Neutral heavy lepton candidate in e+e− interactions

An event of the form e⁺e^? → μ⁺μ^? + (2 jets) recently observed at √s = 43.45 GeV is interpreted as production of a pair of neutral heavy leptons N, each with mass 20.5 ± 1.0 Gev/c². Two possibilities are explored: (i) the lepton is a wak isodoublet neutrino, produced in pairs by virtual Z⁰ decay. In this case, one expects $\text{B(}\text{Z}{}^0\text{→}\text{N}\text{N}\text{) ≈ 5\%}$; (ii) the lepton is a “right-handed neutrino”, produced in pairs via a new vector boson Z_χ. In this case, in one model, the Z_χ must lie between about 50 and 67 GeV/c². More generally, it must be very weakly coupled to ordinary quarks and leptons in order not to conflict with low-q² neutral-current data. Suggestions are made for further observation of N$\text{N}$ pairs and other effects of Z_χ in forthcoming e⁺e^? and p$\text{p}$ collisions.     

Second order QCD contributions to thrust and spherocity

In e⁺e^? annihilation there are regions of high spherocity S and low thrust $\text{T(S >}\text{16}\text{3π}{}^2\text{and}\text{T <}\text{2}\text{3}$ in which these distributions are given in QCD perturbation theory by the subprocesses e⁺e^? → qq?GG and e⁺e^? → qq?qq? neglecting only cubic and higher order terms in α_S. We give the corresponding QCD predictions which suggest that the calculable corrections to these variables may be slowly convergent.     

Full O(αew) electroweak corrections to e+e−→HHZ

We calculate the full $\text{O}\text{(α}{}_{\mathrm{<mtext>ew</mtext>}}\text{)}$ electroweak corrections to the Higgs pair production process e⁺e⁻→HHZ at an electron–positron linear collider in the standard model, and analyze the dependence of the Born cross section and the corrected cross section on the Higgs boson mass m_H and the c.m. energy $\text{s}$. To see the origin of some of the large corrections clearly, we calculate the QED and genuine weak corrections separately. The numerical results show that the corrections significantly suppress or enhance the Born cross section, depending on the values of m_H and $\text{s}$. For the c.m. energy $\text{s}\text{=500}$ GeV, which is the most favorable colliding energy for HHZ production with intermediate Higgs boson mass, the relative correction decreases from −5.3% to −11.5% as m_H increases from 100 to 150 GeV. For the range of the c.m. energy where the cross section is relatively large, the genuine weak relative correction is small, less than 5%.     

Production of charmed particles at the CERN intersecting storage rings in events triggered by an electron

Production of charmed particles has been investigated at √s = 63 GeV usi ng the Lampshade Magnet detector triggered by electrons and positrons emitted at 30% from the ISR beam axis. The results of a search for Λ_c and $\text{Λ}$_c signals in the K^?pπ⁺ and K⁺$\text{p}$π^? channels are presented. Cross sections for the reactions pp → $\text{D}$Λ_cX and pp → Λ_c$\text{Λ}$_cX, and upper limits. for pp → D$\text{D}$X, are evaluated under various models and compared with other values obtained at the ISR.     

QCD corrections to jet multiplicity moments

QCD predictions of hadronic multiplicity moments in jets, including corrections of relative order $\text{α}{}_{\mathrm{s}}\text{(Q}{}^2\text{)}$, are presented. They agree with e⁺e^? annihilation data for reasonable values of α_s, but the corrections are so large that terms of yet higher order are unlikely to be negligible.     

Charmed meson decays and right-handed currents

In the presence of right-handed currents including $\text{(}\text{c}\text{s}\text{)}{}_{\mathrm{<mtext>R</mtext>}}$, it is emphasized that the dominant parity-violating (-conserving) Hamiltonian for nonleptonic decays of charmed hadrons transforms like $\text{45}\text{+}\text{45}{}^1\text{(}\text{20″ +}\text{84}\text{)}$ of SU(4), and leads to distinctive results especially in D⁺ → K_Sπ⁺, F⁺ → μ⁺ν_μ and D⁰ → K^?e⁺ν_e, etc.     

