Limits on low scale gravity from e+e−→W+W−, ZZ and γγ

It has been proposed recently that the scale of quantum gravity (“the string scale”) can be M_S∼few TeV with n≥2 extra dimensions of size R≲mm so that, at distances greater than R, Newtonian gravity with M_Pl∼10¹⁸ GeV is reproduced if M_Pl²∼RⁿM_Sⁿ⁺². Exchange of virtual gravitons in this theory generates higher-dimensional operators involving SM fields, suppressed by powers of M_S. We discuss constraints on this scenario from the contribution of these operators to the processes e⁺e⁻→W⁺W⁻, ZZ, γγ. We find that LEP2 can place a limit M_S≈1 TeV from e⁺e⁻→W⁺W⁻, ZZ, γγ.     

Limiting soft particle emission in e + e −, hadronic and nuclear collisions

In e ⁺ e ^? collisions the particle spectra at low momenta reflect the properties of the underlying “soft” QCD gluon bremsstrahlung: the particle density, in the limit p→0, becomes independent of the incoming energy $\sqrt{s}$ and directly proportional to the colour factors C _A , C _F for primary gluons or quarks respectively. We find that experimental data from the pp and nuclear reactions reveal the same behaviour: in the limit p _T→0 the invariant particle spectra become independent of the collision energy, and their intensities in e ⁺ e ^?, pp and nuclear reactions are compatible with the expected colour factors C _F : C _A : (N _part/2)C _A for N _part nucleons, participating in the interaction. Coherent soft gluon bremsstrahlung is, therefore, suggested to be the dominant QCD mechanism for the soft particle production in all these reactions. These “soft” particles probe the very early stage of hadron formation in the collision. Future measurements at the LHC will provide crucial tests on the contributions from possible incoherent multi-component processes.     

Measurement of the branching ratio for Υ(1S) state intoπ + π − andsearch for decaysΥ(1S)→π + π −,K + K −,p \bar p

In the experiment withe ⁺ e ^?-beams performed at the VEPP-4 storage ring with the MD-1 detector we have measuredB _μμ, the branching ratio for the decay of Υ(1S) state intoμ ⁺ μ ^?. We obtainedB _μμ=(2.12+0.20+0.10)%. It is shown that the continuum and resonance interference should be taken into account. For the first time the upper limits on the branching ratio for the decaysΥ→π ⁺ π ^?,K ⁺ K ^?,p \(\bar p\) have been measured: Br(Υ→π ⁺ π ^?)<5·10^?4, Br(Υ→K ⁺ K ^?)<5·10^?4, Br(Υ→p \(\bar p\) <9·10^?4 (90% CL).     

K+ momentum spectrum from (K−, K+) reactions in the intranuclear cascade model

In the framework of intranuclear cascade (INC) type calculations, we study the momentum spectrum in the reactions (K⁻, K⁺) at a beam momentum of 1.65 GeV/c. The INC model calculations are compared with the relativistic impulse approximation (RIA) calculations to perform a detailed study of the reaction mechanism. We find that the INC model can reproduce the experimental data on various targets. Especially, in the low-momentum region, the forward-angle cross sections of the (K⁻, K⁺) reaction from light to heavy targets are consistently explained with the two-step strangeness exchange and production processes with various intermediate mesons, and φ, a₀ and f₀ productions and their decay into K⁺K⁻. In the two-step processes, inclusion of meson and hyperon resonances is found to be essential.     

B_d (\bar B_d ) → ρ ± π ∓,ρ + ρ −,π + π −: Hunting for alpha

We determine the domains of the values of unitarity-triangle angle α allowed by charmless strangeless $B_d (\bar B_d )$ decays.     

(e,e′), (γ, π+ and (π−, γ) on12C and13C

A detailed theoretical analysis of spin degrees of freedom in carbon isotopes is performed, probing them by electron scattering, pion photoproduction and radiative pion capture from the mesoatomic orbits.Dedicated by the co-authors to the memory of J. Gmitro.The present paper is one of the last works made together with our colleague Marian Gmitro. We had to complete it without him. We mourn for his sudden death and we will always keep alive the memory of his bright personality.     

