Extended operator expansion method for neutrinoless double beta decay

Reliable calculations of nuclear matrix elements are a prerequisite for the determination of the effective neutrino mass and other particle physics parameters from neutrinoless double beta decay. Here, the operator expansion method is improved by including Coulomb, tensor and central interactions simultaneously. Furthermore, the formalism of the OEM is extended to those matrix elements necessary to extract the right-handed parameters and from 0 decay. OEM includes the dependence of the nuclear matrix elements on the intermediate states implicitly and can therefore be understood as a step beyond the closure approximation. Numerical studies are carried out for the isotope⁷⁶Ge combining the OEM expressions with ground-state wave functions calculated within a proton-neutron quasiparticle Random Phase Approximation (pn-QRPA) model. The influence and relative importance of central, tensor and Coulomb interactions is investigated. Within the OEM, contributions from the Coulomb force are found to be negligible in 0 decay, while the tensor force leads to a moderate change of the results, of the order of (10–30)%, giving a better agreement between sets of calculations which employ different NN-interactions. Generally, results of the OEM+QRPA calculation are similar to previous calculations of 0 decay matrix elements, indicating that 0 decay is not sensitive to model approximations and might therefore be more accurately calculated than the strongly suppressed 2 decay matrix elements.     

Understanding the scalar mesonq\bar q nonet

It is shown that one can fit the available data on thea _o(980),f _o(1300) andK _o ^* (1430) mesons as a distorted 0⁺⁺ nonet using very few (5–6) parameters and an improved version of the unitarized quark model. This includes all light two-pseudoscalar thresholds, constraints from Adler zeroes, flavour symmetric couplings, unitarity and physically acceptable analyticity. The parameters include a bare or mass, an over-all coupling constant, a cutoff and a strange quark mass of 100 MeV, which is in accord with expectations from the quark model. It is found that in particular for thea ₀(980) andf ₀(980) the component, in the wave function is large, i.e., for a large fraction of the time the state is transformed into a virtual pair. This component, together with a similar component of for thea ₀(980), and , and components for thef ₀(980), causes the substantial shift to a lower mass than what is naively expected from the component alone. Mass, width and mixing parameters, including sheet and pole positions, of the four resonances are given, with a detailed pedagogical discussion of their meaning.     

Binary reactions in $$\bar pp$$ collisions at intermediate energies

We discuss here the binary reactions of strange and charmed particle production in collisions at intermediate energies. In the case of baryon production with only one strange or charmed quark the cross section is determined by planar diagrams withK ^*,K ^** orD ^*,D ^**-meson poles in thet-channel. We calculated these diagrams in the frame of quark-gluon string model (QGSM) proposed earlier. We obtained also the cross-sections for reactions with baryon exchange in thet-channel with and pair in the final state. Predicted cross-sections for the reactions of production are of the order of hundred nanobarns. Using reggeon calculus we estimated cross-sections of binary reactions with two or three strange quarks in the final state: and . We discuss also the possible manifestation of color transparency effects in reactions with antiprotons on nuclei where all antiproton quarks annihilate.     

From the deuteron to deusons,an analysis of deuteronlike meson-meson bound states

A systematic study of possible deuteronlike twomeson bound states,deusons, is presented. Previous arguments that many such bound states may exist are elaborated with detailed arguments and numerical calculations including, in particular, the tensor potential. This tensor potential which is crucial for the deuteron binding is shown to be very important also in the mesonic case. Especially, in the pseudoscalar³ P ₀ pseudoscalar-vector and vector-vector channels the important observation is made that the centrifugal barrier from theP-wave can be overcome by the 1/r ² and 1/r ³ terms of the tensor potential. In the heavy meson sector one-pion exchange alone is strong enough to form at least deuteronlike and composites bound by approximately 50 MeV. Composites of and states bound by pion exchange alone are expected near the thresholds, while in the light meson sector one generally needs some additional short range attraction to form bound states. The quantum numbers of these states areI=0, andJ ^PC=0^–+, 1⁺⁺ for the states andI=0,J ^PC=0⁺⁺, O^–+, 1^+– and 2⁺⁺ for the composites. In the states: ^b (10545), _b1(10562) are predicted and in , one finds the states: ^b (10590), _bQ (10582),h _b(10608), _b2(10602). Near the threshold the states: ^c (3870), _c0(3870) are predicted, and near the threshold one finds the states: _b0(4015), ^c (4015),h _c(4015), _c2(4015). Within the light meson sector pion exchange gives strong attraction for and systems with quantum numbers where the best non- candidates exist, although pion exchange alone is not strong enough to support such bound states. Thus, although one cannot conclude with certainty it to be the case, this fact does favour the picture that the (1440) and thef ₁ (1420) are mainly composites and thef ₀(1710) mainly a bound state, while thef ₀(1515) andf ₂(1520) could be predominantly composites. If the predicted and states are found, these would support this interpretation of the light states. In channels with exotic flavour orCP quantum numbers pion exchange is generally repulsive or quite weak. Therefore one does not expect that such deuteronlike bound states exist, althoughB*B* may be an exception.     

