1 / 16

ECAL (inter)calibration and monitoring

ECAL (inter)calibration and monitoring. ECAL è un rivelatore bellissimo ma non esattamente facile per farlo funzionare. La difficoltà aumenta tanto più il calorimetro è preciso, ogni cosa diventa importante per raggiungere la precisione voluta.

cale
Download Presentation

ECAL (inter)calibration and monitoring

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. ECAL(inter)calibration and monitoring ECAL è un rivelatore bellissimo ma non esattamente facile per farlo funzionare. La difficoltà aumenta tanto più il calorimetro è preciso, ogni cosa diventa importante per raggiungere la precisione voluta. ECAL ha tanti fisici quanti DT, RPC e CSC sommati (ma siamo la meta’ del TRK…), circa 30 persone lavorano in ‘calibration & monitoring’.

  2. Toyoko Orimoto, Caltech ECAL Intercalibration • Problem: the same photon (or electron) gives a different answer (in ADC counts) depending upon the crystals it hits. • each crystal has a specific light yield • each photodetector has its specific gain (important in the endcaps) • => poor resolution • Solution: find 75848 coefficients which make every crystal answer in the same way 2100 ADC 2000 ADC

  3. ECAL monitoring • The calorimeter response varies due to many factors: • Temperature: • Crystal light yield changes -2.1%/C • Barrel photodetectors (APD) -2.4%/C • Magnetic field: • Endcaps photodetectors (VPT) • Rate: • Endcaps photodetectors (VPT) • Radiation: • Crystals • Solution: a very powerful monitoring system which has 4 lasers, 2 sets of LED flashers and an almost crystal-by-crystal temperature monitoring system

  4. ECAL Detector Design 6.4m • Barrel (EB): • 61200 crystals • 36 Supermodules (SM), each 1.7k crystals 2.6m 1 Endcap Super-Crystal 1 Super-Module • Endcap (EE): • 14648 crystals • 4 Dees • SuperCrystals of 5x5 xtals Pb-Si Pre-shower 1 Dee

  5. Crystal production Crystals are grown in ingots (in Russia and China) and then cut into the right shape. Each crystal is different, with a different value of transparency and light yield

  6. Intercalibration & Energy resolution ‘Energy resolution’: how well do we reconstruct signals as a function of energy? For every calorimeter we have: • Noise term: • Electronic (pre-amps,APD) • Pile-up s = a √E + c E + b It dominates at high energy, so it should be kept small Measured: s = 2.8% √E + 125 MeV + 0.3% E • Stochastic Term: • Photostatistics • Sampling (not for ECAL!) • Gain stage • Constant term: • Calibration & intercalibration • Rear leakage • Light yield non-uniformity

  7. From ADC to GeV • Calibration aims at the best estimate of the energy of e and ’s • Energy deposited over multiple crystals: • Ee/ = Fe/G i ci Ai [ +EES ] • Amplitude in ADC counts Ai • Intercalibration: uniform single channel response to a reference ci • Global scale calibration G • Particle-specific corrections (containment, clustering for e/’s) Fe/ • Preshower included in the sum in endcaps • There’s inter-play across the different terms and a strategy to dis-entangle

  8. Present status of ci • Intercalibration has been achieved in several ways, with different precision: • BARREL: • - Using data collected in the laboratories (all): Crystal response, APD gain, electronics constants: 4.5-6% • Cosmic ray (all): expose each SM to cosmic rays: 1-2 % • TestBeam (11 SM): electrons at a given energy in each crystal ~ 0.3 % • ENDCAP: • Using data collected in the laboratories (all): Crystal response, VPTgain, electronics constants. Production: 9%, Pre-production:15% • Beam splash (all): expose each Dee to muons: 15 % • TestBeam (450): electrons at a given energy in each crystal < 1 %

  9. What if LHC starts tomorrow Hγγ width Zee width EB EB EE • Performance acceptable for most physics in EB, nearly in EE • Target: • Target precision: 0.5% set by H benchmark channel • Approach a.s.a.p. in view of  resonances

