1. |
- 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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2. |
- 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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3. |
- Adlarson, Patrik, et al.
(author)
-
Backward single-pion production in the pd -> He-3 pi(0)reaction with WASA-at-COSY
- 2018
-
In: European Physical Journal A. - : SPRINGER. - 1434-6001 .- 1434-601X. ; 54:9
-
Journal article (peer-reviewed)abstract
- New data on the production of single neutral pions in the pd -> He-3 pi(0) reaction are presented. For fifteen proton beam momenta between p(p) = 1.60GeV/c and p(p) = 1.74 GeV/c, differential cross sections are determined over a large fraction of the backward hemisphere. Since the only previous systematic measurements of single-pion production at these energies were made in collinear kinematics, the present work constitutes a significant extension of the current knowledge on this reaction. Even this far above the production threshold, significant changes are found in the behaviour of the angular distributions over small intervals in beam momentum.
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4. |
- 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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5. |
- 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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6. |
- Adlarson, Patrik, et al.
(author)
-
Examination of the production of an isotensor dibaryon in the pp -> pp pi(+)pi(-) reaction
- 2019
-
In: Physical Review C. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 99:2
-
Journal article (peer-reviewed)abstract
- The quasifree pp -> pp pi(+)pi(-) reaction has been measured by means of pd collisions at T-p = 1.2 GeV using the WASA detector setup at COSY enabling exclusive and kinematically complete measurements. Total and differential cross sections have been extracted for the energy region T-p = 1.08-1.36 GeV (root s = 2.35-2.46 GeV) covering thus the regions of N* (1440 ) and Delta(1232)Delta(1232) resonance excitations. Calculations describing these excitations by t-channel meson exchange as well as isospin relations based on the pp -> pp pi(0)pi(0) data underpredict substantially the measured total cross section. The calculations are also at variance with specific experimental differential cross sections. An isotensor Delta N dibaryon resonance with I(J(P)) = 2(1(+) ) produced associatedly with a pion is able to overcome these deficiencies. Such a dibaryon was predicted by Dyson and Xuong [Phys. Rev. Lett. 13, 815 (1964)] and more recently calculated by A. Gal and H. Garcilazo [Nucl. Phys. A 928, 73 (2014)].
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7. |
- 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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8. |
- Adlarson, Patrik, et al.
(author)
-
Importance of d-wave contributions in the charge symmetry breaking reaction dd -> He-4 pi(0)
- 2018
-
In: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 781, s. 645-650
-
Journal article (peer-reviewed)abstract
- This letter reports a first quantitative analysis of the contribution of higher partial waves in the charge symmetry breaking reaction dd -> He-4 pi(0) using the WASA-at-COSY detector setup at an excess energy of Q = 60 MeV. The determined differential cross section can be parametrized as d sigma/d Omega = a + b cos(2) theta*, where theta* is the production angle of the pion in the center-of-mass coordinate system, and the results for the parameters are a = (1.55 +/- 0.46(stat)(-0.8)(+0.32)(syst)) pb/sr and b = (13.1 +/- 2.1(stat)(-2.7)(+1.0)(syst)) pb/sr. The data are compatible with vanishing p-waves and a sizable d-wave contribution. This finding should strongly constrain the contribution of the A isobar to the dd -> He-4 pi(0) reaction and is, therefore, crucial for a quantitative understanding of quark mass effects in nuclear production reactions.
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9. |
- 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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10. |
- Adlarson, Patrik, et al.
(author)
-
Isoscalar single-pion production in the region of Roper and d*(2380) resonances
- 2017
-
In: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 774, s. 599-607
-
Journal article (peer-reviewed)abstract
- Exclusive measurements of the quasi-free pn -> pp pi(-) and pp -> pp pi(0) reactions have been performed by means of pd collisions at T-p= 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region T-p= 0.95-1.3 GeV (root s = 2.3-2.46 GeV), which includes the regions of triangle(1232), N*(1440) and d*(2380) resonance excitations. From these measurements the isoscalar single-pion production has been extracted, for which data existed so far only below T-p = 1 GeV. We observe a substantial increase of this cross section around 1 GeV, which can be related to the Roper resonance N*(1440), the strength of which shows up isolated from the triangle resonance in the isoscalar (N pi)(I=0) invariant-mass spectrum. No evidence for a decay of the dibaryon resonance d*(2380) into the isoscalar (NN pi)(I=0) channel is found. An upper limit of 180 mu b (90% CL.) corresponding to a branching ratio of 9% has been deduced.
