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2008 BEAM TEST ANALYSIS OF CASTOR CALORIMETER AND PEDESTAL
*
STABILITY OF HCAL DURING GLOBAL RUNS
CASTOR Kalorimetresinin 2008 Hüzme Testi Analizleri ve HCAL’İN Genel Veri
Alımı Sırasındaki Pedestal Kararlılığı
Emine GÜRPINAR
Fizik Anabilim Dalı
Gülsen ÖNENGÜT
Fizik Anabilim Dalı
ABSTRACT
Centauro and Strange Object Research (CASTOR) which is a tungsten/quartz
Cerenkov sampling calorimeter, is installed in the very forward region of the
Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC). It
will cover the pseudo rapidity range 5.1<eta <6.6 and will be placed 14.38 m away
from the interaction point. In order to test the performance of the CASTOR
Calorimeter, CASTOR prototype IV was tested at CERN/SPS H2 beam line in
2008. In my analysis X-surface scan is studied using E=50 GeV pions and E=100
GeV electrons.
Hadronic Calorimeter (HCAL) which is a subsystem of the CMS experiment at
the LHC, consists of four subdetectors, Hadronic Barrel (HB), Hadronic Endcap
(HE), Hadronic Outer (HO) and Hadronic Forward (HF). In HCAL, pedestal is
important to determine the muon energy deposits and for quality of calibration of
HCAL. Also in my analysis, I studied pedestal stability of all subdetectors of HCAL
by using data taken during CRAFT (Cosmic Ray at Four Tesla) runs.
Key Words : CASTOR, HCAL, CMS, LHC.
ÖZET
Centauro ve Acayip Cisim Arastırmaları detektörü (CASTOR), Büyük Hadron
Carpıştırıcısı (LHC)’deki Compact Muon Solenoid (CMS) deneyinin ileri bölgesine
yerleştirilecek olan Çerenkov ışıması ilkesine dayanan bir tungsten-kuvartz
örnekleme kalorimetresidir. Etkileşme noktasından 14.38 m uzaklığa konulacaktır
ve 5.1<ŋ<6.6 pseudorapidite aralığını kaplayacaktır. CASTOR kalorimetresinin
performansını test etmek amacıyla 2008 yılında CASTOR’un IV. prototipinin
CERN/SPS H2 deney alanında hüzme testi yapılmıştır.
LHC’de CMS deneyinin alt sistemi olan Hadronik Kalorimetre (HCAL) Hadronik
fıçı (HB), Hadronik kapak (HE), dış kısım (HO), ve ileri kalorimetre (HF) gibi 4 alt
dedektör içermektedir. HCAL’de pedestal, müon enerjisini ve kalibrasyonun
kalitesini belirlediği için önemlidir. Analizimde ayrıca Cosmic Run At Four Tesla
(CRAFT) sırasında alınan veriler kullanarak HCAL’in tüm altdedektörlerinin
pedestal kararlılığı araştırılmıştır.
Anahtar Kelimeler: CASTOR, HCAL, CMS, LHC.
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Yüksek Lisans Tezi-MSc. Tehsis
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Introduction
High energy physics searches the elementary constituents of matter and the
interactions between them. It concentrates on subatomic particles. These contain
atomic constituents like electrons, protons, and neutrons. Protons and neutrons are
really combined particles which are made up of quarks. All the particles and their
interactions observed until now can almost be described entirely by a quantum field
theory called Standard Model (SM). The Standard Model is the common theory of
quarks and leptons and their electromagnetic, weak and strong interactions. But it
is not a complete theory because it has many important unanswered questions.
Because of this, beyond the Standard model physics research is needed. Beyond
the SM physics will be studied of the experiments A Torodial LHC Apparatus
(ATLAS), Compact Muon Solenoid (CMS), A Large Ion Collider Experiment
(ALICE) and A Large Hadron Collider Beauty (LHC-B) on the Large Hadron
Collider (LHC) ring at European Nuclear Research Laboratory (CERN).
.
The Large Hadron Collider (LHC)
The Large Hadron Collider (LHC) which is the world’s highest-energy particle
accelerator, was built by the European Organization for Nuclear Research (CERN).
