Yoshitaka Hatta, Toshihiro Matsuo
We compute the inclusive spectrum of produced particles in e+e- annihilation in confining gauge theories that have a gravity dual and show that the momentum distribution exhibits the thermal behavior.
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In the framework of quark-hadron duality, the cross section values of charmonium and doubly charmed baryon production in $e^+e^-$-annihilations have been estimated at interaction energy $\sqrt{s}=10.6$ GeV. It has been shown that the approach under discussion allows to resolve some contradictions between the experimental data and pQCD predictions.
We provide a brief summary of recent developments in QCD calculations in and beyond fixed-order perturbation theory, for observables in $e^{+}e^{-}$ annihilation as well as hadron collisions.
We study factorization of processes involving two fragmentation functions in the case of very small transverse momenta. We consider two-hadron production in inclusive $e^+ e^-$ annihilation and demonstrate a new simple and illustrative method of factorization for such processes including leading order $α_S$ corrections.
It is shown that simple extension of the modified negative binomial distribution describes negatively charged particle multiplicity distributions in e+e- annihilation, measured in the whole phase space, as well as the modified negative binomial.
We study deep inelastic scattering at large-'t Hooft coupling and finite $x$ from gauge/string duality beyond single-hadron final states which gives the leading large-$N_c$ contribution. Within the supergravity approximation, we calculate the subleading large-$N_c$ contribution by introducing an extra hadron into the final states. We find the contribution from these double-hadron final states will dominate in the Bjorken limit $q^2\rightarrow \infty$ compared with the single-hadron states. We discuss the implications of our results.
The experimental charged particles multiplicity distributions in $e^+e^-$ annihilation to hadrons are compared with the distributions obtained by PYTHIA. The ratio $χ^2$/degrees of freedom is calculated for 6 energies at $\sqrt{s}$ 14 -- 206.2 GeV. The necessity of more subtle tuning of PYTHIA at the energy of $Z^0$ peak is discussed.
It is shown that charged hadron multiplicity distributions in restricted (pseudo)rapidity intervals in e+e- annihilation and in e+p scattering at HERA are quite well described by the modified negative binomial distribution and its simple extension.
We study the scaling regime of hadron-(anti)-hadron annihilation into a deeply virtual photon and a real photon, H anti-H -> gamma^* gamma, and deep backward virtual Compton scattering, gamma^* H -> H gamma. We advocate that there is a kinematical region where the scattering amplitude factorizes into a short-distance matrix element and a long-distance dominated object: a transition distribution amplitude which describes the hadron to photon transition.
A new treatment of Bose-Einstein correlations is incorporated in a space-time parton-shower model for e+ e- annihilation into hadrons. Two alternative afterburners are discussed, and we use a simple calculable model to demonstrate that they reproduce successfully the size of the hadron emission region. One of the afterburners is used to calculate two-pion correlations in e+ e- -> Z^0 -> hadrons and e+ e- -> W+ W- -> hadrons. Results are shown with and without resonance decays, for correlations along and transverse to the thrust jet axis in these two classes of events.
We study the structures in cross sections and R ratios concerning electron-positron annihilation reactions, for open-strangeness, open-charm and open-beauty hadron-pair production, from the perspective of a recently developed production formalism. Special attention is paid to non-resonant contributions. Known, tentative, and yet unknown resonances are spotted, with estimates for their masses and widths.
We discuss the production of two hadrons in e+e- annihilation within the framework of perturbative QCD. The cross section for this process is calculated to next-to-leading order accuracy with a selection of variables that allows the consideration of events where the two hadrons are detected in the same jet. In this configuration we contemplate the possibility that the hadrons come from a double fragmentation of a single parton. The double-fragmentation functions required to describe the transition of a parton to two hadrons are also necessary to completely factorize all collinear singularities…
We present the first genuine QCD five-loop calculation of the vacuum polarization functions: analytical terms of order alpha_s^4 n_f^2 to the absorptive parts of vector and scalar correlators. These corrections form an important gauge-invariant subset of the full O(alpha_s^4) correction to $e^+ e^- annihilation into hadrons and the Higgs decay rate into hadrons respectively. They discriminate between different widely used estimates of the full result.
