A
bstract
Transverse momentum spectra of identified particles produced in heavy-ion collisions at the Large Hadron Collider are described with relativistic fluid dynamics. We perform a systematic ...comparison of experimental data for pions, kaons and protons up to a transverse momentum of 3 GeV
/c
with calculations using the F
luid
u
M code package to solve the evolution equations of fluid dynamics, the T
r
ENT
o
model to describe the initial state and the F
ast
R
eso
code to take resonance decays into account. Using data in five centrality classes at the center-of-mass collision energy per nucleon pair
s
NN
= 2
.
76 TeV, we determine systematically the most likely parameters of our theoretical model including the shear and bulk viscosity to entropy ratios, the initialization time, initial density and freeze-out temperature through a global search and quantify their posterior probability. This is facilitated by the very efficient numerical implementation of F
luid
u
M and F
ast
R
eso
. Based on the most likely model parameters we present predictions for the transverse momentum spectra of multi-strange hadrons as well as identified particle spectra from Pb-Pb collisions at
s
NN
= 5
.
02 TeV.
ALICE at the LHC is the experiment dedicated to study the physics of nucleus-nucleus collisions. The apparatus is well suited for the measurement of heavy-quark hadron production, making use of the ...high spatial resolution provided by the tracking detectors and the excellent particle identification, which are distinctive of the ALICE apparatus.
Results from proton–proton collisions at s=2.76 and 7 TeV, and from Pb–Pb collisions at sNN=2.76 TeV are presented. The measurements in pp collisions provide an important test of perturbative QCD predictions. The precise vertex reconstruction together with the electron identification, allows the separation of the charm and the beauty components. Furthermore, the pp results are essential as a reference for the measurements in heavy-ion collisions. Nuclear modification factors were measured for D mesons, for electrons and for muons from heavy-flavour hadron decays. The elliptic flow of D mesons is also discussed. These measurements are important because they will provide information on the Quark–Gluon Plasma produced in heavy-ion collisions, via the energy loss of the heavy partons in the strongly interacting medium, and hints on the medium thermalization.
We report on broadly based systematic investigations of the modeling components for open heavy-flavor diffusion and energy loss in strongly interacting matter in their application to heavy-flavor ...observables in high-energy heavy–ion collisions, conducted within an EMMI Rapid Reaction Task Force framework. Initial spectra including cold-nuclear-matter effects, a wide variety of space-time evolution models, heavy-flavor transport coefficients, and hadronization mechanisms are scrutinized in an effort to quantify pertinent uncertainties in the calculations of nuclear modification factors and elliptic flow of open heavy-flavor particles in nuclear collisions. We develop procedures for error assessments and criteria for common model components to improve quantitative estimates for the (low-momentum) heavy-flavor diffusion coefficient as a long-wavelength characteristic of QCD matter as a function of temperature, and for energy loss coefficients of high-momentum heavy-flavor particles.
A novel approach for designing the next generation of vertex detectors foresees to employ wafer-scale sensors that can be bent to truly cylindrical geometries after thinning them to thicknesses of ...20–40 μm. To solidify this concept, the feasibility of operating bent MAPS was demonstrated using 1.5cm×3cm ALPIDE chips. Already with their thickness of 50µm, they can be successfully bent to radii of about 2cm without any signs of mechanical or electrical damage. During a subsequent characterisation using a 5.4GeV electron beam, it was further confirmed that they preserve their full electrical functionality as well as particle detection performance.
In this article, the bending procedure and the setup used for characterisation are detailed. Furthermore, the analysis of the beam test, including the measurement of the detection efficiency as a function of beam position and local inclination angle, is discussed. The results show that the sensors maintain their excellent performance after bending to radii of 2cm, with detection efficiencies above 99.9% at typical operating conditions, paving the way towards a new class of detectors with unprecedented low material budget and ideal geometrical properties.
This paper presents the design of a front-end circuit for monolithic active pixel sensors. The circuit operates with a sensor featuring a small, low-capacitance (< 2 fF) collection electrode and is ...integrated in the DPTS chip, a proof-of-principle prototype of 1.5 mm × 1.5 mm including a matrix of 32 × 32 pixels with a pitch of 15 μm. The chip is implemented in the 65 nm imaging technology from the Tower Partners Semiconductor Co. foundry and was developed in the framework of the EP-R&D program at CERN to explore this technology for particle detection. The front-end circuit has an area of 42 μm 2 and can operate with a power consumption as low as 12 nW. Measurements on the prototype relevant to the front-end will be shown to support its design.
Secondary discharge studies in single- and multi-GEM structures Deisting, A.; Garabatos, C.; Gasik, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2019, Volume:
937
Journal Article
Peer reviewed
Open access
Secondary discharges, which consist of the breakdown of a gap near a GEM foil upon a primary discharge across that GEM, are studied in this work.
Their main characteristics are the occurrence a few ...10μs after the primary, the relatively sharp onset at moderate electric fields across the gap, the absence of increased fields in the system, and their occurrence under both field directions.
They can be mitigated using series resistors in the high-voltage connection to the GEM electrode facing towards an anode. The electric field at which the onset of secondary discharges occurs indeed increases with increasing resistance. Discharge propagation from GEM to GEM in a multi-GEM system affects the occurrence probability of secondary discharges in the gaps between neighbouring GEMs.
Furthermore, evidence of charges flowing through the gap after the primary discharge are reported. Such currents may or may not lead to a secondary discharge. A characteristic charge, of the order of 1010 electrons, has been measured as the threshold for a primary discharge to be followed by a secondary discharge, and this number slightly depends on the gas composition. A mechanism involving the heating of the cathode surface as trigger for secondary discharges is proposed.
Abstract The exclusive photoproduction reactions γp → J/ψ(1S)p and γp → ψ(2S)p have been measured at an ep centre-of-mass energy of 318 GeV with the ZEUS detector at HERA using an integrated ...luminosity of 373 pb −1. The measurement was made in the kinematic range 30 < W < 180 GeV, Q 2 < 1 GeV2 and |t| < 1 GeV2, where W is the photon-proton centre-of-mass energy, Q 2 is the photon virtuality and t is the squared four-momentum transfer at the proton vertex. The decay channels used were J/ψ(1S) → μ + μ − , ψ(2S) → μ + μ − and ψ(2S) → J/ψ(1S)π + π − with subsequent decay J/ψ(1S) → μ + μ − . The ratio of the production cross sections, R = σ ψ(2S) /σ J/ψ(1S), has been measured as a function of W and |t| and compared to previous data in photoproduction and deep inelastic scattering and with predictions of QCD-inspired models of exclusive vector-meson production, which are in reasonable agreement with the data.
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