arXiv subjects

R. Bellwied

Publications and source records attributed to R. Bellwied.

226 records · Page 13Linked to original sources

arXiv2005

Expression of Interest for a Comprehensive New Detector at RHIC II

There are compelling physics questions to be addressed by a new comprehensive detector at a future, high-luminosity RHIC II collider. These form the basis for this Expression of Interest. What precisely are the properties of the strongly-coupled Quark Gluon Plasma (sQGP)? Can a more weakly interacting QGP state be formed and investigated at RHIC? How do particles acquire mass and what is the effect of chiral symmetry restoration on hadronization in a dense medium? What is the chiral structure of the QCD vacuum and its influence on and contributions of different QCD vacuum states to the masses of particles? Is there another phase of matter at low Bjorken-x, i.e. the Color Glass Condensate (CGC)? If present, what are its features and how does it evolve into the QGP? If not, are parton distribution functions understood at low Bjorken-x and can they describe particle production? What are the structure and dynamics inside the proton, including parton spin and orbital angular momentum? What are the contributions of gluons and the QCD sea to the polarization of the proton? What is the flavor-dependence? Are there tests for new physics beyond the Standard Model from spin measurements at RHIC II (such as parity-violating interactions)? We propose that a new comprehensive detector system is needed for RHIC II to address these questions adequately and in an effective way.

nucl-ex↗

arXiv2004

A Comprehensive New Detector for Detailed Study of the Quark Gluon Plasma, Initial Conditions and Spin Physics at RHIC II

A case is presented for compelling physics at a high luminosity RHIC II collider and a comprehensive new detector system to address this physics. The experimental focus is on detailed jet tomography of the quark gluon plasma (QGP), measuring gluon saturation in the nucleus, investigating the color glass condensate, measuring effects of the QCD vacuum on particle masses, determining the structure and dynamics within the proton, and possible new phenomena. The physics and detector capabilities are introduced.

nucl-ex↗

arXiv2002

Track Timing at $e^{+}e^{-}$ Linear Colliders with a Silicon Drift Detector Main Tracker

The track timing capabilities of a silicon drift detector based tracker for a future linear electron-positron collider are evaluated. We show such a detector can time tracks at the nanosecond, and for high-$P_{T}$, sub-nanosecond level. This implies that, even for collider designs with the bunch spacing at 1.4 ns, every track can be assigned to a particular bunch crossing at a confidence level of up to two standard deviations. We suggest a choice for the drift axes in the tracker layers to simultaneously optimize the momentum resolution and track timing.

hep-ex↗

arXiv2000

Directed flow of antiprotons in Au+Au collisions at AGS

Directed flow of antiprotons is studied in Au+Au collisions at a beam momentum of 11.5A GeV/c. It is shown that antiproton directed flow is anti-correlated to proton flow. The measured transverse momentum dependence of the antiproton flow is compared with predictions of the RQMD event generator.

nucl-ex↗

arXiv2000

Time Dependence of Chemical Freeze-out in Relativistic Heavy Ion Collisions

We investigate chemical and thermal freeze-out time dependencies for strange particle production for CERN SPS heavy ion collisions in the framework of a dynamical hadronic transport code. We show that the Lambda yield changes considerably after hadronization in the case of Pb+Pb collisions, whereas for smaller system sizes (e.g. S+S) the direct particle production dominates over production from inelastic rescattering. Chemical freeze-out times for strange baryons in Pb+Pb are smaller than for non-strange baryons, but they are still sufficiently long for hadronic rescattering to contribute significantly to the final Lambda yield. Based on inelastic and elastic cross section estimates we expect the trend of shorter freeze-out times (chemical and kinetic), and thus less particle production after hadronization, to continue for multi-strange baryons.

hep-ph↗

arXiv1998

Survival Probabilities of Disoriented Chiral Domains in Relativistic Heavy Ion Collisions

By using a dynamical transport code we show that chirally disoriented domains might survive the hadronization phase in a central relativistic heavy ion collision. A successful measurement of such domains after freeze-out will depend on the domain size and the manifestation of the disorientation in the low part of the charged pion momentum spectrum. We investigated the measurement of the transverse momentum and the pseudo-rapidity spectrum of pions below 200 MeV/c. In all cases the successful determination of a realistic domain requires first and second moment analyses of the phase space.

nucl-th↗

arXiv1998

Directed Flow of Light Nuclei in Au+Au Collisions at AGS Energies

Directed flow of deuterons, tritons, $^3$He, and $^4$He is studied in Au+Au collisions at a beam momentum of about 10.8 $A$ GeV/c. Flow of all particles is analyzed as a function of transverse momentum for different centralities of the collision. The directed flow signal, $v_1(p_t)$, is found to increase with particle mass. This mass dependence is strongest in the projectile rapidity region.

nucl-ex↗

arXiv1998

${\barΛ}/{\bar p}$ ratios in heavy ion collisions at 11.6 AGeV/c

We attempt to explain the ${\bar Λ}/\bar p$ ratios measured in heavy ion collisions at $11.6~{\rm A\cdot GeV}/c$ beam momentum within a hadronic framework. This ratio is enhanced relative to corresponding ratios in $pp$ collisions, and is large when compared with thermal fits to heavy ion data. Using a detailed cascade calculation, we show that different annihilation cross--sections of $\bar Λ$'s and $\bar p$'s, and the net conversion of $\bar p$'s to $\bar Λ$'s, do not account for the enhancement in central collisions. For larger impact parameters, however, hadronic mechanisms may well suffice to produce the observed enhancement. Uncertainties in elementary cross--sections and formation times are considered.

nucl-th↗

arXiv1998

Anti-Lambda/Anti-Proton ratios at the AGS

We attempt to explain the large ${\bar Λ}/\bar p$ ratios measured in heavy ion collisions at $12~{\rm A\cdot GeV}/c$ beam momentum within an hadronic framework. The ratios are large compared to corresponding ratios in $pp$ collisions, and to thermal fits. We show using a simple model and a detailed cascade calculation that different annihilation cross--sections of $\bar Λ$'s and $\bar p$'s, and the net conversion of $\bar p$'s to $\bar Λ$'s, do not account for the enhancement. Uncertainties in elementary cross--sections and formation times are also considered.

nucl-th↗

arXiv1997

Two-pion correlations in Au+Au collisions at 10.8 GeV/c per nucleon

Two-particle correlation functions for positive and negative pions have been measured in Au+Au collisions at 10.8~GeV/c per nucleon. The data were analyzed using one- and three-dimensional correlation functions. From the results of the three-dimensional fit the phase space density of pions was calculated. It is consistent with local thermal equilibrium.

physics.acc-ph↗