Quarkonium formation time in quark-gluon plasma

The quarkonium formation time in a quark-gluon plasma (QGP) is determined from the space-time correlator of heavy quark vector currents using the quarkonium in-medium mass and wave function obtained from heavy quark potentials extracted from the lattice QCD. It is found that the formation time of a quarkonium increases with the temperature of the QGP and diverges near its dissociation temperature. Also, the quarkonium formation time is longer if the heavy quark potential is taken to be the free energy from lattice calculations for a heavy quark pair, compared to that based on the more negative internal energy.Comment: 5 pages, 4 figure

Quarkonium formation time in relativistic heavy-ion collisions

We calculate the quarkonium formation time in relativistic heavy-ion collisions from the space-time correlator of heavy quark vector currents in a hydrodynamics background with the initial nonequilibrium stage expanding only in the longitudinal direction. Using in-medium quarkonia properties determined with the heavy quark potential taken to be the free energy from lattice calculations and the fact that quarkonia can only be formed below their dissociation temperatures due to color screening, we find that $\Upsilon$(1S), $\Upsilon$(2S), $\Upsilon$(3S), $J/\psi$ and $\psi^\prime$ are formed, respectively, at 1.2, 6.6, 8.8, 5.8, and 11.0 fm/c after the quark pair are produced in central Au+Au collisions at the top energy of Relativistic Heavy Ion Collider (RHIC), and these times become shorter in semi-central collisions. We further show, as an example, that including the effect of formation time enhances appreciably the survivability of $\Upsilon$(1S) in the produced hot dense matter.Comment: 6 pages, 4 figure

Keberkesanan komunikasi organisasi: satu analisis multidimensi

Communication is pervasive in all areas of organizational life. A review of the communication studies literature indicates very little attention has been given to research examining the relationship between communication satisfaction and organizational commitment within Malaysian contexts. Moreover, the relationship between communication satisfaction and organizational commitment of the employees has been inferred without the benefit of demonstrated empirical evidence in all kinds of organizations.Therefore, this study focuses on the relationship between organizational communication satisfaction and the organizational commitment in Malaysia. Data were collected using the Downs’s (1990) Communication Satisfaction Questionnaire, and Organizational Commitment Questionnaire by Meyer and Allen (1990). A total of 317 respondents were involved in the study.Results indicated that there is an obvious positive relationship between communication satisfaction and employees’ organizational commitment. This study also highlights the importance of recognizing that communication satisfaction is multidimensional. Each dimension may affect organizational commitment differently

Stock Options and Chief Executive Compensation

Although stock options are commonly observed in chief executive officer (CEO) com- pensation contracts, there is theoretical controversy about whether stock options are part of the optimal contract. Using a sample of Fortune 500 companies, we solve an agency model calibrated to the company-specifc data and we find that stock options are almost always part of the optimal contract. This result is robust to alternative assumptions about the level of CEO risk-aversion and the disutility associated with their effort. In a supplementary analysis, we solve for the optimal contract when there are no restrictions on the contract space. We find that the optimal contract (which is characterized as a state-contingent payoff to the CEO) typically has option-like features over the most probable range of outcomes.Stock Options, Incentives, Agency Model

Keberkesanan Program Keselamatan Jalanraya Di Kalangan Penunggang Motosikal Di Daerah Baling, Kedah

