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Performance and Upgrade Plans of the Belle Calorimeter

Performance and Upgrade Plans of the Belle Calorimeter. B.Shwartz, Budker Institite of Nuclear Physics Novosibirsk on behalf of BELLE calorimeter group. BELLE detector at KEKB B-factory. Lmax=7  10 35 cm -2 s -1 Logged (24.03)=62fm -1. The main tasks of the calorimeter.

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Performance and Upgrade Plans of the Belle Calorimeter

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  1. Performance and Upgrade Plans of the Belle Calorimeter B.Shwartz, Budker Institite of Nuclear Physics Novosibirsk on behalf of BELLE calorimeter group CALOR 2002

  2. BELLE detector at KEKB B-factory Lmax=71035cm-2s-1 Logged (24.03)=62fm-1 CALOR 2002

  3. The main tasks of the calorimeter • detection of gamma-quanta with high efficiency • photon energy measurements • photon coordinates determination • electron/hadron separation • generation of the proper signals for trigger • luminosity measurement – on-line and off-line CALOR 2002

  4. Alkali-halide crystals for precision calorimetry CALOR 2002

  5. BELLE Electromagnetic Calorimeterfor KEKB energy asymmetric B-factory Lcr = 30 cm = 16.2X0 Tower structure projected to the vicinity of IP. 30 cm long (16.2 X0), 8736 CsI(Tl) crystals (6624 in barrel). 12<  < 155 (lab frame) Inner radius – 1250 mm 3 m Total weight is ~43ton CALOR 2002

  6. Calorimeter elements Together with spare, 8851 crystals were produced by 3 manufacturers: Budker Institute of Nuclear Physics (Russia) & Institute of Single Crystals (Ukraine) 5946 Shanghai Institute of Ceramics (China) - 1890 Crismatec (France) - 1017 Light output - 5000 ph.el./MeV electronics noise σ~200 keV CALOR 2002

  7. Calorimeter electronics Q  T  digit low range ~ 0.06 MeV/bin middle range ~ 0.5 MeV/bin high range ~ 4 MeV/bin CALOR 2002

  8. Energy resolution e+e   (3.5 < Eg < 8 GeV) The energy deposition distribution can be well approximated by the logarithmic gaussian form : • where Ep is peak energy; σ - FWHM/2.35; • - asymmetry parameter; s can be expressed as: ξ=2.35 CALOR 2002

  9. BELLE Energy resolution D*0→D0(→Kp)g Eg>300MeV <Eg>~400MeV sE/E~2.6% MC – 2% Test beam CALOR 2002

  10. Calorimeter angular resolution Photon angles (or coordinates) in the crystal calorimeters are measured usually as corrected center of gravity of the energy deposition: ; Correction functions (F) can be usually written as a function of one of the angles and energy. CALOR 2002

  11. Electron identification • Combine: • Energy / momentum ratio • CsI shower shape • track- cluster matching • dE/ dx • TOF • ACC efficiency fake rate CALOR 2002

  12. Radiation dose monitoring 1 rad = 6.241010 MeV/kg where: K= 6.241010 MeV/kg; L- lightoutput, photoelectrons/MeV; m – mass of the crystal; e – electron charge; I= I – Idark Dose = 100 rad/2.5 nA for 107 sec The total current at bias voltage applied to photodiodes is measured for each group CALOR 2002

  13. Bias current monitoring It’s noticed that PD dark current is gradually increasing. This effect is much high than that could be caused by measured dose. Neutron irradiation? CALOR 2002

  14. Radiation damage of the crystals CALOR 2002

  15. Radiation damage of the crystals No big problem even at 1035 luminosity. CALOR 2002

  16. Pile up effect sn(beam)/sn(no beam) 1 MeV BELLE eg, MeV sp = <eg> ·(fb·sh) 360 mA  360 mA CALOR 2002

  17. Beam background Occupancy for random trigger, L=3.51033cm-2s-1 I+=750 mA, I-=650mA <Eg>=35 MeV, Ng(>20 MeV)  3 CALOR 2002

  18. Anticipating L=1035cm-2s-1 at Super KEKB I+=10 A, I-=4.4 A, Vacuum= (1 10)10-7 • Calorimeter electronics will be changed from present (QT+TDC) chain to pipeline readout • The option of pure CsI usage in the end caps is under study CALOR 2002

  19. Online Luminosity monitor Bhabha counting rates of Fwd&Bwd endcap 160Hz @5x1033cm-2s-1 Fwd CsI endcap Bwd CsI endcap 4 quarters f segmentation CALOR 2002

  20. Offline luminosity • Selection of Bhabha events • Back-to-back 2 tracks in barrel part • 2 EM clusters (Esum>4GeV) • Uncertainty of offline luminosity measurement • the difference of front material between real data and MC 0.2% • Other physics backgroundnegligible • Accuracy of MC generators 1.3% • Accuracy of run-dependent correction 0.4% →accuracy of experimental measurements 0.4% accuracy of MC 1.3% CALOR 2002

  21. Online/offline luminosity Online lum. Offline Bhabha lum. Offline gg lum. Offline Bhabha lum. ±0.5% ±1% Overall stability of Online luminosity ~1% CALOR 2002

  22. Conclusion • Belle calorimeter performance is good and the parameters are close to the project. • Mass resolution • p0 : 4.8MeV/c2 • h : 12.1MeV/c2 • Energy resolution of g (>3.5GeV) 1.7% • Luminosity measurement is stable ~1% • R&D works to match the calorimeter to 1035 luminosity are in progress CALOR 2002

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