CMS ECAL Cosmic Calibration Jason Haupt University Of Minnesota On behalf of the CMS ECAL collaboration

Compact Muon Soleniod (CMS) CALORIMETERS SUPERCONDUCTING COIL ECAL e  Scintillating PbWO4 Crystals HCAL Plastic scintillator/ brass sampling IRON YOKE TRACKER Silicon Micro Strips Pixels CMS, near Cessy France. Talk outward from the center (interaction point). First within a 4T magnetic field Silicon Tracker first… used for charge and momentum measurements in the mag field ECAL, lead tungstate scintillating crystals. For photon and electron identification HCAL, brass/scintillator sampling. Hadronic interactions Muon (Chambers). 3 types. Charge determination, momentum measurement. 4 T magnetic Field Total Weight 12,500 t Overall Diameter 15m Overall Length 21.6m MUON BARREL Drift Tube Resistive Plate Chambers ( ) DT Chambers ( ) RPC 7/31/2019

ECAL 61200 14684 Module 1 Module 2 Module 3 Module 4 Note the 4 modules per SM. Note eta ranges of ECAL. Shape differences between the different modules. 61,200 barrel crystals. Endcap out to eta of 3. 7/31/2019

PbWO4 Crystals Lead Tungstate Crystals Moliére radius 2.2cm Radiation Length 0.89cm Scintillation decay time 80% at 35ns Been shown to be radiation resistant Low LY compared to other commonly used crystals (CsI BGO …) -1.9%/oC temp dependence Lead Tungstate Crystals in CMS (Barrel) “Average size”, 2.4x2.4cm2 and 23cm in length 34 Different crystal shapes 25.8 Xo 36 Supermodules make up the barrel calorimeter Each Supermodule has 1700 crystals Lead Tungstate Crystals: Good qualities… (Maybe more about radiation hardness/recovery) Mention the reasonable LY and acceptable Temperature dependence. This is kept small by keeping the temperature to be known to within 0.1 degrees C. Also mention the average size and makeup of the different crystals. Size of a super module 7/31/2019

ECAL Barrel Optical Readout Two 5x5 mm2 APD’s/crystal Gain – 50 QE – 75% @ 420 nm Temp sensitivity – -2.4%/oC APD’s Nice QE. Great Linearity. Temperature sensitivity. Important that PMT’s cannot be used due to the high magnetic field. ≈ 4.5 photo-electrons/MeV 122400 Total APD’s Very Linear Devices 7/31/2019

ECAL Inter-calibration Goals Energy Resolution Goal : constant term “c”  0.5%  /E  0.5% (For High Energies) In-situ Calibrations Z  e+e- ~1 day 1% (with  ring inter-calibration) W±  e± ~2 months E/p from Tracker 0 , 0  , etc. Initial inter−calibrations LY ~4% Cosmics ~2% Test Beam ~0.3% (Not available for all SM’s) Reason for pre−calibration Uniform detector response at startup Can mention the other terms if needed, or include all of the energy resolution terms. Here I just want to point out that the dominate term at high energies is the constant term. In situ there are a few ways of accomplishing that 0.5% goal. Strict mass constraint on the Z decay and the W also provide excellent inter-calibrations. Pre inter-calibrations are critical to ensure a uniform detector response at startup. a = stochastic term (Shower containment fluctuations…) b = noise term (Pileup and electronics noise) c = contant term (Temp, uniformity, inter-calibration, …) 7/31/2019

Calibration Chain Crystal Energy → ADC count Crystal optical response APD Gain Amplifier Gain ADC 12bit Out Calibration Chain x12 x6 x1 MGPA Logic 12 bit ADC 2 1 12 bits 2 bits HV APD/VPT VFE architecture for single channel Calibration Chain. Calibration Number includes all of the above components. Test pulse takes out the electronics effects. Laser can look at the whole chain. 7/31/2019

Performance Checks Cross Checks Test Pulse (after APD) Compared to previous test pulses Laser allows for self referencing Compare one laser run to another x12 x6 x1 MGPA Logic 12 bit ADC 2 1 12 bits 2 bits HV APD/VPT VFE architecture for single channel Laser Calibration Chain. Calibration Number includes all of the above components. Test pulse takes out the electronics effects. Laser can look at the whole chain. Test Pulse 7/31/2019

