1. |
- Adlarson, Patrik, et al.
(author)
-
Measurement of the eta -> pi(+)pi(-)pi(0) Dalitz plot distribution
- 2014
-
In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 90:4, s. 045207-
-
Journal article (peer-reviewed)abstract
- The Dalitz plot distribution of the eta -> pi(+)pi(-)pi(0) decay is determined by using a data sample of 1.2 x 10(7) eta mesons from the pd -> He-3 eta reaction at 1 GeV collected by the WASA detector at COSY.
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2. |
- Adlarson, Patrik, et al.
(author)
-
Abashian-Booth-Crowe Effect in Basic Double-Pionic Fusion : A New Resonance?
- 2011
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 106:24, s. 242302-
-
Journal article (peer-reviewed)abstract
- We report on an exclusive and kinematically complete high-statistics measurement of the basic double-pionic fusion reaction pn -> d pi(0)pi(0) over the full energy region of the ABC effect, a pronounced low-mass enhancement in the pi pi-invariant mass spectrum. The measurements, which cover also the transition region to the conventional t- channel Delta Delta process, were performed with the upgraded WASA detector setup at COSY. The data reveal the Abashian-Booth-Crowe effect to be uniquely correlated with a Lorentzian energy dependence in the integral cross section. The observables are consistent with a narrow resonance with m = 2.37 GeV, Gamma approximate to 70 MeV and I(J(P)) = 0(3(+)) in both pn and Delta Delta systems. Necessary further tests of the resonance interpretation are discussed.
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3. |
- Adlarson, Patrik, et al.
(author)
-
Abashian-Booth-Crowe resonance structure in the double pionic fusion to He-4
- 2012
-
In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 86:3, s. 032201-
-
Journal article (peer-reviewed)abstract
- Exclusive and kinematically complete high-statistics measurements of the double pionic fusion reaction dd -> He-4 pi(0)pi(0) have been performed in the energy range 0.8-1.4 GeV covering thus the region of the Abashian-Booth-Crowe effect, which denotes a pronounced low-mass enhancement in the pi pi invariant mass spectrum. The experiments were carried out with the WASA detector setup at the cooler synchrotron at Forshungszentrum Julich GmbH. Similar to the observation in the basic pn -> d pi(0)pi(0) reaction, the data reveal a correlation between the ABC effect and a resonancelike energy dependence in the total cross section. The maximum occurs at m = 2.37 GeV + 2m(N), i.e., at the same position as in the basic reaction. The observed resonance width Gamma approximate to 160 MeV can be understood from broadening due to Fermi motion of the nucleons in initial and final nuclei together with collision damping. Differential cross sections are described equally well by the hypothesis of a pn resonance formation during the reaction process.
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4. |
- Adlarson, Patrik, et al.
(author)
-
Differential cross sections for neutron-proton scattering in the region of the d* (2380) dibaryon resonance
- 2020
-
In: Physical Review C. Nuclear Physics. - : AMER PHYSICAL SOC. - 0556-2813 .- 1089-490X. ; 102:1
-
Journal article (peer-reviewed)abstract
- Differential cross sections have been extracted from exclusive and kinematically complete high-statistics measurements of quasifree polarized (n) over barp scattering performed in the energy region of the d* (2380) dibaryon resonance covering the range of beam energies T-n = 0.98-1.29 GeV (root s = 2.32-2.44 GeV). The experiment was carried out with the WASA-at-COSY setup having a polarized deuteron beam impinged on the hydrogen pellet target and utilizing the quasifree process dp -> np + p(spectator). In this way the np differential cross section sigma (Theta) was measured over a large angular range. The obtained angular distributions complement the corresponding analyzing power A(y)(Theta) measurements published previously. A SAID partial-wave analysis incorporating the new data strengthens the finding of a resonance pole in the coupled D-3(3) - (3)G(3) waves.
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5. |
- Adlarson, Patrik, et al.
(author)
-
Exclusive measurement of the eta -> pi(+) pi(-) gamma decay
- 2012
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 707:2, s. 243-249
-
Journal article (peer-reviewed)abstract
- An exclusive measurement of the decay eta -> pi(+) pi(-) gamma has been performed at the WASA facility at COSY. The eta mesons were produced in the fusion reaction pd -> He-3 X at a proton beam momentum of 1.7 GeV/c. Efficiency corrected differential distributions have been extracted based on 13 960 +/- 140 events after background subtraction. The measured pion angular distribution is consistent with a relative p-wave of the two-pion system, whereas the measured photon energy spectrum was found at variance with the simplest gauge invariant matrix element of eta -> pi(+) pi(-) gamma. A parameterization of the data can be achieved by the additional inclusion of the empirical pion vector form factor multiplied by a first-order polynomial in the squared invariant mass of the pi(+) pi(-) system.
