First Measurement of the D_{s}^{+}→K^{0}μ^{+}ν_{μ} Decay.

Area of Science:

• Particle Physics
• High Energy Physics
• Experimental Physics

Background:

• Semileptonic decays of heavy quarks provide crucial insights into fundamental particle interactions.
• Precise measurements of D_{s}^{+} decays are essential for testing the Standard Model of particle physics.
• Previous measurements of D_{s}^{+}→K^{0}μ^{+}ν_{μ} have limited precision, necessitating further investigation.

Purpose of the Study:

• To report the first measurement of the semileptonic decay D_{s}^{+}→K^{0}μ^{+}ν_{μ}.
• To determine the branching fraction and the product of the form factor f_{+}^{K^{0}}(0) and the CKM matrix element |V_{cd}|.
• To test lepton flavor universality in D_{s}^{+}→K^{0}ℓ^{+}ν_{ℓ} decays.

Main Methods:

• Analysis of e^{+}e^{-} annihilation data collected at center-of-mass energies between 4.128 and 4.226 GeV.
• Utilized a sample with an integrated luminosity of 7.33 fb^{-1} recorded by the BESIII detector.
• Performed a simultaneous fit to partial decay rates in q^{2} intervals for both D_{s}^{+}→K^{0}μ^{+}ν_{μ} and D_{s}^{+}→K^{0}e^{+}ν_{e} decays.

Main Results:

• Measured the branching fraction B(D_{s}^{+}→K^{0}μ^{+}ν_{μ})=(2.89±0.27_{stat}±0.12_{syst})×10^{-3}.
• Determined the product f_{+}^{K^{0}}(0)|V_{cd}|=0.140±0.008_{stat}±0.003_{syst}, the most precise value to date.
• Conducted the first test of lepton flavor universality in D_{s}^{+}→K^{0}ℓ^{+}ν_{ℓ} decays, finding no violation.

Conclusions:

• The study provides the first measurement of the D_{s}^{+}→K^{0}μ^{+}ν_{μ} decay and a highly precise determination of f_{+}^{K^{0}}(0)|V_{cd}|.
• The results offer significant contributions to the understanding of heavy quark decays and CKM matrix elements.
• The test of lepton flavor universality supports the predictions of the Standard Model.