LHCb

Research group

Sub department

About

Differential decay rate of B + → J/ψK + with the LHCb Upgrade I experiment

Journal of High Energy Physics Springer 2026:4 (2026) 170

Authors:

R Aaij, ASW Abdelmotteleb, C Abellan Beteta, F Abudinén, T Ackernley, AA Adefisoye, B Adeva, M Adinolfi, P Adlarson, C Agapopoulou, CA Aidala, Z Ajaltouni, S Akar, K Akiba, M Akthar, P Albicocco, J Albrecht, R Aleksiejunas, F Alessio, P Alvarez Cartelle, R Amalric, S Amato, JL Amey, Y Amhis, L An, D Bacher

Abstract:

The normalised decay rate of B+ → J/ψ(→ μ+μ−)K+ is measured as a function of the lepton helicity angle using a data sample corresponding to an integrated luminosity of 1.1 fb−1 collected during October 2024 with the upgraded (Upgrade I) LHCb detector. This angular distribution can be parameterised by two coefficients, the forward-backward asymmetry, AFB, and the flatness parameter, FH, whose values are constrained by conservation of angular momentum. These coefficients are measured both integrated and differentially across various kinematic and detector-response variables, and the results are found to be in good agreement with expectations. These measurements show that the detector response of the LHCb Upgrade I experiment is understood to the precision required to reliably extract the angular coefficients associated with rare b → sμ+μ− and b → dμ+μ− transitions, which are particularly sensitive to physics beyond the Standard Model.

Observation of a threshold enhancement in the $π^+π^-$ spectrum in $ψ(3686) \rightarrow π^{+}π^{-}J/ψ$ decays

(2026)

Authors:

BESIII Collaboration, M Ablikim, MN Achasov, P Adlarson, XC Ai, R Aliberti, A Amoroso, Q An, Y Bai, O Bakina, Y Ban, H-R Bao, V Batozskaya, K Begzsuren, N Berger, M Berlowski, MB Bertani, D Bettoni, F Bianchi, E Bianco, A Bortone, I Boyko, RA Briere, A Brueggemann, H Cai, MH Cai, X Cai, A Calcaterra, GF Cao, N Cao, SA Cetin, XY Chai, JF Chang, TT Chang, GR Che, YZ Che, CH Chen, Chao Chen, G Chen, HS Chen, HY Chen, ML Chen, SJ Chen, SM Chen, T Chen, XR Chen, XT Chen, XY Chen, YB Chen, YQ Chen, ZK Chen, JC Cheng, LN Cheng, SK Choi, X Chu, G Cibinetto, F Cossio, J Cottee-Meldrum, HL Dai, JP Dai, XC Dai, A Dbeyssi, RE de Boer, D Dedovich, CQ Deng, ZY Deng, A Denig, I Denisenko, M Destefanis, F De Mori, XX Ding, Y Ding, YX Ding, J Dong, LY Dong, MY Dong, X Dong, MC Du, SX Du, SX Du, XL Du, YY Duan, ZH Duan, P Egorov, GF Fan, JJ Fan, YH Fan, J Fang, J Fang, SS Fang, WX Fang, YQ Fang, L Fava, F Feldbauer, G Felici, CQ Feng, JH Feng, L Feng, QX Feng, YT Feng, M Fritsch, CD Fu, JL Fu, YW Fu, H Gao, Y Gao, YN Gao, YN Gao, YY Gao, Z Gao, S Garbolino, I Garzia, L Ge, PT Ge, ZW Ge, C Geng, EM Gersabeck, A Gilman, K Goetzen, JD Gong, L Gong, WX Gong, W Gradl, S Gramigna, M Greco, MH Gu, CY Guan, AQ Guo, JN Guo, LB Guo, MJ Guo, RP Guo, X Guo, YP Guo, A Guskov, J Gutierrez, TT Han, F Hanisch, KD Hao, XQ Hao, FA Harris, CZ He, KL He, FH Heinsius, CH Heinz, YK Heng, C Herold, PC Hong, GY Hou, XT Hou, YR Hou, ZL Hou, HM Hu, JF Hu, QP Hu, SL Hu, T Hu, Y Hu, ZM Hu, GS Huang, KX Huang, LQ Huang, P Huang, XT Huang, YP Huang, YS Huang, T Hussain, N Hüsken, N in der Wiesche, J Jackson, Q Ji, QP Ji, W Ji, XB Ji, XL Ji, XQ Jia, ZK Jia, D Jiang, HB Jiang, PC Jiang, SJ Jiang, XS Jiang, Y Jiang, JB Jiao, JK Jiao, Z Jiao, S Jin, Y Jin, MQ Jing, XM Jing, T Johansson, S Kabana, N Kalantar-Nayestanaki, XL Kang, XS Kang, M Kavatsyuk, BC Ke, V Khachatryan, A Khoukaz, OB Kolcu, B Kopf, M Kuessner, X Kui, N Kumar, A Kupsc, W Kühn, Q Lan, WN Lan, TT Lei, M Lellmann, T Lenz, C Li, C Li, CH Li, CK Li, DM Li, F Li, G Li, HB Li, HJ Li, HL Li, HN Li, Hui Li, JR Li, JS Li, JW Li, K Li, KL Li, LJ Li, Lei Li, MH Li, MR Li, PL Li, PR Li, QM Li, QX Li, R Li, SX Li, Shanshan Li, T Li, TY Li, WD Li, WG Li, X Li, XH Li, XK Li, XL Li, XY Li, XZ Li, Y Li, YG Li, YP Li, ZH Li, ZJ Li, ZX Li, ZY Li, C Liang, H Liang, YF Liang, YT Liang, GR Liao, LB Liao, MH Liao, YP Liao, J Libby, A Limphirat, DX Lin, LQ Lin, T Lin, BJ Liu, BX Liu, CX Liu, F Liu, FH Liu, Feng Liu, GM Liu, H Liu, HB Liu, HH Liu, HM Liu, Huihui Liu, JB Liu, JJ Liu, K Liu, K Liu, KY Liu, Ke Liu, L Liu, LC Liu, Lu Liu, MH Liu, PL Liu, Q Liu, SB Liu, WM Liu, WT Liu, X Liu, XK Liu, XL Liu, XY Liu, Y Liu, Y Liu, YB Liu, ZA Liu, ZD Liu, ZQ Liu, ZY Liu, XC Lou, HJ Lu, JG Lu, XL Lu, Y Lu, YH Lu, YP Lu, ZH Lu, CL Luo, JR Luo, JS Luo, MX Luo, T Luo, XL Luo, ZY Lv, XR Lyu, YF Lyu, YH Lyu, FC Ma, HL Ma, Heng Ma, JL Ma, LL Ma, LR Ma, QM Ma, RQ Ma, RY Ma, T Ma, XT Ma, XY Ma, YM Ma, FE Maas, I MacKay, M Maggiora, S Malde, QA Malik, HX Mao, YJ Mao, ZP Mao, S Marcello, A Marshall, FM Melendi, YH Meng, ZX Meng, G Mezzadri, H Miao, TJ Min, RE