We report a measurement of the lifetime of the cesium 7s 2 S 1/2 state using time-correlated singlephoton counting spectroscopy in a vapor cell. We excite the atoms using a Doppler-free two-photon transition from the 6s 2 S 1/2 ground state, and detect the 1.47 µm photons from the spontaneous decay of the 7s 2 S 1/2 to the 6p 2 P 3/2 state. We use a gated single photon detector in an asynchronous mode, allowing us to capture the fluorescence profile for a window much larger than the detector gate length. Analysis of the exponential decay of the photon count yields a 7s 2 S 1/2 lifetime of 48.28 ± 0.07 ns, an uncertainty of 0.14%. These measurements provide sensitive tests of theoretical models of the Cs atom, which play a central role in parity violation measurements. PACS numbers: 32.70.CsPrecision laboratory measurements of electric dipole (E1) matrix elements are critical for the advancement of atomic parity violation (PV) studies in several regards: Precise models of atomic structure are required to extract the weak charge Q w from any measurement of the PV transition moment; E1 matrix elements are included explicitly in the perturbative expansion for the PV moment; and measurements of the PV amplitude are always carried out relative to a different optical transition amplitude, such as a Stark-induced amplitude. Thus, we require precise determinations of electric dipole matrix elements, through a variety of laboratory measurements, and detailed comparison with ab initio theoretical results.The most precise determination of a PV moment in any atomic system is that of the 6s 2 S 1/2 → 7s 2 S 1/2 transition in cesium, carried out by Wood et al. in 1997 [1]. In the past 30 years, several advances in models of the atomic structure of the cesium atom [2][3][4][5][6][7][8][9][10][11][12], and measurements of key transition amplitudes [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] have been reported. The uncertainty in the E1 transition moment 7s||r||6p 1/2 is presently one of the primary contributors, along with the 7p 1/2 ||r||6s matrix element, to the uncertainty in the PV moment for the 6s 2 S 1/2 → 7s 2 S 1/2 transition [11,23]. Similarly, the uncertainties in 7s||r||6p 1/2 and 7s||r||6p 3/2 are primary contributors to the uncertainty of the scalar Stark polarizability for the 6s → 7s transition [20,23].In this paper we present our measurement of the lifetime of the cesium 7s 2 S 1/2 state using an asynchronous time-correlated single-photon counting (TCSPC) technique. By measuring the lifetime of the 7s state, we indirectly measure the matrix elements named above. We find a lifetime value of 48.28 ± 0.07 ns, in good agreement with the previous measurement by Bouchiat et al.[13], but with much smaller uncertainty, and in agreement with several theoretical determinations [3-6, 9, 11]. This work paves the way to reducing the uncertainty of the PV transition amplitude and Stark polarizability, and complements progress we are making toward a new atomic PV measurement in cesium [24,28].Cesium atoms in t...