Results and techniques of multi-loop calculations

In this review some recent multi-loop results obtained in the framework of perturbative quantum chromodynamics (QCD) and quantum electrodynamics (QED) are discussed. After reviewing the most advanced techniques used for the computation of renormalization group functions, we consider the decoupling of heavy quarks. In particular, an effective method for the evaluation of the decoupling constants is presented and explicit results are given. Furthermore, the connection to observables involving a scalar Higgs boson is worked out in detail. An all-order low-energy theorem is derived which establishes a relation between the coefficient functions in the hadronic Higgs decay and the decoupling constants. We review the radiative corrections of a Higgs boson into gluons and quarks and present explicit results up to order α_s⁴ and α_s³, respectively. In this review special emphasis is put on the applications of asymptotic expansions. A method is described which combines expansion terms of different kinematical regions with the help of conformal mapping and Padé approximation. This method allows us to proceed beyond the present scope of exact multi-loop calculations. As far as physical processes are concerned, we review the computation of three-loop current correlators in QCD taking into account the full mass dependence. In particular, we concentrate on the evaluation of the total cross section for the production of hadrons in e⁺e⁻ annihilation. The knowledge of the complete mass dependence at order α_s² has triggered a bunch of theory-driven analyses of the hadronic contribution to the electromagnetic coupling evaluated at high energy scales. The status is summarized in this review. In a further application four-loop diagrams are considered which contribute to the order α² QED corrections to the μ decay. Its relevance for the determination of the Fermi constant G_F is discussed. Finally, the calculation of the three-loop relation between the $\text{MS}$ and on-shell quark mass definitions is presented and physical applications are given. To complete the presentation, some technical details are presented in the appendix, where also explicit analytical results are listed.     

Radiative production of gravitinos and photinos in e+e− annihilation

We evaluate cross sections for the two processes e⁺e^? → γ-photino-antiphotino, e⁺e^? → γ-gravitino-antiphotino. In the local limit approximation they are proportional to $\text{α}{}^3\text{s}\text{m}{}^4$ (spin-0 electron) and $\text{G}{}_{\mathrm{Newton}}\text{α}{}^2\text{s}\text{m}{}^2$ (gravitino), respectively. I If spin-0 electrons have masses between 16 and $\text{40}\text{GeV}\text{c}{}^2$, the γ-photino-antiphotino production cross section would be of the order of 0.4 to 0.1 pb at $\text{s}\text{= 40}\text{GeV}$, with the cuts indicated in the text. Detecting this process is within the range of possibilities at PETRA. If no such signal is found the existence of light photinos coupled to spin-0 electrons lighter than $\text{≈40}\text{GeV}\text{c}{}^2$, or to gravitinos lighter than $\text{≈10}{}^{\mathrm{?6}}\text{eV}\text{c}{}^2$, would be excluded.     

Tests of quantum chromodynamics and a direct measurement of the strong coupling constant αs at √s=30 GeV

We report the measurement of the reaction e⁺ + e^? → hadronic jets at a center-of-mass energy √s=30 GeV using the MARK-J detector at PETRA. By measuring the energy and angular distribution of both neutrals and charged particles we were able to isolate unambiguously the three-jet events in a kinematic region where the backgrounds from q$\text{q}$ and phase space contributions and other processes are small. Various comparisons of the data with quantum chromodynamics were made. The relative yield of three-jet events and the shape distribution of the events enable us to determine α_s = 0.23 ± 0.02 (statistical error) with a systematic error of ± 0.04.     

SU(2)×U(1) effects in e+e− annihilation: Generalized charge asymmetry

The observability of the SU(2)×U(1) electroweak charge asymmetry effects in e⁺e^? annihilation at $\text{s}\text{=29}\text{GeV}$ is addressed in the context of a Feynman-Field type fragmentation model. We assume three colors of five flavored quarks and one heavy lepton τ. We neglect, at this time, the hard gluon bremsstrahlung events. We take b→c+X as the b-decay mode and we assume all τ's and heavy hadrons decay within the resolution of the detector so thatonly light hadrons and leptons are detected. Allowing all these decays to occur, we then compute the expected front-back asymmetry of negatively charged particles weighted with zⁿ for z?0.0175, where n = 0.5, 1…, 7, 10, and z is the light-cone momentum fraction. We find, for example, that such an asymmetry is ≈5% for n=2for sin²θ_w=0.236 and Λ_{QCD=0.34 GeV}. In other words, due to the large number of charge particles produced per event, this SU(2)×U(1) charge asymmetry may be accessible experimentally in e⁺e^? → X already at PEP and PETRA energies.     

SUSY-QCD corrections to scalar quark pair production in e+e− annihilation

We calculate the supersymmetric O(α_s) QCD corrections to the cross section e⁺e⁻ → q̃_iq̃_j (i, j = 1,2) within the Minimal Supersymmetric Standard Model. We pay particular attention to the case of the left-right squark mixing and to the renormalization of the mixing angle. The corrections due to gluino exchange turn out to be smaller than those due to gluon exchange, but they can be significant at higher energies, even for a gluino mass of a few hundred GeV.     

