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1.
G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》1999,11(2):217-238
Gluon jets are identified in hadronic Z decays as all the particles in a hemisphere opposite to a hemisphere containing two tagged quark jets. Gluon jets defined
in this manner are equivalent to gluon jets produced from a color singlet point source and thus correspond to the definition
employed for most theoretical calculations. In a separate stage of the analysis, we select quark jets in a manner to correspond
to calculations, as the particles in hemispheres of flavor tagged light quark (uds) events. We present the distributions of
rapidity, scaled energy, the logarithm of the momentum, and transverse momentum with respect to the jet axes, for charged
particles in these gluon and quark jets. We also examine the charged particle multiplicity distributions of the jets in restricted
intervals of rapidity. For soft particles at large , we observe the charged particle multiplicity ratio of gluon to quark jets to be , in agreement with the prediction that this ratio should approximately equal the ratio of QCD color factors, . The intervals used to define soft particles and large for this result, GeV/ and GeV/, are motivated by the predictions of the Herwig Monte Carlo multihadronic event generator. Additionally, our gluon jet data
allow a sensitive test of the phenomenon of non-leading QCD terms known as color reconnection. We test the model of color
reconnection implemented in the Ariadne Monte Carlo multihadronic event generator and find it to be disfavored by our data.
Received: 24 February 1999 / Published online: 8 September 1999 相似文献
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《Physics letters. [Part B]》1987,199(1):134-138
I extend a model of energy flow in hadronic jets to discuss pion production. I fix the parameter ϱ≈2 GeV of the jet model in terms of the height of the rapidity plateau and the typical transverse energy of pions in e+e− jets. I find a relation between the jet shape and the fragmentation function for a quark into pions. I relate the height of the rapidity plateau to the power (1 − xp) that appears in the fragmentation function. 相似文献
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G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2002,23(4):597-613
The charged particle multiplicities of two- and three-jet events from the reaction ee
Z are measured for Z decays to light quark (uds) flavors. Using recent theoretical expressions to account for biases from event selection, results
corresponding to unbiased gluon jets are extracted over a range of jet energies from about 11 to 30 GeV. We find consistency
between these results and direct measurements of unbiased gluon jet multiplicity from and Z decays. The unbiased gluon jet data including the direct measurements are compared to corresponding results for quark jets.
We perform fits based on analytic expressions for particle multiplicity in jets to determine the ratio of multiplicities between gluon and quark jets as a function of energy. We also determine the ratio of slopes, , and of curvatures, , where y specifies the energy scale. At 30 GeV, we find and , where the uncertainties are the statistical and systematic terms added in quadrature. These results are in general agreement
with theoretical predictions. In addition, we use the measurements of the energy dependence of and to determine an effective value of the ratio of QCD color factors, . Our result, (total), is consistent with the QCD value of 2.25.
Received: 25 October 2001 / Revised version: 20 January 2002 / Published online: 5 April 2002 相似文献
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《Nuclear Physics A》1986,452(4):723-737
A thermodynamically consistent treatment of the nuclear interaction is employed to study the dependence of pion production on the nuclear equation of state in heavy-ion collisions. Massive baryon resonances, heavy mesons and the Bose condensation of pions are incorporated into a macrocanonical relativistic quantum-statistical treatment of the highly excited system. The measured pion multiplicities, which vary over eight orders of magnitude in the bombarding energy range from 30 MeV/nucleon to 4 GeV/nucleon, are reproduced within a simple one-dimensional fluiddynamical model if it is assumed that nuclear matter is rather incompressible. The pion yields are in this model directly related to the compression energy, which amounts to one-half of the total center-of-mass energy at all BEVALAC energies. The maximum compression derived is uncertain by about 10% and 30% at Elab = 0.4 and 1.8 GeV/nucleon, respectively. The temperatures of the system in the moment of the chemical freeze-out of the pion/delta degree of freedom are determined from the measured pion yields and range from 10 MeV to 100 MeV. An extrapolation to CERN/BNL energies, i.e. Elab > 10 GeV/nucleon, yields T = 150–200 MeV. A strong energy dependence of the cross sections and the slopes of hard γ's is predicted by this model. The calculated photon yields are in surprising agreement with the data on γ- production at intermediate energies. 相似文献
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Hasegawa M Aliu E Andringa S Aoki S Argyriades J Asakura K Ashie R Berns H Bhang H Blondel A Borghi S Bouchez J Burguet-Castell J Casper D Cavata C Cervera A Chen SM Cho KO Choi JH Dore U Espinal X Fechner M Fernandez E Fukuda Y Gomez-Cadenas J Gran R Hara T Hasegawa T Hayashi K Hayato Y Helmer RL Hill J Hiraide K Hosaka J Ichikawa AK Iinuma M Ikeda A Inagaki T Ishida T Ishihara K Ishii T Ishitsuka M Itow Y Iwashita T Jang HI Jeon EJ Jeong IS Joo KK Jover G Jung CK Kajita T Kameda J Kaneyuki K 《Physical review letters》2005,95(25):252301