  10. Next step: in situ intercalibration • Once we will be taking data we will exploit several channels to bring intercalibration coefficient to a much higher precisions: • symmetry: based on the phi invariance, actually severely more complicated that it looked on the beginning (Stefano, Margherita). Statistically limited after a few hours of data taking. • Goal: 1-2% in barrel, a few in the endcaps • po mass: huge rate, 1 week at 2*1030. • Goal: 0.5 % in barrel, a few in the endcap • Z mass: needs good luminosity…

  11. In situ strategy • Derive intercalibrations ci from phi-inv. and 0/η • Fix absolute scale G and corrections (η, ET and cluster shape dependent) Fe/ with electrons from Ze+e- • ES calibration (mip) and EE-ES inter-calibration • Long-term also other channels: isolated electrons Weν • There’s sufficient redundancy of calibration sources to disentangle interplay between G/Fe/ and ci : • Validation and combination of calibration sets • Release new sets for reconstruction as long as precision improves. Further sets for monitoring. • Ee/ = Fe/G i ci Ai

  12. Monitoring • Il nostro calorimetro cambia la risposta per varie ragioni: • Temperatura: sia i cristalli che gli APD diminuiscono la risposta (luce o guadagno) se la temperatura aumenta (la combinazione dei due è -3.8%/C) • Irradiazione: i cristalli si ingialliscono a causa del danno da radiazione, tuttavia un pochino recuperano… • Fluenza: i VPT cambiano la risposta quando sono sottoposti ad un flusso continuo di particelle, quindi durante il ‘fill’ perdono brillantezza, ma poi la recuperano nell’interfill • Flusso totale: i VPT perdono brillantezza tanto più carica viene depositata sul loro catodo • Soluzione: un sistema di laser/led che continuamente spara segnali ‘calibrati’ nei cristalli per monitorare la loro risposta.

  13. 4 LASER Monitoring System Hardware • Laser light sources • Light distribution system (fibers, optical switches, diffusing spheres, etc.) • Very stable PN-diodes used as reference system (MEM) • Precision pulsing system for electronics calibration (separate hardware for MEMs) • LED pulsing system for the EE, injecting into level 1 fan-out APD PN APD VPT

  14. Stability of the ECAL response: Crystal transparency ECAL response will vary, depending on dose rate with a sequence of crystals transparency drops and recoveries 2010 run: transparency change expected in innermost crystals of EE assuming luminosity will reach L = 1031 cm-2s-1 • ‘Classic VPT effect’ induced by LHC on/off changes in cathode current; mitigated by LED constant pulsing to limit current excursions: on average 1% Simulation of transparency: η=0.92 @ L = 2 x 1033cm-2s-1) Scenario comparable to (ECAL TDR): η=3 @1031cm-2s-1 rel. Crystal response • Transparency variation measured via response R/R0 to blue laser pulses injected in each channel in the LHC abort gap • Correction to crystal energies proportional to: (R/R0 )α • with α=1.5 BCTP crystals, α=1 SIC crystals

  15. Stability of the ECAL response:VPT gain • ‘Classic VPT effect’ induced by LHC on/off changes in cathode current; mitigated by LED constant pulsing to limit current excursions: on average 1% • Long term ageing: irrelevant in 2010 Black: load=10kHz, <IC>~0.25nA; 46 days h=2.1 and L=2.5*1033cm2s-1 Grey : load=20kHz, <IC>~1.0nA; 134 days h=2.1 and L=1034cm2s-1 Rel. VPT gain Rel. VPT gain ~25% Response to blue laser/LED and orange LED sensitive to VPT gain changes Correction to crystal energies simply proportional to monitored change (α=1)

  16. Speriamo bene… • Ci sono circa 30 persone che lavorano alla calibrazione e monitoraggio di ECAL • Per ora sembra che riusciremo a farlo…

More Related