62897747
Self-Consistency Requirements of the Renormalization Group for Setting the Renormalization Scale
In conventional treatments, predictions from fixed-order perturbative QCD calculations cannot be fixed with certainty due to ambiguities in the choice of the renormalization scale as well as the renormalization scheme. In this paper we present a general discussion of the constraints of the renormalization group (RG) invariance on the choice of the renormalization scale. We adopt the RG based equations, which incorporate the scheme parameters, for a general exposition of RG invariance, since they simultaneously express the invariance of physical observables under both the variation of the renormalization scale and the renormalization scheme parameters. We then discuss the self-consistency requirements of the RG, such as reflexivity, symmetry, and transitivity, which must be satisfied by the scale-setting method. The Principle of Minimal Sensitivity (PMS) requires the slope of the approximant of an observable to vanish at the renormalization point. This criterion provides a scheme-independent estimation, but it violates the symmetry and transitivity properties of the RG and does not reproduce the Gell-Mann-Low scale for QED observables. The Principle of Maximum Conformality (PMC) satisfies all of the deductions of the RG invariance - reflectivity, symmetry, and transitivity. Using the PMC, all non-conformal {βRi}-terms (R stands for an arbitrary renormalization scheme) in themore » perturbative expansion series are summed into the running coupling, and one obtains a unique, scale-fixed, scheme-independent prediction at any finite order. The PMC scales and the resulting finite-order PMC predictions are both to high accuracy independent of the choice of initial renormalization scale, consistent with RG invariance.« less
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.
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.
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.
14502174
On black hole masses, radio-loudness and bulge luminosities of Seyfert galaxies
We estimated black hole masses for 9 Seyfert 1 and 13 Seyfert 2 galaxies in the Palomar and CfA bright Seyfert samples using the tight correlation between black hole mass and bulge velocity dispersion. Combining other 13 Seyfert 1s and 2 Seyfert 2s in these samples but with black hole masses measured recently by reverberation mapping and stellar/gas dynamics, we studied the correlations of black hole masses with radio-loudness and bulge luminosities for a sample of 37 Seyfert galaxies. We found that if radio-loudness is measured using the optical and radio luminosities of the nuclear components, the black hole masses of radio-loud Seyfert 1s tend to increase with the radio-loudness. The black hole masses of all Seyfert galaxies increase with the radio power, but Seyfert galaxies have larger radio powers than nearby galaxies with the same black hole masses. In addition, the correlation between black hole masses and bulge V -band luminosities for Seyfert galaxies is consistent with that found for quasars and normal galaxies. The combined sample of 37 Seyfert galaxies, 15 quasars and 30 normal galaxies suggests a possible universal nonlinear relation between black hole and bulge masses, MBH/ M 1:740:14 bulge , which is slightly steeper than that found recently by Laor (2001) for a smaller sample. This nonlinear relation is supported by a larger sample including 65 Seyfert galaxies. The dierent MBH=M bulge ratio for galaxies with dierent bulge luminosities or dierent black hole masses may be explained by this relation. These results are consistent with some theoretical implications and are important for understanding the nature of radio emissions and the formation and evolution of supermassive black holes and galaxies.
