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Proceedings ArticleDOI

Performance of the CMS Electromagnetic Calorimeter at the LHC

01 Oct 2011-pp 1476-1479
TL;DR: The CMS Electromagnetic Calorimeter (ECAL) as discussed by the authors is a high resolution fine-grained calorimeter devised to measure photons and electrons at the LHC, which plays a crucial role in the search for new physics as well as in precision measurements of the Standard Model.
Abstract: The CMS Electromagnetic Calorimeter (ECAL) is a high resolution, fine-grained calorimeter devised to measure photons and electrons at the LHC. Built of lead tungstate crystals, it plays a crucial role in the search for new physics as well as in precision measurements of the Standard Model. A preshower detector composed of sandwiches of lead and silicon strips improves π0/γ separation in the forward region. The operation and performance of the ECAL during the 2010 run at the LHC, with pp collisions at √s = 7 TeV will be reviewed, and to some extent for the 2011 running as well. Pure samples of electrons and photons from decays of known resonances have been exploited to improve and verify the trigger efficiency, the reconstruction algorithms, the detector calibration and stability, and the particle identification efficiency. A review of these aspects will be given.

Summary (2 min read)

Introduction

  • Pure samples of electrons and photons from decays of known resonances have been exploited to improve and verify the trigger efficiency, the reconstruction algorithms, the detector calibration and stability, and the particle identification efficiency.
  • A preshower detector composed of sandwiches of lead and silicon strips improves π0/γ separation in the forward region.
  • Pure samples of electrons and photons from decays of known resonances have been exploited to improve and verify the trigger efficiency, the reconstruction algorithms, the detector calibration and stability, and the particle identification efficiency.

II. STATUS AND STABILITY

  • During the first months of collisions at LHC, in 2010 and 2011, the percentage of fully working channels in the ECAL Barrel and Endcap detectors is about 99.2% and 98.7%, respectively.
  • For the Preshower, the same percentage is around 95.1%.
  • The stability of the calorimeter as a whole is crucial to reach the design goal for the constant term in the energy resolution.
  • In particular, the monitoring of the temperature of the ECAL detectors is very important, since any change affects both the crystal transparency (−2.2%/°C) and the APD gain (−2.4%/°C).
  • Fig. 2 shows the RMS deviation of the temperature measurements for each sensor: the results are well within the stringent requirements (0.05°C for the Barrel and 0.1°C for the Endcap) imposed to achieve a constant term in the energy resolution of 0.5% [7].

III. ENERGY CALIBRATION

  • The ECAL energy reconstruction aims at the most accurate measurement of the scintillation light produced by the crystals from the energy impinging on the calorimeter.
  • A digital filtering technique is applied to the reconstructed signal amplitudes in the Barrel and Endcap crystals, starting from the samples of the pulse shape coming from the photodetectors, amplified and then digitized by the front-end electronics [8].
  • The response of the individual channels are equalized by means of inter-calibration coefficients.
  • Since an electromagnetic shower spreads over more than one crystal (only about 70% of the energy of an unconverted photon impinging on the centre of a Barrel crystal is contained within that crystal), to achieve the best estimate of the energy of the incoming particle, algorithms for clustering the energy deposits have been developed.

B. Crystal transparency monitoring

  • The design energy resolution of the ECAL detector depends on the accurate measurement and correction of the timedependent changes in the crystal light yield caused by light transmission losses due to radiation damage, Lxtal(t) [6].
  • Fig. 5 shows the doubleratio of the blue and infra-red laser measurements, for typical crystals in the ECAL Barrel and Endcap detectors.
  • The invariant mass is normalized to unity at the beginning of the period considered.
  • The uncorrected plot shows a 1% drop over this period.
  • Fig. 7 shows the history plot of the ratio E/p of the electron energy E as measured in the ECAL Barrel detector, to the electron track momentum p as measured by the CMS silicon Tracker, for electrons from W→eν decays, before and after the applying the transparency loss corrections.

IV. ENERGY SCALE

  • The energy scale, G, initially set using electron test beam measurements, has been tuned using Z→ee events from LHC collisions for both the ECAL Barrel and Endcap detectors [4].
  • Data events are corrected for the crystal transparency losses.
  • The left-hand plot shows only events where both electrons are in the barrel region, the right-hand plot contains only events where both electrons are in the endcap regions.
  • The plots show good agreement between data and simulation.
  • Fig. 9 shows the ratio Ereco/Ekin− 1 for Z→ µµγ events, in the ECAL Barrel (left) and Endcap detectors, where Ereco is the measured energy of the photon, and Ekin is the predicted photon energy from the difference between the Z mass [11] and the invariant mass of the µµ system.

