M Ablikim, M N Achasov, S Ahmed, M Albrecht, M Alekseev, A Amoroso, F F An, Q An, Y Bai, O Bakina, R Baldini Ferroli, Y Ban, K Begzsuren, D W Bennett, J V Bennett, N Berger, M Bertani, D Bettoni, F Bianchi, I Boyko, R A Briere, H Cai, X Cai, O Cakir, A Calcaterra, G F Cao, S A Cetin, J Chai, J F Chang, W L Chang, G Chelkov, G Chen, H S Chen, J C Chen, M L Chen, P L Chen, S J Chen, Y B Chen, G Cibinetto, F Cossio, H L Dai, J P Dai, A Dbeyssi, D Dedovich, Z Y Deng, A Denig, I Denysenko, M Destefanis, F De Mori, Y Ding, C Dong, J Dong, L Y Dong, M Y Dong, Z L Dou, S X Du, P F Duan, J Z Fan, J Fang, S S Fang, Y Fang, R Farinelli, L Fava, S Fegan, F Feldbauer, G Felici, C Q Feng, M Fritsch, C D Fu, Y Fu, Q Gao, X L Gao, Y Gao, Y G Gao, Z Gao, B Garillon, I Garzia, A Gilman, K Goetzen, L Gong, W X Gong, W Gradl, M Greco, L M Gu, M H Gu, Y T Gu, A Q Guo, L B Guo, R P Guo, Y P Guo, A Guskov, Z Haddadi, S Han, X Q Hao, F A Harris, K L He, F H Heinsius, T Held, Y K Heng, T Holtmann, Z L Hou, H M Hu, J F Hu, T Hu, Y Hu, G S Huang, J S Huang, X T Huang, X Z Huang, Z L Huang, T Hussain, W Ikegami Andersson, M Irshad, Q Ji, Q P Ji, X B Ji, X L Ji, X S Jiang, X Y Jiang, J B Jiao, Z Jiao, D P Jin, S Jin, Y Jin, T Johansson, A Julin, N Kalantar-Nayestanaki, X S Kang, M Kavatsyuk, B C Ke, T Khan, A Khoukaz, P Kiese, R Kliemt, L Koch, O B Kolcu, B Kopf, M Kornicer, M Kuemmel, M Kuessner, A Kupsc, M Kurth, W Kühn, J S Lange, M Lara, P Larin, L Lavezzi, S Leiber, H Leithoff, C Li, Cheng Li, D M Li, F Li, F Y Li, G Li, H B Li, H J Li, J C Li, J W Li, Ke Li, Lei Li, P L Li, P R Li, Q Y Li, T Li, W D Li, W G Li, X L Li, X N Li, X Q Li, Z B Li, H Liang, Y F Liang, Y T Liang, G R Liao, L Z Liao, J Libby, C X Lin, D X Lin, B Liu, B J Liu, C X Liu, D Liu, D Y Liu, F H Liu, Fang Liu, Feng Liu, H B Liu, H L Liu, H M Liu, Huanhuan Liu, Huihui Liu, J B Liu, J Y Liu, K Liu, K Y Liu, Ke Liu, Q Liu, S B Liu, X Liu, Y B Liu, Z A Liu, Zhiqing Liu, Y F Long, X C Lou, H J Lu, J D Lu, J G Lu, Y Lu, Y P Lu, C L Luo, M X Luo, X L Luo, S Lusso, X R Lyu, F C Ma, H L Ma, L L Ma, M M Ma, Q M Ma, X N Ma, X X Ma, X Y Ma, Y M Ma, F E Maas, M Maggiora, Q A Malik, A Mangoni, Y J Mao, Z P Mao, S Marcello, Z X Meng, J G Messchendorp, G Mezzadri, J Min, T J Min, R E Mitchell, X H Mo, Y J Mo, C Morales Morales, G Morello, N Yu Muchnoi, H Muramatsu, A Mustafa, S Nakhoul, Y Nefedov, F Nerling, I B Nikolaev, Z Ning, S Nisar, S L Niu, S L Olsen, Q Ouyang, S Pacetti, Y Pan, M Papenbrock, P Patteri, M Pelizaeus, J Pellegrino, H