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Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 1 1 ECAL (inter)calibration and monitoring ECAL è un rivelatore bellissimo ma non esattamente facile.

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Presentazione sul tema: "Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 1 1 ECAL (inter)calibration and monitoring ECAL è un rivelatore bellissimo ma non esattamente facile."— Transcript della presentazione:

1 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 1 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 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 2 Photons with CMS Detector Toyoko Orimoto, Caltech 2 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 coefficients which make every crystal answer in the same way 2000 ADC 2100 ADC

3 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 3 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 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 4 4 ECAL Detector Design 2.6m 6.4m 1 Super-Module 1 Dee 1 Endcap Super-Crystal Pb-Si Pre-shower Barrel (EB): crystals 36 Supermodules (SM), each 1.7k crystals Endcap (EE): crystals 4 Dees SuperCrystals of 5x5 xtals

5 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 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 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 6 Intercalibration & Energy resolution Energy resolution: how well do we reconstruct signals as a function of energy? For every calorimeter we have: Stochastic Term: Photostatistics Sampling (not for ECAL!) Gain stage = a E + c E Constant term: Calibration & intercalibration Rear leakage Light yield non-uniformity + b Noise term: Electronic (pre-amps,APD) Pile-up It dominates at high energy, so it should be kept small Measured: 2.8% E MeV + 0.3% E

7 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 7 From ADC to GeV Calibration aims at the best estimate of the energy of e and s Energy deposited over multiple crystals: E e/ = F e/ G i c i A i [ +E ES ] Amplitude in ADC counts A i Intercalibration: uniform single channel response to a reference c i Global scale calibration G Particle-specific corrections (containment, clustering for e/ s) F e/ Preshower included in the sum in endcaps Theres inter-play across the different terms and a strategy to dis-entangle

8 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 8 Present status of c i 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 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 9 What if LHC starts tomorrow EB EE Z ee width H γγ width EB 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 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 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 o mass: huge rate, 1 week at 2* Goal: 0.5 % in barrel, a few in the endcap Z mass: needs good luminosity…

11 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 11 In situ strategy Derive intercalibrations c i from phi-inv. and 0 /η Fix absolute scale G and corrections (η, E T and cluster shape dependent) F e/ with electrons from Z e + e - ES calibration (mip) and EE-ES inter-calibration Long-term also other channels: isolated electrons Weν Theres sufficient redundancy of calibration sources to disentangle interplay between G/F e/ and c i : Validation and combination of calibration sets Release new sets for reconstruction as long as precision improves. Further sets for monitoring. E e/ = F e/ G i c i A i

12 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 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 nellinterfill 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 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 13 LASER Monitoring System Hardware 4 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 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 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 = cm -2 s -1 Simulation of transparency: L = 2 x cm -2 s -1 ) Scenario comparable to (ECAL TDR): cm -2 s -1 rel. Crystal response Transparency variation measured via response R/R 0 to blue laser pulses injected in each channel in the LHC abort gap Correction to crystal energies proportional to: (R/R 0 ) α with α=1.5 BCTP crystals, α=1 SIC crystals Classic VPT effect induced by LHC on/off changes in cathode current; mitigated by LED constant pulsing to limit current excursions: on average 1%

15 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 15 Stability of the ECAL response: VPT gain Black: load=10kHz, ~0.25nA; 46 days =2.1 and L=2.5*10 33 cm 2 s -1 Grey : load=20kHz, ~1.0nA; 134 days =2.1 and L=10 34 cm 2 s -1 Rel. VPT gain ~25% Rel. VPT gain Response to blue laser/LED and orange LED sensitive to VPT gain changes Correction to crystal energies simply proportional to monitored change (α=1) Long term ageing: irrelevant in 2010Classic VPT effect induced by LHC on/off changes in cathode current; mitigated by LED constant pulsing to limit current excursions: on average 1%

16 Nov. 13 th, 2009 Nicolo Cartiglia, INFN, Turin, Italy 16 Speriamo bene… Ci sono circa 30 persone che lavorano alla calibrazione e monitoraggio di ECAL Per ora sembra che riusciremo a farlo…


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