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11. |
- 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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12. |
- Adlarson, Patrik, et al.
(author)
-
Isotensor Dibaryon in the pp -> pp pi(+)pi(-) Reaction?
- 2018
-
In: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 121:5
-
Journal article (peer-reviewed)abstract
- Exclusive measurements of the quasifree pp -> pp pi(+)pi(-) reaction have been carried out at WASA@ COSY by means of pd collisions at T-p = 1.2 GeV. Total and differential cross sections have been extracted covering the energy region T-p = 1.08-1.36 GeV, which is the region of N* (1440) and Delta(123)Delta(1232) resonance excitations. Calculations describing these excitations by t-channel meson exchange are at variance with the measured differential cross sections and underpredict substantially the experimental total cross section. An isotensor Delta N dibaryon resonance with I(J(P)) = 2(1(+)) produced associatedly with a pion is able to overcome these deficiencies.
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13. |
- 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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14. |
- Adlarson, Patrik, et al.
(author)
-
Measurement of the (n)over-right-arrowp -> d pi(0) pi(0) reaction with polarized beam in the region of the d(*)(2380) resonance
- 2016
-
In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 52:5, s. 1-7
-
Journal article (peer-reviewed)abstract
- We report on a high-statistics measurement of the most basic double-pionic fusion reaction over the energy region of the d (*)(2380) resonance by use of a polarized deuteron beam and observing the double fusion reaction in the quasifree scattering mode. The measurements were performed with the WASA detector setup at COSY. The data reveal substantial analyzing powers and confirm conclusions about the d(*) resonance obtained from unpolarized measurements. We also confirm the previous unpolarized data obtained under complementary kinematic conditions.
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15. |
- 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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16. |
- Adlarson, Patrik, et al.
(author)
-
Measurement of the ω → π+π−π0 Dalitz plot distribution : The WASA-at-COSY Collaboration
- 2017
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 770, s. 418-425
-
Journal article (peer-reviewed)abstract
- Using the production reactions pd -> He-3 omega and pp -> pp omega, the Dalitz plot distribution for the omega -> pi(+)pi(-)pi(0)decay is studied with the WASA detector at COSY, based on a combined data sample of (4.408 +/- 0.042) x 10(4) events. The Dalitz plot density is parametrised by a product of the P-wave phase space and a polynomial expansion in the normalised polar Dalitz plot variables Z and phi. For the first time, a deviation from pure P-wave phase space is observed with a significance of 4.1 sigma. The deviation is parametrised by a linear term 1+2 alpha Z, with alpha determined to be +0.147 +/- 0.036, consistent with the expectations of rho-meson-type final-state interactions of the P-wave pion pairs. (C) 2017 The Author. Published by Elsevier B.V.
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17. |
- Adlarson, Patrik, et al.
(author)
-
Measurements of branching ratios for eta decays into charged particles
- 2016
-
In: PHYSICAL REVIEW C. - 2469-9985. ; 94:6
-
Journal article (peer-reviewed)abstract
- The WASA-at-COSY experiment has collected 3 x 10(7) events with eta mesons produced via the reaction pd -> He-3 eta at T = 1.0 GeV. Using this data set, we evaluate the branching ratios of the decays eta -> pi(+)pi(-)gamma, eta -> e(+)e(-)gamma, eta -> pi(+)pi(-)e(+)e(-), and eta -> e(+)e(-)e(+)e(-). The branching ratios are normalized to the eta -> pi(+)pi(-) pi(0) decay. In addition an upper limit on a CP-violating asymmetry in eta -> pi(+)pi(-)e(+)e(-) is extracted.
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18. |
- 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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19. |
- 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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20. |
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21. |
- Adlarson, Patrik, et al.
