Light scalar mesons in experimental data on the decay ϕ → π 0 π 0 γ and ππ scattering

Results of a simultaneous analysis of data from the KLOE detector (Italy) on the decay ? → π ⁰ π ⁰ γ and data on ππ scattering and on the reaction ππ → K $ \bar K Results of a simultaneous analysis of data from the KLOE detector (Italy) on the decay ϕ → π ⁰ π ⁰ γ and data on ππ scattering and on the reaction ππ → K are presented. These data are described with allowance for the chiral shielding of the σ(600) meson. The results favor the four-quark nature of the σ(600) and f ₀(980) mesons. Original Russian Text ? N.N. Achasov, A.V. Kiselev, 2007, published in Yadernaya Fizika, 2007, Vol. 70, No. 11, pp. 2005–2021.     

Electroweak radiative corrections to e+e− → Z0Z0

The cross section for e⁺e⁻ → Z⁰Z⁰ with arbitrary polarizations of the leptons and bosons is calculated in the standard electroweak model including the complete one-loop virtual and soft-photon bremsstrahlung corrections. All necessary analytical formulas are presented; numerical results are discussed for the unpolarized case and for the polarization asymmetry. At LEP 200 energies the weak corrections are dominated by the self-energy of the external Z⁰-bosons which contributes about +15%. With increasing energy, the weak corrections decrease up to -18% at 1 TeV due to other contributions.     

Supersymmetric Box Contributions toe + e −→Z 0 h 0 ande + e −→A 0 h 0

Within the MSSM we calculate the electroweak 1-loop box contributions to the processese ⁺ e ^–Z ⁰ h ⁰ ande ⁺ e ^–Z ⁰ h ⁰. We present detailed results for c.m. energies and as well as for tan =2 and tan =50. The box contributions to the processe ⁺ e ^–Z ⁰ h ⁰ are, depending on and tan , of the order –2 to –20% and toe ⁺ e ^– A ⁰ h ⁰ of 2 to 10%.     

TheC-metric withm = 0,e ≠ 0

TheC-metric with parametersm = 0,e 0 is transformed to Weyl form; the sources then appear as a spherical cap of chargee, and an uncharged semi-infinite line mass. Next, the Weyl metric is enlarged by a further transformation. The enlarged space-time has as its source two uniformly accelerated charged caps. In an appropriate approximation, the electromagnetic field components of this solution are identical to those of the Born solution of classical electrodynamics.     

The e + e −→π0π0γ process below 1.0 GeV

The e ⁺ e ^?→π⁰π⁰ γreaction was studied in the energy range 0.36–0.97 GeV on a VEPP-2M e ⁺ e ^? collider with an SND detector. The decay probabilities were found to be B(ω→ π⁰π⁰γ)= (7.8 ±2.7±2.0)×10^?5 and B(π→ π⁰π⁰γ)= (4.8 _?1.8 ^+3.4 ±0.2)×10^?5.     

e+e-→e+e-π0π0 at DAΦNE

The production of the σ(500) meson in γγ→π⁰π⁰ is studied. In particular, the KLOE data collected during the DAΦNE run at are appropriate to this purpose because of the strong reduction of kaon backgrounds. PACS 12.39.-x     

Measurement of the single-spin asymmetry in the reaction π − d ↑ → π 0 X in the beam-fragmentation region at 40 GeV and p T of up to 2 GeV/c

The single-spin asymmetry A _N in the reaction π ^? + d _↑ → π ⁰ + X in the beam-fragmentation region at the energy of 40 GeV was investigated by using the PROZA setup installed at the U-70 accelerator of the Institute for High Energy Physics (IHEP, Protvino). It was measured to be A _N = (13.6 ± 2.6(stat.) ± 2.0(syst.))% in the intervals 0.7 < x _F < 1.0 and 1.0 < p _T < 1.8 GeV/c. The results agree with the asymmetry of π ⁰ mesons in the charge-exchange reaction π ^? + p _↑ → π ⁰ + n at the same values of the transverse momentum and beam energy. The asymmetry in the reaction K ^? + d _↑ → π ⁰ + X was simultaneously measured and found to be A _N = (11 ± 14)% for p _T > 1.2 GeV/c.     

恢复系数e一定满足0≤e≤1吗？

作者从恢复系数e的一般定义出发，引入了“穿透”碰撞与“爆炸”碰撞的概念，从而将e的取值范围扩大到实数。     

恢复系数e一定满足0≤e≤1吗?

