Measurement of the branching fractions and forward-backward asymmetries of the Z0 into light quarks

Using approximately 4.3 million hadronic Z⁰ decays collected with the OPAL detector at LEP between 1990 and 1995, we measure the branching fractions of the Z⁰ into up-type and down-type light quarks, Rq, and the forwardbackward asymmetries, A_FB(q), using high-momentum stable particles as a tag. Adopting a method that employs double tagged events to determine the flavour tagging efficiencies, and assuming the flavour independence of strong interactions and SU(2) isospin symmetry, we measure:     

Does the enhancement mechanism work in non-leptonic decays of heavy pseudoscalar mesons with new flavors (b and t)?

We show that the enhancement mechanism proposed for non-leptonic decays of charmed mesons (D⁰, F⁺) is still important for decays of pseudoscalar mesons with b flavor, while its effect is small for mesons with t flavor. For the semi-leptonic branching ratios of B^? (b$\text{u}$), B⁰(b$\text{d}$) and B_S⁰(b$\text{s}$) we predict BR (B^? → evX ～' 9%, BR(B⁰ → evX) ～' BR(B_s⁰ → evX) ～' 5%. We can also derive the enhancement of the branching ratios of uncharmed final states in B decays, i.e. $\text{BR}\text{(}\text{B}{}^{\mathrm{?}}\text{→}\text{X}{}_{\mathrm{<mtext>s</mtext><mtext>u</mtext>}}\text{)}$ ～' 20 %, $\text{BR}\text{(}\text{B}{}^0\text{→}\text{X}{}_{\mathrm{<mtext>s</mtext><mtext>d</mtext>}}\text{)}$ ≈ 10%, where $\text{X}{}_{\mathrm{<mtext>s</mtext><mtext>u</mtext><mtext>(</mtext><mtext>s</mtext><mtext>d</mtext><mtext>)</mtext>}}$ = $\text{K}$π + ... + $\text{K}$K$\text{K}$ + ... .     

The quark mixing matrix in a composite model

The generalized mixing matrix of quarks is computed based on a composite model of quarks and leptons. Among potentials between constituent particles examined V(r) = Ar^s (As > 0) and A ln r (A > 0), it is shown that potentials with exponent 0 ? s ? 3 or ln r are consistent with current experimental data for the mixing matrix elements.     

An improved measurement of R b using a double tagging method

This paper describes an update of the double tagging measurement of the fraction, R _b, of Z⁰ → bb? events in hadronic Z⁰ decays, with statistics improved by including the data collected in 1994. The presence of electrons or muons from semileptonic decays of bottom hadrons and the detection of bottom hadron decay vertices were used together to obtain an event sample enriched in Z⁰ → bb? decays. The efficiency of the bb? event tagging was obtained from the data by comparing the numbers of events having a bottom signature in either one or both thrust hemispheres. Efficiency correlations between opposite event hemispheres are small (< 0.5%) and well understood through comparisons between the real and simulated data samples. A value of R _b = 0.2175 ± 0.0014 ± 0.0017 was obtained, where the first error is statistical and the second systematic. The uncertainty on the decay width Γ(Z⁰ → cc?) is not included in these errors. The result depends on R _c as follows: $${? Delta R_{? b}?er R_{? b}}=-0.084{? Delta R_{? c}?er R_{? c}},$$ where ΔR _c is the deviation of R _c from the value 0.172 predicted by the Standard Model.     

Analyticity properties and a convergent expansion for the inverse correlation length of the high-temperatured-dimensional Ising model

We show that the inverse correlation lengthm(β) (= mass of the fundamental particle of the associated lattice quantum field theory) of the spin-spin correlation function 〈s _x s _y 〉,x, y εZ ^d , of thed-dimensional Ising model admits the representation $$m(\beta ) = - ln\beta + r(\beta )$$ for small inverse temperaturesβ > 0.r(β) is ad-dependent function, analytic atβ = 0.c _n , the nth β = 0 Taylor series coefficient of r(β) can be computed explicitly from the Z^d limit of a finite number of finite lattice A spin-spin correlation functions 〈s₀s_x〉t>Afor a finite number ofx = (x ₁,x₂, ..., x_d), ¦x¦ = ∑ _i ^d 1¦x_i¦< R(n), where R(n) increases withn. Furthermore, there exists aβ' > 0, such that for eachβ ε (0,β')m(β) is analytic. Similar results are also obtained for the dispersion curve ω(p), ω(p)=ω(0)=m, pε(-π, π]^d?1, of the fundamental particle of the associated lattice quantum field theory.     

