Search

The muon anomalous magnetic moment is one of the most precisely measured quantities in particle physics and a persistent discrepancy of about 3 σ between standard model (SM) prediction and the experimental measurement has been observed. The leading order contribution aμhlo is actually the main source of uncertainty in the theoretical evaluation of the muon anomaly. It is obtained by a dispersion integral using the precision measurement of hadronic cross section. The KLOE experiment at the DAΦNE ϕ−factory in Frascati was the first to exploit Initial State Radiation (ISR) processes to obtain the e+e−→π+π−(γ) cross section below 1 GeV, that accounts for most (70%) of the leading order contribution to the muon anomaly. In year 2005 and 2008 the KLOE-collaboration has published two measurements of the π+π− cross section with the photon in the initial state emitted at small angle, and an independent measurement with the photon emitted at large angle was finalized in year 2011. These measurements were normalized using luminosity from Bhabha. In the last years, a new analysis of KLOE data has been performed for obtaining the pion form factor directly from the bin-by-bin π+π−γ to μ+μ−γ ratio. We present the results of this new measurement, showing the comparison with our previous measurements, and its impact on the hadronic contribution to the muon anomaly.

The ratio R-eta = Gamma(eta -> pi(+)pi(-)gamma)/Gamma(eta -> pi(+)pi(-)pi(0)) has been measured by analysing 22 million phi -> eta gamma decays collected by the KLOE experiment at DANE, corresponding to an integrated luminosity of 558 pb(-1). The eta -> pi(+)pi(-)gamma proceeds both via the rho resonant contribution, and possibly a non-resonant direct term, connected to the box anomaly. Our result, R-eta = 0.1856 +/- 0.0005(stat)+/- 0.0028(syst), points out a sizable contribution of the direct term to the total width. The di-pion invariant mass for the eta -> pi(+)pi(-)gamma decay could be described in a model-independent approach in terms of a(-) single free parameter, alpha. The determined value of the parameter alpha is alpha = (1.32 +/- 0.08(stat-0.09syst)(+0.10) +/- 0.02(theo)) GeV-2. 2012 Elsevier B.V. All rights reserved.

"We have carried out a new direct search for the CP violating decay KS→3π0 with 1.7 fb−1 of e+e− collisions collected by the KLOE detector at the Φ-factory DAΦ NE. We have searched for this decay in a sample of about 5.9×108KSKL events tagging the KS by means of the KL interaction in the calorimeter and requiring six prompt photons. With respect to our previous search, the analysis has been improved by increasing of a factor four the tagged sample and by a more effective background rejection of fake KS tags and spurious clusters. We find no candidates in data and simulated background samples, while we expect 0.12 standard model events. Normalizing to the number of KS→2π0 events in the same sample, we set the upper limit on BR(KS→3π0)⩽2.6×10−8 at 90% C.L., five times lower than the previous limit. We also set the upper limit on the η000 parameter, |η000|⩽0.0088 at 90% C.L., improving by a factor two the latest direct measurement.. . . "

Exclusive measurements of the production of eta mesons in the p+p->p+p+eta reaction have been carried out at excess energies of 16 and 37 MeV above threshold. The deviations from phase space are dominated by the proton-proton final state interaction and this influences particularly the energy distribution of the eta meson. However, evidence is also presented at the higher energy for the existence of an anisotropy in the angular distributions of the eta meson and also of the final proton-proton pair, probably to be associated with D-waves in this system interfering with the dominant S-wave term. The sign of the eta angular anisotropy suggests that rho-exchange is important for this reaction.

Different π and η meson production channels in proton-proton and proton-deuteron collisions have been studied at the CELSIUS storage ring using an internal cluster-jet target setup [1]. During the last years more emphasis has been put on ππ and all but one of the possible channels in proton-proton collisions have been studied. Recently also the quasi-free p+nd+η reaction cross section has been measured at threshold using 1295 MeV protons and target deuterium. Excess energies from threshold to 10 MeV in the center of mass of the final dη system were covered. Approaching the threshold the cross section is enhanced compared to phase-space expectations. This behaviour is typical for a strong final-state interaction.

