2,076 research outputs found
Operational Experience with the ALICE Pixel detector
The Silicon Pixel Detector (SPD) constitutes the two innermost layers of the
Inner Tracking System of the ALICE experiment and it is the closest detector to
the interaction point. As a vertex detector, it has the unique feature of
generating a trigger signal that contributes to the L0 trigger of the ALICE
experiment. The SPD started collecting data since the very first pp collisions
at LHC in 2009 and since then it has taken part in all pp, Pb-Pb and p-Pb data
taking campaigns. This contribution will present the main features of the SPD,
the detector performance and the operational experience, including calibration
and optimization activities from Run 1 to Run 2
The heavy-ion programme of the ALICE experiment at LHC
The ALICE experiment at LHC is mainly dedicated to heavy-ion physics. An overview of its performances, some predictions related to its first measurements and QGP observable measurements will be given.The ALICE experiment at LHC is mainly dedicated to heavy-ion physics. An overview of its performances, some predictions related to its first measurements and QGP observable measurements will be given
φ(1020)-meson identification with the HMPID detector in the ALICE experiment
The ALICE experiment at CERN is devoted to study hadronic
matter at extreme conditions of temperature, energy density and its phase transition to QGP. The φ(1020)-meson is a good probe for studying the features of the quarkgluon
plasma. The ALICE detectors will identify particles at high momenta. In particular the HMPID would identify kaons with 1 ≤ p ≤ 3 GeV/c, therefore it will be possible to identify φ-mesons through the channel φ → K+K− up to 6 GeV/c. In this paper will be shown the physical motivations for the study of φ-meson and its invariant mass spectrum
On the different flavours of Lense–Thirring precession around accreting stellar mass black holes
Type-C quasi-periodic oscillations (QPOs) in X-ray binaries have been often interpreted as a consequence of relativistic Lense-Thirring precession around a spinning black hole and they potentially offer a way to measure black hole spins and masses. The connection between relativistic precession and the resulting QPOs has been made either in terms of a simplified model involving a single test particle producing the QPO, or in terms of a global model where a geometrically thick accretion flow precesses coherently as a rigid body. In this paper, we analyse similarities and differences between these two models, sometimes considered as in opposition to each other. We demonstrate that the former is the limiting case of the latter when the radial extent of the precessing flow is very small, and that solid lower limits to the black hole spin can be obtained by considering the test particle model alone. We also show that the global precession model naturally accounts for the range of frequencies observed for type-C QPOs without the need to invoke a truncation of the inner accretion flow before it reaches the innermost stable circular orbit. Finally, we show that, in order to maintain rigid precession, the thick accretion flow should be radially narrow, and that if it extends beyond 10-10(2) gravitational radii, it aligns with the black hole spin too fast to produce a coherent QPO
Modelling correlated variability in accreting black holes:the effect of high density and variable ionization on reverberation lags
We present a new release of the RELTRANS model to fit the complex
cross-spectrum of accreting black holes as a function of energy. The model
accounts for continuum lags and reverberation lags self-consistently in order
to consider the widest possible range of X-ray variability timescales. We
introduce a more self-consistent treatment of the reverberation lags,
accounting for how the time variations of the illuminating flux change the
ionisation level of the accretion disc. This process varies the shape of the
reflection spectrum in time causing an additional source of lags besides the
light crossing delay. We also consider electron densities in the accretion disc
up to cm, which are found in most of the stellar mass black
holes and in some AGN. These high densities increase the amplitude of the
reverberation lags below keV since the reflection flux enhances in the same
energy range. In addition, we investigate the properties of hard lags produced
by variations in the power-law index of the continuum spectrum, which can be
interpreted as due to roughly variability in the corona's optical depth
and temperature. As a test case, we simultaneously fit the lag energy spectra
in a wide range of Fourier frequency for the black hole candidate MAXI
J1820+070 observed with NICER. The best fit shows how the reverberation lags
contribute even at the longer timescales where the hard lags are important.
This proves the importance of modelling these two lags together and
self-consistently in order to constrain the parameters of the system.Comment: Accepted for publication in MNRA
Contribution of the HMPID detector to the high-pT physics at LHC
The LHC will deliver unexplored energy regimes for proton-proton and
heavy-ion collisions. As shown by the RHIC experiments, particle identification
over a large momentum range is essential to disentangle physics processes,
especially in the intermediate p (1 GeV/c) region. The novel
design of the High-Momentum Particle Identification Detector (HMPID), based on
large surface CsI photocathodes, is able to identify , ,
and in the momentum region where bulk medium properties and hard
scatterings interplay. Furthermore, measurement of resonance particles such as
the could provide information on the system evolution. The
HMPID layout and segmentation are optimized to study particle correlations at
high momenta describing the early phase and the dynamical evolution of the
collision. At LHC, the increased hard cross section will significantly be
enhanced compared to RHIC. Jet reconstruction via Deterministic Annealing can
address jet quenching and detailed measurements of jet properties. In this
paper, we present these selected topics from the possible HMPID contributions
to the physics goals of LHC.Comment: 6 pages, 7 figures, Contribution to QCD @ Work 2007: International
Workshop on Quantum Chromodynamics Theory and Experiment, Martina Franca,
Italy, 16-20 June 200
Highly-coherent quasi-periodic oscillations in the 'heartbeat' black hole X-ray binary IGR J17091-3624
IGR J17091-3624 is a black hole X-ray binary (BHXB), often referred to as the
'twin' of GRS 1915+105 because it is the only other known BHXB that can show
exotic 'heartbeat'-like variability that is highly structured and repeated.
Here we report on observations of IGR J17091-3624 from its 2022 outburst, where
we detect an unusually coherent quasi-periodic oscillation (QPO) when the
broadband variability is low (total fractional rms 6%) and the
spectrum is dominated by the accretion disk. Such spectral and variability
behavior is characteristic of the soft state of typical BHXBs (i.e., those that
do not show heartbeats), but we also find that this QPO is strongest when there
is some exotic heartbeat-like variability (so-called Class V variability). This
QPO is detected at frequencies between 5 and 8 Hz and has Q-factors (defined as
the QPO frequency divided by the width) 50, making it one of the most
highly coherent low-frequency QPO ever seen in a BHXB. The extremely high Q
factor makes this QPO distinct from typical low-frequency QPOs that are
conventionally classified into Type-A/B/C QPOs. Instead, we find evidence that
archival observations of GRS 1915+105 also showed a similarly high-coherence
QPO in the same frequency range, suggesting that this unusually coherent and
strong QPO may be unique to BHXBs that can exhibit 'heartbeat'-like
variability.Comment: 11 pages, 10 figures, 2 tables, accepted to be published in Ap
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