16 research outputs found
J/psi Production at the LHC
We firstly examine hadroproduction of prompt J/psi's at the Fermilab Tevatron
in a Monte Carlo Framework by means of the event generator PYTHIA 5.7 in which
those colour-octet matrix elements processes relevant for charmonium production
have been implemented accordingly. We find that colour-octet matrix elements
presented in literature from p-pbar collider data are systematically
overestimated due to overlooking of the effective primordial transverse
momentum of partons (i.e. including higher-order QCD effects). We estimate the
size of these effects using different parton distribution functions. Finally,
after normalization to Tevatron data, we extrapolate up to LHC energies making
a prediction on the expected pt differential cross-section for charmonium.Comment: 4 pages, LaTex, 3 Figures included in the text, Contribution to the
2nd Int. Conference on Hyperons, charm and beauty hadrons (Montreal, Aug
27-30, 1996
Charmonia production in hadron colliders and the extraction of colour-octet matrix elements
We present the results of our analysis on charmonia ( and )
hadroproduction taking into account higher-order QCD effects induced by
initial-state radiation in a Monte Carlo framework, with the colour-octet
mechanism implemented in the event generation. We find that those colour-octet
matrix elements extracted so far from Fermilab Tevatron data for both
and production have to be lowered significantly. We finally make
predictions for charmonia production at the LHC, presenting a code for a fast
simulation with PYTHIA based on the colour-octet model.Comment: 17 pages, LaTex, 5 Figures included in the tex
D-wave heavy quarkonium production in fixed target experiments
We calculate the -wave heavy quarkonium production at fixed target
experiments under the NRQCD factorization formalism. We find that the color
octet contributions are two orders of magnitude larger than color-singlet
contributions if color-octet matrix elements are taken according to the NRQCD
velocity scaling rules. Within the theoretical uncertainties, the prediction
for the production rate of -wave charmonium state agrees with the
preliminary result of E705 and other experiments. Searching for the
-wave state is further suggested.Comment: 13pages, 4 PS figures, final vertion to appear in PR
QCD analysis of inclusive B decay into charmonium
We compute the decay rates and -energy distributions of mesons into
the final state , where can be any one of the -wave or -wave
charmonia, at next-to-leading order in the strong coupling. We find that a
significant fraction of the observed , and must be
produced through pairs in a colour octet state and should therefore
be accompanied by more than one light hadron. At the same time we obtain
stringent constraints on some of the long-distance parameters for colour octet
production.Comment: 40 pages, RevTeX, 4 figure
Color Octet Contribution to J/psi Photoproduction Asymmetries
We investigate photoproduction asymmetries in the framework of the
NRQCD factorization approach. It is shown that the color octet contribution
leads to large uncertainties in the predicted asymmetries which rules out the
possibility to precisely measure the gluon polarization in the nucleon through
this final state. For small values of the color octet parameters being
compatible with photoproduction data it appears possible that a
measurement of asymmetries could provide a new test for the NRQCD
factorization approach, on one hand, or a measurement of the polarized gluon
distribution from low inelasticity events , on the otherComment: 12 pages, LaTeX, with 6 figs. Final version published in Phys.Rev.
Power counting and effective field theory for charmonium
We hypothesize that the correct power counting for charmonia is in the
parameter Lambda_QCD/m_c, but is not based purely on dimensional analysis (as
is HQET). This power counting leads to predictions which differ from those
resulting from the usual velocity power counting rules of NRQCD. In particular,
we show that while Lambda_QCD/m_c power counting preserves the empirically
verified predictions of spin symmetry in decays, it also leads to new
predictions which include: A hierarchy between spin singlet and triplet octet
matrix elements in the J/psi system. A quenching of the net polarization in
production at large transverse momentum. No end point enhancement in radiative
decays. We discuss explicit tests which can differentiate between the
traditional and new theories of NRQCD.Comment: 18 pages, 1 figure Replaced plot of the psi polarization parameter
alpha as a function of transverse momentum. Alpha is now closer to zero for
large transverse moment
Inelastic production in polarized photon-hadron collisions
Presented here is a calculation of inelastic production in polarized
photon-hadron collisions under the framework of NRQCD factorization formalism.
We consider the photoproduction of \jpsi in the energy range relevant to
HERA. The Weizs\"acker-Williams approximation is adopted in the evaluation of
the cross sections for collisions. We found that this process can give
another independent test for the color-octet mechanism, and the different
features for the two color-octet processes may provide further informations on
the mechanism for inelastic \jpsi photoproduction. And the discrepancy on the
production asymmetry between various sets of polarized gluon distribution
functions is also found to be distinctive.Comment: 14pages, 6 PS figure
Deep inelastic production at HERA in the -factorization approach and its consequences for the nonrelativistic QCD
In the framework of the -factorization approach, we analyse the
inclusive and inelastic production of particles in deep inelastic
scattering. We take into account both colour-singlet and colour-octet
production channels. We inspect the sensitivity of theoretical predictions to
the choice of model parameters. Our theoretical results agree reasonably well
with recent experimental data collected by the collaboration H1 at HERA.Comment: 14 pages, 6 figure
J/psi Production at LEP: Revisited and Resummed
We present the leading order differential and total rates for J/\psi
production at LEP. By leading order we mean all terms of the form
alpha_s[alpha_s log(M_Z^2/M_{psi}^2)]^n and alpha_s^{n+1} log^l(z^2)
log^m(M_Z^2/M_{psi}^2), (l+m=2n-1), in the regions z=2E_psi/M_Z ~ O(1) and z <<
1, respectively. In the intermediate region we interpolate using the available
data. This resummation eliminates the O[alpha_s(M_psi)/alpha_s(M_Z)]~ 2
theoretical uncertainties in previous calculations. The log(z) resummation
results in a suppression of the small z region due to coherent gluon emission.
Comparing the zeroth moment with the LEP data we find the value for the
effective octet matrix element to be =0.019 GeV^3. The
theoretical uncertainties are substantially smaller than those from Tevatron
extractions. Using this value of the octet matrix element we make a prediction
for the first moment of the differential rate and find that the resummed
differential decay rate is in much better agreement with preliminary data than
the color singlet result or the unresummed color octet prediction.Comment: LATEX, 17 pages, 3 figures included. References to ALEPH
collaboration change
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