Mitchell, XH Mo, B Moses, N Yu Muchnoi, J Muskalla, Y Nefedov, F Nerling, Z Ning, S Nisar, WD Niu, Y Niu, C Normand, SL Olsen, Q Ouyang, S Pacetti, X Pan, Y Pan, A Pathak, YP Pei, M Pelizaeus, HP Peng, XJ Peng, K Peters, K Petridis, JL Ping, RG Ping, S Plura, V Prasad, FZ Qi, HR Qi, M Qi, S Qian, WB Qian, CF Qiao, JH Qiao, JJ Qin, JL Qin, LQ Qin, LY Qin, PB Qin, XP Qin, XS Qin, ZH Qin, JF Qiu, ZH Qu, J Rademacker, CF Redmer, A Rivetti, M Rolo, G Rong, SS Rong, F Rosini, Ch Rosner, MQ Ruan, N Salone, A Sarantsev, Y Schelhaas, K Schoenning, M Scodeggio, W Shan, XY Shan, ZJ Shang, JF Shangguan, LG Shao, M Shao, CP Shen, HF Shen, WH Shen, XY Shen, BA Shi, H Shi, JL Shi, JY Shi, SY Shi, X Shi, HL Song, JJ Song, MH Song, TZ Song, WM Song, YX Song, Zirong Song, S Sosio, S Spataro, S Stansilaus, F Stieler, SS Su, GB Sun, GX Sun, H Sun, HK Sun, JF Sun, K Sun, L Sun, R Sun, SS Sun, T Sun, YC Sun, YH Sun, YJ Sun, YZ Sun, ZQ Sun, ZT Sun, CJ Tang, GY Tang, J Tang, JJ Tang, LF Tang, YA Tang, LY Tao, M Tat, JX Teng, JY Tian, WH Tian, Y Tian, ZF Tian, I Uman, B Wang, B Wang, Bo Wang, C Wang, C Wang, Cong Wang, DY Wang, HJ Wang, J Wang, JJ Wang, JP Wang, K Wang, LL Wang, LW Wang, M Wang, M Wang, NY Wang, S Wang, S Wang, T Wang, TJ Wang, W Wang, WP Wang, X Wang, XF Wang, XL Wang, XN Wang, Xin Wang, Y Wang, YD Wang, YF Wang, YH Wang, YJ Wang, YL Wang, YN Wang, YN Wang, Yaqian Wang, Yi Wang, Yuan Wang, Z Wang, Z Wang, ZL Wang, ZQ Wang, ZY Wang, Ziyi Wang, D Wei, DH Wei, HR Wei, F Weidner, SP Wen, U Wiedner, G Wilkinson, M Wolke, JF Wu, LH Wu, LJ Wu, LJ Wu, Lianjie Wu, SG Wu, SM Wu, X Wu, YJ Wu, Z Wu, L Xia, BH Xiang, D Xiao, GY Xiao, H Xiao, YL Xiao, ZJ Xiao, C Xie, KJ Xie, Y Xie, YG Xie, YH Xie, ZP Xie, TY Xing, CJ Xu, GF Xu, HY Xu, M Xu, QJ Xu, QN Xu, TD Xu, XP Xu, Y Xu, YC Xu, ZS Xu, F Yan, L Yan, WB Yan, WC Yan, WH Yan, WP Yan, XQ Yan, HJ Yang, HL Yang, HX Yang, JH Yang, RJ Yang, Y Yang, YH Yang, YQ Yang, YZ Yang, ZP Yao, M Ye, MH Ye, ZJ Ye, Junhao Yin, ZY You, BX Yu, CX Yu, G Yu, JS Yu, LW Yu, T Yu, XD Yu, YC Yu, YC Yu, CZ Yuan, H Yuan, J Yuan, J Yuan, L Yuan, MK Yuan, SH Yuan, Y Yuan, CX Yue, Ying Yue, AA Zafar, FR Zeng, SH Zeng, X Zeng, YJ Zeng, YJ Zeng, YC Zhai, YH Zhan, Shunan Zhang, BL Zhang, BX Zhang, DH Zhang, GY Zhang, GY Zhang, H Zhang, H Zhang, HC Zhang, HH Zhang, HQ Zhang, HR Zhang, HY Zhang, J Zhang, JJ Zhang, JL Zhang, JQ Zhang, JS Zhang, JW Zhang, JX Zhang, JY Zhang, JZ Zhang, Jianyu Zhang, LM Zhang, Lei Zhang, N Zhang, P Zhang, Q Zhang, QY Zhang, RY Zhang, SH Zhang, Shulei Zhang, XM Zhang, XY Zhang, Y Zhang, Y Zhang, YT Zhang, YH Zhang, YP Zhang, ZD Zhang, ZH Zhang, ZL Zhang, ZL Zhang, ZX Zhang, ZY Zhang, ZY Zhang, ZZ Zhang, Zh Zh Zhang, G Zhao, JY Zhao, JZ Zhao, L Zhao, L Zhao, MG Zhao, SJ Zhao, YB Zhao, YL Zhao, YX Zhao, ZG Zhao, A Zhemchugov, B Zheng, BM Zheng, JP Zheng, WJ Zheng, XR Zheng, YH Zheng, B Zhong, C Zhong, H Zhou, JQ Zhou, S Zhou, X Zhou, XK Zhou, XR Zhou, XY Zhou, YX Zhou, YZ Zhou, AN Zhu, J Zhu, K Zhu, KJ Zhu, KS Zhu, L Zhu, LX Zhu, SH Zhu, TJ Zhu, WD Zhu, WJ Zhu, WZ Zhu, YC Zhu, ZA Zhu, XY Zhuang, JH Zou, J Zu

