697 research outputs found
Measurement of the eta->pi+pi-pi0 decay with WASA-at-COSY detector
One of the objectives of the physics programme of the WASA-at-COSY facility
is to study the isospin violating eta hadronic decays into pi+pi-pi0$ systems
driven by the term of QCD Lagrangian which depends on the d and u quark mass
difference. These studies can be made in terms of the Dalitz plot parameters
describing the density population which is proportional to the square of the
amplitude |A(x,y)|^2. This contribution describes the current status of the
analysis of the eta->pi+pi-pi0 decay in the pd->3He eta and as well in the
pp->pp eta reaction with WASA-at-COSY
Study of the decay
The decay is studied
in proton-proton collisions at a center-of-mass energy of TeV
using data corresponding to an integrated luminosity of 5
collected by the LHCb experiment. In the system, the
state observed at the BaBar and Belle experiments is
resolved into two narrower states, and ,
whose masses and widths are measured to be where the first uncertainties are statistical and the second
systematic. The results are consistent with a previous LHCb measurement using a
prompt sample. Evidence of a new
state is found with a local significance of , whose mass and width
are measured to be and , respectively. In addition, evidence of a new decay mode
is found with a significance of
. The relative branching fraction of with respect to the
decay is measured to be , where the first
uncertainty is statistical, the second systematic and the third originates from
the branching fractions of charm hadron decays.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-028.html (LHCb
public pages
Measurement of the ratios of branching fractions and
The ratios of branching fractions
and are measured, assuming isospin symmetry, using a
sample of proton-proton collision data corresponding to 3.0 fb of
integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The
tau lepton is identified in the decay mode
. The measured values are
and
, where the first uncertainty is
statistical and the second is systematic. The correlation between these
measurements is . Results are consistent with the current average
of these quantities and are at a combined 1.9 standard deviations from the
predictions based on lepton flavor universality in the Standard Model.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-039.html (LHCb
public pages
Recent Results on Meson Decays from A2
Light meson decays are used to investigate topics related to fundamental aspects of particle physics. Precision measurements of meson Dalitz decays give input to theoretical evaluations of the Hadronic Light-by-Light contribution (HLbL) to the anomalous magnetic moment of the muon. The A2 collaboration, using the Crystal Ball/TAPS setup at MAMI, has recently published several high precision results on transition form factors which are related to HLbL. Pseudoscalar η’ decays allow for studies of topics like ππ scattering lengths, effective field theories and fundamental symmetries. In 2014 the collaboration had a dedicated experimental campaign with one of its main goals to measure the dynamics of η’→ π0π0η with high precision. A brief overview of the experimental setup, physics motivations, analyses and results are given
Studies of the Decay η→π+π-π0 with WASA-at-COSY
In 2008 a large statistics sample of approximately 1·107 η-decays has been collected with the WASA detector at COSY using the pd→3Heη reaction at the beam kinetic energy of 1 GeV. These data are being used to study the not so rare η decays involving charged pions, like η→π+π-π0. This decay proceeds mainly via a strong isospin violating contribution, where the decay width is proportional to the light quark mass difference squared, (md-mu)2. In addition this decay can be used to search for C-violating effects. The analysis is presented and the Dalitz plot parameters with statistical and systematical uncertainties are determined from a sample of 1.33·105 η→π+π-π0 events in the Dalitz plot. The asymmetry parameters with statistical uncertainties are presented which show no evidence of C-violation.WASA-at-COS
Studies of the Decay η→π+π-π0 with WASA-at-COSY
In 2008 a large statistics sample of approximately 1·107 η-decays has been collected with the WASA detector at COSY using the pd→3Heη reaction at the beam kinetic energy of 1 GeV. These data are being used to study the not so rare η decays involving charged pions, like η→π+π-π0. This decay proceeds mainly via a strong isospin violating contribution, where the decay width is proportional to the light quark mass difference squared, (md-mu)2. In addition this decay can be used to search for C-violating effects. The analysis is presented and the Dalitz plot parameters with statistical and systematical uncertainties are determined from a sample of 1.33·105 η→π+π-π0 events in the Dalitz plot. The asymmetry parameters with statistical uncertainties are presented which show no evidence of C-violation.WASA-at-COS