V. ENERGY RESOLUTION

  • The energy resolution performance has been measured with an electron test beam in the energy range between 10 GeV and 180 GeV [10].
  • After the installation, the resolution has been studied using di-photon pairs from π0 decays and Z→ee events produced in proton-proton collisions [6].
  • On the left-hand, the full sample of events with both electrons in the barrel region are shown.
  • The distributions are fitted to a convolution of a Breit-Wigner (BW) and a CrystalBall (CB) function using an unbinned likelihood fit, to extract the Z peak shape parameters from the values of ∆mCB , the difference (in GeV) between the CB mean and the Z mass [11], and σCB , the width of the CB function.
  • The BW parameters are fixed to their PDG values [11].

VI. SUMMARY

  • The CMS ECAL detector status and performances with the first proton-proton collisions at the Large Hadron Collider have been presented.
  • The results match extremely well the expectations, thanks to the impressive preparatory work, and are close to the design goals.

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Content maybe subject to copyright    Report

Available on CMS information server CMS CR -2011/297
The Compact Muon Solenoid Experiment
Mailing address: CMS CERN, CH-1211 GENEVA 23, Switzerland
Conference Report
11 November 2011 (v2, 02 December 2011)
Performance of the CMS Electromagnetic
Calorimeter at the LHC
Giuseppe Della Ricca for the CMS Collaboration
Abstract
The CMS Electromagnetic Calorimeter (ECAL) is a high resolution, fine-grained calorimeter devised
to measure photons and electrons at the LHC. Built of lead tungstate crystals, it plays a crucial role
in the search for new physics as well as in precision measurements of the Standard Model. A pre-
shower detector composed of sandwiches of lead and silicon strips improves π
0
separation in the
forward region. The operation and performance of the ECAL during the 2010 run at the LHC, with
pp collisions at
s = 7 TeV will be reviewed, and to some extent for the 2011 running as well. Pure
samples of electrons and photons from decays of known resonances have been exploited to improve
and verify the trigger efficiency, the reconstruction algorithms, the detector calibration and stability,
and the particle identification efficiency. A review of these aspects will be given.
Presented at IEEE-nss-mic-rtsd2011: IEEE2011: Nuclear Science Symposium and Medical Imaging Conference

