Experimental study of the time-dependent rate of K → πππ

The time-dependence of the decay rate of initially pure K⁰ into the final state (π⁺π⁻π⁰) has been studied in search for the decay k_S⁰→π⁺π⁻π⁰. No evidence is found in a sample of 384 observed events. The ratio of the CP -violating K_S⁰ amplitude and the K_L⁰ amplitude is η₊₋₀ = (0.13_−0.20^+0.17) + i(0.17_−0.26^+0.27); the ratio of the CP-conserving K_S⁰ amplitude and the K_L⁰ amplitude is < 0.4. The energy dependence of the K⁰→π⁺π⁻π⁰ matrix element is found to be a₊₋₀ = −0.31 ± 0.03.     

B→ηlν decays and the flavor-singlet form factors

We study semileptonic decays B→η^(′)lν, taking into account the flavor-singlet contribution (F^singlet₊) to the B→η^(′) form factors, which arises from the two-gluon emission in a decaying B meson. It has been recently pointed out that, in addition to large weak annihilation effects, the unknown value of F^singlet₊ prevents accurate theoretical estimates in the analysis of B→η′K decays in QCD factorization. We present a certain method to determine F^singlet₊ with a reasonable accuracy, using B→η^(′)lν and B→πlν decays. We also investigate the possible effect of F^singlet₊ on the estimated branching ratios (BRs) for B→η^(′)lν and find that the BR for B→η′lν is particularly sensitive to the effect of F^singlet₊.     

Determination of the K(1800) spin parity

A spherical harmonic moment analysis of the reactions K⁻p → K⁻π⁺n and K⁺p → K⁺π⁻Δ⁺⁺ at 13 GeV/c demonstrates the existence of a broad K^* state with mass in the vicinity of 1800 MeV and spin parity 3⁻.     

Tests of second-class currents

We argue that the presence of second-class neutral currents can be tested from the observations of and electron polarisation in η→π⁰e⁺e^-. Consequences of this model in η→π^±eν_e,τ^±→ηπ^±ν_τ and τ^±→ωπ^±ν_τ decays which would establish second-class charged currents are also discussed.     

Deux trajectoires de regge dans la reaction πp → πn

The possibility of describing the high-energy reaction π⁻p^→π⁰n with two Regge trajectories (t) and _'(t) is studied in more detail. These trajectories are assumed to be exactly linear in t, with (t) constrained to pass through (m²) = 1. We examine hypotheses in which (t) obeys either the Gell-Mann mechanism or the Chew mechanism, and in which '(t) is or is not a conspiring trajectory. The model is in good agreement with the data in practically all cases; greater experimental accuracy would be necessary to distinguish between the various hypothesis. Predictions are given for the neutron polarization at |t| < 1 GeV².     

Hadronic production by ee collisions at the energy 990 MeV with the Orsay storage ring

Data were taken at the energy 2E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the , ω andφ production by e⁺e⁻ annilations. Assuming a π⁺π⁻π⁰π⁰ production by the quasi two-body process e⁺e⁻ → → ωπ⁰ we give the correspondi ng cross section σ(e⁺e⁻ → π⁺π⁻π⁰π⁰) = (1.1 ± 0.5) 10⁻³² cm². Since no events with 3 and 4 charged pions have been observed σ(e⁺e⁻ → π⁺π⁻π⁰π⁻) 1.5 × 10⁻³³ cm².     

Single and double dissociation in πp collisions at 11 and 16 GeV/c

The reactions π⁻p → 2π⁻π⁺p, π⁻p → 2π⁻π⁺π^op and π⁻p → 2π⁻2π⁺n are analysed at 11 and 16 GeV/c using longitudinal phase space (LPS) plots. The weighted LPS distributions for π⁻p → 2π⁻π⁺p is dominated by two well separated structures corresponding to single diffraction dissociation of the pion, π⁻p → (2π⁻π⁺)p, and of the proton, π⁻p → π⁻(π⁻π⁺p). The former is more abundant than the latter, and both are approximately constant with energy. In contrast, processes of type π⁻p → (2π)(πp) decrease with increasing energy.

In the five-body reactions the weighted LPS distribution reveals especially at 16 GeV/c a maximum for single dissociation of the proton into 3πp, namely π⁻p → π⁻(π⁻π⁺π^op); this process is likely to be diffractive. The neutron channel has a corresponding maximum displaced toward a multiperipheral configuration π⁻p → π⁻(π⁻2π⁺)n. Another strong maximum corresponds to the pion dissociation π⁻p → (2π⁻π⁺π^o)p. This is interpreted to be an ω-exchange process because no analogous structure occurs in π⁻p → (2π⁻2π⁺)n. Finally, a broad structure reveals double dissociation of both incident particles; it occurs in the two channels π⁻p → (2π⁻π⁺)(π^op) and π⁻p → (2π⁻π⁺)(π⁺n), being stronger in the latter. Further analysis of this process in terms of isospin exchange suggests that it is partially diffractive. Factorization is also discussed.