We suggested that longitudinal polarization of Lambda produced in e+e- annihilation at LEP energies can provide useful information on hadronization mechanism in general and on testing the validity of different pictures for the spin content of baryon in describing the fragmentation process in particular. We present the results obtained from the calculations based on two very much different pictures.We compare the results with the recent ALEPH data and make suggestions for future measurements.
We discuss the production of hadrons in $e^+e^-$ collisions at $\sqrt s=91$ GeV. We address the question wether the particle yields measured in the final states are consistent with the statistical model predictions. In the model formulation we account for exact conservation of all relevant quantum numbers using the canonical description of the partition function. Within our model the validity of the thermodynamical approach to quantify particle production in $e^+e^-$ annihilations is not obvious.
We compute the nonleptonic weak decay width of a heavy-light meson in 1+1 spacetime dimensions with a large number of QCD colors (the 't Hooft model) as a function of the heavy quark mass. In this limit, QCD is exactly soluble, and decay modes are dominated by two-particle final states. We compare the results to the tree-level partonic decay width of the heavy quark in order to test quark-hadron duality in this universe. We find that this duality is surprisingly well satisfied in the heavy quark limit, in that the difference between the sum of exclusive partial widths and the tree-level parton…
The charged particles multiplicity distribution in the KNO form is discussed in processes of $e^+e^-$ annihilation at energies $\sqrt{s}$ 14 -- 206.2 GeV. The experimental data are compared to data, obtained with Monte Carlo simulation in PYTHIA in the Lund quark string model. It is shown, that both experimental and simulated data are described by the same distribution function in the KNO form. It is shown, that the KNO scaling is consequence of quark string hadronization dynamics in the Lund string model.
The multiple hadron production in the events induced by the heavy primary quarks in $e^+e^-$ annihilation is reconsidered with account of corrected experimental data. New value for the multiplicity in $b\bar{b}$ events is presented on the basis of pQCD estimates.
We apply collinear expansion to inclusive hadron production in $e^+e^-$ annihilation and derive a formalism suitable for systematic study of leading as well as higher twist contributions to fragmentation functions at the tree level. We make the calculations for hadrons with spin-0, spin-1/2 as well as spin-1 and obtain the results in terms of different components of fragmentation functions for the hadronic tensors, the differential cross section as well as hadron polarizations in different cases. The results show a number of interesting features such as the existence of transverse polarization…
We present the results of the tree-level calculation of inclusive two-hadron production in electron-positron annihilation via one photon up to subleading order in 1/Q. We consider the situation where the two hadrons belong to different, back-to-back jets. We include polarization of the produced hadrons and discuss azimuthal dependences of asymmetries. New asymmetries are found, in particular there is a leading cos(2 phi) asymmetry, which is even present when hadron polarization is absent, since it arises solely due to the intrinsic transverse momenta of the quarks.
Modeling spin effects in electron-positron annihilation to hadrons
本研究将string+${}^3P_0$自旋相关强子化模型应用于$e^+e^-$湮灭产生的纠缠自旋夸克反夸克弦的碎裂，构建可用于蒙特卡洛事件产生器的递归方案，验证其能重现QCD预期的强子方位角分布。
The nearly energy independent hadron emitter dimension $r$, measured in $e^+e^-$ annihilation in the energy range 10 to 91 GeV via the Bose-Einstein correlation of two identical charged pions, is shown to be well accounted for by choosing the hadron jets as independent pion sources. To this end the known normalised factorial cumulant moments dependence on particle sources is adapted to the Bose-Einstein correlation formalism to yield a relation between $r$ and these sources. This approach is also able to account for the measured $r$ values obtained for the $Z^0$ decays into two and three hadro…
We apply the positive-weight Monte Carlo method of Nason for simulating QCD processes accurate to Next-To-Leading Order to the case of e+e- annihilation to hadrons. The method entails the generation of the hardest gluon emission first and then subsequently adding a `truncated' shower before the emission. We have interfaced our result to the Herwig++ shower Monte Carlo program and obtained better results than those obtained with Herwig++ at leading order with a matrix element correction.
