16057922
Dynamical screening and radiative parton energy loss in a quark-gluon plasma
Abstract Dynamical screening in the magnetic part of the one-gluon exchange interaction is included in the study of radiative energy loss of a fast parton propagating inside a quark-gluon plasma. As a result the final radiative energy loss is about twice as large as when only the electric part of one-gluon exchange interaction is considered. A non-perturbative magnetic screening mass is also used in the estimate of the mean-free-path of parton scattering in a hot QCD matter.
126140598
Report of the RHIC Workshop p + A subgroup
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.
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.
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.
59430123
Drive Laser and Optical Transport Line for Photoinjector
A Photo-Cathode RF Gun is under development at NSRL. In this paper, the drive laser system is introduced and performance parameters are presented. We adopt a BNL type gun with laser illuminating the cathode at oblique incidence. To correct “time slew” and “elliptical spot” problems arisen on the cathode, an adjustable optical transport line is designed. INTRODUCTION Drive laser system is the key component of photocathode high-brightness injector. To ensure the high quality of electron beams offered for FEL, the injector request a reliable laser with prominent performance parameters, such as: pulse duration, beam profile, energy stability, pulse to pulse stability, pointing stability and phase jitter. We adopted a BNL type gun with p-polarized laser at oblique incidence, as to acquire high quantum efficiency and low thermal emittance [1]. But, the problems of “time slew” and “elliptical spot” will arise on the cathode. To correct them, an adjustable optical transport line was designed. DRIVE LASER SYSTEM We employed a drive laser system developed by High Q Laser Production GmbH [2]. It consisted of three main parts: oscillator with a timing stabilizer, a regenerative amplifier, and the frequency conversion part. Fig.1 is the layout of the drive laser system. Figure 1: Layout of the drive laser system Oscillator The seeding laser is a passive mode-locked laser with a semiconductor absorber mirror (SESAM). Its repetition rate is 102MHz, equal to 1/28 of 2856MHz S-band radio frequency, which is used for RF-gun. The timing stabilizer measure the phase offset between laser pulses and reference RF signal,then adjust the cavity length by putting one laser resonator mirror on a voltage controlled piezo to synchronize the two signals. Regenerative Amplifier The Pockels Cell captures pulses from the continuous seeding laser and determines the pass times of pulse in the regenerative amplifier cavity. The repetition rate of amplified pulses is optional from 10 to 100Hz. Frequency Conversion Part The SHG convert the IR light (1047nm) to green light (523nm), then the FHG convert the green light to UV light (262nm). The conversion efficiency is about 20% from the fundamental to the 4-th harmonics. LASER PERFORMANCE Pulse Duration The autocorrelation measurement result of IR pulse width was 8.3ps FWHW (deconvolved value taken from the Fig.2). The UV pulse width could be close to this value. Figure 2: Pulse width @ 1047 nm measured after Regenerative Amplifier @ 10Hz Beam Profile and Diameter The beam profile and diameter of UV laser pulse was measured by a CCD camera. Beam profile was shown as Fig.3. The beam diameter in X and Y direction were 2.051mm and 1.927mm respectively, which were statistical results of 300 shots. ___________________________________________ *Work supported by the second phase of “985” project hezhg@mail.ustc.edu.cn Proceedings of IPAC’10, Kyoto, Japan TUPEA035 07 Accelerator Technology T24 Lasers 1405 Pulse to Pulse Stability The UV pulse to pulse stability was measured by a photodiode connected with an oscilloscope. The area integration was measured. The fluctuation was calculated as: σ/μ∗100%. The result was about 0.8% over two hours, as shown in Fig.4. Figure 3: Beam profile of UV laser Figure 4: Pulse stability of UV over 2h: measured with 50 Ohm feed-through-terminated input; 500 MHz Bandwidth Tektronix TDS 3052, DC-coupled) Figure 5: Pointing stability measurement Figure 6:Long term energy stability measurement results Pointing Stability Beam pointing stability was measured with a lens of 600mm focal length. The CCD camera was placed at a distance of 700mm from the lens. Pointing stability of the beam centroid were 6.13μrad rms in X direction and 19.31μrad rms in Y direction. Fig.5 showed us the measured pointing stability of centroid point and also peak point. Energy Stability The long term (over 17 hours) energy fluctuation of UV measured by an energy meter was about 0.6% rms, as shown in Fig.6. The measurement precision is dependent on resolution of energy sensor. We think the actual value is higher than the measured one. Phase Jitter The phase jitter between oscillator and reference signal (signal generator: E8257D) was measured. The output signal was presented in Fig.7. Jitter calculation as: 6 0 1 1 14.2 360 102 10 360 rms rms OSC Jitter U mV f Hz = = × ∗ × o 387 rms Jitter fs = Scaling: 1000 1 mV = o To gain a low jitter, a signal generator with low phase noise is required. Signal generators E8257D and E8663B from Agilent are suitable. All of the laser performance parameters were listed on Table 1. OPTICAL TRANSPORT LINE Because of oblique incidence design of BNL type gun, two problems of “time slew” and “elliptical spot” will arise on photo-cathode. To correct them, two prisms were used to add appropriate negative time slew and TUPEA035 Proceedings of IPAC’10, Kyoto, Japan 1406 07 Accelerator Technology T24 Lasers ellipticity on laser pulse wave front. The added time slew is: τ=f(r,α), α is the angle of prism, r is the laser diameter on the prism. A variable beam expander was used to adjust the r . Therefore, the added time slew can be adjustable. The beam diameter on cathode can be controlled by a movable lens at the end of optical line. The Y direction beam diameter was also fore-adjusted by prisms. The sketch of optical transport line was shown as Fig.8. The beam profile after the two prisms was measured by a CCD camera, which was showed in Fig.9. The X direction diameter was compressed to 1.0mm, The Y direction diameter was still about 1.9mm. To compress the Y direction diameter, one just needs to rotate the prisms. The transmission efficiency of the two prisms is about 92%. Figure 7: SYNC-phase output signal, RMS=14.2mV Figure 8: Sketch of optical transport line Figure 9: Beam profile after two prisms Table 1: The performance of drive laser system 1 Wave length/nm 262 2 Pulse duration (FWHM) /ps 8.3 3 Oscillator frequency/MHz 102 4 UV repeat rate/Hz 10-100 5 UV energy/mJ 0-0.65 6 Energy fluctuation/rms 0.6% 7 Pulse to pulse stability/rms 0.8% 8 X direction Point stability/μrad 6.13 9 Y direction Point stability/μrad 19.31 10 Phase jitter/fs 387 11 X direction beam diameter/(1/emm) 2.051 12 Y direction beam diameter/(1/emm) 1.927 SUMMARY We described the drive laser system and presented the measured laser performance parameters. We also reported a preparatory design of optical transport line used to correct “time slew” and “elliptical spot” problems. We are going to reshape the laser pulse. In the aspect of spatial shaping, a commercial production from pi-shaper [3] and GBS-UVH [4] may be considered. Both of them showed favourable shaping effects [5] [6]. In the aspect of temporal shaping, we are going to try the pulse stacking method [6] [7]. REFERENCES [1] Xiang D et al. Nuclear Instruments and Methods in Physics Research A, 2006, (562): 48-52. [2] http://www.highqlaser.at/ [3] http://www.pishaper.com/ [4] http://search.newport.com/?sku=GBS-UV-H [5] D.H. Dowell et al., Proceedings of PAC07, Albuquerque, New Mexico, USA TUPMS058. [6] A.K. Sharma, T, Tsang, and T. Rao, PHYSICAL REVIEW SPECIAL TOPICS ACCELERATORS AND BEAMS 12, 033501 (2009). [7] H. Tomizawa et al., Proceedings of FEL 2007, Novosibirsk, Russia WEBAU01. Proceedings of IPAC’10, Kyoto, Japan TUPEA035 07 Accelerator Technology T24 Lasers 1407
118745183
WISE DETECTION OF THE GALACTIC LOW-MASS X-RAY BINARIES
We report on the results from our search for the Wide-field Infrared Survey Explorer (WISE) detection of the Galactic low-mass X-ray binaries (LMXBs). Among 187 binaries cataloged in Liu et al., we find 13 counterparts and 2 candidate counterparts. For the 13 counterparts, 2 (4U 0614+091 and GX 339–4) have already been confirmed by previous studies to have a jet and 1 (GRS 1915+105) to have a candidate circumbinary disk, from which the detected infrared emission arose. Having collected the broadband optical and near-infrared data in the literature and constructed flux density spectra for the other 10 binaries, we identify that 3 (A0620–00, XTE J1118+480, and GX 1+4) are candidate circumbinary disk systems, 4 (Cen X-4, 4U 1700+24, 3A 1954+319, and Cyg X-2) had thermal emission from their companion stars, and 3 (Sco X-1, Her X-1, and Swift J1753.5–0127) are peculiar systems with the origin of their infrared emission rather uncertain. We discuss the results and WISE counterparts' brightness distribution among the known LMXBs, and suggest that more than half of the LMXBs would have a jet, a circumbinary disk, or both.
223459
The single t-quark productions via the flavor-changing processes in the topcolor-assisted technicolor model at the hadron colliders
In the framework of topcolor-assisted technicolor(TC2) model, there exist tree-level flavor-changing (FC) couplings which can result in the loop-level FC coupling tcg. Such tcg coupling can contribute significant clues at the forthcoming Large Hadron Collider (LHC) experiments. In this paper, based on the TC2 model, we study some single tquark production processes involving tcg coupling at the Tevatron and LHC: pp(pp̄) → tq̄(q = u, d, s), tg. We calculate the cross sections of these processes. The results show that the cross sections at the Tevatron are too small to observe the signal, but at the LHC it can reach a few pb. With the high luminosity, the LHC has considerable capability to find the single t-quark signal produced via some FC processes involving coupling tcg. On the other hand, these processes can also provide some valuable information of the coupling tcg with detailed study of the processes and furthermore provide the reliable evidence to test the TC2 model. PACS number(s): 12.60Nz, 14.80.Mz, 12.15.LK, 14.65.Ha Email Address: wangxuelei@sina.com Email Address: xiaozhenjun@njnu.edu.cn
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.
123670045
Total cross sections inN-body problems: Finiteness and high energy asymptotics
We study the finiteness of total scattering cross sections from an arbitrary channel to a two-cluster channel and establish the high energy asymptotics for total scattering cross sections with initial two-cluster channel and those from an arbitrary channel to a two-cluster channel.