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6. |
- Adlarson, Patrik, et al.
(author)
-
Investigation of the dd -> (3)Hen pi(0) reaction with the FZ Julich WASA-at-COSY facility
- 2013
-
In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 88:1, s. 014004-
-
Journal article (peer-reviewed)abstract
- An exclusive measurement of the dd -> (3)Hen pi(0) reaction was carried out at a beam momentum of p(d) = 1.2 GeV/c using the WASA-at-COSY facility. Information on the total cross section as well as differential distributions was obtained. The data are described by a phenomenological approach based on a combination of a quasifree model and a partial wave expansion for the 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 quasifree processes ( with the beam or target neutron being a spectator) accounts for 38% of the total cross section and dominates the differential distributions in specific regions of phase space. The remaining part of the cross section can be described by a partial wave decomposition indicating the significance of p-wave contributions in the final state.
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7. |
- Adlarson, P., et al.
(author)
-
Isospin decomposition of the basic double-pionic fusion in the region of the ABC effect
- 2013
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 721:4-5, s. 229-236
-
Journal article (peer-reviewed)abstract
- Exclusive and kinematically complete high-statistics measurements of the basic double-pionic fusion reactions pn -> d pi(0)pi(0), pn -> d pi(+)pi(-) and pp -> d pi(+)pi(0) have been carried out simultaneously over the energy region of the ABC effect using the WASA detector setup at COSY. Whereas the isoscalar reaction part given by the d pi(0)pi(0) channel exhibits the ABC effect, i.e. a low-mass enhancement in the pi pi-invariant mass distribution, as well as the associated resonance structure in the total cross section, the isovector part given by the d pi(+)pi(0) channel shows a smooth behavior consistent with the conventional t-channel Delta Delta process. The d pi(+)pi(-) data are very well reproduced by combining the data for isovector and isoscalar contributions, if the kinematical consequences of the isospin violation due to different masses for charged and neutral pions are taken into account.
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8. |
- Adlarson, Patrik, et al.
(author)
-
Measurement of the pn -> pp pi(0)pi(-) reaction in search for the recently observed resonance structure in d pi(0)pi(0) and d pi(+)pi(-) systems
- 2013
-
In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 88:5, s. 055208-
-
Journal article (peer-reviewed)abstract
- Exclusive measurements of the quasifree pn -> pp pi(0)pi(-) reaction have been performed by means of pd collisions at T-p = 1.2 GeV using the wide angle shower apparatus (WASA) detector setup at the cooler synchrotron COSY (Institut fur Kernphysik, Julich). Total and differential cross sections have been obtained covering the energy region root s = (2.35-2.46) GeV, which includes the region of the ABC effect and its associated resonance structure. NoABCeffect, i.e., low-mass enhancement is found in the pi(0)pi(-) -invariant mass spectrum, in agreement with the constraint from Bose statistics that the isovector pion pair can not be in relative s wave. At the upper end of the covered energy region t-channel processes for Roper, Delta(1600) and Delta Delta excitations provide a reasonable description of the data, but at low energies the measured cross sections are much larger than predicted by such processes. Adding a resonance amplitude for the resonance at m = 2.37 GeV with Gamma = 70 MeV and I (J(P)) = 0(3(+)) observed recently in pn -> d pi(0)pi(0) and pn -> d pi(+)pi(-) reactions leads to an agreement with the data also at low energies.
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9. |
- Adlarson, Patrik, et al.
(author)
-
pi(0)pi(0) Production in proton-proton collisions at T-p=1.4 GeV The WASA-at-COSY Collaboration
- 2012
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 706:4-5, s. 256-262
-
Journal article (peer-reviewed)abstract
- The reaction pp -> pp pi(0)pi(0) has been investigated at a beam energy of 1.4 GeV using the WASA-at-COSY facility. The total cross section is found to be (324 +/- 21(systematic) +/- 58(normalization)) mu b. In order to study the production mechanism, differential kinematic distributions have been evaluated. The differential distributions indicate that both initial state protons are excited into intermediate Delta(1232) resonances, each decaying into a proton and a single pion, thereby producing the pion pair in the final state. No significant contribution of the Roper resonance N*(1440) via its decay into a proton and two pions is found.
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10. |
- Adlarson, Patrik, et al.