We calculate the probability for rapidity gaps in the parton cascade for different approximations within the perturbative QCD and compare the results with recent measurements. The aim is to find out whether the dual connection between the parton and hadron final states -- observed so far in various inclusive measurements -- holds as well for the extreme kinematic configurations with colour sources separated by large rapidity gaps. A description of the data is possible indeed choosing the parameters of the cascade in the range suggested by recent analyses of the energy spectra (the $k_\perp$ cu…
A novel procedure for extracting hadron characteristics from QCD sum rules, based on effective continuum thresholds (necessary for the implementation of quark-hadron duality) which may depend on the involved momenta and on the Borel parameter(s), enables us to quantify the uncertainties induced by the quark-hadron duality approximation and to achieve a significantly higher accuracy of our predictions for the properties of hadronic bound states.
The explicit expression for the R-ratio of electron-positron annihilation into hadrons, which properly accounts for all the effects due to continuation of the spacelike perturbative results into the timelike domain, is obtained at an arbitrary loop level. Several equivalent ways to derive a commonly employed approximation of the R-ratio are recapped and the impact of discarded in the latter higher-order pi2-terms on the evaluation of the strong running coupling is elucidated. The obtained results substantially facilitate the theoretical study of electron-positron annihilation into hadrons and …
The collimation $C$ of a hadronic event in the e^+e^- annihilation is defined as the average of $\cosθ$, $C=<\cosθ>$, where $θ$ is the angle of each hadron measured from the thrust axis, and the average is over all the hadrons produced in an event. It is an infrared-stable event-shape parameter. $1-\bar C$, the difference between the unity and the average collimation at a given energy, is proportional to the anomalous dimension of the hadron multiplicity at the leading order in MLLA. Its next-to-leading order corrections are calculated.
In reference to the recently observed high Q^2, large x events in deep-inelastic positron-proton scattering at HERA, various leptoquark and supersymmetric scenarios are discussed. We study the impact of virtual leptoquark or R-parity breaking squark exchange as well as generic contact interaction on the production of quark-antiquark pairs in $e^+e^-$ annihilation, in particular at LEP2.
We present the leading unpolarized and single spin asymmetries in inclusive two-hadron production in electron-positron annihilation at the Z pole. The azimuthal dependence in the unpolarized differential cross section of almost back-to-back hadrons is a leading cos(2 phi) asymmetry, which arises solely due to the intrinsic transverse momenta of the quarks. An extensive discussion on how to measure this asymmetry and the accompanying time-reversal odd fragmentation functions is given. A simple estimate indicates that the asymmetry could be of the order of a percent.
In this paper we present an analysis of the multiple hadron production induced by primary heavy quarks in e+e- annihilation with the account of most complete and corrected experimental data. In the framework of perturbative QCD, new theoretical bounds on the asymptotically constant differences of the multiplicities in processes with light and heavy quarks are given.
Electron-positron annihilation into hadrons plus an energetic photon from initial state radiation allows the hadronic cross-section to be measured over a wide range of energies. The full next-to-leading order QED corrections for the cross-section for e^+ e^- annihilation into a real tagged photon and a virtual photon converting into hadrons are calculated where the tagged photon is radiated off the initial electron or positron. This includes virtual and soft photon corrections to the process e^+ e^- \to γ+γ^* and the emission of two real hard photons: e^+ e^- \to γ+ γ+ γ^*. A Monte Carlo gener…
We show that heavy meson hadronic decay widths satisfy quark-hadron duality when smeared over the heavy quark mass, M, to an accuracy of order 1/M^2.