MO analysis of the high statistics Belle results on γ γ→π + π −, π 0 π 0 with chiral constraints

We reconsider Muskhelishvili–Omnès (MO) dispersive representations of photon–photon scattering to two pions, motivated by the very high statistics results recently released by the Belle collaboration for charged as well as neutral pion pairs and also by recent progress in the determination of the low-energy π π scattering amplitude. Applicability of this formalism is extended beyond 1 GeV by taking into account inelasticity due to  $K\bar{K}$ . A modified MO representation is derived which has the advantage that all polynomial ambiguities are collected into the subtraction constants and have simple relations to pion polarizabilities. It is obtained by treating differently the exactly known QED Born term and the other components of the left-hand cut. These components are approximated by a sum over resonances. All resonances up to spin two and masses up to ?1.3 GeV are included. The tensor contributions to the left-hand cut are found to be numerically important. We perform fits to the data imposing chiral constraints, in particular, using a model independent sum-rule result on the p ⁶ chiral coupling c ₃₄. Such theoretical constraints are necessary because the experimental errors are dominantly systematic. Results on further p ⁶ couplings and pion dipole and quadrupole polarizabilities are then derived from the fit. The relevance of the new data for distinguishing between two possible scenarios of isospin breaking in the f ₀(980) region is discussed.     

Experimental results on40Ca(μ−,v μγ)40K* and16O(μ−,v μγ)16N**)

Photon spectra from radiative muon capture in doubly closed shell nuclei¹⁶O and⁴⁰Ca have been measured with a pairspectrometer. The⁴⁰Ca data agree with the most recent of the three previous experiments, for¹⁶O no other measurements exist. The comparison with theoretical calculations indicates that a careful treatment of the nuclear response function is required, ifg _P is to be determined from the data.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.     

Deeply bound pionic states with the (Σ −,Λ) reaction

We study the reaction ^– +A + (A ^–) with the ^– bound in the nucleus, as a means of producing deeply bound pionic states in nuclei, so far unobserved. The reaction is similar to the (n, p) reaction but, because of the ^–, mass difference, it allows the reaction to occur with smaller momentum transfer, thus increasing the transition probability and reducing the effects of distortion. The ratios of signal to background are one to two orders of magnitude better than in the (n, p) reaction.We would like to thank C. Dover and G. Tamas who helped us to get a perspective of the present and future possibilities of this and other reactions.One of us, J. Nieves wishes to acknowledge a fellowship from the Ministerio de Educatión y Ciencia. This work is partially supported by the CICYT. All the calculations have been done in the Centro Informático de la Universidad de Valencia.     

The study of hypernuclei via the (K−, π0) reaction

A significant improvement in the resolution of hypernuclear levels could be attained by studying the (K^–, ⁰) reaction at rest. The new LAMPF neutral meson spectrometer can attain a ⁰ energy resolution of 200 keV. It is shown that, even today, an experiment is feasible and would shed significant light on our understanding of hypernuclei.     

Formation of Light p-shell Ξ − Hypernucleus Via (K −, K +) Reaction

We have calculated ⁷Li(K ^?, K ⁺) reaction spectrum at ${p_{K^-} = 1.65}$ GeV/c and ${\theta_{K}^{+} = 0^\circ}$ within the framework of distorted wave impulse approximation (DWIA) using the ${[\Xi^-{-}^6{\rm He}(0^+)]-[\Xi^-{-}^6{\rm He}^*(2^+)]}$ coupled-channel Green’s function approach, and examined whether the peak corresponding to the Ξ ^? hypernuclear states can be visible in the reaction spectrum, by employing various Ξ ^??⁶He effective potentials.     

Study of Neutron-Rich Hypernuclei by the (π −, K +) Reaction at J-PARC

We are planning to perform an experiment at J-PARC and produce new neutron-rich Λ hypernuclei by using the (π ^?, K ⁺) reaction (J-PARC E10). As the first step, we are planning to produce ${^6_{\Lambda}{\rm H}}$ hypernuclei with a ⁶Li target. To conduct this experiment, we are developing new detectors, those are scintillating fiber tracker, and silicon strip detector, for high rate operation to aim at increasing beam intensity up to 10⁷/spill. As a result of beam test in Jun 2012, we are going to use high-rate beam at least 10⁷/spill.     

On the reactions p + p↦p + Λ + K+ and p + p↦p + Σ0 + K+ near thresholds

The cross-sections for the reactions of the strange production p + p ↦ p + Λ + K⁺ and p + p ↦ p + Σ⁰ + K⁺ near thresholds of the final states pΛK⁺ and pΣ⁰K⁺ are calculated in the effective Lagrangian approach. Our approach is based on the dominant contribution of the one-pion exchange and strong interaction of the colliding protons in the initial state. The theoretical values of the cross-sections agree reasonably well with the experimental data. The polarization properties of the Λ- and Σ⁰-hyperons are discussed.     