(author)
-
Search for an isospin I=3 dibaryon
- 2016
-
In: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 762, s. 455-461
-
Journal article (peer-reviewed)abstract
- Various theoretical calculations based on QCD or hadronic interactions predict that in addition to the recently observed dibaryon resonance d*(2380) with I(J(P)) = 3(0(+)) there should also exist a dibaryon resonance with mirrored quantum numbers I(J(P)) = 3(0(+)). We report here on a search for such a NN-decoupled state in data on the pp -> pp pi(+) pi(+) pi(-) pi(-) reaction. Since no clear-cut evidence has been found, we give upper limits for the production cross section of such a resonance in the mass range 2280-2500 MeV.
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22. |
- Adlarson, Patrik, et al.
(author)
-
Search for C violation in the decay eta -> pi(0)e(+)e(-) with WASA-at-COSY
- 2018
-
In: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 784, s. 378-384
-
Journal article (peer-reviewed)abstract
- We report on the search for the rare decay eta -> pi(0)e(+)e(-) which is of interest to study C violation in the electromagnetic interaction which would indicate contributions from physics beyond the Standard Model, since the allowed decay via a two-photon intermediate state is strongly suppressed. The experiment has been performed using the WASA-at-COSY installation, located at the COSY accelerator of the Forschungszentrum Julich, Germany. In total 3 x 10(7) events of the reaction pd -> He-3 eta have been recorded at an excess energy of Q = 59.8MeV. Based on this data set the C parity violating decay eta -> pi(0)gamma* -> pi(0)e(+)e(-) via a single-photon intermediate state has been searched for, resulting in new upper limits of Gamma(eta -> pi(0)e(+) e(-))/Gamma(eta -> pi(+) pi(-) pi(0)) < 3.28 x 10(-5) and Gamma(eta -> pi(0)e(+) e(-))/Gamma(eta -> all)< 7.5 x 10(-6) (CL=90%), respectively.
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23. |
- Adlarson, Patrik, et al.
(author)
-
Search for eta-mesic He-4 in the dd -> (3)Hen pi(0) and dd -> (3)Hep pi(-) reactions with the WASA-at-COSY facility
- 2017
-
In: Nuclear Physics A. - : ELSEVIER SCIENCE BV. - 0375-9474 .- 1873-1554. ; 959, s. 102-115
-
Journal article (peer-reviewed)abstract
- The search for He-4-eta bound states was performed with the WASA-at-COSY facility via the measurement of the excitation function for the dd -> (3)Hen pi(0) and dd -> (3)Hep pi(-) processes. The deuteron beam momentum was varied continuously between 2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd -> He-4 eta reaction ranging from Q = 70 MeV to Q = 30 MeV. The luminosity was determined based on the dd -> (3)Hen reaction and the quasi-free proton proton scattering via dd -> ppn(spectator)n(spectator) reactions. The excitation functions, determined independently for the measured reactions, do not reveal a structure which could be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the total cross sections for the bound state production and decay in dd -> (4He-eta)(bound) -> (3)Hen pi(0) and dd -> (He-4-eta)(bound) -> (3)Hep pi(-) processes were determined taking into account the isospin relation between the both of the considered channels. The results of the analysis depend on the assumptions of the N* (1535) momentum distribution in the anticipated mesic-He-4. Assuming, as in the previous works, that this is identical with the distribution of nucleons bound with 20 MeV in He-4, we determined that (for the mesic bound state width in the range from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about 3 nb and about 6 nb for n pi(0) and p pi(-) channels, respectively. However, based on the recent theoretical findings of the N*(1535) momentum distribution in the N*-He-3 nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector acceptance decreases and hence the corresponding upper limits are 5 nb and 10 nb for n pi(0) and p pi(-) channels respectively. (C) 2017 Elsevier B.V. All rights reserved.
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24. |
- Adlarson, Patrik, et al.
