1,231 research outputs found
The 3rd Flow Component as a QGP Signal
Earlier fluid dynamical calculations with QGP show a softening of the
directed flow while with hadronic matter this effect is absent. On the other
hand, we indicated that a third flow component shows up in the reaction plane
as an enhanced emission, which is orthogonal to the directed flow. This is not
shadowed by the deflected projectile and target, and shows up at measurable
rapidities, . To study the formation of this effect initial stages
of relativistic heavy ion collisions are studied. An effective string rope
model is presented for heavy ion collisions at RHIC energies. Our model takes
into account baryon recoil for both target and projectile, arising from the
acceleration of partons in an effective field. The typical field strength
(string tension) for RHIC energies is about 5-12 GeV/fm, what allows us to talk
about "string ropes". The results show that QGP forms a tilted disk, such that
the direction of the largest pressure gradient stays in the reaction plane, but
deviates from both the beam and the usual transverse flow directions. The
produced initial state can be used as an initial condition for further
hydrodynamical calculations. Such initial conditions lead to the creation of
third flow component. Recent measurements are promising that this effect
can be used as a diagnostic tool of the QGP
Proton tracking in a high-granularity Digital Tracking Calorimeter for proton CT purposes
Radiation therapy with protons as of today utilizes information from x-ray CT
in order to estimate the proton stopping power of the traversed tissue in a
patient. The conversion from x-ray attenuation to proton stopping power in
tissue introduces range uncertainties of the order of 2-3% of the range,
uncertainties that are contributing to an increase of the necessary planning
margins added to the target volume in a patient. Imaging methods and
modalities, such as Dual Energy CT and proton CT, have come into consideration
in the pursuit of obtaining an as good as possible estimate of the proton
stopping power. In this study, a Digital Tracking Calorimeter is benchmarked
for proof-of-concept for proton CT purposes. The Digital Tracking Calorimeteris
applied for reconstruction of the tracks and energies of individual high energy
protons. The presented prototype forms the basis for a proton CT system using a
single technology for tracking and calorimetry. This advantage simplifies the
setup and reduces the cost of a proton CT system assembly, and it is a unique
feature of the Digital Tracking Calorimeter. Data from the AGORFIRM beamline at
KVI-CART in Groningen in the Netherlands and Monte Carlo simulation results are
used to in order to develop a tracking algorithm for the estimation of the
residual ranges of a high number of concurrent proton tracks. The range of the
individual protons can at present be estimated with a resolution of 4%. The
readout system for this prototype is able to handle an effective proton
frequency of 1 MHz by using 500 concurrent proton tracks in each readout frame,
which is at the high end range of present similar prototypes. A future further
optimized prototype will enable a high-speed and more accurate determination of
the ranges of individual protons in a therapeutic beam.Comment: 21 pages, 8 figure
Real-time TPC Analysis with the ALICE High-Level Trigger
The ALICE High-Level Trigger processes data online, to either select
interesting (sub-) events, or to compress data efficiently by modeling
techniques.
Focusing on the main data source, the Time Projection Chamber, the
architecure of the system and the current state of the tracking and compression
methods are outlined.Comment: 6 pages, 5 figures, to be published in NIM
Dilepton Production at SPS-energy Heavy Ion Collisions
The production of dileptons is studied within a hadronic transport model. We
investigate the sensitivity of the dilepton spectra to the initial
configuration of the hadronic phase in a ultrarelativistic heavy ion collision.
