2,056 research outputs found
Extracting the equation of state from a microscopic non-equilibrium model
No full textWe study the thermodynamic properties of infinite nuclear matter with the Ultrarelativistic Quantum Molecular Dynamics (URQMD), a semiclassical transport model, running in a box with periodic boundary conditions. It appears that the energy density rises faster than T4 at high temperatures of T approx. 200 - 300 MeV. This indicates an increase in the number of degrees of freedom. Moreover, We have calculated direct photon production in Pb+Pb collisions at 160 GeV/u within this model. The direct photon slope from the microscopic calculation equals that from a hydrodynamical calculation without a phase transition in the equation of state of the photon source
Direct Photon Production in 158 A GeV PB+ PB Collisions
No full textA measurement of direct photon production in Pb+Pb collisions at 158 AGeV has been carried out in the CERN WA98 experiment. The invariant yield of direct photons in central collisions is extracted as a function of transverse momentum in the interval 0.5 1.5 GeV/c. The results constitute the first observation of direct photons in ultrarelativistic heavy-ion collisions which could be significant for diagnosis of quark gluon plasma formation
Single electrons from heavy-flavor decays in p+p collisions at Vs=200 GeV
No full textThe invariant differential cross section for inclusive electron production in p+p collisions at Vs=200 GeV has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over the transverse momentum range 0.4≤pT≤5.0 GeV/c in the central rapidity region (|η|≤0.35). The contribution to the inclusive electron spectrum from semileptonic decays of hadrons carrying heavy flavor, i.e., charm quarks or, at high pT, bottom quarks, is determined via three independent methods. The resulting electron spectrum from heavy-flavor decays is compared to recent leading and next-to-leading order perturbative QCD calculations. The total cross section of charm quark-antiquark pair production is determined to be σcc̅ =0.92±0.15(stat)±0.54(syst) mb
Summary: current theories and directions of strangeness signals for quark matter
No full textA summary of the theory part of the Strangeness and Quark Matter Symposium is given
Azimuthal Anisotropy of Strange and Charm Hadrons: Measured in Pb-Pb Collisions at 2.76 TeV
No full textThe structure of this document is the following: Chapter 2 contains a brief description of the ALICE sub-detectors relevant for this analysis. In chapter 3, the approach to vn of decaying particles by multi-particle correlations and reconstruction of the Qn vectors is discussed. Chapter 4 encloses the description of the reconstruction of candidates and their v2. Chapter 5 is where the measurements are presented and discussed. Final remarks will be given in chapter 6
Measurements with a High-Granularity Digital Electromagnetic Calorimeter
No full textThe low-x structure of protons and in particular nuclei is not well constrained experimentally, while the knowledge about it is a crucial ingredient for the interpretation of many measurements at high-energy hadron colliders. It is widely expected that the growth of parton densities at low x predicted from linear QCD evolution cannot continue indefinitely, and that non-linear effects will lead to gluon saturation. Many experimental observations are compatible with saturation, however no real proof has been found yet. We propose the measurement of forward direct photons in proton-nucleus collisions at the LHC as a decisive probe of gluon saturation. Due to the harsh environment of such a measurement, existing detectors are not suitable. In particular an extremely high-granularity electromagnetic calorimeter is required, which we propose as a detector upgrade to the ALICE experiment, the Forward Calorimeter (FoCal). To facilitate the design of the upgrade and to perform generic R&D necessary for such a novel calorimeter, a compact full high-granularity electromagnetic calorimeter prototype has been built. This prototype is a Si/W sampling calorimeter using CMOS sensors of the MIMOSA type with a pixel pitch of 30 micron and binary readout with a total of ~39 million pixels. About 85% of the total volume is W absorber, a small Molière radius of 10.5 mm is expected. The raw data shows the properties and limitations of this prototype. To obtain a good performance, several selection procedures and an additional analysis methodology based on hit density is applied. In simulation, to make a valid comparison, misalignment, noise, and charge diffusion are considered. A realistic detector is simulated, a realistic number of noise pixels has also been added. To study the effects of dead areas, both the `ideal detector' and `real detector' are simulated. We present on performance studies of the prototype with test beams at DESY and CERN in a broad energy range. The results of the measurements demonstrate that a very small Molière radius and good linearity of the response. Unique results on the detailed lateral shower shape, which are crucial for the two-shower separation capabilities. The studies demonstrate the feasibility of this high-granularity technology for use in the proposed detector upgrade. Furthermore, they show the extremely high potential of this technology for future calorimeter development
