Werner K. Sauter
In this work is presented several results for cross sections of exotic particles production in electron-positron collisions in future linear electron-positron colliders. It is shown that the central production of exotic leptons, dilatons, radions, axions and technipions in this type of collision can be measurable for the predicted kinematic parameters for linear colliders.
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We study the prospects for the exotic Higgs decay mode $h\to ss\to 4τ$ at planned electron-positron colliders in the case where the beyond-the-Standard Model particle $s$ is too light to decay into $b \bar b$ pairs. We find that with 5 ab$^{-1}$ of unpolarized collisions at 240 GeV, the branching ratio into this final state can be constrained to be below $\sim 1.3\times 10^{-4}$ at 95\% CL, depending on the mass of $s$ and the assumed tracking efficiency.
We consider the electromagnetic production of positron and electron in collisions of slow heavy nuclei. This process is dominated by emission of positron, with the electron captured by nucleus.
The total and differential cross sections for the production of $Ω_{scb}$ baryons in electron-positron collisions are calculated at the $Z$-boson pole.
A fully massive Monte Carlo program to compute all four-fermion processes in electron positron collisions, including Higgs boson production, is presented. Leading higher order effects are discussed and included.
The production and decay of exotic leptons are discussed in the context of the vector singlet, vector doublet and fer\-mion mirror-fer\-mion models, at c.m. energies $\sqrt{s}=190GeV$ (LEP II) and $\sqrt{s}=500GeV$ (NLC). The model dependence of total cross sections and kinematic distributions at these energies is shown to be weak for these three extended models, indicating that it would be difficult to establish which of them is best fit to describe the underlying new physics, should exotic leptons be detected. We suggest that, in order to resolve this difficulty, one should measure the angul…
We calculated the cross section of double electron-positron pair production with two-electron capture for the collisions of Pb+Pb ions and we did our calculations at LHC energies. We applied a similar methodology for the calculation of bound-free electron-positron pair production. We used perturbation theory and implemented Monte Carlo integration techniques to calculate the lowest order Feynman diagrams. We also compared our double electron-positron pair production with two-electron capture cross section results obtained in the literature. These calculations may help us to learn more about st…
We introduce a new, fully massive, Monte Carlo program to compute all four-fermion processes in electron-positron collisions, including Higgs production. We outline our strategy for the matrix element evaluation, the phase space generation and the implementation of the leading higher order effects, and show, where available, comparisons with existing results.
Expressions for Sudakov form factors for heavy quarks are presented. They are used to construct resummed jet rates in electron-positron annihilation. Predictions are given for production of bottom quarks at LEP and top quarks at the Linear Collider.
We consider the production of ultrarelativistic parapositronium and orthopositronium atoms in collisions of high energy electrons with laser photons. Our results demonstrate the opportunity of intensive positronium beam formation with Lorentz-factor 10^6 using laser beam conversion on high energy electrons at the future Electron Linear Accelerators.
Angular and energy distributions of positrons created in subcritical and supercritical slow collisions of heavy nuclei
本文在超越单极近似的双中心框架下，利用广义伪谱方法求解含时Dirac方程，研究了重核慢碰撞中亚临界与超临界机制的正电子产生概率、能谱及角分布，发现发射正电子的角分布具有高度各向同性。
We present the CoLoRFulNNLO method to compute higher order radiative corrections to jet cross sections in perturbative QCD. We apply our method to the computation of event shape observables in electron-positron collisions at NNLO accuracy and validate our code by comparing our predictions to previous results in the literature. We also calculate for the first time jet cone energy fraction at NNLO.
The results of a complete one-loop calculation for the production of chargino pairs in electron-positron collisions, including the option of polarized beams, are presented. The calculation has been performed in the on-shell renormalization scheme. Applications to the integrated cross section, to the forward-backward asymmetry for unpolarized beams, and to the left-right asymmetry show that the higher-order effects have a sizeable influence on the theoretical predictions and therefore should be properly taken into account for detailed studies in the MSSM.
We introduce a subtraction method for jet cross sections at next-to-next-to-leading order (NNLO) accuracy in the strong coupling and use it to compute event shapes in three-jet production in electron-positron collisions. We validate our method on two event shapes, thrust and C-parameter, which are already known in the literature at NNLO accuracy and compute for the first time oblateness and the energy-energy correlation at the same accuracy.