Performance of the CMS Electromagnetic
Calorimeter at the LHC
Giuseppe Della Ricca, on behalf of the CMS Collaboration
Abstract—The CMS Electromagnetic Calorimeter (ECAL) is
a high resolution, fine-grained calorimeter devised to measure
photons and electrons at the LHC. Built of lead tungstate crystals,
it plays a crucial role in the search for new physics as well
as in precision measurements of the Standard Model. A pre-
shower detector composed of sandwiches of lead and silicon strips
improves π
0
separation in the forward region. The operation
and performance of the ECAL during the 2010 run at the LHC,
with pp collisions at
s = 7 TeV will be reviewed, and to some
extent for the 2011 running as well. Pure samples of electrons and
photons from decays of known resonances have been exploited
to improve and verify the trigger efficiency, the reconstruction
algorithms, the detector calibration and stability, and the particle
identification efficiency. A review of these aspects will be given.
I. DESCRIPTION OF THE DETECTOR
T
HE Compact Muon Solenoid (CMS) [1] electromagnetic
calorimeter (ECAL) [2] at the Large Hadron Collider
(LHC) [3] is an hermetic, homogeneous calorimeter compris-
ing 61200 lead tungstate (PbWO
4
) crystals mounted in the
central Barrel part, closed by 7324 crystals in each of the two
Endcaps (see Fig. 1). The use of PbWO
4
crystals has allowed
Fig. 1. View of the CMS ECAL structure: Barrel (one supermodule in
yellow), Endcap (in green), Preshower (in red).
the design of a compact calorimeter inside the solenoid that
is fast, has fine granularity, and is radiation resistant. The
Barrel section (EB) has an inner radius of 129 cm, and
is structured as 36 identical “supermodules”, each covering
half the barrel length and corresponding to a pseudorapidity
interval of 0 < |η| < 1.479. The crystals have a front face
Manuscript received November 14, 2011.
G. Della Ricca is with the Universit
`
a degli Studi di Trieste, I-34127 Trieste,
Italy, and with the Istituto Nazionale di Fisica Nucleare, Sezione di Trieste,
I-34127 Trieste, IT (e-mail: giuseppe.della-ricca@ts.infn.it).
cross-section of about 22×22 mm
2
and a length of 230 mm,
corresponding to 25.8 X
0
. The Endcaps (EE) are located at a
distance of 314 cm from the vertex and cover a pseudorapidity
range of 1.479 < |η| < 3.0. The endcap crystals have a
front face cross section of 28.6×28.6 mm
2
and a length of
220 mm, corresponding to 24.7 X
0
. A Preshower detector
(ES) is placed in front of the crystal calorimeter over the
endcap pseudorapidity range 1.653 < |η| < 2.6. Its active
elements are two planes of silicon strip detectors, with a pitch
of 1.9 mm, which lie behind disks of lead absorber at depths
of 2 X
0
and 3 X
0
. The calorimeter is immersed within the
3.8 T magnetic field produced by the CMS solenoid. The
scintillation light produced in the crystals is read-out by a
pair of avalanche photodiodes (APD) for each EB crystal, and
a vacuum phototriode for each EE crystal. The small Moli
`
ere
radius (R
M
= 2.2 cm) in combination with the large number
of crystals results in a fine granularity for the lateral shower
shape. In the forward region the granularity is further improved
by the Preshower detector. An extended description of the
ECAL detector is provided in Ref. [4].
The ECAL detector has a crucial role in the physics program
of CMS. Its design has been driven by the requirement of an
excellent energy resolution [5]. This is needed in particular for
the search of the Higgs boson in the H γγ decay channel,
one of the primary goals of the LHC physics program, where
a good di-photon invariant mass energy resolution is essential
to discriminate a signal with a small cross section over a large
irreducible Standard Model background.
The ECAL energy resolution measured in electron test
beams is parametrized as
σ(E)
E
=
2.8%
p
E(GeV)
12%
E(GeV)
0.3%, (1)
for electrons incident on the center of crystals [6]. The three
contributions correspond to the stochastic term, the noise
term and the constant term. The stochastic term depends on
the event-by-event fluctuations in the electromagnetic shower
development, on the photo-statistics and on the photodetector
excess noise factor. The noise term depends on the level of the
electronic noise and event pile-up. The constant term depends
on the non-uniformity of the longitudinal light collection, on
the leakage of energy from the rear face of the crystals and
on the accuracy of the detector inter-calibration constants.
For electromagnetic showers of energies above 100 GeV
the energy resolution is dominated by the constant term.
As a consequence, in the CMS environment the detector’s
performance will depend mainly on the quality of its inter-
calibration and monitoring [7].