LHC aims to collide opposing particle beams, protons at a center of mass energy
of 14 TeV. Experiments on the LHC are believed strongly to help scientist to
answer the existence of mysterious questions like what gives mass to a particle?,
what is the nature of dark matter?, do extra dimensions exist? etc.
LHC has four big experiments. They are the Compact Muon Solenoid (CMS), A
Large Torodial LHC Apparatus (ATLAS), Large Hadron Collider b-quark
experiment (LHC-b) and A Large Ion Collider Experiment (ALICE). The CMS and
ATLAS are multipurpose experiments. They have the same scientific aims but the
technical solution and design of detector magnet system are different. The LHC-b
is a specialized experiment which will be investigating the differences between
matter and antimatter by studying a type of particle called the ’beauty quark’. The
ALICE will study the quark-gluon plasma in heavy ion collisions.
CMS Deneyi
The CMS experiment is a general-purpose detector. CMS experiment will
investigate new physics at TeV scale, discover the Higgs boson and look for
evidence of physics beyond the SM, SUSY or extra dimensions.
The CMS detector consists of subdetectors which are a silicon tracker, an
electromagnetic calorimeter and a hadron calorimeter, surrounded by a solenoid
which generates a strong magnetic field of 4 T, in order to measure the tracks,
energy and momentum of photons, electrons, muons and the other particles over a
large energy range and at high luminosity. An overall picture of the CMS can be
seen in Figure 1.
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Figure 1. The CMS detector. (The Collaboration, 2007)
Hadronic Calorimeter (HCAL)
HCAL which will measure quark, gluon and neutrino directions and energies by
means of measuring the energy and direction of particle jets and of the missing
transverse energy flow, is subsystem of the CMS detector.
The HCAL consists of four subdetectors which are Hadronic Barrel (HB),
Hadronic Endcap (HE), Hadronic Outer (HO) and Hadronic Forward (HF). HB
covers the ŋ range -1.4< |ŋ| < 1.4 and the HCAL endcaps (HE) cover the
pseudorapidity range 1.3< |ŋ| <3.0. They are the sampling calorimeters which
consist of plastic scintillators as active material inserted between copper absorber
plates, which are placed between the ECAL and the magnet. Light collected from
the scintillators are read out by the HybridPhoto Diodes (HPD). The HB is not deep
enough to contain a hadronic shower fully. Thus, the HO comes in to play to catch
the tails of a hadronic shower. The HO contains scintillators with a thickness of 10
mm, is physically located inside the barrel muon system. It covers the region 1.26< |ŋ| <1.26. It is divided into 5 sections along ŋ, called rings -2, -1, 0, 1, and 2.
The HF calorimeters, the last subdetector of HCAL, are placed 11 m away
from the interaction point. The HF calorimeter is located at 3.0< |ŋ| <5.0. It uses the
quartz fibers as the active medium.
The CASTOR Calorimeter
The Centauro and Strange Object Research (CASTOR) calorimeter which will
search the Centauro-type events in heavy-ion collisions, is one of the forward
detectors of CMS. The CASTOR calorimeter (see Figure 2.) has been a part of the
CMS detector since June 2009. It will search the electromagnetic and hadronic
contents of the interactions by measuring the energies of the particles.
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Figure 2. The CASTOR Calorimeter
It is a tungsten/quartz Cerenkov electromagnetic and hadronic sampling
calorimeter, an octagonal cylinder in shape. Castor will cover the region 5.2 ≤ |ŋ| ≤
6.4. It is divided into 16 sectors in azimuth. Also it is divided longitudinally into 14
sections, 2 sections for the EM part and 12 sections for the HAD parts in depth.
The electromagnetic section consists of 2x16 channels. The hadronic section has
12x16 channels. CASTOR calorimeter consists of successive layers of tungsten
plates (W) as absorber and fused silica quartz (Q) plates as active medium.