(author)
-
ABC effect and resonance structure in the double-pionic fusion to He-3
- 2015
-
In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 91:1, s. 015201-
-
Journal article (peer-reviewed)abstract
- Exclusive and kinematically complete measurements of the double pionic fusion to He-3 have been performed in the energy region of the so-called ABC effect, which denotes a pronounced low-mass enhancement in the pi pi-invariant mass spectrum. The experiments were carried out with the WASA detector setup at COSY (the cooler synchrotron at Forschungszentrum Julich). Similar to the observations in the basic pn -> d pi(0)pi(0) reaction and in the dd -> He-4 pi(0)pi(0) reaction, the data reveal a correlation between the ABC effect and a resonance-like energy dependence in the total cross section. Differential cross sections are well described by the hypothesis of d* resonance formation during the reaction process in addition to the conventional t-channel Delta Delta mechanism. The deduced d* resonance width can be understood from collision broadening due to Fermi motion of the nucleons in initial and final nuclei.
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11. |
- Adlarson, Patrik, et al.
(author)
-
Charge symmetry breaking in dd -> He-4 pi(0) with WASA-at-COSY
- 2014
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 739, s. 44-49
-
Journal article (peer-reviewed)abstract
- Charge symmetry breaking (CSB) observables are a suitable experimental tool to examine effects induced by quark masses on the nuclear level. Previous high precision data from TRIUMF and IUCF are currently used to develop a consistent description of CSB within the framework of chiral perturbation theory. In this work the experimental studies on the reaction dd -> He-4 pi(0) have been extended towards higher excess energies in order to provide information on the contribution of p-waves in the final state. For this, an exclusive measurement has been carried out at a beam momentum of p(d) = 1.2GeV/c using the WASA-at-COSY facility. The total cross section amounts to sigma(tot) =(118 +/- 18(stat) +/- 13(sys) +/- 8(ext)) p band first data on the differential cross section are consistent with s-wave pion production.
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12. |
- Adlarson, Patrik, et al.
(author)
-
Cross section ratio and angular distributions of the reaction p + d -> He-3 + eta at 48.8MeV and 59.8MeV excess energy
- 2014
-
In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 50:6, s. 100-
-
Journal article (peer-reviewed)abstract
- We present new data for angular distributions and on the cross section ratio of the p+d -> He-3+eta reaction at excess energies of Q - 48.8MeV and Q - 59.8 MeV. The data have been obtained at the WASA-at-COSY experiment (Forschungszentrum Julich) using a proton beam and a deuterium pellet target. While the shape of obtained angular distributions show only a slow variation with the energy, the new results indicate a distinct and unexpected total cross section fluctuation between Q = 20MeV and Q = 60 MeV, which might indicate the variation of the production mechanism within this energy interval.
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13. |
- Adlarson, Patrik, et al.
(author)
-
Evidence for a New Resonance from Polarized Neutron-Proton Scattering
- 2014
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 112:20, s. 202301-
-
Journal article (peer-reviewed)abstract
- Exclusive and kinematically complete high-statistics measurements of quasifree polarized (n) over right arrowp scattering have been performed in the energy region of the narrow resonancelike structure d* with I(J(P)) = 0(3(+)),M approximate to 2380 MeV, and Gamma approximate to 70 MeV observed recently in the double-pionic fusion channels pn -> d pi(0)pi(0) and pn -> d pi(+)pi(-). The experiment was carried out with the WASA detector setup at COSY having a polarized deuteron beam impinged on the hydrogen pellet target and utilizing the quasifree process (d) over right arrowp -> np + p(spectator). This allowed the np analyzing power, A(y), to be measured over a broad angular range. The obtained A(y) angular distributions deviate systematically from the current SAID SP07 NN partial-wave solution. Incorporating the new A(y) data into the SAID analysis produces a pole in the D-3(3) - (3)G(3) waves in support of the d* resonance hypothesis.
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14. |
- Adlarson, Patrik, et al.
(author)
-
Neutron-proton scattering in the context of the d*(2380) resonance
- 2014
-
In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 90:3, s. 035204-
-
Journal article (peer-reviewed)abstract
- New data on quasifree polarized neutron-proton scattering in the region of the recently observed d* resonance structure are obtained by exclusive and kinematically complete high-statistics measurements with WASA at COSY. This paper details the determination of the beam polarization, checks of the quasifree character of the scattering process, on all obtained Ay angular distributions and on the new partial-wave analysis, which includes the new data producing a resonance pole in D-3(3)-(3)G(3) coupled partial waves at (2380 +/- 10 - i40 +/- 5) MeV-in accordance with the d* dibaryon resonance hypothesis. The effect of the new partial-wave solution on the description of total and differential cross-section data as well as specific combinations of spin-correlation and spin-transfer observables available from COSY-ANKE measurements at T-d = 2.27 GeV is discussed.
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15. |
- Adlarsona, Patrik, et al.
