共查询到20条相似文献,搜索用时 15 毫秒
1.
G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》1999,10(4):547-561
Di-jet production is studied in collisions of quasi-real photons radiated by the LEP beams at ee centre-of-mass energies and 172 GeV. The jets are reconstructed using a cone jet finding algorithm. The angular distributions of direct and double-resolved
processes are measured and compared to the predictions of leading order and next-to-leading order perturbative QCD. The jet
energy profiles are also studied. The inclusive di-jet cross-section is measured as a function of and and compared to next-to-leading order perturbative QCD calculations. The inclusive di-jet cross-section as a function of
is compared to the prediction of the leading order Monte Carlo generators PYTHIA and PHOJET. The Monte Carlo predictions
are calculated with different parametrisations of the parton distributions of the photon. The influence of the ‘underlying
event’ has been studied to reduce the model dependence of the predicted jet cross-sections from the Monte Carlo generators.
Received: 15 July 1999 / Published online: 12 August 1999 相似文献
2.
J.M. Campbell M.A. Cullen E.W.N. Glover 《The European Physical Journal C - Particles and Fields》1999,9(2):245-265
We report next-to-leading order perturbative QCD predictions of 4 jet event shape variables for the process obtained using the general purpose Monte Carlo EERAD2. This program is based on the known `squared' one loop matrix elements for the virtual parton contribution and squared matrix elements for 5 parton production. To combine the two distinct final states numerically
we present a hybrid of the commonly used subtraction and slicing schemes based on the colour antenna structure of the final
state which can be readily applied to other processes. We have checked that the numerical results obtained with EERAD2 are consistent with next-to-leading order estimates of the distributions of previously determined four jet-like event variables.
We also report the next-to-leading order scale independent coefficients for some previously uncalculated observables; the
light hemisphere mass, narrow jet broadening and the 4 jet transition variables with respect to the JADE and Geneva jet finding
algorithms. For each of these observables, the next-to-leading order corrections calculated at the physical scale significantly
increase the rate compared to leading order (the K factor is approximately 1.5–2). With the exception of the 4 jet transition
variables, the published DELPHI data lies well above the predictions. The renormalisation scale uncertainty is still large and in most cases the data prefers a scale significantly
smaller than the physical scale. This situation is reminiscent of that for three jet shape variables, and should be improved
by the inclusion of power corrections and resummation of large infrared logarithms.
Received: 17 November 1998 / Revised version: 26 January 1999 / Published online: 7 April 1999 相似文献
3.
O. Kodolova I. Vardanyan A. Nikitenko A. Oulianov 《The European Physical Journal C - Particles and Fields》2007,50(1):117-123
A jet reconstruction algorithm is developed for events with a high particle density in the calorimetric system. The performance
of the reconstruction of hard QCD jets with initial parton energies 50–300 GeV is studied in central Pb–Pb collisions with
a modified cone jet finder which includes an algorithm for event-by-event background subtraction. The heavy ion background
is simulated using the HIJING Monte Carlo generator with . Results on the achieved jet reconstruction efficiency, purity, energy and spatial resolution are presented. 相似文献
4.
X. Liu Q. Lu P. Liu M. Zhao Z. Wang M. Ying F. Li L. Qin 《Applied Physics A: Materials Science & Processing》2003,76(2):273-275
Range distributions for bismuth ions implanted in AgGaSe2 in the energy range 80–300 keV were investigated by using 2.1-MeV He2+ Rutherford backscattering spectrometry (RBS). A convolution calculation method was used to extract the true distributions
of bismuth from the measured RBS spectra. The range distribution parameters, Rp and ΔRp, were obtained and compared with those obtained from Monte Carlo simulation. The experimental Rp values agree with the Monte Carlo simulation values very well, but the experimental ΔRp values are systematically larger than those from the theoretical simulation.
Received: 28 January 2002 / Accepted: 11 April 2002 / Published online: 10 September 2002
RID="*"
ID="*"Corresponding author. Fax: +86-531/856-5167, E-mail: xdliu@sdu.edu.cn 相似文献
5.
《The European Physical Journal C - Particles and Fields》2006,47(2):273-294
Soft photons inside hadronic jets converted in front of the DELPHI main tracker (TPC) in events of qq̄ disintegrations of
the Z0 were studied in the kinematic range 0.2<Eγ<1 GeV and transverse momentum with respect to the closest jet direction pT<80 MeV/c. A clear excess of photons in the experimental data as compared to the Monte Carlo predictions is observed. This
excess (uncorrected for the photon detection efficiency) is (1.17±0.06±0.27)×10-3 γ/jet in the specified kinematic region, while the expected level of the inner hadronic bremsstrahlung (which is not included
in the Monte Carlo) is (0.340±0.001±0.038)×10-3 γ/jet. The ratio of the excess to the predicted bremsstrahlung rate is then (3.4±0.2±0.8), which is similar in strength to
the anomalous soft photon signal observed in fixed target experiments with hadronic beams. 相似文献
6.
