The CMS electromagnetic calorimeter: status, performance with cosmic and first LHC data Cristina...

The CMS electromagnetic calorimeter: status, performance with cosmic and

first LHC data

The CMS electromagnetic calorimeter: status, performance with cosmic and

first LHC data

Cristina Biino* - INFN Torino

11th ICATPP Conference onAstroparticle, Particle, Space Physics, Detectors and Medical Physics

ApplicationsVilla Olmo, 5‐9 October, 2009

*On behalf of the CMS Electromagnetic Calorimeter Group

Cristina Biino* - INFN Torino

11th ICATPP Conference onAstroparticle, Particle, Space Physics, Detectors and Medical Physics

ApplicationsVilla Olmo, 5‐9 October, 2009

*On behalf of the CMS Electromagnetic Calorimeter Group

• Electromagnetic calorimeter at CMS– System description

• Results from cosmic ray running– Performances

– Response stability

• Results from LHC beams data• Current status• Conclusions

Outline Outline

PixelsTrackerECALHCAL

SolenoidMuons

• Benchmark channel: discovery of low mass Higgs in H channel

• Target energy resolution 0.5% at high energy for unconverted photons

ECAL BarrelECAL BarrelECAL EndcapECAL Endcap

The CMS detector requirements The CMS detector requirements

Scintillating PbWO4 crystals; Pb/Si preshower

E.M. Calorimeters:ECal barrel & endcap

• Compact & modular

• Hermetic

• Large Energy Range

• Fast & Stable

• Radiation Resistant

• Excellent Energy Resolution

CMS ECAL status ECAL Detector C. Biino – ICATPP 09

Barrel (EB)36 SuperModules (18 per half barrel)

61,200 crystalsTotal crystal mass 67.4t

|| < 1.48 x = 0.0175 x 0.0175

Barrel (EB)36 SuperModules (18 per half barrel)

61,200 crystalsTotal crystal mass 67.4t

|| < 1.48 x = 0.0175 x 0.0175

Endcap Preshower (ES)Pb (2Xo) / Si (1Xo) 4 Dees (2 per endcap)

4,300 Si strips1.8mm x 63mm1.65< || < 2.6

Endcap Preshower (ES)Pb (2Xo) / Si (1Xo) 4 Dees (2 per endcap)

4,300 Si strips1.8mm x 63mm1.65< || < 2.6

Endcaps (EE)4 Dees (2 per endcap)

14,648 crystals Total crystal mass 22.9t

1.48< || < 3 x = 0.01752 ↔ 0.052

Endcaps (EE)4 Dees (2 per endcap)

14,648 crystals Total crystal mass 22.9t

1.48< || < 3 x = 0.01752 ↔ 0.052

Barrel crystals

Pb/Si EndcapPreshower

Endcap ‘Dee’ with ‘Supercrystals’

ECAL design and layout ECAL design and layout


Crystals are projective and positioned pointing slightly off the IP to avoid cracks.

Homogenous Lead Tungstate (PbWO4) Crystal Calorimeter & Pb-Si Preshower

Challenges:Crystal LY temperature dependence -2.2%/OC

Need excellent thermal stability (±0.05 OC)

Formation/decay of colour centres Need precise light monitoring system

Low light yield (1.3% NaI) Need photodetectors with gain in magnetic

field

Challenges:Crystal LY temperature dependence -2.2%/OC

Need excellent thermal stability (±0.05 OC)

Formation/decay of colour centres Need precise light monitoring system

Low light yield (1.3% NaI) Need photodetectors with gain in magnetic

field

Properties: Homogeneous medium

Fast light emission ~80% in 25 ns

Short radiation length X0 = 0.89 cm

Small Molière radius RM = 2.10 cm

Emission peak 425nmReasonable radiation resistance to very high doses

Light yield (23cm) 100 /Mev

Properties: Homogeneous medium

Fast light emission ~80% in 25 ns

Short radiation length X0 = 0.89 cm

Small Molière radius RM = 2.10 cm

Emission peak 425nmReasonable radiation resistance to very high doses

Light yield (23cm) 100 /Mev

23cm 25.8Xo

22cm 24.7Xo

• EB crystal, tapered34 types, ~(2.6x2.6 cm2 at rear)x23cm

• Two avalanche photodiodes (APD), 5x5 mm2 each, QE ~75%, Temperature coeff.: -2.4%/°C

• EB crystal, tapered34 types, ~(2.6x2.6 cm2 at rear)x23cm

• Two avalanche photodiodes (APD), 5x5 mm2 each, QE ~75%, Temperature coeff.: -2.4%/°C