(author)
-
Search for eta-mesic He-4 with the WASA-at-COSY detector
- 2013
-
In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 87:3, s. 035204-
-
Journal article (peer-reviewed)abstract
- An exclusive measurement of the excitation function for the dd -> (3)Hep pi(-) reaction was performed at the Cooler Synchrotron COSY-Julich with the WASA-at-COSY detection system. The data were taken during a slow acceleration of the beam from 2.185 to 2.400 GeV/c crossing the kinematic threshold for the eta-meson production in the dd -> He-4 eta reaction at 2.336 GeV/c. The corresponding excess energy with respect to the He-4-eta system varied from -51.4 to 22 MeV. The integrated luminosity in the experiment was determined using the dd -> (3)Hen reaction. The shape of the excitation function for the dd -> (3)Hep pi(-) reaction was examined. No signal of the He-4-eta bound state was observed. An upper limit for the cross section for the bound state formation and decay in the process dd -> (He-4-eta)(bound) -> (3)Hep pi(-) was determined on the 90% confidence level and it varies from 20 to 27 nb for the bound state width ranging from 5 to 35 MeV, respectively.
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25. |
- Adlarson, Patrik, et al.
(author)
-
Search for the eta mesic He-3 in the pd -> dp pi(0) reaction with the WASA-at-COSY facility
- 2020
-
In: Physical Review C. Nuclear Physics. - : AMER PHYSICAL SOC. - 0556-2813 .- 1089-490X. ; 102:4
-
Journal article (peer-reviewed)abstract
- The excitation function for the pd -> dp pi(0) reaction has been measured byWASA-at-COSY experiment with the aim of searching for He-3-h mesic nuclei. The measurement in the vicinity of h meson production was performed using a ramped proton beam. The data analysis and interpretation was carried out with the assumption that the h mesic helium decays via the formation of an intermediate N*(1535) resonance. No direct signal of the. mesic nucleus is observed in the excitation function. We determine a new improved upper limit for the total cross section for the bound state production and decay in the pd -> (He-3-eta)(bound) -> dp pi(0) process. It varies between 13 nb to 24 nb for the bound state with width in the range Gamma is an element of ( 5, 50) MeV.
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26. |
- Adlarson, Patrik, et al.
(author)
-
Search for η mesic 3He with the WASA-at-COSY facility in the pd -> 3He2γ and pd -> 3He6γ reaction
- 2020
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 802
-
Journal article (peer-reviewed)abstract
- We report on the experimental search for the bound state of an eta meson and He-3 nucleus performed using the WASA-at-COSY detector setup. In order to search for the eta-mesic nucleus decay, the pd -> (3)He2(gamma) and pd -> (3)He6 gamma channels have been analysed. These reactions manifest the direct decay of the ti meson bound in a He-3 nucleus. This non-mesonic decay channel has been considered for the first time. When taking into account only statistical errors, the obtained excitation functions reveal a slight indication for a possible bound state signal corresponding to a He-3-eta nucleus width Gamma above 20 MeV and binding energy B-s between 0 and 15 MeV. However, the determined cross sections are consistent with zero in the range of the systematic uncertainty. Therefore, as final result we estimate only the upper limit for the cross section of the eta-mesic He-3 nucleus formation followed by the eta meson decay which varies between 2 nb and 15 nb depending on possible bound state parameters.
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27. |
- Adlarson, Patrik, et al.
(author)
-
Spin Dependence of eta Meson Production in Proton-Proton Collisions Close to Threshold
- 2018
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 120:2
-
Journal article (peer-reviewed)abstract
- Taking advantage of the high acceptance and axial symmetry of the WASA-at-COSY detector, and the high polarization degree of the proton beam of COSY, the reaction →pp→ppη has been measured close to threshold to explore the analyzing power Ay. The angular distribution of Ay is determined with the precision improved by more than 1 order of magnitude with respect to previous results, allowing a first accurate comparison with theoretical predictions. The determined analyzing power is consistent with zero for an excess energy of Q=15 MeV, signaling s-wave production with no evidence for higher partial waves. At Q=72 MeV the data reveal strong interference of Ps and Pp partial waves and cancellation of (Pp)2 and Ss∗Sd contributions. These results rule out the presently available theoretical predictions for the production mechanism of the η meson.
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28. |
- Adlarson, Patrik, et al.
(author)
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Three-nucleon dynamics in dp breakup collisions using the WASA detector at COSY-Julich
- 2020
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In: Physical Review C. - 2469-9985 .- 2469-9993. ; 101:4
-
Journal article (peer-reviewed)abstract
- The differential cross section for the H-1(d, pp)n breakup reaction at deuteron beam energy of 340 MeV has been measured with the use of the WASA detector at COSY-Jillich. The set of proton-proton coincidences registered at the Forward Detector has been analyzed on a dense grid of kinematic variables, giving in total around 5600 data points. The cross-section data are compared to theoretical predictions based on the state-ofthe-art nucleon-nucleon potentials, combined with a three-nucleon force or the Coulomb interaction or carried out in a relativistic regime.