P Peng, K Peters, J Pettersson, J L Ping, R G Ping, A Pitka, R Poling, V Prasad, H R Qi, M Qi, T Y Qi, S Qian, C F Qiao, N Qin, X S Qin, Z H Qin, J F Qiu, K H Rashid, C F Redmer, M Richter, M Ripka, M Rolo, G Rong, Ch Rosner, A Sarantsev, M Savrié, C Schnier, K Schoenning, W Shan, X Y Shan, M Shao, C P Shen, P X Shen, X Y Shen, H Y Sheng, X Shi, J J Song, W M Song, X Y Song, S Sosio, C Sowa, S Spataro, G X Sun, J F Sun, L Sun, S S Sun, X H Sun, Y J Sun, Y K Sun, Y Z Sun, Z J Sun, Z T Sun, Y T Tan, C J Tang, G Y Tang, X Tang, I Tapan, M Tiemens, B Tsednee, I Uman, G S Varner, B Wang, B L Wang, C W Wang, D Y Wang, Dan Wang, K Wang, L L Wang, L S Wang, M Wang, Meng Wang, P Wang, P L Wang, W P Wang, X F Wang, Y Wang, Y F Wang, Y Q Wang, Z Wang, Z G Wang, Z Y Wang, Zongyuan Wang, T Weber, D H Wei, P Weidenkaff, S P Wen, U Wiedner, M Wolke, L H Wu, L J Wu, Z Wu, L Xia, X Xia, Y Xia, D Xiao, Y J Xiao, Z J Xiao, Y G Xie, Y H Xie, X A Xiong, Q L Xiu, G F Xu, J J Xu, L Xu, Q J Xu, Q N Xu, X P Xu, F Yan, L Yan, W B Yan, W C Yan, Y H Yan, H J Yang, H X Yang, L Yang, S L Yang, Y H Yang, Y X Yang, Yifan Yang, M Ye, M H Ye, J H Yin, Z Y You, B X Yu, C X Yu, C Z Yuan, Y Yuan, A Yuncu, A A Zafar, A Zallo, Y Zeng, Z Zeng, B X Zhang, B Y Zhang, C C Zhang, D H Zhang, H H Zhang, H Y Zhang, J Zhang, J L Zhang, J Q Zhang, J W Zhang, J Y Zhang, J Z Zhang, K Zhang, L Zhang, S F Zhang, T J Zhang, X Y Zhang, Y Zhang, Y H Zhang, Y T Zhang, Yang Zhang, Yao Zhang, Yu Zhang, Z H Zhang, Z P Zhang, Z Y Zhang, G Zhao, J W Zhao, J Y Zhao, J Z Zhao, Lei Zhao, Ling Zhao, M G Zhao, Q Zhao, S J Zhao, T C Zhao, Y B Zhao, Z G Zhao, A Zhemchugov, B Zheng, J P Zheng, W J Zheng, Y H Zheng, B Zhong, L Zhou, Q Zhou, X Zhou, X K Zhou, X R Zhou, X Y Zhou, A N Zhu, J Zhu, J Zhu, K Zhu, K J Zhu, S Zhu, S H Zhu, X L Zhu, Y C Zhu, Y S Zhu, Z A Zhu, J Zhuang, B S Zou, J H Zou

Using a 3.19 fb^{-1} data sample collected at an e^{+}e^{-} center-of-mass energy of E_{cm}=4.178 GeV with the BESIII detector, we measure the branching fraction of the leptonic decay D_{s}^{+}→μ^{+}ν_{μ} to be B_{D_{s}^{+}→μ^{+}ν_{μ}}=(5.49±0.16_{stat}±0.15_{syst})×10^{-3}. Combining our branching fraction with the masses of the D_{s}^{+} and μ^{+} and the lifetime of the D_{s}^{+}, we determine f_{D_{s}^{+}}|V_{cs}|=246.2±3.6_{stat}±3.5_{syst} MeV. Using the c→s quark mixing matrix element |V_{cs}| determined from a global standard model fit, we evaluate the D_{s}^{+} decay constant f_{D_{s}^{+}}=252...

*February 22, 2019: Physical Review Letters*