15961214
Multiple collisions and induced gluon Bremsstrahlung in QCD
Abstract Induced soft gluon bremsstrahlung associated with multiple collisions is calculated via perturbative QCD. We derive the non-abelian analog of the Landau-Pomeranchuk effect that suppresses induced soft radiation with formation times exceeding the mean free path. The dependence of the suppression effect on the SU( N ) representation of the jet parton as well as the kinematic variables is expressed through a radiation formation factor. The soft radiation with k ⊥ μ , where μ is the infrared screening scale in the medium, is shown to lead to an approximately constant radiative energy loss per unit length.
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.
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.
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.
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.
119023635
Dynamics of giant-gravitons in the LLM geometry and the fractional quantum Hall effect
Abstract The LLM's 1 / 2 BPS solutions of IIB supergravity are known to be closely related to the integer quantum Hall droplets with filling factor ν = 1 , and the giant gravitons in the LLM geometry behave like the quasi-holes in those droplets. In this paper we consider how the fractional quantum Hall effect may arise in this context, by studying the dynamics of giant graviton probes in a special LLM geometry, the AdS 5 × S 5 background, that corresponds to a circular droplet. The giant gravitons we study are D3-branes wrapping on a 3-sphere in S 5 . Their low energy world-volume theory, truncated to the 1 / 2 BPS sector, is shown to be described by a Chern–Simons finite-matrix model. We demonstrate that these giant gravitons may condense at right density further into fractional quantum Hall fluid due to the repulsive interaction in the model, giving rise to the new states in IIB string theory. Some features of the novel physics of these new states are discussed.
94690392
Isovector channel of quarkmeson-coupling model and its effect on symmetry energy
Abstract The non-relativistic approximation of the quark–meson-coupling model has been discussed and compared with the Skyrme–Hartree–Fock model which includes spin exchanges. Calculations show that the spin-exchange interaction has important effect on the descriptions of finite nuclei and nuclear matter through the Fock exchange. Also in the quark–meson-coupling model, it is the Fock exchange that leads to a nonlinear density-dependent isovector channel and changes the density-dependent behavior of the symmetry energy.
33137217
Exponential growth, superradiance, and tunability of a seeded free electron laser.
Exponential growth and superradiance regimes in a high-gain free electron laser (FEL) are studied in this paper for both a seeded FEL and a Self-Amplified Spontaneous Emission (SASE) FEL. The results are compared to the earlier superrdaince theory and the recent experimental observation. The influence of an initial energy chirp along the electron bunch on the superradiance mode is explored for the first time. With a short seed to increase the initial seed bandwidth, a tunable seeded FEL is possible.
120209602
Longitudinal Double Spin Asymmetries in Heavy Flavor Production in Polarized p+p Collisions at s = 200 GeV
One of the main goals of the RHIC spin program is to determine the contribution of gluons to the proton spin. At RHIC energies, heavy quark (charm and beauty) production is expected to be dominated by gluon‐gluon interactions, so a measurement of the double longitudinal spin asymmetry ALL in heavy quark production in polarized p+p collisions directly probes the polarized gluon distribution inside the proton. We present the latest results on an ALL measurement for J/Ψ and open charm production measured by the PHENIX detector.
140119573
ELECTROMAGNETIC PARAMETERS STUDY OF MICROWAVE- ABSORBING MATERIAL FeSiAl FOR COLLINEAR LOAD OF LINAC*
Microwave-absorbing material is an essential part of LINAC collinear load. It is coated on the inner walls of several trailing accelerating cavities to transform the remnant microwave power into heat. Fe-85%Si-9.6%Al5.4% alloy, which reveals low outgassing rate and high attenuation, is selected for collinear load R&D. To measure the permittivity and permeability of FeSiAl at 2856 MHz, the coaxial transmission-reflection method is adopted. The system is firstly examined by testing the hollow coaxial fixture and comparing the results with the electromagnetic parameters of the air. Measurements of two PTFE rings show that the air gaps between the fixture and samples influence the test results seriously. CST is utilized to simulate the effects on the FeSiAl measurements. Eventually a scheme of molding the samples of FeSiAl powder mixed with paraffin to form a wax mold is proposed and the permittivity and permeability of FeSiAl are derived from the electromagnetic parameters equivalent formulas of mixed medium. INTRODUCTION In order to ensure LINAC running safely, the remnant microwave power has to be absorbed at the end of the accelerator tube. Waveguide load is regularly adopted, but the structures would make it difficult to miniaturize the LINAC. Collinear load is a new structure of LINAC load, which consists of several accelerating cavities coaxially extending the normal accelerating tube with efficient microwave-absorbing material coated on the inner walls. The remnant power is dissipated and transformed into heat, which is carried out through cavity walls by external cooling water. Without output coupler, the structure not only brings about simplification on focusing coils installation, but also makes the construction compact and the quality of beam current improved [1]. Absorbing material is an essential part of the collinear load and its absorbing capability depends on its electromagnetic parameters [2], which would be significant to the performance of the collinear load. There are two types of electromagnetic measurement methods for microwaveabsorbing materials: the network parameters method and the resonance cavity method. The resonance cavity method is fit for low loss materials, while the network parameter method is more suitable for higher loss materials. The latter consists of coaxial transmissionreflection method [3], free space method and so on. In this paper, coaxial transmission-reflection method is used to test the FeSiAl alloy which is an efficient absorbing material and prepared by Institute of Electronics, Chinese Academy of Sciences. THEORY OF TRANSMISSIONREFLECTION METHOD The transmission line is a reciprocal two-port network when the sample is a homogeneous, linear and isotropic medium. As shown in Fig. 1, the electromagnetic wave transmits and reflects back and forth in the medium. 1 R 2 (1 ) R T R 2 2 (1 ) R R T 3 2 4 (1 ) R R T 5 2 6 (1 ) R R T 7 2 8 (1 ) R R T 2 2 3 (1 ) R R T 8 2 9 (1 ) R R T 6 2 7 (1 ) R R T 4 2 5 (1 ) R R T 1 .... ..... .... .... 11 S 21 S Figure 1: The electromagnetic wave reflection and transmission in medium. Supposing that the reflection coefficient of the airmedium interface (A) is R, reflection coefficient of the medium-air interface (B) is -R and the transmission coefficient of the medium is T with the length of L, the complex number S11 of reflection sum in the A interface and S21 of transmission sum in the B interface will be