共查询到20条相似文献,搜索用时 687 毫秒
1.
The analysis of electron–positron annihilations to hadrons at high energies shows that apart from two-jet events, there are also signs of three-jet events which are interpreted according to the QCD, as a gluon radiated by a quark. In this paper, we investigate the fragmentation of quarks and gluons to hadron jets. We show that gluon jets have a higher multiplicity compared to quark jets of the same energy. Furthermore, inclusion of different flavours in the distributions shows that quark jets are flavour-dependent, but gluon jets are not. The differences between quark and gluon jets also manifest themselves in the fragmentation functions. We observe that the fragmentation for gluon jet is softer than that for quark jet, because the radiation of soft gluons is larger for gluon jets and that gluon cannot be present as a valence parton inside a produced hadron. We provide possible explanations for these features in this paper. 相似文献
2.
G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2000,17(3):373-387
We compared the multiplicities of and of charged particles in quark and gluon jets in 3-jet events, as measured by the OPAL experiment at LEP. The comparisons
were performed for distributions unfolded to 100% pure quark and gluon jets, at an effective scale which took into account topological dependences of the 3-jet environment. The ratio of particle multiplicity in gluon jets
to that in quark jets as a function of for or was found to be independent of the particle species. This is consistent with the QCD prediction that the observed enhancement
in the mean particle rate in gluon jets with respect to quark jets should be independent of particle species. In contrast
to some theoretical predictions and previous observations, we observed no evidence for an enhancement of meson production in gluon jets with respect to quark jets, beyond that observed for charged particles. We measured the ratio
of the slope of the average charged particle multiplicity in gluon jets to that in quark jets, C, and we compared it to a
next-to-next-to-next-to leading order calculation. Our result, is about one standard deviation higher than the perturbative prediction.
Received: 31 March 2000 / Published online: 25 September 2000 相似文献
3.
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
4.
U. P. Sukhatme 《Zeitschrift fur Physik C Particles and Fields》1979,2(4):321-324
We compute observable quantities like the multiplicity and momentum distributions of hadrons in gluon and quark jets in the framework of a recursive cascade model, which is strongly motivated by the fundamental interactions of QCD. Fragmentation occurs via 3 types of breakups: quark → meson+ quark, gluon→meson+gluon, gluon→quark+ antiquark. In our model gluon jets are softer than quark jets. The ratio of gluon jet to quark jet multiplicity is found to be 2 asymptotically, but much less at lower energies. Some phenomenological consequences for λ decay are discussed. 相似文献
5.
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
6.
《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
7.
We argue in this paper the following. (i) A large part of what is observed in high-energy hadron reactions may be rather directly interpretable in terms of gluon interactions. Since gluons do not interact directly with leptons and photons this could be a valuable way to study them experimentally. Earlier work in this direction is briefly summarized. We suggest how several quantities can be reinterpreted in terms of gluon interactions; the rise in σtot, and the more rapid increase of multiplicity with energy at very high energies, are particularly fruitful to examine. The possibility of interpreting inclusive polarization data in terms of gluon spin properties is considered. Most importantly, we propose that if certain of our predictions on central region particle ratios are correct, then the gluon distribution as a function of x may be measurable at energies in the ISABELLE range. (ii) The structure of gluon jets in mass, multiplicity and momentum is discussed; we suggest that gluon jets will be quite different from quark jets, with more of the energy of the gluon jet going into mass, so hard gluon jets may not exist. 相似文献
8.
We provide a novel development in jet physics by predicting the energy profiles of light-quark and gluon jets in the framework of perturbative QCD. Resumming large logarithmic contributions to all orders in the coupling constant, our predictions are shown to agree well with Tevatron CDF and Large Hadron Collider CMS data. We also extend our resummation formalism to the invariant mass distributions of light-quark and gluon jets produced in hadron collisions. The predicted peak positions and heights in jet mass distributions are consistent with CDF data within uncertainties induced by parton distribution functions. 相似文献
9.
用蒙特卡洛模拟Jetset 7.4产生质心能量为91.2GeV的正负电子对撞事件. 在引入喷注的圆锥角后, 对不同味的夸克喷注和由不同味夸克发射的胶子产生的喷注的角分布特性进行了仔细研究. 结果发现, 在相同的能量下, 胶子喷注的角分布范围比夸克喷注的角分布范围要明显宽一些. 在带电粒子数、横动量相同的条件下, 胶子喷注的平均圆锥角比夸克喷注的平均圆锥角大很多. 喷注的平均圆锥角随带电多重数以及喷注的横动量的分布都呈线性正关联. 由不同味的夸克发射的胶子产生的喷注的圆锥角分布特性相同;而不同味的夸克喷注的圆锥角分布存在明显的差异. 相似文献
10.
OPAL Collaboration G. Alexander J. Allison N. Altekamp K. Ametewee K. J. Anderson S. Anderson S. Arcelli S. Asai D. Axen et al. 《Zeitschrift fur Physik C Particles and Fields》1995,69(1):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 thek
⊥ jet finder withy
cut=0.02, we find
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
11.
12.
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
13.
