119115796
Dominant spin-flip effects for the hadronic-produced J/{psi} polarization at the Tevatron
Dominant spin-flip effects for the direct and prompt J/{psi} polarizations at Tevatron run II with collision energy 1.96 TeV and rapidity cut |y{sup J/{psi}}|<0.6 are systematically studied. The spin-flip effect for the transition of (cc){sub 8}[{sup 3}S{sub 1}] into J/{psi} is especially discussed with care. It is found that the spin-flip effect shall always dilute the J/{psi} polarization, and with a suitable choice of the parameters a{sub 0,1} and c{sub 0,1,2}, the J/{psi} polarization puzzle can be solved to a certain degree. At large transverse momentum p{sub t}, {alpha} for the prompt J/{psi} is reduced by {approx}50% for f{sub 0}=v{sup 2} and by {approx}80% for f{sub 0}=1. We also study the indirect J/{psi} polarization from the b decays, which however is slightly affected by the same spin-flip effect and then shall provide a better platform to determine the color-octet matrix elements.
28851116
GENXICC2.1: An improved version of GENXICC for hadronic production of doubly heavy baryons
We present an improved version of GENXICC, which is a generator for hadronic production of the doubly heavy baryons $\Xi_{cc}$, $\Xi_{bc}$ and $\Xi_{bb}$ and has been raised by C.H. Chang, J.X. Wang and X.G. Wu [Comput. Phys. Commun. 177 (2007) 467; Comput. Phys. Commun. 181 (2010) 1144]. In comparison with the previous GENXICC versions, we update the program in order to generate the unweighted baryon events more effectively under various simulation environments, whose distributions are now generated according to the probability proportional to the integrand. One Les Houches Event (LHE) common block has been added to produce a standard LHE data file that contains useful information of the doubly heavy baryon and its accompanying partons. Such LHE data can be conveniently imported into PYTHIA to do further hadronization and decay simulation, especially, the color-flow problem can be solved with PYTHIA8.0.
119260697
Photoproduction of doubly heavy baryon at the ILC
A bstractIn the present paper, we make a detailed study on the doubly heavy baryon photoproduction in the future e+e− International Linear Collider (ILC). The baryons Ξcc, Ξbc, and Ξbb are produced via the channel γγ→ΞQQ′+Q¯′+Q¯$$ \gamma \gamma \to {\Xi}_{QQ\prime }+\overline{Q}^{\prime }+\overline{Q} $$, where Q and Q′ stand for heavy c or b quark, respectively. As for the ΞQQ′-baryon production, it shall first generate a (QQ′)[n]-diquark and then form the final baryon via fragmentation, where [n] stands for the color- and spin- configurations for the (QQ′)-diquark states. According to the non-relativistic QCD theory, four diquark configurations shall provide sizable contributions to the baryon production, e.g., [n] equals 3S13¯,1S06,3S16,or1S03¯$$ {\left[{}^3{S}_1\right]}_{\overline{3}},\;{\left[{}^1{S}_0\right]}_6,\;{\left[{}^3{S}_1\right]}_6,\;\mathrm{or}\kern0.37em {\left[{}^1{S}_0\right]}_{\overline{3}} $$, respectively. We adopt the improved helicity amplitude approach for the hard scattering amplitude to improve the calculation efficiency. Total and differential cross sections of those channels, as well as the theoretical uncertainties, are presented. We show that sizable amounts of baryon events can be generated at the ILC, i.e., about 2.0 × 106 Ξcc, 2.2 × 105 Ξbc, as well as 3.0 × 103 Ξbb events are to be generated in one operation year for S=500$$ \sqrt{S}=500 $$ GeV and ℒ ≃ 1036 cm−2s−1.