Optimization of the Track Reconstruction Algorithm in a Pixel Based Range Telescope for Proton Computed Tomography
No full textThe use of protons to treat cancer has expanded rapidly in the past two decades. For safe and effective proton therapy, the proton range in a patient’s body must be accurately determined. Current treatment planning is based on X-ray computed tomography images, which might cause uncertainty because of the different behaviour between protons and X-rays. As an alternative, proton Computed Tomography (pCT) has been proposed to directly measure the Relative Stopping Power (RSP) map in the patient and reduce this uncertainty. During a proton CT scan, a high-energy proton beam is directed at the patient. Then, the proton’s residual energy and position are measured with a detector placed behind the patient. This information is used to calculate the volumetric RSP. In the case of using a pixel based detector, a tracking algorithm is required in order to increase the proton intensity capacity of the detector. A proton track reconstruction system has been already developed by Pettersen [1], however, it has some limitations on the track density that can be reconstructed correctly. The algorithm is based on the track-following scheme, in which a growing track searches for deeper- laying activated pixels. This thesis introduces proton therapy and the advantages of pCT and proton radiography for treatment planning. Then, the main track reconstruction techniques found in the literature are reviewed. Improvements in the reconstruction process are proposed and their efficiencies are discussed. While current algorithm begins from the layer closest to the patient, in the present study a new reconstruction algorithm is developed. It differs by starting the reconstruction process from the distal end of the detector. Based on this new algorithm, studies related to its optimization are conducted. Lastly, an algorithm based on the identification of the most probable scenario is developed. The potential algorithms are evaluated on data simulated with GATE (based on Monte Carlo interactions) and PROCASIM (design to simplify the physical interactions between protons and the detector). The fraction of correctly reconstructed tracks and the computational eciency of the algorithms are analyzed to determine the most viable one. [1] H. E. S. Pettersen. A Digital Tracking Calorimeter for Proton Computed Tomography. PhD thesis, University of Bergen, Norway, February 2018.Biomedical Engineerin
Measurements with a high-granularity digital electromagnetic calorimeter
No full textThe low-x structure of protons and in particular nuclei is not well constrained experimentally, while the knowledge about it is a crucial ingredient for the interpretation of many measurements at high-energy hadron colliders. It is widely expected that the growth of parton densities at low x predicted from linear QCD evolution cannot continue indefinitely, and that non-linear effects will lead to gluon saturation. Many experimental observations are compatible with saturation, however no real proof has been found yet. We propose the measurement of forward direct photons in proton-nucleus collisions at the LHC as a decisive probe of gluon saturation. Due to the harsh environment of such a measurement, existing detectors are not suitable. In particular an extremely high-granularity electromagnetic calorimeter is required, which we propose as a detector upgrade to the ALICE experiment, the Forward Calorimeter (FoCal). To facilitate the design of the upgrade and to perform generic R&D necessary for such a novel calorimeter, a compact full high-granularity electromagnetic calorimeter prototype has been built. This prototype is a Si/W sampling calorimeter using CMOS sensors of the MIMOSA type with a pixel pitch of 30 micron and binary readout with a total of ~39 million pixels. About 85% of the total volume is W absorber, a small Molière radius of 10.5 mm is expected. The raw data shows the properties