1. CAL CALIBRATION Overview and Stability Thomas Schörner-Sadenius Hamburg University ESCALE Meeting DESY, 7 June 2005

2. DESY 7 June 2005TSS: CAL Calibration2 INTRODUCTION TO THE ZEUS UCAL Depleted Uranium for calibration and compensation Principle Depleted Uranium – scintillator calorimeter; analog pipelined PMT readout. Analog electronics on front-end cards on detector; digital electronics in 3rd floor of rucksack. Division in F/B/RCAL with 2172/2592/1154 cells, 2 PMTs per cell EM cell size: 5  20 (10  20) cm 2 in F/BCAL (RCAL) HA cell size: 20  20 cm 2. Resolution:  (e)/E=17%/  E,  (h)/E=35%/  E Claim: absolute energy scale known to 1%. 98.1% 238 U,  decay to 234 Th,  decays to 234 PA and then 234 U,  cascades in between. E max (  )=2.3 MeV, E(  )=10-1000keV  (U)=4.5 Gy (Giga-years)  rather stable signal of ZEUS lifetime. Use UNO (Uranium noise) signal to monitor CAL behaviour with time Calibration Uranium Idea

3. DESY 7 June 2005TSS: CAL Calibration3 READOUT OVERVIEW Necessary for understanding of calibration constants. shaperpipelinebuffer shaperpipelinebuffer To trigger 55pC I UNO 20ms integration time over UNO current Q high Q low V DAC DAC V ref V ref =1.67V UNO Energy Q Current I PMT Charge Q Voltage V ADC counts Digital electronics Necessary: Calibration of particle/jet energy to ADC counts PMT

4. DESY 7 June 2005TSS: CAL Calibration4 CALIBRATION IDEA Use stable Uranium noise as calibration signal Uranium activity stable in time. UNO signal stable in time to about 1% (CERN testbeam) e/UNO or h/UNO for given E e, E h stable in time (studying the ratio cancels some uncertainties  more precise result e,h response linear in energy (CERN testbeam) Assumption 1 Assumption 2 Assumption 3 Assumption 4 STEP A STEP B Keep UNO signal stable  trimming of HV settings  UNO scale factors (offline GAFs) From known and linear e/UNO (h/UNO) then estimate energy of e,h. One of the many complications: UNO signal and (fast) physics signal go through different signal paths on front-end card! UNO[ADC] fixed e(E)[ADC]/UNO[ADC]: CERN! then e[ADC]  e[GeV]

5. DESY 7 June 2005TSS: CAL Calibration5 “1%” CALIBRATION Refers to rather different things Intermodule/interregion calibration After UNO calibration: compare various modules in their response to well-defined input energies (test beam)  spread of various modules ~ 1% 1% - the first 1% - the second Determination of absolute scale E(particle)  ADC: after UNO calibration (UNO gives precise ADC count): absolute scale delivered by (using the test beam results): Two important questions/tasks here: -- Keep the UNO signal to the nominal as closely as possible (UNO scale factors, but also other smaller corrections for front-end, signal path etc.) -- Derive offline correction factors from physics data (kin. Peak, E-p z, etc.) ‘one-to-one relation between ADC and energy. Within one module response from towers is gaussian with width ~1%!  in testbeam fix scale to 1%!

6. DESY 7 June 2005TSS: CAL Calibration6 UNO SCALE FACTORS CAL offline GAFs – the one that always stop the reconstruction For all CAL regions means within few permille around 1. Widths below 1%. Channel-by-channel comp- arison of two UNO GAFs from 010305 and 080505. Means ~1permille. Widths ~0.5%. Several HV adjustments between the two dates. No systematic trends, distributions gaussian  absolute calibration preserved at 1%-level!

7. DESY 7 June 2005TSS: CAL Calibration7 UNO SCALE FACTORS Module by Module comparisons of relative UNO differences No significant changes between modules  intermodule calibration still at 1%-level!

8. DESY 7 June 2005TSS: CAL Calibration8 FURTHER OFFLINE CORRECTIONS Motivated by physics; take into account dead material etc. PHANTOM routine escale03.fpp (default in ORANGE) applies corrections for F/B/RCAL, separately for EMC and HAC; in addition cell corrections for some RCAL cells FEMC: 1.024 FHAC: 0.941 BEMC: 1.003*1.05 BHAC: 1.044*1.05 REMC: 1.022 RHAC: 1.022 Corrections derived from kinematic peak events and DA measurements. -- repeat in newer data? -- dependence on physics case? -- any manpower currently involved?

9. DESY 7 June 2005TSS: CAL Calibration9 SUMMARY and possible outlook Started to look into long-term stability of CAL calibration (UNO scale factors).  absolute calibration seems stable to within 1% over time.  intermodule calibration within about 1%  if initial absolute energy calibration good to 1%, then this quality is probably preserved until today. Needed: Better understand of calibration in detail; only then can judge on quality of calibration. Important:  control of offline CAL regional (caltru) correction factors  use physics events for that (kin. peak, E-p z, DA method etc.)