(author)
-
Measurement of the np -> np pi(0)pi(0) reaction in search for the recently observed d* (2380) resonance
- 2015
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 743, s. 325-332
-
Journal article (peer-reviewed)abstract
- Exclusive measurements of the quasi-free np --> np pi(0)pi(0) reaction have been performed by means of dp collisions at T-d = 2.27 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region root s = (2.35-2.46) GeV, which includes the region of the ABC effect and its associated d* (2380) resonance. Adding the d* resonance amplitude to that for the conventional processes leads to a reasonable description of the data. The observed resonance effect in the total cross section is in agreement with the predictions of Faldt and Wilkin as well with those of Albadajedo and Oset. The ABC effect, i.e. the low-mass enhancement in the pi(0)pi(0)-invariant mass spectrum, is found to be very modest - if present at all, which might pose a problem to some of its interpretations.
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16. |
- Babusci, D., et al.
(author)
-
Measurement of Γ(η→π+π-γ)/Γ(η→π+π-π0) with the KLOE detector
- 2013
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 718:3, s. 910-914
-
Journal article (peer-reviewed)abstract
- The ratio Rη=Γ(η→π+π-γ)/Γ(η→π+π-π0) has been measured by analysing 22 million φ→ηγ decays collected by the KLOE experiment at DAΦNE, corresponding to an integrated luminosity of 558 pb-1. The η→π+π-γ proceeds both via the ρ resonant contribution, and possibly a non-resonant direct term, connected to the box anomaly. Our result, Rη=0.1856±0.0005stat±0.0028syst, points out a sizable contribution of the direct term to the total width. The di-pion invariant mass for the η→π+π-γ decay could be described in a model-independent approach in terms of a single free parameter, α. The determined value of the parameter α is α=(1.32±0.08stat-0.09syst+0.10±0.02theo) GeV-2.
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17. |
- Amelino-Camelia, G., et al.
(author)
-
Physics with the KLOE-2 experiment at the upgraded DA Phi NE
- 2010
-
In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 68:3-4, s. 619-681
-
Research review (peer-reviewed)abstract
- Investigation at a f-factory can shed light on several debated issues in particle physics. We discuss: (i) recent theoretical development and experimental progress in kaon physics relevant for the Standard Model tests in the flavor sector, (ii) the sensitivity we can reach in probing CPT and Quantum Mechanics from time evolution of entangled-kaon states, (iii) the interest for improving on the present measurements of non-leptonic and radiative decays of kaons and eta/eta' mesons, (iv) the contribution to understand the nature of light scalar mesons, and (v) the opportunity to search for narrow di-lepton resonances suggested by recent models proposing a hidden dark-matter sector. We also report on the e(+)e(-) physics in the continuum with the measurements of (multi) hadronic cross sections and the study of gamma gamma processes.
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18. |
- Bargholtz, Chr., et al.
(author)
-
The WASA detector facility at CELSIUS
- 2008
-
In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 594:3, s. 339-350
-
Journal article (peer-reviewed)abstract
- The WASA 4 pi 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 unique feature of the system is the use of hydrogen pellets as internal targets for the first time. A detailed description of the design, together with the anticipated and achieved performance parameters are given. (C) 2008 Elsevier B.V. All rights reserved.
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19. |
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20. |
- Bondar, A., et al.
(author)
-
The pp → ppπ0 reaction near the kinematical threshold
- 1995
-
In: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 356:1, s. 8-12
-
Journal article (peer-reviewed)abstract
- The reaction pp → ppπ0 has been measured using electron-cooled protons incident on an internal gas-jet target at seven different incident beam energies, from 280.7 MeV (1 MeV above the reaction threshold) up to 310.2 MeV. The pions were measured by their decay photons. In the overlapping energy region, the measured total cross sections agree with those measured in a recent Indiana experiment. The angular distributions are consistent with a 3P0 → 1S0S0 transition in the full energy range studied. The kinematical distributions are well described when taking into account the final state and the Coulomb interactions.
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21. |
- Calén, H., et al.
(author)
-
Detector setup for a storage ring with an internal target
- 1996
-
In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 379:1, s. 57-75
-
Journal article (peer-reviewed)abstract
- 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.
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22. |
- Calén, H., et al.
(author)
-
The pp → ppη reaction near the kinematical threshold
- 1996
-
In: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 366:1-4, s. 39-43
-
Journal article (peer-reviewed)abstract
- The pp → ppη reaction has been measured at six energies close to threshold, from 1258 MeV to 1352 MeV, using an internal cluster gas jet target in the CELSIUS storage ring. The η is detected through its decay photons, in an array of CsI detectors, and the forward-going protons are detected in a plastic scintillator spectrometer. A complete event reconstruction is obtained at the higher energies in the measured interval. The new data, together with earlier data, give an accurate determination of the energy dependence close to threshold. The influence of the η-proton FSI is seen in the total cross section data as well as in a Dalitz plot of the η-p invariant mass distributions.
