Highlights from the 9 th Pisa Meeting on Advanced Detectors Calorimetry Session

Transcription

1 Highlights from the 9 th Pisa Meeting on Advanced Detectors Calorimetry Session Riccardo Paramatti University of Rome La Sapienza and INFN Rome Detector Seminar CERN 18/07/2003

2 9 th Pisa Meeting 2

3 9 th Pisa Meeting: the program Tracking Sessions: talk by Silvia Schuh (4 th july) 3

4 9th Pisa Meeting:calorimetry session 4

5 Liquid-Xenon photon detector for µ-> eγ Physics motivations: in the Standard Model this decay is forbidden; in the SM + Neutrino Oscillation this decay is strongly suppressed; in SUSY framework the Branching Ratio could be just below the current limit by MEGA (BR ). MEG sensitivity down to Continuos PSI (10 8 µ/s) on a stopping target Positron and photon back-to-back and in time Photon detected by Liquid Xe Photon Detector Positron detected by the Solenoidal Magnetic Spectrometer with a graded magnetic field 5

6 Liquid-Xenon photon detector for µ-> eγ (2) Signal: a positron and a photon back-to-back with E = 52.8 MeV Background: Radiativeµ + decay (if neutrinos carry small amount of energy) Positron from usual decay with E = m µ /2 and photon from radiative muon decay or from annihilation in flight of positron (not in time) Requirements: fast response, good energy, position and time resolution -> Liquid Xenon Absorption of scintillation light The emission reaction can t happen in the reverse way; only impurity (water, oxygen) could absorb the light. Absorption length increased, 7cm -> >1 m by Xenon purification. 6

7 Liquid-Xenon photon detector for µ-> eγ (3) Small prototype: 32 PMT surrounding 2.34 litres of active volume withoutpurificationsystem gamma-rays sources of different elements α source for PMT calibration Energy, position and time resolution measurements in agreement with Montecarlo simulation. Results published in Energy (MeV) 7

8 Liquid-Xenon photon detector for µ-> eγ (4) Large prototype: 228 PMT surrounding 68.6 liters of active volume (120 liters of liquid xenon in total) development and test of purification system for Xenon PMT long term operation at low temp. gamma beam test up to 40 MeV 60 MeV electron beam absorption length measurement 8

9 GLAST Calorimeter High energy gamma rays: 20 MeV 300 GeV GLAST will be launched in september 2006 The CDE have to operate in space at C 2 of 4 long side depolished to increase the tapering 9

10 GLAST Calorimeter (2) 14 CDE have been assembled and tested with cosmic muons The CsI LY decrease with temperature: test C -> 30 0 C 10

11 ATLAS Electromagnetic Calorimeter Lead - liquid Argon sampling calorimeter Accordion geometry 2 half-barrels: η < endcaps: < η < 3.2 Outside the solenoid The ATLAS calorimeter is built in 8 construction sites: Annecy, Saclay, CERN, Grenoble, Stockholm (barrel) and Marseille, Madrid, Novosibirsk (endcap) 11

12 ATLAS Electromagnetic Calorimeter (2) Longitudinal segmentation will provide good particle ID. uniform 12

13 CMS Electromagnetic Calorimeter Crystal calorimeter lead tungstate PbW0 4 crystals Magnetic field: B = 4 T Endcap preshower: 1.65 < η < 2.6 ECAL Two barrel Regional Centers: CERN (lab 27) and INFN/ENEA - Rome Endcap construction: UK, CERN 13

14 CMS Electromagnetic Calorimeter (2) Fast scintillation Small Xo and Rm Intrinsic radiation hardness Relatively easy to grow Massive production capability Low Light Yield High index of refraction Strong LY dependance on T 14

15 ATLAS: construction status Electromagnetic shower simulation Electrode composition Module assembly Geometrical measurements Gap thickness measurements Electrical test during assembly - HV performance (2200 V) Modulecabling Tests in final configuration 15

