Showing papers in "European Physical Journal C in 1990"

New algorithms for one-loop integrals

Abstract: New algorithms are presented for evaluating the scalar one loop integrals for three- and four-point functions for arbitrary masses and external momenta. These formulations are useful both for analytic integration and for numerical evaluation in a computer program. The expressions are very compact and provide for an easy isolation of asymptotic behaviour and potential numerical problems. The tensor integrals have also been rewritten according to new algorithms, making it very easy to express amplitudes in terms of scalar loop integrals.

Three Loop Relation of Quark (Modified) Ms and Pole Masses

Abstract: We calculate, exactly, the next-to-leading correction to the relation between the $$\overline {MS} $$ quark mass, $$\bar m$$ , and the scheme-independent pole mass,M, and obtain $$\begin{gathered} \frac{M}{{\bar m(M)}} \approx 1 + \frac{4}{3}\frac{{\bar \alpha _s (M)}}{\pi } + \left[ {16.11 - 1.04\sum\limits_{i = 1}^{N_F - 1} {(1 - M_i /M)} } \right] \hfill \\ \cdot \left( {\frac{{\bar \alpha _s (M)}}{\pi }} \right)^2 + 0(\bar \alpha _s^3 (M)), \hfill \\ \end{gathered} $$ as an accurate approximation forN F−1 light quarks of massesM i

Conformal Invariance and Pion Wave Functions of Nonleading Twist

Abstract: The restrictions are studied for the general structure of pion wave functions of twist 3 and twist 4 imposed by the conformal symmetry and the equations of motion. A systematic expansion of wave functions in the conformal spin is built and the first order corrections to asymptotic formulae are calculated by the QCD sum rule method. In particular, we have found a multiplicatively renormalizable contribution into the two-particle wave function of twist 4 which cannot be expanded in a finite set of Gegenbauer polynonials.

Exclusive Semileptonic Heavy Meson Decays Including Lepton Mass Effects

Abstract: We discuss the exclusive semi-leptonic (s.l.) bottom meson decaysB→D(D*)+l+v where we include non-zero lepton mass effects in the kinematics and dynamics. We develop the general formalism for the non-zero lepton mass case. We then look at how rates, spectra and angular correlations are affected by non-zero lepton masses in the context of a specific spectator quark model. Numerical results are presented for s.l. decays involving thee-, μ- and τ-leptons. We also discuss the s.l. decaysB→π(ρ),D→K(K*) and the free quark decay model.

Tensor representation of the quantum group SL q (2,C) and quantum Minkowski space

Abstract: We investigate the structure of the tensor product representation of the quantum groupSLq(2,C) by using the 2-dimensional quantum plane as a building block. Two types of 4-dimensional spaces are constructed applying the methods used in twistor theory. We show that the 4-dimensional real representation ofSLq(2,C) generates a consistent non-commutative algebra, and thus it provides a quantum deformation of Minkowski space. The transformation of this 4-dimensional space gives the quantum Lorentz groupSOq(3, 1).

Transversely polarized parton densities, their evolution and their measurement

Abstract: The transverse spin asymmetry of a quark in a baryon and the linear polarization of a gluon in a vector meson are studied from thet-channel point of view. Using the Altarelli-Parisi approach, they are shown to obey independent evolution equations and to decrease with increasingQ2. We investigate the possibility to measure them at leading twist, to leading order in α and αs and without analyzing the final polarizations. This requires simultaneous polarization of the beam and the target; the observable effect is in the azimuthal distribution of the highPT particle or jet. Assuming a simple (quark+scalar diquark) model for the baryon, a large asymmetry is expected inp\(\bar p\) Drell-Yan collisions, a smaller one in highPTpp collisions, from the interference term in the scattering of two identical quarks.

The master two-loop diagram with masses

Abstract: In every mass case needed for QCD and QED two-point functions, the most difficult two-loop scalar Feynman diagram is reduced, by a systematic dispersive method, to a single integral of logarithms, whose expansion is obtained for large and, when appropriate, small momenta. The new results for the case with an intermediate state comprising three massive particles are needed for the two-loop calculation of fermion propagators.

Global jet properties at 14–44 GeV center of mass energy in e + e − annihilation

Abstract: Jet properties ine + e − annihilation at center of mass energies of 14, 22, 35 and 43.7 GeV were studied with the data collected in the TASSO detector at PETRA, using the same evaluation procedures for all the energies. The total hadronic cross section ratio for the center of mass energy interval 39–47 GeV was determined to be ℛ=4.11±0.05 (stat)±0.18(syst.) at $$\langle \sqrt s \rangle = 43 - 7$$ GeV. Corrected distributions of global shape variables are presented as well as the inclusive charged particle distributions for scaled momentum and transverse momentum. The center of mass energy evolution of the average sphericity, thrust, aplanarity and particle momentum is shown.

