CMS ECAL performance and upgrade Anton Karneyeu (INR, Moscow) CMS Collaboration INSTR14, Novosibirsk, Russia, 27 February 2014

INSTR14, 27/02/2014, Anton Karneyeu 2 CMS experiment HCAL: hadronic calorimeter Muon chambers (white) and return yoke Solenoid: 3.8 T Compact Muon Solenoid A General purpose experiment at LHC for Higgs boson and New Physics searches Weight: tonnes External diameter: 15.0 m Length: 21.5 m Magnetic field: 3.8 T ECAL inside the coil Tracker coverage |η|<2.5 Tracker: charged- particle tracks and momentum measurements ECAL: photon and electron energy and position

INSTR14, 27/02/2014, Anton Karneyeu 3 Pb/Si preshower 1.65 < |  | < 2.6 Barrel (EB) |  | < crystals Endcaps (EE) 1.48 < |  | < crystals ENERGY RESOLUTION (BARREL, test-beam results) The energy resolution for photons from H→γγ in EB is 1.1% to 2.6% and in EE 2.2% to 5%. Timing resolution is 190 ps and 280 ps in EB and EE. Electromagnetic calorimeter Weight: 90 t Length: 7.8 m Diameter: 3.5 m

INSTR14, 27/02/2014, Anton Karneyeu 4 Crystals (PbWO 4 ) Reasons for choice: Homogeneous medium 8.3 g/cm 3 Fast light emission ~ 80% in 25 ns Short radiation length 0.89 cm Small Molière radius 2.20 cm Emission peak 420 nm Caveats: Low light yield (LY ~ 100 γ/MeV ) Need photodetectors with gain in magnetic field LY temperature dependence ~ −2.2%/C Need to stabilise to few 0.05 C Obtained stability: ~ 0.03 C Formation/decay of colour centres under irradiation altering crystal transparency Need precise monitoring system LY spread between crystals ~ 10% Need intercalibration Producers: Bogoroditsk Techno-Chemical Plant, Russia (> 95% of crystals) Shanghai Institute of Ceramic, China

INSTR14, 27/02/2014, Anton Karneyeu 5 Photodetectors Barrel: Avalanche photo-diodes (APD, Hamamatsu) Two 5x5 mm 2 APDs/crystal, ~ 4.5 p.e./MeV Gain 50 QE ~ 75% at 420 nm Temperature dependence 1/G ΔG/ΔT = −2.4%/C High-Voltage dependence 1/G ΔG/ΔV = 3.1%/V Need to stabilize HV at 30 mV Measured HV fluctuation: ~30 mV Endcaps: Vacuum photo-triodes (VPT, Research Institute “Electron”, Russia) More radiation resistant than Si diodes UV glass window Active area ~ 280 mm 2 /crystal, ~ 4.5 p.e./MeV Gain (B=4T) Q.E. ~ 20% at 420 nm Gain spread among VPTs ~ 25% Need intercalibration

INSTR14, 27/02/2014, Anton Karneyeu 6 Response monitoring system Sources of response variations under irradiation: Crystal transparency loss and recovery VPT ageing (not yet disentangle from transparency loss) Monitoring with LASER: Laser: 447 nm (main laser), green and infra-red Laser light injection in each crystal every ~ 40 minutes Light also injected in PN diodes ECAL signals compared event by event to PN reference Energy corrections derived Also LED (blue/orange) in endcaps. Laser

INSTR14, 27/02/2014, Anton Karneyeu 7 Response monitoring system Observed response change is from 6% (barrel) to 70% (endcap). These measurements are used to correct the physics data.

INSTR14, 27/02/2014, Anton Karneyeu 8 Calibration 1.π 0 /η → γγ method: equalizes measured π 0 /η peaks for individual crystals. 2.φ-symmetry: invariance around the beam axis of the energy flow in zero-bias events. 3.single-electrons from W decays: use E/p ratio where p is measured in the tracker and E in the ECAL. In addition to single-crystal intercalibration, this method also intercalibrates the average response of 248 φ-rings. 4.di-electrons from Z decays: use measured invariant mass to obtain the global scale corrections and study the ECAL resolution. Precalibration in performed using test beams, cosmic rays, radiation source and "beam splashes" during the first LHC runs. ~30% of the Barrel and 400 crystals in the endcaps were calibrated in the test beams to the design-goal single-crystal precision of 0.5%.

INSTR14, 27/02/2014, Anton Karneyeu 9 Calibration The precision of the phi-symmetry and photon calibrations is at the level of the systematic errors. The precision of the electron calibration is still dominated by the statistical errors for |η|>1.

INSTR14, 27/02/2014, Anton Karneyeu 10 ECAL energy calibration Impact on the Z → e+e- energy scale and resolution of corrections which account for the intrinsic spread in crystal and photo-detector response, and compensate crystal response lost.

INSTR14, 27/02/2014, Anton Karneyeu 11 ECAL supercluster energy Impact on the Z → e+e- energy scale and resolution from the incorporation of more sophisticated clustering and cluster correction algorithms.