作者从恢复系数ｅ的一般定义出发，引入了“穿透”碰撞与“爆炸”碰撞的概念，从而将ｅ的取值范围扩大到实数．     

Photoproduction of π + p pairs on nuclei

The photoproduction of pion-nucleon pairs on nuclei was analyzed. The contributions of both nucleonic and isobar configurations in the ground state of nuclei were taken into account. The cross section for the photoproduction of pion-proton pairs in the reactions ¹⁶O(??, ?? ⁺ p)¹⁵C and ¹²C(??, ?? ⁺ p)¹¹Be were calculated.     

Comments on preliminary data on the reactions e + e −→φ→γ f 0(980)→γπ0π0

Preliminary data on the reactions e ⁺ e ⁻→φ→γ f ₀(980)→γπ⁰π⁰ together with data on ππ scattering and the reactions J/ψ→φπ⁺π⁻ and K ⁻ p→π ⁺π⁻(Λ,Σ) are analyzed. The analysis shows that the mass of the f ₀(980) meson is = 950 MeV, and BR(φ→γf ₀→γπ⁰π⁰)≃ 1× 10⁻⁴, indicating that the f ₀(980) resonance is of a four-quark nature. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 445–449 (10 April 1998)     

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.     

QCD studies and discoveries with e + e − colliders and future perspectives

Observations of new charmonium(-like) and bottomonium(-like) states (sometimes refered to as “XYZ” states) at e ^?+? e ^??? colliders have changed our picture of quarkonia systems as QCD bound states. Potential models with a linear confinement ansatz, which were able to predict many conventional states with an accuracy of ～1 MeV, absolutely fail in describing many of the new states. Symmetries play an important role e.g. in the determination of the quantum numbers (such as charge conjugation in the radiative decays) or in trying to explain surprising properties such as isospin violation.     

The process e + e − → ωπ0 near the Φ resonance

The reaction e ⁺ e ^?→ωπ⁰ near a Φ resonance was studied with a spherical neutral detector at VEPP-2M e ⁺ e ^? collider. Both main modes of decay of a ω meson were investigated: ω→π⁺π^?π⁰ and ω→π ⁰γ. The probability of decay Φ→ωπ⁰ was obtained from the magnitude of the interference wave in the cross section for the reaction e ⁺ e ^?→ωπ⁰→ π⁺π^?π⁰π⁰: B(Φ→ωπ⁰) = (5.5 _?1.4 ^+1.6 ±0.3) ×10^?5. The ratio of the partial widths of the ω meson was obtained from the ratio of the cross sections for the two modes: Γ(ω→π⁰γ )/Γ(ω→π⁺π^?π⁰) = 0.0994 ± 0.0036 ± 0.0038.     

Investigation of the reaction π − p → η′π 0 n at the VES spectrometer

Results obtained by investigating the reaction π ^? p → η′π ⁰ n at the VES spectrometer (Institute for High Energy Physics, Protvino) are presented. The effective-mass spectrum and angular distributions of η′π ⁰ events are compared with their counterparts for ηπ ⁰ and η′π ^? events selected from the same data sample. The ratio R of the branching fractions for the decays of a ₂ ⁰ (1320) mesons into η′π and ηπ is measured. The result is R=0.047±0.018, which agrees with the value measured previously for a ₂ ^? . An investigation of P-wave production in the η′π ⁰ and ηπ ⁰ systems over the effective-mass interval 1.45–1.9 GeV/c2 leads to the conclusion that the coupling of the exotic object π ₁ (1600) to the ρπ channel is suppressed in relation to its coupling to the η′π or the b ₁(1235)π channel.     

Comparative study of Z′ searches in e+e− and e−e− scattering

We consider indirect searches for additional neutral vector bosons in e⁺e⁻ and e⁻e⁻ collisions, and compare these two linear collider modes with similar analysis procedures and assumptions. Discovery limits and resolving power are discussed in a model-independent way.     

Discovering and studying bileptons with e−e− collisions

We analyze the prospects for discovering and unraveling the nature of doubly charged bileptons at a linear collider of the next generation running in its e⁻e⁻ mode. We stress the importance of initial state radiation, beam spread and polarization, and compute the discovery bounds. The gauge nature of vector bileptons can be determined by studying hard photon emission.