Rare Decay Modes Research Articles

A modified QDD spectrometer for η meson decay measurements

We propose a modified structure of a QDD spectrometer for studying rare andforbidden decay modes of the eta metal. Such a modified structure is based on replacing the quadrupole with a special magnet which provides a quadrupole field along the spectrometer axis and two dipolar field zones extending below and above the beam axis for momentum analyses of decay particles. Particularly, a modified structure of the spectrometer SPES II, that has been in use at the LNS and CERN for more than a decade, is presented. First order and ray-tracing calculations show that the beam optics and momentum resolution of such a modified structure are of a comparable quality to those of the SPES II. In addition, the intrinsic resolution of the special magnet as a momentum analyzer is well below 0.5% and can be realized if the longitudinal extension of the object (reaction vertex) is limited to ±5 mm and its transverse extension (beam spot on target) to ±2 mm.

Exclusive semileptonic B-meson decays

We study the semileptonic processes B → D l ν and B → D ∗ l ν and show that the invariant hadronic form factors describing the decays can be measured directly by observing the angular correlations of the decay products. We emphasize that this allows an almost model-independent determination of the V cb quark mixing-matrix element. We examine the theoretical models for the form factors in terms of the spectator quark approach. We present a general formalism for semileptonic decays which includes lepton mass effects, since the decay into τ-leptons may be important as background events in the search for rare decay modes involving missing particles.

A Progress Report of Fermilab Experiment E‐731: A Precision Experiment to Measure ɛ;/ɛ and Rare Decay Modes of the Neutral Kaon

Annals of the New York Academy of SciencesVolume 578, Issue 1 p. 162-170 A Progress Report of Fermilab Experiment E-731: A Precision Experiment to Measure ɛ;/ɛ and Rare Decay Modes of the Neutral Kaon Y. W. WAH, Y. W. WAH Department of Physics and The Enrico Fermi Institute The University of Chicago Chicago, Illinois 60637Search for more papers by this author Y. W. WAH, Y. W. WAH Department of Physics and The Enrico Fermi Institute The University of Chicago Chicago, Illinois 60637Search for more papers by this author First published: December 1989 https://doi.org/10.1111/j.1749-6632.1989.tb50607.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume578, Issue1The Fourth Family of Quarks and Leptons: Second International SymposiumDecember 1989Pages 162-170 RelatedInformation

A Progress Report of Fermilab Experiment E-731: A Precision Experiment to Measure ?'/? and Rare Decay Modes of the Neutral Kaon

A Progress Report of Fermilab Experiment E-731: A Precision Experiment to Measure ?'/? and Rare Decay Modes of the Neutral Kaon

Search for KL--> pi 0 gamma gamma.

A search for the rare decay mode ${K}_{L}$\ensuremath{\rightarrow}${\ensuremath{\pi}}^{0}$\ensuremath{\gamma}\ensuremath{\gamma} was performed using a data set from Fermilab experiment E-731. The decay is of interest in the context of chiral perturbation theory and for its contribution to the decay ${K}_{L}$\ensuremath{\rightarrow}${\ensuremath{\pi}}^{0}$${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$. The result is B(${K}_{L}$\ensuremath{\rightarrow}${\ensuremath{\pi}}^{0}$\ensuremath{\gamma}\ensuremath{\gamma})2.7 \ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$ (90% confidence level) which is nearly a two-order-of magnitude improvement over the previous best limit.

Resonance background to the decays b-->sl+l-, B-->Kl+l-, and B-->Kl+l-

We consider background to the rare decay modes b\ensuremath{\rightarrow}${\mathrm{sl}}^{+}$${l}^{\mathrm{\ensuremath{-}}}$, B\ensuremath{\rightarrow}${K}^{\mathrm{*}}$${l}^{+}$${l}^{\mathrm{\ensuremath{-}}}$, and B\ensuremath{\rightarrow}${\mathrm{Kl}}^{+}$${l}^{\mathrm{\ensuremath{-}}}$ arising from the process b\ensuremath{\rightarrow}${\mathrm{sV}}_{i}$ followed by on- and off-resonance transition ${V}_{i}$\ensuremath{\rightarrow}${l}^{+}$${l}^{\mathrm{\ensuremath{-}}}$. We obtain dilepton mass spectrum including short-distance effects and then suggest cuts to enhance the signal over background.

