共查询到20条相似文献,搜索用时 0 毫秒
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Charmonium rescattering effects in the M1 transition of $ \psi$ (2S) $ \rightarrow$ $ \gamma$ $ \eta_{c}^{}$ are investigated by modeling a $ \chi_{{cJ}}^{}$ or J/ $ \psi$ rescattering into a $ \eta_{c}^{}$ final state. The absorptive and dispersive part of the transition amplitudes for the rescattering loops of $ \eta$ $ \psi$ ( $ \gamma^{{\ast}}_{}$ ) and $ \gamma$ $ \chi$ ( $ \psi$ ) are separately evaluated. The numerical results show that the contribution from the $ \gamma$ $ \chi$ ( $ \psi$ ) rescattering process is negligible. Compared with the virtual D $ \bar{{D}}$ (D *) rescattering processes, the $ \eta$ $ \psi$ ( $ \gamma^{{\ast}}_{}$ ) process may be regarded as the next-leading order of the hadronic loop mechanism, which only offers the partial decay width of ~ 0.045 keV to the $ \psi$ (2S) $ \rightarrow$ $ \gamma$ $ \eta_{c}^{}$ . 相似文献
3.
The hadronic photon structure function
is measured from data taken with the ALEPH detector at LEP. At centre-of-mass energies between
and
an integrated luminosity of
is analyzed in two ranges of Q2 with
GeV2 and 67.2 GeV2. Detector effects and acceptance are corrected for with a Tikhonov unfolding procedure. The results are compared to theoretical predictions and measurements from other experiments.Received: 12 June 2003, Published online: 11 August 2003 相似文献
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The OPAL Collaboration G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2003,27(4):483-495
We have analysed the data collected by OPAL at centre-of-mass energies between 189 and 209 GeV searching for Higgs boson
candidates from the process followed by the decay of where is the CP-odd Higgs boson. The search is done in the region where the mass, , is below the production threshold for , and the CP-even Higgs boson mass is within the range 45-86 GeV/c
2
. In this kinematic range, the decay of may be dominant and previous Higgs boson searches have very small sensitivities. This search can be interpreted within any
model that predicts the existence of at least one scalar and one pseudoscalar Higgs boson. No excess of events is observed
above the expected Standard Model backgrounds. Model-independent limits on the cross-section for the process are derived assuming 100% decays of the into and 100% decays of the into each of the following final states: , , , , and . The results are also interpreted in the CP-conserving no-mixing MSSM scenario, where the region and is excluded.
Received: 13 March 2002 / Published online: 26 February 2003 相似文献
6.
The measurement of $\alpha_s$ from event shapes with the DELPHI detector at the highest LEP energies
Searches for pair-production of supersymmetric particles under the assumption of non-conservation of R-parity with a dominant LL
or
term have been performed using the data collected by the DELPHI experiment at LEP in e + e- collisions at centre-of-mass energies from 192 up to 208 GeV. No excess of data above Standard Model expectations was observed. The results were used to constrain the MSSM parameter space and to derive limits on the masses of supersymmetric particles.Received: 4 March 2004, Revised: 5 May 2004, Published online: 23 June 2004An Erratum to this article can be found at 相似文献
7.
A. V. Kisselev V. A. Petrov O. P. Yushchenko 《Zeitschrift fur Physik C Particles and Fields》1988,41(3):521-525
Charged particle multiplicities ine + e ? annihilation into hadronic states have been studied. Events with light and heavy initial quarks are treated separately. Particular attention is paid to multiple production int \(\bar t\) events at LEP energies. 相似文献
8.
We have studied the quantum dynamics of collisions between spin-stretched Na atoms and Na2 molecules. Cross-sections and rate coefficients for vibrational relaxation of Na2(v,j = 0) have been computed in the 1 nK-0.1 mK energy range using an accurate time-independent method based on hyperspherical coordinates. The complex scattering length and the extension of the Wigner region have been determined. A detailed study of the sensitivity of collisional quantities on the three-body interaction at short distance has been performed. They are very sensitive to three-body effects for the vibrational state v = 1 of Na2. Rotational distributions have also been calculated and show a more pronounced sensitivity on the three-body interaction, even for v = 2 and 3.Received: 29 March 2004, Published online: 22 June 2004PACS:
34.50.-s Scattering of atoms and molecules 相似文献
9.
