Abstract
In the past years, it has been observed at several beam test campaigns that
irradiated LGAD sensors break with a typical star shaped burn mark when
operated at voltages much lower than those ...at which they were safely operated
during laboratory tests. The study presented in this paper was designed to
determine the safe operating voltage that these sensors can withstand. Many
irradiated sensors from various producers were tested in two test beam
facilities, DESY (Hamburg) and CERN-SPS (Geneva), as part of ATLAS High
Granularity Timing Detector (HGTD) beam tests. The samples were placed in the
beam and kept under bias over a long period of time in order to reach a high
number of particles crossing each sensor. Both beam tests lead to a similar
conclusion, that these destructive events begin to occur when the average
electric field in the sensor becomes larger than
12 V/μm.
Abstract
This paper presents the design and characterisation of a front-end prototype ASIC for the ATLAS High Granularity Timing Detector, which is planned for the High-Luminosity phase of the LHC.
...This prototype, called ALTIROC1, consists of a 5 × 5-pad matrix and contains the analog
part of the single-channel readout (preamplifier, discriminator, two TDCs and SRAM).
Two preamplifier architectures (transimpedance and voltage) were implemented and tested.
The ASIC was characterised both alone and as a module when connected to a 5 × 5-pad array of LGAD sensors.
In calibration measurements, the ASIC operating alone was found to satisfy the technical requirements for the project, with similar performances for both preamplifier types. In particular, the jitter was found to be 15 ± 1 ps (35 ± 1 ps) for an injected charge of 10 fC (4 fC).
A degradation in performance was observed when the ASIC was connected to the LGAD array. This is attributed to digital couplings at the entrance of the preamplifiers.
When the ASIC is connected to the LGAD array, the lowest detectable charge increased from 1.5 fC to 3.4 fC. As a consequence, the jitter increased for an injected charge of 4 fC. Despite this increase, ALTIROC1 still satisfies the maximum jitter specification (below 65 ps) for the HGTD project.
This coupling issue also affects the time over threshold measurements and the time-walk correction can only be performed with transimpedance preamplifiers.
Beam test measurements with a pion beam at CERN were also undertaken to evaluate the performance of the module. The best time resolution obtained using only ALTIROC TDC data was 46.3 ± 0.7 ps for a restricted time of arrival range where the coupling issue is minimized.
The residual time-walk contribution is equal to 23 ps and is the dominant electronic noise contribution to the time resolution at 15 fC.
AbstractThe potential for the discovery of a Standard Model Higgs boson in the mass range mH < 2 mZ in the vector boson fusion mode has been studied for the ATLAS experiment at the LHC. The ...characteristic signatures of additional jets in the forward regions of the detector and of low jet activity in the central region allow for an efficient background rejection. Analyses for the H → WW(*) and H → ττ decay modes have been performed using a realistic simulation of the expected detector performance. The results obtained demonstrate the large discovery potential in the H → WW(*) decay channel and the sensitivity to Higgs boson decays into τ-pairs in the low-mass region around 120 GeV/c2.
► Prospects for DM searches with CTA at various targets. ► Prospects for ALP searches with CTA. ► Prospects for LIV searches with CTA. ► Prospects for neutrinos, magnetic monopoles and gravitational ...waves searches with CTA.
The Cherenkov Telescope Array (CTA) is a project for a next-generation observatory for very high energy (GeV–TeV) ground-based gamma-ray astronomy, currently in its design phase, and foreseen to be operative a few years from now. Several tens of telescopes of 2–3 different sizes, distributed over a large area, will allow for a sensitivity about a factor 10 better than current instruments such as H.E.S.S, MAGIC and VERITAS, an energy coverage from a few tens of GeV to several tens of TeV, and a field of view of up to 10°. In the following study, we investigate the prospects for CTA to study several science questions that can profoundly influence our current knowledge of fundamental physics. Based on conservative assumptions for the performance of the different CTA telescope configurations currently under discussion, we employ a Monte Carlo based approach to evaluate the prospects for detection and characterisation of new physics with the array.
