Lepton Spectrum Research Articles

Limit on theb→uCoupling from SemileptonicBDecay

We have used the momentum spectrum of leptons produced in semileptonic B-meson decays to set a 90%-confidence-level upper limit on GAMMA(b..-->..ul..nu..)/GAMMA(b..-->..cl..nu..) of 4%. We also measure the semileptonic branching fractions of the B meson to be (12.0 +- 0.7 +- 0.5)% for electrons and (10.8 +- 0.6 +- 1.0)% for muons.

Charge operators in simple Lie groups

Charge operators for representations of dimension less than or equal to 16 are computed in all simple Lie groups. The representations for which the charge operator reproduces the charge spectrum of leptons and quarks of one family are analyzed from a GUT point of view.

A confining SU(2) L × SU(2) R gauge model of the weak interactions

With the aim of understanding weak interactions as residual hypercolor interactions among composite quarks and leptons, we investigate a confining SU(2) L × SU(2) R hypercolor gauge theory with only fundamental fermions (i.e. without fundamental scalars). A scenario with two different confinement scales, Λ L ∼ G F − 1 2 ∼ 300 GeV and Λ R > Λ L, is systematically analyzed as a function of the parameter ξ = Λ R/ Λ L. The general requirement of anomaly saturation is combined with effective lagrangian techniques—a powerful procedure also of interest for more general confining product groups. Two solutions, separated by a phase boundary, emerge. Phase I for 1 ⩽ ξ < ξ crit: a left-right symmetric spectrum of massless composite quarks and leptons with a possibility for dominance of V-A effective low-energy interactions. Phase II for ξ > ξ crit: only left-handed massless composite quarks and leptons (of the Abbott-Farhi type). Phase II results from separate anomaly saturation at the two scales Λ R and Λ L, Phase I from joint anomaly saturation (matching). Dynamical insight comes from treating confinement in two steps, at Λ R and Λ L consecutively, which amounts to a complementary version of the technicolor mechanism; it necessarily entails the appearance of Goldstone bosons in the intermediate momentum range, Λ < p < Λ R, which play the rôle of dynamical scalars being subject to SU(2) L confinement.

Understanding of spin ½, family structure, and mass pattern of leptons and quarks in a composite model

A relativistic three-preon interaction with a spin dependence ${\ensuremath{\Sigma}}^{a}\ensuremath{\equiv}{\ensuremath{\sigma}}_{\ensuremath{\mu}\ensuremath{\nu}}^{(1)}{\ensuremath{\sigma}}_{\ensuremath{\nu}\ensuremath{\lambda}}^{(2)}{\ensuremath{\sigma}}_{\ensuremath{\lambda}\ensuremath{\mu}}^{(3)}$ is proposed for an SU(2) preon ($t, v$) model. The ${\ensuremath{\Sigma}}^{a}$ operator (i) gives zero force for $S=\frac{3}{2}$ states, thus rendering them dynamically irrelevant, and (ii) has the complex combinations ${\ensuremath{\chi}}^{\ensuremath{'}\ensuremath{'}}\ifmmode\pm\else\textpm\fi{}i{\ensuremath{\chi}}^{\ensuremath{'}}$ of the two spin-\textonehalf{} functions (${\ensuremath{\chi}}^{\ensuremath{'}}, {\ensuremath{\chi}}^{\ensuremath{'}\ensuremath{'}}$) as eigenstates with eigenvalues of opposite signs so that only one combination is relevant for confinement. This feature in turn leads to just three ${\mathrm{S}}_{3}$-symmetry classes (out of six available ones) of spatial wave function, again in complex form which are sought to be identified with the generation structures. Their spatial functional forms are such as to obey severe selection rules preventing electromagnetic transitions such as $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$. Apart from these qualitative features which are shown to remain valid within a fairly general (Bethe-Salpeter-type) dynamical framework, a quantitative model of confinement with a very steep potential ($\ensuremath{\sim}{R}^{12}$) is proposed for a unified description of lepton and quark spectra. This leads to a universal ($l, q$) mass formula for all three generations with only two free parameters, in rather good agreement with the observed pattern. In particular the lepton mass ratios which do not involve any free parameter are predicted as $\frac{{m}_{\ensuremath{\mu}}}{{m}_{e}}=196.7$ and $\frac{{m}_{\ensuremath{\tau}}}{{m}_{\ensuremath{\mu}}}=14.3$.

