LHCb HCAL performance and calibration Yu Guz IHEP

LHCb HCAL: performance and calibration Yu. Guz, IHEP, Protvino on behalf of the LHCb collaboration Calor 2008, Pavia 1. structure 2. performance 3. LED monitoring system 4. 137 Cs 5. current status calibration system 1

LHCb HCAL: design goals Part of the experiment’s calorimetric system, intended to provide L 0 high-E T hadronic trigger Requirements: fast (25 ns cycle) moderate resolution is sufficient longitudinal depth limitations radiation tolerance: ~50 krad/year in the inner zone HCAL is a very important subdetector: it is supposed to give 70% of the L 0 output 2

LHCb HCAL The whole detector assembly 2 independent sides, each containing 26 modules stacked on movable platform size: 8. 4 x 6. 8 m 2 instrumented depth: 120 cm cell size: w outer zone 262 x 262 mm 2 w inner zone 131 x 131 mm 2 1488 cells (608 outer + 880 inner) Features: ✔ built-in 137 Cs calibration system for calibration in situ ✔ LED monitoring system Installed in 2005 3

LHCb HCAL The iron-scintillator structure arranged along the beam direction was chosen: spacers Master plates 6 mm Spacers 4 mm Scintillator 3 mm particles scintillators WLS fibers Sampling: longitudinal lateral 20 cm 2 cm master plate light guide PMT 6 longitudinal sections (5. 6 λI) (high energy showers not fully contained – but does not spoil the trigger operation) 4

LHCb HCAL module: self-supporting structure containing either 16 outer or 8 outer + 32 inner cells Weight : ~9. 5 ton Absorber and mechanics assembly: at IHEP Protvino Optics assembly: at CERN 5

LHCb HCAL Scintillator pads: polystyrene +1. 5% PTP +0. 03% POPOP 256 x 197 mm (full tile), 127 x 197 mm (half tile) wrapped by 100μ Tyvek WLS fibers: KURARAY Y 11(250)MS Ø 1. 2 mm attenuation length ~ 3. 5 m τD ~ 7 ns rad. hard to 500 krad ✜ ends of fibers aluminized ✜ compensation of light attenuation: length of contact with tile depends on depth 6

LHCb HCAL PMT: HAMAMATSU R 7899 -20 Specially designed for LHCb bialcali photocathode, UV glass (185 -650 nm) QE 15% at 520 nm 10 dynodes pulse linearity: within ± 2% dark current: < 2. 5 n. A max average current: 100 μA HV supplied by means of individual CW circuit for each PM rate effect: < 1% at I > 10 n. A Clipping circuit on 1. 15 m coax cable is used to compensate the 7 ns decay time of fibers (this cable also feeds the PMT current into the integrators of 137 Cs calibration system). The parameters of the clipping circuit were optimized for the signal from hadrons 7

LHCb HCAL: performance from beam tests ~3% angular dependence at higher energies: shower not fully contained in 5. 6 λI Average light yield: 105 ph. el. /Ge. V 8

LHCb HCAL Front-end electronics: “dead timeless”: integration over 25 ns 12 bit flash ADC sensitivity 20 f. C / ADC count ADC samples every 25 ns FIFO depth 256 cell-to-cell time alignment: sampling time adjustable, step 1 ns trigger processing: w sum of signals in 2 x 2 clusters w individual multiplication factor for each channel built-in test system: charge injection 9

LHCb HCAL 25 ns HV settings for physics: correspond to Emax=15 Ge. V/sin(Θ) (trigger on ET) ▲ ♦ Row 1 Row 2 Row 3 Row 4 Row 5 Row 6 PM gains: 20 k … 350 k PM transit time (~1/√HV) +time of flight vary by ~5 ns Signal cable delay spread: ~2 ns The pulse shapes from each tile row were obtained at beam test with the ebeam directed transversely into the corresponding row of a HCAL module. “Long” detector +mirrors at fiber ends: several % of signal outside 25 ns careful time alignment is necessary for the operation @ LHC 10

LHCb HCAL: LED monitoring system • blue LEDs (WU-14 -750 BC) • two independent LEDs per module • adjustable LED pulse amplitude • monitoring PIN photodiode at each LED, in order to account for LED instability • light distribution with clear fibers of same length • timing of the LED flashing pulse adjustable with 1 ns step –time alignment tool 11

