119671436
B → ρ transition form factors and the ρ-meson transverse leading-twist distribution amplitude
The QCD light-cone sum rules (LCSR) provide an effective way for dealing with heavy-to-light transition form factors (TFFs), in which the non-perturbative dynamics are parameterized into the light-meson’s light-cone distribution amplitudes (LCDAs). By taking the chiral correlator as the starting point, we derive new LCSRs for TFFs up to twist-4 accuracy. In those LCSRs, the twist-2 transverse LCDA provides dominant contribution, while the twist-3 and twist-4 contributions are δ2-suppressed (). Thus, they provide good platforms for testing behavior. For the purpose, we suggest a WH-model for , in which a single parameter dominantly controls its longitudinal distribution. When setting , varies from the single-peak behavior to the double-humped behavior. We present a detailed comparison of the LCSR estimation for TFFs with those predicted by pQCD and lattice QCD calculations. The TFFs become smaller with the increment of and a larger is not allowed by lattice QCD predictions. By using the extrapolated TFFs, we further predict the Cabibbo–Kobayashi–Maskawa (CKM)-matrix element with the help of two semi-leptonic decays. The predicted increases with the increment of , i.e. we have for and for . If treating the BABAR prediction on as a criteria, we observe that should be within the region of [−0.20, +0.10], which indicates that the ρ-meson LCDA prefers a single-peak behavior rather than a double-humped behavior.
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.
18567598
Pion Electromagnetic Form Factor in the KT Factorization Formulae
Based on the light-cone (LC) framework and the kT factorization formalism, the transverse momentum effects and the different helicity components' contributions to the pion form factor Fπ(Q2) are recalculated. In particular, the contribution to the pion form factor from the higher helicity components (λ1 + λ2 = ±1), which come from the spin-space Wigner rotation, are analyzed in the soft and hard energy regions respectively. Our results show that the right power behavior of the hard contribution from the higher helicity components can only be obtained by fully keeping the kT dependence in the hard amplitude, and that the kT dependence in LC wavefunction affects the hard and soft contributions substantially. A model for the twist-3 wavefunction ψp(x,k⊥) of the pion has been constructed based on the moment calculation by applying the QCD sum rules, whose distribution amplitude has a better end-point behavior than that of the asymptotic one. With this model wavefunction, the twist-3 contributions including both the usual helicity components (λ1 + λ2 = 0) and the higher helicity components (λ1 + λ2 = ±1) to the pion form factor have been studied within the modified pQCD approach. Our results show that the twist-3 contribution drops fast and it becomes less than the twist-2 contribution at Q2~10GeV2. The higher helicity components in the twist-3 wavefunction will give an extra suppression to the pion form factor. When all the power contributions, which include higher order in αs, higher helicities, higher twists in DA and etc., have been taken into account, it is expected that the hard contributions will fit the present experimental data well at the energy region where pQCD is applicable.
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.
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.
54195518
Twist-3 distribution amplitudes of the pion and kaon from the QCD sum rules
Abstract.Twist-3 distribution amplitudes of the pion and kaon are studied in this paper. We calculate the first several moments for the twist-3 distribution amplitudes ($ \phi_{p,\sigma}^\pi$ and $ \phi_{p,\sigma}^K$) of the pion and kaon by applying the QCD sum rules. Our results show that (i) the first three moments of $ \phi_p^K $ and the first two moments of $ \phi_p^\pi $ and $ \phi_\sigma^{\pi,K} $ of the pion and kaon can be obtained with 30$\%$ uncertainty; (ii) the fourth moment of the $ \phi_p^\pi $ and the second moment of the $ \phi_\sigma^K $ can be obtained when the uncertainty are relaxed to 35$\%$; (iii) the fourth moment of the $ \phi_\sigma^\pi $ can be obtained only when the uncertainty are relaxed to 40$\%$; (iv) we have $m_{0\pi}^p = 1.10\pm 0.08 {\mathrm {GeV}}$ and $m_{0K}^p = 1.25\pm 0.15 {\mathrm {GeV}}$ after including the $\alpha_{\mathrm {s}}$-corrections to the perturbative part. These moments will be helpful for constructing the twist-3 wave functions of the pion and kaon.
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.
2515645
The Black Hole Fundamental Plane: Revisited with a Larger Sample of Radio and X-Ray-Emitting Broad-Line AGNs
We use a recently released SDSS catalog of X-ray-emitting AGNs in conjunction with the FIRST radio survey to investigate the black hole (BH) fundamental plane relationship between the 1.4 GHz radio luminosity ( -->Lr), 0.1-2.4 keV X-ray luminosity ( -->LX), and black hole mass ( -->M), namely, -->log Lr = ξRXlog LX + ξRMlog M + constant . For this purpose, we compile a large sample of 725 broad-line AGNs, which consists of 498 radio-loud sources and 227 radio-quiet sources. We confirm that radio-loud objects have a steeper slope ( -->ξRX) with respect to radio-quiet objects and that the dependence of the BH fundamental plane on the BH mass ( -->ξRM) is weak. We also find tight correlation with a similar slope between the soft X-ray luminosity and broad emission-line luminosity for both radio-loud and radio-quiet AGNs, which implies that their soft X-ray emission is unbeamed and probably related to the accretion process. With the current larger sample, we find that there is no clear evidence of evolution for radio-quiet AGNs, while for radio-loud ones there is a weak trend in which -->ξRM decreases as the redshift increases. This may be understood in part as due to the observed evolution of the radio spectral index as a function of redshift. Finally, we discuss the relativistic beaming effect and other uncertainties related to the BH fundamental plane. We conclude that, although it does introduce scatter into the fundamental plane relation, Doppler boosting alone is not enough to explain the observed steeper value of -->ξRX in the radio-loud subsample with respect to the radio-quiet ones.
119073126
Improved approach to the heavy to light form-factors in the light cone QCD sum rules
A systematic analysis shows that the main uncertainties in the form factors are due to the twist-3 wave functions of the light mesons in the light-cone QCD sum rules. We propose an improved approach, in which the twist-3 wave functions do not make any contribution and therefore the possible pollution by them can be avoided, to reexamine B-->pi semileptonic form factors. Also, a comparison between previous results and our results from the light-cone QCD sum rules is made. Our method will be beneficial to the precise extraction of \V-ub\ from the experimental data on the processes B-->pil )over tilde>(l).
5433221
A feedback compression star formation model and the black hole-bulge relations
We present a feedback compression model to describe galactic spheroid formation and its relation with the central nuclear activity. We suggest that the star formation itself can serve as the positive feedback in some extremely dense region to trigger the starburst. The star formation rate, as well as the related stellar feedback-induced turbulence, will be maximized under the regulation of the background dark halo's gravity. There is also stellar feedback acting inward to confine and obscure the central black hole (BH) until the BH grows sufficiently large to satisfy a balance condition between the accretion disk wind and the inward stellar feedback. The extremely vigorous star formation activity, the BH-bulge relations, the maximum velocity dispersion, and the maximum BH mass are investigated on the basis of such a scenario and are found to be consistent with observations.