Lower bounds on the slope parameter

A rigorous lower bound on the slope parameter γ(s, t) = d ln A(s, t)/dt is derived for 0 < t < t₀ where A(s, t) is the absorptive part of the elastic scattering amplitude and t₀ is related to the right extreme of the Lehmann-Martin ellipse. When A(s, t) has high-energy behavior like s^α(t)ln^η(t)s…, this lower bound on α(s, t) is used to obtain lower bounds on α′(t) for 0 < t < t₀, which saturate for ‘parabolic trajectories’. We also obtain a lower bound on γ(s, t) for t < 0 which can be used to find the nearforward region in which γ(s, t) cannot vanish.     

Quark masses and cabibbo angles

A simple symmetric pattern of Higgs fields in an SU (2)_L × SU (2)_R × U (1) gauge model with six quarks yields: tan²θ_c = m_d/m_s and θ_c = 15° in good agreement with experiment. A eight-quark extension of the model leads to successful determination of the three Cabibbo-like angles connecting the first six quarks and to the prediction m_t ～ 9.3 m_c ～ 14 GeV.     

Critical properties of high-spin Ising models on anisotropic lattices

The coordinates of the critical points of spin-S Ising models with coupling constants J and J′ are calculated for 1/2 ≤ S ≤ 13/2. The calculations are performed for several values of S and Δ ≡ J′/J independently by using the phenomenological renormalization-group method or (approximate) self-duality. Numerical results combined with a mean-field analysis show that the critical coupling strength for Δ ～ 1 (weakly anisotropic lattice) is K _c ^(S) (Δ) = K _c ^(S) (1)[1 + a(1 ? Δ)], where a = (d ? 1)/d is independent of S (d is the space dimension). Both free energy and internal energy are determined at the critical points. An extremum of the critical internal energy is found at Δ* ∈ (0, 1). The parameter Δ* can be used as a criterion that separates quasi-isotropic and quasi-one-dimensional regimes (Δ* < Δ ≤ 1 and Δ < Δ*, respectively). The finite-size scaling amplitudes A _s and A _e of the inverse spin-spin and energy-energy correlation lengths are estimated. Calculations show that the amplitudes A _s and A _e are independent of S within the accuracy of the adopted approximations. Moreover, their ratio A _e/A _s is independent of the anisotropy parameter Δ. These results support the Ising universality hypothesis.     

Flavor non-universal gauge interactions and anomalies in B-meson decays

Motivated by flavor non-universaity and anomalies in semi-leptonic B-meson decays, we present a general and systematic discussion about how to construct anomaly-free U(1)' gauge theories based on an extended standard model with only three right-handed neutrinos. If all standard model fermions are vector-like under this new gauge symmetry, the most general family non-universal charge assignments,(a,b,c) for three-generation quarks and(d,e,f)for leptons, need satisfy just one condition to be anomaly-free, 3(a+b+c) =-(d+e+f). Any assignment can be linear combinations of five independent anomaly-free solutions. We also illustrate how such models can generally lead to flavor-changing interactions and easily resolve the anomalies in B-meson decays. Probes with B_s-B_s mixing, decay into τ~±, dilepton and dijet searches at colliders are also discussed.     

Perturbation of the Laplacian supported by null sets,with applications to polymer measures and quantum fields

We discuss hamiltonians in L²(R^d, dx) of the form H = ?Δ + V, with V a potential supported by a zero measure set C. In particular if C is a path of a brownian motion b such that V(x) = ∫₀¹λ(x, ω)δ(x-b(s, ω)) ds, we show that H exists as a nontrivial, self-adjoint, lower bounded perturbation of ?Δ when d ?5. We must choose λ to be an infinitesimal, negative function for d = 4,5, but for d ? 3 any bounded real-valued function λ will do. The connection with Edward's model of polymers as well as with quantum fields of the ?_d⁴-type is also discussed. The proofs use methods of nonstandard analysis.     