Neutral strange particle production in neutrino and antineutrino charged current interactions on protons

The production of the neutral strange particlesK ⁰, and invp and charged current interactions is studied in an experiment with the Big European Bubble Chamber. Mean multiplicities are measured as a function of the event variablesE _v,W ² andQ ² and of the hadron variablesx _F,z andp _T ² .K ^*± (892) and ^*± (1385) signals are observed, whereas there is no evidence for ^*- (1385) production invp scattering. Forward, backward and total mean multiplicities are found to compare well with the predictions of an empirical model for deep-inelastic reactions in the case of the strange mesonsK ⁰ andK ^*± (892) but less so for the strange baryons , and ^*± (1385). The strange baryon multiplicities are used to obtain the decuplet to octet baryon production ratio and to assess the probabilities of auu orud system to break up.     

Chargino-neutralino production inp\bar p-collisions for the left-right supersymmetric model

An extension of the Supersymmetric Standard Model to the supersymmetricSU(2) _L×SU(2) _R×U(1) _B–L model is considered. The gauge group contains a bidoublet and triplet Higgs field. We investigate the possibility of detecting chargino and neutralino production in -collisions atCDF, namely . A numerical analysis is performed for , tan 1 and a lower bound on the lightest supersymmetric particle (LSP) mass, GeV. Using conservative assumptions ofM _WR300 GeV andgg _Lg _R, we find the cross sections are: , and pb, and thus _L 24 _L at TeV. Cross sections are also given for larger values of the center of mass energy up to those available at the SSC. The results are compared with the prompt-lepton background of theW _{L, R} ^– decays from . Both decays for bosons show Jacobian peaks for (p _T150 GeV forM _WR) at =90°. Furthermore the chargino signature unlike the promptlepton background is symmetric under the Jacobian peak. We also exhibit the dependence of the angular distribution of the chargino on the c.m. angle forp _T40 GeV, 150 GeV at TeV.     

Search for muon to electron neutrino oscillations

A search for _e and oscillations has been carried out with the CHARM II detector exposed to the CERN wide band neutrino beam. The data were collected over five years, alternating beams mainly composed of muon-neutrinos and muon-antineutrinos. The number of interactions of _e and observed is comparable with the number of events expected from flux calculations. For large squared mass differences the upper limits obtained on the mixing angle aresin ²2 < 9.4=" ·=">^–3 for oscillating to _e andsin ²2 < 4.8=" ·=">^–3 for to , at the 90% confidence level. Combining neutrino and antineutrino data the upper limit is 5.6 · 10^–3.On leave of absence from ITEP (Moscow)     

CP violation in charmlessB 0 decays: A coupled channel approach

We consider the CP-violating asymmetry betweenB ⁰f and f in the case thatf is a CP-eigenstate containing no charmed quarks. The asymmetry is assumed to arise as a result of mixing with other channelsf having the same quantum numbers but containing ac pair. Inelastic unitarity is implemented by means of the K-Matrix formalism, in which the constraints of CPT are manifestly satisfied. The formalism is applied to a hypothetical two-channel problemB ⁰M ,M , and then to a realistic four-channel situationB ^{0 + –}, ^{0 0},D ⁺ D ^–,D ^{0 0}. Asymmetries and branching ratios are estimated for the decaysB ^{0 + –}, ^{0 0}.     

Aspects of χ and ψ production in polarized proton-proton collisions

Several topics of relevance to low transverse momentum and _1,2(c ) production in polarized proton-proton collisions are discussed. The leadingO( _S ³ ) contributions to the lowp _{T 1} production cross-sections viagg, qg, andq initial states are calculated as well as the corresponding spin-spin asymmetries. We find that ₁ production increases relative to direct and ₂ production, providing up to 25% of the observablee ^* e ^– pairs arising from decays inpp collisions at s=500 GeV. The spin-dependence of ₁ production, however, is much smaller than for either direct or ₂ production and so will likely be far less useful than either process in probing the polarized gluon structure function of the proton. A subset of theO( _S ³ ) radiative corrections to ₂ production involving initial state quarks are also performed and compared to leading ordergg₂ predictions.     

Production of neutral strange particles in muon-nucleon scattering at 490 GeV

The production ofK ⁰, and particles is studied in the E665 muon-nucleon experiment at Fermilab. The average multiplicities and squared transverse momenta are measured as a function ofx _F andW ². Most features of the data can be well described by the Lund model. Within this model, the data on the K⁰/^± ratios and on the averageK ⁰ multiplicity in the forward region favor a strangeness suppression factors/u in the fragmentation process near 0.20. Clear evidence for QCD effects is seen in the average squared transverse momentum ofK ⁰ and particles.Deceased     

Studies of the reactionπ − p→η ′ π 0 n at 38 and 100 GeV/c

The production of ⁰ system in ^– _p charge-exchange interactions at ^– momenta 38 GeV/c and 100 GeV/c has been studied. The 2 and ^{0 0} decay modes of leading to 4 and 8 final states respectively have been detected. No statistically significant peak is observed in the ⁰ mass spectrum in the range of 1.2 GeV÷2.1 GeV. An upper limit of 6·10^–3 has been established for thea ₂ ⁰ (1320) ⁰ branching ratio.     