Excitation and photon decay of giant multipole resonances — the role and future of medium-energy heavy ions

Inelastic scattering of medium energy heavy ions provides very large cross sections and peak-to-continuum ratios for excitation of giant resonances. For energies above about 50 MeV/nucleon, giant resonances are excited primarily through Coulomb excitation, which is indifferent to isospin, thus providing a good probe for the study of isovector giant resonances. The extremely large cross sections available from heavy ion excitation permit the study of rare decay modes of the giant resonances. In particular, recent measurements have been made of the photon decay of giant resonances following excitation by 22 and 84 MeV/nucleon 17O projectiles. The singles results at 84 MeV/nucleon yield peak cross sections for the isoscalar giant quadrupole resonance and the isovector giant dipole resonance of approximately 0.8 and 3 barns/sr, respectively. Data on the ground state decay of the isoscalar giant quadrupole and isovector giant dipole resonances are presented and compared with calculations. Decays to low-lying excited states are also discussed. Preliminary results from an experiment to isolate the 208Pb isovector quadrupole resonance using its gamma decay are presented.

The microscopic approach to the rates of radioactive decay by emission of heavy clusters

We have applied a simple microscopic decay theory to the analysis of the rare decay modes. The absolute decay rates are estimated by using the shell model and resonance formation factors and optical model penetrabilities. The resonance formation factors are deduced from the strong interaction form of the theory where the wave function in the internal region is represented in terms of compound nucleus decay. In order to account fully for the data, the implication of internal degrees of freedom was found to be necessary, but no adjustment of Gamow factor was needed. The results have been discussed in the light of the previously reported results and data.

Probing ZWW couplings through Z 0→Wff′

We investigated the possibility of probing the ZWW couplings through the rare decay mode Z 0→Wff′ of Z 0. Neglecting masses of the fermions, we computed the combined polarization density matrix of Z and W as a function of the most general ZWW couplings. Integrations over phase space are carried out and the diagonal matrix elements are expressed as quadratic forms of the seven independent couplings. We found that several charge symmetrix polarization channels are particularly sensitive to the CP-violating coupling f 6, which is proportional to the weak magnetic quadrupole moment.

Search techniques for charged and neutral intermediate-mass Higgs bosons

If fundamental scalar bosons exist, a natural implication of theories based on supersymmetry or superstrings, Higgs boson masses are likely to be of order m Z within roughly a factor of two. We term this the intermediate mass range. We study how such Higgs bosons could be detected at e +e − and, particularly, at hadron colliders. At a hadron collider it appears to be necessary to use rare decay modes of the Higgs boson, and we examine H 0→ γγ, τ + τ −, Z γ , Zℓ +ℓ −, Θγ,and b b . Since charged scalars also occur in all theories beyond the minimal Standard Model, we examine ways to find the H ±, concentrating on H ±→ τ ± ν, W ±H 0, W ±H 0 γ, W ± γ, and W ±Z. Because obtaining data about the spectrum of Higgs bosons is so essential, our approach is to ask what facilities would be sufficient to cover the entire intermediate mass range.

Fourth family quark masses, B 0 [formula omitted] mixing, and rare decay modes, in a canonical structure of the 4×4 km matrix

The implications of a canonical structure of the 4 × 4 KM matrix proposed by Shin, Chivukula and Flynn are reexamined in the light of the recently reported ARGUS result on B 4 0 B d 0 mixing and UA1's lower bound on m t. The reported B d 0 B d 0 mixing is shown to be consistent with m t=50–90 GeV provided B K<0.3, even if | V ub|/| V cb| is as small as 0.05–0.07. For B K⩾0.3, m b′ is predicted to be less than 55 GeV if m t⩾60 GeV, implying the very possibility of discovering the b′- or t-quark below 60 GeV in the near future. The B s 0 B s 0 mixing parameter r s is predicted to be maximal if the reported ARGUS result on r d is valid. The branching ratios of some flavor-changing rare decay modes, which will be measured in the next generation of experiments, are predicted to be BR( K + → π +ν ν)=(0.41−18.7) × 10 −10, BR( b→ sν ν)=(0.27−6.2)×10 −5, BR( b→ sℓ +ℓ −)= (2.2–9.9)×10 −6 , and BR(b→s γ)=(1.0−7.0) × 10 −5. Among these BR( K +→π +v v) and BR(b→sv v) are shown to be the best candidates for distinguishing the four-family KM model from that of the three-family KM model.