Laboratory Inter-Calibration Two current methods to LY measurements (Basically Quality Checks) automated 1. Direct LY along crystal ~1.2 MeV source 2. Transmission through crystals longitudinally at 360nm Combined Laboratory constants Laboratory measurements are combined; LY, APD gain, the preamp. Result of a ~4.0% agreement compared to testbeam calibration constants Comparing ~1.2 MeV Source to 120 GeV testbeam! 60Co Laboratory measurements were done on the elctronics and have shown to be well know and can be tested well with the test pulse. LY measurements then add to make a laboratory inter-calibration constant. LY refers to the direct number of pe’s per MeV. Mention just “briefly” that the transmission is also included in the measurement. (It has been shown that the LY and the Transmission at 360nm are well correlated. They are independent measurements and can be combined together to a single intercalibration constant) The overall agreement is well. This was validated with test beam in 2004. There have been some recent improvements along these lines. 7/31/2019

Cosmic Ray Muons Cosmic ray muons deposit ~11 MeV/cm in PbWO4 crystals A through going muon will deposit ~250 MeV in a 23cm crystal APD gain was increased factor of 4 to get away from the ~38 MeV electronics noise. Actual gain ratio is found with laser. Also to improve the neighbor veto. 1 ADC count ~9 MeV Goal Improve measurement for all 61,200 barrel crystals with full readout chain Excellent way to run each SM ~10 days as a final “burn-in” step Maybe not call them “MIPs” they are on the relativistic rise of the dE/dx curve. Ave ~4 GeV (MIP ~0.5 GeV). Really note that the reason for the gain change is to keep the S/N as low as possible for this measurement. Also emphasize that the cosmic test is a great way to do the “burn-in” and electronics tests on a fully constructed Super Module. Really mention the Full Readout Chain. 7/31/2019

Cosmic Muon Trigger The trigger is a coincidence of one of 6 plastic scintillator counters spread over the bottom of the Super-Module with another counter placed near the interaction point. Trigger is designed as to select muons that are through-going. In this situation the amount of deposited energy is most well determined. 85x20 iηxi grid One SM has more than 34 Million Triggers Most have 4-7 M 23 SM’s have been calibrated with cosmics iη (85) Main reason of the trigger is to eliminate the need for a tracker. Doing a calorimetric selection really shows the ability of the crystals. The trigger was setup to collect data when a muon is through-going. Also some muons that are “mostly” through-going are selected as well. This was an effort to maximize the useful triggers  i (20) 10o 24o 7/31/2019

Cosmic Trigger Setup Trigger Counters Top Frame 6 Bottom Counters 4 5 1 2 3 Just a reiteration of the trigger/cosmic setup. Top Frame 7/31/2019

Crystal Selection E1 is the Energy of the Maximal crystal E2 is the energy of the next highest crystal around the max RED marks selection E1 > 10 ADC Counts Single Crystal E2 E1 E2 < 3 ADC Counts 2004 data SM10 G4 MC Here I go over the selection for all 3 types of data. Mention that they are independent selections. All calorimetric selections. 7/31/2019

All 3 selection types are independent Crystal Selection E3 EA is the Energy of the Maximal crystal EB is the energy of the next highest crystal around the max E3 refers to all other surrounding crystals Magenta marks selection  EA EB Double Crystal η All 3 selection types are independent E3 Same  EA EA & EB > 3 ADC counts EB EA + EB > 12 ADC counts Same  E3 < 3 ADC counts 2004 data SM10 Here I go over the selection for all 3 types of data. Mention that they are independent selections. All calorimetric selections. 7/31/2019

Useful Events ~25% of the triggers combined! Of the triggers Single ~10% Same eta ~6.8% Same phi ~8.6% ~500,000 Triggers/Day ~10 Days ~25% of the triggers combined! The numbers here are currently relative numbers. And relate to a specific SM. They are close to the average. So the number of useful triggers is more than doubled. 7/31/2019

MC Reference distributions Single Crystal Method Pulse-height distributions of the crystal of highest energy deposited (E1) are made for each crystal Pulse-height distributions are also generated from MC information. 17 different η dependent MC energy distributions are created. The constant is then found by adjusting the pulse-height to MC with an unbinned maximum likelihood method. Factor: Relative Scale = Calibration constant MC Reference distributions Soon, these E1 reference histograms will be made from a beam calibrated SM rather than relying on the Monte Carlo. But the number of reference distributions are expected to remain the same. Here are two fits from the CMS not quoted at the end of the paper. 7/31/2019 ADC ADC

Two Crystal Method (Matrix Inversion) Energy = Sum of both crystals Define a 2 Minimize the 2 for each constant Fill Matrix event by event Invert Only Input is the mean of the MC distributions 17 Monte Carlo (MC) E1+E2 reference distributions are made The mean is extracted from each within the selection range Reference distributions are created for special cases. Module Borders  edges η edges This sum of energies is only for the two crystals. E1 and E2. The chi sq’ed is minimized wrt to each crystal because we are taking the mean of a reference distribution and trying to equate it to the average of the data. Inputs are needed for the 17 different crystal types as well as for the special cases. 7/31/2019