II. STATUS AND STABILITY
During the first months of collisions at LHC, in 2010
and 2011, the percentage of fully working channels in the
ECAL Barrel and Endcap detectors is about 99.2% and 98.7%,
respectively. For the Preshower, the same percentage is around
95.1%. The stability of the calorimeter as a whole is crucial
to reach the design goal for the constant term in the energy
resolution. In particular, the monitoring of the temperature of
the ECAL detectors is very important, since any change affects
both the crystal transparency (2.2%/°C) and the APD gain
(2.4%/°C). The calorimeter has thus been instrumented with
nearly 7000 thermistors to provide accurate monitoring. Fig. 2
shows the RMS deviation of the temperature measurements
for each sensor: the results are well within the stringent
requirements (0.05°C for the Barrel and 0.1°C for the Endcap)
imposed to achieve a constant term in the energy resolution
of 0.5% [7].
Fig. 2. Distribution of the spread in the temperature measurements of the
ECAL Barrel and Endcap thermistors in the second half of 2010.
III. ENERGY CALIBRATION
The ECAL energy reconstruction aims at the most accurate
measurement of the scintillation light produced by the crystals
from the energy impinging on the calorimeter. A digital filter-
ing technique is applied to the reconstructed signal amplitudes
in the Barrel and Endcap crystals, starting from the samples
of the pulse shape coming from the photodetectors, amplified
and then digitized by the front-end electronics [8]. The energy
deposited in a single crystal is proportional to the amplitude of
the digital pulse. The response of the individual channels are
equalized by means of inter-calibration coefficients. Since an
electromagnetic shower spreads over more than one crystal
(only about 70% of the energy of an unconverted photon
impinging on the centre of a Barrel crystal is contained within
that crystal), to achieve the best estimate of the energy of
the incoming particle, algorithms for clustering the energy
deposits have been developed. The energy of electrons and
photons can thus be expressed as:
E
e,γ
= F
e,γ
· G ·
X
xtal
L
xtal
(t) · C
xtal
· A
xtal
, (2)
where the sum is performed over the crystals in a cluster, A
xtal
is the measured APD’s/VPT’s raw ADC amplitude, C
xtal
is
the crystal inter-calibration coefficient, L
xtal
(t) is the time-
dependent correction for the radiation-induced transparency
loss, G is the ADC-to-GeV energy scale, and F
e,γ
is an
additional correction factor, which depends on the type of the
particle and on its energy, and takes into account geometry and
material effects like shower leakage and bremsstrahlung losses.
The ECAL detector has been calibrated prior to the LHC
startup with an overall precision of 0.5% 2% in the Barrel,
and 5% in the Endcap, using a combination of laboratory
measurements of the light yield and photodetector gain (with
a precision of 4.5% 6%), electron test beam measurements
(for 25% of the channels in the Barrel, with a precision of
0.5%), and muons from cosmic rays (with a precision of
1.4% 3.5%) and beam dumps (with a precision of about
6%). Before the installation in CMS, the global energy scale
has been defined using test beam data, and then tuned by
reconstructing di-photon and di-electron invariant mass peaks
of known particles with unconverted photons and electrons
with very low bremmstrahlung [7].
A. Inter-calibration
The start-up calibration precision is improved using proton-
proton collision data, combining different methods [9]:
the azimuthal symmetry method, exploiting the energy-
flow invariance around the beam axis in minimum bias
events, to inter-calibrate crystals at the same pseudora-
pidity;
π
0
and η resonances inter-calibration, using the invariant
mass peaks of di-photon events from π
0
(η) γγ
candidates (also useful to monitor the energy scale);
isolated, high energy electrons from Weν and Zee
decays, comparing the energy measured in ECAL with
the track momentum measured in the CMS silicon
Tracker;
radiative Z decays, using Z µµγ, assuming the correct
muon energy scale, to check the photon energy scale.
Fig. 3 shows the precision of the inter-calibration coefficients,
C
xcal
, as a function of the crystal η index for the azimuthal
symmetry method, and limited by the inhomogeneities in the
material in front of the calorimeter to about 1.5% 3%
depending on the pseudorapidity. Fig. 4 shows the precision
Fig. 3. Calibration precision from the azimuthal symmetry method, from
minimum-bias events, for the ECAL Barrel detector.
obtained combining all the different calibration strategies,
resulting in a precision of less than 0.5% at low values of
|η|, and increasing due to the material in front of the detector