Hadron multiplicities in the presence of light gluinos

We consider the effect of a massless gluino on the evolution of a parton shower. The hadron multiplicity distribution is predicted to evolve as a function of the collider energy in the same way as in the absence of gluinos, except for a slower running of _s. A comparison of the predicted average hadron multiplicity with experimental data is presented as a fit constraining the values of the strong coupling constant at the Z⁰ peak _s(m_Z) and the scale of the onset of hadronizationm ₀. It appears that light gluinos are unlikely to be detected this way with less than 500 GeV of centre of mass energy.     

Proton decays and neutron oscillations in the rishon model

We analyze proton decays and neutron oscillations in the rishon model. Proton decay is forbidden in lowest order of the compositeness scale Λ_H. In a one-generation rishon model, the leading proton decays violate B?L (e.g., p→νπ⁺). The lifetime is given by τ_p～Λ_H⁸/(U_R²m_p⁷), where U_R～M(W_R) is the mass scale of the right-handed W boson and m_p is the proton mass. For U_R～500 GeV, the obtained limit for the compositeness scale is Λ_H?10⁸ GeV. Neutron oscillations are also proportional to Λ_H⁸ and cannot be detected in the foreseeable future. All of these predictions may depend strongly on the understanding of higher generations of quarks and leptons within the model.     

Laser-rf double-resonance hyperfine structure measurements of the metastable 3d 4s 1 D 2 state of43Ca

The hyperfine structure of the (3(d 4s)¹ D ₂metastable state of⁴³Ca has been measured using theABMR-LIRF method (atomic beam magnetic resonance, detected by laser induced resonance fluorescence). The measurements yielded for the magnetic dipole and electric quadrupole constantsA=?17.650(2) MHz andB=?4.642(12) MHz, respectively. From the measuredB factor the spectroscopic electric quadrupole moment (uncorrected for shielding effects) has been calculated to beQ(⁴³Ca)=?0.062(12) barn. In addition, isotope shifts in the lines (3d 4s)¹ D ₂(3d 4p)¹ F ₃ ⁰ and (3d 4s)¹ D ₂(4s 5p)¹ p ₁ ⁰ for the stable calcium isotopes have been obtained by high resolution laser spectroscopy.     

Final state photon bremsstrahlung ine + e −→Z 0→hadrons as a tool for a precise measurement of the weak quark couplings

We discuss for the processe ⁺ e ^?→Z ⁰→q \(\bar q\) how final state photons can be used to disentangle the weak couplings of up and down type quarks. Since the flavour composition of multihadronic events with final state photons is different from that of all multihadrons, a combination of observables from the two samples allows the couplings to be determined. Both theZ ⁰ width and the forward-backward charge asymmetry at centre-of-mass energies aroundM _Z0 can be used to constrain the weak couplings. Taking into account the theoretical uncertainties a precision for the sum of the square axial and vector couplings of δ(v ²+a ²)～4% for up and down type quarks separately seems feasible for 10⁶ Z ⁰'s. The precision from asymmetry measurements will be less significant.     

A mechanical definition of the thermodynamic pressure

A dynamical definition of pressure for grand-canonical Gibbs measures in bounded regions Λ is rigorously discussed: It measures the momentum transferred to the walls of the container by the elastically colliding particles. The local pressureP(r, δΛ) so obtained is proportional to the temperature and the local density at the boundaries of Λ. This allows us to obtain a rigorous proof of the virial theorem of Clausius. In this picture the thermodynamic pressureP ^d (Λ) is obtained as the average ofP(r, δΛ) onδΛ. Its relationship with the usual equilibrium pressureP _eq(Λ) = (βsΛ¦)^?1lnZ _Λ (Z _Λ is the grand-canonical partition function) is then discussed. In the particular case in which the regions A are spheres, it is shown that P_d(Λ) converges in average so that, if the limit of P_d(Λ) exists, it equals P_eq, the thermodynamic limit of the equilibrium pressure P_eq(Λ). Finally, convergence ofP _d(Λ) is proven to hold in the particular case of one-dimensional hard cores in the absence of phase transitions.     