118517819
Quasar candidate selection and photometric redshift estimation based on SDSS and UKIDSS data
We present a sample of 8498 quasars with both SDSS ugriz optical and UKIDSS Y JHK near-IR photometric data. With this sample, we obtain the median colour-z relations based on 7400 quasars with magnitude uncertainties less than 0.1mag in all bands. By analyzing the quasar colours, we propose an empirical criterion in the Y K vs. g z colour-colour diagram to separate stars and quasars with redshift z < 4, and two other criteria for selecting high redshift quasars. Using the SDSS-UKIDSS colourz relations, we estimate the photometric redshifts of 8498 SDSS-UKIDSS quasars, and find that 85.0% of them are consistent with the spectroscopic redshifts within |�z| < 0.2, which leads to a significant increase of the photometric redshift accuracy than that based on the SDSS colour-z relations only. As two tests, we compare our colour selection criterion with a small UKIDSS/EDR quasar/star sample and a sample of 4671 variable sources in the SDSS Stripe 82 region with both SDSS and UKIDSS data. We find that they can be clearly divided into two classes (quasars and stars) by our criterion in the Y K vs. g z plot. We select 3834 quasar candidates from the variable sources with g < 20.5 in Stripe 82, 826 of them being SDSS quasars and the rest without SDSS spectroscopy. We estimate the photometric redshifts for 3519 quasar candidates with all UKIDSS Y JHK data and find an accuracy of 87.5% within |�z| < 0.2 with the spectroscopic redshifts of 819 SDSS-UKIDSS identified quasars among them. We demonstrate that even at the same spectroscopy limit as SDSS, with our criterion we can at least partially recover the missing quasars with z � 2.7 in SDSS. The SDSS identified quasars only take a small fraction (21.5%) of our quasar candidates selected from the variable sources in Stripe 82, indicating that a deeper spectroscopy is very promising in producing a much larger sample of quasars than SDSS. The implications of our current results to the future Chinese LAMOST quasar survey are also discussed.
119144104
Age constraints on the Agegraphic Dark Energy Model
We investigate the age constraint on the agegraphic dark energy model by using two old galaxies (LBDS 53W091 and LBDS 53W069) and the old high redshift quasar APM 08279+5255. We find that the agegraphic dark energy model can easily accommodate LBDS 53W091 and LBDS 53W069. To accommodate APM 08279+5255, one can take the reduced Hubble parameter as large as h=0.64, when the fraction matter energy density $\Omega_{m0}\approx 0.22$.
16404927
The Black Hole Fundamental Plane from a Uniform Sample of Radio and X-Ray-emitting Broad-Line AGNs
We derived the black hole 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) from a uniform broad-line SDSS AGN sample including both radio-loud and radio-quiet X-ray-emitting sources. We found in our sample that the fundamental plane relation has a very weak dependence on the black hole mass, and a tight correlation also exists between the Eddington-luminosity-scaled X-ray and radio luminosities for the radio-quiet subsample. In addition, we noticed that the radio-quiet and radio-loud AGNs have different power-law slopes in the radio-X-ray nonlinear relationship. The radio-loud sample displays a slope of 1.39, which seems consistent with the jet-dominated X-ray model. However, it may also be partly due to the relativistic beaming effect. For the radio-quiet sample the slope of the radio-X-ray relationship is about 0.85, which is possibly consistent with the theoretical prediction from the accretion-flow-dominated X-ray model. We briefly discuss the reason why our derived relationship is different from some previous works and expect the future spectral studies in radio and X-ray bands on individual sources in our sample to confirm our result.
197492896
Discovery of six high-redshift quasars with the Lijiang 2.4m telescope and MMT
Quasars with redshifts greater than four are rare, and can provide us important helps in probing the nature of the early universe. Here we report the discovery of six new quasars with $i$-band magnitudes brighter than 19.5 and redshifts between 2.4 and 4.6 from the spectroscopic observations made with the YFOSC instrument of the Lijiang 2.4m telescope in February, 2012. These six quasars are in the list of high redshift ($z>3.6$) quasar candidates selected by using our proposed J-K/i-Y criterion and the photometric redshift estimations from the SDSS optical and UKIDSS near-IR photometric data. Nine candidates were observed by YFOSC, and five among six new quasars were identified as $z>3.6$ quasars. One of the other three objects was identified as a star and the rest two were unidentified due to the lower signal-to-noise ratio of their spectra. This is the first time to discover quasars with redshifts greater than four with a telescope in China. Thanks to the Chinese Telescope Access Program (TAP), the redshift of 4.6 for one of these new quasars was confirmed by the MMT Red Channel spectroscopy. The continuum and emission line properties of these six quasars, as well as their central black hole masses and Eddington ratios, were obtained.