Thicknesses of W plates and Q-plates are 5mm and 2mm respectively for hadronic
section the W and Q plates have thicknesses of 10mm and 4mm larger, than the W
0
plates and Q plates of EM, tilted at 45 with respect to the direction of the impinging
particles due to capture maximum of Cerenkov light in the quartz. Cerenkov light is
produced by the passage of particles through the medium and is collected in
sections of 5 W/Q then focused by air-core light guides onto the PMTs.
The CASTOR Calorimeter has 224 (16x14) subdivisions in total. The Cerenkov
light produced in each one is collected and focused by air-core light guides onto
the corresponding PMTs. There are 5 tungsten/quartz layers called Sampling Units
(SU) in both the EM and HAD sections, each read by a Readout Unit (RU)
(CASTOR EDR, 2007). This calorimeter design and components are shown in
Figure 3.
Figure 3. The details of the CASTOR Calorimeter
Analysis And Results
Introduction
In this chapter, I present the analysis results of the CASTOR calorimeter test
beam of prototype IV data collected at CERN in the summer of 2008. My analysis
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consists of two parts:I studied the X-surface scan by using E=80 GeV pion and
E=100 GeV electrons
Beam Test of CASTOR Prototype-IV
The beam test of prototype IV was performed in the H2 line at CERN
Super Proton Synchrotron (SPS). The energy linearity, resolution and uniformity,
as well as the surface scan were studied for electrons, pions and muons of various
energies. The prototype IV was a full-length octant which consisted of EM and
HAD sections with a total of 28 readout-units (RUs). W plates, as absorber, and Q
plates as active medium were installed in one octant of Castor prototype-IV. Light
is produced by the passage of relativistic particles via Q medium and collected by 5
W/Q layers. Then it is focused by air-core light guides onto the PMTs. Schematic
drawing of the beam test with 28 RUs indicated are shown in Figure 4. The beam
comes from the left impinging on the EM sections.
Figure 4. Schematic drawing of Castor prototype-IV (Aslanoglou et al., 2008).
X-Surface Scan Analysis
X-Surface Scan with electron runs
Electron beams at 100 GeV energy with various X-positions were used to
study X-surface scan for electron runs. I have analyzed 16 electron runs.
A beam cut was applied to the beam profile for all runs, the beam for each
point was subdivided into a number of smaller parts, each of diameter 2 cm, so
more impact points could finally be used. Also some spatial cuts were applied for
all runs. These are scintillator cuts, muon cuts, electromagnetic fraction cut.
Scintillator cuts (SC1, SC2, SC4) were applied to tag the single particle events.
Muons were rejected using the muon veto counter (MVB) placed behind the
CASTOR prototype. For rejection of pions, FEM cut which requires that the ratio of
the mean value of total electromagnetic channels (EM) to the mean value of total
channels (EM+HAD) has to be larger than 0.95 used. Figure 5. exhibits the signal
distribution for the electron beam of E = 100 GeV before and after all the cuts. The
results of the X-scan analysis are shown in Figure 6. It shows the response of the
EM two semi-octants (Saleve and Jura side) as the beam impact point moves
across the front face of the calorimeter. The sigmoid nature of the response curve
is evident. The X-derivative of the response is calculated, giving the width of the
electromagnetic shower. We observe that one standard deviation amounts to σEM
=1.903 mm for the (Saleve side) EM shower and σEM =1.601 for the (Jura side) EM
shower.
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Figure 5. Signal distribution of the sum of the signals in EM1, EM3 and HAD1
channels after applied all cuts (a), Signal distribution of the sum of the signals in
EM1, EM3 and HAD1 channels after applied all cuts (b).
Figure 6. Response of the semi-octant of the EM section (Saleve side, Jura side)
as the beam scans the front face of the calorimeter (a). The derivative of the
response with respect to x, indicating the width (σ=1.903 mm for Saleve side,
σ=1.601 mm for Jura side) of the EM shower (b).