First, we discuss CTA prospects for cold dark matter searches, following different observational strategies: in dwarf satellite galaxies of the Milky Way, which are virtually void of astrophysical background and have a relatively well known dark matter density; in the region close to the Galactic Centre, where the dark matter density is expected to be large while the astrophysical background due to the Galactic Centre can be excluded; and in clusters of galaxies, where the intrinsic flux may be boosted significantly by the large number of halo substructures. The possible search for spatial signatures, facilitated by the larger field of view of CTA, is also discussed. Next we consider searches for axion-like particles which, besides being possible candidates for dark matter may also explain the unexpectedly low absorption by extragalactic background light of gamma-rays from very distant blazars. We establish the axion mass range CTA could probe through observation of long-lasting flares in distant sources. Simulated light-curves of flaring sources are also used to determine the sensitivity to violations of Lorentz invariance by detection of the possible delay between the arrival times of photons at different energies. Finally, we mention searches for other exotic physics with CTA.
Abstract
The High Granularity Timing Detector (HGTD) will be
installed in the ATLAS detector to mitigate pile-up effects during
the High Luminosity (HL) upgrade of the Large Hadron Collider (LHC)
at ...CERN. The design of the HGTD is based on the use of Low Gain
Avalanche Detectors (LGADs), with an active thickness of
50 μm, that allow to measure with high-precision the time of
arrival of particles. The HGTD will improve the particle-vertex
assignment by measuring the track time with a resolution ranging
from approximately 30 ps at the beginning of the HL-LHC operations
to 50 ps at the end. Performances of several unirradiated, as well
as neutron- and proton-irradiated, LGAD sensors from different
vendors have been measured in beam test campaigns during the years
2018 and 2019 at CERN SPS and DESY. This paper presents the results
obtained with data recorded by an oscilloscope synchronized with a
beam telescope which provides particle position information within a
resolution of a few μm. Collected charge, time resolution and
hit efficiency are presented. In addition to these properties, the
charge uniformity is also studied as a function of the position of
the incident particle inside the sensor pad.
The local hadronic calibration scheme developed for the reconstruction and calibration of jets and missing transverse energy in ATLAS has been evaluated using data obtained during combined beam tests ...of modules of the ATLAS liquid argon endcap and forward calorimeters. These tests covered the pseudorapidity range of 2.5 < | ? | < 4.0 . The analysis has been performed using special sets of calibration weights and corrections obtained with the Geant4 simulation of a detailed beam-test setup. The evaluation itself has been performed through the careful study of specific calorimeter performance parameters such as e.g. energy response and resolution, shower shapes, as well as different physics lists of the Geant4 simulation.
The local hadronic calibration scheme developed for the reconstruction and calibration of jets and missing transverse energy in ATLAS has been evaluated using data obtained during combined beam tests ...of modules of the ATLAS liquid argon endcap and forward calorimeters. These tests covered the pseudorapidity range of 2.5<|η|<4.0. The analysis has been performed using special sets of calibration weights and corrections obtained with the Geant4 simulation of a detailed beam-test setup. The evaluation itself has been performed through the careful study of specific calorimeter performance parameters such as e.g. energy response and resolution, shower shapes, as well as different physics lists of the Geant4 simulation.
Muon pair production is studied in
p-
W and
S
U collisions at 200 GeV per nucleon, as a function of transverse momentum
P
Tμμ
. The inclusive
ϱ+
ω and Φ differential cross-sections
dσ
dP
T
are ...measured in the dimuon decay channel, for
P
T
≥ 0.6 GeV/c, in the central rapidity region, 3.0≤
y ≤ 4.0. Assuming the power law A-dependence
σ =
σ
0(
A
beam·
A
target)
α
, the study of the integrated cross-sections for
p-
W and
S
U collisions leads to
α
ϱ+
ω
= 1.00±0.02±0.07 and
α
Φ
= 1.23±0.03±0.05, showing clear evidence of Φ enhancement in
S
U interactions as compared to
p-
W collisions.
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