An appendix gives general aspects of the LPS analysis for the asymptotic study of n-body collisions at very high energy.     

What can we learn from B→DsKπ, Bd→DsKπ and Bd→DsK decays?

We study the nonresonant three-body decays of B⁺→D^(*)−_sK⁺π⁺ and B_d→D_s^(*)−K⁰π⁺. We find that these decays can provide the information on the time-like form factors of D^(*)_sK. We also explicitly investigate B_d→D_s^(*)−K^*+ decays by discriminating the nonresonant contributions with the unknown D^(*)_s wave functions being fixed by the measured mode of B_d→D_s⁻K⁺.     

Trying to catch the elusive A and more. Reactions initiated by b-quarks and the Higgs sector of the MSSM

We study the cross sections for the production of neneural, intermediate mass Higgs boson in the process pp→ tq′φ, pp→tW⁻φ and pp→bZ⁰φ in the Minimal Supersymmetric Standard Model (φ = H⁰, h⁰ and A⁰) at Supercollider energies. The additional heavy particles (t, W, Z) in the final state can be used for tagging purposes, increasing the signal to background ratio. These reactions are dominated by bg and bg fusion. Their relevance for Higgs particle searches is discussed taking into account the expected efficiencies and purities for b-tagging. We find that, for tan β = 30, the cross sections for pp → bZ⁰φ are larger than 14 pb, over the whole intemediate range of M_A⁰, for A⁰ and at least one of the other two Higgses. Therefore this reaction is an excellent candidate for the discovery of one or more MSSM Higgs particles.     

Radiative decay of ρ and φ mesons in a chiral unitary approach

We study the ρ⁰ and φ decays into π⁺π⁻γ, π⁰π⁰γ and φ into π⁰ηγ using a chiral unitary approach to deal with the final state interaction of the MM system. The final state interaction modifies only moderately the large momenta tail of the photon spectrum of the ρ⁰→π⁺π⁻γ decay. In the case of φ decay the contribution to π⁺π⁻γ and π⁰π⁰γ decay proceeds via kaonic loops and gives a distribution of ππ invariant masses in which the f₀(980) resonance shows up with a very distinct peak. The spectrum found for φ→π⁰π⁰γ decay agrees with the recent experimental results obtained at Novosibirsk. The branching ratio for φ→π⁰ηγ, dominated by the a₀(980), is also in agreement with recent Novosibirsk results.     

Investigation of light scalar resonances a0(980)/ƒ0(980) with ANKE

A program to investigate the light scalar resonances a₀(980)/ƒ₀(980) in hadronic interactions via their decay into the πη and channels has started at the ANKE spectrometer of COSY-Jülich. As the first step the reactions pp → dπ⁺X and pp → dK⁺X have been measured at two energies, T_p = 2.65 GeV and 2.83 GeV. The status of the analysis at T_p = 2.65 GeV is presented. A total cross section of about 50 nb has been determined for the reaction .     

Symmetry breaking and the decays ψ′ → J/ψπ(η) and J/ψ → η(η′) γ

The theoretical mechanisms for the decays ψ′ → ψπ⁰ and ψ′ → ψη, which violate SU₂ and SU₃, respectively discussed. It is argued that symmetry breaking in the decay amplitudes may be as important as π⁰ −η −η′ mixing. The π⁰ −η mechanism ψ′ → ψν → ψπ⁰ leads to Γ(ψ′ → ψπ⁰) = (3.3±1.0) × 10⁻³ Γ(ψ′ → ψν), but this number may be enhanced by a factor as large as 12 by π⁰−η′ mixing and isospin violation in the decay amplitude. The related decays ψ → ηγ and ψ → η′γ are also discussed.     

Non-1/mb power suppressed contributions to inclusive B → Xsll decays

We compute non-perturbative contributions to B → X_sl⁺l⁻ that are not explicitly suppressed by powers of the b-quark mass. They are proportional to and arise from an interference between the free-quark amplitude and high order terms in the matrix element of the four-quark operator s⁻γ^μ(1 − γ₅)cc^−βγ_μ(1 − γ₅)b_β. This correction is found to be small over most of the dalitz plot except near the charm threshold. Unfortunately, the perturbative computation we have performed is invalid near charm threshold and we do not except to see the structure found at lowest order reproduced in the data. We conclude that these non-perturbative contributions do not significantly modify the previous analysis of B → X_sl⁺l⁻.     