D. Bardin 《The European Physical Journal C - Particles and Fields》2002,24(3):373-383
We study predictions for the reaction . The complete one-loop corrections are taken into account and higher order contributions, in particular those for the observed
real photons, are added whenever necessary. The event generator MC, a general-purpose Monte Carlo generator for the process based on the method of exclusive exponentiation, is used as the environment. We extend its applicability to the process ,, where the observation of at least a single is required. The exponentiation is implemented in much the same way as for the s-channel process alone. In particular, all photonic effects present in the case of W exchange, which cannot be included in the s-channel exponentiation scheme, are calculated to a finite order only. The real hard photon matrix element is calculated up
to . Leading logarithmic contributions of the two-loop corrections and one-loop photonic corrections accompanying real single-photon
emission are included. The electroweak corrections are calculated with the DIZET library of the ZFITTER package. Numerical
tests and predictions for typical observables are presented.
Received: 30 October 2001 / Revised version: 5 March 2002 / Published online: 22 May 2002 相似文献
10.
The ALEPH Collaboration A. Heister et al. 《The European Physical Journal C - Particles and Fields》2003,28(1):1-13
Events containing only energetic photons are analysed in a sample of of data recorded from collisions at centre-of-mass energies between 189 and 209 GeV by the ALEPH detector at LEP. The and cross sections are measured and found to be in agreement with the standard model predictions. The number of light
neutrino generations is determined to be . Upper limits are derived on the cross sections for photon production in the context of several supersymmetric models. Limits
are also set on the parameters of models with extra spatial dimensions, with contact interactions and with excited electrons.
Received: 27 May 2002 / Published online: 14 March 2003 相似文献
11.
《The European Physical Journal C - Particles and Fields》2007,49(2):395-410
Measurements of inclusive production of the Λ, Ξ- and Ξ*(1530) baryons in two-photon collisions with the L3 detector at LEP are presented. The inclusive differential cross sections
for Λ and Ξ- are measured as a function of the baryon transverse momentum, pt, and pseudo-rapidity, η. The mean number of Λ, Ξ- and Ξ*(1530) baryons per hadronic two-photon event is determined in the kinematic range 0.4 GeV<pt<2.5 GeV, |η|<1.2. Overall agreement with the theoretical models and Monte Carlo predictions is observed. A search for inclusive
production of the pentaquark θ+(1540) in two-photon collisions through the decay θ+→pK0
S is also presented. No evidence for production of this state is found. 相似文献
12.
We consider the interaction of the partonic fluctuation of a scalar photon with an external color field to calculate the leading and next-to-leading order gluon distribution of the proton following the work done by Dosch-Hebecker-Metz-Pirner. We relate these gluon distributions to the short and long distance behavior of the cross section of an adjoint dipole scattering off a proton. The leading order result is a constant, while the next-to-leading order result shows a
enhancement at small x. To get numerical results for the gluon distributions at the initial scale Q20 = 1.8 GeV2, we compute the adjoint dipole-proton cross section in the loop-loop correlation model. Quark distributions at the same initial scale are parameterized according to Regge theory. We evolve quark and gluon distributions to higher Q2 values using the DGLAP equation and compute charm and proton structure functions in the small-x region for different Q2 values.Received: 13 September 2003, Revised: 22 November 2003, Published online: 15 January 2003 相似文献
13.
We discuss here the binary reactions of strange and charmed particle production in
collisions at intermediate energies. In the case of baryon production with only one strange or charmed quark the cross section is determined by planar diagrams withK
*,K
** orD
*,D
**-meson poles in thet-channel. We calculated these diagrams in the frame of quark-gluon string model (QGSM) proposed earlier. We obtained also the cross-sections for reactions with baryon exchange in thet-channel with
and
pair in the final state. Predicted cross-sections for the reactions of
production are of the order of hundred nanobarns. Using reggeon calculus we estimated cross-sections of binary reactions with two or three strange quarks in the final state:
and . We discuss also the possible manifestation of color transparency effects in reactions with antiprotons on nuclei where all antiproton quarks annihilate. 相似文献
14.