for |η| > 1 in the ECAL Barrel, and less than 2% for
1.65 < |η| < 2.6 in the Endcap, corresponding to the region
covered by the Preshower detector.
Fig. 4. Combined inter-calibration precision for the ECAL Barrel (EB, left)
and Endcap (EE, right) detectors.
B. Crystal transparency monitoring
The design energy resolution of the ECAL detector depends
on the accurate measurement and correction of the time-
dependent changes in the crystal light yield caused by light
transmission losses due to radiation damage, L
xtal
(t) [6]. The
ECAL monitoring system is required to monitor transparency
changes at the level of 0.2%, with one measurement every
20 30 minutes. It consists of two different lasers: a blue
laser with a wavelength (400 nm) close to the emission peak
of scintillation light from the PbWO
4
crystals, and an infra-
red laser (796 nm), to compensate for variations that are
not due to the transparency loss. Fig. 5 shows the double-
ratio of the blue and infra-red laser measurements, for typical
crystals in the ECAL Barrel and Endcap detectors. The effects
of the transparency loss due to irradiation (about 1% in the
Barrel and about 4% in the Endcap detector), and subsequent
recovery, are clearly seen and are in good agreement with the
expectations from the LHC instantaneous luminosity. Fig. 6
Fig. 5. Measured crystal transparency loss due to irradiation in 2010 for the
ECAL Barrel (left) and Endcap (right) detectors.
shows the π
0
invariant mass history plot for photons in the
ECAL Barrel detector, before and after the corrections to the
crystal energy due to the transparency loss are applied. The
invariant mass is normalized to unity at the beginning of the
period considered. The uncorrected plot shows a 1% drop over
this period. After correction, the invariant mass distributions
are flat to within 0.2% for the majority of the running period.
Fig. 7 shows the history plot of the ratio E/p of the electron
energy E as measured in the ECAL Barrel detector, to the
electron track momentum p as measured by the CMS silicon
Fig. 6. π
0
invariant mass history plot in 2010 for the ECAL Barrel detector,
before and after the corrections for the crystal transparency loss.
Tracker, for electrons from Weν decays, before and after
the applying the transparency loss corrections. The ratio is
normalized to unity at the beginning of the period considered.
The uncorrected ratio shows a drop of 1.5% in the Barrel
detector (and correspondingly 6% in the Endcap detector)
during this period. After correction, the E/p histories are flat
to within 0.2% and 1%, respectively.
Fig. 7. E/p history plot, with E = ECAL electron energy, p = Tracker
electron momentum, for Weν decays measured in 2010 with the ECAL
Barrel detector.
IV. ENERGY SCALE
The energy scale, G, initially set using electron test beam
measurements, has been tuned using Zee events from LHC
collisions for both the ECAL Barrel and Endcap detectors [4].
Fig. 8 shows the invariant mass distribution for di-electron
events from Zee events, for both data and Monte Carlo
simulation. Data events are corrected for the crystal trans-
parency losses. The left-hand plot shows only events where
both electrons are in the barrel region, the right-hand plot
contains only events where both electrons are in the endcap
regions. The plots show good agreement between data and
simulation. The total systematic uncertainty on the ECAL
energy scale is 0.6% for the Barrel and 1.5% for the Endcap
detectors. Fig. 9 shows the ratio E
reco
/E
kin
1 for Z µµγ
events, in the ECAL Barrel (left) and Endcap (right) detectors,
where E
reco
is the measured energy of the photon, and E
kin
is the predicted photon energy from the difference between the
Z mass [11] and the invariant mass of the µµ system. Energies
are corrected for the crystal transparency losses. The photon
energy scale agrees well with the expectations at the 1% level.