On the production mechanism of Σ-hypernuclear systems in A(K −, π±) reactions

It is shown that the new data on the excitation energy E _exc spectrum of the residual nuclear system in the Σ-hypernuclear region in the reactions (K ^?, π^±) on ⁹Be and in the reaction (K ^?, π⁺) on ⁴He and ¹²C can be described without assuming the existence of excited Σ-hypernuclear states. The basis is formed by a simultaneous consideration of the quasifree Σ production and Σ-nuclear rescattering (elastic and with Σ → Λ conversion) with allowance for the interference of the respective amplitudes. To answer completely the question on the nature of the irregularities in E _exc spectrum, it is proposed to study the picture corresponding to the so-called moving complex singularity of the triangle graph with Σ rescattering: the position and the width of the peak in E _exc distribution should be appreciably changed with momentum transferred from the initial kaon to the final pion.     

Production Spectra of the ΣNN Quasibound States in 3He(K −, π ∓) Reactions

We theoretically demonstrate the inclusive and semiexclusive spectra in the ³He (K ^?, π ^?) reactions at 600 MeV/c (4°) within a distorted-wave impulse approximation, using a coupled (2N ? Λ) + (2N ? Σ) model with a spreading potential. It is shown that a signal of a ${^3_\Sigma{\rm He}}$ quasibound state is clearly observed near the Σ threshold in the π ^? spectrum, whereas a peak of a ${^3_\Sigma{\rm n}}$ quasibound state is relatively reduced in the π ⁺ spectrum. The mechanism of Σ production for these spectra is discussed.     

On polarization of strange baryons in reactions p + p↦p + Λ0 + K+ and p + p↦p + Σ0 + K+ near thresholds

Polarization properties of strange baryons produced in pp reactions, p + p↦p + Λ⁰ + K⁺ and p + p↦p + Σ⁰ + K⁺, near thresholds of the final states pΛ⁰K⁺ and pΣ⁰K⁺ are analysed relative to polarizations of colliding protons. The cross-sections for pp reactions are calculated within the effective Lagrangian approach accounting for strong pp rescattering in the initial state of colliding protons with a dominant contribution of the one-pion exchange and strong final-state interaction of daughter hadrons (Eur. Phys. J. A 9, 425 (2000)). Received: 22 October 2001 / Accepted: 14 November 2001     

Search for lepton number violating decays B+ → π- μ+ μ+ and B+ → K- μ+ μ+

A search is performed for the lepton number violating decay B+ → h- μ+ μ+, where h- represents a K- or a π-, using an integrated luminosity of 36 pb(-1) of data collected with the LHCb detector. The decay is forbidden in the standard model but allowed in models with a Majorana neutrino. No signal is observed in either channel and limits of B(B+ → K- μ+ μ+) < 5.4×10(-8) and B(B+ → π- μ+ μ+) < 5.8×10(-8) are set at the 95% confidence level. These improve the previous best limits by factors of 40 and 30, respectively.     

Production of Ξ−-Hypernuclei via the (K −, K +) Reaction in a Quark-Meson Coupling Model

We study the production of Ξ^?-hypernuclei, ${^{12}{_{\Xi^-}}}$ Be and ${^{28}{_{\Xi^-}}}$ Mg, via the (K ^?, K ⁺) reaction within a covariant effective Lagrangian model, employing the bound Ξ^? and proton spinors calculated by the latest quark-meson coupling model. The present treatment yields the 0° differential cross sections for the formation of simple s-state Ξ^? particle-hole states peak at a beam momentum around 1.0 GeV/c with a value in excess of 1 μb.     

Annihilation of + \bar p + p → e + + e ? + π0 and + \bar p + p → γ + π0 through an ω-Meson intermediate state

The s-channel annihilation of a proton and an antiproton into a neutral pion and a real or virtual photon followed by lepton pair emission is studied. Such a mechanism is expected to play a role at moderate values of the total energy $ \sqrt s $ , when the pion is emitted in the angular region around 90° in the center-of-mass system. A fair comparison with the existing data is obtained taking scattering and annihilation channels into account. The cross section is calculated and numerical results are given in the kinematical range accessible in the PANDA experiment at FAIR.