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1.
《Zeitschrift fur Physik C Particles and Fields》1996,69(4):543-560
Symmetric three-jet events are selected from hadronic Z0 decays such that the two lower energy jets are each produced at an angle of about 150° with respect to the highest energy jet. In some cases, a displaced secondary vertex is reconstructed in one of the two lower energy jets, which permits the other lower energy jet to be identified as a gluon jet through anti-tagging. In other cases, the highest energy jet is tagged as a b jet or as a light quark (uds) jet using secondary vertex or track impact parameter and momentum information. Comparing the two lower energy jets of the events with a tag in the highest energy jet to the anti-tagged gluon jets yields a direct comparison of b, uds and gluon jets, which are produced with the same energy of about 24 GeV and under the same conditions. We observe b jets and gluon jets to have similar properties as measured by the angular distribution of particle energy around the jet directions and by the fragmentation functions. In contrast, gluon jets are found to be significantly broader and to have a markedly softer fragmentation function than uds jets. For the k ⊥ jet finder with y cut=0.02, we find $${«ngle n^{? ch.}»ngle {? gluon}?er «ngle n^{? ch.}»ngle {? b} {? quark}}=1.089pm 0.024 ({? stat.})pm0.024 ({? syst.})$$ $${«ngle n^{? ch.}»ngle {? gluon}?er «ngle n^{? ch.}»ngle {? uds} {? quark}}=1.390pm 0.038 ({? stat.})pm0.032 ({? syst.})$$ as the ratios of the mean charged particle multiplicity in the gluon jets compared to the b and uds jets. Results are also reported using the cone jet finder. 相似文献
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Pumplin J 《Physical review D: Particles and fields》1991,44(7):2025-2032
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Bo Andersson Gösta Gustafson Torbjörn Sjöstrand 《Zeitschrift fur Physik C Particles and Fields》1980,6(3):235-240
Based on the assumption that a color force-field has a stringlike character (like a stretchedout bag_ with no excited degrees of freedom transverse to the field direction (which is strongly supported by the observed polarization of inclusively produced Λ-particles) we derive the probability to produce heavy flavor quark-antiquark pairs and pairs with transverse momentum in the field. We show how to incorporate the results into a soft hadronisation scheme for particle distributions in quark and gluon jets. We point to some non-trivial effects from the finite (longitudinal) size of the force-field which result on the one hand in important correlations between the longitudinal scaling variable and the transverse momentum and on the other hand leads to correstions to the simple iterative cascade scheme. 相似文献
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P. Abreu et al. 《The European Physical Journal C - Particles and Fields》2000,17(2):207-222
A sample of 2.2 million hadronic Z decays, selected from the data recorded by the Delphi detector at Lep during 1994–1995 was used for an improved measurement of inclusive distributions of and p and their antiparticles in gluon and quark jets. The production spectra of the individual identified particles were found
to be softer in gluon jets compared to quark jets, with a higher multiplicity in gluon jets as observed for inclusive charged
particles. A significant proton enhancement in gluon jets is observed indicating that baryon production proceeds directly
from colour objects. The maxima, , of the -distributions for kaons in gluon and quark jets are observed to be different.
Received: 24 January 2000 / Revised version: 15 May 2000 / Published online: 8 September 2000 相似文献
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P. Abreu et al. 《The European Physical Journal C - Particles and Fields》2000,13(4):573-589
The fragmentation functions of quarks and gluons are measured in various three-jet topologies in Z decays from the full data
set collected with the Delphi detector at the Z resonance between 1992 and 1995. The results at different values of transverse momentum-like scales are
compared. A parameterization of the quark and gluon fragmentation functions at a fixed reference scale is given. The quark
and gluon fragmentation functions show the predicted pattern of scaling violations. The scaling violation for quark jets as
a function of a transverse momentum-like scale is in a good agreement with that observed in lower energy annihilation experiments. For gluon jets it appears to be significantly stronger. The scale dependences of the gluon and
quark fragmentation functions agree with the prediction of the DGLAP evolution equations from which the colour factor ratio
is measured to be:
Received: 5 November 1999 / Published online: 25 February 2000 相似文献
10.
Investigation of the splitting of quark and gluon jets 总被引:1,自引:0,他引:1
The splitting processes in identified quark and gluon jets are investigated using longitudinal and transverse observables.
