1,792 research outputs found

### On the Field Renormalization Constant for Unstable Particles

A recently proposed normalization condition for the imaginary part of the
self-energy of an unstable particle is shown to lead to a closed expression for
the field renormalization constant Z. In turn, the exact expression for Z is
necessary, in some important cases, in order to avoid power-like infrared
divergences in high orders of perturbation theory. In the same examples, the
width plays the r\^ole of an infrared cutoff and, consequently, Z is not an
analytic function of the coupling constant.Comment: 7 pages (Latex

### Considerations Concerning the QCD Corrections to $\Delta\rho$

Using recent results of Avdeev et al. and an expansion for \mu_t/\mms
($M_t$ is the pole mass and $\mu_t\equiv \hat{m_t}(\mu_t)$ ), it is shown that
when deltarho is expressed in terms of $\hat{m_t}^2(M_t)$, the QCD correction
is only $(2-3)\times 10^{-3}$ in the NLO approximation. As a consequence, in
terms of $M_t^2$ the correction to \dr is almost entirely contained in
\mmss/M_t^2, a pure QCD effect.
The latter is studied using various optimization procedures, and the results
compared with the expansion proposed by Avdeev et al.. Implications for \ew
physics are discussed. Threshold effects are analyzed on the basis of a simple
sum rule.Comment: 11 pages plain LaTeX including 2 table

### Massive-Evolution Effects on Charmonium Hadroproduction

The fragmentation functions D_{a -> H}(x,mu^2) of a heavy hadron H, with mass
m_H, satisfy the phase-space constraint D_{a - > H}(x,mu^2)=0 for x <
m_H^2/mu^2, which is violated by the naive mu^2 evolution equations. Using
appropriately generalized mu^2 evolution equations, we reconsider the inclusive
hadroproduction of prompt J/psi mesons with high transverse momenta in the
framework of the factorization formalism of nonrelativistic quantum
chromodynamics, and determine the resulting shifts in the values of the leading
colour-octet matrix elements, which are fitted to data from the Fermilab
Tevatron.Comment: 8 pages (Latex), 3 figures (Postscript

### Inclusive b and b anti-b production with quasi-multi-Regge kinematics at the Tevatron

We consider b-jet hadroproduction in the quasi-multi-Regge-kinematics
approach based on the hypothesis of gluon and quark Reggeization in t-channel
exchanges at high energies. The preliminary data on inclusive b-jet and b
anti-b-dijet production taken by the CDF Collaboration at the Fermilab Tevatron
are well described without adjusting parameters. We find the main contribution
to inclusive b-jet production to be the scattering of a Reggeized gluon and a
Reggeized b-quark to a b quark, which is described by the effective
Reggeon-Reggeon-quark vertex. The main contribution to b anti-b-pair production
arises from the scattering of two Reggeized gluons to a b anti-b pair, which is
described by the effective Reggeon-Reggeon-quark-quark vertex. Our anaysis is
based on the Kimber-Martin-Ryskin prescription for unintegrated gluon and quark
distribution functions using as input the Martin-Roberts-Stirling-Thorne
collinear parton distribution functions of the proton.Comment: 14 pages, 4 figures; formulas for effective vertices included,
discussion of errors somewhat expanded; accepted for publication in Phys.
Rev.

### $M(B^*_c)-M(B_c)$ Splitting from Nonrelativistic Renormalization Group

We compute the hyperfine splitting in a heavy quarkonium composed of
different flavors in next-to-leading logarithmic approximation using the
nonrelativistic renormalization group. We predict the mass difference of the
vector and pseudoscalar charm-bottom mesons to be $M(B^*_c)-M(B_c)=46 \pm 15
{(\rm th)} {}^{+13}_{-11} (\delta\alpha_s)$ MeV.Comment: Eq.(22) and Appendix corrected, numerical results slightly changed.
arXiv admin note: text overlap with arXiv:hep-ph/031208

### Third-order non-Coulomb correction to the S-wave quarkonium wave functions at the origin

We compute the third-order correction to the S-wave quarkonium wave functions
|\psi_n(0)|^2 at the origin from non-Coulomb potentials in the effective
non-relativistic Lagrangian. Together with previous results on the Coulomb
correction and the ultrasoft correction computed in a companion paper, this
completes the third-order calculation up to a few unknown matching
coefficients. Numerical estimates of the new correction for bottomonium and
toponium are given.Comment: 12 pages, v2: matches published version, missing factors in eq. (9),
(29) adde

### Quarkonium production in deep-inelastic scattering

We discuss the inclusive production of J/psi mesons in deep-inelastic
scattering (DIS) via the electromagnetic, weak neutral, and charged currents
within the factorization formalism of nonrelativistic quantum chromodynamics.
Theoretical predictions are confronted with experimental data of e p and nu N
DIS taken by the H1 Collaboration at DESY HERA and the CHORUS Collaboration at
CERN, respectively.Comment: 6 pages (Latex), 6 figures (Postscript); to appear in the Proceedings
of the 6th International Symposium on Radiative Corrections: Application of
Quantum Field Theory to Phenomenology (RADCOR 2002), Kloster Banz, Germany,
September 8-13, 200

### Radiative corrections to single Higgs boson production in $e^+ e^-$ annihilation

For energies relevant to future linear colliders, \sqrt{s} \gsim 500 GeV,
the WW fusion channel dominates the Higgs boson production cross section $e^+
e^- \to \bar{\nu} \nu h^0$. We have calculated the one-loop corrections to this
process due to fermion and sfermion loops in the context of the MSSM. As a
special case, the contribution of the fermion loops in the SM has also been
studied. In general, the correction is negative and sizeable of the order of 10
percent, the bulk of it being due to fermion loops.Comment: Version to appear in Phys. Lett.

### Inclusive electroproduction of light hadrons with large p_T at next-to-leading order

We review recent results on the inclusive electroproduction of light hadrons
at next-to-leading order in the parton model of quantum chromodynamics
implemented with fragmentation functions and present updated predictions for
HERA experiments based on the new AKK set.Comment: 4 pages, 5 figures, to appear in the proceedings of the XIII
International Workshop on Deep Inelastic Scattering (DIS 2005

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