Fig. 8. Invariant mass distribution for Zee, with both electrons in the ECAL
Barrel (left) and Endcap (right) detectors. Data and Monte Carlo distributions
are shown.
Fig. 9. Estimation of the photon energy scale from Z µµγ events, for
photons in the ECAL Barrel (left) and in the Endcap (right) detectors.
V. ENERGY RESOLUTION
The energy resolution performance has been measured with
an electron test beam in the energy range between 10 GeV
and 180 GeV [10]. After the installation, the resolution has
been studied using di-photon pairs from π
0
decays and Zee
events produced in proton-proton collisions [6]. Fig. 10 shows
the invariant mass distributions for di-electron events, for
data and Monte Carlo simulation. On the left-hand, the full
sample of events with both electrons in the barrel region are
shown. On the right-hand the sub-sample of non-showering
(low bremmstrahlung) electrons is shown. The distributions are
Fig. 10. Invariant mass distribution for Zee events in the ECAL Barrel
detector: (left) full sample of Zee events, (right) sub-sample of non-
showering electrons (low bremmstrahlung). Data and Monte Carlo distribution
are shown.
fitted to a convolution of a Breit-Wigner (BW) and a Crystal-
Ball (CB) function using an unbinned likelihood fit, to extract
the Z peak shape parameters from the values of m
CB
, the
difference (in GeV) between the CB mean and the Z mass [11],
and σ
CB
, the width of the CB function. The BW parameters
are fixed to their PDG values [11]. There is a good agreement
between the CB width for data and Monte Carlo distributions,
showing the good detector modeling in the simulation, with the
CB width being around 1 GeV for non-showering electrons.
VI. SUMMARY
The CMS ECAL detector status and performances with the
first proton-proton collisions at the Large Hadron Collider
have been presented. The results match extremely well the
expectations, thanks to the impressive preparatory work, and
are close to the design goals.
ACKNOWLEDGMENT
The author would like to thank the organizers of this
Conference for their invitation to come to the beautiful city of
Valencia, and present the CMS ECAL detector status.
REFERENCES
[1] The CMS Collaboration, The CMS experiment at the CERN LHC, J. Inst.
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[3] L. Evans, P. Bryant (editors), The LHC machine, J. Inst. 3 (2008) -
S08001.
[4] The CMS Collaboration, Performance and operation of the CMS electro-
magnetic calorimeter, J. Inst. 5 (2010) - T03010.
[5] The CMS Collaboration, CMS Physics Technical Design Report, Volume
1: Detector Performance and Software, CERN-LHCC 2006-001.
[6] P. Adzic, et al., Energy resolution of the barrel of the CMS Electromag-
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[7] The CMS Collaboration, Electromagnetic calorimeter commissioning and
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Citations
More filters
01 Jan 2013
TL;DR: In this paper, the authors analyzed data recorded by the Compact Muon Solenoid (CMS) experiment to study the production of high-mass muon pairs in proton-proton collisions at the LHC (Large Hadron Collider).
Abstract: Data recorded by the CMS (Compact Muon Solenoid) experiment is analyzed to study the production of high-mass muon pairs in proton-proton collisions at the LHC (Large Hadron Collider). Most of the presented results are based on a dataset of 5.3 fb−1 at a center-of-mass energy of √ s = 7 TeV. The interpretation of the measured dimuon mass spectrum focuses on a potential non-resonant signal from s-channel graviton exchange. Such a signature of new physics is motivated by the ADD (Arkani-Hamed, Dimopoulos, Dvali) model of large spatial extra dimensions. The main background for the search is given by the SM (Standard Model) prediction of neutral current Drell-Yan events. Other background sources like for example tt̄ production are also considered. The Standard Model expectation is evaluated based on simulation studies and can be tested for dimuon masses below the signal region. Estimates of theory uncertainties on the background prediction and uncertainties related to the detector performance are included in the statistical evaluation of the measurement. The dimuon mass spectrum observed in the 2011 CMS dataset is found to be compatible with the SM expectation. For masses greater than 1.3 TeV, signal cross sections of greater than 0.84 fb−1 can be excluded at 95% confidence level. This result corresponds to an exclusion of values below 3.0 TeV for the ADD model parameters ΛT. A combination of dimuon, dielectron and diphoton results based on a dataset of about 2.0 fb−1 extends the excluded range to ΛT < 3.3 TeV. Also limits based on the 2012 CMS dataset at collision energies of √ s = 8 TeV and some aspects of the CMS search for new dilepton resonances are briefly discussed.

14 citations


Cites background from "Performance of the CMS Electromagne..."

  • ...Studies with Z → ee events report an estimated systematic uncertainty on the ECAL energy scale of ≈ 1% at energies close to mZ/2 [157]....

    [...]

DOI
01 Jan 2012
TL;DR: In this article, the authors present a search for resonant top quark pair production in the muon+jets channel at CMS, using the 2011 dataset of proton-proton collisions at 7TeV with a luminosity of 5.0/fb.
Abstract: This thesis presents a search for resonant top quark pair production in the muon+jets channel at CMS, using the 2011 dataset of proton-proton collisions at sqrt(s)=7TeV with a luminosity of 5.0/fb. No excess over standard model backgrounds is found and exclusion limits on resonances decaying to top quark pairs are set.

11 citations


Cites background from "Performance of the CMS Electromagne..."

  • ...Around 99% of the channels of the barrel and endcap and about 95% of the channels in the preshower detector have been operational in 2011, and the observed resolution in data agrees with the expected resolution from test-beam measurements and simulation [82]....

    [...]

References
More filters
Journal ArticleDOI
TL;DR: The Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC) at CERN as mentioned in this paper was designed to study proton-proton (and lead-lead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 10(34)cm(-2)s(-1)
Abstract: The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron Collider (LHC) at CERN. It was conceived to study proton-proton (and lead-lead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 10(34)cm(-2)s(-1) (10(27)cm(-2)s(-1)). At the core of the CMS detector sits a high-magnetic-field and large-bore superconducting solenoid surrounding an all-silicon pixel and strip tracker, a lead-tungstate scintillating-crystals electromagnetic calorimeter, and a brass-scintillator sampling hadron calorimeter. The iron yoke of the flux-return is instrumented with four stations of muon detectors covering most of the 4 pi solid angle. Forward sampling calorimeters extend the pseudo-rapidity coverage to high values (vertical bar eta vertical bar <= 5) assuring very good hermeticity. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m and a total weight of 12500 t.