X-Surface Scan with pion runs
Pion beams at 80 GeV energy were used to study X-surface scan with pion
runs. The main goals of X-surface scan with pion runs are to determine the width of
the HAD shower profile. To study the X-surface scan of the hadronic section of the
calorimeter, a central point in the Saleve side sector was exposed to beams of
various positions at 80 GeV. I have analyzed 16 pion runs. The beam for each
point was subdivided into a number of smaller parts, each of diameter is 2 cm. In
X-surface scan with pion runs analysis, some cuts were used to select the pion
events such as the scintillator cut, muon cut, FEM cut. As can be seen in Figure
7., the quality of the spectra was significantly improved after applying all the cuts,
although a significant fraction of the events was finally filtered out reducing the
available statistics. The surface response of the prototype calorimeter to pions was
obtained from hadronic semi-octant sectors, by moving the beam along the X-
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direction. Figure 8. (a) (b) show the X-scan for pions of 80 GeV energy (right) and
the derivative of this response with respect to x (left).
Figure 7
Figure 8
Figure 7. Energy spectrum for an pion beam of E=80, before and after applying all
cuts (a), Signal distribution after applied all cuts (b).
Figure 8. X-scan along the face of prototype for 80 GeV pions (a). The derivative of
the response with respect to X, the width of the HAD shower is given by (σ=6.081
mm) (b).
HCAL PEDESTAL STABILITY STUDIES IN CMS
Introduction
In HCAL, pedestal subtraction is important to determine the muon energy
deposits and for calorimetry based muon isolation. Precision of pedestal
determination has also a direct impact on the quality of calibration of HCAL. In this
method, pedestal is defined on an event-by-event basis. During September and
November 2008 (Cosmic Run At Four Tesla (CRAFT) period) we have studied the
stability of HCAL pedestals. We have analyzed over 50 CRAFT global runs
In general, during CRAFT individual HCAL channels were stable. Run to
run variation (RMS) of pedestals for most of the channels was in the range of 0.001
to 0.002 ADC per Time Slice (TS). Assuming 8 time slices were used to reconstruct
the HCAL energy, this variation is equivalent to RMS of 2 to 4 MeV per readout
channel. For few individual channels, pedestals were not stable and exhibited not
just a shift, but short or long term drifts. Pedestal shifts of individual channels were
not correlated (Barbaro, 2009).
Stability of HCAL Pedestals during CRAFT
Pedestal Definition
Cosmic ray muons permeate only few HCAL towers (out of a total of over
ten thousand HCAL readout channels). So reliable source of data to monitor the
stability of HCAL pedestals is provided by events triggered by cosmic ray muons
(Barbaro, 2009). HCAL uses Charge Integrator and Encoder (QIE) cards which are
7 bit ADC. HCAL ADCs rotate via four independent capacitors (CapIDs) for each
readout channel to measure the charge. Pedestal values averaged over four
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CapIDs are more stable than the values calculated for individual CaIDs (Barbaro,
2009). We can calculate the average pedestal value of four CapIDs:
ped(channel,run) =
1
8  N trig
 ADCTS
where NTRIG is number of trigger and ADCTS is ADC per time slice.
Pedestal Calculation
Pedestal mean is given by,
(ped)  RMS  ped  / 8  N trig
RMS(ped) is RMS of pedestal for a single channel in a single run, is defined as:
RMS(ped)=
1
ADC (channel , TS )  ped (channel , run)2
NS
where ADC(channel,TS) is ADC of a channel per time slice and ped(channel,run)
is pedestal of a channel per run.
Stability of the HE and HB pedestals during CRAFT
We have analyzed the stability of the pedestals of HE and HB channels.
During CRAFT the average pedestal of all HB-HE channels is very stable. Run to
run RMS of the average pedestal is equal to 0.9 MeV for HB and 0.5 MeV for HE.
23 out of a total of 5184 channels in HB and HE, less 0.5 percent of the total
showed run-to-run shifts of pedestals above the level of 0.010 ADC per TS. For
few individual channels, pedestals were not stable. There were not just a shift, but
short or long term drifts. Pedestal shifts of individual channels were not correlated.
(Barbaro, 2009).
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Figure 9. Pedestal mean versus run number for individual HCAL channels, HB
(eta=2, phi=23,depth=1) and HE (eta=18, phi=8, depth=1). For these two channels,
pedestal shifts were apparent throughout several runs (long term drifts, as opposed
to shift) (Barbaro, 2009).
