10358981
Fluctuations of rare particles as a measure of chemical equilibration
LBL-47721 Mc-Gill-preprint-01-09 GSI-Preprint/2001-10 Fluctuations of rare particles as a measure of chemical equilibration Nuclear Science Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 GSI, D-64291 Darmstadt, Germany and Institute of Theoretical Physics, University of Wroclaw, PL-50204 Wroclaw, Poland †Department of Physics, McGill University, 3600 University Street, Montreal, QC H3A-2T8, Canada ∗RIKEN-BNL Research Center, Brookhaven National Laboratory, Upton, NY 11973 (August 17, 2001) We calculate the time evolution of ﬂuctuations for rare particles such as e.g. kaons in 1 AGeV or charmonium in 200 AGeV heavy ion collisions. We ﬁnd that these ﬂuctuations are a very sensitive probe of the degree of chemical equilibration reached in these collisions. Furthermore, measuring the second factorial moment the size of the initial population can be determined. a S. Jeon a †∗ , V. Koch a , K. Redlich a,c , and X.-N. Wang a c arXiv:nucl-th/0105035 v1 15 May 2001 I. INTRODUCTION Statistical models have long been used as a tool to de- scribe particle production in heavy ion and in high energy particle collisions [1–3]. Recent analysis have shown that these models can indeed give a satisfactory description of the multiplicities of most hadrons measured in A-A collisions for bombarding energies ranging from 1 AGeV (SIS) to 160 AGeV (SPS) [4,5]. Especially at the low energies (SIS) and for the rare particles such as kaons, the success of the statistical description has been a puz- zle and could not be understood within the state-of-the- art transport models [6]. For instance a recent analy- sis for chemical equilibration within a transport model [6] gives chemical equilibration time of the order of 300 fm/c for a situation relevant to 1 AGeV heavy ion col- lisions, considerably larger than the typical duration of such reaction, which is of the order of 30-50 fm/c. On the other hand the success of the statistical model cannot be disputed. Not only are the particle ratios reproduced for central collision over a wide range of bombarding en- ergy, but also the centrality dependence at low energies is consistent with the predictions of the statistical mod- els. In particular the almost quadratic dependence of the kaon multiplicity on the number of participating nucleon at SIS follows directly from the statistical model, once strangeness conservation is taken into account exactly [7]. Transport models on the other hand fail to reproduce the observed centrality dependence and particularly energy dependence of the K/π-ratio [8]. In a recent paper [9] some of us have shown, that the chemical equilibration time is considerably shortened if the strangeness conservation is taken into account ex- plicitly. However, using the new rate equations derived in this work combined with the cross sections as given in [14] one still arrives at equilibration time substantially exceeding the lifetime of the system. Does this mean that the success of the statistical model is a pure coincidence? This is very unlikely as statistical model naturally explains most of the basic features of experimental data in a very broad energy range from SIS up to SPS. It is conceivable that there are additional processes at work, like e.g. many particle collisions [15] or in medium modiﬁcations of hadron properties [16], which are not yet taken into account in transport models. Thus, a direct experimental determination of the rate of equilibration in heavy ion collisions is called for as it would possibly provide evidence for new physics. In this paper we will demonstrate that the ﬂuctuations of rare particles is a very sensitive probe of the degree of equili- bration reached in these collisions. Such a measurement, though certainly diﬃcult, could for the ﬁrst time provide a direct experimental evidence for chemical equilibration in heavy ion reactions. This paper is organized as follows. In the following sec- tion we set up the formalism. Then we present the results for the time dependence of the second factorial moment for several initial conditions. Before we turn to observa- tional issues we also will discuss the case when no con- straints from any U (1) charge conservation are present. II. FORMALISM In Ref. [9] the rate equation for particles which are sub- ject to an explicit U (1) “charge” conservation has been derived. Considering a binary process a 1 a 2 → b 1 b 2 with a = b one arrives at the following master equation for the probabilities P n to ﬁnd n particles dP n = [P n−1 − P n ] dτ
126140598
Report of the RHIC Workshop p + A subgroup
33523602
Role of multiple minijets in high-energy hadronic reactions.