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29. |
- Adlarson, Patrik, et al.
(author)
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Total and differential cross sections of η-production in proton–deuteron fusion for excess energies between Qη = 13 MeV and Qη = 81 MeV
- 2018
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 782, s. 297-304
-
Journal article (peer-reviewed)abstract
- New data on both total and differential cross sections of the production of eta mesons in proton-deuteron fusion to He-3 eta in the excess energy region 13.6 MeV <= Q(eta) <= 80.9 MeV are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum Julich, using a proton beam at 15 different beam momenta between p(p) = 1.60 GeV/c and p(p) = 1.74 GeV/c. While significant structure of the total cross section is observed in the energy region 20 MeV less than or similar to Q(eta) less than or similar to 60 MeV, a previously reported sharp variation around Q(eta) approximate to 50 MeV cannot be confirmed. Angular distributions show the typical forward- peaking that was noted earlier. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a wide interval.
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30. |
- Adlarsona, Patrik, et al.
(author)
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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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31. |
- Anastasi, A., et al.
(author)
-
Limit on the production of a new vector boson in e+e− → Uγ, U → π+π− with the KLOE experiment
- 2016
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 757, s. 356-361
-
Journal article (peer-reviewed)abstract
- Abstract The recent interest in a light gauge boson in the framework of an extra U(1) symmetry motivates searches in the mass range below 1 GeV. We present a search for such a particle, the dark photon, in e + e − → U γ , U → π + π − based on 28 million e + e − → π + π − γ events collected at DAΦNE by the KLOE experiment. The π + π − production by initial-state radiation compensates for a loss of sensitivity of previous KLOE U → e + e − , μ + μ − searches due to the small branching ratios in the ρ – ω resonance region. We found no evidence for a signal and set a limit at 90% CL on the mixing strength between the photon and the dark photon, ε 2 , in the U mass range between 527 and 987 MeV . Above 700 MeV this new limit is more stringent than previous ones.
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32. |
- Anastasi, A., et al.
(author)
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Measurement of the running of the fine structure constant below 1 GeV with the KLOE detector
- 2017
-
In: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 767, s. 485-492
-
Journal article (peer-reviewed)abstract
- We have measured the running of the effective QED coupling constant alpha(s) in the time-like region 0.6 < root s < 0.975 GeV with the KLOE detector at DA Phi NE using the Initial-State Radiation process e(+) e(-) -> mu(+) mu(-)gamma. It represents the first measurement of the running of alpha(s) in this energy region. Our results show a more than 5 sigma significance of the hadronic contribution to the running of alpha(s), which is the strongest direct evidence both in time- and space-like regions achieved in a single measurement. By using the e(+) e(-) -> pi(+) pi(-) cross section measured by KLOE, the real and imaginary parts of the shift Delta alpha(s) have been extracted. From a fit of the real part of Delta alpha(s) and assuming the lepton universality the branching ratio BR(omega -> mu(+) mu(-)) = (6.6 +/- 1.4(stat) +/- 1.7(syst)) (.) 10 (5)has been determined.
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33. |
- Anastasi, Antonio, et al.
(author)
-
Measurement of the ϕ→π0e+e− transition form factor with the KLOE detector
- 2016
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 757, s. 362-367
-
Journal article (peer-reviewed)abstract
- A measurement of the vector to pseudoscalar conversion decay ϕ→π0e+e− with the KLOE experiment is presented. A sample of ∼9500 signal events was selected from a data set of 1.7 fb−1 of e+e− collisions at s√∼mϕ collected at the DAΦNE e+e− collider. These events were used to obtain the first measurement of the transition form factor |Fϕπ0(q2)| and a new measurement of the branching ratio of the decay: BR(ϕ→π0e+e−)=(1.35±0.05+0.05−0.10)×10−5. The result improves significantly on previous measurements and is in agreement with theoretical predictions.