16 ATLAS: construction status (2) η = 0 η = 1.5 η = 1.4 η =

17 ATLAS: construction status (3) 17

18 ATLAS: construction status (4) 18

19 CMS: construction status Crystal R&D phase ( ) 6000 crystal preproduction ( ) Crystal production (2001-> ); 2-in-one crystal production is starting now 2 in one! BARREL ingot Further increase of the PbWO ingot diameter is foreseen: 2Endcap or 4Barrel crystals in one ingot are in test phase 19

20 CMS: construction status (2) CERN (lab 27) and INFN/ENEA (Casaccia) Regional Centers: Automatic measurements of: crystal dimensions, trasmission, light yield and uniformity Submodule assembly (10 crystals) Module assembly (40-50 submodules) Module type 2 - Rome Module type 4 - Cern 20

21 CMS: construction status (3) Modules from Rome RC Supermodule assembly at CERN Modules production 21

22 Energy Resolution The discovery potential of an intermediate mass Higgs boson via the two photon decay channel depends on the energy resolution. σ E = a E b E c a: stochastic term from Poisson-like fluctuations sampling contribution (natural advantage of omogeneous calorimeters) b: noise term from electronic and pile-up relevant at low energy c: constant term dangerous limitation to high energy resolution important contribution from intercalibration constants 22

23 the stochastic term CMS photostatistics contibution: -light yield - light collection efficiency - geometrical efficiency of the photodetector - photocatode quantum efficiency ATLAS pure sampling fluctuations deterioration for increasing η: - increase of amount of material - decrease of sampling frequency electron current multiplication in APD lateral containment of the shower Total stochastic term a = 2.7 % Total stochastic term: a 10 % 23

24 CMS: the constant term leakage (front, rear, dead material) CMS full shower simulation < 0.2 % temperature stabilization < 0.1 ûc (dly/dt = 18ûC ; dm/dt ~ -2.3 %/ûc) APD bias stabilization (±20 mv / 400 V) (dm/dv = 3%/V) light collection uniformity (next slide) intercalibration by monitor and physics signals Total constant term c = 0.5 % 24

25 CMS: the constant term (2) A non uniformity of the light collection in the shower max region may significantly contribute to the constant term in the energy resolution. Uniformity can be controlled by depolishing one lateral face with a given roughness Ideal light collection shape FNUF (crystals all polished) Max Front d(ly)/dx 0 =±0.35%/X 0 C fnuf < 0.3% Lab measurement 25

26 ATLAS: the constant term Absorber and gap thickness Ionization signal dependence with temperature (argon density vs T = %/ûc drift velocity vs T = %/ûc) High Voltage stabilization Leakage, material in front of calorimeter Local constant term c = 0.5 % over a small area ( η x φ = 0.2 x 0.4 -> 128 cells in the middle sector) with independent cell to cell electronics calibration Global constant term c = 0.7 % in situ-calibration with Z e+ e- decays to correct long-range non-uniformity 26

27 Performance: H -> γγ Events / 2 GeV m γγ (GeV) Signal-background, events / 2 GeV m γγ (GeV) ATLAS fb - M H =120 GeV S/ B 6.5->4.3 with M H = 120->150 GeV CMS fb -1 M H =130 GeV S/ B 13->8 with M H = 120->150 GeV 27

28 ATLAS: Test beam : barrel and endcap full-size prototype : 7 (4 barrel and 3 endcap) production modules 2002: combined endcap run with hadronic For every tested point: stochastic term a < 10 % (barrel) a < 12,5% (endcap) 28

29 ATLAS: Test beam (2) barrel endcap σ/e=0.49% Global non-uniformity 0.6% for whole module Global non-uniformity 0.5% for whole module Global constant term 0.7% within specifications 29

30 ATLAS: Future test beam 30

31 CMS: Precalibration Only few Supermodules will be calibrated at the Cern Test Beam facilities (intercalibration 2%) All crystals are intercalibrated in the lab. module assembly phase by Light Yield measurements ( 4%) LY meas. of reference crystals in INFN/ENEA Regional Center σ = 3-4% (with PMT and tyvek wrapping at 18 0 C) 31

