56125878
BCVEGPY: an event generator for hadronic production of the B-c meson
We have written a Fortran program BCVEGPY, which is an event generator for the hadronic production of the B-c meson through the dominant hard subprocess gg --> B-c(B-c(*)) + b + c. To achieve a compact program, we have written the amplitude of the subprocess with the particle helicity technique and made it as symmetric as possible, by decomposing the gluon self couplings and then applying the symmetries. To check the program, various cross sections of the subprocess have been computed numerically and compared with those in the literature. BCVEGPY is written in a PYTHIA-compatible format, thus it is easy to implement in PYTHIA.
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.
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.
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.
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.
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.
119181453
THE CORRELATIONS BETWEEN OPTICAL VARIABILITY AND PHYSICAL PARAMETERS OF QUASARS IN SDSS STRIPE 82
We investigate the optical variability of 7658 quasars from SDSS Stripe 82. Taking advantage of a larger sample and relatively more data points for each quasar, we estimate variability amplitudes and divide the sample into small bins of redshift, rest-frame wavelength, black hole mass, Eddington ratio, and bolometric luminosity, respectively, to investigate the relationships between variability and these parameters. An anti-correlation between variability and rest-frame wavelength is found. The variability amplitude of radio-quiet quasars shows almost no cosmological evolution, but that of radio-loud ones may weakly anti-correlate with redshift. In addition, variability increases as either luminosity or Eddington ratio decreases. However, the relationship between variability and black hole mass is uncertain; it is negative when the influence of Eddington ratio is excluded, but positive when the influence of luminosity is excluded. The intrinsic distribution of variability amplitudes for radio-loud and radio-quiet quasars are different. Both radio-loud and radio-quiet quasars exhibit a bluer-when-brighter chromatism. Assuming that quasar variability is caused by variations of accretion rate, the Shakura-Sunyaev disk model can reproduce the tendencies of observed correlations between variability and rest-frame wavelength, luminosity as well as Eddington ratio, supporting that changes of accretion rate play an important role in producing the observed optical variability. However, the predicted positive correlation between variability and black hole mass seems to be inconsistent with the observed negative correlation between them in small bins of Eddington ratio, which suggests that other physical mechanisms may still need to be considered in modifying the simple accretion disk model.
118599552
Some mass relations for mesons and baryons in Regge phenomenology
In the quasilinear Regge trajectory ansatz, some useful linear mass inequalities, quadratic mass inequalities, and quadratic mass equalities are derived for mesons and baryons. Based on these relations, mass ranges of some mesons and baryons are given. The masses of bc and ss belonging to the pseudoscalar, vector, and tensor meson multiplets are also extracted. The J{sup P} of the baryon {xi}{sub cc}{sup +}(3520) is assigned to be (1/2){sup +}. The parameters of the (1/2){sup +} and (3/2){sup +} SU(4) baryon trajectories are extracted and the masses of the orbital excited baryons lying on the (1/2){sup +} and (3/2){sup +} trajectories are estimated. The J{sup P} assignments of baryons {xi}{sub c}(2980), {xi}{sub c}(3055), {xi}{sub c}(3077), and {xi}{sub c}(3123) are discussed. The predictions are in reasonable agreement with the existing experimental data and those suggested in many other different approaches. The mass relations and the predictions may be useful for the discovery of the unobserved meson and baryon states and the J{sup P} assignment of these states.
9257590
Black hole mass estimation using a relation between the BLR size and emission line luminosity of AGN
An empirical relation between the broad line region (BLR) size and optical continuum luminosity is often adopted to estimate the BLR size and then the black hole mass of AGNs. However, optical luminosity may not be a good indicator of photoionizing luminosity for extremely radio-loud AGNs because the jets usually contribute significantly to the optical continuum. Therefore, the black hole masses derived for blazar-type AGNs with this method are probably overestimated. Here we first derived a tight empirical relation between the BLR size and the H β  emission line luminosity, $R({\rm light-days})= 24.05(L_{{\rm H}_\beta}/10^{42}$ ergs s$^{-1})^{0.68}$, from a sample of 34 AGNs with the BLR size estimated with the reverberation mapping technique. Then we applied this relation to estimate the black hole masses of some AGNs and found that for many extremely radio-loud AGNs the black hole masses obtained with the $R-L_{\rm H_\beta}$ relation are systematically lower than those derived previously with the $R-L_{5100~{\rm \AA}}$ relation, while for radio-quiet and slightly radio-loud AGNs the results obtained with these two methods are almost the same. The difference of black hole masses estimated with these two relations increases with the radio-loudness for extremely radio-loud AGNs, which is consistent with the fact that their equivalent widths of the H$_{\beta}$ emission line become smaller at greater radio-loudness. If the small H$_{\beta}$ equivalent widths of extremely radio-loud  AGNs are indeed caused by the beaming effect, we argue that the optical emission line luminosity may be a better tracer of ionizing luminosity for blazar-type AGNs and the black hole masses derived with the $R-L_{{\rm H}_\beta}$ relation are probably more accurate.
2132712
Inclinations and black hole masses of Seyfert 1 galaxies
A tight correlation between black hole mass (MBH) and central velocity dispersion (σ) has been found recently for both active and quiescent galaxies. By applying this correlation, we develop a simple method to derive the inclination angles for a sample of 11 Seyfert 1 galaxies that have both measured central velocity dispersions and black hole masses estimated by reverberation mapping. These angles, with a mean value of 36° that agrees well with the result obtained by fitting the iron Kα lines of Seyfert 1 galaxies observed with ASCA, provide further support to the orientation-dependent unification scheme of active galactic nuclei (AGNs). A positive correlation of the inclinations with observed FWHMs of the Hβ line and a possible anticorrelation with the nuclear radio loudness have been found. We conclude that more accurate knowledge of inclinations and broad-line region dynamics is needed to improve the black hole mass determination of AGNs with the reverberation mapping technique.
118830580
Dynamics of holographic vacuum energy in the DGP model
We consider the evolution of the vacuum energy in the Dvali-Gabadadze-Porrati (DGP) model according to the holographic principle under the assumption that the relation linking the IR and UV cutoffs still holds in this scenario. The model is studied when the IR cutoff is chosen to be the Hubble scale H(-1), the particle horizon R(ph), and the future event horizon R(eh), respectively. The two branches of the DGP model are also taken into account. Through numerical analysis, we find that in the cases of H(-1) in the (+) branch and R(eh) in both branches, the vacuum energy can play the role of dark energy. Moreover, when considering the combination of the vacuum energy and the 5D gravity effect in both branches, the equation of state of the effective dark energy may cross -1, which may lead to the big rip singularity. Besides, we constrain the model with the Type Ia supernovae and baryon oscillation data and find that our model is consistent with current data within 1 sigma, and that the observations prefer either a pure holographic dark energy or a pure DGP model.