1. Studies of Electroweak Interactions and Searches for New Physics Using Photonic Events with Missing Energy at the Large Electron-Positron Collider Marat Gataullin November 22, 2005

2. BGO Electromagnetic Calorimeter Barrel: 7680 crystals, 2x24 rings of 160 crystals. Endcaps: 1527 crystals, 17 rings of 46-128 crystals each.

3. BGO Energy Reconstruction Narrow profile -- 94% in S 9 To correct for leakage define:

4. BGO Performance at the Beginning of LEP2 1997 Data 4 events, MC 0.5 Beam tests in 1987-88:

5. RFQ Calibration System 1. 30 keV H - ion source (output current 7.5 mA) 2. 1.85 MeV RFQ accelerator (transmission 75%) 3. Steering and focusing magnets 4. Nitrogen-cell beam neutralizer (efficiency 60%) Output H 0 flux up to 4 mA Output H 0 flux up to 4 mA

6. RFQ System

7. RFQ Concept Radiative capture of protons produces a flux of 17.6 MeV photons Simultaneous calibration of the entire BGO calorimeter RFQ runs performed twice each year, no major hardware problems. BGO calorimeter in standby mode. Average trigger rate of 80 Hz, giving 20 million triggers after 4 days.

8. RFQ Occupancy

9. RFQ Calibration HH+ defined as a point half-way below and to the right of the calibration maximum

10. RFQ Calibration Constants

11. RFQ-Only Calibration with 45 GeV Bhabha electrons RFQ-Only Calibration with 45 GeV Bhabha electrons However, statistical precision was found to be about 1%. Significant systematic effects from variations in the photon incident angle and energy extrapolation. Solution: use Bhabha electrons to set the absolute scale.

12. Bhabha Calibration Sample Select back-to-back events. Shower-shape cuts also applied. LEP calibration runs 15-20 days/year and L=4pb/year. 50k showers in the barrel and 850k showers in the endcaps.

13. RFQ+Bhabha Calibration Algorithm  Starting set of constants provided by the RFQ calibration.  Typically only 4-5 iterations required to converge.  Robust, now used in CMS calibration studies.  Easy to implement corrections for dead crystals.

14. Calibration Results Also checked with π and η two-photon decays

15. Dead Crystals  About 1.5% of all BGO channels were malfunctioning  12% of selected showers had a dead crystal in 3x3 matrix  5% were on the edges between the barrel and endcaps  Energy loss taken into account both during the calibration and physics analysis and physics analysis

16. Dead Crystals

17. BGO Aging Checked using 45 GeV Bhabhas, source unknown. Loss of about -0.5% per year.

18. BGO Non-Linearity Checked using Bhabhas with energies between 45 and 103 GeV. Going from 45 and 103 GeV increased the BGO response by about 0.4%. Overall conclusion: the energy scale was known to better than 0.3%.