We report the result from a search for charged-current coherent pion production induced by muon neutrinos with a mean energy of 1.3 GeV. The data are collected with a fully active scintillator detector in the K2K long-baseline neutrino oscillation experiment. No evidence for coherent pion production is observed, and an upper limit of is set on the cross section ratio of coherent pion production to the total charged-current interaction at 90% confidence level. This is the first experimental limit for coherent charged pion production in the energy region of a few GeV. 相似文献
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M. BannerJ.L. Hamel J.P. PansartA.V. Stirling J. TeigerH. Zaccone J. Zsembery 《Physics letters. [Part B]》1972
The transverse momentum distribution at 90° of pions, protons and antiprotons have been measured at the CERN intersecting storage rings for C.M. energies between 23.2 and 52.7 GeV. In this energy range, the pion and proton distributions are almost energy independent. The antiproton production rises by a factor of two between 23.2 and 52.7 GeV. 相似文献
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Acosta D Affolder T Albrow MG Ambrose D Amidei D Anikeev K Antos J Apollinari G Arisawa T Artikov A Ashmanskas W Azfar F Azzi-Bacchetta P Bacchetta N Bachacou H Badgett W Barbaro-Galtieri A Barnes VE Barnett BA Baroiant S Barone M Bauer G Bedeschi F Behari S Belforte S Bell WH Bellettini G Bellinger J Benjamin D Beretvas A Bhatti A Binkley M Bisello D Bishai M Blair RE Blocker C Bloom K Blumenfeld B Bocci A Bodek A Bolla G Bolshov A Bortoletto D Boudreau J Bromberg C Brubaker E Budagov J 《Physical review letters》2005,94(17):171802
We report the first largely model independent measurement of charged particle multiplicities in quark and gluon jets, Nq and Ng, produced at the Fermilab Tevatron in pp collisions with a center-of-mass energy of 1.8 TeV and recorded by the Collider Detector at Fermilab. The measurements are made for jets with average energies of 41 and 53 GeV by counting charged particle tracks in cones with opening angles of theta(c) = 0.28, 0.36, and 0.47 rad around the jet axis. The corresponding jet hardness Q = Ejet theta c varies in the range from 12 to 25 GeV. At Q = 19.2 GeV, the ratio of multiplicities r = Ng/Nq is found to be 1.64+/-0.17, where statistical and systematic uncertainties are added in quadrature. The results are in agreement with resummed perturbative QCD calculations. 相似文献
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We performed a measurement of differential and integral jet shapes in proton-carbon, proton-tungsten and proton-aluminium
collisions at 920 GeV/c proton momentum with the HERA-B detector at HERA for the jet transverse energies in the range 4 GeV<ET(jet)< 12 GeV. Jets were identified using the kT-clustering algorithm. The measurements were performed for the hardest jet in the event, directed towards the opposite side
with respect to the trigger direction. Jets become narrower with increasing transverse energy and measured distributions agree
well with predictions of the PYTHIA 6.2 model. We do not observe any significant difference in the jet shape for the carbon
and the aluminium targets. Nevertheless, the transverse energy flow at small and large radii for the tungsten sample is slightly
less than for light nuclei. This observation indicates some influence of the nuclear environment on the formation of jets
in heavy nuclei, especially at lower transverse energies, 5 GeV<ET(jet)< 6 GeV.
PACS 13.85.-t; 13.87.-a; 13.87.Fh 相似文献
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Jonathan Dorfan 《Zeitschrift fur Physik C Particles and Fields》1981,7(4):349-356
A cluster algorithm using angular correlations and leading particle effects is presented which is applicable to the study of jets produced in high energy storage ring collisions. The algorithm uses the concept of a minimal spanning tree and is computationally very efficient. Events are classified by their cluster number and the cluster number frequency distribution can be used for comparison with particle production models. Individual particles are assigned to the clusters and the vector sum of their momenta generate a cluster axis. These cluster properties permit the study of the dynamics of the jet production and fragmentation processes. The example of two and three jet production at PEP and PETRA energies is used to illustrate this technique. 相似文献
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E. P. Shabalin 《Physics of Atomic Nuclei》2000,63(4):594-605
The scattering of a pion on a pion in the energy region $\sqrt s $ ≤1 GeV is successfully described on the basis of pole diagrams featuring spinless, spin-1, and spin-2 intermediate particles, provided that the properties of these particles and of their interactions are deduced from the basic principles of QCD and from the requirements of chiral theory. 相似文献
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GAO Ying-Jia ZHANG Yu-Jie CHAO Kuang-Ta 《理论物理通讯》2006,46(6):1017-1022
We study radiative decays of T to light quark jets in nonrelativistic QCD by taking both the color singlet and color octet b^-b operators into consideration. The cut for quark jet energy and cut for the angle between two quark jets are introduced. The sensitivity to the soft and collinear singularities in the loop integrals are greatly reduced by these cuts. With the jet energy cut of about 1 GeV, and the jet angle cut of about 36°, the branching ratio for γ→ rq^- is found to be 8.2 × 10^-4 from color singlet contributions. The color octet contributions could be much larger than that of color singlet, depending on the estimate of the color octet matrix elements. This process may provide a new test for the color octet mechanism in nonrelativistic QCD. 相似文献
16.
