123412047
UNIVERSALLY TREATING THE QUARK PAIR WITH A VACUUM QUANTUM NUMBER IN THE RELATED CHARM DECAYS
A method for universally treating the quark pair with a vacuum quantum number is proposed and it is applied to calculating some charm meson decays as examples. The smallness for W-exchange and annihilation mechanisms has new explanation and the result obtained by means of the proposed method on the decay fits the experimental data well.
122372922
A GENERAL-METHOD FOR CALCULATING PRINCIPAL VALUE INTEGRALS NUMERICALLY IN AN N-DIMENSIONAL REGION
Abstract Based on the antithetic cancellation technique, we propose a numerical method to calculate the N -dimensional principal value integrals. This method is powerful for numerically evaluating a multi-dimensional Feynman parameter integral with the singularity which occurs in loop calculations of quantum field theories, when some internal lines of the related Feynman diagrams are allowed by kinematics to approach to the corresponding mass shells.
119071655
The $J/\psi$ production associated with a hard photon and the color octet signature in $e^{+} e^{-}$ annihilation
$J/\ensuremath{\psi}$ production associated with a hard photon in ${e}^{+}{e}^{\ensuremath{-}}$ annihilation, being of a QED nature, is investigated thoroughly in this paper. To show its influence on the observation of the color-octet signature in ${e}^{+}{e}^{\ensuremath{-}}$ annihilation via $J/\ensuremath{\psi}$ inclusive production, the cross sections of $J/\ensuremath{\psi}$ production through different mechanisms at various energies are compared quantitatively by presenting them in figures together. The contribution from the production associated with a hard photon to the inclusive production of $J/\ensuremath{\psi}$ is pointed out to be significant at the concerned energies; thus, the influence of it on the observation of the color-octet signature should be dealt with carefully.
118291411
Next-to-Leading-Order QCD corrections to $J/\psi (\upsilon) + \gamma$ production at the LHC
In this work, we calculate the next-to-leading-order (NLO) QCD corrections to the process $p+p \to J/\psi + \gamma$ via the color-singlet mechanism at the LHC. The results show that the partial cross section ($p_t^{J/\psi}>$3GeV and $|y^{J/\psi,\gamma}|<$3) is enhanced by a factor of about 2.0, and the differential cross section can be enhanced by two orders of magnitude in the large transverse momentum region of $J/\psi$. Furthermore, the polarization of $J/\psi$ changes from transverse polarization at leading-order to longitudinal polarization at NLO. For the inclusive $J/\psi$ hadroproduction, it is known that the color-octet contributions are one order of magnitude larger than the color-singlet contribution, and the polarization distribution is dominated by the color-octet behavior at NLO. In contrast, for $J/\psi+\gamma$ production the color-singlet contribution is of the same order as the color-octet contribution, and the polarization distribution arises from both the color-singlet and color-octet. Therefore, measurements of $J/\psi$ production associated with a direct photon at the hadron collider could be an important supplement to testify the theoretical framework treating with the heavy quarkonium. In addition, an NLO QCD correction to $\Upsilon+\gamma$ production at the LHC is also presented in this paper.
33938812
Projection scheme for handling large-number cancellation related to gauge invariance.
A scheme, the so-called {open_quote}{open_quote}projection,{close_quote}{close_quote} for handling singularities in processes such as {ital e}{sup +}{ital e}{sup {minus}}{r_arrow}{ital t{bar b}e{sup {minus}}}{bar {nu}} (or {ital e}{sup +}{ital e}{sup {minus}}{r_arrow}{ital u{bar d}e{sup {minus}}}{bar {nu}}) is proposed. In the scheme, with the help of gauge invariance, the large power quantities ({ital s}/{ital m}{sup 2}{sub {ital e}}){sup {ital n}} ({ital n}{ge}1;{ital s}{r_arrow}{infinity}) are removed from the calculation totally, while in the usual schemes the large quantities appear and only will be canceled at last. The advantages of the scheme in numerical calculations are obvious; thus, we focus our discussions mainly on the advantages of the scheme in the special case where the absorptive part for some propagators relevant to the process could not be ignored, and a not satisfactory but widely adopted approximation is made; i.e., a finite constant {open_quote}{open_quote}width{close_quote}{close_quote} is introduced to approximate the absorptive part of the propagators phenomenologically even though QED gauge invariance is violated. {copyright} {ital 1996 The American Physical Society.}
3155142
Further study on U(1) gauge invariance restoration
To further investigate the applicability of the projection scheme for eliminating the unphysical divergence s/m(e)(2) due to U(1) gauge invariance violation, we study the process e(-) + W+ --> e(-) + (t) over bar + b which possesses advantages of simplicity and clearness. Our study indicates that the projection scheme can indeed eliminate the unphysical divergence s/m(e)(2) caused by the U(1) gauge invariance violation and the scheme can be applied to very high energy region.
36580647
Precision determination of the D0 mass.
A precision measurement of the D0 meson mass has been made using approximately 281 pb(-1) of e+e- annihilation data taken with the CLEO-c detector at the psi(3770) resonance. The exclusive decay D0-->K_{S}phi has been used to obtain M(D0)=1864.847+/-0.150(stat)+/-0.095(syst) MeV. This corresponds to M(D0D*0)=3871.81+/-0.36 MeV, and leads to a well-constrained determination of the binding energy of the proposed D0D*0 molecule X(3872), as Eb=0.6+/-0.6 MeV.