Spectral intensities in the ν1 band of NH3

Intensities have been measured for individual transitions in the Q and R branches of the ν₁ band of NH₃ using a difference-frequency laser spectrometer. The data yield an integrated band strength of S⁰_v=219.36±1.03 cm^-2/MPa at 297 K, corresponding to a transition moment of μ_v = 8.535(20) × 10^-32 C·m, and a Herman-Wallis correction factor, (1 + _jm)², where _j = 0.0209(20). The intensities of a few lines for K 7 were noticeably perturbed by a perpendicular Coriolis interaction with 2ν₄ (E, L = 2), so were excluded from the fit. A small sample of ν₃ band lines occurring in the ν₁ band scans also yields a rough estimate of the ν₃ band intensity with evident irregular perturbations.     

Supersymmetric contributions to direct CP violation in K→ππγ decays

We analyze the supersymmetric contributions to direct–CP–violating observables in K→ππγ decays induced by gluino–mediated magnetic–penguin operators. We find that ε′_+−γ and the differential width asymmetry of K^±→π^±π⁰γ decays could be substantially enhanced with respect to their Standard Model values, especially in the scenario where ε′/ε is dominated by supersymmetric contributions. These observables could therefore provide a useful tool to search for New Physics effects in |ΔS|=1 transitions, complementary to ε′/ε and rare decays.     

Photoproduction of Θ and other pentaquark states

We present constraints on the relative photoproduction cross sections of positive parity pentaquark states, Σ₅, Λ₅, and N₅, based on a minimum phenomenology gained in and their baryon–meson couplings as in the work of Close and Dudek. The possibility of anomalous signals in γp→K⁰_S(Θ⁺;Σ_d⁺) is discussed. We emphasize the importance of comparing with “conventional” states such as γN→KΣ(1660).     

Interactions between a tetraanionic porphyrin and the methylviologen dication in methanol studied by fluorescence quenching reaction

Fluorescence decay curves for 5,10,15,20-tetrakis(4-sulfonatophenyl)-21H,23H-porphine tetraanion (TPPS⁴⁻) have been measured in the absence and presence of the methylviologen dication (MV²⁺) with various ionic strengths in methanol. In the presence of MV²⁺ the fluorescence decays can be expressed by a double exponential function, I(t = I₁exp(−t/τ₁) + I₂exp(−t/τ₂). The contribution by the faster decay component to the total fluorescence signal increases with increasing MV²⁺ concentration. The faster decay process is attributed to fluorescence from the excited state of a solvent-separated ion pair (SSIP) formed between TPPS⁴⁻ and MV²⁺, and the slower process is attributed to fluorescence from free TPPS⁴⁻ ions in the solution. Rate constants for the quenching of fluorescence from free TPPS⁴⁻ by MV²⁺ (k_q) and formation constants for the SSIP (K_SSIP) were calculated and both are found to decrease with increasing ionic strength. The decrease in k_q and K_SSIP values can be interpreted in terms of the shielding of electrostatic attraction between the ions.     

Magnetic moment of the Δ (1232) resonance

The reaction γp → π^°γ′p has been measured with the TAPS BaF₂ calorimeter at the Mainz Microtron accelerator facility MAMI for energies between √2 = 1221–1331 MeV. Cross sections differential in angle and energy have been determined for the photon γ′ in three bins of the excitation energy. This reaction channel provides access to the magnetic dipole moment of the Δ⁺(1232) resonance and, for the first time, a value of μ_Δ+ = (2.7^+1.0_−1.3(stat) ± 1.5(syst) ± (theor)) π_N has been extracted.     

Simulations of migration, fragmentation and coalescence of non-wetting fluids in porous media

A model based on invasion percolation was used to simulate the migration on a non-wetting fluid through a porous medium filled with an immiscible wetting fluid under the influence of a gradient such as that provided by gravity. The migrating fluid clusters undergo both fragmentation and coalescence. The fragment size distribution obtained from two-dimensional simulations in which the gradient g is slowly increased from 0 can be represented by the scaling form N_s(g)s^-2ƒ(s|g|^-z where z=1+(D−1)ν(ν+1). Here D is the fractal dimensionality of invasion percolation, with trapping, and ν is the ordinary percolation correlation length exponent.     

Search for narrow NNπ resonances in exclusive pp→ppππ measurements

Narrow structures in the range of a few MeV have been searched for in ppπ⁺ and ppπ⁻ invariant mass spectra (M_ppπ⁺ and M_ppπ⁻) obtained from exclusive measurements of the pp→ppπ⁺π⁻ reaction at T_p=725,750 and 775 MeV using the PROMICE/WASA detector at CELSIUS. The selected reaction is particularly well suited for the search for dibaryon resonances decoupled from NN and/or NΔ. In the mass range 2020 MeV/c²<m_dibaryon<2085 MeV/c² no narrow structures could be identified on the 3σ level of statistical significance neither in M_ppπ⁻ nor in M_ppπ⁺ giving an upper limit (95% C.L.) for dibaryon production in this reaction of σ<20 nb.