The validity of the equivalent-photon approximation for two-photon processes in electron--positron collisions is critically examined. Commonly used forms to describe hadronic two-photon production are shown to lead to sizeable errors. An improved two-photon luminosity function is presented, which includes beyond-leading-logarithmic effects and scalar-photon contributions. Comparisons of various approximate expressions with the exact calculation in the case of the total hadronic cross section are given. Furthermore, effects of the poorly known low-Q2 behaviour of the virtual hadronic cross sect…
The scaling of charged hadron fragmentation functions to the Tsallis distribution for $0.01 \lessapprox x \lessapprox 0.2$ is presented for various $e^+e^-$ collision energies. A possible microcanonical generalisation of the Tsallis distribution is proposed, which gives good agreement with measured data up to $x\approx1$. The proposal is based on superstatistics and a $KNO$ like scaling of multiplicity distributions in $e^+e^-$ experiments.
Three-dimensional calculations of positron creation in supercritical collisions of heavy nuclei
该研究超越单极近似，用广义赝谱法求解含时狄拉克方程，计算重核超临界碰撞中正电子产生的三维分布，发现分布高度各向同性且旋转耦合影响小。
Structure and production of doubly charmed tetraquarks T_cc (cc ubar dbar) are studied from the viewpoint of color configurations. Based on the diquark correlation, the tetraquark T_cc with I(JP)=0(1+) is considered to be stable against strong decay. We discuss that the mixing probability of color antitriplet and sextet cc components in T_cc is suppressed by 1/m_c^2, so the two configurations are separately realized in the heavy quark limit. Utilizing the nonrelativistic QCD framework, we evaluate the production cross sections of T_cc in electron-positron collisions. The momentum dependence of…
A study of the dynamical fluctuation property of jets is carried out using the Monte Carlo method. The results suggest that, the anisotropy of dynamical fluctuations in the hadronic system inside jets, changes abruptly with the variation of the cut parameter y_cut. A transition point exists, where these fluctuations behave like those in soft hadronic collisions, i.e. being circular in the transverse plane with respect to dynamical fluctuations.
We discuss the possibility of detecting heavy spin-3/2 leptons at LEP2 and NLC energies. The angular distributions of primary ordinary leptons are shown to be a good measure to discriminate between a heavy spin-3/2 lepton and a similar nonstandard spin-1/2 signal.
$(τ^+τ^-)_b$ is an atom of simple hydrogenlike structure similar to positronium $(e^+e^-)_b$ and $(μ^+μ^-)_b$. In this paper energy levels and decay widths of different decay channels of $(τ^+τ^-)_b$ are given. Cross section of production of this atomic system in $e^+e^-$ annihilation taking into account radiative corrections is calculated. According to our estimates 886 $(τ^+τ^-)_b$ atoms may be produced at BEPCII and 29 $(τ^+τ^-)_b$ atoms are produced at VEPP-4M under the present experimental conditions.
A new approach to phenomenological description of the charged particle multiplicity distributions in proton-(anti)proton and electron-positron collisions is presented. The observed features of the data are interpreted on the basis of stochastic-physical ideas of multiple production. Besides the processes of parton immigration and absorption, two and three patron incremental and decremental recombinations are considered. The complex behaviour of the multiplicity distributions at different energies is described by four parametric generalized hypergeometric distribution (GHD). Application of the …
The production of various heavy-quark-containing baryons in electron-positron annihilation is considered. On the basis of exact formulas that we obtained previously within full perturbation theory, new numerical calculations of the respective cross sections are performed, and simple approximate expressions are then constructed for the results of these calculations. The dependence of the total cross sections on the masses of constituent quarks is discussed. The application of the Peterson fragmentation function and a Reggeon-type fragmentation function to describing differential cross sections …
Enhancements of electron-positron pair production at very low transverse momentum in peripheral hadronic A + A collisions
针对STAR、ALICE观测到的边缘重离子碰撞中低横动量轻子对超额现象，指出现有研究因忽略多电子-正电子对产生导致幺正性破坏，证明该过程截面大需纳入计算以解释横动量展宽。
Influence of the nuclear magnetic field on electron-positron pair production in low-energy heavy-nuclei collisions
本文通过相对论双中心方法研究低能重核碰撞中核磁场对正电子产生的影响，发现磁相互作用使临界核间距略增、正电子产额提高至多几个百分点，但不改变能量和角分布。
The baryons containing two heavy quarks and a light quark are believed to have the diquark-quark structure and the diquark is composed of the two heavy quarks which is a spin-0 or spin-1 object. The superflavor symmetry can associate productions of such heavy baryon-antibaryon pair with the heavy meson productions. The whole scenario is presented in some details in this work, and the observation prospect in future experiments is discussed.
