3,084 research outputs found
Forward photon measurements in ALICE as a probe for low-x gluons
The low-x gluon density in the proton and, in particular, in nuclei is only
very poorly constrained, while a better understanding of the low-x structure is
crucial for measurements at the LHC and also for the planning of experiments at
future hadron colliders. In addition, deviations from linear QCD evolution are
expected to appear at low x, potentially leading to gluon saturation and a
universal state of hadronic matter, the color-glass condensate. However, these
effects have not been unambiguously proven to date. Fortunately, data from the
LHC can be used directly to provide better constraints of the parton
distribution functions (PDFs). In this context, a Forward Calorimeter (FoCal)
is proposed as an addition to the ALICE experiment, to be installed in the Long
Shutdown 3.
The main goal of the FoCal proposal is to measure forward direct photons in
pp and p-Pb collisions to obtain experimental constraints on proton and nuclear
PDFs in a new region of low x. Based on the current knowledge from DIS
experiments and first results from LHC, we will discuss the physics case for
this proposed detector. While open charm measurements do provide important
constraints, a photon measurement would provide additional unique information.
The direct photon measurement requires a new electromagnetic calorimeter with
extremely high granularity. The corresponding innovative design principle of a
high-resolution Si-W sandwich calorimeter is discussed.Comment: Proceedings of Hard Probes 2018, 30 September - 5 October,
Aix-Les-Bains, Franc
Direct Photons from Relativistic Heavy-Ion Collisions
Direct photons have been proposed as a promising signature for the
quark-gluon plasma (QGP) formation in relativistic heavy-ion collisions.
Recently WA98 presented the first data on direct photons in Pb+Pb-collisions at
SPS. At the same time RHIC started with its experimental program. The discovery
of the QGP in these experiments relies on a comparison of data with theoretical
predictions for QGP signals. In the case of direct photons new results for the
production rates of thermal photons from the QGP and a hot hadron gas as well
as for prompt photons from initial hard parton scatterings have been proposed
recently. Based on these rates a variety of different hydrodynamic models,
describing the space-time evolution of the fireball, have been adopted for
calculating the direct photon spectra. The results have been compared to the
WA98 data and predictions for RHIC and LHC have been made. So far the
conclusions of the various models are controversial.
The aim of the present review is to provide a comprehensive and up-to-date
survey and status report on the experimental and theoretical aspects of direct
photons in relativistic heavy-ion collisions.Comment: 91 pages, 44 figures, revised version to be published in Phys. Re
Studying Intermediate pT Hadron Production with Fluctuations
Mechanisms for particle production at intermediate pT in nuclear collisions
at RHIC are discussed, emphasizing the differences in associated jet-like
correlations between color-neutral and colored production. An alternative
production mechanism involving both recombination and fragmentation is
suggested, which might simultaneously lead to an enhancement of baryons and to
jet-like correlations. To gain more insight into the relative importance of
different mechanisms a study of constrained distributions of associated
multiplicity is proposed. In a simple model it is shown that these multiplicity
distributions may change significantly, if the nature of the production
mechanism fluctuates from event to event.Comment: 7 pages, 4 figures, talk at Hot Quarks 2004 conferenc
ALICE detector upgrades
The LHC with its unprecedented energy offers unique opportunities for
groundbreaking measurements in p+p, p+A and A+A collisions even beyond the
baseline experimental designs. ALICE is setting up a program of detector
upgrades, which could to a large extent be installed in the LHC shutdown
planned for 2017/18, to address the new scientific challenges. We will discuss
examples of the scientific frontiers and will present the corresponding upgrade
projects under study for the ALICE experiment.Comment: Contribution to QM2011, 4 pages, second version with minor textual
changes after review proces
Charge dependent azimuthal correlations in Pb--Pb collisions at TeV
Separation of charges along the extreme magnetic field created in non-central
relativistic heavy--ion collisions is predicted to be a signature of local
parity violation in strong interactions. We report on results for charge
dependent two particle azimuthal correlations with respect to the reaction
plane for Pb--Pb collisions at TeV recorded in 2010 with
ALICE at the LHC. The results are compared with measurements at RHIC energies
and against currently available model predictions for LHC. Systematic studies
of possible background effects including comparison with conventional
(parity-even) correlations simulated with Monte Carlo event generators of
heavy--ion collisions are also presented.Comment: Published in the proceedings of "Quark Matter 2011", Annecy-Franc
Measurement of pion, kaon and proton production in proton-proton collisions at TeV
The measurement of primary , K, p and
production at mid-rapidity ( 0.5) in proton-proton collisions at
TeV performed with ALICE (A Large Ion Collider Experiment) at
the Large Hadron Collider (LHC) is reported. Particle identification is
performed using the specific ionization energy loss and time-of-flight
information, the ring-imaging Cherenkov technique and the kink-topology
identification of weak decays of charged kaons. Transverse momentum spectra are
measured from 0.1 up to 3 GeV/ for pions, from 0.2 up to 6 GeV/ for kaons
and from 0.3 up to 6 GeV/ for protons. The measured spectra and particle
ratios are compared with QCD-inspired models, tuned to reproduce also the
earlier measurements performed at the LHC. Furthermore, the integrated particle
yields and ratios as well as the average transverse momenta are compared with
results at lower collision energies.Comment: 33 pages, 19 captioned figures, 3 tables, authors from page 28,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/156
Measurement of an excess in the yield of J/ at very low in Pb-Pb collisions at = 2.76 TeV
We report on the first measurement of an excess in the yield of J/ at
very low transverse momentum ( GeV/) in peripheral hadronic
Pb-Pb collisions at = 2.76 TeV, performed by ALICE at the
CERN LHC. Remarkably, the measured nuclear modification factor of J/ in
the rapidity range reaches about 7 (2) in the range 0-0.3
GeV/ in the 70-90% (50-70%) centrality class. The J/ production cross
section associated with the observed excess is obtained under the hypothesis
that coherent photoproduction of J/ is the underlying physics mechanism.