The first measurement of the cross section of the quasifree $p\stackrel{\ensuremath{\rightarrow}}{n}\mathrm{pn}\ensuremath{\eta}$ reaction has been carried out at the CELSIUS storage ring using a deuterium internal cluster jet target. The energy dependence of the cross section is extracted using a fixed incident proton energy of ${T}_{p}=1350 \mathrm{MeV}$ and exploiting the Fermi momentum of the struck neutron. The data cover a range of center-of-mass excess energies from 16 to 109 MeV. The shape of the excitation function is broadly similar to that of the $p\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{pp}\ensuremath{\eta}$ reaction, though with a cross section about a factor of 6.5 larger.

The quasifree p + n --> d + eta reaction cross section has been measured at the threshold using 1295 MeV protons in the CELSIUS storage ring and an internal cluster-jet deuterium target. The kinematics is chosen such that the target proton can be assumed

The quasifree p+n{r_arrow}d+{eta} reaction cross section has been measured in the near-threshold region using deuterium from an internal cluster-jet target and 1350 MeV protons in the CELSIUS storage ring of the The Svedberg Laboratory, Uppsala. The energy dependence of the cross section is extracted by exploiting the Fermi momentum of the target neutron and reconstructing the kinematics on an event-by-event basis. The data cover center of mass excess energies from 16 to 113 MeV. {copyright} {ital 1997} {ital The American Physical Society}

An exclusive measurement of the dd -> 3He n \pi 0 reaction was carried at a beam momentum of p = 1.2 GeV/c using the WASA-at-COSY facility. For the first time data on the total cross section as well as differential distributions were obtained. The data are described with a phenomenological approach based on a combination of a quasi-free model and a partial wave expansion for three-body reaction. The total cross section is found to be \sigma(tot) = (2.89 +- 0.01(stat) +- 0.06(sys) +- 0.29(norm)) \mu b. The contribution of the quasi-free processes (with the neutron being target or beam spectator) accounts for 38% of the total cross section and dominates the differential distributions in specific regions of the phase space. The remaining part of the cross section can be described within a partial wave decomposition indicating the significance of p-wave contributions in the final state.

The ϕ-factory DAΦNE offers a possibility to select pure kaon beams, charged and neutral ones. In particular, neutral kaons from ϕ → K S K L are produced in pairs and the detection of a K S ( K L ) tags the presence of a K L ( K S ) . This allows to perform precise measurements of kaon properties by means of KLOE detector. Another advantage of a ϕ-factory consists in fact that the neutral kaon pairs are produced in a pure quantum state ( J P C = 1 − − ) , which allows to investigate CP and CPT symmetries via quantum interference effects, as well as the basic principles of quantum mechanics. A review of the most recent results of the KLOE experiment at DAΦNE using pure kaon beams or via quantum interferometry is presented together with prospects for kaon physics at KLOE–2.

A detector setup for the cooler storage ring CELSIUS is described. The setup detects particles produced in interactions between the internal beam and a cluster-jet target. Particles emitted in the forward direction are measured by means of arrays of plastic scintillators and proportional counters. Particles, particularly photons, emitted more isotropically are measured by means of two calorimeters containing CsI(Na) crystals. The performance of the setup is given for neutral meson production in proton-proton and proton-deuteron interactions in the energy range 290–1360 MeV.

The production of omega mesons in the pd -> He-3 omega reaction has been studied at two energies near the kinematic threshold, T-p = 1450 MeV and T-p = 1360 MeV. The differential cross section w ...

The WASA 4pi multidetector system, aimed at investigating light meson production in light ion collisions and eta meson rare decays at the CELSIUS storage ring in Uppsala is presented. A detailed description of the design, together with the anticipated and achieved performance parameters are given., 25 pages, 20 figures

The CELSIUS-WASA setup is used to measure the 3{pi}{sup 0} decay of {eta} mesons produced in pp interactions with beam kinetic energies of 1.36 and 1.45 GeV. The efficiency-corrected Dalitz plot and density distributions for this decay are shown, together with a fit of the quadratic slope parameter {alpha} yielding {alpha}=-0.026{+-}0.010(stat){+-}0.010(syst). This value is compared to recent experimental results and theoretical predictions.

The reaction pp -> pp pi(0) was studied with the WASA detector at the CELSIUS storage ring. The center of mass angular distribution of the pi(0) was obtained by detection of the gamma decay prod ...