• EE crystal, tapered 1 type, (3x3 cm2 at rear)x22cm

• Vacuum phototriodes (VPT), more rad hard than diodes; gain 8 -10 (B=3.8T), Q.E. ~20% at 420nm

• EE crystal, tapered 1 type, (3x3 cm2 at rear)x22cm

• Vacuum phototriodes (VPT), more rad hard than diodes; gain 8 -10 (B=3.8T), Q.E. ~20% at 420nm

Scintillating crystals and photodetectors Scintillating crystals and photodetectors

PbWO4 Producers:

BTCP (Bogoroditsk, Russia)

SIC (Shanghai, China)

PbWO4 Producers:

BTCP (Bogoroditsk, Russia)

SIC (Shanghai, China)


ECAL readout & pulse shape reconstruction ECAL readout & pulse shape reconstruction

• VFE card: 3-gain amplification, shaping, digitization & sampling every 25nsec

• From ten time samples reconstruct the signal amplitude A and Tmax using digital filtering technique, weights, fit and ratio methods.

• Subtract the pedestal P on event-to-event

digitization via ADC


Energy resolution goal is 0.5% at high energyTime resolution goal is 0.1 nsec

2007:2007:Individual signoff

of each SM during installation in P5; H4 EE Test Beam

2006 2007 2008

2006:2006:H4 Test Beam:

9 SM calibrated;H2 Combined Test Beam:

ECAL&HCAL

2006-20072006-2007::Commissioning & calibration of each SM with cosmics on

surface

2006:2006:2 SM tested with B-field on surface

(MTCC)

2008:2008:Endcap

Installation; Commissioning

with cosmics and first beam in-situ

2009:2009:Installation of

Preshower and commissioning

of Endcap trigger

2009

Highlights from ECAL project timeline Highlights from ECAL project timeline


Toyoko Orimoto, Caltech 8

EB Module: 400/500 crystals

EB @ P5EB SM with electronics

EE Dee

EE Dee 1 & 2 @ P5

SuperCrystal

ECAL construction ECAL construction


ECAL barrel installation in 2007 ECAL barrel installation in 2007


ECAL Endcaps assembly in 2008 ECAL Endcaps assembly in 2008


ECAL Endcaps installation in 2008 ECAL Endcaps installation in 2008


basic cluster

super-cluster

Particle energy reconstructionElectrons and Photons are essential in:• at least two of the Higgs decay channels • decay of a new heavy bosons• Supersymmetry• Standard electroweak and QCD processes

containement correction

CMS ECAL Performance ECAL Perfomance C. Biino – ICATPP 09

• Unconverted Photons– Best energy estimate: energy sum in fixed arrays of

crystals (97% of the shower contained in a 5x5 arrays)

– Containment corrections (position dependent) precisely measured at test beam with electrons

• Electrons/Converted Photons– Require recovery of Bremsstrahlung in tracker

material (1 X0)– Super-clusters of clusters along (bending direction)– In the endcaps, add also the energy deposited in the

preshower

ECAL energy resolution ECAL energy resolution Nine Barrel SuperModules were studied at test beam with electrons

in the energy range 15-230 GeV. • Achieved constant term in energy resolution better than 0.5%• Noise is at 40 MeV level per channel, as expected.

Each Barrel SuperModule was exposed to cosmics for at least one week with increased APD gain.• 5M triggers per SM (average of about

500 good events per crystal)

(σ/E)2 = (3.37%/√E) 2 + (108 MeV/E) 2 + (0.25) 2

Only 500 Endcap channels were calibrated with 120 GeV electrons.Light yield measurement for each

crystal; photocathode QE, gain and total photo-electron yield measured for each VPT

CMS ECAL Performance ECAL Performance C. Biino – ICATPP 09

Calibration & MonitoringSome Results

CMS ECAL Performance ECAL Perfomance C. Biino – ICATPP 09

ECAL Calibration & Monitoring

Uncalibrated Supermodule : 13%-25% spread in resolution among channels

Lab Pre-Calibration: 4% EB, 10% EE (all crystals)

Cosmic Pre-Calibration: 1.5-2.5% (all EB)

TestBeam Pre-Calibration: 0.3% (1/4 of EB & 500 EE xtals)

In-Situ Physics Calibration: 0.5% resolution

• Without inter-calibration, same signal would produce different outputs in different crystals.

• Also need overall energy scale

Calibration of ECAL crucial to maintain high energy resolution.