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23. |
- Clement, H., et al.
(author)
-
Search for narrow NN-decoupled resonances in the πNN-system : An overview
- 1996
-
In: Progress in Particle and Nuclear Physics. - : Elsevier BV. - 0146-6410 .- 1873-2224. ; 36, s. 369-378
-
Journal article (peer-reviewed)abstract
- The status of the search for NN-decoupled resonances in the πNN-system is reviewed. After a short survey on the history of dibaryon searches reactions suitable for detecting such resonances are discussed. Special emphasis is put on the pionic double charge exchange, where recently evidence for the signature of a narrow πNN resonance, called d′, with I(J P) = even (0 -) and m = 2.06 GeV has been quoted. Further reactions discussed in this context are the pion photoproduction on the deuteron and the two-pion production in nucleon-nucleon collisions.
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24. |
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25. |
- Babusci, D., et al.
(author)
-
A new limit on the CP violating decay K-S -> 3 pi(0) with the KLOE experiment
- 2013
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 723:1-3, s. 54-60
-
Journal article (peer-reviewed)abstract
- We have carried out a new direct search for the CP violating decay K-S -> 3 pi(0) with 1.7 fb(-1) of e(+)e(-) collisions collected by the KLOE detector at the Phi-factory DA Phi NE. We have searched for this decay in a sample of about 5.9 x 10(8) KSKL events tagging the K-S by means of the K-L 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 K-S 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 K-S -> 2 pi(0) events in the same sample, we set the upper limit on BR(K-S -> 3 pi(0)) <= 2.6 x 10(-8) at 90% C.L., five times lower than the previous limit. We also set the upper limit on the eta(000) parameter, vertical bar eta(000)vertical bar <= 0.0088 at 90% C.L., improving by a factor two the latest direct measurement. (c) 2013 Elsevier B.V. All rights reserved.
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26. |
- Babusci, D., et al.
(author)
-
Limit on the production of a light vector gauge boson in phi meson decays with the KLOE detector
- 2013
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 720:1-3, s. 111-115
-
Journal article (peer-reviewed)abstract
- We present a new limit on the production of a light dark-force mediator with the KLOE detector at DA Phi NE. This boson, called U, has been searched for in the decay phi -> eta U, U -> e(+)e(-), analyzing the. decay eta -> pi(0)pi(0)pi(0) in a data sample of 1.7 fb(-1). No structures are observed in the e(+)e(-) invariant mass distribution over the background. This search is combined with a previous result obtained from the decay eta -> pi(+)pi(-)pi(0), increasing the sensitivity. We set an upper limit at 90% C.L. on the ratio between the U boson coupling constant and the fine structure constant of alpha'/alpha < 1.7 x 10(-5) for 30 < M-U < 400 MeV and alpha'/alpha <= 8 x 10(-6) for the sub-region 50 < M-U <210 MeV. This result assumes the Vector Meson Dominance expectations for the phi eta gamma* transition form factor. The dependence of this limit on the transition form factor has also been studied.
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27. |
- Babusci, D., et al.
(author)
-
Measurement of eta meson production in gamma gamma interactions and Gamma(eta -> gamma gamma) with the KLOE detector
- 2013
-
In: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :1, s. 119-
-
Journal article (peer-reviewed)abstract
- We present a measurement of eta meson production in photon-photon interactions produced by electron-positron beams colliding with root s = 1 GeV. The measurement is done with the KLOE detector at the phi-factory DA Phi NE with an integrated luminosity of 0.24 fb(-1). The e(+)e(-) -> e(+)e(-)eta cross section is measured without detecting the outgoing electron and positron, selecting the decays eta -> pi(+)pi(-)pi(0) and eta -> pi(0)pi(0)pi(0). The most relevant background is due to e(+)e(-) -> eta gamma when the monochromatic photon escapes detection. The cross section for this process is measured as sigma(e(+)e(-) -> eta gamma) = (856 +/- 8(stat) +/- 16(syst)) pb. The combined result for the e(+)e(-) -> e(+)e(-)eta cross section is sigma(e(+)e(-) -> e(+)e(-)eta) = (32.72 +/- 1.27(stat) +/- 0.70(syst)) pb. From this we derive the partial width Gamma(eta -> gamma gamma) = (520 +/- 20(stat) +/- 13(syst)) eV. This is in agreement with the world average and is the most precise measurement to date.
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28. |
- Bargholtz, Chr., et al.