The processes of D^{(*)}-mesons and Λ_c-baryons production in e^+e^--annihilation at 10.58 GeV and 91.18 GeV energies are concerned. At the 10.58 GeV energy the production of charmed particles via the B-mesons decays is also concerned. Scaling violation of the fragmentation functions is calculated at the NLL-accuracy. Nonperturbative fragmentation functions are retrieved from the experimental data of B-factories and are approximated by simple analytic expressions. It is proved, that the difference between nonperturbative fragmentation functions of mesons and baryons can be easily explained by …
We report on the analytic calculation of the second-order QCD corrections to semi-inclusive hadron production in electron-positron annihilation. The calculation of the single-particle inclusive cross-section in time-like kinematics is performed in Mellin N-space and uses an algorithmic evaluation of inclusive phase-space integrals, based on the unitarity cutting rules and integration-by-parts. We obtain splitting functions and coefficient functions up to second order in the strong coupling alpha_s. Our results are in agreement with earlier calculations in the literature by Rijken and van Neerv…
Recursive solution for a general homogeneous in time pure birth branching process with simultaneous production of any number of particles and with continuous evolution parameter is given. Calculational algorithm based on the use of Koenigs function and functional Schroder equation is described. It is shown that multiplicity distributions in e+e- annihilation into hadrons for c.m. energies up to 189 GeV are well described by the modified negative binomial distribution, explained by simple pure birth branching process without multiple simultaneous particle production. The energy dependence of th…
Assuming so called global duality we argue that it is very likely that local duality needed to obtain results for the hadronic width of heavy meson decays within the $1/m_Q$ expansion holds. Hence, if the discrepancy between experiment and the theory concerning charm counting, the semileptonic branching fraction and the lifetimes of $b$ hadrons persist, it may be taken as a hint at some qualitatively new effect in (nonperturbative) QCD or even as a new physics.
We show that, based on the idea of string fragmentation, the production rates of light flavored mesons and baryons originating from fragmentation can be described by the spin, the binding energy of the particle, and a strangeness suppression factor. Apart from a normalization factor, $e^+ e^-$ data at different center-of-mass energies can be described simultaneously. Applying to the heavy flavor production, we find that our predictions are in good agreement with data.
High-energy behavior of R-ratio of electron-positron annihilation into hadrons is studied. In particular, it is argued that at any given order of perturbation theory the re-expansion of the R-ratio in the ultraviolet asymptotic can be reduced to the form of power series in the naive continuation of the strong running coupling into the timelike domain. The convergence range of the re-expanded R-ratio and the corresponding higher-order pi2-terms are discussed.
We present nonperturbative fragmentation functions (FFs) for bottom-flavored ($B$) hadrons both at next-to-leading (NLO) and, for the first time, at next-to-next-to-leading order (NNLO) in the $\overline{\mathrm{MS}}$ factorization scheme with five massless quark flavors. They are determined by fitting all available experimental data of inclusive single $B$-hadron production in $e^+e^-$ annihilation, from the ALEPH, DELPHI, and OPAL Collaborations at CERN LEP1 and the SLD Collaboration at SLAC SLC. The uncertainties in these FFs as well as in the corresponding observables are estimated using t…
The forward-backward asymmetry is an important measurable quantity which can enable independent determination of the neutral-current couplings of fermions. In this paper, we extend the definition of the asymmetry from the partonic level to the hadronic level by calculating this asymmetry of the hadron pair in the semi-inclusive electron position annihilation process. Semi-inclusive implies that a back-to-back jet is also measured in addition to the hadron pair. Due to the limitation of the factorization theorem, we calculate this process up to leading order twist-4 level by applying the collin…
Quark-hadron duality addresses some of the most fundamental issues in strong interaction physics, in particular the nature of the transition from the perturbative to non-perturbative regions of QCD. I summarize recent developments in quark-hadron duality in lepton-hadron scattering, and outline how duality can be studied at future high-luminosity facilities such as Jefferson Lab at 12 GeV, or an electron-hadron collider such as EPIC.
Quark-meson duality for two-point functions of vector and axial-vector QCD currents is investigated in the large-Nc approximation. We find that the joint constraints of duality and chiral symmetry imply degeneracy of excited vector and axial-vector mesons in the large-Nc limit. We compare model-independent constraints with expectations based on the Veneziano-Lovelace-Shapiro string model. Several models of duality are constructed, and phenomenological implications are discussed.