ECAL Stability (<< 0.5%):Monitored with Laser System

Transparency Change Correction:Signal Change under Irradiation, Measured with Laser Monitoring System

ECAL Monitoring (Monitor Stability and Measure Radiation Effects):

CMS ECAL Performance ECAL Calibration & Monitoring C. Biino – ICATPP 09

ECAL In-Situ CalibrationGoal: improve startup calibration as quickly as possible in-situ

Strategy Time Precision

symmetry: use invariance of mean energy deposited by jets at fixed Few hours ~ 2-3%

0 : mass peak @ low luminosity Few days <= 1%

Zee: absolute energy calibration 100 pb-1 < 1%

We: E/p measurement 5-10 fb-1 0.5%

CMS PreliminaryL=2x1030cm-2s-1

CMS PreliminaryL=2x1030cm-2s-1


• During LHC cycles the ECAL response will vary, depending on irradiation conditions and crystal characteristics:– Transparency changes and fast recovery

(a few hours)

• Damage and recovery are monitored by laser light injected into each crystal through optical fibres– Blue light (440 nm) tracks response– Infrared (796 nm) provides a check

• The laser is pulsed during the LHC ‘orbit gaps’

• An optical switch directs light to onehalf-supermodule or one quarter-Dee in turn. A complete cycle takes ~ 20 min.

• Small transparency changes at start-up (L = 1030–1031 cm-2s-1)

• Corrected response• Raw response

Time (hours)

ADC

2/ndf =73.9/68

Test beam data

Simulation of crystal transparency evolution

at LHC (L = 2 x 1033cm-2s-1)

- based on test beam irradiation results

0.2%

Stability of the crystal responseStability of the crystal response

Laser monitoring system Laser monitoring system


Performance with CosmicsSome Results

CMS ECAL Performance CRAFT – ECAL Perfomance with Cosmics C. Biino – ICATPP 09

Commissioning ECAL with cosmicsCommissioning ECAL with cosmics

CRAFT: Cosmic Run At Four Tesla

– continuous running for several weeks to gain operational experience

– > 300 M cosmic events collected

– magnetic field operated at 3.8T

– most of CMS subsystems participating

Minimum ionizing particles deposit 250 MeV in ECAL. Increase efficiency: signal/noise enhanced (x4) in EB to the value of 20, by increasing the gain of the APD.


ECAL: timing and occupancy

SUSY09A. David

ϕ

Eseed > 100 MeV

Timing – bottom is late (t.o.f.)

Occupancy – top is busier (shaft side)

Top

Bottom

20

CRAFT


(25 nsec units)

3x3 crystal energy deposit confirms absolute energy scale to few %

<260> MeV

3x3 crystal energy deposit confirms absolute energy scale to few %

<260> MeV

Energy deposits per ECAL cluster from cosmics.

Depend on track length inside the active ECAl volume

Cosmic rays


Validate ECAL calibration with muons: measure energy deposition vs muon momentum

ECAL stopping power

Collision loss

Bre

mss

trahl

ung

Tracker momentum matches well with ECAL energy loss, energy scale is correct

CRAFT

momentum p measured in the CMS silicon tracker

dE: energy from ECAL cluster

dx: length traversed in ECAL crystals

dE/ρdx energy deposit matched to the track corrected for muon path length

Experimental data vs Expected stopping power for PbWO4 from literature

Not a fit !Not a fit !


LHC Beam (Sept. 2008)Some Results

CMS ECAL Performance First LHC Beam – ECAL Perfomance C. Biino – ICATPP 09

First LHC Beam in 2008

“Splash” Event

Wed, 10 Sept. 2008“Splash” events observed when beam (450 GeV, 4.109 p) struck closed collimators 150m upstream of CMS Halo muons observed once beam (uncaptured and captured) started passing through CMS

Data-taking with LHC beam.

Data-taking with LHC beam.

High energy deposit in the calorimeters, particles travelling horizontally

useful to commission forward detectorsAll systems ON except Tracker and Solenoid


Commissioning ECAL with first beamCommissioning ECAL with first beamBeam Splash Events: Single beam shots of 2109 protons onto

closed collimators 150m upstream of CMS

Longitudinal views

BEAMDebris

Transverse views

BEAM

Collimators

146m

CMSCMSDebris

Beam Splash Schematic

BEAM450 GeV

A “wave” or “splash” of secondary particles

passed through CMS, depositing a huge amount

of energy

ECAL ECAL EnergEnerg

yy


Beam Splash: ECAL Energy

• More than 99% of ECAL channels fired

• Estimated hundreds of thousands of muons passing through CMS per event

• ~200 TeV energy deposited in EB+EE

• Inter-crystals timing established (< 1ns), inter-crystal calibration: EB (1.5-2.5% - test beam + cosmics), EE (~7% from splash events)