The ABC effect -- an intriguing low-mass enhancement in the $\pi\pi$ invariant mass spectrum -- is known from inclusive measurements of two-pion production in nuclear fusion reactions. First exclusive measurements carried out at CELSIUS-WASA for the fusion reactions leading to d or $^3$He reveal this effect to be a $\sigma$ channel phenomenon associated with the formation of a $\Delta\Delta$ system in the intermediate state and combined with a resonance-like behavior in the total cross section. Together with the observation that the differential distributions do not change in shape over the resonance region the features fulfill the criteria of an isoscalar s-channel resonance in $pn$ and $NN\pi\pi$ systems, if the two emitted nucleons are bound. It obviously is robust enough to survive in nuclei as a dibaryonic resonance configuration. In this context also the phenomenon of $N\Delta$ resonances is reexamined., Comment: 8 pages,3 figures, Proc. Int. School Nucl. Phys., 29th course on Quarks in Hadrons and Nuclei, Erice 2007 (to be published in Progress in Particle and Nuclear Physics)

The pd-->pdeta reaction has been studied in a kinematically complete experiment at five beam energies 927, 961, 996, 1032, and 1096 MeV. In contrast to our measurement of the pd-->(3)Heeta at the same energies, all the c.m. angular distributions are consistent with isotropy. The energy dependence of the total cross section seems to follow a three-body phase space as modified by a proton-deuteron final-state interaction, and such an extrapolation is consistent with other near-threshold data. The distributions of the pd and peta invariant mass at fixed beam energy are both close to those of phase space. However, this is not the case for the deta invariant mass, which shows significant structure in the first few MeV above threshold. This behavior is similar to that observed in the energy variation of the pn-->deta total cross section and is the sign of a large eta-deuteron scattering length that has been predicted in many theoretical models.

Exclusive measurements of the $p\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{pp}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ reaction have been carried out at ${T}_{p}=775\mathrm{MeV}$ at CELSIUS using the PROMICE/WASA setup. Together with data obtained at lower energy, they point to a dominance of the Roper excitation in this process. From the observed interference of its decay routes ${N}^{*}\ensuremath{\rightarrow}N\ensuremath{\sigma}$ and ${N}^{*}\ensuremath{\rightarrow}\ensuremath{\Delta}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\pi}}N\ensuremath{\sigma},$ their energy-dependent relative branching ratio is determined.

The $\mathrm{pp}\ensuremath{\rightarrow}\mathrm{pp}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ reaction has been measured exclusively near threshold at CELSIUS. The total cross sections are nearly an order of magnitude lower than expected from previous inclusive measurements. The differential cross sections reveal $\mathrm{pp}\ensuremath{\rightarrow}{\mathrm{pp}}^{*}(1440)\ensuremath{\rightarrow}\mathrm{pp}\ensuremath{\sigma}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}pp({\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{)}_{I\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{\ell}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0}$ as the dominant process as well as significant contributions from ${p}^{*}\ensuremath{\rightarrow}{\ensuremath{\Delta}}^{++}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\rightarrow}p\ensuremath{\sigma}$. The observed anisotropy in the proton angular dependence is consistent with heavy-meson exchange. In the invariant mass spectra, no narrow structures of statistical relevance $(3\ensuremath{\sigma})$ are found.

Quasifree Bremsstrahlung in the dp --> dp gamma reaction above the pion production threshold

The pp--pp pi(+) pi(-) reaction has been measured exclusively near threshold at CELSIUS. The total cross sections are nearly an order of magnitude lower than expected from previous inclusive measurements. The differential cross sections reveal pp--pp(*)(1440)--pp sigma = pp(pi(+)pi(-))(I = l = 0) as the dominant process as well as significant contributions from p(*)--Delta(++)pi(-)--psigma. The observed anisotropy in the proton angular dependence is consistent with heavy-meson exchange. In the invariant mass spectra, no narrow structures of statistical relevance (3sigma) are found.

Preliminary results of the measurement of pd→ppnγγ reaction at around 1 GeV are presented. The reaction was measured at the CELSIUS storage ring using the WASA/PROMICE set-up. The quasi free mechanism was found to be dominant with Δ(1232) excitation in the proton-pion system. The signal at the position of Roper resonance was observed in the proton-π0 invariant mass. A class of “non-spectator” events was observed with small proton-proton invariant mass.

One of the main topics in the experimental programme at the CELSIUS cooler/storage ring of the The Svedberg Laboratory, Uppsala is meson production in light ion collisions near threshold. The PROMICE/WASA collaboration is studying π0 and 2π production in pp collisions and ŋ production in pN collisions. Some of the reaction channels have been measured for the first time in any detail. The experimental method is reviewed and some results are presented, together with an outlook.