The jets are selected from symmetric three-jet events measured in Z decays with the Delphi detector in 1991-1994. Gluon jets are identified using heavy quark anti-tagging. Scaling violations in identified gluon jets
are observed for the first time. The scale energy dependence of the gluon fragmentation function is found to be about two
times larger than for the corresponding quark jets, consistent with the QCD expectation . The primary splitting of gluons and quarks into subjets agrees with fragmentation models and, for specific regions of the
jet resolution , with NLLA calculations. The maximum of the ratio of the primary subjet splittings in quark and gluon jets is . Due to non-perturbative effects, the data are below the expectation at small . The transition from the perturbative to the non-perturbative domain appears at smaller for quark jets than for gluon jets. Combined with the observed behaviour of the higher rank splittings, this explains the
relatively small multiplicity ratio between gluon and quark jets.
Received: 18 February 1998 / Published online: 24 April 1998 相似文献
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Alam MS Kim IJ Nemati B O'Neill JJ Romero V Severini H Sun CR Wang P Zoeller MM Crawford G Fulton R Gan KK Kagan H Kass R Lee J Malchow R Morrow F Sung M White C Whitmore J Wilson P Butler F Fu X Kalbfleisch G Lambrecht M Skubic P Snow J Bortoletto D Brown DN Dominick J McIlwain RL Miao T Miller DH Modesitt M Schaffner SF Shibata EI Shipsey IP Battle M Ernst J Kroha H Roberts S Sparks K Thorndike EH Wang C Artuso M Goldberg M Haupt T Horwitz N Kennett R Moneti GC Playfer S Rozen Y Rubin P 《Physical review D: Particles and fields》1992,46(11):4822-4827
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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
14.
A. H. Sørensen 《Zeitschrift fur Physik C Particles and Fields》1992,53(4):595-600
Suppression of the gluon-emission probability due to secondary scattering (the Landau-Pomeranchuk effect) is considered for an ultra-relativistic quark penetrating a dense gas of thermal quarks. With some appeal to QED, a simple expression for the suppression factor is obtained which reveals strong damping throughout the gluon spectrum for gas densities typical of nuclear matter. The suppression, which is due to multiple rather than single scattering, is in particular pronounced for soft gluon emission. The obtained reduction factor is believed to describe the damping of the Abelian radiation component to within a factor of \(\sqrt 2 \) . For the non-Abelian component comparison of emission and scattering angles hints at a suppression comparable to that pertaining to the Abelian component. 相似文献
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E. D. Malaza 《Zeitschrift fur Physik C Particles and Fields》1986,31(1):143-150
Moments of the multiplicity distribution of hadrons in QCD jets are presented within the next-to-leading jet calculus frame-work in perturbative QCD. Results, including corrections of relative order α s , are given for a general gauge group. 相似文献
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An experimental investigation of the structure of identified quark and gluon jets is presented. Observables related to both
the global and internal structure of jets are measured; this allows for tests of QCD over a wide range of transverse momentum
scales. The observables include distributions of jet-shape variables, the mean and standard deviation of the subjet multiplicity
distribution and the fragmentation function for charged particles. The data are compared with predictions of perturbative
QCD as well as QCD-based Monte Carlo models. In certain kinematic regions the measurements are sensitive mainly to perturbatively
calculable effects, allowing for a test of QCD. The comparisons are also extended into regions where nonperturbative effects
become large, and in this way the transition from hard to soft QCD is investigated. It is found that by including leading
and next-to-leading logarithmic contributions in the QCD predictions, the agreement with the data can be extended to lower
transverse momentum scales, especially for gluon jets.
Received: 2 February 1998 / Published online: August 9, 2000 相似文献
19.
Kim YK Auchincloss P Blanis D Bodek A Budd H Eno S Fry CA Harada H Ho YH Kumita T Mori T Olsen SL Shaw NM Sill A Thorndike EH Ueno K Zheng HW Imlay R Kirk P Lim J McNeil RR Metcalf W Myung SS Cheng CP Gu P Li J Li YK Mao ZP Xu YT Zhu YC Abashian A Gotow K Hu KP Low EH Mattson ME Piilonen L Sterner KL Lusin S Rosenfeld C Wang AT Wilson S Frautschi M Kagan H Kass R Trahern CG Breedon RE Kim GN Ko W Lander RL Maeshima K Malchow RL Smith JR Stuart D Williams MC Abe K Fujii Y Higashi Y Kim SK 《Physical review letters》1989,63(17):1772-1775
20.
I. M. Dremin 《JETP Letters》1998,68(7):559-562
The difference between the ratio of multiplicities and the ratio of their derivatives with respect to energy for gluon and
quark jets is calculated up to next-to-next-to leading order of perturbative QCD. Its nonzero value is uniquely defined by
the running property of the QCD coupling constant. It is shown that this difference is rather small compared to values which
can be obtained from experimental data. This disagreement can be ascribed either to strong nonperturbative terms or to experimental
problems with a scale choice, jet separation, and inadequate assignment of soft particles to jets.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 7, 535–538 (10 October 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献