• White areas: channels masked from readout

ECAL Endcaps

crystal index ix

cry

sta

l in

dex

iy

crystal index ix

cry

sta

l in

dex

iy

En

erg

y

(GeV

)

TOP BOTTOM

ECAL BarrelECAL Barrel

cry

sta

l in

dex

i

crystal index i

En

erg

y

(GeV

)


• Average energy per crystal over 50 splashes: 5-8 GeV

• Patterns:– shielding structures (square) and

floor of the LHC tunnel (bottom)

– lower energy at large radius of downstream EE, due to shielding effect of barrel

• EE pre-calibrations (spread 25%):

– Measurements from laboratory applied (precision of 9%): smoother and enhanced patterns

– New set being derived assuming local uniformity, to be combined with lab measurements for better startup values


Beam Splash: ECAL Energy

CMSCMS

TANTAN

TCTV

TCTV

TCTH

TCTHTCLP

TCLP

BEAM

Correlation between Correlation between Energies in barrel HCAL Energies in barrel HCAL

and ECALand ECAL

Correlation between ECAL Correlation between ECAL & Beam Loss Monitors& Beam Loss Monitors

~150 TeV deposited in ECAL & ~1000 TeV deposited in HCAL

per splash event

Beam Splash Correlations


Beam Splash: ECAL Timing

Muons

Muons

RED is a profile of the raw data, and BLUE is the nominal timing

according to the equation above.

• Observed pattern is due to pre-synchronization obtained with laser light

• Latency then adjusted w/ splashes: hardware allows steps of 1ns steps

• Further synchronization applied in offline reconstruction, better than 1 ns

• Synchronization from splashes will be start-up condition; better precision w/ LHC data

Beam splash events provide a source of synchronous hits throughout detector, allowing to internally synchronize ECAL


Laser distributi

on modularit

y

Shutdown activities: 1st maintenance cycle

CMS ECAL status Shutdown Activities C. Biino – ICATPP 09

* Only a few/mille channels are not functioning

Preshower:– Installed in the months of

February-March 2009

– First data collected to check out components and connections same status of health as in the laboratory, prior to installation:

• 99.88% good channels (tot 137k)• MIP Signal/noise: 3.6 in low gain

(physics) and 9 in high gain (calib)

Crystal calorimeter:

EB and EE active through LHC beams and extended cosmic ray run in 2008/2009

More than 99.5% of the channels are in good health for physics

System routinely operated in CMS global exercises, collecting data to monitor the detector and consolidate data acquisition and procedures

Trigger commissioning in the endcaps: first data collected, being finalized

Beam pipe

preshower

HCAL

EE

ECAL status of the detector ECAL status of the detector


Closing of CMS: 2009CMS is now closed after a 7-months

long and successfulmaintenance period

and is moving again into “beam-ready” state


Conclusions

• Crystal part of CMS Electromagnetic calorimeter has collected data with LHC circulating beams and during cosmic ray test runs

• Preshower detector installed in feb-march 09– Optimal health

– Joined CMS global runs

• Beam splash events allowed to validate performance and improve:– Endcap startup calibrations

– Internal synchronization

• Long cosmic ray run has allowed to validate energy scale in the barrel and assess stability of temperature and transparency monitoring, both matching specifications

• CMS ECAL on track for first LHC collision data


Spares

CMS ECAL Performance ECAL Calibration C. Biino – ICATPP 09

precision vs index (ring)

• Intercalibration precision at start-up• ECAL Barrel:

– 0.3% on 10 SM (electron beams)– 1.5-2.5% on 26 SM (cosmic

rays)

• ECAL Endcaps: – 1015% (LY measurement VPT gain)

• High energy electron test beam (0.3%) “Single crystal maximum response”

• Cosmic ray calibration (1.5-2.5%) Muons aligned to crystal axis Reference signal 250 MeV

• Crystal LY and transmission (4%) Co-60 gamma source

– Both validated against test beam data

36 Supermodules (100%) intercalibrated with cosmics

electron beam calibration

reproducibility (Aug - Sept)

/2 = 0.2%

10 Supermodules (25%) intercalibrated

with e-

Precalibration

1%

Light injected into each crystal using quartz fibres, via the front (Barrel) or

rear (Endcap)

Laser pulse to pulse variations followed with PN diodes to 0.1%

Normalise calorimeter data to the measured changes in transparency

F1 F2

PIN FE

LaserS

PWO

F1 F2

PIN FE

LaserS

PWO

Transparency and colour centres:These form in PbWO4 under irradiation

Partial recovery occurs in a few hours

Damage and recovery during LHC cycles tracked with a laser monitoring system; 2 wavelengths: 440 nm and 796 nm

