A measurement of the ratio of branching fractions of the decays B þ → K þ μ þ μ − and B þ → K þ e þ e − is presented. The proton-proton collision data used correspond to an integrated luminosity of 5.0 fb −1 recorded with the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. For the dilepton mass-squared range 1.1 < q 2 < 6.0 GeV 2 =c 4 the ratio of branching fractions is measured to be R K ¼ 0.846 þ0.060 −0.054 þ0.016 −0.014 , where the first uncertainty is statistical and the second systematic. This is the most precise measurement of R K to date and is compatible with the standard model at the level of 2.5 standard deviations.

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In this paper we test whether national cross cultural differences between joint venture (IV) parents affect JV longevity by comparing that of two categories of JVs placed in the same environment, those between two or more Japanese parents on one hand, and those between Japanese and American parents, on the other. Carefully controlling for n the last ten years the rates of formation and dissolution of international joint ventures (JVs) have both been extremely high. Seventy percent of the partnerships studied by Coopers and Lybrand (1986), two-thirds of those in Auster's (1986) and Kogut's (1989) sample, half of those in Harrigan's (1988), forty percent of those in Millington and Bayother factors that may affect JV longevity, we find that the longevity of Japanese-American JVs is lower than that of Japanese-Japanese JVs. Such effects, however, appear only for dissolutions that result from the sale of the venture to one of the partners, not for those due to liquidation or sale to a third party. liss' (1997) and a third of those in Franko's (1971) eventually broke up. Crosscultural conflicts between parents of different nationalities are often cited as reasons for these high dissolution rates (Brown, Rugman and Verbeke, 1989; Lane and Beamish, 1990; Shenkar and Zeira, 1992). Yet while there is much anecdotal support for this thesis, the sta- *Jean-Franoois Hennart is Professor of International Management at Tilburg University. His main research focus is on the transaction cost theory of international business institutions. He is the author of A Theory of Multinational Enterprise (University of Michigan Press, 1982)and of many theoretical and empirical articles on transaction cost theory and modes of market entry and exit.