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34. |
- Anastasi, A., et al.
(author)
-
Precision measurement of the η → π + π − π 0 Dalitz plot distribution with the KLOE detector
- 2016
-
In: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :5
-
Journal article (peer-reviewed)abstract
- Using 1.6 fb−1 of e + e − → ϕ → ηγ data collected with the KLOE detector at DAΦNE, the Dalitz plot distribution for the η → π + π − π 0 decay is studied with the world’s largest sample of ∼ 4.7 · 106 events. The Dalitz plot density is parametrized as a polynomial expansion up to cubic terms in the normalized dimensionless variables X and Y . The experiment is sensitive to all charge conjugation conserving terms of the expansion, including a gX 2 Y term. The statistical uncertainty of all parameters is improved by a factor two with respect to earlier measurements.
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35. |
- 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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36. |
- 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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37. |
- 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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38. |
- Babusci, D., et al.
(author)
-
Precision measurement of sigma (e(+)e(-) -> pi(+)pi(-)gamma)/sigma(e(+)e(-) ->mu(+)mu(-)gamma) and determination of the pi(+)pi(-) contribution to the muon anomaly with the KLOE detector
- 2013
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 720:4-5, s. 336-343
-
Journal article (peer-reviewed)abstract
- We have measured the ratio cr (e(+)e(-) -> pi(+)pi(-)gamma)/sigma(e(+)e(-) -> mu(+)mu(-)gamma), with the KLOE detector at DA Phi NE for a total integrated luminosity of similar to 240 pb(-1). From this ratio we obtain the cross section sigma (e(+)e(-) -> pi(+)pi(-)gamma). From the cross section we determine the pion form factor vertical bar F-pi vertical bar(2) and the two-pion contribution to the muon anomaly a(mu) for 0.592< M-pi pi < 0.975 GeV, Delta(pi pi) a(mu) = (385.1 +/- 1.1(stat) +/- 2.7(sys+theo)) x 10(-10). This result confirms the current discrepancy between the Standard Model calculation and the experimental measurement of the muon anomaly. (c) 2013 Elsevier B.V. All rights reserved.
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39. |
- Babusci, D., et al.
(author)
-
Search for light vector boson production in e(+)e(-) -> mu(+)mu(-)gamma interactions with the KLOE experiment
- 2014
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 736, s. 459-464
-
Journal article (peer-reviewed)abstract
- We have searched for a light vector boson U, the possible carrier of a "dark force", with the KLOE detector at the DA Phi NE e(+)e(-) collider, motivated by astrophysical evidence for the presence of dark matter in the Universe. Using e(+)e(-) collisions collected with an integrated luminosity of 239.3 pb(-1), we look for a dimuon mass peak in the reaction e(+)e(-) -> mu(+)mu(-)gamma, corresponding to the decay U -> mu(+)mu(-). We find no evidence for a U vector boson signal. We set a 90% CL upper limit for the mixing parameter squared between the photon and the U boson of 1.6 x 10(-5) to 8.6 x 10(-7) for the mass region 520 < m(U) < 980 MeV.
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40. |
- Babusci, D., et al.
(author)
-
Study of the Dalitz decay phi -> eta e(+)e(-) with the KLOE detector
- 2015
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 742, s. 1-6
-
Journal article (peer-reviewed)abstract
- We have studied the vector to pseudoscalar conversion decay phi -> eta e(+)e(-), with.. eta -> pi(0)pi(0)pi(0), with the KLOE detector at DA phi NE. The data set of 1.7 fb(-1) of e(+)e(-) collisions at root s similar to M-phi contains a clear conversion decay signal of similar to 31,000 events from which we measured a value of BR(phi -> eta e(+)e-) = (1.075 +/- 0.007 +/- 0.038) x 10(-4). The same sample is used to determine the transition form factor by a fit to the e(+)e(-) invariant mass spectrum, obtaining b(phi eta)=( 1.28 +/- 0.10(-0.08)(+0.09)) GeV-2, that improves by a factor of five the precision of the previous measurement and is in good agreement with VMD expectations.
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41. |
- Babuscih, D., et al.
