Research output: Contribution to journal › Letter › peer-review
Polarization and entanglement in baryon–antibaryon pair production in electron–positron annihilation. / BESIII Collaboration.
In: Nature Physics, Vol. 15, No. 7, 01.07.2019, p. 631-634.Research output: Contribution to journal › Letter › peer-review
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TY - JOUR
T1 - Polarization and entanglement in baryon–antibaryon pair production in electron–positron annihilation
AU - BESIII Collaboration
AU - Ablikim, M.
AU - Achasov, M. N.
AU - Ahmed, S.
AU - Albrecht, M.
AU - Alekseev, M.
AU - Amoroso, A.
AU - An, F. F.
AU - An, Q.
AU - Bai, Y.
AU - Bakina, O.
AU - Baldini Ferroli, R.
AU - Ban, Y.
AU - Begzsuren, K.
AU - Bennett, D. W.
AU - Bennett, J. V.
AU - Berger, N.
AU - Bertani, M.
AU - Bettoni, D.
AU - Bianchi, F.
AU - Boger, E.
AU - Boyko, I.
AU - Briere, R. A.
AU - Cai, H.
AU - Cai, X.
AU - Calcaterra, A.
AU - Cao, G. F.
AU - Cetin, S. A.
AU - Chai, J.
AU - Chang, J. F.
AU - Chang, W. L.
AU - Chelkov, G.
AU - Chen, G.
AU - Chen, H. S.
AU - Chen, J. C.
AU - Chen, M. L.
AU - Chen, P. L.
AU - Chen, S. J.
AU - Chen, X. R.
AU - Chen, Y. B.
AU - Cheng, W.
AU - Chu, X. K.
AU - Cibinetto, G.
AU - Cossio, F.
AU - Dai, H. L.
AU - Dai, J. P.
AU - Dbeyssi, A.
AU - Dedovich, D.
AU - Deng, Z. Y.
AU - Muchnoi, N. Yu
AU - Nikolaev, I. B.
PY - 2019/7/1
Y1 - 2019/7/1
N2 - Particles directly produced at electron–positron colliders, such as the J/ψ meson, decay with relatively high probability into a baryon–antibaryon pair 1 . For spin-1/2 baryons, the pair can have the same or opposite helicites. A non-vanishing phase ΔΦ between the transition amplitudes to these helicity states results in a transverse polarization of the baryons 2–4 . From the joint angular distribution of the decay products of the baryons, this phase as well as the parameters characterizing the baryon and the antibaryon decays can be determined. Here, we report the measurement of ΔΦ = 42.4 ± 0.6 ± 0.5° using Λ → pπ − and Λ¯ → p¯ π + , n¯ π decays at BESIII. We find a value for the Λ → pπ − decay parameter of α − = 0.750 ± 0.009 ± 0.004, 17 ± 3% higher than the current world average, which has been used as input for all Λ polarization measurements since 1978 5,6 . For Λ¯ → p¯ π + we find α + = −0.758 ± 0.010 ± 0.007, giving A CP = (α − + α + )/(α − − α + ) = −0.006 ± 0.012 ± 0.007, a precise direct test of charge–parity symmetry (CP) violation in Λ decays.
AB - Particles directly produced at electron–positron colliders, such as the J/ψ meson, decay with relatively high probability into a baryon–antibaryon pair 1 . For spin-1/2 baryons, the pair can have the same or opposite helicites. A non-vanishing phase ΔΦ between the transition amplitudes to these helicity states results in a transverse polarization of the baryons 2–4 . From the joint angular distribution of the decay products of the baryons, this phase as well as the parameters characterizing the baryon and the antibaryon decays can be determined. Here, we report the measurement of ΔΦ = 42.4 ± 0.6 ± 0.5° using Λ → pπ − and Λ¯ → p¯ π + , n¯ π decays at BESIII. We find a value for the Λ → pπ − decay parameter of α − = 0.750 ± 0.009 ± 0.004, 17 ± 3% higher than the current world average, which has been used as input for all Λ polarization measurements since 1978 5,6 . For Λ¯ → p¯ π + we find α + = −0.758 ± 0.010 ± 0.007, giving A CP = (α − + α + )/(α − − α + ) = −0.006 ± 0.012 ± 0.007, a precise direct test of charge–parity symmetry (CP) violation in Λ decays.
KW - ANALYZING POWER
KW - PARAMETER
KW - J/PSI
KW - DECAY
KW - HYPERON
KW - LAMBDA(LAMBDA)OVER-BAR
KW - OBSERVABLES
KW - E(+)E(-)
KW - LAMBDA
UR - http://www.scopus.com/inward/record.url?scp=85065295770&partnerID=8YFLogxK
U2 - 10.1038/s41567-019-0494-8
DO - 10.1038/s41567-019-0494-8
M3 - Letter
AN - SCOPUS:85065295770
VL - 15
SP - 631
EP - 634
JO - Nature Physics
JF - Nature Physics
SN - 1745-2473
IS - 7
ER -
ID: 20180996