B.R. Webber 《Nuclear Physics B》1984,238(3):492-528
A new model for hadronic jet fragmentation in hard processes is presented. It is based on a QCD parton branching mechanism with correct treatment of leading collinear and infra-red singularities (i.e. including soft gluon interference). Hadronization occurs via preconfinement of colour singlet clusters, which decay according to a simple phase-space scheme. Although tightly constrained, the model gives a good account of existing e+ e? annihilation data. It predicts significant differences between quark and gluon jets. Comparisons with datadata on the CERN p?p collider jets suggest that a large fraction of them are gluon jets. The model predicts soft gluon interference effects in hadron distributions which are probably not yet observable for pions but should be clear for kaons and baryons. 相似文献
14.
Being able to distinguish light-quark jets from gluon jets on an event-by-event basis could significantly enhance the reach for many new physics searches at the Large Hadron Collider. Through an exhaustive search of existing and novel jet substructure observables, we find that a multivariate approach can filter out over 95% of the gluon jets while keeping more than half of the light-quark jets. Moreover, a combination of two simple variables, the charge track multiplicity and the p(T)-weighted linear radial moment (girth), can achieve similar results. Our study is only Monte Carlo based, so other observables constructed using different jet sizes and parameters are used to highlight areas that deserve further theoretical and experimental scrutiny. Additional information, including distributions of around 10,000 variables, can be found at http://jets.physics.harvard.edu/qvg/. 相似文献
15.
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
16.
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
17.
A quark or gluon jet traversing through a quark-gluon plasma can be converted to a gluon or quark jet through scattering with
the thermal quarks and gluons in the quark-gluon plasma. Their conversion rates due to two-body elastic
and inelastic
scattering have recently been evaluated in the lowest order in QCD. Including both energy loss and conversions of quark and
gluon jets in the expanding quark-gluon plasma produced in relativistic heavy ion collisions, a net conversion of quark jets
to gluon jets has been found. This reduces the difference between the nuclear modification factors for quark and gluon jets
in heavy ion collisions and thus enhances the ratios of high transverse momentum protons and antiprotons to pions that are
produced from the fragmentation of these jets. To account for the observed similar ratios in central Au + Au and p + p collisions at same energy requires, however, a much larger net quark to gluon jet conversion rate than that given by the
lowest-order QCD, indicating the importance of higher-order processes and the strongly coupling properties of the quark-gluon
plasma in describing the propagation of jets in the quark-gluon plasma.
B.-W. Zhang: On leave from: Institute of Particle Physics, Huazhong Normal University, Wuhan 430079, China
Correspondence: C.-M. Ko, Cyclotron Institute and Physics Department, Texas A&M University, College Station, TX 77843-3366,
USA 相似文献
18.
A method is introduced for distinguishing top jets (boosted, hadronically decaying top quarks) from light-quark and gluon jets using jet substructure. The procedure involves parsing the jet cluster to resolve its subjets and then imposing kinematic constraints. With this method, light-quark or gluon jets with p{T} approximately 1 TeV can be rejected with an efficiency of around 99% while retaining up to 40% of top jets. This reduces the dijet background to heavy tt[over ] resonances by a factor of approximately 10 000, thereby allowing resonance searches in tt[over ] to be extended into the all-hadronic channel. In addition, top tagging can be used in tt[over ] events when one of the top quarks decays semileptonically, in events with missing energy, and in studies of b-tagging efficiency at high p{T}. 相似文献
19.
The averaged jet charge characterizes the electric charge of the initiating parton and provides a powerful tool to distinguish quark jets from gluon jets.We predict,for the first time,the medium modification of the averaged jet charge in the heavy-ion collisions at the LHC,where jet productions in p+p collisions are simulated by PYTHIA6,and the parton energy loss in QGP is calculated with two Monte Carlo models of jet quenching:PYQUEN and JEWEL.We found that the distribution of averaged jet charge is significantly suppressed by initial state isospin effects due to the participation of neutrons with zero electric charge during nuclear collisions.The considerable enhancement of the averaged jet charge in central Pb+Pb collisions is observed relative to peripheral collisions,since the jet quenching effect is more pronounced in central collisions.The distinct feature of the averaged jet charge between quark and gluon jets,along with the sensitivity of medium modifications on the jet charge to flavor dependence of the parton energy loss,could be very useful to discriminate the energy loss pattern between quark and gluon jets in heavy-ion collisions. 相似文献
20.
A. I. Ahmadov Yu. M. Bystritskiy E. A. Kuraev 《Journal of Experimental and Theoretical Physics》2011,113(4):637-646
Differential cross sections of processes with high-energy p(-p)p collisions—creation of a scalar, a pseudoscalar and a lepton pair—are considered in the Weizsacker-Williams approximation
in QED in the QCD framework, processes with conversion of the initial proton (antiproton) to fermionic jets accompanied with
one gluon jet and the state of two gluons and a quark-antiquark pair (without a rapidity gap) are considered in the framework
of the effective Regge action of Lipatov’s theory. The process of creation of a Higgs boson accompanied with two fermionic
jets is considered. The azimuthal correlation in the process of two gluon jets separated by a rapidity gap is investigated.
The gluon Reggeization effects are taken into account. Some distributions are illustrated by numerical calculations. 相似文献