(author)
-
Measurement of the absolute branching ratio of the K+ -> pi(+) pi(-) pi(+) (gamma) decay with the KLOE detector
- 2014
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 738, s. 128-133
-
Journal article (peer-reviewed)abstract
- The absolute branching ratio of the K+ -> pi(+) pi(-) pi(+) (gamma) decay, inclusive of final-state radiation, has been measured using similar to 17 million tagged K+ mesons collected with the KLOE detector at DA Phi NE, the Frascati phi-factory. The result is: BR(K+ -> pi(+) pi(-) pi(+) (gamma)) = 0.05565 +/- 0.00031(stat) +/- 0.00025(syst) a factor similar or equal to 5 more precise with respect to the previous result. This work completes the program of precision measurements of the dominant kaon branching ratios at KLOE.
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42. |
- Heijkenskjöld, Lena, 1985-
(author)
-
Hadronic Decays of the ω Meson
- 2016
-
Doctoral thesis (other academic/artistic)abstract
- Two decay channels of the ω(782) meson, into π+π-π0 and π+π-, are studied. The dynamics of the three-pion channel is represented using a two-dimensional distribution, called a Dalitz plot. A high-statistics Dalitz plot distribution is needed to test theoretical predictions and increase understanding of the decay mechanism. The isospin-breaking two-pion decay gives insight into the ρ-ω mixing. The ω→π+π- decay has previously been studied in π+π- spectra in high statistics e+e- experiments and with lower statistics in hadroproduction experiments. The collected evidence indicates that the resulting interference pattern strongly depends on the production reaction.In 2011 an experiment to investigate ω hadronic decays in pd→3Heω reaction was performed with the WASA detector. Two studies based on the collected data are included in this thesis. In the first, the dominant decay channel ω→π+π-π0 is selected and two experimental Dalitz plot distributions are created. Each distribution corresponds to one of the two incident beam energies used in the experiment. A fit to the Dalitz plots is performed using a parametrisation including the expected P-wave shape. The result indicates an onset of the intermediate ρ in the two-pion channel, as predicted by theoretical models. The efficiency corrected Dalitz plot bin contents are reported to facilitate comparison to theoretical predictions by direct fits to the experimental data. In the second study, the ω→π+π- decay channel is selected. For events with a 3Heπ+π- final state, the 3He missing mass is constructed in search for the ρ-ω interference pattern in pd production. No significant deviations around the ω mass position was found. Dedicated studies using experimental data to estimate background contribution and to extract signal acceptance shows that the background is too large to observe the expected signal with the collected data sample.The last part of the thesis presents pre-studies for using data collected at the KLOE detector for an ω→π+π-π0 Dalitz plot analysis. Since the ω mesons are produced in the e+e-→ωπ0 reaction, the study focuses on the impact of the π0-π0 interference.
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43. |
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44. |
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45. |
- Skorodko, Tatiana, et al.
(author)
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Measurement of the p n ---> p p pi0 pi- reaction in search of the ABC resonance
- 2012
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In: Proceedings of 12th International Workshop on Production, properties and interaction of mesons (MESON 2012). - Les Ulis Cedex, France : EDP Sciences. ; , s. 09033-
-
Conference paper (other academic/artistic)abstract
- With pd collisions at T_p = 1.2 GeV exclusive measurements of the quasi-free pn -> pppi^0pi^- reaction have been carried out. Using the WASA detector setup at COSY total and differential cross sections have been obtained for the energy region &radics = 2.35 - 2.48 GeV. Though this includes the region of the ABC effect and its associated resonance structure, no low-mass enhancement (ABC effect) is found in the pi^0pi^--invariant mass spectrum - in agreement with the constraint from Bose statistics demanding the isovector pion pair to be in relative p-wave. Conventional calculations including t-channel processes for Roper, Delta(1600) and DeltaDelta excitations and their decays, which are well-known from the study of the two-pion production in pp collisions, provide a reasonable description of the data at high energies, but fall low at low energies. From this we conclude that a large contribution from a so far unknown isoscalar low-energy process is missed in the calculations. Inclusion of the ABC resonance at m = 2.37 GeV with Gamma = 70 MeV and I(J^P) = 0(3^+), which was recently observed in the pn -> dpi^0pi^0 reaction, leads to a much improved description of the data at low energies.
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