(author)
-
Measurement of the eta -> pi(+)pi(-)e(+)e(-) decay branching ratio
- 2007
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 644:5-6, s. 299-303
-
Journal article (peer-reviewed)abstract
- The reaction pd -> He-3 eta at threshold was used to provide a clean source of eta mesons for decay studies with the WASA detector at CELSIUS. The branching ratio of the decay eta -> pi(+)pi(-)e(+)e(-) is measured to be (4.3 +/- 1.3 +/- 0.4) x 10(-4).
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29. |
- Bashkanov, M., et al.
(author)
-
Double-Pionic Fusion of Nuclear Systems and the "ABC" Effect : Approaching a Puzzle by Exclusive and Kinematically Complete Measurements
- 2009
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:5, s. 052301-
-
Journal article (peer-reviewed)abstract
- The ABC effect-a puzzling low-mass enhancement in the pi pi invariant mass spectrum, first observed by Abashian, Booth, and Crowe-is well known from inclusive measurements of two-pion production in nuclear fusion reactions. Here we report on the first exclusive and kinematically complete measurements of the most basic double-pionic fusion reaction pn -> d pi(0)pi(0) at beam energies of 1.03 and 1.35 GeV. The measurements, which have been carried out at CELSIUS-WASA, reveal the ABC effect to be a (pi pi)(I=L=0) channel phenomenon associated with both a resonancelike energy dependence in the integral cross section and the formation of a Delta Delta system in the intermediate state. A corresponding simple s-channel resonance ansatz provides a surprisingly good description of the data.
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30. |
- Bashkanov, M., et al.
(author)
-
Exclusive measurements of pd -> He-3 pi pi : The ABC effect revisited
- 2006
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 637:4-5, s. 223-228
-
Journal article (peer-reviewed)abstract
- Exclusive measurements of the reactions pd -> He-3 pi(+)7 pi(-) and pd -> He-3 pi(0)pi(0) have been carried out at T-p = 0.893 GeV at the CELSIUS storage ring using the WASA detector. The pi(+)pi(-) channel evidences a pronounced enhancement at low invariant pi pi masses-as anticipated from previous inclusive measurements of the ABC effect. This enhancement is seen to be even much larger in the isoscalar pi(0)pi(0) channel. The differential distributions prove this enhancement to be of scalar-isoscalar nature. Delta Delta calculations give a good description of the data, if a boundstate condition is imposed for the intermediate Delta Delta system.
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31. |
- Bashkanov, M., et al.
(author)
-
Measurement of the slope parameter for the η → 3π0 decay in the pp → ppη reaction
- 2007
-
In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 76:4, s. 048201-
-
Journal article (peer-reviewed)abstract
- The CELSIUS-WASA setup is used to measure the 3π0 decay of η 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 α yielding α = −0.026 ± 0.010(stat) ± 0.010(syst). This value is compared to recent experimental results and theoretical predictions.
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32. |
- Berlowski, M., et al.
(author)
-
Measurement of eta meson decays into lepton-antilepton pairs
- 2008
-
In: Physical Review D. Particles and fields. - : American Physical Society. - 0556-2821 .- 1089-4918. ; 77:3, s. 032004-
-
Journal article (peer-reviewed)abstract
- A search for rare lepton decays of the eta meson was performed using the WASA detector at CELSIUS. Two candidates for double Dalitz decay eta -> e(+)e(-)e(+)e(-) events are reported with a background of 1.3 +/- 0.2 events. This allows to set an upper limit to the branching ratio of 9.7x10(-5) (90% CL). The branching ratio for the decay eta -> e(+)e(-)gamma is determined to (7.8 +/- 0.5(stat)+/- 0.8(syst))x10(-3) in agreement with world average value. An upper limit (90% CL) for the branching ratio for the eta -> e(+)e(-) decay is 2.7x10(-5) and a limit for the sum of the eta ->mu(+)mu(-)mu(+)mu(-) and eta ->pi(+)pi(-)mu(+)mu(-) decays is 3.6x10(-4).
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33. |
- Betsch, A, et al.
(author)
-
Observation of strong final-state effects in pi(+) production in pp collisions at 400 MeV
- 1999
-
In: PHYSICS LETTERS B. - : ELSEVIER SCIENCE BV. - 0370-2693. ; 446:2, s. 179-184
-
Journal article (peer-reviewed)abstract
- Differential cross sections of the reactions pp --> d pi(+) and pp --> pn pi(+) have been measured at T-p = 400 MeV by detecting the charged ejectiles in the angular range 4 degrees less than or equal to Theta(Lab) less than or equal to 21 degrees. The de
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34. |
- Bilger, R, et al.
