HV=1900V DCHoccupancyt [%] time • NDCH= 0.044+0.191 ILER +0.0402 I2LER + 1.03 IHER +0.113 I2HER + 0.147 £ G. Eigen, University of Bergen

  25. Conclusion on Drift Chambers • Total dose depends on ∫£dt: at 20 fb-1 accumulated 100 rads • For £peak > 11035 it is very unlikely that drift chambers will work One needs other devices: straws, TPC with GEM readout, Si tracker G. Eigen, University of Bergen

  26. GEM Layout G. Eigen, University of Bergen

  27. GEM Layout G. Eigen, University of Bergen

  28. DIRC PARTICLE IDENTIFICATION G. Eigen, University of Bergen

  29. Composition of DIRC Background 21033 10345 1035 5 1036 total ILER IHER DIRC occupancy [ kHz] time • NDIRC [kHz] = 35 ILER + 8.5 IHER + 25 £ G. Eigen, University of Bergen

  30. Conclusion on DIRC • BABAR DIRC is ok up to £peak =61034, however the water tank provides a huge Cherenkov detector • At high luminosities £peak>11035 another approach is needed: a compact readout using focussing or timing G. Eigen, University of Bergen

  31. Different DIRC Imaging Methods • Note that different imaging methods can be chosen in each space dimension G. Eigen, University of Bergen

  32. DIRC Readout B. Ratcliff G. Eigen, University of Bergen

  33. Separation Performance vs Random Rates G. Eigen, University of Bergen

  34. ELECTROMAGNETICCALORIMETER G. Eigen, University of Bergen

  35. Average Occupancy in EMC Crystals Single Crystal occupancy # Crystals with > 10 MeV • NEMC (E> 1MeV)= 9.8 + 2.2 IHER +2.2 ILER + 1.4 £ NEMC (E> 10MeV)= 4.7 IHER + 0.23 I2HER +2.4 ILER + 0.33 I2LER + 0.6 £ with beam currents in units of [A] and luminosity in units of [1033 cm-1 s-1] G. Eigen, University of Bergen

  36. Light Yield Changes in EMC G. Eigen, University of Bergen

  37. Worst Dose Rate in EMC G. Eigen, University of Bergen

  38. Effect of Background on 0 Reconstruction • Background photons both increase 0 background levels and degrade mass resolution G. Eigen, University of Bergen

  39. Composition of EMC Backgrounds • > 10 MeV • > 1 MeV 21033 10345 1035 5 1036 21033 10345 1035 5 1036 total ILER IHER noise total ILER IHER # EMC crystals EMC occupancyt [%] time time • NEMC (E> 1MeV)= 9.8 + 2.2 IHER +2.2 ILER + 1.4 £ NEMC (E> 10MeV)= 4.7 IHER + 0.23 I2HER +2.4 ILER + 0.33 I2LER + 0.6 £ G. Eigen, University of Bergen

  40. Conclusion on Electromagnetic Calorimeters • For luminosities < 1.51034 integrated radiation dose for CsI(Tl) crystals is not expected to be a problem if observed light losses scale as expected • Impact of large number of low-energy photons on EMC energy resolution depends on clustering algorithm, digital filtering, etc (needs further study) Expect luminosity contribution to be dominant • Expect reduction of background rates through improvements of vacuum near IR combined with effective collimation against e+ from distant Coulomb scattering • For luminosities >11035 light loss due to radiation and occupancy levels for present CsI(Tl) crystals are not acceptable  need R&D studies and look into other scintillator (pure CsI, LSO, GSO?)

  41. Properties of Scintillating Crystals G. Eigen, University of Bergen

  42. INSTRUMENTED FLUX RETURN G. Eigen, University of Bergen

  43. Conclusion on IFR • Main issue is high occupancy in outer layers due to beam-related backgrounds • Presently outer RPC layer has random occupancy of several % • At design currents and at higher luminosity this will become an unacceptably high contribution to p/m misidentification • Solution for £peak ~ 3-51034: build 5 cm thick Fe shield following outer-most chamber • At £peak > 11035occupancy becomes an issue despite shielding RPC’s are not suited, replace them with scintillating fibers G. Eigen, University of Bergen

  44. TRIGGERS G. Eigen, University of Bergen

  45. L1 Trigger Rate vs Current in Machine G. Eigen, University of Bergen

  46. Trigger Rates 21033 10345 1035 5 1036 Total (L) IHER ILER Background Total trigger rate [Hz] time • Expected L1 trigger rate: L1 [Hz]=130 (cosmics)+ 130 ILER + 360 IHER + 70 £ G. Eigen, University of Bergen

  47. Extrapolation on Trigger Rates • For £peak ~1.51034 in BABAR trigger needs to be upgraded to cope with high rates • For higher luminosities one could do more stringent prescaling of Bhabhas, radiative Bhabhas, beam gas, (want to keep all b, c decays) One needs to design appropriate tracking device used in trigger • LHC experiments can accept L1 trigger rates of 100 kHz (ATLAS) bunch crossing is 40 MHz G. Eigen, University of Bergen

  48. Trigger for High Luminosity Machine G. Eigen, University of Bergen

  49. Trigger for High Luminosity Machine G. Eigen, University of Bergen

  50. The angular acceptance is limited by beam focussing elements to 300mr • By keeping present boost =0.58 and a resolution improved by a factor of two one needs to move closer to IP  1cm gold-plated Be beam pipe • To cope with occupancy problems near IR, use Si pixel detectors for first 2 layers of vertex detector, 3 layers Si strip detectors • For central tracker consider either all Si strips, straw tubes or TPC with GEMs readout • For particle identification consider Super DIRC • For EMC consider scintillating crystal calorimeter based on pure CsI, LSO or GSO • For IFR use Fe plates read out with scintillating fibers • Strawman designs resulted in discussions in breakout sessions: G. Dubois-Felsman, G. E., M. Giorgio, D. Hitlin, X. Lou, D. Leith, E. Paoloni, I. Peruzzi, M. Piccolo, M. Sokoloff, H. Yamamoto Detector Considerations

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