The WASA 4π detector at the The Svedberg Laboratory in Uppsala is now being commissioned. This detector will make possible new detailed studies of many interesting rare processes in intermediate energy light-ion physics. WASA is built around a new target system, providing well defined internal hydrogen (and deuterium) targets of high density. It has a detection coverage of close to 4π sr for high energy photons and charged particles and it includes a strong magnetic field provided by an extremely thin-walled superconducting solenoid.

Differential cross sections of the reactions $pp \to d\pi^+$ and $pp \to pn\pi^+$ have been measured at $T_p = 400$ MeV by detecting the charged ejectiles in the angular range $4^0 \leq \Theta_{Lab} \leq 21^\circ$. The deduced total cross sections agree well with those published previously for neighbouring energies. The invariant mass spectra are observed to be strongly affected by $\Delta$ production and $NN$ final-state interaction. The data are well described by Monte Carlo simulations including both these effects. The ratio of $pp \to pn\pi^+$ and $pp \to d\pi^+$ cross sections also compares favourably to a recent theoretical prediction which suggests a dominance of $np$-production in the relative $^3S_1$-state., Comment: 17 pages, 5 figures

The CLAMSUD spectrometer has been recently installed at the jet-target position of the CELSIUS ring at “THE SVEDBERG LABORATORY.” The physical purpose is the study of kaon production at energies below the N-N threshold. Due to the low cross-section and short lifetime of kaons we increased the solid angle by means of two quadrupoles positioned at the entrance of the dipole. The experimental quality of the measurements due both to the beam characteristics and to the CLAMSUD detector will be shown.

The PROMICE and WASA collaborations are engaged in a common programme in studies of pp and pd reactions at the CELSIUS storage ring at the The Svedberg Laboratory, Uppsala. Emphasis is placed on measurements of neutral meson production in the threshold region. The experimental set-up is presented together with a review of results obtained.

A new type of compact pair spectrometer is developed for studies of radiative capture reactions and internal pair production at intermediate energies. The first results from capture reactions on 11B are presented together with theoretical predictions based on a continuum shell model calculation.

The neutron pickup reaction (p,d) has been studied at a proton energy of 800 MeV on targets of /sup 7/Li, /sup 12/C, /sup 13/C, /sup 16/O, /sup 25/Mg, /sup 28/Si, and /sup 40/Ca. States known to correspond to single-hole excitations are seen and in most cases the data are properly understood through distorted-wave Born approximation calculations. High-spin final states are prominent, and some are shown to be excited through multiple step processes. The strongest states seen in the data do not correspond to known levels.

We have measured the reactions $^{3,4}\mathrm{He}({\ensuremath{\pi}}^{\ensuremath{-}}, n)^{2,3}\mathrm{H}$ at ${T}_{\ensuremath{\pi}}=285, 428, 525, \mathrm{and} 575$ MeV over an angular range ${\ensuremath{\theta}}_{n}=18\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}134\ifmmode^\circ\else\textdegree\fi{}$ in the center-of-momentum frame, and the reaction $^{3}\mathrm{He}({\ensuremath{\pi}}^{\ensuremath{-}}, {\ensuremath{\pi}}^{0})^{3}\mathrm{H}$ at ${T}_{\ensuremath{\pi}}=285, 428, \mathrm{and} 525$ MeV over an angular range ${\ensuremath{\theta}}_{{\ensuremath{\pi}}^{0}}=60\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}140\ifmmode^\circ\else\textdegree\fi{}$. The pion absorption is found to proceed by a two-nucleon mechanism, with an energy dependence consistent with the formation of an $I=\frac{1}{2}$ resonance in the intermediate state. The pion single-charge exchange is discussed within the framework of the optical and Glauber models, and the dependence on the $^{3}\mathrm{He}$ electromagnetic form factors is discussed. We also examine the isospin dependence of the $\ensuremath{\pi}$-nuclear Hamiltonian.NUCLEAR REACTIONS $^{3,4}\mathrm{He}({\ensuremath{\pi}}^{\ensuremath{-}}, n)^{2,3}\mathrm{H}$, ${T}_{\ensuremath{\pi}}=285\ensuremath{-}575$ MeV, ${\ensuremath{\theta}}_{n}=18\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}134\ifmmode^\circ\else\textdegree\fi{}$; and $^{3}\mathrm{He}({\ensuremath{\pi}}^{\ensuremath{-}}, {\ensuremath{\pi}}^{0})^{3}\mathrm{H}$,, ${T}_{\ensuremath{\pi}}=285\ensuremath{-}525$ MeV, ${\ensuremath{\theta}}_{{\ensuremath{\pi}}^{0}}=60\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}140\ifmmode^\circ\else\textdegree\fi{}$; measured $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}$; discussed reaction mechanism, effects of form factors.