A study of W-pair production in annihilations at LEP is presented, based on candidates corresponding to an integrated luminosity of 57 pb at GeV. Assuming that the angular distributions of the W-pair production and decay, as well as their branching fractions, are
described by the Standard Model, the W-pair production cross-section is measured to be pb. Assuming lepton universality and combining with our results from lower centre-of-mass energies, the W branching fraction
to hadrons is determined to be %. The number of W-pair candidates and the angular distributions for each final state (, are used to determine the triple gauge boson couplings. After combining these values with our results from lower centre-of-mass
energies we obtain , and , where the errors include both statistical and systematic uncertainties and each coupling is determined by setting the other
two couplings to the Standard Model value. The fraction of W bosons produced with a longitudinal polarisation is measured
to be . All these measurements are consistent with the Standard Model expectations.
Received: 23 October 1998 / Published online: 1 March 1999 相似文献
15.
A proof is given for the existence of two and only two modular invariant partition functions in affine
theories at heightsn=k+3 which are prime numbers. Arithmetic properties of the ring of algebraic integers () which is related toSU(3) weights are extensively used.Chercheur IISN, Address after October 1: Dublin Institute for Advanced Studies, Dublin, IrelandChercheur IISN 相似文献
16.
Hadron production and lepton-pair production in e+e- collisions are studied with data collected with the L3 detector at LEP at centre-of-mass energies
. Using a total integrated luminosity of 453 pb-1, 36057 hadronic events and 12863 lepton-pair events are selected. The cross sections for hadron production and lepton-pair
production are measured for the full sample and for events where no high-energy initial-state-radiation photon is emitted
prior to the collisions. Lepton-pair events are further investigated and forward-backward asymmetries are measured. Finally,
the differential cross sections for electron-positron pair-production is determined as a function of the scattering angle.
An overall good agreement is found with Standard Model predictions. 相似文献
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《The European Physical Journal C - Particles and Fields》2006,46(2):307-341
Searches were performed for topologies predicted by gauge-mediated supersymmetry breaking models (GMSB). All possible lifetimes of the next-to-lightest SUSY particle (NLSP), either the lightest neutralino or slepton, decaying into the lightest SUSY particle, the gravitino, were considered. No evidence for GMSB signatures was found in the OPAL data sample collected at centre-of-mass energies up to $\sqrt{s}=209 \mathrm{GeV}$ at LEP. Limits on the product of the production cross-sections and branching fractions are presented for all search topologies. To test the impact of the searches, a complete scan over the parameters of the minimal model of GMSB was performed. NLSP masses below $53.5 \mathrm{GeV}/c^2$ in the neutralino NLSP scenario, below $87.4 \mathrm{GeV}/c^2$ in the stau NLSP scenario and below $91.9 \mathrm{GeV}/c^2$ in the slepton co-NLSP scenario are excluded at 95% confidence level for all NLSP lifetimes. The scan determines constraints on the universal SUSY mass scale Λ from the direct SUSY particle searches of Λ>40, 27, 21, 17, $15 \mathrm{GeV}/c^2$ for messenger indices N=1,2,3,4,5 for all NLSP lifetimes. 相似文献
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The OPAL Collaboration G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2002,23(1):1-11
A search for first generation scalar and vector leptoquarks (LQ) as well as for squarks () in R-parity violating SUSY models with the direct decay of the into Standard Model particles has been performed using ee collisions collected with the OPAL detector at LEP at an ee centre-of-mass energy of 189 GeV. The data correspond to an integrated luminosity of about 160 pb. The dominant process for this search is , where a photon, which has been radiated by one of the beam electrons, serves as a source of quarks. The numbers of selected
events found in the two decay channels are in agreement with the expectations from Standard Model processes. This result allows
to set lower limits at the 95% confidence level on the mass of first generation scalar and vector leptoquarks, and of squarks
in R-parity violating SUSY models. For Yukawa couplings to fermions larger than , the mass limits range from 121 GeV to GeV ( GeV to GeV) depending on the branching ratio of the scalar (vector) leptoquark state. Furthermore, limits are set on the Yukawa couplings for leptoquarks and for squarks, and on as a function of the scalar leptoquark/squark mass.
Received: 22 May 2001 / Published online: 25 January 2002 相似文献