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’→ π
0
π
0
η with high precision. A brief overview of the experimental setup, physics motivations, analyses and results are given.
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 pseudoscalar
η
' decays allow for studies of topics like
ππ
scattering lengths, effective field theories and fundamental symmetries. 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. The value obtained for the slope parameter of the
π
0
electromagnetic (e/m) transition form factor (TFF) is
α
π
= 0.030 ± 0.010
tot
. The slope parameters for the e/m TFFs of
ηγ
and
ωπ
0
are see formula in PDF and see formula in PDF, respectively. In 2014 the collaboration had a dedicated experimental campaign for the production of
η
' mesons. One of the main goals was to measure the dynamics of
η
' →
ηπ
0
π
0
with high precision. An overview of the physics cases, the experimental setup and the results are given.
We analyze joint angular distributions of a charmonium decay to the ΞΞ¯ pair using the Ξ→Λπ→pπ−π 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 ΞΞ¯ due to the spin correlations between the weak decay chains. Contrary to the recently measured e+e−→J/ψ→ΛΛ¯ process, the transverse polarization of the cascade is not needed and has almost no impact on the uncertainties of the decay parameters.
Nonleptonic two-body weak decays of baryons are an important tool to probe the combined charge conjugation-parity symmetry (CP) violation. We explain why the decays of strange baryons provide ...complementary information to the decays of kaons. A model-independent parametrization of the nonleptonic decays of the Lambda and Xi baryons is reviewed, and the amplitudes are updated according to the latest experimental input. We demonstrate the potential of performing precision tests in strange baryon decays at the nextgeneration electron-positron J/psi factories with luminosity of 10(35) cm(-2) s(-1). The copious production of spinentangled hyperon-antihyperon pairs via the J/psi resonance allows for a direct comparison of the baryon and antibaryon decay properties. Using analytic approximations and numerical calculations, we study the quantitative impact of spin correlations and polarization in such CP tests. We show that by using a longitudinally polarized electron beam the statistical precision of the CP tests can be significantly improved compared to the experiments without polarized beams. Furthermore, we map out further directions for possible improvements, like analysis of incompletely reconstructed events or a combination of the isospin related processes. Altogether, these methods are promising for the observation of a statistically significant CP-violation signal with a strength corresponding to the standard model predictions. Our conclusions should encourage more detailed feasibility studies, including optimization of the measurement methods and studies of systematic effects. Finally, our results call for an update of the theory predictions with increased precision.
A study of prompt Ξ + 𝑐 production in proton-lead collisions is performed with the LHCb experiment at a center-of-mass energy per nucleon pair of 8.16 TeV in 2016 in 𝑝Pb and Pb𝑝 collisions with ...an estimated integrated luminosity of approximately 12.5 and 17.4 nb −1 , respectively. The Ξ + 𝑐 production cross section, as well as the Ξ + 𝑐 to Λ + 𝑐 production cross-section ratio, are measured as a function of the transverse momentum and rapidity and compared to the latest theory predictions. The forward-backward asymmetry is also measured as a function of the Ξ + 𝑐 transverse momentum. The results provide strong constraints on theoretical calculation and are a unique input for hadronization studies in different collision systems.
The first measurement of the Z boson production cross-section at centre-of-massenergy √s = 5.02 TeV in the forward region is reported, using pp collision data collected bythe LHCb experiment in year ...2017, corresponding to an integrated luminosity of 100 ± 2 pb−1.The production cross-section is measured for final-state muons in the pseudorapidity range2.0 < η < 4.5 with transverse momentum pT > 20 GeV/c. The integrated cross-sectionis determined to be
σZ→μ+μ− = 39.6 ± 0.7(stat) ± 0.6(syst) ± 0.8(lumi) pb
for the di-muon invariant mass in the range 60 < Mμμ < 120 GeV/c2. This result andthe differential cross-section results are in good agreement with theoretical predictions atnext-to-next-to-leading order in the strong coupling constant.Based on a previous LHCb measurement of the Z boson production cross-section in pPbcollisions at √sNN = 5.02 TeV, the nuclear modification factor RpPb is measured for the firsttime at this energy. The measured values are 1.2+0.5−0.3(stat) ± 0.1(syst) in the forward region(1.53 < y∗μ < 4.03) and 3.6+1.6−0.9(stat) ± 0.2 (syst) in the backward region (−4.97 < y∗μ < −2.47),where y∗μ represents the muon rapidity in the centre-of-mass frame.
The production of prompt D+ and D + s mesons is studied in proton-lead collisions at a centre-of-mass energy of √s NN = 5.02TeV. The data sample corresponding to an integrated luminosity of (1.58 ± ...0.02)nb -1 is collected by the LHCb experiment at the LHC. The differential production cross-sections are measured using D + and D + s candidates with transverse momentum in the range of 0 < p T < 14 GeV/c and rapidities in the ranges of 1.5 < y* < 4.0 and -5.0 < y* < -2.5 in the nucleon-nucleon centre-of-mass system. For both particles, the nuclear modification factor and the forward-backward production ratio are determined. These results are compared with theoretical models that include initial-state nuclear effects. In addition, measurements of the cross-section ratios between D + , D + s and D 0 mesons are presented, providing a baseline for studying the charm hadronization in lead-lead collisions at LHC energies.
A flavor-tagged time-dependent angular analysis of the decay B0s -> phi phi is performed using pp collision integrated luminosity of 6 fb-1. The CP-violating phase and direct CP-violation ...parameter are measured to s = -0.042 +/- 0.075 +/- 0.009 rad and l lambda l = 1.004 +/- 0.030 +/- 0.009, respectively, assuming the same values for all polarization states of the phi phi system. In these results, the first uncertainties are statistical and the second systematic. These parameters are also determined separately for each polarization state, showing no evidence for polarization dependence. The results are combined with previous LHCb measurements using pp collisions at center-of-mass energies of 7 and 8 TeV, yielding phi sss over bar s = -0.074 +/- 0.069 rad and l lambda l = 1.009 +/- 0.030. This is the most precise study of time-dependent CP violation in a penguindominated B meson decay. The results are consistent with CP symmetry and with the standard model predictions.
The time-integrated CP asymmetry in the Cabibbo suppressed decay PKK is measured using proton proton collision data, corresponding to an integrated luminosity of 5.7 th collected at a center of mass ...energy of 13 TeV with the LHCb detector. The D mesons are required to originate from promptly produced DD's decays, and the charge of the companion pion is used to determine the flavor of the charm meson at production. The time integrated CP asymmetry is measured to be Acr(KK) 6,815.41.6 x 10 where the first uncertainty is statistical and the second systematic. The direct CP asymmetries in D-K-K and D -> decays, and are derived by combining Ace(KK) with the time integrated CP asymmetry differ ence, AAcr-Acr(KK)-A(x), and other inputs, giving a (7.715.7) x 10, (23.2 16.1) x 10, with a correlation coefficient corresponding to p=0.88. The compatibility of these results with CP symmetry is 1.4 and 3.8 standard deviations for DKK and D degrees-xx decays, respectively. This is the first evidence for direct CP violation in a specific Do decay.
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