We investigate the origin of the quark-hadron duality-violating terms in the expansion of the QCD two-point vector correlation function at large energies in the complex $q^2$ plane. Starting from the dispersive representation for the associated polarization, the analytic continuation of the operator product expansion from the Euclidean to the Minkowski region is performed by means of a generalized Borel-Laplace transform, borrowing techniques from hyperasymptotics. We establish a connection between singularities in the Borel plane and quark-hadron duality violating contributions. Starting with…
Factorizing the cross section for single hadron production in $e^+e^-$ annihilations, differential in $z_h$, $P_T$ and thrust, is a highly non trivial task. We have devised a factorization scheme that allows us to recast the $e^+e^- \to hX$ cross section in the convolution of a perturbatively calculable coefficient and a universal Transverse Momentum Dependent (TMD) Fragmentation Function (FF). The predictions obtained from our NLO-NLL perturbative computation, together with a simple ansatz to model the non-perturbative part of the TMD, are applied to the experimental measurements of the BELLE…
The precise determination of the cross section for electron-positron annihilation into hadrons is one of the central tasks of ongoing experiments at low energy colliders. These measurements have to be complemented by Monte Carlo generators which simulate a large number of final states and include higher order radiative corrections. With this motivation in mind the generator PHOKHARA is extended to allow for the simulation of final states with zero, one or two real photons. At the same time corrections from the emission of one or two virtual photons are included, such that a full next-to-next-t…
Duality is not violated at order Delta/M once j=3/2 and j=1/2+ states are properly accounted for.
Quark-hadron duality and its potential applications are discussed. We focus on theoretical efforts to model duality.
The annihilation of the $B_c$ meson to leptons and inclusive light hadrons is analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find that the decay mode, which escapes from the helicity suppression, contributes a sizable fraction width. According to the analysis, the branching ratio due to the contribution from the color-singlet component of the meson $B_c$ can be of order (10^{-2}). We also estimate the contributions from the color-octet components. With the velocity scaling rule of NRQCD, we find that the color-octet contributions are sizable too, especially, in cert…
We present the complete leading-order results for the azimuthal dependences and polarization observables in $e^+e^-\to h_1 h_2 + X$ processes, where the two hadrons are produced almost back-to-back, within a transverse momentum dependent (TMD) factorization scheme. We consider spinless (or unpolarized) and spin-1/2 hadron production and give the full set of the corresponding quark and gluon TMD fragmentation functions (TMD-FFs). By adopting the helicity formalism, which allows for a more direct probabilistic interpretation, single- and double-polarization cases are discussed in detail. Simplif…
We provide complete analytic expressions for the inclusive prompt photon production cross section in hadronic final states of $e^+e^-$ annihilation reactions through one-loop order in quantum chromodynamics perturbation theory. Computed explicitly are direct photon production through first order in the electromagnetic strength $α_{em}$ and the quark-to-photon and gluon-to-photon fragmentation contributions through first order in the strong coupling $α_s$. The full angular dependence of the cross sections is displayed, separated into transverse $(1 +\cos ^2θ_γ)$ and longitudinal $(\sin ^2θ_γ)$ …
The reactions of electron-positron to nucleon-antinucleon pairs are studied in a non-perturbative quark model. The work suggests that the two-step process, in which the primary quark-antiquark pair forms first a vector meson which in turn decays into a hadron pair, is dominant over the one-step process in which the primary quark-antiquark pair is directly dressed by additional quark-antiquark pairs to form a hadron pair. To reproduce the experimental data of the reactions of electron-positron to proton-antiproton and electron-positron to neutron-antineutron a D-wave omega-like vector meson wit…
Interplay between axial anomaly and quark-hadron duality in the presence of strong mixing is considered. The anomaly sum rule for meson transition form factors based on the dispersive representation of axial anomaly and quark-hadron duality in octet channel is analyzed. The comparison of this sum rule to the experimental data on $η$ and $η'$ mesons transition form factors shows that the interval of duality in this channel is rather small, contradicting the usual understanding of quark-hadron duality. The same values of interval of duality are supported by considering the two-point correlator i…
Single-inclusive hadron production in electron-positron annihilation at next-to-next-to-next-to-leading order in QCD
本研究首次完成电子-正电子湮灭单举强子产生过程的QCD N³LO阶系数函数解析计算，以BaBar数据为基准验证其可降低标度不确定性、提升实验数据描述精度，推动强子化动力学研究。
We discuss (i) the evaluation of the expectation values of four-quark operators assuming that the heavy quark expansion for $b$ sector converges at the third order in $1/m_Q$, and (ii) the estimation of the duality breaking short distance nonperturbative corrections to the parton decay rate. We finally point out the implications of the result obtained for the assumption of quark-hadron duality in heavy quark expansion.