Counting neutrinos and families in the standard electroweak model

Let n ν be the number if neutrinos much lighter than their charged lepton partners. In the standard electroweak model, using low-energy particle physics data, we prove that n ν <137. If moreover the up-type and down type quarks are also highly nondegenerate in mass n ν <47. The limits are much tighter for nondegenerate leptonic mass spectra. If the ratio of the lepton masses in two consecutive families is about 10 then there are at most two neutrinos beyond the known ν e, ν μ and ν τ . The same result is obtained for a mass spectrum à la Froggat and Nielsen.

Leptonic decay of heavy flavors: A theoretical update

The spectrum of charged leptons in semileptonic B and D decays is reanalyzed. Special emphasis is given to the behaviour near the end point which is of importance for the determination of the b → u versus b → c couplings. In particular the effects of soft gluons are studied and their contribution is resummed in leading double logarithmic approximation. This effect determines the end-point behaviour for the decay of a heavy quark into massless quark and leptons, such as b→u e−νe. Bound-state corrections to the parton picture are treated in a model which satisfies all kinematical constraints. A comparison of predictions for charm decay with experimental data is also presented.

Bounds and prospects for the majoron model of left-handed neutrino masses

We analyze further implications of the existence of a massless boson - the Majoron - mainly coupled to left-handed neutrinos. Final lepton spectrum in pion leptonic decay is affected by Majoron bremsstrahlung, yielding a bound on Majoron-neutrino coupling from experimental data. Supernova dynamics is another issue discussed here. We address possible effects of the frequent neutrino-neutrino collisions, neutrino interconversion and light boson bremsstrahlung in neutrino scattering. In particular, we focus on the question of lepton number non-conservation. We find that deleptonization of the core and high-entropy collapse can occur, via a subtle interplay of neutrino interconversion and light boson bremsstrahlung. Then, we propose an unorthodox solution to the missing mass problem in the universe. Finally, we address the problem of galaxy formation, which appears in a new perspective within our model.

Consequences of diffractive heavy flavor production

We calculate the lepton spectrum inpp collisions from the production and semileptonic decay ofΛc andΛb, and find limits on their production cross sections. Total cross sections in excess of 1 mb forΛc and 2 1/2μb forΛb violate the experimental fact that (μ/π)≲10−4. Abundant production ofΛc has led to speculations on the existence of a large intrinsic charm sea inside the proton. We discuss alternative ways of probing such a structure inside the proton: jets opposite highpT direct photons and central production of ψ.

Lepton-spectrum-inducing potentials—Elementary construction

In a former paper a potential giving a discrete spectrum of three consecutives-states and a level spacing in accordance with the phenomenological mass spectrum of the charged leptons has been constructed by using the inverse-scattering transformation. The result of this calculation is reconfirmed by using a more elementary method which gives at the same time insight into the bound-state wave functions. The potential need not be energy dependent (as assumed before), but the spectrum is strongly dependent on the potential parameters.

An attempt to interpret generation in the composite quark-lepton model

An interpretation of generation in quark and lepton spectrum is proposed in a standpoint of the composite quark-lepton model. We introduce three fermions, V, Wl and Wq, in an exact\(SU_{2^N ,H_2 } \times SU_{3,H_1 } \times SU_{3,c} \) gauge theory (N = 1, 2, 3, ...), where\(SU_{2^N ,H_2 } \) and\(SU_{3,H_1 } \) gauge theories are postulated in two sublevels under the quarklepton level. The\(SU_{2^N ,H_2 } \) gauge theory provides a scalar mesons S0, which is composed, of 2N number of V-fermions and transforms like a (3, 3) representation of\(SU_{3,H_1 } \times SU_{3,c} \). In the\(SU_{3,H_1 } \) confinement the generation is labelled by the S0-meson number in bound states. Higgs mesons for dynamical symmetry breakdown of parity are also provided in\(SU_{3,H_1 } \) confinement. A comment on new scalar-type interactions is also made.

Leptonic signals for nonstandard heavy quarks

Alternatives to the standard sequential six-quark and six-lepton model of weak and electromagnetic interactions include several in which heavy quarks decay only semileptonically. The rates of inclusive and several semi-inclusive lepton-production channels in e/sup +/e/sup -/ annihilation are estimated for such models and a comparison is made with the standard-model expectations. Consideration is given to lepton spectra, and it is pointed out that a hard spectrum could be the signal of purely leptonic decay of heavy, spinless hadrons. The latter process is predicted to be prominent in several alternative schemes, one of which is outlined here. The leptonic spectrum appears to provide a realistic method of detecting unexpected hadronic physics. Even if the b quark turns out to be of standard sequential type, it is stressed that it is important to test for anomalies in leptonic production rate and spectrum shape at higher PEP and PETRA energies.