and limitations of this prototype. To obtain a good performance, several selection procedures and an additional analysis methodology based on hit density is applied. In simulation, to make a valid comparison, misalignment, noise, and charge diffusion are considered. A realistic detector is simulated, a realistic number of noise pixels has also been added. To study the effects of dead areas, both the `ideal detector' and `real detector' are simulated. We present on performance studies of the prototype with test beams at DESY and CERN in a broad energy range. The results of the measurements demonstrate that a very small Molière radius and good linearity of the response. Unique results on the detailed lateral shower shape, which are crucial for the two-shower separation capabilities. The studies demonstrate the feasibility of this high-granularity technology for use in the proposed detector upgrade. Furthermore, they show the extremely high potential of this technology for future calorimeter development
High transverse momentum η meson production in p+p,d+Au, and Au+Au collisions at VsNN=200 GeV
No full textInclusive transverse momentum spectra of η mesons in the range pT≈2–12 GeV/c have been measured at midrapidity (|η
D^{∗+}-meson production in proton-proton and proton-lead collisions in ALICE
No full textD^{*+} meson results in proton-proton collisions at \sqrt{s}=13 TeV and proton-lead collisions at \sqrt{s_{NN}}=5.02 TeV at the Large Hadron Collider collected with the ALICE detector are presented.
Heavy quarks, such as the charm quark that is a constituent of the D^{*+} meson, are effective probes for the study of the properties of the Quark-Gluon Plasma formed in high energy Pb--Pb collisions, as heavy quarks are mainly produced in hard scattering processes in the initial stages of the collision.
In p--Pb collisions the production of heavy flavour quarks can be influenced by Cold Nuclear Matter (CNM) effects.
The nuclear modification, R_{AA} (R_{\rm pPb}) measures the plasma (CNM) effects in Pb--Pb (p--Pb) collisions on the
transverse momentum(pt)-distribution of the final state particles compared to a particles distribution from minimum bias pp collisions.
The comparison of heavy flavour production in proton-Pb and Pb--Pb collisions via the nuclear modification factor allows to distinguish between CNM effects and hot-nuclear matter effects present in Pb--Pb collisions.
Measurements of the heavy flavour hadron cross-section in proton-proton collisions allows to test pertubative Quantum Chromo Dynamic calculations and forms a reference measurement for the R_{\rm{AA}} or R_{\rm pPb}.
Ratio measurements of the cross-section in pp collisions between different collision energies make it possible to probe the gluonic properties of the theory with measurements at low D-meson pt.
The proton-proton results presented in this thesis are within uncertainty consistent with FONLL predictions, though consistently above the central value.
The presented preliminary results of the ratio of the cross-section at 13 TeV with respect to 5 TeV are fully consistent with predictions, and the uncertainty on the measurement and theory are similar. An increase in statistics could
significantly improve these results and might make it possible to separate fluctuations from actual differences especially at low transverse momenta as well as further constrain the FONLL predictions.
The presented proton-lead results are consistent with the results in proton-proton collisions. The nuclear modification factor for the average of D-mesons shows a flat trend for transverse momenta above 3GeV/c. These results are in agreement with various models that include CNM effects in the full pt range, disfavouring a calculation based on incoherent multiple scatterings at low transverse momenta. Models including also
some form of Quark-Gluon Plasma show a different trend with respect to pt, but cannot fully be excluded based on the current measurements.
Measurements done in multiplicity sets in proton-lead collisions show hints of a non-flat shape.
These results also show a non-unity centrality ratio at 3sigma precision of which
the shape is seen at all centralities, hinting towards some form of flow in p--Pb. Measurements of heavy flavour decay electrons find a non-zero , possibly due to fluctuations
in the initial state geometry, but it can also be explained by a very small QGP in proton-lead collisions.
The ongoing upgrades on the ITS will allow the ALICE detector to do more precise measurements at lower pt. The extra precision will also allow us to
correct for any B-decay D^{*+} mesons via measurement
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