4 research outputs found
Resumming the color-octet contribution to e+ e- -> J/psi + X
Recent observations of the spectrum of J/psi produced in e+ e- collisions at
the Upsilon(4S) resonance are in conflict with fixed-order calculations using
the Non-Relativistic QCD (NRQCD) effective field theory. One problem is that
leading order color-octet mechanisms predict an enhancement of the cross
section for J/psi with maximal energy that is not observed in the data.
However, in this region of phase space large perturbative corrections (Sudakov
logarithms) as well as enhanced nonperturbative effects are important. In this
paper we use the newly developed Soft-Collinear Effective Theory (SCET) to
systematically include these effects. We find that these corrections
significantly broaden the color-octet contribution to the J/psi spectrum. Our
calculation employs a one-stage renormalization group evolution rather than the
two-stage evolution used in previous SCET calculations. We give a simple
argument for why the two methods yield identical results to lowest order in the
SCET power counting.Comment: 27 pages, 7 figure
Determination of color-octet matrix elements from e^+e- process at low energies
We present an analysis of the preliminary experimental data of direct j/psi
production in e^e- process at low energies. We find that the color-octet
contributions are crucially important to the cross section at this energy
region, and their inclusion produces a good description of the data. By fitting
to the data, we extract the individual values of two color-octet matrix
elements: \approx 1.1\times 10^{-2} GeV^3, <{\cal
O}_8^{\psi}(^3P_0)> m_c^2\approx 7.4\times 10^{-3}GeV^3. We discuss the allowed
range of the two matrix elements constrained by the theoretical uncertainties.
We find that is poorly determined because it is
sensitive to the variation of the choice of m_c, \alpha_s and <{\cal
O}_1^{\psi}(^3S_1)>. However m_c^2 is quite stable
(about (6-9)\times 10^{-3}GeV^3) when the parameters vary in reasonable ranges.
The uncertainties due to large experimental errors are also discussed.Comment: 13 page, RevTex, 2 figures in postscript. To appear in Phys. Rev.
Inclusive Charmonium Production via Double in Annihilation
Motivated by the recent observation of double charm quark pair production by
the Belle Collaboration, we calculate the complete
inclusive production cross sections for , , and
(J=0, 1, 2) plus in annihilation through a
virtual photon. We consider both color-singlet and color-octet contributions,
and give the analytical expressions for these cross sections. The complete
color-singlet calculations are compared with the approximate fragmentation
calculations as functions of the center-of-mass energy . We find that
most of the fragmentation results substantially overestimate the cross sections
(e.g. by a factor of 4 for and ) at the Belle and
BaBar energy GeV. The fragmentation results become a good
approximation only when is higher than about 100GeV. We further
calculate the color-octet contributions to these cross sections with analytical
expressions. We find that while the color-octet contribution to
inclusive production via double charm is negligible (only about 3%), the
color-octet contributions to and can be significant.Comment: 23 pages, 9 figures; color-octet contributions to the double charm
inclusive production of J/psi and chi_{cJ} (J=0,1,2) are added; references
are added; No change for the color-singlet par