Transparency and colour centres:These form in PbWO4 under irradiation

Partial recovery occurs in a few hours

Damage and recovery during LHC cycles tracked with a laser monitoring system; 2 wavelengths: 440 nm and 796 nm

Black: irradiation at test beamRed: after correction

1%

Reference diode

Transparency correction:Response to laser pulses relative to initial response provides correction

for loss of light yield loss PbWO4

Test beam irradiation exercises showed precision of correction of 0.15% on several channels

Transparency correction:Response to laser pulses relative to initial response provides correction

for loss of light yield loss PbWO4

Test beam irradiation exercises showed precision of correction of 0.15% on several channels

ECAL Laser monitoring system ECAL Laser monitoring system


ECAL: laser calibration chain ready

Data from a 300 h sequence

RMS (APD/PN) (RMS) VPt/PN

J.Malcles & laser team

% %

•Readout of PN ref working

•< 1 permill reproducibility

achieved•LED ‘stabilizer’

pulsing fully commissioned for

endcaps

Missing FEDs used for development

EE+

EE-

On EE- concurrent with LED load test

CMS ECAL Performance ECAL Calibration & Monitoring C. Biino – ICATPP 09CMS ECAL Performance CRAFT – ECAL Perfomance with Cosmics C. Biino – ICATPP 09

RMS (%)

Most of EB: stability better 1‰

In absence of transparency variation, the stability of the monitoring system can be assessed

• Laser data collected throughout CRAFT; laser sequence loops over all ECAL channels every 20 minutes;• For each channel and each sequence (600 events), the average <APD/APDref> is employed as monitoring variable• “Stability” is defined as the RMS over all laser sequences of normalized <APD/APDref>• Stabilities are computed for each channel on a period of 200 hours with stable laser conditions • APDref is chosen as a reference because of readout problems with PN reference diodes, which are being fixed• White regions lack statistics (2 supermodules were not readout for LV problems, now fixed)

CMS preliminary

Transparency monitoring stability (1)


CRAFT

Mean = 0.3 ‰RMS = 0.2 ‰

99.6% of channels with RMS<1‰99.9% of channels with RMS<2‰

CMS preliminary

• 1-d projection of map in previous slideTransparency monitoring system stable in EB to better than than 2‰ in99.9% of the channels (Consistent with specifications needed to achieve the design resolution)

Transparency monitoring stability (2)


CRAFT

°C

Average spread: 0.009

°C

CMS preliminary

• EB equipped with one precision temperature sensor every 10 channels, in good thermal contact with APD and crystal

• For each sensor, thermal stability is quantified with the RMS of the temperature measurements over one month of data taking

• The observed stability is 0.009°C on average and better than 0.05°C in all the channels.

1 month

Temperature stability during CRAFT


CRAFT

• At the end of CRAFT fully readout ( albeit with some synch problems on few FEDs)

• Latency scan performed

• Data being analysed ES residuals: distribution dominated by track extrapolation error

Preshower fully part of CMS Preshower fully part of CMS


• Following a meeting with the LHC people, experiments and CERN management the plan to restart has been agreed.

• Once collisions at injection energy are established will move to collision at 7 TeV center-of-mass energy.

• In consultation with experiments and LHC operation will move to higher energy once some luminosity will be accumulated by the experiments and experience gained by the machine operations.

Prospects for 2009-2010 Run


Early Physics Programme Detector commissioning – much already done using cosmics/testbeam,..

Early beam: splash events, first collisions at injection energy, then at 7 TeV

Detector synchronization, alignment with beam-halo events, minimum-bias events. Earliest in-situ alignment and calibration

Early beam - collisions, up to 10-20 pb-1 @ 7 TeV Commission trigger, start “physics commissioning” – “rediscover SM”:

Physics objects; measure jet and lepton rates; observe W, Z, top And, of course, first look at possible extraordinary signatures…

7 TeV, up to 100 pb-1 measure Standard Model, start searches Per pb-1: 3000 W l (l = e,); 300 Z ll (l =e, ); 5 ttbar +X

Improved understanding of physics objects; jet energy scale from W j j’; extensive use (and understanding) of b-tagging

Measure/understand backgrounds to SUSY and Higgs searches Early look for excesses from SUSY & Z’ resonances.

Collisions at higher energy: extend searches; Explore large part of SUSY and resonances at ~ few TeV ~ 1000 pb-1 entering Higgs discovery era

CMS Physics Early Physics Prospects C. Biino – ICATPP 09

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The CMS electromagnetic calorimeter: status, performance with cosmic and first LHC data Cristina...

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