Search for heavy-ion radioactivity from 241Am.

Using phosphate glass detectors capable of withstanding a background dose of \ensuremath{\sim}${10}^{14}$ alpha particles per ${\mathrm{cm}}^{2}$, we have searched for rare decay modes of $^{241}\mathrm{Am}$ involving emission of energetic heavy ions. Predictions of the branching ratio for $^{34}\mathrm{Si}$ emission relative to alpha decay of $^{241}\mathrm{Am}$ range from 4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ to 4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$. In a six-month exposure to 8 mg of $^{241}\mathrm{Am}$, with detectors subtending a solid angle of 2.51 sr, we detected no particles with $12\ensuremath{\le}Z\ensuremath{\le}16$, from which we infer an upper limit ($2\ensuremath{\sigma}$) of 7.4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$.

An ultra-heavy top quark?

We consider an ansatz for the mass of the t-quark yielding a value as high as it is allowed to be viz. about 200 GeV. We check the consistency of this hypothesis with all known low energy physics and delineate the consequences for ϵ′ ϵ mixing in B d 0− B d 0 and B s 0B̄ s 0 systems and rare decay modes of K and B. An interesting feature is the existence of two classes of solutions for the Kobayashi-Maskawa angles; one of which corresponds to small ϵ′/ϵ and large B d 0B̄ d 0 mixing and the other to large ϵ′ /ϵ and small B d 0B̄ d 0 mixing.

Search for rare radiative decays of?-meson at VEPP-2M

Results of the search for rare radiative decay modes of the ϕ-meson performed with the Neutral Detector at the VEPP-2M collider are presented. For the first time upper limits for the branching ratios of the following decay modes have been placed at 90% confidence level: $$\begin{gathered} B(\phi \to \eta '\gamma )< 4 \cdot 10^{ - 4} , \hfill \\ B(\phi \to \pi ^0 \pi ^0 \gamma )< 10^{ - 3} , \hfill \\ B(\phi \to f_0 (975)\gamma )< 2 \cdot 10^{ - 3} , \hfill \\ B(\phi \to H\gamma )< 3 \cdot 10^{ - 4} , \hfill \\ \end{gathered} $$ whereH is a scalar (Higgs) boson with a mass 600 MeV<mH<1000 MeV, the real measurement isB(φ→Hγ)·B(H→2π0)<0.8·10-4, the quoted result is model dependent, as explained in the text, $$\begin{gathered} B(\phi \to a\gamma ) \cdot B(a \to e^ + e^ - )< 5 \cdot 10^{ - 5} , \hfill \\ B(\phi \to a\gamma ) \cdot B(a \to \gamma \gamma )< 2 \cdot 10^{ - 3} , \hfill \\ \end{gathered} $$ wherea is a particle with a low mass and a short lifetime, $$B(\phi \to a\gamma )< 0.7 \cdot 10^{ - 5} ,$$ wherea is a particle with a low mass not observed in the detector.

Phosphate glasses for identification of heavy ions

Some problems in nuclear physics and cosmic-ray astrophysics require a detector that can precisely identify one type of heavily ionizing particle against a background of other particles of higher or lower ionization rate. Films of polymers such as bisphenol acetone polycarbonate (for example, Lexan), polyethylene terephthalate (for example, Cronar) and allyl diglycol polycarbonate (for example, CR-39) are most commonly used for this purpose1. For some new applications, track detectors made of phosphate glass of suitable composition, chemically etched in an optimally chosen reagent, are proving to be much better than polymeric track detectors. One such application is the study of rare radioactive decay modes involving the occasional emission of a specific energetic nuclide such as 24Ne or 34Si in an enormous background of alpha particles or spontaneous fission fragments2,3. Another is the possibility of resolving neighbouring elements, or isotopes of a given element, in relativistic cosmic rays when the fractional difference in charge or mass is very small, as with Pb (Z = 82) and Bi (Z = 83), or 56Fe and 57Fe4. Here we present the results of a study of the relative sensitivities of a large number of phosphate glasses to relativistic ions of U, Au and La, indicating which ones are particularly useful for particle identification.