We investigate the production and signatures of a single, pair of heavy-exotic leptons via the electron-positron induced process and a pair of heavy exotic leptons via the Drell-Yan process at the CERN Large Hadron Collider (LHC). We show that the cross-section for the case of the production of heavy pair exotic leptons are competitive with the ones for the single production of exotic leptons. We also exhibit some kinematical distributions.
It is shown that $BR(χ_{b1}(1P)\rightarrow Z\rightarrow e^+e^-)\simeq 3.3\cdot 10^{-7}$, $BR(χ_{b1}(2P)\rightarrow Z\rightarrow e^+e^-)\simeq 4.1\cdot 10^{-7}$ and $BR(χ_{c1}(1P)\rightarrow Z\rightarrow e^+e^-)\simeq 10^{-8}$ that give a good chance to search for the direct production of pseudovector $^3P_1$ heavy quarkonia in $e^+e^-$ collisions ($e^+e^-\rightarrow Z\rightarrow ^3P_1$) even at current facilities not to mention $b$ and $c-τ$ factories. Leading radiative corrections to annihilation of quarkonia in QCD are discussed.
Muon pair production in electron-positron collisions close to threshold in the presence of a strong laser field
研究在强激光场中电子与正电子碰撞接近阈值时μ子对产生，关注略低于阈值情况，通过多光子吸收克服能隙，计算过程截面，探讨其与能隙和激光参数非微扰依赖，确定三种相互作用 regime，发现类似施温格效应的指数依赖。
We propose the characterization of fragmentation functions by the energy fraction x, a hadron takes away from the energy of the jet measured in the frame co-moving with the jet. Besides, we propose the usage of the jet mass as the fragmentation scale Q. We show that these two Lorentz-invariant variables emerge naturally in a microcanonical ensemble with conserved fourmomentum. Then, we construct a statistical hadronisation model, in which, two features of the hadronic final states in various high-energy reactions (power law spectra and negative-binomial multiplicity distributions) can be conne…
We consider the electromagnetic production of positron in collision of slow heavy nuclei, with the simultaneously produced electron captured by one of the nuclei. The cross-section of the discussed process exceeds essentially the cross-section of $e^+e^-$ production.
Nucleus-nucleus collisions offer a great opportunity for analyzing and determining the intrinsic nature of heavy and exotic hadrons. In this sense, here we discuss how the production and dissociation of hadron states are affected by reactions during the expansion of hadronic matter in a heavy-ion collision environment. We give emphasis to recent works on exotic states, revisiting as a case study the time evolution of the abundances of the $X_{0,1}(2900)$ states.
This paper presents the high-precision theoretical predictions for $e^+e^- \to l^-l^+$ scattering. Calculations are performed using the {\tt SANC} system. They take into account complete one-loop electroweak radiative corrections as well as longitudinal polarization of initial beams. Reaction observables are obtained using the helicity amplitude method with taking into account initial and final state fermion masses. Numerical results are given for the center-of-mass energy range $\sqrt{s}=250-1000$ GeV with various degrees of polarization.
We consider the cross-section of electromagnetic production of $e^+ e^-$ pair in adiabatic scattering of heavy nuclei.
Positron supercritical resonances and spontaneous positron creation in slow collisions of heavy nuclei
本文利用复标度广义伪谱方法研究了双高电荷裸核系统中的正电子超临界共振，计算了共振位置与宽度，并估计了慢速U和Cm碰撞中自发产生正电子的概率。
Production of $1^{-+}$ exotic charmonium-like states in electron-positron collisions
本研究探讨了在正负电子碰撞中产生具有奇异量子数1-+的类粲偶素强子分子态的产生率，通过计算相关矢量态的辐射衰变宽度，估算了在Super τ-Charm Facility中的产生截面和事件数，并指出4.44和4.50 GeV附近是观测这些态的理想能量区域。
We discuss special type of polarization asymmetry (``handedness") in the process $e^+e^-\to 4π$, when one of initial particles is longitudinally polarized. The asymmetry is proportional to the degree of polarization and to the width to mass ratio of rho-meson. It can reach 4-5\% in some kinematical region. Both channels $2 π^+ 2 π^-$ and $2 π^0 π^+ π^-$ are considered in the framework of the effective chiral lagrangian with vector mesons, in the energy range $\sim 1$ GeV. The corresponding total cross sections are also calculated.