32 CMS: Test Beam 2002 Intercalibration: lab. measurements vs test beam σ = 4.7% 32

33 CMS: Laser Monitoring Total dose after 10 years of running (5x10 5 pb -1 ) Only e.m. radiation produces a damage Scintillation mechanism is not affected [cm] EB EE Only crystal transparency is reduced creation of color centers Damage level depends on dose rate [Gy] creation and annealing of color centers at room temperature EB EE 0.15 Damage level reaches an equilibrium after a small administered dose Partial damage recovery in few hours Loss in extracted light of few % is tolerable and can be followed with a monitor system Dose rates [Gy/h] in ECAL at luminosity L=10 34 cm -2 s -1 33

34 CMS: Test Beam 2002 (2) The relation between XL response to e (S/S 0 ) and response to laser (R/R 0 ) varies in the same way during recovery and irradiation phases. Crystals irradiated 2-3 times produce same slope α Light monitoring system operational and stable α α σ/µ = 6.1% α α 34

35 CMS: Laser Monitoring (2) High luminosity simulation at η=0, based on data taken in test beam Time scale for absolute calibration with Z events Filling Collisions Dose 2.5 Gy in 8 h laser OK for correction of electron response 2003 test beam with other modules (different pseudorapidity) and more statistics 35

36 CMS: In situ calibration In-situ calibration with physics events: this is the main tool to reduce the constant term to the design goal of 0.5%. At the beginning of detector operation -> fast intercalibration method based on the φ symmetry in minimum bias events. Energetic electrons from Z e + e - decay -> intercalibration of different regions and absolute energy scale setting. Once the Tracker fully functional -> intercalibration of individual crystals with E/p measurement (W eν events). TRACKER MATERIAL: the amount of material (~ 1 X 0 ) between interaction point and ECAL is the main difficulty in performing calibration. 36

37 CMS: In situ calibration (2) φ symmetry Assumption: the total transverse energy deposited from a large number of events should be the same for all crystals at fixed η Aim: reduce the number of intercalibration constants at the startup: from (crystals) to 170 (rings) in the barrel. Studies with fully simulated Montecarlo give a precision of 1.3% - 3.5%, in case of limited knowledge of φ inhomogeneity. 37

38 CMS: In situ calibration (3) Z e + e - The rings can rapidly be intercalibrated using Z e + e - without tracker momentum measurements, using reconstruction of the invariant mass A large fraction of events allows to intercalibrate the endcaps with respect to the barrel The Z e + e - rate is ~ 1 Hz (almost flat in η) W e ν The electron shower involves many crystals -> algorithm to unscramble individually the calibration constants. The W eν rate is ~ 10 Hz. In few weeks at 2*10 33 cm -2 s 1, exploiting the full tracker information, 38 this high statistics channel will allow to reach 0.5% resolution

39 ATLAS: In-situ calibration constant 39

40 (not only) Tracker Material Complex tracking system + frames + cooling + cables and services Some radiation lenghts between the interaction point and the electromagnetic calorimeter! Bremsstrahlung and photon conversion (big non-gaussian tails in physical distributions) CMS ATLAS 40

41 Bremsstrahlung The electron cluster is spread by Bremsstrahlung (mainly in φ) Too little recostructed cluster: not full containment of brem. photons Too big recostructed cluster: noise, pile-up γ e ATLAS Energy recovery: cluster with fixed and optimized dimension. CMS Energy recovery: SuperCluster = clustering with dynamic algos. 41

42 ATLAS: electron reconstruction η η φ φ 42

43 CMS: electron reconstruction SUPERCLUSTERs Hybrid Algorithm: Used in the barrel Island Algorithm: Used in the endcaps single electrons, p t > 28 GeV only single clusters super- clusters Electronic noise No Pile-Up Electronic noise No Pile-Up To be compared with intrinsic calorimeter resolution < 0.9% 43

44 ATLAS: position resolution η 44

45 A brief ECAL comparison Barrel construction status Endcaps construction status Energy resolution: stocastic term Energy resolution: constant term ATLAS " # CMS # " # 45

46 A brief ECAL comparison (2) Intercalibration in situ with physics events Electron reconstruction γ/π o separation Tracker material, (bremsstrahlung and photon conv.) ATLAS # # "" CMS # "" 46