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Polarization and Entanglement in Baryon-Antibaryon Pair Production in Electron-Positron Annihilation
Authors:
BESIII Collaboration,
M. Ablikim,
M. N. Achasov,
S. Ahmed,
M. Albrecht,
M. Alekseev,
A. Amoroso,
F. F. An,
Q. An,
Y. Bai,
O. Bakina,
R. Baldini Ferroli,
Y. Ban,
K. Begzsuren,
D. W. Bennett,
J. V. Bennett,
N. Berger,
M. Bertani,
D. Bettoni,
F. Bianchi,
E. Boger,
I. Boyko,
R. A. Briere,
H. Cai,
X. Cai
, et al. (444 additional authors not shown)
Abstract:
Using a sample of $1.31\times 10^9$ $J/ψ$ events collected with the BESIII detector, we report the first observation of spin polarization of $Λ$ and $\barΛ$ hyperons from the coherent production in the $J/ψ\toΛ\barΛ$ decay. We measure the phase between the hadronic form factors to be $ΔΦ=(42.4\pm0.6\pm0.5)^\circ$. The decay parameters for $Λ\to pπ^-$ ($α_-$), $\barΛ\to\bar pπ^+$ ($α_+$) and…
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Using a sample of $1.31\times 10^9$ $J/ψ$ events collected with the BESIII detector, we report the first observation of spin polarization of $Λ$ and $\barΛ$ hyperons from the coherent production in the $J/ψ\toΛ\barΛ$ decay. We measure the phase between the hadronic form factors to be $ΔΦ=(42.4\pm0.6\pm0.5)^\circ$. The decay parameters for $Λ\to pπ^-$ ($α_-$), $\barΛ\to\bar pπ^+$ ($α_+$) and $\barΛ\to\bar nπ^0$ ($\barα_0$) are measured to be $α_-=0.750\pm0.009\pm0.004$, $α_+=-0.758\pm0.010\pm0.007$ and $\barα_0=-0.692\pm0.016\pm0.006$, respectively. The obtained value of $α_-$ is higher by $(17\pm 3)\%$ than the current world average. In addition, the $CP$ asymmetry of $-0.006\pm0.012\pm0.007$ is extracted with substantially improved precision. The ratio $\barα_0/α_{+} = 0.913\pm 0.028 \pm 0.012$ is also measured.
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Submitted 27 August, 2018;
originally announced August 2018.
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Determination of the $\mathbf{Σ(1385)^{0}/Λ(1405)}$ ratio in p+p collisions at 3.5 GeV
Authors:
G. Agakishiev,
A. Balanda,
D. Belver,
A. V. Belyaev,
A. Blanco,
M. Böhmer,
J. L. Boyard,
P. Cabanelas,
E. Castro,
J. C. Chen,
S. Chernenko,
T. Christ,
M. Destefanis,
F. Dohrmann,
A. Dybczak,
E. Epple,
L. Fabbietti,
O. V. Fateev,
P. Finocchiaro,
P. Fonte,
J. Friese,
I. Fröhlich,
T. Galatyuk,
J. A. Garzón,
R. Gernhäuser
, et al. (76 additional authors not shown)
Abstract:
The aim of the present analysis is to determine the relative production cross sections of the $Λ$(1405) and $Σ(1385)^{0}$ resonances in p+p collisions at E$_{kin}$=3.5 GeV measured with HADES. Upper and lower limits have been determined for the ratio $σ_{(Σ(1385)^{0}+p+K^{+})}/σ_{(Λ(1405)+p+K^{+})}=0.76_{-0.26}^{+0.54}$. The knowledge of this ratio is an essential input for the analysis of the dec…
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The aim of the present analysis is to determine the relative production cross sections of the $Λ$(1405) and $Σ(1385)^{0}$ resonances in p+p collisions at E$_{kin}$=3.5 GeV measured with HADES. Upper and lower limits have been determined for the ratio $σ_{(Σ(1385)^{0}+p+K^{+})}/σ_{(Λ(1405)+p+K^{+})}=0.76_{-0.26}^{+0.54}$. The knowledge of this ratio is an essential input for the analysis of the decay $Λ(1405)\rightarrowΣ^{\pm}π^{\mp}$, where an unambiguous separation of the $Λ$(1405) and $Σ(1385)^{0}$ signals is not possible.