The multiplicity distributions of charged particles in high-energy hadron collisions including the production of multiple minijets are considered in the framework of the eikonal formalism. Large-multiplicity events at high energies are found to be dominated by the production of many jets with 2{le}{ital P}{sub {ital T}}{le}4 GeV. The contributions from larger-{ital P}{sub {ital T}} minijets become prevailing for high-multiplicity fluctuations in narrow rapidity intervals.
42468399
Berry curvature and four-dimensional monopoles in the relativistic chiral kinetic equation.
We derive a relativistic chiral kinetic equation with manifest Lorentz covariance from Wigner functions of spin-1/2 massless fermions in a constant background electromagnetic field. It contains vorticity terms and a four-dimensional Euclidean Berry monopole which gives an axial anomaly. By integrating out the zeroth component of the 4-momentum p, we reproduce the previous three-dimensional results derived from the Hamiltonian approach, together with the newly derived vorticity terms. The phase space continuity equation has an anomalous source term proportional to the product of electric and magnetic fields (FσρF[over ˜]σρ∼EσBσ). This provides a unified interpretation of the chiral magnetic and vortical effects, chiral anomaly, Berry curvature, and the Berry monopole in the framework of Wigner functions.
119298211
Relics of Minijets amid Anisotropic Flows in High-energy Heavy-ion Collisions
Two dimensional low-$p_T$ dihadron correlations in azimuthal angle $\phi$ and pseudo-rapidity $\eta$ in high-energy heavy-ion collisions are investigated within both the HIJING Monte Carlo model and an event-by-event (3+1)D ideal hydrodynamic model. Without final-state interaction and collective expansion, dihadron correlations from HIJING simulations have a typical structure from minijets that contains a near-side two-dimensional peak and an away-side ridge along the $\eta$-direction. In contrast, event-by-event (3+1)D ideal hydrodynamic simulations with fluctuating initial conditions from the HIJING+AMPT model produce a strong dihadron correlation that has an away-side as well as a near-side ridge. Relics of intrinsic dihadron correlation from minijets in the initial conditions still remain as superimposed on the two ridges. By varying initial conditions from HIJING+AMPT, we study effects of minijets, non-vanishing initial flow and longitudinal fluctuation on the final state dihadron correlations. With a large rapidity gap, one can exclude near-side correlations from minijet relics and dihadron correlations can be described by the superposition of harmonic flows up to the 6th order. When long-range correlations with a large rapidity gap are subtracted from short-range correlations with a small rapidity gap, the remaining near-side dihadron correlations result solely from relics of minijets. Low transverse momentum hadron yields per trigger ($p_T^{\rm trig} <4$ GeV/$c$, $p_T^{\rm asso}<2$ GeV/$c$) in central heavy-ion collisions are significantly enhanced over that in p+p collisions while widths in azimuthal angle remain the same, in qualitative agreement with experimental data.
17734649
Probe initial parton density and formation time via jet quenching
Medium modification of jet fragmentation function due to multiple scattering and induced gluon radiation leads directly to jet quenching or suppression of leading particle distribution from jet fragmentation. One can extract an effective total parton energy loss which can be related to the total transverse momentum broadening. For an expanding medium, both are shown to be sensitive to the initial parton density and formation time. Therefore, one can extract the initial parton density and formation time from simultaneous measurements of parton energy loss and transverse momentum broadening. Implication of the recent experimental data on effects of detailed balance in parton energy loss is also discussed.