5,193 citations

Journal ArticleDOI
Petar Adzic, R. Alemany-Fernandez, Carlos Almeida, N. Almeida  +265 moreInstitutions (26)
TL;DR: In this paper, the energy resolution of the barrel part of the CMS Electromagnetic Calorimeter has been studied using electrons of 20 to 250 GeV in a test beam, and the incident electron's energy was reconstructed by summing the energy measured in arrays of 3 × 3 or 5 × 5 channels.
Abstract: The energy resolution of the barrel part of the CMS Electromagnetic Calorimeter has been studied using electrons of 20 to 250 GeV in a test beam. The incident electron's energy was reconstructed by summing the energy measured in arrays of 3 × 3 or 5 × 5 channels. There was no significant amount of correlated noise observed within these arrays. For electrons incident at the centre of the studied 3 × 3 arrays of crystals, the mean stochastic term was measured to be 2.8% and the mean constant term to be 0.3%. The amount of the incident electrons' energy which is contained within the array depends on its position of incidence. The variation of the containment with position is corrected for using the distribution of the measured energy within the array. For uniform illumination of a crystal with 120 GeV electrons a resolution of 0.5% was achieved. The energy resolution meets the design goal for the detector.

128 citations

Journal ArticleDOI
TL;DR: In this article, the operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muons are described and the stability of crucial operational parameters, such as high voltage, temperature and electronic noise, is summarised and the performance of light monitoring system is presented.
Abstract: The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muons are described. These muons were recorded after the closure of the CMS detector in late 2008. The calorimeter is made of lead tungstate crystals and the overall status of the 75 848 channels corresponding to the barrel and endcap detectors is reported. The stability of crucial operational parameters, such as high voltage, temperature and electronic noise, is summarised and the performance of the light monitoring system is presented.

100 citations

Journal ArticleDOI
Petar Adzic1, R. Alemany-Fernandez, Carlos Almeida, N. Almeida  +266 moreInstitutions (31)
TL;DR: In this paper, the amplitude of the signal collected from the PbWO4 crystals of the CMS electromagnetic calorimeter is reconstructed by a digital filtering technique using test beam data recorded from a fully equipped barrel supermodule.
Abstract: The amplitude of the signal collected from the PbWO4 crystals of the CMS electromagnetic calorimeter is reconstructed by a digital filtering technique. The amplitude reconstruction has been studied with test beam data recorded from a fully equipped barrel supermodule. Issues specific to data taken in the test beam are investigated, and the implementation of the method for CMS data taking is discussed.

61 citations

Journal ArticleDOI
TL;DR: In this article, the relative response of the individual channels of the barrel electromagnetic calorimeter of the CMS detector with cosmic ray muons and test beams was investigated, and the intercalibration was found to be reproducible to a precision of about 0.3%.
Abstract: Calibration of the relative response of the individual channels of the barrel electromagnetic calorimeter of the CMS detector was accomplished, before installation, with cosmic ray muons and test beams. One fourth of the calorimeter was exposed to a beam of high energy electrons and the relative calibration of the channels, the intercalibration, was found to be reproducible to a precision of about 0.3%. Additionally, data were collected with cosmic rays for the entire ECAL barrel during the commissioning phase. By comparing the intercalibration constants obtained with the electron beam data with those from the cosmic ray data, it is demonstrated that the latter provide an intercalibration precision of 1.5% over most of the barrel ECAL. The best intercalibration precision is expected to come from the analysis of events collected in situ during the LHC operation. Using data collected with both electrons and pion beams, several aspects of the intercalibration procedures based on electrons or neutral pions were investigated.

39 citations

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Q1. What have the authors contributed in "Performance of the cms electromagnetic calorimeter at the lhc" ?

Pure samples of electrons and photons from decays of known resonances have been exploited to improve and verify the trigger efficiency, the reconstruction algorithms, the detector calibration and stability, and the particle identification efficiency. Pure samples of electrons and photons from decays of known resonances have been exploited to improve and verify the trigger efficiency, the reconstruction algorithms, the detector calibration and stability, and the particle identification efficiency. Pure samples of electrons and photons from decays of known resonances have been exploited to improve and verify the trigger efficiency, the reconstruction algorithms, the detector calibration and stability, and the particle identification efficiency. An extended description of the ECAL detector is provided in Ref. [ 4 ]. In the forward region the granularity is further improved by the Preshower detector.