Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 1 Calibrazioni del calorimetro: esperienze (L3) e prospettive Egidio Longo

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 2 a ~ 2.5%/√E b < 200 MeV c ~ 0.5% and an angular resolution   ~ 50 mrad/  E CMS ECAL benchmark m  = 2 E 1 E 2 (1 - cos  )  H (m H  100 GeV) ~ 2 – 100 MeV  H /m H ≤ target  low mass Higgs discovery:

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 3 resolution: stocastic term a photostatistics contribution, including –LY –light collection efficiency –geometrical efficiency of the photodetector –photocatode quantum efficiency N pe /GeV = 4000 for 0.5 cm 2 APD  1.6% electron current multiplication in APD, contributing a square root of excess noise factor, F =  1.4 = 2.25% Lateral containment (5  5 matrix)  1.5% Total stochastic term a = 2.7 %

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 4 resolution: noise term b 40 ns shaping time, summed over 5x5 channels Serial noise (p.d. capacitance)  1/  t –150 MeV Parallel noise (dark current)   t, mostly radiation induced –negligible at the start of the experiment –30 MeV after one year at low luminosity –100 MeV after one year at high luminosity Physics pile-up (simulated, with big uncertainties) –low luminosity 30 MeV –high luminosity 100 MeV Total contribution –low luminosity 155 MeV –high luminosity 210 MeV

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 5 resolution: constant term c leakage (front, rear, blind material) CMS full shower simulation < 0.2 % system instabilities designed to be at the permill level –temperature stabilization < 0.1 ˚C (  LY = -1.9 % per ˚C) –APD bias stable at 20 mV (dM/dV = 3%/V) light collection uniformity, Specifications to stay < 0.3%  reached by single face depolishing Key issue to have c  0.5 %  intercalibration by monitor and physics signals at 0.5 % including the radiation damage effect

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 6 resolution at test beam on 1999 prototype 30 preproduction crystals and APDs fit as a function of E: (few crystal intercalibration)

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 7 Is it realistic to require a target 0.5 % intercalibration for such a large scale calorimeter? Look at L3 experience intercalibration

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 8 L3 BGO calorimeter 7680 (barrel) (EC) BGO Crystals PIN diode read-out (no gain) 12 bit ADC for 6 gains (1 to 512) noise level around 1 MeV sparse scan (zero suppression) read-out

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 9 L3 calibration tools Individual Test beam calibration (2-50 GeV e - ) Xenon monitor of the response once per day Bhabha events at Z pole (45 GeV e  ) at LEP200, RFQ calibration (17 MeV  ) Standard in situ procedure: Individual intercalibration with Xe lamps Absolute calibration with bhabha electrons for groups of crystals sharing the same Xe lamp

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 10 test beam calibrations Individual calibration for 7680 crystals –two half barrels in two years (1987,1988) –first half barrel recalibrated in 1988 –4 energies (2, 10, 20 and 50 GeV) –temperature control (nominal ± 0.5 ºC) –temperature monitor (1300 sensors) at 0.2 ºC –fully automated procedure: sequence, positioning, monitor and quality check

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 11 intercalibration in 1990 after Xe corrections 1.25 % % 0.87 % measured resolution MC predicted intercalibration spread (average response decreased by 5 %, due to ageing of some optical component) 1990 Bhabha spectrum

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo years of follow-up system able to track this response decrease (few %/year) porting of previous year calibration: 1.3% spread after Xe+Bhabha corrections: 0.8%

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 13 follow-up at LEP200 at LEP200 (too few Bhabha) add RFQ gun send protons on Li target, producing 17 MeV photons, million events in few days year after year, algorithms improved –several months of work to get final calibrations every year latest result: 1.06% resolution measured on GeV Bhabha electrons  intercalibration contribution 0.5 %

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 14 conclusions for L3 L3 BGO calibration combined test-beam precalibration, monitor and physics events Porting from test-beam to the experiment was performed at < 1.5% After all corrections, first year intercalibration was known at 0.9% After ten years of improvements, intercalibration known at 0.5%

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 15 CMS-ECAL calibration scheme individual crystal precalibration at beam test at several energies intercalibration porting to the experiment via laser monitor system follow-up of radiation damage by laser monitor system calibration by physics events every few months

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 16 calibration ground rules

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 17 ECAL installation in V31 SM assembly electronics calibration

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 18 precalibration We probably will not be able to precalibrate all ECAL supermodules We may be forced to choose between the “production serial precalibration” of the maximum number of modules, or the precalibration of a smaller number of modules with deeper understanding of a few modules to be recalibrated several times

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 19 intercalibration Issue is crystal intercalibration (the energy scale can be fixed relatively simply reconstructing the Z invariant mass with just a few Z  ee) –Raw intercalibration from lab measurements < 6% –Target test beam pre-calibration < 2% –Target final intercalibration using electrons 0.4 Is precalibration crucial? –Not clear how well HLT system will work with 6 % intercalibration –Much easier to understand what is going on with 2 % intercalibration –Precalibration ultimate system test before LHC data taking (F. Cavallari)

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 20 in situ calibrations Baseline intercalibration uses W electrons measured in tracker Calibration electron selection and its efficiency What efficiency to select ‘good’ (not much brem) electrons that can be well reconstructed in 5x5 crystals? Calibration algorithm How many electrons per crystal needed; what is best algorithm to unscramble the calibration constants? To do: simulate the whole procedure (milestone 3/02): Introduce inter-calibration errors and show how well they can be recovered Use of Z  ee invariant mass 5 times less events “internal” ECAL calibration (minimal tracker information needed) can be combined with monitor for absolute calibration Large samples of W’s and Z’s to study these issues (  P. Meriadiani talk)

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 21 alternative intercalibrations What to do if missing pre-calibration and poor electron capability (tracker) ? look at the energy flow in minimum bias –  dependence,  simmetry (?) –trigger bias study on sample of 500k fully simulated mb events available cut out noise

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 22 energy flow calibration (1) Total energy after truncation cuts (200 MeV). Each entry in histogram represents total energy in a single crystal. 360 crystals at the same  Since MC crystals are perfectly calibrated, the width represents the error on intercalibration achievable with 500k events 2% requires 11 M min-bias events  6.6 M crossings  183 hours (at 10Hz) (< 2 months for 30% duty cycle)  2 hours (at 1kHz —to do in HLT farm)

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 23 energy flow calibration (2) limitations: –intercalibration per  raws only (combine with Z absolute calibration ?) –tracker inhomogeneities needs for realistic tracker services simulation (and a combined tracker-ECAL test beam?) –sentitivity to channel-to-channel noise variations better algorithms? –slope of E T rather than truncated mean

Roma, 22/11/01CMS Software & Computing Workshop - E. Longo 24 conclusioni 0.5% difficili ma possibili baseline calibrazioni in situ con W  milestone per 03/02 Roma partecipa attivamente agli studi di calibrazioni con W e Z precalibrazione completa impossibile; studi su possibili alternative iniziati da poco simulazione realistica del tracker essenziale per le prossime produzioni test beam con sezioni di tracker e calorimetro auspicabili