Masuo Suzuki 《Journal of statistical physics》1986,43(5-6):883-909
A short review is given concerning the quantum statistical Monte Carlo method based on the equivalence theorem(1) thatd-dimensional quantum systems are mapped onto (d+1)-dimensional classical systems. The convergence property of this approximate tansformation is discussed in detail. Some
applications of this geneal appoach to quantum spin systems are reviewed. A new Monte Carlo method, “thermo field Monte Carlo
method,” is presented, which is an extension of the projection Monte Carlo method at zero temperature to that at finite temperatures.
Invited talk presented at “Frontiers of Quantum Monte Carlo,” Los Alamos National Laboratory, September 3–6, 1985. 相似文献
7.
The Michel parameters of the leptonic decays are measured using the OPAL detector at LEP. The parameters , , (with ) and are extracted from the energy spectra of the charged decay leptons and from their energy–energy correlations. A new method
involving a global likelihood fit of Monte Carlo generated events with complete detector simulation and background treatment
has been applied to the data recorded at center-of-mass energies close to corresponding to an integrated luminosity of 155 pb. If e- universality is assumed and inferring the polarization from neutral current data, the measured Michel parameters are: where the value of has been constrained using the published OPAL measurements of the leptonic branching ratios and the lifetime. Limits on non-standard coupling constants and on the masses of new gauge bosons are obtained. The results are in
agreement with the V–A prediction of the Standard Model.
Received: 25 June 1998 / Published online: 1 March 1999 相似文献
8.
The photon structure function has been measured using data taken by the OPAL detector at centre-of-mass energies of 91 GeV, 183 GeVand 189 \GeV, in ranges of 1.5–30.0 GeV (LEP1), and 7.0–30.0 GeV (LEP2), probing lower values of x than ever before. Since previous OPAL analyses, new Monte Carlo models and new methods, such as multi-variable unfolding,
have been introduced, reducing significantly the model dependent systematic errors in the measurement. The results do not
conclusively prove, but are completely consistent with, the presence of a rise in at low-x as expected from QCD.
Received: 9 June 2000 / Published online: 13 November 2000 相似文献
9.
Weilun Jiang 《中国物理 B》2022,31(4):40504-040504
We systematically test the performance of several Monte Carlo update schemes for the (2+1)d XY phase transition of quantum rotor model. By comparing the local Metropolis (LM), LM plus over-relaxation (OR), Wolff-cluster (WC), hybrid Monte Carlo (HM), hybrid Monte Carlo with Fourier acceleration (FA) schemes, it is clear that among the five different update schemes, at the quantum critical point, the WC and FA schemes acquire the smallest autocorrelation time and cost the least amount of CPU hours in achieving the same level of relative error, and FA enjoys a further advantage of easily implementable for more complicated interactions such as the long-range ones. These results bestow one with the necessary knowledge of extending the quantum rotor model, which plays the role of ferromagnetic/antiferromagnetic critical bosons or Z2 topological order, to more realistic and yet challenging models such as Fermi surface Yukawa-coupled to quantum rotor models. 相似文献
10.
11.
《The European Physical Journal C - Particles and Fields》2007,52(3):515-530
Forward jet cross sections have been measured in neutral current deep inelastic scattering at low Bjorken-x with the ZEUS
detector at HERA using an integrated luminosity of 81.8 pb-1. Measurements are presented for inclusive forward jets as well as for forward jets accompanied by a dijet system. The explored
phase space, with jet pseudorapidity up to 4.3 is expected to be particularly sensitive to the dynamics of QCD parton evolution
at low x. The measurements are compared to fixed-order QCD calculations and to leading-order parton-shower Monte Carlo models. 相似文献
12.
Steven C. Pieper 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):75-79
Quantum Monte Carlo calculations using realistic two- and three-nucleon interactions are presented for nuclei with up to ten
nucleons. Our Green's function Monte Carlo calculations are accurate to ∼1-2% for the binding energy. We have constructed
Hamiltonians using the Argonne v18
NN interaction and reasonable three-nucleon interactions that reproduce the energies of these nuclear states with only ∼500
keV rms error. Other predictions, such as form factors, decay rates, and spectroscopic factors also agree well with data.
Some of these results are presented to show that ab initio calculations of light nuclei are now well in hand.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
13.