125624266
beta-delayed proton decays near the proton drip line
We briefly reviewed and summarized the experimental study on {beta}-delayed proton decays published by our group over the last 8 years, namely the experimental observation of {beta}-delayed proton decays of nine new nuclides in the rare-earth region near the proton drip line and five nuclides in the mass 90 region with N{approx}Z by utilizing the p-{gamma} coincidence technique in combination with a He-jet tape transport system. In addition, important technical details of the experiments were provided. The experimental results were compared to the theoretical predictions of some nuclear models, resulting in the following conclusions. (1) The experimental half-lives for {sup 85}Mo, {sup 92}Rh, as well as the predicted 'waiting point' nuclei {sup 89}Ru and {sup 93}Pd were 5-10 times longer than the macroscopic-microscopic model predictions of Moeller et al. [At. Data Nucl. Data Tables 66,131(1997)]. These data considerably influenced the predictions of the mass abundances of the nuclides produced in the rp process. (2) The experimental assignments of spin and parity for the drip-line nuclei {sup 142}Ho and {sup 128}Pm could not be well predicted by any of the nuclear models. Nevertheless, the configuration-constrained nuclear potential-energy surfaces calculated by means of a Woods-Saxon-Strutinsky method could reproduce the assignments. (3) Themore » ALICE code overestimated by one or two orders of magnitude the production-reaction cross sections of the nine studied rare-earth nuclei, while the HIVAP code overestimated them by approximately one order of magnitude.« less
118839380
The associated productions of the new gauge boson $B_{H}$ in the littlest Higgs model with a SM gauge boson via $e^+e^-$ collision
With the high energy and luminosity, the planned ILC has the considerable capability to probe the new heavy particles predicted by the new physics models. In this paper, we study the potential to discover the lightest new gauge boson $B_{H}$ of the littlest Higgs model via the processes $e^+e^- \to \gamma (Z)B_H$ at the ILC. The results show that the production rates of these two processes are large enough to detect $B_H$ in a wide range of the parameter space, specially for the process $e^+e^- \to \gamma B_H$. Furthermore, there exist some decay modes for $B_H$ which can provide the typical signal and clean background. Therefore, the new gauge boson $B_H$ should be observable via these production processes with the running of the ILC if it exists indeed.
110357550
Specialized Technical Services at ESS
The European Spallation Source (ESS), a world class lab for neutron science currently under construction in Lund, Sweden requires a number of technical services that extend across the various project areas (accelerator, target and neutron science). These services include: cryogenics, vacuum and technical electrical and cooling systems. This effort constitutes more than 70 million Euros of construction cost. Rather than have separate support groups in each of the project areas, ESS has created a Specialized Technical Services group within the Accelerator Division to provide these services. This approach permits standardization, development of synergies and improved communication. The STS group also provides cryomodule testing to the accelerator project. This paper describes the scope of work, current design status and future plans for Specialized Technical services at ESS.
115539522
Pair production of charged top-pions in the $\gamma\gamma$ collisions at the ILC
The top-color assisted technicolor (TC2) mode predicts the existence of a pair of charged top-pions $\pi^{\pm}_t$. In this paper, we study the production of the charged top-pions pair $\pi^{\pm}_t$ at next generation $\gamma\gamma$ colliders. The results show that the production rates can reach the level of $10^2$ fb with reasonable parameter space. With a large number of events and the clean background, the charged top-pion should be observable at the $\gamma\gamma$ colliders. Therefore, our studies can help us to search for charged top-pion, and furthermore, to test the TC2 model.
625892
The productions of the top-pions and top-Higgs associated with the charm quark at the hadron colliders
In the topcolor-assisted technicolor (TC2) model, the typical physical particles, top-pions and top-Higgs, are predicted and the existence of these particles could be regarded as robust evidence for the model. These particles are accessible at the Tevatron and LHC, and furthermore the flavor-changing (FC) feature of the TC2 model may provide us with a unique opportunity to probe them. In this paper, we study some interesting FC production processes of top-pions and top-Higgs particles at the Tevatron and LHC, i.e., cΠt- and cΠt0(ht0) productions. We find that the light charged top-pions are not favorable by the Tevatron experiments, and the Tevatron has little capability to probe the neutral top-pion and top-Higgs particles via these FC production processes. At LHC, however, the cross section can reach the level of 10–100 pb for cΠt- production and 10–100 fb for cΠt0(ht0) production. So one can expect that enough signals could be produced at the LHC experiments. Furthermore, the SM backgrounds should be clean due to the FC feature of the processes, and the FC decay modes Πt-→bc̄, Πt0(ht0)→tc̄ can provide us with the signal typical for the detection of the top-pions and top-Higgs particles. Therefore, one may have hope to find the signal of top-pions and top-Higgs particles with the running of LHC via these FC processes.