The role of instantons in generation of mesonic mass spectrum

It is suggested that instantons play the leading role in the mixing of $\text{s}\text{s and}\text{u}\text{u}\text{+}\text{d}\text{d}$ quark states in mesonic nonets and in the explanation of the Okubo-Zweig-Iizuka (OZI) rule. The non-diagonal polarization operator Π^su = 〈0|T{j^s(x)j^u(y)}0〉 is considered where $\text{j}{}^{\mathrm{<mtext>s</mtext>}}\text{=}\text{s}\text{O}\text{s}$ and $\text{j}{}^{\mathrm{<mtext>u</mtext>}}\text{=}\text{u}\text{O}\text{u}$ are the currents of the s and u quarks. It is proved that in the dilute instanton gas approximation for quarks in the external instanton field Π^su = 0 for the vector and tensor currents and Π^su≠0 for the axial current. Hence, after saturating Π^su by the low-lying mesonic states, we obtain the qualitative explanation of the OZI rule. The Q² dependence of the non-diagonal polarization operator of the axial currents, Π^su(Q²), is calculated and compared with the η′ meson pole term. Taking account of terms ～m_q² allows one, using the experimentally known ηη′ mixing angle, to find the η′ meson coupling constant with the axial current F_η′ ≈ 150 MeV and to estimate the η′π mixing angle.     

High precision measurements of the hyperfine structure of seven metastable atomic states of57Fe by laser-Rf double-resonance

The hyperfine structure of the metastable atomic states (3d ⁷4s)⁵ F _2,3,4,5 and (3d ⁷ 4s)³ F _2,3,4 of⁵⁷Fe has been measured using theABMR- LIRF method (atomic beam magnetic resonance detected by laser induced resonance fluorescence). From these measurements the following hfs constantsA of the magnetic dipole interaction have been obtained (corrected for second order effects):A(⁵ F ₂)=55.994(7) MHzA(⁵ F ₃)=69.632(5) MHzA(⁵ F ₄)=78.435(4) MHzA(⁵ F ₅)=87.246(3) MHzA(³ F ₂)=143.328(4) MHzA(³ F ₃)=50.602(10) MHzA(³ F ₄)=13.456(5) MHz     

From kaonic atoms to kaonic nuclei: A search for antikaon-mediated bound nuclear systems

Strong interaction processes were intensively studied at low energy with exotic atoms, touching one of the fundamental problems in hadron physic today — the still unsolved question of how hadron masses are generated. The question of the origin of the large hadron masses made up of light quarks, the current mass of the up (u) and down (d) quarks (m_u,d≈5 MeV) is two orders of magnitude smaller than a typical hadron mass of about 1 GeV, will be discussed in the context with the experimental work done in the field of exotic atoms expanded to exotic nuclei.An overview of the properties of exotic hydrogen atoms made of pions and kaons are presented, using high precision experiments unrevealing the nature of strong interaction physics at low energy. A new field which contributes to the understanding of the origin of the large hadron mass is the study of the mass modification in a nuclear medium. Antikaon mediated bound nuclear systems would be an ideal tool, if they exist, to look for chiral restoration at high density and zero temperature or even more exotic to look for phase transitions.     

The far-infrared spectra and ring puckering potential functions of several deuterated analogs of trimethylene sulfide

The far-infrared spectra in the region of 50–200 cm^?1 of several deuterated analogs of trimethylene sulfide (viz α-d₂, β-d₂, α,α′-d₄ and d₆) are reported. The bands are assigned to ring puckering transitions. The potential constants in the function, V(Z) = A(Z⁴ + BZ²), Z the reduced puckering coordinate, were determined for each compound separately. The barrier height, $\text{AB}{}^2\text{4}$, is found to vary upon isotopic substitution in the quadratic-quartic approximation.