The problem of road accidents in this country is very serious and it has achieved an alarming rate especially among the motorcyclists and pillion rider in the rural areas. The aim of this research was to determine the effectiveness of the road safety campaigns taken by the authorities to the road users. In addition, the research also aimed at identifying the level of motor cyclist riding skills, the users' attitudes and demographical factors of the teenagers who were the high risk group. This research utilised the evaluation Model of Context, Input, Process and Product (CIPP) but with more attention on the Process and Product components in order to assess the effectiveness and results of the implementation of the road safety programmes among the motorcyclists. This descriptive research involved 264 secondary school students in the Baling District who were either motorcyclists or pillion riders. Interviews also involved 6 respondents, 2 teachers, 2 Kedah Traffic Police officers and 2 members of the State Road Safety Council of Kedah. The results of the researh showed that the Road Safety Campaign was effective and reached the intended target group. However, riding skills of the motorcyclists were low as most of them did not have valid licence. This means that many of them did not really know the traffic rules and regulations even though they had the experience in riding motorcycles. The explanation for this contradictory situation was that most of the motor cyclists had the attitude of not giving due importance to their own safety and tend not to abide the traffic regulations. It is hope that the results of the research can add to the available information, and the suggestions can be used by various authorities to make decisions and to take appropriate actions to lessen this problem on road accidents

J/ψJ/\psi production and elliptic flow in relativistic heavy-ion collisions

Using a two-component model for charmonium production, which includes contributions from both the initial hard nucleon-nucleon scattering and from the regeneration in the quark-gluon plasma, we study the nuclear modification factor $R_{AA}$ and elliptic flow $v_2$ of $J/\psi$ in relativistic heavy ion collisions. For the expansion dynamics of produced hot dense matter, we introduce a schematic fireball model with its transverse acceleration determined from the pressure gradient inside the fireball and azimuthally anisotropic expansion parameterized to reproduce measured $v_2$ of light hadrons. We assume that light hadrons freeze out at the temperature of 120 MeV while charmonia at 160 MeV, similar to the kinetic and chemical freeze-out temperatures in the statistical model, respectively. For the properties of charmonia in the quark-gluon plasma, we use the screening mass between their charm and anticharm quarks and their dissociation cross sections given by the perturbative QCD (pQCD) in the leading order and up to the next-to-leading order, respectively. For the relaxation time of charm and anticharm quarks in the quark-gluon plasma, we also use the one calculated in the leading order of pQCD. Modeling the effect of higher-order corrections in pQCD by introducing multiplicative factors to the dissociation cross section of charmonia and the elastic scattering cross sections of charm and anticharm quarks, we find that this effect is small for the $R_{AA}$ of $J/\psi$ as they suppress the number of initially produced $J/\psi$ but enhance the number of regenerated ones. The higher-order corrections increase, however, the $v_2$ of $J/\psi$. Our results suggest that the $v_2$ of $J/\psi$ can play an important role in discriminating between $J/\psi$ production from the initial hard collisions and from the regeneration in the quark-gluon plasma.Comment: 15 pages, 14 figure

Heavy baryon/meson ratios in relativistic heavy ion collisions

Heavy baryon/meson ratios $\Lambda_c/D^0$ and $\Lambda_b/\bar{B}^0$ in relativistic heavy ion collisions are studied in the quark coalescence model. For heavy baryons, we include production from coalescence of heavy quarks with free light quarks as well as with bounded light diquarks that might exist in the strongly coupled quark-gluon plasma produced in these collisions. Including the contribution from decays of heavy hadron resonances and also that due to fragmentation of heavy quarks that are left in the system after coalescence, the resulting $\Lambda_c/D^0$ and $\Lambda_b/\bar{B}^0$ ratios in midrapidity ($|y|\le 0.5$) from central Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV are about a factor of five and ten, respectively, larger than those given by the thermal model, and about a factor of ten and twelve, respectively, larger than corresponding ratios in the PYTHIA model for $pp$ collisions. These ratios are reduced by a factor of about 1.6 if there are no diquarks in the quark-gluon plasma. The transverse momentum dependence of the heavy baryon/meson ratios is found to be sensitive to the heavy quark mass, with the $\Lambda_b/\bar{B}^0$ ratio being much flatter than the $\Lambda_c/D^0$ ratio. The latter peaks at the transverse momentum $p_T^{} \simeq 0.8$ GeV but the peak shifts to $p_T^{} \simeq 2$ GeV in the absence of diquarks.Comment: 11 pages, 2 figure