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Submitted 1 February, 2012;
originally announced February 2012.
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Inclusive dielectron spectra in p+p collisions at 3.5 GeV
Authors:
G. Agakishiev,
A. Balanda,
D. Belver,
A. Belyaev,
A. Blanco,
M. Böhmer,
J. L. Boyard,
P. Cabanelas,
E. Castro,
J. C. Chen,
S. Chernenko,
T. Christ,
M. Destefanis,
F. Dohrmann,
A. Dybczak,
E. Epple,
L. Fabbietti,
O. Fateev,
P. Finocchiaro,
P. Fonte,
J. Friese,
I. Fröhlich,
T. Galatyuk,
J. A. Garzón,
R. Gernhäuser
, et al. (76 additional authors not shown)
Abstract:
We present the inclusive invariant-mass, transverse momentum and rapidity distributions of dielectrons (e$^{+}$e$^{-}$ pairs) in p+p interactions at 3.5 GeV beam kinetic energy. In the vector-meson mass region, a distinct peak corresponding to direct $ω$ decays is reconstructed with 2% mass resolution. The data is compared to predictions from three model calculations. Due to the large acceptance o…
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We present the inclusive invariant-mass, transverse momentum and rapidity distributions of dielectrons (e$^{+}$e$^{-}$ pairs) in p+p interactions at 3.5 GeV beam kinetic energy. In the vector-meson mass region, a distinct peak corresponding to direct $ω$ decays is reconstructed with 2% mass resolution. The data is compared to predictions from three model calculations. Due to the large acceptance of the HADES apparatus for $e^{+}e^{-}$ invariant masses above 0.2 GeV/$c^{2}$ and for transverse pair momenta p$_{t}$ $ <$ 1 GeV/$c$, acceptance corrections are to a large extent model independent. This allows us to extract from dielectron data for the first time at this energy the inclusive production cross sections for light vector mesons. Inclusive production cross sections for $π^o$ and $η$ mesons are also reported. The obtained results will serve as an important reference for the study of vector meson production in proton-nucleus and heavy-ion collisions. Furthermore, using this data, an improved value for the upper bound of the branching ratio for direct $η$ decays into the electron-positron channel is obtained.
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Submitted 15 December, 2011;
originally announced December 2011.
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Baryonic resonances close to the Kbar-N threshold: the case of Sigma(1385)^+ in pp collisions
Authors:
G. Agakishiev,
A. Balanda,
D. Belver,
A. V. Belyaev,
A. Blanco,
M. Boehmer,
J. L. Boyard,
P. Cabanelas,
E. Castro,
J. C. Chen,
S. Chernenko,
T. Christ,
M. Destefanis,
F. Dohrmann,
A. Dybczak,
E. Epple,
T. Eberl,
L. Fabbietti,
O. V. Fateev,
P. Finocchiaro,
P. Fonte,
J. Friese,
I. Froehlich,
T. Galatyuk,
J. A. Garzon
, et al. (77 additional authors not shown)
Abstract:
We present results of an exclusive measurement of the first excited state of the Sigma hyperon, Sigma(1385)^+, produced in p+p -> Sigma^+ + K^+ + n at 3.5 GeV beam energy. The extracted data allow to study in detail the invariant mass distribution of the Sigma(1385)^+. The mass distribution is well described by a relativistic Breit-Wigner function with a maximum at m_0 = 1383.2 +- 0.9 MeV/c^2 and…
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We present results of an exclusive measurement of the first excited state of the Sigma hyperon, Sigma(1385)^+, produced in p+p -> Sigma^+ + K^+ + n at 3.5 GeV beam energy. The extracted data allow to study in detail the invariant mass distribution of the Sigma(1385)^+. The mass distribution is well described by a relativistic Breit-Wigner function with a maximum at m_0 = 1383.2 +- 0.9 MeV/c^2 and a width of 40.2 +- 2.1 MeV/c^2. The exclusive production cross-section comes out to be 22.27 +- 0.89 +- 1.56 +3.07 -2.10 mu b. Angular distributions of the Sigma(1385)^+ in different reference frames are found to be compatible with the hypothesis that 33 % of Sigma(1385)^+ result from the decay of an intermediate Delta^{++} resonance.
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Submitted 30 September, 2011;
originally announced September 2011.