INSTR14, 27/02/2014, Anton Karneyeu 12 Electron energy resolution Relative energy resolution of electron (from Z→e+e- decays) => Affected by the amount of material in front of the ECAL => Degraded near eta cracks between ECAL modules (vertical lines in the plot) => Dedicated calibration improves resolution significantly

INSTR14, 27/02/2014, Anton Karneyeu 13 Z → e+e- mass resolution The mass resolution of the Z → e+e- as a function of time. => Mass resolution is stable at the per mill level.

INSTR14, 27/02/2014, Anton Karneyeu 14 Physics results: H →γγ High energy resolution of the ECAL was critical for the discovery of the Higgs => Latest results on Moriond 2014 conference (March 15th - 22nd)

INSTR14, 27/02/2014, Anton Karneyeu 15 LHC schedule ECM=13 TeV L=1 ·10 34 cm -2 s fb -1 per year 3 years L=2 ·10 34 cm -2 s -1 ≥50 fb -1 per year 3 years ~ 300 fb -1 HL-LHC: L=5 ·10 34 cm -2 s fb -1 per year ~140 events per bunch- crossing Phase1 Phase2 A new machine, for high luminosity, to measure the H couplings, H rare decays, HH, Vector boson scattering, other searches and difficult SUSY benchmarks, measure properties of other particles eventually discovered in Phase1. LS 2 LS1 LS 3 ~ 3000 fb -1

INSTR14, 27/02/2014, Anton Karneyeu 16 Detector challenges at HL-LHC Number of events per bunch crossing (pile- up): ~ 140 Radiation levels will be 6 times higher than for the nominal LHC design. Strong η dependence in the endcaps (at η=2.6 hadron fluence 2·10 14 /cm 2, gamma radiation: 30 Gy/h, total: 300kGy) MARS calculations, P.C. Bhat et al., CERN-CMS-NOTE

INSTR14, 27/02/2014, Anton Karneyeu 17 Crystal radiation damage Gamma irradiation damage is spontaneously recovered at room temperature. Hadron damage creates clusters of defects which cause light transmission loss. The damage is permanent and cumulative at room temperature. Plot shows “external” optical transmission of crystal after diffent irradiation doses PbWO 4 emission spectrum

INSTR14, 27/02/2014, Anton Karneyeu 18 ECAL endcap response evolution Simulation 50 GeV e- Extensive test-beam studies with proton-irradiated crystals Reduction of light output causes: Worsening of stochastic term Amplification of the noise light collection non-uniformity (impact on the constant term) Progressive deterioration of energy resolution and trigger efficiency, with strong η dependence Performance for e/y is acceptable up to 500 fb-1 ECAL endcaps should be replaced during LS3 Fraction of ECAL response

INSTR14, 27/02/2014, Anton Karneyeu 19 Endcap calorimetry options for HL-LHC CMS plan is to replace the Endcap calorimeters in LS3 HE EE Two possible scenarios: 1. HE absorber is left, only active material is replaced. New EE will be a standalone calorimeter 2. HE is fully replaced. This opens the possibility of a more coherent redesign of the endcap calorimeters. Aim: radiation hardness, high granularity, precision timing

INSTR14, 27/02/2014, Anton Karneyeu 20 Scenario 1: standalone EE Shashlik Calorimeter in a sampling configuration with inorganic scintillator (LYSO or CeF 3 ) and W as absorber. Light readout via wavelength shifting fibers (WLS) Transverse dimensions are 14x14mm → fine grained Light path is short → rad- hard Challenges: rad-hard fibers, photo-detectors, mechanical mounting (tolerances)

INSTR14, 27/02/2014, Anton Karneyeu 21 Scenario 2: Combined Forward Calorimeter Dual Readout: simultaneous measurements of Cherenkov and scintillation signal (2 types of fibers) enables event-by-event compensation resulting in superior hadron and jet measurement (DREAM/RD52 collaboration) Challenges: rad-hard fibers, photo- detectors, mechanical design, triggering Scintillation fiber Cherenkov fiber Brass absorber

INSTR14, 27/02/2014, Anton Karneyeu 22 Scenario 2: High Granularity Calorimeter Layers of silicon “pads” (1 cm 2 ) separated by absorber (lead/Cu) Measure charged particle momentum with the inner tracker, and neutrals in the calorimeter. Key point: resolving/separating showers through a finely granulated and longitudinally segmented calorimeter. Challenges: number of channels, compact and inexpensive electronics, trigger, cooling, performance in high pile-up, linearity

INSTR14, 27/02/2014, Anton Karneyeu 23 Pile-up Mitigation Within tracker acceptance, charged particles are well reconstructed (Z vertex resolution ~ 0.1 mm) Pile-up is critical in the forward region: 1. Increased granularity and segmentation. 2. High precision (pico second) timing. Studies are ongoing for pile-up mitigation through time-of-flight. Desired resolution is ps. HL-LHC expected luminosity region: Gaussian width of ~ 10 cm Number of events per bunch crossing (pile-up) ~ 140

INSTR14, 27/02/2014, Anton Karneyeu 24 Conclusions The excellent ECAL performance was crucial for the Higgs boson discovery by CMS ECAL will continue to be highly performant throughout all Phase 1 The HL-LHC poses severe requirements to detectors in terms of performance and radiation hardness. ECAL endcaps should be replaced at the end of the LHC phase1 (after 500 fb -1 ). New calorimeter options are being studied. Key points are radiation hardness, granularity and segmentation. Timing resolution may add important information for pile- up mitigation.