1,407 research outputs found

### Inclusive $h_c$ production at $B$ factories

Within the nonrelativistic QCD (NRQCD) factorization framework, we
investigate the inclusive production of the $h_c$ meson associated with either
light hadrons or charmed hadrons at $B$ factory energy $\sqrt{s}=10.58$ GeV.
Both the leading color-singlet and color-octet channels are included. For the
$h_c$ production associated with light hadrons, the total production rate is
dominated by the color-octet channel, thus the future measurement of this
process may impose useful constraint on the value of the color-octet matrix
element $$; for the $h_c$ production associated with
charmed hadrons, the total production rate is about one order of magnitude
smaller, and dominated by the color-singlet channel.Comment: v2, 23 pages, 1 table, 6 figures. Minor corrections, and a note
added, accepted for publication in PR

### Short-range force between two Higgs bosons

The $S$-wave scattering length and the effective range of the Higgs boson in
Standard Model are studied using effective-field-theory approach. After
incorporating the first-order electroweak correction, the short-range force
between two Higgs bosons remains weakly attractive for $M_H=126$ GeV. It is
interesting to find that the force range is about two order-of-magnitude larger
than the Compton wavelength of the Higgs boson, almost comparable with the
typical length scale of the strong interaction.Comment: v2, 11 pages, 2 figures, the version accepted for publication in
Phys. Lett.

### Reconciling the nonrelativistic QCD prediction and the $J/\psi\to 3\gamma$ data

It has been a long-standing problem that the rare electromagnetic decay
process $J/\psi\to 3\gamma$ is plagued with both large and negative radiative
and relativistic corrections. To date it remains futile to make a definite
prediction to confront with the branching fraction of $J/\psi\to 3\gamma$
recently measured by the \textsf{CLEO-c} and \textsf{BESIII} Collaborations. In
this work, we investigate the joint perturbative and relativistic correction
(i.e. the ${\mathcal O}(\alpha_s v^2)$ correction, where $v$ denotes the
characteristic velocity of the charm quark inside the $J/\psi$) for this decay
process, which turns out to be very significant. After incorporating the
contribution from this new ingredient, with the reasonable choice of the input
parameters, we are able to account for the measured decay rates in a
satisfactory degree.Comment: 7 pages, 1 figure, version accepted for publication in PRD R

### Can NRQCD explain the $\gamma\gamma^* \to \eta_c$ transition form factor data?

Unlike the bewildering situation in the $\gamma\gamma^*\to \pi$ form factor,
a widespread view is that perturbative QCD can decently account for the recent
\textsc{BaBar} measurement of $\gamma\gamma^*\to \eta_c$ transition form
factor. The next-to-next-to-leading order (NNLO) perturbative correction to the
$\gamma\gamma^*\to \eta_{c,b}$ form factor, is investigated in the NRQCD
factorization framework for the first time. As a byproduct, we obtain by far
the most precise order-$\alpha_s^2$ NRQCD matching coefficient for the
$\eta_{c,b}\to \gamma\gamma$ process. After including the substantial negative
order-$\alpha_s^2$ correction, the good agreement between NRQCD prediction and
the measured $\gamma\gamma^*\to \eta_c$ form factor is completely ruined over a
wide range of momentum transfer squared. This eminent discrepancy casts some
doubts on the applicability of NRQCD approach to hard exclusive reactions
involving charmonium.Comment: 6 pages, 3 figures and 1 table; adding Eqs.(8) and (9) as well as
some references, correcting errors in Table 1, updating Fig.3 to include the
"light-by-light" contributions, devoting a paragraph to discuss why our
strategy of interpreting the NNLO corrections is justified; Accepted by PR

### Next-to-next-to-leading-order QCD corrections to $e^+e^-\to J/\psi+\eta_c$ at $B$ factories

Within the nonrelativistic QCD (NRQCD) factorization framework, we compute
the long-awaited ${\mathcal O}(\alpha_s^2)$ correction for the exclusive double
charmonium production process at $B$ factories, i.e., $e^+e^-\to J/\psi+\eta_c$
at $\sqrt{s}=10.58$ GeV. For the first time, we confirm that NRQCD
factorization does hold at next-to-next-to-leading-order (NNLO) for exclusive
double charmonium production. It is found that including the NNLO QCD
correction greatly reduces the renormalization scale dependence, and also
implies the reasonable perturbative convergence behavior for this process. Our
state-of-the-art prediction is consistent with the BaBar measurement.Comment: 6 pages, 2 figures, 1 tabl

### Next-to-leading-order QCD corrections to $e^+e^-\to H+\gamma$

The associated production of Higgs boson with a hard photon at lepton
collider, i.e., $e^+e^-\to H\gamma$, is known to bear a rather small cross
section in Standard Model, and can serve as a sensitive probe for the potential
new physics signals. Similar to the loop-induced Higgs decay channels $H\to
\gamma\gamma, Z\gamma$, the $e^+e^-\to H\gamma$ process also starts at one-loop
order provided that the tiny electron mass is neglected. In this work, we
calculate the next-to-leading-order (NLO) QCD corrections to this associated
$H+\gamma$ production process, which mainly stem from the gluonic dressing to
the top quark loop. The QCD corrections are found to be rather modest at lower
center-of-mass energy range ($\sqrt{s}<300$ GeV), thus of negligible impact on
Higgs factory such as CEPC. Nevertheless, when the energy is boosted to the ILC
energy range ($\sqrt{s}\approx 400$ GeV), QCD corrections may enhance the
leading-order cross section by $20\%$. In any event, the $e^+e^-\to H\gamma$
process has a maximal production rate $\sigma_{\rm max}\approx 0.08$ fb around
$\sqrt{s}= 250$ GeV, thus CEPC turns out to be the best place to look for this
rare Higgs production process. In the high energy limit, the effect of NLO QCD
corrections become completely negligible, which can be simply attributed to the
different asymptotic scaling behaviors of the LO and NLO cross sections, where
the former exhibits a milder decrement $\propto 1/s$ , but the latter undergoes
a much faster decrease $\propto 1/s^2$.Comment: v4, 11 pages, 6 figures, 2 tables; errors in Appendix are fixed;
version accepted for publication at PL

### Relativistic Corrections to the Exclusive Decays of C-even Bottomonia into S-wave Charmonium Pairs

Within the nonrelativistic quantum chromodynamics (NRQCD) factorization
formalism, we compute the relativistic corrections to the exclusive decays of
bottomonia with even charge conjugation parity into $S$-wave charmonium pairs
at leading order in the strong coupling constant. Relativistic corrections are
resummed for a class of color-singlet contributions to all orders in the
charm-quark velocity $v_c$ in the charmonium rest frame. Almost every process
that we consider in this work has negative relativistic corrections ranging
from -20 to -35,%. Among the various processes, the relativistic corrections of
the next-to-leading order in $v_c$ to the decay rate for $\chi_{b2}\to
\eta_c(mS)+\eta_c(nS)$ with $m,$ $n=1$ or 2 are very large. In every case, the
resummation of the relativistic corrections enhances the rate in comparison
with the next-to-leading-order results. We compare our results with available
predictions based on the NRQCD factorization formalism. The NRQCD predictions
are significantly smaller than those based on the light-cone formalism by an or
two orders of magnitudes.Comment: 20 pages, 1 figure. Typos corrected, published versio

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