A measurement of global event shape distributions in the hadronic decays of the Z 0

Abstract: We present measurements of global event shape distributions in the hadronic decays of theZ0. The data sample, corresponding to an integrated luminosity of about 1.3 pb−1, was collected with the OPAL detector at LEP. Most of the experimental distributions we present are unfolded for the finite acceptance and resolution of the OPAL detector. Through comparison with our unfolded data, we tune the parameter values of several Monte Carlo computer programs which simulate perturbative QCD and the hadronization of partons. Jetset version 7.2, Herwig version 3.4 and Ariadne version 3.1 all provide good descriptions of the experimental distributions. They in addition describe lower energy data with the parameter values adjusted at theZ0 energy. A complete second order matrix element Monte Carlo program with a modified perturbation scale is also compared to our 91 GeV data and its parameter values are adjusted. We obtained an unfolded value for the mean charged multiplicity of 21.28±0.04±0.84, where the first error is statistical and the second is systematic.

Neutral strange particle production in sulphur-sulphur and proton-sulphur collisions at 200 GeV/nucleon

Abstract: The production of Λ, $$\bar \Lambda$$ andK 0 has been studied in 200 GeV/nucleonp+S and S+S collisions in the streamer chamber of the NA35 experiment at the CERN SPS. Significant enhancement of the multiplicities of all observed strange particles relative to negative hadrons was observed in central S+S collisions, as compared top+p andp+S collisions. The latter collisions show no overall (relative) strangeness enhancement overp+p, but the rapidity distributions and hadron multiplicities indicate some secondary cascading production of Λ particles in thep+S andp+Au collisions. The Λ polarization in central S+S collisions was found to be compatible with zero up top T =2 GeV/c.

Exclusive hadronic decays of B mesons

Abstract: Using the ARGUS detector at thee + e − storage ring DORIS II, we have measuredB decays into exclusive final states containing aD orD * meson plus several pions, or containing aJ/ψ or ψ′ meson plus a strange particle. Some of these channels have not been seen before, while others represent updated measurements of previous results. The branching ratios are compared with the predictions of the model of Bauer, Stech and Wirbel. Using the cleanest decay channels, the mass of the charged and neutralB meson are found to bem B −=(5280.5±1.0±2.0) MeV/c2 andm B 0=(5279.6±0.7±2.0) MeV/c2 respectively, yielding a mass differencem B 0−m B − =(−0.9±1.2±0.5) MeV/c2.

Electroweak Parameters From a High Statistics Neutrino Nucleon Scattering Experiment

Abstract: The final results from the WA 1/2 neutrino experiment in the 1984 CERN 160 GeV narrow band beam are presented. The ratiosR ν and\(R_{\bar v} \) of neutral to charged current interaction rates of neutrinos and antineutrinos in iron are measured to beR ν=0.3072±0.0033 and\(R_{\bar v} \)=0.382±0.016. A value of the electroweak parameter sin2 θ w = 1 −m W 2 /m Z 2 is extracted fromR ν. The result is sin2 θ w =0.228+0.013(m c −1.5)±0.0003 (theor.) wherem c is the mass of the charmed quark in GeV form t =60 GeV,M H =100 GeV, ρ=1. CombiningR ν and\(R_{\bar v} \) one obtains a value for ρ=0.991+0.023(m c −1.5)±0.020(exp.). Alternatively,R ν and\(R_{\bar v} \) yield a precise value of the ratio of intermediate vector boson massesm W /m Z =0.880−0.007(m c −1.5)±0.002(exp.)±0.002(theor.). Comparison of these results with those from direct measurements of the vector boson masses are presented. In a model-independent analysis the left- and right-handed neutral current coupling constants,g L 2 andg R 2 , are determined.

(eb), (et) type leptoquarks atep colliders

Abstract: Leptoquarks with quantum numbers of (eb) and (et) compounds can be generated in electron-gluon collisions. Production rates and signatures are discussed for HERA energies and beyond.

Baryon pairs production ine + e − annihilation at $$\sqrt s = 2.4 GeV$$

Abstract: Search for baryon pairs production ine+e− annihilation at\(\sqrt s = 2386 MeV\) is reported. The data relate to a luminosity of 161 nb−1 collected by the DM2 experiment at DCI, the Orsay colliding ring. First measurements of directe+e− annihilation into\(\Lambda \bar \Lambda \) and ofe+e−→\(p\bar p\) at this energy are presented. First observation of a goode+e−→\(n\bar n\) candidate is reported and upper limits are given fore+e−→\(n\bar n, \Lambda \bar \sum ^0 + c.c.\) and\(\Sigma ^0 \bar \Sigma ^0 \).

