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排序方式: 共有816条查询结果,搜索用时 15 毫秒
91.
Using a data sample of integrated luminosity of about 33 pb-1 collected around 3.773 GeV with the BESII detector at the BEPC collider, the semileptonic decays D+→φe+νe, D+→φμ+νμ and the hadronic decay D+→φπ+ are studied. The upper limits of the branching fractions are set to be BF(D+→φe+νe)<2.01% and BF(D+→φμ+νμ)<2.04% at the 90% confidence level. The ratio of the branching fractions for D+→φπ+ relative to D+→K-π+π+ is measured to be 0.057±0.011±0.003. In addition, the branching fraction for D+→φπ+ is obtained to be (5.2±1.0±0.4)×10-3. 相似文献
92.
I. V. Ajinenko Yu. A. Belokopytoy H. Bialkowska H. Boettcher F. Bottorweck P. V. Chliapnikov F. Crijns A. de Roeck E. A. de Wolf K. Dziunikowska A. M. F. Endler A. Eskreys Z. C. Garutchava Y. Golubkov H. Graessler G. R. Gulkanyan P. van Hal R. Sh. Hakobyan T. Haupt W. Kittel D. Kisielewska B. B. Levchenko F. Meijers A. B. Micha?owska Th. Naumann V. I. Nikolaenko K. Olkiewicz B. Pawlik L. P. Petrovikh R. P?ll?nen V. M. Ronjin A. M. Rybin H. M. T. Saarikko W. Schmitz L. Scholten L. N. Smirnova O. G. Tchikilev A. G. Tomaradze V. A. Uvarov F. Verbeure R. Wischnewski EHS-NA Collaboration 《Zeitschrift fur Physik C Particles and Fields》1989,42(3):377-385
Multiplicity distributions, observed inK + interactions with Al and Au nuclei at 250 GeV/c incident momentum are presented. They are analyzed in the framework of multiple collisions of the incident particle inside a nucleus. The probability distribution of the number of grey tracks is well described by the model of Andersson et al., if a negative binomial distribution is assumed for the distribution of the number of grey protons produced per elementary collision instead of the usual geometrical distribution. The analysis of the average and dispersion of the charge multiplicity distribution supports the validity of the multiple collision model, including results on correlations between forward and backward multiplicities. 相似文献
93.
94.
Bearden IG Beavis D Besliu C Blyakhman Y Budick B Bøggild H Chasman C Christensen CH Christiansen P Cibor J Debbe R Enger E Gaardhøje JJ Germinario M Hagel K Hansen O Holm A Holme AK Ito H Jakobsen E Jipa A Jundt F Jørdre JI Jørgensen CE Karabowicz R Keutgen T Kim EJ Kozik T Larsen TM Lee JH Lee YK Løvhøiden G Majka Z Makeev A McBreen B Mikelsen M Murray M Natowitz J Nielsen BS Norris J Olchanski K Olness J Ouerdane D Płaneta R Rami F Ristea C Röhrich D Samset BH Sandberg D Sanders SJ 《Physical review letters》2003,90(10):102301
We present ratios of the numbers of charged antihadrons to hadrons (pions, kaons, and protons) in Au+Au collisions at sqrt[s(NN)]=200 GeV as a function of rapidity in the range y=0-3. While the ratios at midrapidity are approaching unity, the K(-)/K(+) and p;/p ratios decrease significantly at forward rapidities. An interpretation of the results within the statistical model indicates a reduction of the baryon chemical potential from mu(B) approximately 130 MeV at y=3 to mu(B) approximately 25 MeV at y=0. 相似文献
95.
Franklin David Rincón Marcelo Esposito Pedro Henrique Hermes de Araújo Claudia Sayer Galo Antonio Carrillo Le Roux 《大分子反应工程》2013,7(1):24-35
Reaction calorimetry is a very useful tool to monitor exothermic polymerization reactions as it is based on the estimation of the heat generated by the reaction. The objective of this work is to analyze the performance of an unscented Kalman filter (UKF) for online monitoring of batch vinyl acetate emulsion polymerization reactions. Reactions are performed in isoperibolic and isothermal conditions. The UKF is compared to an extended Kalman filter that has a very poor performance. The results show that the UKF is able to provide good estimates for the conversion, for the reactor and jacket temperatures, for the overall heat transfer coefficient between the reaction medium and the jacket, and for the heat loss from the jacket to the surroundings.
96.
