260 research outputs found
Multiparticle production processes from the Information Theory point of view
We look at multiparticle production processes from the Information Theory
point of view, both in its extensive and nonextensive versions. Examples of
both symmetric (like pp or AA) and asymmetric (like pA) collisions are
considered showing that some ways of description of experimental data used in
the literature are of more general validity than usually anticipated.}Comment: Talk given at 4th Budapest Winter School On Heavy Ion Physics (2004)
16 pages, 5 figures; version published in APH (HIP
Quantum Clan Model description of Bose Einstein Correlations
We propose a novel numerical method of modelling Bose-Einstein correlations
(BEC) observed among identical (bosonic) particles produced in multiparticle
production reactions. We argue that the most natural approach is to work
directly in the momentum space in which the Bose statistics of secondaries
reveals itself in their tendency to bunch in a specific way in the available
phase space. Because such procedure is essentially identical to the clan model
of multiparticle distributions proposed some time ago, therefore we call it the
Quantum Clan Model.Comment: Talk given at 4th Budapest Winter School On Eavy Ion Physics (2004),
6 pages, two figures; version published in APH (HIP
Intriguing feature of multiplicity distributions
Multiplicity distributions, P(N), provide valuable information on the
mechanism of the production process. We argue that the observed P(N) contain
more information (located in the small N region) than expected and used so far.
We demonstrate that it can be retrieved by analysing specific combinations of
the experimentally measured values of P(N) which we call {it modified
combinants, Cj, and which show distinct oscillatory behavior, not observed in
the usual phenomenological forms of the P(N) used to fit data. We discuss the
possible sources of these oscillations and their impact on our understanding of
the multiparticle production mechanism.Comment: Invited talk presented at XLVIII International Symposium on
Multiparticle Dynamics (ISMD2018), 3 to 7 September 2018, Singapore; 10
pages, 6 figures. To be published in EPJ Web of Conference
On the chemical composition of cosmic rays of highest energy
We present arguments aiming at reconciling apparently contradictory results
concerning the chemical composition of cosmic rays of highest energy, coming
recently from the Auger and HiRes collaborations. In particular, we argue that
the energy dependence of the mean value and root mean square fluctuation of
shower maxima distributions observed by the Auger experiment are not
necessarily caused by the change of nuclear composition of primary cosmic rays.
They could also be caused by the change of distribution of the first
interaction point in the cascade. A new observable, in which this influence is
strongly suppressed, is proposed and tested.Comment: Version accepted by J.Phys. G (2011
Application of nonextensive statistics to particle and nuclear physics
We present an overview of possible imprints of non-extensitivity in particle
and nucler physics. Special emphasis is put on the intrinsic fluctuations
present in the system under consideration as the possible source of
nonextensivity. The possible connection of nonextensivity and the self
organized criticality apparently being observed in some cosmic rays and
hadronic experiments will also be discussed.Comment: Contribution to International School and Conference on "Non Extensive
Thermodynamics and physical applications", Villasimius-Capo Boi (Cagliari),
Italy, 23-30 March 200
Transverse momentum versus multiplicity fluctuations in high-energy nuclear collisions
We discuss recently measured event-by-event fluctuations of transverse
momentum and of multiplicity in relativistic heavy-ion collisions. It is shown
that the non-monotonic behavior of the p_T-fluctuations as a function of
collision centrality can be fully explained by the observed non-monotonic
multiplicity fluctuations. A possible mechanism responsible for the
multiplicity fluctuations is also considered.Comment: 5 pages, 3 figures, revised & extended, to appear in Phys. Rev.
Effect of CT misalignment on attenuation — corrected myocardial perfusion SPECT
BACKGROUND: Use of CT based attenuation correction (AC) for myocardial perfusion SPECT (MPS) is growing fast due to a rapid development of hybrid SPECT/CT systems. SPECT and CT studies are performed in a sequential way extending total study acquisition and making a patient movement more likely. The present work aims at answering the question how large misalignment between SPECT and CT studies should be considered significant and how often those misregistrations are observed.
MATERIAL AND METHODS: A retrospective study applying AC was performed in 107 patients who had coronary angiography (CA) performed within 3 months. Patients underwent a stress/rest Tc-99m MIBI 2 day SPECT/CT myocardial perfusion study. In case of SPECT and CT misalignment CT slices were shifted manually; shifts along 3 axes were recorded and after realignment a repeat reconstruction was performed. Euclidean distance of misalignment was also calculated. Images were analyzed by two experienced nuclear medicine specialists (consensus) applying visual semiquantitative method. Perfusion of three arteries was scored using a 5 grade scale. CA results were used as a reference for MPS findings.
RESULTS: In 47 patients (44%) CT realignment was necessary. CT was shifted mostly along x and y axes, and less often along z axis. Euclidean distance S exceeded 2 pixels in 3 stress and 2 rest studies. Only in 7 patients changes of scores assigned to coronary vessels were noted as a result of CT realignment. These changes concerned 9 vessel areas. In 7 out of 9 cases changes were noted toward a better agreement with results of CA. Only in one patient, with stress S > 3 pixels and negative result of CA, CT realignment changed vessel area score significantly, from probably abnormal to normal.
CONCLUSIONS: Only misalignments large enough, exceeding 2–3 pixels, have negative impact on attenuation corrected images. Such misalignments are rare, in our material were observed in 3 stress and 2 rest studies (3% and 2% of all studies, respectively). Only in one patient (below 1% of all studied patients) CT misalignment caused a significant study misinterpretation. Although alignment of SPECT and CT studies should be checked in every patient, small misalignments do not affect study interpretation
Numerical modelling of Bose-Einstein correlations
We propose extension of the algorithm for numerical modelling of
Bose-Einstein correlations (BEC), which was presented some time ago in the
literature. It is formulated on quantum statistical level for a single event
and uses the fact that identical particles subjected to Bose statistics do
bunch themselves, in a maximal possible way, in the same cells in phase-space.
The bunching effect is in our case obtained in novel way allowing for broad
applications and fast numerical calculations. First comparison with
annihilations data performed by using simple cascade hadronization model is
very encouraging.Comment: LaTeX file and 5 eps file with figures, 9 pages altogethe
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