5502533
A trick to improve the efficiency of generating unweighted Bc events from BCVEGPY
In the present paper, we provide an addendum to improve the efficiency of generating unweighted events within PYTHIA environment for the generator BCVEGPY2.1 [C.H. Chang, J.X. Wang, X.G. Wu, Comput. Phys. Commun. 174 (2006) 241]. This trick is helpful for experimental simulation. Moreover, the BCVEGPY output has also been improved, i.e. one Les Houches Event common block has been added so as to generate a standard Les Houches Event file that contains the information of the generated Bc meson and the accompanying partons, which can be more conveniently used for further simulation.
119268284
Uncertainties in estimating the indirect production of Bc and its excited states via top quark decays at CERN LHC
Abstract Main theoretical uncertainties in estimating the indirect production of ( b c ¯ ) -quarkonium ( B c − meson and its excited states) via top quark decays, t → ( b c ¯ ) + c + W + , are studied within the non-relativistic QCD framework. It is found that the dimensionless reduced decay width for a particular ( b c ¯ ) -quarkonium state, Γ ¯ n = Γ n / Γ t → W + + b , is very sensitive to the c -quark mass, while the uncertainties from the b -quark and t -quark masses are small, where n stands for the eight ( b c ¯ ) -quarkonium states up to O ( v 4 ) : | ( b c ¯ ) ( S 0 1 ) 1 〉 , | ( b c ¯ ) ( S 1 3 ) 1 〉 , | ( b c ¯ ) ( P 1 1 ) 1 〉 , | ( b c ¯ ) ( P J 3 ) 1 〉 (with J = ( 1 , 2 , 3 ) ), | ( b c ¯ ) ( S 0 1 ) 8 g 〉 and | ( b c ¯ ) ( S 1 3 ) 8 g 〉 respectively. About 10 8 t t ¯ -pairs shall be produced per year at CERN LHC, if adopting the assumption that all the higher Fock states decay to the ground state with 100% probability, then we shall have ( 1.038 −0.782 +1.353 ) × 10 5 B c − events per year. So the indirect production provides another important way to study the properties of B c − meson in comparison to that of the direct hadronic production at CERN LHC.
118560703
Application of the principle of maximum conformality to the top-quark forward-backward asymmetry at the Tevatron
¯p¯ FB at the Tevatron will be increased by 42% in comparison to the previous estimates obtained by using conventional scale setting; i.e. we obtain A t ¯PMC FB ≃ 12.5% and A p¯ p,PMC FB ≃ 8.28%. Moreover, we obtain A t ¯ t,PMC FB (Mt¯ > 450 GeV) ≃ 35.0%. These predictions have a 1�-deviation from the present CDF and D0 measurements; the large discrepancies of the top quark forward-backward asymmetry between the Standard Model estimate and the CDF and D0 data are thus greatly reduced.
14447660
The local stability of accretion disks with advection
The local stability of accretion disks with advection is studied together with the considerations of radial viscous force and thermal diffusion. For a geometrically thin, radiative cooling dominated disk, the thermal diffusion has nearly no effects on the thermal and viscous modes. The including of thermal diffusion, however, tends to stabilize the acoustic modes which, if without advection, are unstable if the disk is optically thick, radiation pressure dominated or optically thin, and are stable if the disk is optically thick, gas pressure dominated. The including of very little advection has significant effects on two acoustic modes. Independent on the optical depth, the instability of the outward propagating mode (O-mode) is enhanced and that of the inward propagating mode (I-mode) is damped if the disk is gas pressure dominated, while the instability of O-mode is damped and that of I-mode is enhanced if the disk is radiation pressure dominated. For a geometrically slim, advection-dominated disk, both the thermal and viscous modes, as well as I-mode, are always stable if the disk is optically thin. The including of thermal diffusion tends to make these modes more stable. However, the O-mode can become unstable when $q/m$ is very large ($q$ is the ratio of advective to viscous dissipated energy and $m$ the Mach number), even if the thermal diffusion is considered. On the other hand, if the advection-dominated disk is optically thick, we found there is no self-consistent acoustic modes in our local analyses. The thermal diffusion has no effect on the stable viscous mode but has a significant contribution to enhance the thermal instability.