We have measured the cross section of /sup 3/He(..pi../sup -/,..pi../sup 0/)/sup 3/H at T = 285, 428, and 525 MeV for angles in the range of 60/sup 0/< or approx. =theta< or approx. =135/sup 0/ covering the momentum transfer range 0.5< or approx. =q< or approx. =1.0 GeV/c. Comparison is made with Glauber model calculations to discuss the sensitivity to nuclear structure and pion-nucleus interaction effects.

Differential cross sections are reported for (${\ensuremath{\pi}}^{+}$,$p$) reactions to discrete final states over the range $\ensuremath{\theta}=20\ensuremath{-}95 (116\ifmmode^\circ\else\textdegree\fi{})$ and for the inclusive (${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$,$p$) reactions in $^{6}\mathrm{Li}$ at $\ensuremath{\theta}=20\ifmmode^\circ\else\textdegree\fi{}$ to the continuum. The continuum cross sections indicate the predominance of the two-nucleon pion absorption mechanism where (${\ensuremath{\pi}}^{\ensuremath{-}}$,$p$) shows the importance of multiple (charge-exchange) scattering. The combined use of the exclusive and inclusive cross sections is discussed.NUCLEAR REACTIONS $^{6,7}\mathrm{Li}$(${\ensuremath{\pi}}^{+}$,$p$)$^{5,6}\mathrm{Li}$, ${T}_{\ensuremath{\pi}}=75$ MeV, $\ensuremath{\theta}=20\ensuremath{-}116\ifmmode^\circ\else\textdegree\fi{}$, ${T}_{\ensuremath{\pi}}=175$ MeV, ${\ensuremath{\theta}}_{p}=20\ensuremath{-}95\ifmmode^\circ\else\textdegree\fi{}$ measured $\ensuremath{\sigma}(\ensuremath{\theta})$; $^{6}\mathrm{Li}$(${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$,$p$), ${T}_{\ensuremath{\pi}}=75, 175$ MeV, ${\ensuremath{\theta}}_{p}=20\ifmmode^\circ\else\textdegree\fi{}$ measured $\ensuremath{\sigma}({T}_{p})$; discussed reaction mechanism effects.

Angular distributions of the differential cross section and the analyzing power for the 9Be( p , π+)10Be and the 9Be( p , π−)10C reactions have been measured at 650 MeV. A phenomenological comparison, based on a model for pion emission from the target nucleus, is made between the analyzing power from the ( p , π) data and polarization data from πN scattering.

The (..pi../sup +/, p) reaction has been studied at T/sub ..pi../ = 90 and 180 MeV on /sup 12/C, and at T/sub ..pi../ = 90 and 170 MeV on /sup 13/C. The resolution was sufficient to resolve many single levels in the residual nuclei, and angular distributions were obtained between laboratory angles of 10/sup 0/ and 115/sup 0/. A comparison between the present (..pi.., p) data and existing high-energy (p,d) data in terms of a model assuming intermediate pion exchange in the (p,d) reaction indicates that the (..pi..,p) reaction is an important subprocess in the (p,d) reaction. The present data also suggest that pion rescattering is likely to be a fundamental part of the (..pi.., p) reaction mechanism.

Angular distributions from the (p, π+) reaction on 90Zr and 208Pb leading to discrete nuclear states in the residual nuclei have been recorded at 180 MeV. The data are compared with calculations in the one nucleon model. The (p, π+) differential cross section is found to be unusually small. This result is not predicted by a DWBA calculation.

The instrument described is intended for the detection and measurement of α particles from coherent interactions of high-energy particles with 4 He nuclei. It allows the determination of the magnitude and the direction of the momenta of the helium recoils from interactions in a pressurized gas target. The measurements are carried out with spark chambers and scintillation counters. Recoils emitted at angles greater than 65° with respect to the beam direction are accepted and the range of azimuth angles covered is 294°.

Asymmetries for elastic scattering of transversely polarised 800 MeV protons from Hydrogen in the coulomb interference region are presented and compared with the predictions of a recent phase shift analysis.