We study the transverse momentum distributions of single inclusive hadron production in ${e^ + }{e^ - }$ annihilation processes. Although the only available experimental data are scarce and quite old, we find that the fundamental features of transverse momentum dependent (TMD) evolution, historically addressed in Drell-Yan processes and, more recently, in Semi-inclusive deep inelastic scattering processes, are visible in ${e^ + }{e^ - }$ annihilations as well. Interesting effects related to its non-perturbative regime can be observed. We test two different parameterizations for the $p_\perp$ d…
In this work we discuss the practical and conceptual issues related to quark-hadron-duality in heavy-heavy systems. Recent measurements in the charmonium region allow a direct test of quark-hadron-duality. We present a formula for non-resonant background production in e^+ e^- \to D{\bar D} and extract the resonance parameters of the ψ(3S)-ψ(6S). The obtained results are used to investigate the upsilon energy range.
We discuss the allowed parameter regime in the coupling-mass plane implied by the existing LEP2 data on e+ e- -> hadrons at 172.3 GeV for the leptoquark interpretation of the anomalous DESY positron-jet events for four different models of the leptoquark charges and chiral couplings to quarks, for both a loose cut on s'/s and a tight cut on s'/s. We find that this interpretation of the DESY phenomenon is still consistent with the LEP2 data although, for vector leptoquarks, a significant regime of the relevant parameter space is already excluded.
The process $e^+e^- \to q \bar q γ$ contains radiation zeros, i.e. configurations of the four-momenta for which the scattering amplitude vanishes. We calculate the positions of these zeros for $u$--quark and $d$--quark production and assess the feasibility of identifying the zeros in experiments at high energies. The radiation zeros are shown to occur also for massive quarks, and we discuss how the $b \bar b γ$ final state may offer a particularly clean environment in which to observe them.
Explicit quark-hadron duality in the limit of heavy quark mass is studied using the 't Hooft model, where both partonic and hadronic amplitudes may be computed exactly. Results for weak decays of heavy mesons are presented for both standard spectator decays, where the duality limit is convincingly approached, and annihilation decays of the valence quark-antiquark pair, where the approach to asymptotic duality is much less precise.
The leptonic tensor for the process $e^+ e^- \to γ+γ^*$, which describes the next-to-leading order virtual and soft QED corrections to initial state radiation in $e^+ e^-$ annihilation with emission of an extra virtual photon decaying into hadrons, is calculated. A Monte Carlo generator for the reaction $e^+ e^- \to γ+ π^+ π^-$ has been set up which includes these corrections. It thus describes configurations where the invariant mass of the hadrons plus photon is very close to $\sqrt{s}$. Predictions for cms energies of 1 to 10 GeV, corresponding to the energies of DAPHNE and B-meson factories…
We discuss the issue of the local quark-hadron duality at high energies in two- and four-dimensional QCD. A mechanism of the dynamical realization of the quark-hadron duality in two- dimensional QCD in the limit of large number of colors, N_c -> \infty, (the 't Hooft model) is considered. A similar mechanism of dynamical smearing may be relevant in four-dimensional QCD. Although particular details of our results are model-dependent, the general features of the duality implementation conjectured previously get further support.
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