Testing the Higgs system at a photon-photon collider

The level of sensitivity of the processes ZZ, W ⁺ W ^– and to the Higgs sector of the Standard Model Lagrangian in the energy region between 200 GeV and 1 TeV is examined. The elementary Higgs boson is taken to have a mass less than 1 TeV. Sizeable effects are found in theZZ and channels if the incoming photons have the same helicity. Also the possibility that the elementary Higgs boson does not exist is examined. Assuming new physics to show up in the TeV energy region the cross sections are evaluated according to the heavy Higgs model. For center of mass energy values close to 1 TeV interesting effects are found in the channel if the photons have the same helicity. The limit of large Higgs mass is not unique. The parametrization of this arbitrariness may be interpreted as a representation of the new physics. The effects for the processes ZZ and are investigated. These effects may be correlated to a possible resonance inWW scattering in the TeV region.     

Translation group and spectrum condition

Let {A, ^d ,} be aC*-dynamical system, where ^d is thed-dimensional vector group. LetV be a convex cone in ^d and its dual cone. We will characterize those representations ofA with the properties (i) _a ,a ^d is weakly inner, (ii) the corresponding unitary representationU(a) is continuous, and (iii) the spectrum ofU(a) is contained in .     

Chiral approach to theK L −K S mass difference

A complete analysis of the long range part of theK _L –K _S mass difference in next-to-leading-order of chiral perturbation theory is presented. We find a large positive contribution from transitions via S=2 vertices and irreducible loop diagrams involving two separate weak interactions. Single-particle pole contributions are small if an approximate nonet symmetry for the couplings of the singlet ₁ holds. They tend to cancel the short distance contribution from box diagrams. In total, good agreement with experiment is obtained. In a second part we study theK _L –K _S mass difference in a phenomenological model of nonleptonic weak transitions which explains the I=1/2 rule in terms of non-perturbative quark-quark correlations. The numerical results agree well with those presented before.     

Tau decays into K* mesons

Using the ARGUS detector at the storage ring DORIS II we have measured decays into three charged mesons containingK ^* mesons. Exploiting the good particle identification capabilities of the detector we have determined the following branching ratios: ,B _r (^–K ^*0 K ^– v )= (0.20±0.05±0.04)%, andB _r (^–K ^*– X ⁰ v ) =(1.15±0.15_–0.18 ^+0.13)%.Supported by the German Bundesministerium für Forschung und Technologie, under contract number 054DO51P.     

Properties of multihadron final states inB-meson decays

The general approach to calculation of inclusive spectra of particles produced in multihadron decays ofB mesons is developed. This approach is based on concept of theq -string production and fragmentation combined with standard electroweak theory. Parameters of fragmentation functions are inferred from the theory of hadroproduction in high energy hadronic collisions. Numerical results for spectra of pions produced inB-meson nonleptonic and semileptonic decays, induced by eitherbc orbu transitions, are presented.Laboratoire associé au Centre National de la Recherche Scientifique     

Characterizations of Boolean algebras of idempotents

The notions of the left (right) Jordan groupoids are introduced. IfR is an associative^* ring with the identity and ifU(R) [resp.P(R)] denotes the set of all idempotents (resp. projections) of the^* ringR, then the operationsp q =p – 2pq – qp + 4qpq andp q =q – 2pq – 2qp + 4pqp ifp, q U(R) [resp.p, q P(R)] are the nonassociative linear operations inU(R) [resp. inP(R)]. The present paper shows that the operations and are associative iffpq=qp forp, q U(R) [resp.p, q P(R)]. As a corollary it follows from this that the orthomodular poset (U(R), , 0, 1,) is a Boolean algebra [which is commutative, i.e.,pq= qp, p, q U(R)] iff (U(R), , 0, 1,) or (U(R), , 0, 1,) are Jordan associative groupoids. Similar results hold for (P(R), ,0, 1, ).     

Scaling and thermal equilibrium of hadrons fromZ 0 decays

An analysis of secondary hadrons fromZ ⁰ (91) decays of the LEP experiments indicates that the scaling of distributions implies the same temperatureT=0.261 GeV for all the secondaries. The multiplicities ofZ ⁰,K ⁰, ,..., and computed with their quark contents and the sameT agree with the data. The ratio of to the phase-space covered by the rapidity distribution, depends only on the energy, , fore ⁺ e ^– annihilations and collisions as well.     

CP-violating effects inZ decays to τ leptons

We calculate CP-odd correlations inZ decays to leptons, . These correlations are sensitive to the weak dipole moment of the . With 10⁷ producedZ particles and with observation of the decay channels and v we estimate that can be determined with an accuracy of about (1 s.d.).