(author)
-
2 pi production in pp collisions close to threshold
- 2000
-
In: NUCLEAR PHYSICS A. - : ELSEVIER SCIENCE BV. ; , s. 469C-472C
-
Conference paper (peer-reviewed)abstract
- The reaction pp --> NN pi pi has been measured close to threshold in the energy range from 650 to 775 MeV using the PROMICE/WASA setup at CELSIUS. These data constitute the first exclusive high-statistics measurements of this reaction on a pure hydrogen t
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35. |
- Bilger, R, et al.
(author)
-
CELSIUS as an eta factory
- 1997
-
In: NUCLEAR PHYSICS A. - : ELSEVIER SCIENCE BV. - 0375-9474. ; 626:1-2, s. 93C-96C
-
Journal article (peer-reviewed)abstract
- The WASA project at the CELSIUS storage ring is being prepared for high-luminosity experiments to study rare decays of light mesons, in particular the eta meson. The CELSIUS ring together with the newly developed pellet target will serve as an efficient e
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36. |
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37. |
- Bilger, R, et al.
(author)
-
Recent measurements of the eta production in pd collisions at CELSIUS
- 1996
-
In: ACTA PHYSICA POLONICA B. - : ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS. ; , s. 2985-2991
-
Conference paper (peer-reviewed)abstract
- The reactions pd --> eta + X have been measured at four beam energies: 930, 965, 1037 and 1100 MeV. The reactions were identified by detecting charged particles in plastic scintillator detectors and the eta photons in two arrays of CsI(Na) crystals. A pre
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38. |
- Bilger, R, et al.
(author)
-
Search for a narrow pi NN-resonance in pp->pp pi(+)pi(-)
- 1996
-
In: PROGRESS IN PARTICLE AND NUCLEAR PHYSICS. - : PERGAMON PRESS LTD. ; , s. 379-381
-
Conference paper (peer-reviewed)abstract
- We report on the current status of the search for the pi NN-resonance d' with I(J(P)) = 0(0(-)) and M = 2.06 GeV in the 2 pi production in pp collisions.
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39. |
- Bilger, R, et al.
(author)
-
Threshold eta production in pN reactions at Celsius
- 1998
-
In: ACTA PHYSICA POLONICA B. - : ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS. ; , s. 2981-2985
-
Conference paper (peer-reviewed)abstract
- The quasi-free p+n-->d+eta reaction cross section has been measured at threshold using 1295 MeV protons in the CELSIUS storage ring and an internal cluster-jet deuterium target [1]. Excess energies from threshold to 10 MeV in the center of mass of the fin
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40. |
- Brodowski, W, et al.
(author)
-
A signal of a narrow pi NN resonance in pp->pp pi(-)pi(+)
- 1996
-
In: ZEITSCHRIFT FUR PHYSIK A-HADRONS AND NUCLEI. - : SPRINGER VERLAG. - 0939-7922. ; 355:1, s. 5-8
-
Journal article (peer-reviewed)abstract
- We report on the first exclusive measurement of the 2 pi production in NN collisions at T-p = 750 MeV using a H-2 cluster jet target and the WASA/PROMICE detector at CELSIUS. In the invariant-mass spectrum M(pp pi-) we observe a narrow peak at 2.063(2) Ge
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41. |
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42. |
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43. |
- Calén, H., et al.
(author)
-
Deuteron breakup by 1.15 GeV protons and excitation of the Δ isobar
- 1993
-
In: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 303:1-2, s. 10-15
-
Journal article (peer-reviewed)abstract
- The pd→npp reaction has been measured using circulating 1.15 GeV protons, a gas jet target and scintillation detectors selecting scattered protons with energy above 30 MeV. The distribution of the two-proton invariant mass has a maximum at 2.13 ± 0.01 GeV/c2 and a width of 130 ± 10 MeV/c2 (FWHM). We see no evidence of narrow (Γ < 30 MeV/c2) peaks in the phase-space region selected. The mass of X, excited in the pN→nX elementary process, is 40 MeV/c2 smaller than the mass of a real Δ isobar.
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44. |
- Calén, H, et al.
(author)
-
Deuteron breakup in the Δ-isobar region
- 1993
-
In: Physica Scripta. - : Institute of Physics (IOP). - 0031-8949 .- 1402-4896. ; 48:1, s. 86-91
-
Journal article (peer-reviewed)abstract
- The pd → npp charge exchange reaction has been studied at 1.15 GeV incident proton energy in a selected kinematical region. The distributions of two-proton invariant mass Mpp, of angle of a single proton and the differential cross section dσ/dt of the (p, n) reaction are presented and compared with model predictions corrected for the acceptance of the experimental apparatus. We see no evidence of narrow (Γ < 30 MeV/c2) peaks in the Mpp interval 2.1-2.3 GeV/c2. The production of an intermediate Δ isobar in the primary (p, n) charge exchange and its subsequent absorption in a final state ΔN → pp process together with the background from quasi-free charge exchange scattering reasonably reproduces the general trends of the data.