If confirmed, the observation of J/ coherent photoproduction in Pb-Pb
collisions at impact parameters smaller than twice the nuclear radius opens new
theoretical and experimental challenges and opportunities. In particular,
coherent photoproduction accompanying hadronic collisions may provide insight
into the dynamics of photoproduction and nuclear reactions, as well as become a
novel probe of the Quark-Gluon Plasma.Comment: 18 pages, 3 captioned figures, 1 table, authors from page 13,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/191
Image quality of list-mode proton imaging without front trackers
List mode proton imaging relies on accurate reconstruction of the proton most likely path (MLP) through the patient. This typically requires two sets of position sensitive detector systems, one upstream (front) and one downstream (rear) of the patient. However, for a clinical implementation it can be preferable to omit the front trackers (single-sided proton imaging). For such a system, the MLP can be computed from information available through the beam delivery system and the remaining rear tracker set. In this work, we use Monte Carlo simulations to compare a conventional double-sided (using both front and rear detector systems) with a single-sided system (only rear detector system) by evaluating the spatial resolution of proton radiographs (pRad) and proton CT images (pCT) acquired with these set-ups. Both the pencil beam spot size, as well as the spacing between spots was also adjusted to identify the impact of these beam parameters on the image quality.
Relying only on the pencil beam central position for computing the MLP resulted in severe image artifacts both in pRad and pCT. Using the recently extended-MLP formalism that incorporate pencil beam uncertainty removed these image artifacts. However, using a more focused pencil beam with this algorithm induced image artifacts when the spot spacing was the same as the beam spot size. The spatial resolution tested with a sharp edge gradient technique was reduced by 40% for single-sided (MTF10% = 3.0 lp/cm) compared to double-sided (MTF10% = 4.9 lp/cm) pRad with ideal tracking detectors. Using realistic trackers the difference decreased to 30%, with MTF10% of 4.0 lp/cm for the realistic double-sided and 2.7 lp/cm for the realistic single-sided setup. When studying an anthropomorphic paediatric head phantom both single- and double-sided set-ups performed similarly where the difference in water equivalent thickness (WET) between the two set-ups were less than 0.01 mm in homogeneous areas of the head. Larger discrepancies between the two set-ups were visible in high density gradients like the facial structures. A complete CT reconstruction of a Catphan module was performed. Assuming ideal detectors, the obtained spatial resolution was 5.1 lp/cm for double-sided and 3.8 lp/cm for the single-sided setup. Double- and single-sided pRad with realistic tracker properties returned a spatial resolution of 3.8 lp/cm and 3.2 lp/cm, respectively. Future studies should investigate the development of dedicated reconstruction algorithms targeted for single-sided particle imaging.publishedVersio
Розвиток ідеї європейської інтеграції та її значення для України
У статті аналізується сутність ідеї європейської інтеграції,
її еволюція протягом століть. Досліджуються теоретичні основи
формування та розвитку Європейського Союзу, обґрунтовується
необхідність євроінтеграційної стратегії України як ключового
пріоритету зовнішньої та внутрішньої політики нашої держави.The article analyses the essence of the idea of European integration,
its evolution during the centuries and researches the theoretical
foundations of the formation and development of the European Union,
proves the need for European integration strategy of Ukraine as a key
priority of foreign and internal policy
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