Lepton spectrum in semileptonic charm decay

Virtual and real gluon corrections to the charged lepton spectrum in the decay c→s ℓ + ν e are computed, for arbitrary masses of c and s quarks. A comparison with D semileptonic decay data is done, taking into account the Fermi motion of the charmed quark. Good agreement is found for M c=1.75 GeV, M s=0.5 GeV, and with a Fermi momentum of about 0.5 GeV. With the value of M c thus found, the prediction for the charmed particles lifetime is reduced, with respect to previous estimates, to τ c=5·10 −13 s.

On a possible similarity between the heavy lepton and heavy constituent quark mass spectra

We raise the possibility that the heavy (charged) lepton mass spectrum and the heavy constituent quark mass spectrum are both geometric with ratio fixed by the weak and strong interaction coupling constants, respectively.

Gluon correction to semileptonic decays of heavy quarks

Abstract The lowest-order correction is calculated to the simple quark model of semileptonic heavy quark decays in quantum chromodynamics. The semileptonic decay rates are suppressed substantially, as much as 35% for the charmed quark, and the inclusive energy spectra of final quarks and leptons are softened enough to reproduce well the inclusive lepton spectrum observed for the charmed hadron decays.

Use of neutrino reactions on nuclei to determine the pion dispersion relation in nuclear matter

Because of the effects of the medium on the pion dispersion relation, the lepton spectrum in the inclusive reaction $\overline{\ensuremath{\nu}}+\mathrm{nucleus}\ensuremath{\rightarrow}{l}^{+}+\mathrm{anything}$ will show sharp peaks due to production of a pion into the nuclear matter in the interior of the nucleus. For the case of a 420 MeV incident $\overline{\ensuremath{\nu}}$, detailed calculations show that these peaks will be far above expected backgrounds and that their observation can give a direct, point by point determination of the pion dispersion relation in nuclear matter.NUCLEAR REACTIONS Neutrino reactions on nuclei to determine pion dispersion relation.

U(1) ⊗ SU(4)L⊗ SU(4)R-Based Weak-Electromagnetic Synthesis with Manifest Left-Right Symmetry

We present a gauge theory of weak and electromagnetic interactions which is based on the group U(1) \ensuremath{\bigotimes} SU${(4)}_{\mathrm{L}}$ \ensuremath{\bigotimes} SU${(4)}_{\mathrm{R}}$ and which implements manifest left-right symmetry in a natural way. The theory is characterized by a rich lepton spectrum and is consistent with recent experimental results in atomic physics and weak trimuon production. Some novel predictions of the theory are discussed.

Lepton energy spectra in e +e − annihilation and other processes

An analysis is presented of the single inclusive lepton spectra expected from the decay of charmed hadrons or heavier particles with new flavors produced in e +e − annihilation. Extremely soft spectra are found, in contrast to the heavy lepton signal. Good detection efficiency at low momentum will therefore continue to be important in future experiments. A range of plausible inclusive D meson spectra abstracted from a parton fragmentation picture is employed. The model is applicable to other processes.

A simple phenomenological description of hadron production

The inclusive production distributions of the non-leading particles in pp collisions are fitted by a simple general formula. The contributions from the ϱ 0, ω, φ, and J ψ decays to the direct lepton spectra are calculated. Possible contributions from the semi-leptonic decay of the conjectured charmed meson are discussed.

On the contribution of semileptonic decays of new particles to single lepton spectra and to dilepton invariant mass distributions

The contributions of semileptonic decays of new particles to single lepton spectrum at large angles and small p T and to the invariant mass distribution dσ dM μμ 2 are investigated. Consistency of experimental results then indicates that either the branching ratio B (new particle→ℓ ν hadrons) ⩽ 2% or that ℓ/ π ⩽ 2 × 10 −5 at 0.5 GeV < p T < 1 GeV, in which case new particles cannot be responsible for the increase observed in pp→ e at p T<1 GeV.

Direct lepton production by soft virtual bremsstrahlung

Internal conversion of soft virtual bremsstrahlung, calculated in an essentially model independent infrared limit, yields numerous low mass-low energy lepton pairs. The resulting single lepton spectra rise sharply towards p T = 0 for large angles θ cm and towards x = 0 for θ cm = 0°. The ratio e π for p T ⩽ 400 MeV/ c exhibits roughly the experimentally observed properties.