On the threshold behaviour of heavy top production

Abstract: If the top is heavy, as now seems likely, the\(t\bar t\) threshold behaviour is given by perturbative QCD The QCD threshold interaction can be formulated in terms of a potential, attractive or repulsive depending on whether the\(t\bar t\) is in a colour singlet or octet state This gives a suppression factor for octet production Singlet production is enhanced, both above threshold and, by resonance formation, below it Whilee+e− annihilation only proceeds in the singlet\(t\bar t\) channel, hadronhadron collisions contain a non-trivial mixture of the two In this paper we review the relevant threshold factor formulae, and present phenomenological consequences for hadron colliders, current and future

Search for Collective Transverse Flow Using Particle Transverse Momentum Spectra in Relativistic Heavy Ion Collisions

Abstract: The particle transverse momentum spectra recently measured in relativistic heavy-ion collisions at CERN and BNL are analysed within an expanding fireball model. All the particle spectra at a given beam energy can be reproduced simultaneously with a single set of intensive parameters for the initial state of the fireball. As typical freeze-out parameters in this beam energy region we find a freeze-out temperatureTf≃110 MeV for most hadrons, and an average transverse expansion velocity at freeze-out of 〈v/c〉≃0.4–0.45. The striking enhancement at transverse momentapT<200 MeV/c in the CERN pion data cannot be fully explained by the existence of transverse flow.

Calculations of electromagnetic nucleon form factors and electroexcitation amplitudes of isobars

Abstract: In this paper, we present numerical results for electroproduction amplitudes of proton resonances and electromagnetic nucleon form factors calculated in a relativized quark model. Interactions with both transversely and longitudinally polarized virtual photons were considered. Contributions of the different effects included in our approach have been analysed through a sample comparison with the available data. We also discuss the validity of the usual single-quark transition ansatz and possible parametrizations of the potential acting between the constituent quarks of the baryon. Impressive agreement is obtained with the nucleon form factor data up to squared momentum transfers of 2.5 GeV2, but still some problems remain with the Δ(1232) and higher resonances.

Charged Higgs production at hadron colliders

Abstract: We study the production and decay of charged Higgs bosons,H±, at TEVATRON and SSC energies as a function of the top massm t and theH± massm H . We give the cross sections for events arising from bothH±→τν andtb decays, together with those of the competing background processes. In particular, form t >m H we studyH±W∓ andW+W − production and thet→bτν decay.

Measurement of resonance production in the reactions γγ →π0π0 and γγ →π0η

Abstract: Resonance production in the γγ reactionse+e−→e+e+e−π0π0 ande+e−π0η has been studied with the JADE detector at PETRA. The decay widths into γγ of thef2(1270),a0(980) anda2(1320) were measured to be\(\Gamma _{\gamma \gamma } (f_2 (1270)) = 3.19 \pm 0.09_{ - 0.38}^{ + 0.22} \) Kev,Γλλ(a0(980))=0.28±0.04±0.10 KeV/BR(a0(980)→π0η) andΓλλ(a2(1320))=1.01±0.14±0.22KeV. For thef0(975) andf4(2050) upper limits of the widths were obtained,Γλλ(f0(975))<0.6 KeV, andΓλλ(f4(2050))<1.1 KeV, both at the 95% C.L. Assuming that the spin 0 background under thef2(1270) is small, thef2(1270) was found to be produced exclusively in a helicity 2 state. The helicity 0 contribution is <15% at the 95% C.L. The cross section forλλ→π0π0 in the mass range 2.0–3.5 GeV/c2 was measured for the first time. Since the cross section forλλ→π+π− is a factor ∼2 larger, ππ production in this range can be interpreted as taking place via isospin 0 production.

Quark - diquark approximation of the three quark structure of baryons in the quark confinement model

Abstract: Octet (1/2+) and decuplet (3/2+) baryons as relativistic three-quark states are investigated using the quark confinement model (QCM), the relativistic quark model, based on some assumptions about hadronization and quark confinement. The quark-diquark approximation of the three-quark, structure of baryons is proposed. In the framework of this approach, the main low-energy characteristics of baryons, such as magnetic moments, electromagnetic radii and form factors, the ratio of axial and vector constants in semileptonic baryon decays, strong form factors and decay widths, are described. The obtained results agree with experimental data.