Probing the color structure of the perfect QCD fluids via soft-hard-event-by-event azimuthal correlations
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We develop a comprehensive dynamical framework, CIBJET, to calculate on an event-by-event basis the dependence of correlations between soft(p_T2 GeV) and hard(p_T10 GeV) azimuthal flow angle harmonics on the color composition of near-perfect QCD fluids produced in high energy nuclear collisions at RHIC and LHC. CIBJET combines consistently predictions of event-by-event VISHNU2+1 viscous hydrodynamic fluid fields with CUJET3.1 predictions of event-by-event jet quenching. We find that recent correlation data favor a temperature dependent color composition including bleached chromo-electric q(T) + g(T) components and an emergent chromo-magnetic degrees of freedom m(T) consistent with non-perturbative lattice QCD information in the confinement/deconfinement temperature range. 相似文献
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Data on the mean multiplicity of strange hadrons produced in minimum bias proton-proton and central nucleus-nucleus collisions at momenta between 2.8 and 400 GeV/c per nucleon have been compiled. The multiplicities for nucleon-nucleon interactions were constructed. The ratios of strange particle multiplicity to participant nucleon as well as to pion multiplicity are larger for central nucleus-nucleus collisions than for nucleon-nucleon interactions at all studied energies. The data at AGS energies suggest that the latter ratio saturates with increasing masses of the colliding nuclei. The strangeness to pion multiplicity ratio observed in nucleon-nucleon interactions increases with collision energy in the whole energy range studied. A qualitatively different behaviour is observed for central nucleus-nucleus collisions: the ratio rapidly increases when going from Dubna to AGS energies and changes little between AGS and SPS energies. This change in the behaviour can be related to the increase in the entropy production observed in central nucleus-nucleus collisions at the same energy range. The results are interpreted within a statistical approach. They are consistent with the hypothesis that the Quark Gluon Plasma is created at SPS energies, the critical collision energy being between AGS and SPS energies. 相似文献
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I. N. Vardanyan I. P. Lokhtin L. I. Sarycheva A. M. Snigirev C. Yu. Teplov 《Physics of Atomic Nuclei》2005,68(2):332-339
The modification of the jet fragmentation function due to the parton-energy loss in dense quark-gluon matter is studied in channels involving the production of leading particles. The “softening” effect for the jet fragmentation function is shown to be determined by the angular distribution of gluons emitted in matter. This effect anticorrelates with the “suppression” of the total yield of jets owing to the energy loss of jet partons outside the jet cone. The possibility of measuring the jet fragmentation function by using leading electromagnetic clusters in heavy-ion collisions at the LHC energies is analyzed. 相似文献
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V. A. Okorokov 《Physics of Atomic Nuclei》2009,72(1):147-160
Experimental results obtained by studying the azimuthal anisotropy of final states in nucleus-nucleus interactions at the energies of the relativistic heavy-ion collider (RHIC) are systematized. The medium is found to exhibit a pronounced collective behavior, which is likely to be formed at an early, parton, stage of the spacetime evolution of product hot and dense matter. Experimental data on the azimuthal anisotropy indicate that strongly interacting matter produced in the final state under extreme conditions behaves as a nearly ideal liquid rather than an ideal gas of quarks and gluons. The experimentally observed suppression of high-transverse-momentum jets and substantial modification of jetlike azimuthal correlations in heavy-ion collisions suggest that the energy loss of partons propagating in high-temperature matter featuring a high density of color charges is extremely large. The dependence of the amount of hardjet suppression in nucleus-nucleus collisions on the orientation of a jet with respect to the reaction plane was first discovered experimentally at RHIC. A strong suppression of the production of high-transverse-momentum particles and jets at RHIC is a unique phenomenon, which was discovered experimentally at lower energies. 相似文献