LHCb HCAL: LED monitoring system The PMT gain will be continuously monitored with LEDs during the LHC run: Normally, LED is more stable than PMT… LEDs will be fired during 0. 2% the series of empty LHC bunches significant variations of the LED amplitude recorded in run DB, for subsequent use in the offline analysis 1. 5% 12

LHCb HCAL: 137 Cs calibration system Six stainless steel pipes pass through the centers of each tile row (27 m per module). All modules of each half calorimeter are connected. A ~ 10 m. Ci 137 Cs source is used. 13

LHCb HCAL: 137 Cs calibration system Measurement of current: 188 8 -channel integrator boards installed at the back of the HCAL nearby PMTs. Readout via the slow control bus (SPECS) (independent of the main DAQ) 4 ranges: 300 n. A, 1500 n. A, 9μA, 50 μA 12 bit ADC Currents in HCAL (MC) ETmax=15 Ge. V, L=2· 1032 cm-2 s-1 Current, n. A Integration time 1. 5 ms Not only for 137 Cs calibration. Currents in HCAL cells will be continuously monitored during physics data taking independent information on relative luminosity, doses etc 14

LHCb HCAL: 137 Cs calibration system I, ADC counts The source moves at constant speed (20. . 30 cm/s) the dependence of current on time I(t) can be fitted with a weighted sum of (empirically obtained) tile response functions placed at equal time intervals Δt: Measured current and fitting function superimposed ci (light yield of each tile) 15

LHCb HCAL: 137 Cs calibration system ± 20% All the HCAL modules passed the Cs test at production: all tile responses were required to be within ± 20% from average Distribution of RMS (%) of the light yield of tiles belonging to the same PMT. Average 4. 7% 16

LHCb HCAL: 137 Cs calibration system The precision of the 137 Cs calibration was studied at beam tests: independent calibrations with Cs and 50 Ge. V π― coincide within 2 -3%. The ratio of sensitivities to 137 Cs radiation and to hadrons was measured: 41. 07 (20. 88) (n. A/m. Ci)/(p. C/Ge. V) for outer (inner) cells. The calibration precision can be affected by e. g. timing Full tile counters Half tile counters 17

LHCb HCAL: current status ✔ Detector installed in the LHCb cavern ✔ Photomultipliers, LED drivers, integrator boards, signal and control cables are mounted on the detector and checked ✜ ≥ 99. 9% of the system operational ✔ hydraulic components and control electronics of the 137 Cs system tested HCAL July 2005 ✔ Frontend electronics, components of DAQ and trigger are installed Ongoing commissioning activities: ➧ studies with LED system: cell-to-cell time alignment long-term PM gain stability trigger operation ➧ studies with cosmic events: coarse inter-subsystem time alignment trigger operation ➧ 137 Cs calibration run: foreseen for mid. June 18

LHCb HCAL: current status Cosmic trigger: coincidence of HCAL and ECAL HCAL: all counters at G~200 k; ECAL: at 300 k With CALO trigger, cosmic events seen also in Pre. Shower/SPD and Muon system 19

Conclusions The LHCb HCAL is a iron - scintillator sampling device with structure arranged parallel to the beam direction. The light is read out by WLS fibers to PMT Its performance is adequate for providing L 0 trigger for high-E T hadrons It is equipped with 137 Cs calibration system and LED monitoring system The detector is installed in LHCb and operational Currently it is under intensive tests with LEDs and cosmic events; the 137 C calibration run is scheduled for mid-June Waiting for the first LHC collisions ! 20

SPARES 21

LHCb HCAL: LED monitoring system Time alignment with LEDs. Goal: determine optimal ADC sampling time for each cell and LED flashing delays time alignment events: ADC sampling several (5) consecutive bunch crossings BXi+1 scanning over LED flashing time, determine optimal delay for each cell account for the difference in [signal cable delay + PM transit time] within each PM group illuminated by one LED using the PIN photodiode signal timing as a reference, we can perform time alignment between groups knowing the time of flight, calculate optimal ADC sampling time settings at HV change, correct using known PM transit time dependence 22