Chiral perturbation theory for anomalous processes

Abstract: A general expression containing all the divergences in Chiral Perturbation Theory at one loop for anomalous processes has been calculated. The nonrenormalization of some amplitudes (Adler-Bardeen theorem) is observed. The different types of corrections are identified. The contributions from vector meson exchange are determined for all anomalous processes. Explicit cancellation of divergences is shown for π0, η and η′ decays to γγ*. The dependence on the γ* mass squared is predicted to be essentially the same for all the three processes. It proceeds mainly through the VMD estimate of the finite parts of the next order Lagrangian and compares reasonably well with the available experimental data.

Differential geometry of the quantum supergroupGL q (1/1)

Abstract: We construct a right-invariant differential calculus on the quantum supergroupGL q (1/1) and we show that the quantum Lie algebra generators satisfy the undeformed Lie superalgebra. The deformation becomes apparent when one studies the comultiplication for these generators. We bring the algebra into the standard Drinfeld-Jimbo form by performing a suitable change of variables, and we check the consistency of the map with the induced comultiplication.

Quasielastic nucleon and hyperon production by neutrinos and antineutrinos with energies below 30 GeV

Abstract: The cross sections of neutrino and antineutrino quasielastic reactions $$vn \to \mu ^ - p,\bar vp \to \mu ^ + n,\bar vp \to \mu ^ + \Lambda$$ were studied in the neutrino energy range between 3 and 30 GeV. In comparison withV-A theory axial mass parameters ofM A =(1.06±0.05±0.14) GeV/c2 from neutrino andM A =(0.71±0.10±0.20) GeV/c2 from antineutrino data were found. The total cross-section for the hyperon production process can be described byM A =1.0 GeV/c2.

Quadratic renormalization of the average potential and the naturalness of quadratic mass relations for the top quark

Abstract: We formulate an effective action for averages of fields for the coupled system of scalars and (chiral) fermions. The renormalization group equations for the scale dependence of the average potential exhibit a quadratic renormalization in addition to the usual logarithmic renormalization. It is independent of the regularization scheme and the momentum cutoff. We investigate to what extent quadratic relations for the top quark mass, which were formerly based on the vanishing of the quadratic divergence, can be motivated in the light of these results.

Gauge invariance and systems with second-class constraints

Abstract: We show that under a certain assumption systems with second-class constraints can be regarded as gauge-fixed systems with first-class constraints. The massive Yang-Mills theory, a point particle on a sphere and theO(N) symmetric non-linear σ-model are considered as concrete examples.

Constraints on non-standard effects from present and futureg μ−2 measurements

Abstract: Motivated by the expected high accuracy of the next AGS measurement of the muong−2 we have computed several types of contributions arising from new particles and interactions. Results are first given for individual terms where limits on new parameters, coming fromg μ−2 are compared to those expected from future colliders. Combined effects due to different contributions are then considered and this reveals that constrained models with a low effective scale could still be allowed.

Jet production in hadronic collisions to0(α s 3 )

Abstract: We present the full0(αs3) QCD corrections to jet production within a small opening angle δ at large transverse momenta for all partonic subprocesses. Results for CERN and Tevatron colliders are given with particular emphasis on the sensitivity to renormalization and factorization mass scales.

Next-to-leading order QCD analysis of structure functions with the help of Jacobi polynomials

Abstract: The method of QCD analysis of singlet and nonsinglet structure functions, based on their Jacobi polynomial reconstruction from perturbative QCD predictions for the Mellin moments, is described. The accuracy and stability of the method are demonstrated with the help of BCDMS hydrogen data.

The reaction Pomeron-Pomeron → π + π - and an unusual production mechanism for the f 2 (1270)

Abstract: Data are presented on Pomeron-Pomeron interactions which produce a centralπ+π− system in proton-proton collisions at\(\sqrt s = 62 GeV\) at the CERN Intersecting Storage Rings. This process may favor the production of gluonic bound states. A partial-wave analysis of theπ+π− system shows evidence for the production of the statesf0(975),f0(1400), andf2(1270). The fitted mass for thef2(1270) is about 50 MeV below the world average. In addition, the production mechanism for thef2(1270) is uniquely different from that for the other final states in that there is a correlation between the outgoing protons. this is consistent with a picture of two-gluon exchange with thef2(1270) produced by gluon fusion, and could indicate that thef2(1270) has a glueball component.

TheW-boson width

Abstract: The analytic formulae for the partial decay widthW+→\(f_1 \bar f_2 \) are presented including the 1-loop electroweak and QCD corrections for arbitrary masses of the fermions. Numerical results are discussed for the physically interesting cases\(W^ + \to t\bar b\) and for the decay into a heavy leptonl+ and a neutrino of a fourth fermion generation. Also the results for the totalW width and the partial width into light fermion pairs are listed.