Stability of HF pedestals during CRAFT
We have analyzed the stability of pedestals of HF channels. Run-to-run
RMS of average HF pedestal is 0.00029 ADC counts (Barbaro, 2009). In general
most of HF channels are stable, with an average RMS of 0.0016 ADC counts.
However, few channels exhibit instabilities. There are ten channels (out of a total of
1728) with run-to-run RMS above 0.0050 ADC counts. In some cases, large RMS
is the result of a single shift, in other cases, pedestal is unstable throughout the
entire CRAFT. In particular, a single with largest RMS has a shift of 0.5 ADC
counts. In HF (eta=-31, phi=7, depth=1) channel there was a systematic shift of
about 0.030 ADC counts/TS . HF (eta=29, phi=71, depth=1) channel was unstable,
with long term drift (down and up) 0.100 ADC counts/TS took place during CRAFT.
Figure 10. Pedestal average for HF (eta=-31, phi=7, depth=1) channel versus run
number (a), Pedestal average for HF (eta=29, phi=71, depth=1) channel versus run
number (b).
Stability of HO pedestal during CRAFT
We have checked the stability of pedestal in HO channels during CRAFT.
Run-to-run RMS average HO pedestal is 0.00044 ADC counts. In general, 99.9%
of HO channels are stable. Average RMS is 0.0012 ADC counts. But few channels
(0.1%) exhibit instabilities. There are seventeen (out of total of 2160 channels) with
run-to-run RMS above 0.0050 ADC counts. In some cases, large RMS is result of a
single shift, in other cases, pedestal is unstable throughout entire CRAFT. In
particular, there is a single channel with largest RMS.
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Figure 11. HO channel (eta=-4, phi=69, depth=4) with unstable pedestal (a). HO
channel (eta=15, phi=24, phi=4) with unstable pedestal. Pedestal value changes by
up to 2 ADC counts (b).
CONCLUSION
My thesis contains two major studies. The first one is the beam test of the
final prototype IV of CASTOR calorimeter. In the second study, I present my
analysis of stability of HCAL pedestals by using data taken during CRAFT .
In the first part of the thesis, surface scan were studied with an electron
beam at 100 GeV, pion beam at 80 GeV. The purposes of the area scanning are to
check the uniformity of the EM calorimeter response to electrons hitting at different
points on the sector area, to estimate the width of the EM shower profile and to
assess the amount of the effects and lateral leakage from the calorimeter which
could lead to cross-talk between neighboring sectors. The derivative of the
response is calculated and the electromagnetic shower width is found to be 1.903
mm for Saleve side and 1.601 mm for Jura side, hadronic shower width is found to
be 6.081 mm for Saleve side, As expected, the pion shower was larger than the
corresponding electromagnetic shower.
In the second part of the thesis HCAL pedestal stability have been studied.
I checked HCAL pedestal stability using CRAFT global runs and looked at over 50
runs. Most (99.9%) of HCAL readout channels have very stable pedestal. So 0.1%
of HCAL channels are unstable. Typical RMS is 0.001 to 0.002 ADC counts. RMS
is 0.001-0.002 ADC/TS. This value is equivalent to RMS of 2-3 MeV per channel.
Some channels (20 out of 5k, <0:5% of total) showed pedestal variation above the
level of 0.010 ADC/TS (equivalent to 15 MeV/channel).
REFERENCES
ASLONLOGLOU et al., 2007, Performance Studies of Prototype II for the CASTOR
forward Calorimeter at the CMS Experiment, arXiv:0706.2641v2 [physics.ins-det].
ASLANOGLOU et al., 2008, Performance studies of the final prototype for the
CASTOR forward calorimeter at the CMS experiment CMS NOTE 2008/-(in
preparation)
CASTOR Engineering Design Report, 2007, CERN,
CMS Collaboration, The Hadron Calorimeter Technical Design Report,
CERN/LHCC 1997-031 (1997)
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DE BARBARO et al., 2009, Stability of HCAL hardware pedestals during CRAFT
and Proposal for definition of pedestal tags and Intervals of Validity (IOVs)
for HCAL energy reconstruction, CMS IN-2009/005
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