Nongauge interactions of vector bosons and rare K decays.

We study the effect of nonstandard vector-boson couplings on the rare decay modes of K mesons. Our results show that as long as the Glashow-Iliopoulos-Maiani mechanism is operative, experimental results on rare K decays do not produce any constraints on nonstandard self-couplings of vector bosons.

Systematics of spontaneous emission of intermediate mass fragments from heavy nuclei.

We have used polycarbonate track-recording films to confirm the rare decay mode of $^{226}\mathrm{Ra}$ by $^{14}\mathrm{C}$ emission and to set stringent upper limits on $^{14}\mathrm{emission}$ rates of $^{221}\mathrm{Fr}$, $^{221}\mathrm{Ra}$, and $^{225}\mathrm{Ac}$. The $^{14}\mathrm{emission}$ rate exhibits a pronounced odd-even effect. For Ra isotopes the hindrance factor for odd-even parents relative to even-even parents is at least 10 times higher for $^{14}\mathrm{C}$ emission than for \ensuremath{\alpha} emission.

Rare decay modes of the K-mesons in the chiral lagrangian

The decays K S → γγ, K L → γγ and K L → μ +μ − are studied within the framework of chiral lagrangians. The one loop contribution to K S → γγ turns out to be finite, giving an unambiguous prediction. The results also indicate that the long-distance dispersive part of K L → μ +μ − is the dominant one. As for K L → γγ, a possible difficulty is pointed out with the recently published value ϑ ⋍ 20° for the η − η′ mixing angle.

Decays of heavy charged Higgs bosons.

We examine the possibility of observing heavy charged Higgs bosons in rare decay modes. In particular, we find that, for , the decays ${H}^{+}$\ensuremath{\rightarrow}${W}^{+}$\ensuremath{\gamma},${W}^{+}$${Z}^{0}$ are potentially important modes for detecting a pseudoscalar charged Higgs boson with appreciable rates as compared with the predominant decay mode ${H}^{+}$\ensuremath{\rightarrow}tb\ifmmode\bar\else\textasciimacron\fi{}.

Measurement of Ω − decay properties in the CERN SPS hyperon beam

In an experiment in the CERN SPS charged hyperon beam, a sample of 16 000Ω − decays was collected at an Ω − momentum of 131 GeV/ c the Ω − lifetime, the branching ratios and decay asymmetry parameters for the main decay modes were measured, giving: τ Ω − =(0.823±0.015)×10 −10 s , Γ(Ω −→Λ K −) Γ(Ω −-→ all) =0.675±0.008 , α(Ω −→Λ K −)= −0.025±0.028, Γ(Ω −→Ξ 0π −) Γ(Ω −→ all) = 0.236±0.008 , α(Ω −→Ξ 0π −)=0.09±0.14, Γ(Ω −→Ξ −π 0) Γ(Ω −→ all) =0.089±0.005 , α(Ω −→Ξ −π 0)=0.05±0.21. For the rare decay modes, the following results for the branching ratios were obtained: if Γ(Ω −→Ξ 0 e − ν) Γ(Ω −→ all) =(0.56±0.28)×10 −2 , if Γ(Ω −→Ξ −π +π −) (Γ(Ω→ all) =(3.7 −1.1 +3.6)×10 −4 , Γ(Ω −→Ξ −γ) (Γ(ω −→ all) <2.2×10 −3 at the 90% confidence level, Γ(Ω −→Λπ −) (Γ(Ω −→ all) <1.9×10 −4 at the 90% confidence level . A sample of 32 000 Ξ − decays collected under the same experimental conditions gave a new measurement of the Ξ − lifetime: τ Ξ − =(1.652±0.051)×10 −10 s . Combining the measurements of the present experiment with those obtained in a previous experiment in the SPS hyperon beam gives: if τ Ω − =(0.823±0.013)×10 −10 s , Γ(Ω −→Λ K −) Γ(Ω −→ all =0.678±0.007 , Γ(Ω −→Ξ 0π −) Γ(Ω −→ all) =0.236±0.007 , Γ(Ω −→Ξ −π 0) Γ(Ω −→ all =0.086±0.004 , Γ(Ω −→Ξ −π +π −) Γ(Ω −→ all =(4.3 −1.3 +3.4)×10 −4 . The experimental results are compared with theoretical calculations.