This paper studies the electroweak production of all possible four fermion states in e+ e- collisions. Since the methods employed to evaluate the complete matrix elements and phase space are very general, all four fermion final states in which the charged particles are detected can be considered. Also all kinds of experimental cuts can be imposed. With the help of the constructed event generator a large number of illustrative results is obtained, which show the relevance of backgrounds to a number of signals. For LEP 200 the W-pair signal and its background are discussed, for higher energies a…
This report summarises the results of the four-fermion working group of the LEP2-MC workshop, held at CERN from 1999 to 2000. Recent developments in the calculation of four-fermion processes in electron-positron collisions at LEP-2 centre-of-mass energies are presented, concentrating on predictions for four main reactions: W-pair production, visible photons in four-fermion events, single-W production and Z-pair production. Based on a comparison of results derived within different approaches, theoretical uncertainties on these predictions are established.
Analytic NNLO QCD corrections to top quark pair production in electron-positron collisions
本文利用光学定理和正则微分方程计算三圈主积分，给出电子-正电子湮灭产生顶夸克对总截面的解析 NNLO QCD 修正及未来轻子对撞机数值结果。
We study radiative corrections to chargino production at linear colliders with polarised electron beams. We calculate the one-loop corrected cross-sections for polarised electon beams due to three families of quarks and squarks, working in the $\bar{MS}$ scheme, extending our previous calculation of the unpolarised cross-section with one-loop corrections due to the third family of quarks and squarks. In some cases we find rather large corrections to the tree-level cross-sections. For example for the case of right-handed polarised electrons and large $\tan β$ the corrections can be of order 30%…
The exclusive production of a fully heavy tetraquark and a photon in electron-positron collision
该研究在非相对论QCD框架下计算了正负电子对撞中全重四夸克态与硬光子伴随产生的独占过程，发现无论紧致态还是分子态，在Belle II或未来Z工厂上观测到这些态的希望渺茫。
We study the spectrum of the bremsstrahlung photons coming from the electrons and positrons, which are produced in the strong electromagnetic fields present in peripheral relativistic heavy ion collisions. We compare different approaches, making use of the exact pair production cross section in heavy ion collisions as well as the double equivalent photon approximation.
Based on the color-spin interaction in diquarks, we argue that charmed multiquark hadrons are likely to exist. Because of the appreciable number of charm quarks produced in central nucleus-nucleus collisions at ultrarelativistic energies, production of charmed multiquark hadrons is expected to be enhanced in these collisions. Using both the quark coalescence model and the statistical hadronization model, we estimate the yield of charmed tetraquark meson $T_{cc}$ and pentaquark baryon $Θ_{cs}$ in heavy ion collisions at RHIC and LHC. We further discuss the decay modes of these charmed exotic ha…
This report summarizes the results of the two-fermion working group of the LEP2-MC workshop, held at CERN from 1999 to 2000. Recent developments in the theoretical calculations of the two fermion production process in the electron-positron collision at LEP2 center of the mass energies are reported. The Bhabha process and the production of muon, tau, neutrino and quark pairs is covered. On the basis of comparison of various calculations, theoretical uncertainties are estimated and compared with those needed for the final LEP2 data analysis. The subjects for the further studies are identified.
Studying exotic hadrons in high energy nuclear collisions
本文探讨高能核碰撞中奇特强子（如χ_{cl}(3872)态）的产生机制及部分子介质效应，表明重离子测量可用于揭示其内部结构与介质内演化。
Production of exotic electromagnetic bound systems in ultra-peripheral heavy ion collisions with two-photon processes
本研究在考虑核形状因子的前提下，用等效光子近似计算超周边重离子碰撞中双光子作用产生的奇特电磁束缚系统，验证了在RHIC和LHC能量下实验研究这类轻子对束缚态的可行性。
Properties of a hypothetical baryonium with the quark content ($uds\ov{u}\ov{d}\ov{s}$) are discussed. The MIT bag model predicts its mass to be unexpectedly low, approximately 1210 MeV. Possible hadronic decay modes of this state are analyzed. Ultrarelativistic heavy-ion collisions provide favorable conditions for the formation of such particles from the baryon-free quark-gluon plasma. We estimate multiplicities of such exotic baryonia on the basis of a simple thermal model.