Possible in medium correction due to the modifications of pions and the pion
form factor in a hadronic gas are discussed.Comment: Dedicated to Gerry Brown in honor of the 32nd celebration of his 39th
birthday. 31 pages Latex including 13 eps-figures, uses psfig.sty and
epsf.st
Experimental determination of the complete spin structure for anti-proton + proton -> anti-\Lambda + \Lambda at anti-proton beam momentum of 1.637 GeV/c
The reaction anti-proton + proton -> anti-\Lambda + \Lambda -> anti-proton +
\pi^+ + proton + \pi^- has been measured with high statistics at anti-proton
beam momentum of 1.637 GeV/c. The use of a transversely-polarized frozen-spin
target combined with the self-analyzing property of \Lambda/anti-\Lambda decay
allows access to unprecedented information on the spin structure of the
interaction. The most general spin-scattering matrix can be written in terms of
eleven real parameters for each bin of scattering angle, each of these
parameters is determined with reasonable precision. From these results all
conceivable spin-correlations are determined with inherent self-consistency.
Good agreement is found with the few previously existing measurements of spin
observables in anti-proton + proton -> anti-\Lambda + \Lambda near this energy.
Existing theoretical models do not give good predictions for those
spin-observables that had not been previously measured.Comment: To be published in Phys. Rev. C. Tables of results (i.e. Ref. 24) are
available at http://www-meg.phys.cmu.edu/~bquinn/ps185_pub/results.tab 24
pages, 16 figure
Chemical equilibration of strangeness
Thermal models are very useful in the understanding of particle production in
general and especially in the case of strangeness. We summarize the assumptions
which go into a thermal model calculation and which differ in the application
of various groups. We compare the different results to each other. Using our
own calculation we discuss the validity of the thermal model and the amount of
strangeness equilibration at CERN-SPS energies. Finally the implications of the
thermal analysis on the reaction dynamics are discussed.Comment: 23 pages, LaTeX (figures included); Talk given at the Int. Symposium
on Strangeness in Quark Matter 1997, Santorini (Greece), April 199
Nuclear Stopping in Au+Au Collisions at sqrt(sNN) = 200 GeV
Transverse momentum spectra and rapidity densities, dN/dy, of protons,
anti-protons, and net--protons (p-pbar) from central (0-5%) Au+Au collisions at
sqrt(sNN) = 200 GeV were measured with the BRAHMS experiment within the
rapidity range 0 < y < 3. The proton and anti-proton dN/dy decrease from
mid-rapidity to y=3. The net-proton yield is roughly constant for y<1 at
dN/dy~7, and increases to dN/dy~12 at y~3. The data show that collisions at
this energy exhibit a high degree of transparency and that the linear scaling
of rapidity loss with rapidity observed at lower energies is broken. The energy
loss per participant nucleon is estimated to be 73 +- 6 GeV.Comment: 5 pages, 4 figure
Quark exchange model for charmonium dissociation in hot hadronic matter
A diagrammatic approach to quark exchange processes in meson-meson scattering
is applied to the case of inelastic reactions of the type
(Q\barQ)+(q\barq)\rightarrow (Q\barq) + (q\barQ), where and refer to
heavy and light quarks, respectively. This string-flip process is discussed as
a microscopic mechanism for charmonium dissociation (absorption) in hadronic
matter. The cross section for the reaction is
calculated using a potential model, which is fitted to the meson mass spectrum.
The temperature dependence of the relaxation time for the \J/Psi distribution
in a homogeneous thermal pion gas is obtained. The use of charmonium for the
diagnostics of the state of hot hadronic matter produced in ultrarelativistic
nucleus-nucleus collisions is discussed.Comment: 24 pages, 3 tables, 7 figure
Software environment for controlling and re-configuration of Xilinx Virtex FPGAs â TWEPP-07
The Time Projection Chamber is one of the detectors of the ALICE experiment, that is currently being commissioned at the Large Hadron Collider at CERN. The Detector Control System is used for control and monitoring of the system. For the TPC Front-End Electronics (FEE) the control node is a Readout Control Unit that communicates to higher layers via Ethernet, using the standard framework DIM. The Readout Control Unit is equipped with commercial SRAM based FPGAs that will experience errors due to the radiation environment they are operating in. This article will present the implemented hardware solution for error correction and will focus on the software environment for configuration and controlling of the system â TWEPP-07
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