C. Daum L. Hertzberger W. Hoogland R. Jongerius S. Peters P. Van Deurzen V. Chabaud A. Gonzalez-Arroyo B. Hyams H. Tiecke P. Weilhammer A. Dwurazny G. Polok M. Rozanska K. Rybicki M. Turala J. Turnau G. Ascoli H. Backer G. Blanar M. Cerrada H. Dietl J. Gallivan M. Glaubmann R. Klanner E. Lorenz G. Lütjens G. Lutz W. Männer U. Stierlin I. Blakey M. Bowler R. Cashmore J. Loken W. Spalding G. Thompson B. Alper C. Damerell A. Gillman C. Hardwick M. Hotchkiss F. Wickens ACCMOR Collaboration 《Zeitschrift fur Physik C Particles and Fields》1981,10(2):95-100
Muon electron pairs were detected in an Al multiplate spark chamber, exposed to a neutrino beam from the CERN PS. The leptons were not accompanied by other particles, except occasionally by protons. The background came mainly from muon associated π0 production, with one decay gamma lost. It was determined empirically, together with the small contribution from υ e reactions. For electron energies above 2 GeV the background is 5.7±1.5 events, whereas 18 (μe)-candidates have been observed. Hence the effect is established, with a rate of about 10?4 as compared to the muonic reactions above 3 GeV. Charm creation as the origin of this (μe)-production process is excluded; heavy neutral lepton production does not fit the kinematics observed. Instead the events are compatible with the two-body decay of an object with variable invariant mass of order 1 GeV, possibly resulting from axion interactions. 相似文献
97.
D. Bisello G. Busetto A. Castro M. Nigro M. Penzo L. Pescara M. Posocco P. Sartori L. Stanco Z. Ajaltouni A. Falvard J. Jousset B. Michel J. C. Montret A. Antonelli R. Baldini A. Calcaterra G. Capon M. Schioppa J. -E. Augustin G. Cosme F. Couchot B. Dudelzak F. Fulda G. Grosdidier B. Jean-Marie S. Jullian D. Lalanne V. Lepeltier F. Manè C. Paulot R. Riskalla Ph. Roy G. Szklarz DM Collaboration 《Zeitschrift fur Physik C Particles and Fields》1988,39(1):13-19
Thee + e ?→K + K ? cross section has been measured from about 750 events in the energy interval \(1350 \leqq \sqrt s \leqq 2400 MeV\) with the DM2 detector at DCI. TheK ± form factor |F F ±| cannot be explained by the ρ, ω, ? and ρ′(1600). An additional resonant amplitude at 1650 MeV has to be added as suggested by a previous experiment. 相似文献
98.
The DELPHI Collaboration J. Abdallah et al. 《The European Physical Journal C - Particles and Fields》2003,27(2):153-172
A search for sleptons, neutralinos, charginos, sgoldstinos and heavy stable charged sleptons in the context of scenarios
where the lightest supersymmetric particle is the gravitino, is presented. Data collected during 2000 with the DELPHI detector
at centre-of-mass energies from 204 to 208 GeV were analysed and combined with all the data collected from 1995 to 1999 at
lower energies. No evidence for the production of sleptons, neutralinos and charginos has been found, therefore new limits
on the mass of these supersymmetric particles and on the model parameter space are set. The search for heavy stable charged
sleptons also updates the stable sleptons mass limit. The absence of evidence for sgoldstino production allows limits to be
set on its mass and on the scale of supersymmetry breaking.
Received: 6 November 2002 / Published online: 14 February 2003 相似文献
99.
100.
The ZEUS Collaboration S. Chekanov et al. 《The European Physical Journal C - Particles and Fields》2002,25(2):169-187
Diffractive dissociation of virtual photons, , has been studied in ep interactions with the ZEUS detector at HERA. The data cover photon virtualities 0.17 < Q
2
< 0.70 GeV2 and 3 < Q
2
< 80 GeV2 with 3 < MX < 38 GeV, where MX is the mass of the hadronic final state. Diffractive events were selected by two methods: the first required the detection
of the scattered proton in the ZEUS leading proton spectrometer (LPS); the second was based on the distribution of MX. The integrated luminosities of the low- and high-Q2 samples used in the LPS-based analysis are 0.9 pb-1 and 3.3 pb-1, respectively. The sample used for the MX-based analysis corresponds to an integrated luminosity of 6.2 pb-1. The dependence of the diffractive cross section on W, the virtual photon-proton centre-of-mass energy, and on Q2 is studied. In the low-Q2 range, the energy dependence is compatible with Regge theory and is used to determine the intercept of the Pomeron trajectory.
The W dependence of the diffractive cross section exhibits no significant change from the low-Q2 to the high-Q2 region. In the low-Q2 range, little Q2 dependence is found, a significantly different behaviour from the rapidly falling cross section measured for Q
2
> 3 GeV2. The ratio of the diffractive to the virtual photon-proton total cross section is studied as a function of W and Q2. Comparisons are made with a model based on perturbative QCD.
Received: 27 March 2002 / Published online: 9 August 2002 相似文献