The BESIII Experiment at the Beijing Electron Positron Collider (BEPCII) collected large data samples for electron-positron collisions with center-of-mass above 4 GeV. The analysis of these samples has resulted in a number of surprising discoveries, such as the discoveries of the electrically charged $\mathrm{Z_c}$ structures, which, if resonant, cannot be accommodated in the traditional charm quark and anti-charm quark picture of charmonium. In this talk, we will review the current status of the analyses of the exotic states, as well as a number of other interesting features in the new BESIII…
Top-quark pair production in electron-positron collisions within the minimal noncommutative Standard Model
本文研究了在最小非交换标准模型框架下电子-正电子碰撞中顶夸克对的产生，通过Seiberg-Witten映射引入非交换效应，并计算了$e^+e^-\to t\bar{t}$过程的平方截面，直至非交换参数$\Theta^{\mu\nu}$的二次项。研究得出了总截面、极角和方位角分布以及反向不对称性，这些结果对时空非交换性敏感。数值结果评估了未来线性对撞机如ILC和CLIC相关的总能量。分析表明，非交换几何可以引起显著偏离标准模型预测的特征，为高能$e^+e^-$$碰撞提供间接探测时空非交换性的可能性。
We demonstrate that the azimuthal dependence of central meson production in hadronic collisions, when suitably binned, provides unambiguous tests of whether the Pomeron couples like a conserved vector-current to protons. We discuss the possibility of discriminating between q-qbar and glueball production in such processes. Our predictions apply also to meson production in tagged two-photon events at electron--positron colliders and to vector-meson production in ep collisions at HERA.
We consider the electromagnetic production of positron in collision of heavy nuclei, with the simultaneously produced electron captured by one of the nuclei. This cross-section exceeds by about four orders of magnitude the cross-section of $e^+ e^-$ production.
I review the most recent progresses in the calculation of four-fermion processes in electron-positron collisions
Based on the NRQCD factorization formalism, we calculate the next-to-next-to-leading order QCD corrections to the heavy quarkonium $η_c (η_b)$ production associated with a photon at electron-positron colliders. By matching the amplitudes calculated in full QCD theory to a series of operators in NRQCD, the short-distance coefficients up to NNLO QCD radiative corrections are determined. It turns out that the full set of master integrals that we obtained could be analytically expressed in terms of Goncharov Polylogarithms, Chen's iterated integrals, and elliptic functions, which mostly do not exi…
Results from a model study on the formation of exotic quark clusters at the hadronization stage of a heavy ion collision are presented. The dynamical quark molecular dynamics (qMD) model which is used is sketched, and results for exotica made of up to six (anti-)quarks are shown. The second part focuses on pentaquarks. The rapidity distribution are shown, and the distribution of strangeness is found to yield an indicator of thermalization and homogenisation of the deconfined quark system. Relative Theta^+ yields are found to be lower than thermal model estimates.
A theoretical investigation of the bound-free electron-positron pair production in relativistic heavy ion collisions is presented. Special attention is paid to the positrons emitted under large angles with respect to the beam direction. The measurement of these positrons in coincidence with the down--charged ions is in principle feasible by LHC experiments. In order to provide reliable estimates for such measurements, we employ the equivalent photon approximation together with the Sauter approach and derive simple analytic expressions for the differential pair--production cross section, which …
The influence of electron-electron interaction on pair production in supercritical collisions of highly charged ions
本研究通过含时密度泛函理论等方法，发现电子屏蔽显著抑制高电荷离子超临界碰撞中的正电子产生及真空衰变特征信号。
Showers of $γ$-rays and positrons are produced when a high-energy electron beam collides with a super-intense laser pulse. We present scaling laws for the electron beam energy loss, the $γ$-ray spectrum, and the positron yield and energy that are valid in the non-linear, radiation-reaction--dominated regime. As an application we demonstrate that by employing the collision of a $>$GeV electron beam with a laser pulse of intensity $>5\times10^{21}\,\text{Wcm}^{-2}$, today's high-intensity laser facilities are capable of producing $O(10^4)$ positrons per shot via light-by-light scattering.
Four-fermion processes with a particle lost in the beam pipe are studied at LEP to perform precision tests of the electroweak theory. Leading higher-order QED corrections to such processes are analyzed within the framework of the Structure Functions (SF) approach. The energy scale entering the QED SF is determined by inspection of the soft and collinear limit of the O(alpha) radiative corrections to the four-fermion final states, paying particular attention to the process of single-W production. Numerical predictions are shown in realistic situations for LEP experiments and compared with exist…
This paper studies the electroweak production of all possible four-fermion states in $e^+e^-$ collisions with non-standard triple gauge boson couplings. All $CP$ conserving couplings are considered. It is an extension of the methods and strategy, which were recently used for the Standard Model electroweak production of four-fermion final states. Since the fermions are taken to be massless the matrix elements can be evaluated efficiently, but certain phase space cuts have to be imposed to avoid singularities. Experimental cuts are of a similar nature. With the help of the constructed event gene…
Recent strong experimental evidence of a narrow exotic S = +1 baryon resonance, $Θ^+$, suggests the existence of other exotic baryons. We discuss the prospects of confirming earlier experimental evidence of $Θ^+$ and the observation of additional hypothetical exotic baryons in $e^+e^-$ annihilations and $γγ$ collisions at LEP and B Factories.
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