118840032
Weighing Super-Massive Black Holes with Narrow Fe K$\alpha$ Line
It has been suggested that the narrow cores of the Fe Kα emission lines in Active Galactic Nuclei (AGNs) are likely produced in the torus, the inner radius of which can be measured by observing the lag time between the V and K band flux variations. In this paper, we compare the virial products of the infrared time lags, and the narrow Fe Kα widths for 10 type 1 AGNs, with the black hole masses from other techniques. We found the narrow Fe Kα line width is in average 2.6 −0.4 times broader than expected, assuming an isotropic velocity distribution of the torus at the distance measured by the infrared lags. We propose the thick disk model of the torus may explain the observed larger line width. Another possibility is the contamination by emission from the broad line region or the outer accretion disk. Alternatively, the narrow iron line might originate from the inner most part of the obscuring torus within the sublimation radius, while the infrared emission may be from the outer cooler part. We note the correlations between the black hole masses based on this new technique and those based on other known techniques are statistically insignificant. We argue that this could be attributed to the small sample size and the very large uncertainties in the measurements of iron K line widths. The next generation of X-ray observatories could help verify the origin of the narrow iron Kα line and the reliability of this new technique. Subject headings: black hole physics – galaxies: active – galaxies: nuclei – galaxies: Seyfert – X-rays: galaxies – infrared: galaxies
448744
Search for neutral B meson decays to two charged leptons
The decays $\mathrm{B_d^0,\,B_s^0 \rightarrow e^+e^-,\,\mu^+\mu^-,\, e^\pm\mu^\mp}$ are searched for in 3.5 million hadronic ${\mathrm{Z}}$ events, which constitute the full LEP I data sample collected by the L3 detector. No signals are observed, therefore upper limits at the 90\%(95\%) confidence levels are set on the following branching fractions: % \begin{center}% {\setlength{\tabcolsep}{2pt} \begin{tabular}{lccccclcccc}% % Br$({\mathrm{B_d^0 \rightarrow {\mathrm{e^+e^-}}}})$ & $ $ & $1.4(1.8)$ & $\times$ & $ 10^{-5}$; & \hspace*{5mm} & Br$({\mathrm{B_s^0 \rightarrow {\mathrm{e^+e^-}}}})$ & $ $ & $5.4(7.0)$ & $\times$ & $ 10^{-5}$; \\% Br$({\mathrm{B_d^0 \rightarrow \mu^+\mu^-}})$ & $ $ & $1.0(1.4)$ & $\times$ & $ 10^{-5}$; & \hspace*{5mm} & Br$({\mathrm{B_s^0 \rightarrow \mu^+\mu^-}})$ & $ $ & $3.8(5.1)$ & $\times$ & $ 10^{-5}$; \\% Br$({\mathrm{B_d^0 \rightarrow {\mathrm{e^\pm\mu^\mp}}}})$ & $ $ & $1.6(2.0)$ & $\times$ & $ 10^{-5}$; & \hspace*{5mm} & Br$({\mathrm{B_s^0 \rightarrow {\mathrm{e^\pm\mu^\mp}}}})$ & $ $ & $4.1(5.3)$ & $\times$ & $ 10^{-5}$. \\% % \end{tabular}% } \end{center}% % The results for ${\mathrm{B_s^0\rightarrow{\mathrm{e^+e^-}}}}$ and ${\mathrm{B_s^0 \rightarrow {\mathrm{e^\pm\mu^\mp}}}}$ are the first limits set on these decay modes.
120128989
Measurement of the inclusive production cross sections for forward jets and for dijet events with one forward and one central jet in pp collisions at $ \sqrt {s} = 7 $ TeV
A bstractThe inclusive production cross sections for forward jets, as well for jets in dijet events with at least one jet emitted at central and the other at forward pseudorapidities, are measured in the range of transverse momenta pT = 35-150 GeV/c in proton-proton collisions at $ \sqrt {s} = 7 $ TeV by the CMS experiment at the LHC. Forward jets are measured within pseudorapidities 3.2 < |η| < 4.7, and central jets within the |η| < 2.8 range. The differential cross sections d2σ/dpT dη are compared to predictions from three approaches in perturbative quantum chromodynamics: (i) next-to-leading-order calculations obtained with and without matching to parton-shower Monte Carlo simulations, (ii) pythia and herwig parton-shower event generators with different tunes of parameters, and (iii) cascade and hej models, including different non-collinear corrections to standard single-parton radiation. The single-jet inclusive forward jet spectrum is well described by all models, but not all predictions are consistent with the spectra observed for the forward-central dijet events.
123584252
Measurement of branching fractions and charge asymmetries for two-body B meson decays with charmonium
We report branching fractions and charge asymmetries for exclusive decays of charged and neutral B mesons to two-body final states containing a charmonium meson, J/Ψ or Ψ/(2S). This result is based on a 29.4 fb-1 data sample collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric e+e- collider. © 2003 The American Physical Society.