16592506
CO Line Width and the Black Hole-Bulge Relationship at High Redshift
Recently, it has been suggested that the CO line width [FWHM(CO)] is a surrogate for the bulge velocity dispersion (σ) of the host galaxies of high-redshift quasars, and the black hole-bulge (MBH-σ) relation obtained with this assumption departs significantly from the MBH-σ relation in the local universe. In this study, we first present an investigation of the correlation between the CO line width and the bulge velocity dispersion using a sample of 33 nearby Seyfert galaxies. We find that the formula adopted in previous studies, σ = FWHM(CO)/2.35, is generally not a good approximation. Using it, one may underestimate the value of bulge velocity dispersion significantly when the CO line is narrower than 400 km s-1. By involving the galactic inclination angle i as an additional parameter, we obtain a tight correlation between the inclination-corrected CO line width and the bulge velocity dispersion, namely, FWHM(CO)/ sin i = − (67.16 ± 80.18) + (3.62 ± 0.68) σ. Using this new relation, we can better estimate the bulge velocity dispersion from the CO line width if the galactic inclination is known. We apply this new relation to nine high-redshift quasars with CO line detections and find that they are consistent with the local MBH-σ relation if their inclination angles are around 15°. The possible smaller inclinations of the high-redshift quasars are preferred because of their relatively greater likelihood of detection, and are also consistent with their relatively smaller CO line widths compared to submillimeter galaxies (SMGs) at high redshift having a similar total amount of molecular gas. Future observations are needed to confirm these results.
118357880
ON THE STRUCTURE OF ACCRETION DISKS WITH OUTFLOWS
To study the outflows from accretion disks, we solve the set of hydrodynamic equations for accretion disks in spherical coordinates (rθ) to obtain the explicit structure along the θ-direction. Using self-similar assumptions in the radial direction, we change the equations to a set of ordinary differential equations about the θ-coordinate, which are then solved with symmetrical boundary conditions in the equatorial plane; the velocity field is then obtained. The α viscosity prescription is applied and an advective factor f is used to simplify the energy equation. The results display thinner, quasi-Keplerian disks for Shakura-Sunyaev disks; thicker, sub-Keplerian disks for advection-dominated accretion flows; and slim disks which are consistent with previous popular analytical models. However, an inflow region and an outflow region always exist, except when the viscosity parameter α is too large, which supports the results of some recent numerical simulation works. Our results indicate that the outflows should be common in various accretion disks and may be stronger in slim disks, where both advection and radiation pressure are dominant. We also present the structure's dependence on the input parameters and discuss their physical meanings. The caveats of this work and possible improvements for the future are discussed.
11920772
How to form bulges/ellipticals in dark halos as fast as central black holes?
Gravity is nearly a universal constant in the cusp of an NFW galaxy halo. Inside this external field an isothermal gas sphere will collapse and trigger a starburst if above a critical central pressure. Thus formed spheroidal stellar systems have Sersic-profile and satisfy the Faber-Jackson relation. The process is consistent with observed starbursts. We also recover the M_BH vs. velocity dispersion relation, if the gas collapse is regulated or resisted by the feedback from radiation from the central BH.
11771360
The Nature of Linearly Polarized Millimeter and Submillimeter Emission in Sagittarius A
The linearly polarized millimeter and sub-millimeter emission in Sagittarius A* is produced within 10 Schwarzschild radii of the supermassive black hole at the Galactic Center and may originate from a hot magnetized accretion disk, where electrons are heated efficiently by turbulent plasma waves. I n such a scenario, the flux density and polarization are very sensitive to the electron heating rate and the inclination angle of disk, respectively, and the major axis of the submillimeter intrinsic polarization, which is aligned with the rotation axis of the disk, is perpendicular to the major axis of the polarized near-infrared emission. In combination with MHD simulations, which study the properties of the magnetic field and viscous stresses, the current spectral and polarization measurements give tight constraints on the model parameters. Simultaneous observations will be able to test the model.