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45. |
- Clement, H, et al.
(author)
-
Search for narrow NN-decoupled resonances in the pi NN-system - An overview
- 1996
-
In: PROGRESS IN PARTICLE AND NUCLEAR PHYSICS. - : PERGAMON PRESS LTD. ; , s. 369-378
-
Conference paper (peer-reviewed)abstract
- The status of the search for NN-decoupled resonances in the pi NN-system is reviewed. After a short survey on the history of dibaryon searches reactions suitable for detecting such resonances are discussed. Special emphasis is put on the pionic double cha
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46. |
- Johansson, Tord, et al.
(author)
-
Meson production in light ion collisions at CELSIUS
- 1997
-
In: NUCLEAR PHYSICS A. - : ELSEVIER SCIENCE BV. ; , s. 29C-40C
-
Conference paper (peer-reviewed)abstract
- 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 re
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47. |
- Kren, F., et al.
(author)
-
Exclusive measurements of pp -> d pi(+)pi(0) : Double-pionic fusion without ABC effect
- 2010
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 684:2-3, s. 110-113
-
Journal article (peer-reviewed)abstract
- Exclusive measurements of the reaction pp -> d pi(+)pi(0) have been carried out at T-p = 1.1 GeV at the CELSIUS storage ring using the WASA detector. The isovector pi(+)pi(0) channel exhibits no enhancement at low invariant pi pi masses, i.e. no ABC effect. Therefore this most basic isovector double-pionic fusion reaction qualifies as an ideal test case for the conventional t-channel Delta Delta excitation process. Indeed, the obtained differential distributions reveal the conventional t-channel Delta Delta mechanism as the appropriate reaction process, which also accounts for the observed energy dependence of the total cross section.
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48. |
- Kren, F., et al.
(author)
-
THE pp -> d pi(+)pi(0) REACTION - A CASE OF Delta Delta EXCITATION WITHOUT ABC-EFFECT
- 2009
-
In: International Journal of Modern Physics A. - 0217-751X .- 1793-656X. ; 24:2-3, s. 561-563
-
Journal article (peer-reviewed)abstract
- The ABC effect, a low-mass enhancement in the invariant pp mass, is observed in double-pionic fusion reactions leading to a bound nuclear system in the final state. From previous measurements there have been indications that this phenomenon is resctricted to the sigma channel of the pp system. With exclusive measurements of the pp -> d pi(+)pi(0) reaction at T-p = 1.1 GeV we demonstrate that, indeed, the ABC effect does not occur in the vector-isovector Delta Delta channel (rho channel) despite the fact that the Delta Delta excitation is oberved to be the dominant reaction process. We also show that this reaction is well described by a t-channel Delta Delta excitation with the subsequent decay into the vector-isovector Delta Delta channel given by the rho channel operator.
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49. |
- Pauly, C., et al.
(author)
-
The pp→ppπππ reaction channels in the threshold region
- 2007
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 649:2-3, s. 122-127
-
Journal article (peer-reviewed)abstract
- The cross section for direct neutral and charged three pion production in pp interactions was measured at excess energies in the range 160–216 MeV. That comprises the first measurement of the pp→ppπ0π0π0 reaction and the direct comparison with the pp→ppπ+π−π0 process. The experiment was performed above the η meson production threshold and the cross section could be directly normalized to the cross section of the pp→ppη reaction, with the η decaying into 3 pions. Since the same final states are selected, the measurement has a low systematical error. The measured cross section ratio σ(pp→ppπ+π−π0)/σ(pp→ppπ0π0π0) is compared to predictions of dominance of different isobars in the intermediate state.
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50. |
- Pettersson, Henrik, et al.
(author)
-
eta PRODUCTION IN PROTON-PROTON COLLISIONS AT 72 MeV EXCESS ENERGY
- 2009
-
In: International Journal of Modern Physics A. - 0217-751X .- 1793-656X. ; 24:2-3, s. 446-449
-
Journal article (peer-reviewed)abstract
- The production of eta mesons at an excess energy of 72 MeV has been studied in the reaction pp -> pp(eta)gamma gamma. It is shown that a simple model with Pp. final states included reproduces observed differential distributions better than the same model restricted to Ss, Sd and Ds final states. The strong influence of the Pp states could be taken as an indication of rho dominance within an one boson exchange model for the excitation of N*(1535).
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