Studies of the Decay η→π+π-π0 with WASA-at-COSY
In 2008 a large statistics sample of approximately 1·107 η-decays has been collected with the WASA detector at COSY using the pd→3Heη reaction at the beam kinetic energy of 1 GeV. These data are being used to study the not so rare η decays involving charged pions, like η→π+π-π0. This decay proceeds mainly via a strong isospin violating contribution, where the decay width is proportional to the light quark mass difference squared, (md-mu)2. In addition this decay can be used to search for C-violating effects. The analysis is presented and the Dalitz plot parameters with statistical and systematical uncertainties are determined from a sample of 1.33·105 η→π+π-π0 events in the Dalitz plot. The asymmetry parameters with statistical uncertainties are presented which show no evidence of C-violation.WASA-at-COS
CP-violation studies of hyperon-antihyperon pairs with BESIII
The BESIII experiment at the electron-positron collider BEPCII in Beijing has collected the world's largest data at the J/ψ and ψ(2S) resonances. The fact that the hyperons are produced with a non-zero spin polarization that is straightforward to parameterize in processes involving virtual photons or vector mesons, enable direct and precise CP tests. These CP-symmetry tests can be performed on e.g. e+e−→J/ψ→ΛΛ¯¯¯¯→pπ−p¯¯¯π+, e+e−→J/ψ→Σ+Σ¯¯¯¯−→pπ0p¯¯¯π0 or e+e−→J/ψ→Ξ−Ξ¯¯¯¯+→Λπ−Λ¯¯¯¯π+→pπ−π−p¯¯¯π+π+. For the Ξ−→Λπ− decay the exclusive measurement of the final state particles allows for three independent CP tests and the determination of the strong and weak phase differences. The weak phase difference is the first measurement for any baryon decay. The decay parameter ϕΞ is measured with a precision similar to the hitherto most precise measurement, performed by the HyperCP experiment at Fermilab. This is despite the fact that the BESIII data sample is three orders of magnitude smaller than that of HyperCP
Hyperon Structure and CP tests at BESIII
Hyperons are a powerful diagnostic tool that can shed light on some of the most intriguing questions in contemporary physics. Electromagnetic form factors (EMFFs) are currently the best way to study hyperon structure. In the time-like region the EMFFs can be complex with a relative phase. A non-zero phase polarizes the final state even when the initial state is unpolarized. A dedicated data sample collected by the BESIII experiment allowed for a first complete reconstruction of Λ in the time-like region. The ratio, R and relative phase between the electric and magnetic form factor, ΔΦ are measured to be 0.96±0.14(stat)±0.002(syst) and 37°±12°(stat)±6°(syst), respectively. In addition, the BESIII experiment has collected the world's largest J/ψ data sample. Due to symmetric excellent detector conditions and low hadronic background, the experiment offers a clean environment for CP-violation tests using . That hyperons can be polarized allows for a simultaneous measurement of angular distributions of hyperons and antihyperons and to test CP symmetry directly. This has been done for the process recently measured by the BESIII experiment. The experimental results showed that the asymmetry decay parameter α(Λ → ππ−) = +0.750±0.009±0.004, is nearly twenty percent larger compared to the old PDG tabulated value. The test on CP symmetry, is the most sensitive test for Λ CP-violation. Preliminary results are presented for the process . The asymmetry decay parameter and −0.015 ± 0.037 ± 0.008 are both measured for the first time
CP symmetry tests in the cascade-anticascade decay of charmonium
We analyze joint angular distributions of a charmonium decay to the Xi(Xi) over bar pair using the Xi -> Lambda pi -> p pi(-) pi weak decay chain for the cascade and the charge conjugated mode for the anticascade. The decays allow a direct comparison of the baryon and antibaryon decay properties and a sensitive test of CP symmetry in the strange baryon sector. We show that all involved decay parameters can be determined separately in vector and (pseudo)scalar charmonia decays into Xi(Xi) over bar due to the spin correlations between the weak decay chains. Contrary to the recently measured ethorne e(+)e(-) -> J/psi -> Lambda(Lambda) over bar process, the transverse polarization of the cascade is not needed and has almost no impact on the uncertainties of the decay parameters
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