Calibration Schema 36 SM’s 10 will have electron testbeam calibration Use the beam inter-calibration constants to build reference distributions for the cosmic data Use these cosmic reference distributions in place of MC Validate method by comparing inter-calibration constants obtained with test beam and with cosmics for different SM’s. Difference → precision Then use cosmic ray data to obtain inter-calibration constants for remainder of SM's. Use 1 beam calibrated SM to build the reference distributions for the other SM’s. We use the comparison of the cosmic to the beam for these other SM’s as a validation of the method. Therefore the Monte Carlo was only used as a tool to define the selection and validate that aspect. Then the reference distributions are valid on all the other SM’s This method isn’t restricted to using a single SM as reference. Just to use it as a validation. All the beam SM’s can be combined to have an actual reference. 7/31/2019

Statistical Precision vs  ½  ½ Each of the 3 data sets are divided in half Odd vs. Even events stat = odd vs. even/2 vs  ½  ½ vs  ½  ½ Single Crystal Double Crystal Each data set is split in half. Odd-even events. The sigma stat is quoted for the 4 different modules within a given SM. The single’s fit well to naïve expectations of peak width over root N. The double have a similar peak width, but they are larger due to the sharing of energy between more than one crystal. 7/31/2019

Test Beam data ECAL setup employs full CMS geometry and electronics setup Using electron beam with energy of 120 GeV Preliminaries available for two supermodules Used SM16 to build references Validate them with SM18 Combine the datasets according to the statistical uncertainties 7/31/2019

Test-Beam Comparison Good to 1.5% in SM16 and 1.9% in SM18 Ignoring edges and module borders This is for all inner-crystals. Neglecting module borders and edges of the SM. 7/31/2019

SM16 TB Comparison by module This is a module by module showing of the comparison of SM16, Which was also the two crystal reference distribution. 7/31/2019

Future Combined results with all beam calibrated SM’s Evaluate systematic uncertainties. Including beam data to check for differences between muons and electrons signals More than 23 SM’s have collected cosmic data. All are now expected to collect cosmic data. SM installation starting soon 7/31/2019

Conclusion → Uniform energy response between all crystals 5 million triggers (10 days), provides a statistically accuracy of 2% or better Testbeam comparisons show an average agreement over an entire SM of less than 2% Cosmic ray muons will provide the most accurate inter-calibrations that will be available to all barrel crystals at CMS startup Using the ~250 MeV cosmic signal we can predict to 2% the calibration constants found at 120 GeV. → Uniform energy response between all crystals 7/31/2019

References LY Cosmic General L. M. Barone et al. “Correlation between Light Yield and Longitudinal Transmission in PbWO4 crystals and impact on the precision of the crystal intercalibration.” CMS RN 2004-005 http://cmsdoc.cern.ch/documents/04/rn04_005.pdf F. Cavallari et al. “Improvement on PbWO4 Crystal Intercalibration Precision from Light Yield Measurements at the INFN-ENEA Regional Center” CMS RN 2004-003 http://cmsdoc.cern.ch/documents/04/rn04_003.pdf F. Cavallari et al. “Relative Light Yield comparison between laboratory and testbeam data for CMS ECAL PbWO4 crystals” CMS RN 2004-002 http://cmsdoc.cern.ch/documents/04/rn04_002.pdf E. Auffray et al. “SPECIFICATIONS FOR LEAD TUNGSTATE CRYSTALS PREPRODUCTION” CMS Note 1998-038 http://cmsdoc.cern.ch/documents/04/rn98_038.pdf Cosmic M. Bonesini et al. “Inter-calibration of the CMS electromagnetic calorimeter with cosmic rays before installation” CMS NOTE 2005/023 W. Bertl et al. “Feasibility of Intercalibration of CMS ECAL Supermodules with Cosmic Rays” CMS NOTE 2004/036 K. Deiters et al. “Test of the Feasibility of Pre-intercalibration of ECAL Supermodules with Cosmic Rays” CMS IN 2004/023 General CMS Collaboration, CMS Technical Proposal, CERN/LHCC 94-38 CMS Collaboration, The Electromagnetic Calorimeter Project TDR, CERN/LHCC 97-33 Particle Data Handbook and references therein 7/31/2019

Extras 7/31/2019

ECAL: Higgs   The reconstructed mass the the Higgs depends on the Energy of both photons as well as the angle between the two. The error of the photon energy is very important Term % expected E for 100GeV H a 2.7%/E 270 MeV c 155 MeV in ET 265 + 355 MeV b 0.5% 500 MeV 7/31/2019

Selection MC Selection from MC 7/31/2019