The WASA detector facility at CELSIUS Bargholtz, Chr; Bashkanov, M.; Berłowski, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2008, Letnik:
594, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The WASA
4
π
multidetector system, aimed at investigating light meson production in light ion collisions and
η
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.
Status of η′ meson decays at BESIII Kupsc, A.
Nuclear and particle physics proceedings,
January-March 2017, 2017-01-00, 2017, Letnik:
282-284
Journal Article
Recenzirano
A sample of 1.31×109J/ψ events collected with the BESIII detector provides a clean source of 6.7×106η′ mesons for decay studies. Some of the highlights include first observations of Dalitz decays ...η′→γe+e− and η′→ωe+e− as well as the most precise up to now studies of η′→π+π−γ and η′→3π dynamics.
An exclusive measurement of the decay η→π+π−γ has been performed at the WASA facility at COSY. The η mesons were produced in the fusion reaction pd→He3 X at a proton beam momentum of 1.7 GeV/c. ...Efficiency corrected differential distributions have been extracted based on 13960±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 η→π+π−γ. 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 π+π− system.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).We present a measurement of eta meson production in photon-photon interactions produced by electron-positron beams ...colliding with ... GeV. The measurement is done with the KLOE detector at the -factory DA Phi NE with an integrated luminosity of 0.24 fb super(-1). The e super(+) e super(-) arrow right e super(+) e super(-) eta cross section is measured without detecting the out-going electron and positron, selecting the decays eta arrow right pi super(+) pi super(-) pi super(0) and eta arrow right pi super(0) pi super(0) pi super(0). The most relevant background is due to e super(+) e super(-) arrow right eta gamma when the monochromatic photon escapes detection. The cross section for this process is measured as sigma (e super(+) e super(-) arrow right eta gamma ) = (856 plus or minus 8 sub(stat) plus or minus 16 sub(syst)) pb. The combined result for the e super(+) e super(-) arrow right e super(+) e super(-) eta cross section is sigma (e super(+) e super(-) arrow right e super(+) e super(-) eta ) = (32.72 plus or minus 1.27 sub(stat) plus or minus 0.70 sub(syst)) pb. From this we derive the partial width Gamma ( eta arrow right gamma gamma ) = (520 plus or minus 20 sub(stat) plus or minus 13 sub(syst)) eV. This is in agreement with the world average and is the most precise measurement to date.
We report on the search for the rare decay η→π0e+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 Jülich, Germany. In total 3×107 events of the reaction pd→3Heη have been recorded at an excess energy of Q=59.8MeV. Based on this data set the C parity violating decay η→π0γ⁎→π0e+e− via a single-photon intermediate state has been searched for, resulting in new upper limits of Γ(η→π0e+e−)/Γ(η→π+π−π0)<3.28×10−5 and Γ(η→π0e+e−)/Γ(η→all)<7.5×10−6 (CL=90%), respectively.
.
In most investigations the Roper resonance is sensed only very indirectly via complex partial-wave analyses. We find indications for its excitation in the invariant
n
π
+
mass spectrum of the
pp
→
...np
π
+
reaction at
M
≈ 1360 MeV with a width of ≈ 150 MeV . The values fit very favorably to the most recent phase shift results as well as to the observations at BES. In the near-threshold two-pion production
pp
→
pp
π
0
π
0
, where the Roper excitation and its subsequent decays via the routes
N
*
→ Δπ →
N
ππ and
N
*
→
N
σ are the only dominant processes, we find its direct decay into the
N
σ channel to be the by far dominating decay process --in favor of a monopole excitation of the Roper resonance.
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.
This letter reports a first quantitative analysis of the contribution of higher partial waves in the charge symmetry breaking reaction dd→4Heπ0 using the WASA-at-COSY detector setup at an excess ...energy of Q=60MeV. The determined differential cross section can be parametrized as dσ/dΩ=a+bcos2θ⁎, where θ⁎ 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)+0.32−0.8(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 Δ isobar to the dd→4Heπ0 reaction and is, therefore, crucial for a quantitative understanding of quark mass effects in nuclear production reactions.
The absolute branching ratio of the K+→π+π−π+(γ) decay, inclusive of final-state radiation, has been measured using ∼17 million tagged K+ mesons collected with the KLOE detector at DAΦNE, the ...Frascati ϕ-factory. The result is:BR(K+→π+π−π+(γ))=0.05565±0.00031stat±0.00025syst a factor ≃ 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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