Phenomenological characteristics of absorption in charge- and hypercharge-exchange reactions

We try to explain in a unique framework charge- and hypercharge-exchange reactions above 3 GeV/c. Our approach is based on exchange degenerate and SU(3) symmetric Regge poles to which absorption corrections are applied.In the absence of a firm theoretical basis for these corrections we adopt the approach of fixing the Regge poles through theoretical and phenomenological considerations; we then determine what kind of absorption we should apply. At intermediate energy (around 5 GeV/c our results indicate complete absorption of the s-wave amplitude. Of the two terms 1 and e^?iπα of the Reggesignature factor, the latter should be more strongly absorbed. This effect may explain especially the breaking of line-reversal symmetry for hypercharge-exchange reactions, π^?p→π⁰n polarization data, and the difference of peripherality of ??ω and A₂?f₀ contributions.In addition, K-exchange in $\text{p}\text{p}\text{→}\text{Λ}\text{Λ}$ has been studied.     

Bound states of heavy quarks on the light plane

We investigate in detail the light plane formulation of bound state equations and of the interactions of bound states. This formalism is particularly well suited to discuss bound states of heavy quarks since these states can be well approximated as two particle states but yet there are significant relativistic corrections to the conventional nonrelativistic approach. Applications are made to electromagnetic decays of charmonium (ψ→e ⁺ e ^?, η _c →γγ, ψ′→η _c γ, etc.).     

Search for heavy isosinglet neutrinos in e+e− annihilation at 130

《Physics letters. [Part B]》1999,461(4):397-404

The QCD effective coupling constant in e+e− annihilation

The QCD effective coupling constant α_s(Q²) is determined by comparing the O(α_s)² jet-distributions with the high-energy e⁺e^? data from PETRA. We get α_s(Q² = 1225 GeV²) = 0.125 ± 0.01, which corresponds to $\text{Λ}{}_{\mathrm{<mtext>MS</mtext>}}\text{= 110}{}^{\mathrm{+70}}{}_{\mathrm{?50}}\text{MeV}$ with five flavours.     

One-pion production in the dp coherent interaction at medium energy

The angular distribution of the dp → dx reaction at an incident deuteron momentum of 2.95 GeV/c has been measured. The known enhancement in the Nπ $\text{I =}\text{1}\text{2}$ state at M_x ～ 1150 MeV/c² has been well confirmed. These data and the previous ones on the αp → αx process have been interpreted by a theoretical model.     

|ΔI| = 12 rule in non-leptonic weak interactions with Han-Nambu quarks

Gauge theories of weak and electromagnetic interactions involving Han-Nambu quarks are constructed with the following features: small $\text{K}{}_{\mathrm{<mtext>L</mtext>}}\text{→ μ}\text{μ}$ amplitude and K_L - K_S mass-splitting; a non-leptonic effective Lagrangian ΔY = ± 1 leading to the usual soft-pion theorems and obeying a fundamental $\text{|ΔI| =}\text{1}\text{2}$ rule, with corrections of order θ²_Cabibbo.     

A search for stable particles heavier than the proton and for Q = −23 quarks produced in e+e− annihilation

We have searched 1.4 × 10⁶e⁺e^? annihilation events for particles with 1–3 GeV/c² mass and charge $\text{Q = ?}\text{2}\text{3}$ from the processes e⁺e^?→q$\text{q}$X and e⁺e^? → q$\text{q}$. Upper limits of RQ ～ 10^?4 for each process are presented which improve the previous limits on free quark production in electromagnetic interactions by 2 orders of magnitude.     

Magnetic moments of composite fermions

There have been a considerable number of papers proposing composite models for leptons and quarks. Recently, Glück and Lipkin have stated that reproducing the observed magnetic moments of these fermions presents a serious difficulty for these composite models. We show for a renormalizable theory that, in contrast to Glück's and Lipkin's nonrelativistic arguments, a deeply bound system (with heavy constituent particle masses m_c) of (total) spin $\text{1}\text{2}$, charge e and mass m has the magnetic moment $\text{(e/2m) [1 +}\text{“usual” (QED + QCD + weak) corrections +O}\text{(m/m}{}_{\mathrm{<mtext>c</mtext>}}\text{)}\text{“new” bindng corrections]}$. Although there remains the considerable dynamical problem of obtaining “light” bound fermions from heavy constituents, there is no separate, additional magnetic moment difficulty.