The average particle multiplicity density dN
ch/dη is the dynamical quantity that reflects some regularities of particle production in the low-p
T
range. The quantity is an important ingredient of z scaling. Experimental results on charged particle density are available for pp, pA, and AA collisions, while experimental properties of the jet density are still an open question. The goal of this work is to find
the variable that will reflect the main features of the jet production in a low transverse energy range and play the role
of the scale factor for the scaling function ψ(z) and variable z in data z-presentation. The appropriate candidate is the variable we called “scaled jet energy density.” The scaled jet energy density
is the probability of having a jet with defined E
T
in defined x
T
and pseudorapidity regions. The PYTHIA6.2 Monte Carlo generator is used for calculation of the scaled jet energy density
in proton-proton collisions over a high energy range
and at η = 0. The properties of the new variable are discussed and sensitivity to “physical scenarios” applied in the standard
Monte Carlo generator is noted. The results of the calculations of scaled jet energy density at LHC energies are presented
and compared with predictions based on z scaling.
The text was submitted by the authors in English. 相似文献
14.
V. I. Kristya 《Technical Physics》1998,43(6):664-667
A numerical method is developed for solving the equation for the heavy-ion total-energy distribution function in the cathode
sheath of a glow discharge in an inert-gas mixture which requires much less computer time than the Monte Carlo method. It
is shown that it allows one to calculate with satisfactory accuracy the energy spectrum of the heavy ions bombarding the cathode
in glow-discharge devices.
Zh. Tekh. Fiz. 68, 56–59 (June 1998) 相似文献
15.
16.
Electron-positron production processes occurring in the interaction of 1018–1020 W/cm2 laser radiation with high-Z targets are examined. Computational results are presented for the pair production and the positron yield from the target
with allowance for the contribution of pair production processes due to electrons and bremsstrahlung photons. Monte Carlo
simulations using the PRIZMA code confirm the estimates obtained. The possible positron yield from high-Z targets irradiated with 102–103 TW laser radiation is estimated to be 109–1011.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 4, 239–244 (25 February 1998) 相似文献
17.
在e+p深度非弹性散射的光子胶子融合过程中有可能出现瞬子. 这是
一类特殊的事件, 称为瞬子参与的深度非弹性散射事件. 本文用蒙特卡罗事件产生器QCDINS讨论了在瞬子参与的深度非弹性散射事件中识别瞬子末态和流喷注的方法. 对各种不同方法作了对比研究. 找到了一种能使重建得到的喷注能量、瞬子能量、瞬子质量与强子化前的取值均比较接近的最佳方法. 相似文献
18.
《The European Physical Journal C - Particles and Fields》2007,49(2):511-522
The photoproduction of prompt photons, together with an accompanying jet, has been studied in ep collisions at a centre-of-mass
energy of 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 77 pb-1. Cross sections were measured for the transverse energy of the photon and the jet larger than 5 and 6 GeV, respectively.
The differential γ+jet cross sections were reconstructed as functions of the transverse energy, pseudorapidity and xγ
obs, the fraction of the incoming photon momentum taken by the photon-jet system. Predictions based on leading-logarithm parton-shower
Monte Carlo models and next-to-leading-order (NLO) QCD generally underestimate the cross sections for the transverse energies
of prompt photons below 7 GeV, while the kT-factorisation QCD calculation agrees with the data better. When the minimum transverse energy of prompt photons is increased
to 7 GeV, both NLO QCD and the kT-factorisation calculations are in good agreement with the data. 相似文献
19.
Inclusive photoproduction of mesons has been measured for photon-proton centre-of-mass energies in the range GeV and photon virtuality 1 GeV. The data sample used corresponds to an integrated luminosity of 37 pb. Total and differential cross sections as functions of the transverse momentum and pseudorapidity are presented in restricted kinematical regions and the data are compared with next-to-leading
order (NLO) perturbative QCD calculations using the “massive charm” and “massless charm” schemes. The measured cross sections
are generally above the NLO calculations, in particular in the forward (proton) direction. The large data sample also allows
the study of dijet production associated with charm. A significant resolved as well as a direct photon component contribute
to the cross section. Leading order QCD Monte Carlo calculations indicate that the resolved contribution arises from a significant
charm component in the photon. A massive charm NLO parton level calculation yields lower cross sections compared to the measured
results in a kinematic region where the resolved photon contribution is significant.
Received: 9 July 1998 / Published online: 22 October 1998 相似文献
20.
J. Piilo E. Lundh K.-A. Suominen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(2):211-222
We have developed Monte Carlo wave function simulation schemes to study
cold collisions between magnesium atoms in a strong red-detuned laser field.
In order to address the strong-field problem, we extend the Monte Carlo wave function framework to include the partial wave
structure of the three-dimensional system. The average heating rate due to radiative collisions is calculated with two different
simulation schemes which are described in detail.
We show that the results of the two methods
agree and give estimates for the radiative collision heating rate for 24Mg atoms in a magneto-optical trap based on the 1S0–1P1 atomic laser cooling transition. 相似文献