118505094
Constraints on the leading-twist pion distribution amplitude from a QCD light-cone sum rule with chiral current
We present an improved analysis of the constraints on the first two Gegenbauer moments, a2π and a4π, of the pion’s leading-twist distribution amplitude from a QCD light-cone sum rule analysis of the B→π weak transition form factor f+(q2). A proper chiral current is adopted in QCD light-cone sum rules so as to eliminate the most uncertain twist-3 contributions to f+(q2), and then we concentrate our attention on the properties of the leading-twist pionic DA. A nearly model-independent f+(q2), based on the spectrum of B→πlν decays from BaBar, together with uncertainties, is adopted as the standard shape for f+(q2) for our discussion. From a minimum χ2-fit and by taking the theoretical uncertainties into account, we obtain a2π(1 GeV)=0.17−0.17+0.15 and a4π(1 GeV)=−0.06−0.22+0.20 at the 1σ confidence level for mb*∈[4.7,4,8] GeV.
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.
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.
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.
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.
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.
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).
118440734
Observational Constraints on Agegraphic Dark Energy
In this paper, we use the Type Ia supernova data as well as the CMB and LSS data to constrain the agegraphic dark energy model recently proposed by Cai. Due to its peculiar nature, the parameter $n$ of this model cannot be well constrained by the SNIa data, while the other parameter $\Omega_{m0}$ can be constrained to be $0.34\pm0.04$. When combined with CMB and LSS data, the range of $1\sigma$ confidence level for $n$ is greatly narrowed, albeit still very large. The best fit result is $\Omega_{m0}=0.28\pm0.02$, which is consistent with most observations like WMAP and SDSS, and $n=3.4$, of which a meaningful range of confidence level can not be obtained due to the fact that the contours are not closed. Despite of this result, we conclude that for $n>1$ this model is consistent with SNIa, CMB and LSS observations. Furthermore, the fitting results indicate a generalized definition for the agegraphic dark energy.
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.
118483748
Reconstructing f(R) theory according to holographic dark energy
Abstract In this Letter a connection between the holographic dark energy model and the f ( R ) theory is established. We treat the f ( R ) theory as an effective description for the holographic dark energy and reconstruct the function f ( R ) with the parameter c > 1 , c = 1 and c 1 , respectively. We show the distinctive behavior of each cases realized in f ( R ) theory, especially for the future evolution.