A method for luminosity determination based on real-time hit reconstruction with the LHCb silicon pixel detector

Journal of Instrumentation IOP Publishing 21:04 (2026) P04011

Authors:

R Aaij, ASW Abdelmotteleb, C Abellan Beteta, F Abudinén, T Ackernley, AA Adefisoye, B Adeva, M Adinolfi, P Adlarson, C Agapopoulou, CA Aidala, Z Ajaltouni, S Akar, K Akiba, P Albicocco, J Albrecht, R Aleksiejunas, F Alessio, P Alvarez Cartelle, R Amalric, S Amato, JL Amey, Y Amhis, L An, L Anderlini, D Bacher

Abstract:

The data acquisition system of the upgraded LHCb experiment includes the fast reconstruction of all hits in the vertex locator (VELO) pixel detector at the beam-crossing rate of 40 MHz, implemented as on-the-fly clustering embedded in the firmware of the readout board FPGAs. The availability of a high rate of reconstructed clusters in real time enables a new fast approach for measuring luminosity and monitoring the LHCb luminous region, directly at the detector readout level. This methodology has been implemented as an array of real-time cluster counters in the VELO readout FPGAs and has been in operation since the start of the 2024 physics run of LHCb. This paper describes the methodology and its features and performance, both on proton-proton and lead-lead collision data. The method shows a statistical resolution better than the percent level, and a sensitivity to variable running conditions of the same level. This is achieved with an intrinsic time granularity better than 100 ms, undersampled to 3 s for analysis purposes. Nonlinear behaviour is compatible with zero in a luminosity range including the LHCb Run 3 operating point.

Observation of $\barΛp\to K^{+}π^{+}π^{-}π^{0}$ and $\barΛp\to K^{+}π^{+}π^{-}2π^{0}$

(2026)

Authors:

BESIII Collaboration, M Ablikim, MN Achasov, P Adlarson, XC Ai, CS Akondi, R Aliberti, A Amoroso, Q An, YH An, Y Bai, O Bakina, Y Ban, H-R Bao, XL Bao, V Batozskaya, K Begzsuren, N Berger, M Berlowski, MB Bertani, D Bettoni, F Bianchi, E Bianco, A Bortone, I Boyko, RA Briere, A Brueggemann, H Cai, MH Cai, X Cai, A Calcaterra, GF Cao, N Cao, SA Cetin, XY Chai, JF Chang, TT Chang, GR Che, YZ Che, CH Chen, Chao Chen, G Chen, HS Chen, HY Chen, ML Chen, SJ Chen, SM Chen, T Chen, W Chen, XR Chen, XT Chen, XY Chen, YB Chen, YQ Chen, ZK Chen, J Cheng, LN Cheng, SK Choi, X Chu, G Cibinetto, F Cossio, J Cottee-Meldrum, HL Dai, JP Dai, XC Dai, A Dbeyssi, RE de Boer, D Dedovich, CQ Deng, ZY Deng, A Denig, I Denisenko, M Destefanis, F De Mori, XX Ding, Y Ding, YX Ding, Yi Ding, J Dong, LY Dong, MY Dong, X Dong, MC Du, SX Du, Shaoxu Du, XL Du, YQ Du, YY Duan, ZH Duan, P Egorov, GF Fan, JJ Fan, YH Fan, J Fang, Jin Fang, SS Fang, WX Fang, YQ Fang, L Fava, F Feldbauer, G Felici, CQ Feng, JH Feng, L Feng, QX Feng, YT Feng, M Fritsch, CD Fu, JL Fu, YW Fu, H Gao, Y Gao, YN Gao, YY Gao, Yunong Gao, Z Gao, S Garbolino, I Garzia, L Ge, PT Ge, ZW Ge, C Geng, EM Gersabeck, A Gilman, K Goetzen, J Gollub, JB Gong, JD Gong, L Gong, WX Gong, W Gradl, S Gramigna, M Greco, MD Gu, MH Gu, CY Guan, AQ Guo, H Guo, JN Guo, LB Guo, MJ Guo, RP Guo, X Guo, YP Guo, Z Guo, A Guskov, J Gutierrez, JY Han, TT Han, X Han, F Hanisch, KD Hao, XQ Hao, FA Harris, CZ He, KK He, KL He, FH Heinsius, CH Heinz, YK Heng, C Herold, PC Hong, GY Hou, XT Hou, YR Hou, ZL Hou, HM Hu, JF Hu, QP Hu, SL Hu, T Hu, Y Hu, YX Hu, ZM Hu, GS Huang, KX Huang, LQ Huang, P Huang, XT Huang, YP Huang, YS Huang, T Hussain, N Hüsken, N in der Wiesche, J Jackson, Q Ji, QP Ji, W Ji, XB Ji, XL Ji, YY Ji, LK Jia, XQ Jia, D Jiang, HB Jiang, PC Jiang, SJ Jiang, XS Jiang, Y Jiang, JB Jiao, JK Jiao, Z Jiao, LCL Jin, S Jin, Y Jin, MQ Jing, XM Jing, T Johansson, S Kabana, XL Kang, XS Kang, BC Ke, V Khachatryan, A Khoukaz, OB Kolcu, B Kopf, L Kröger, L Krümmel, YY Kuang, M Kuessner, X Kui, N Kumar, A Kupsc, W Kühn, Q Lan, WN Lan, TT Lei, M Lellmann, T Lenz, C Li, CH Li, CK Li, Chunkai Li, Cong Li, DM Li, F Li, G Li, HB Li, HJ Li, HL Li, HN Li, HP Li, Hui Li, JS Li, JW Li, K Li, KL Li, LJ Li, Lei Li, MH Li, MR Li, MT Li, PL Li, PR Li, QM Li, QX Li, R Li, S Li, SX Li, SY Li, Shanshan Li, T Li, TY Li, WD Li, WG Li, X Li, XH Li, XK Li, XL Li, XY Li, XZ Li, Y Li, YG Li, YP Li, ZH Li, ZJ Li, ZL Li, ZX Li, ZY Li, C Liang, H Liang, YF Liang, YT Liang, GR Liao, LB Liao, MH Liao, YP Liao, J Libby, A Limphirat, CC Lin, DX Lin, T Lin, BJ Liu, BX Liu, C Liu, CX Liu, F Liu, FH Liu, Feng Liu, GM Liu, H Liu, HB Liu, HM Liu, Huihui Liu, JB Liu, JJ Liu, K Liu, KY Liu, Ke Liu, Kun Liu, L Liu, LC Liu, Lu Liu, MH Liu, PL Liu, Q Liu, SB Liu, T Liu, WM Liu, WT Liu, X Liu, XK Liu, XL Liu, XP Liu, XY Liu, Y Liu, YB Liu, Yi Liu, ZA Liu, ZD Liu, ZL Liu, ZQ Liu, ZY Liu, XC Lou, HJ Lu, JG Lu, XL Lu, Y Lu, YH Lu, YP Lu, ZH Lu, CL Luo, JR Luo, JS Luo, MX Luo, T Luo, XL Luo, ZY Lv, XR Lyu, YF Lyu, YH Lyu, FC Ma, HL Ma, Heng Ma, JL Ma, LL Ma, LR Ma, QM Ma, RQ Ma, RY Ma, T Ma, XT Ma, XY Ma, YM Ma, FE Maas, I MacKay, M Maggiora, S Malde, QA Malik, HX Mao, YJ Mao, ZP Mao, S Marcello, A Marshall, FM Melendi, YH Meng, ZX Meng, G Mezzadri, H Miao, TJ Min, RE Mitchell, XH Mo, B Moses, N Yu Muchnoi, J Muskalla, Y Nefedov, F Nerling, H Neuwirth, Z Ning, S Nisar, QL Niu, WD Niu, Y Niu, C Normand, SL Olsen, Q Ouyang, S Pacetti, X Pan, Y Pan, A Pathak, YP Pei, M Pelizaeus, GL Peng, HP Peng, XJ Peng, YY Peng, K Peters, K Petridis, JL Ping, RG Ping, S Plura, V Prasad, LP Pöpping, FZ Qi, HR Qi, M Qi, S Qian, WB Qian, CF Qiao, JH Qiao, JJ Qin, JL Qin, LQ Qin, LY Qin, PB Qin, XP Qin, XS Qin, ZH Qin, JF Qiu, ZH Qu, J Rademacker, CF Redmer, A Rivetti, M Rolo, G Rong, SS Rong, F Rosini, Ch Rosner, MQ Ruan, N Salone, A Sarantsev, Y Schelhaas, M Schernau, K Schoenning, M Scodeggio, W Shan, XY Shan, ZJ Shang, JF Shangguan, LG Shao, M Shao, CP Shen, HF Shen, WH Shen, XY Shen, BA Shi, Ch Y Shi, H Shi, JL Shi, JY Shi, MH Shi, SY Shi, X Shi, HL Song, JJ Song, MH Song, TZ Song, WM Song, YX Song, Zirong Song, S Sosio, S Spataro, S Stansilaus, F Stieler, M Stolte, SS Su, GB Sun, GX Sun, H Sun, HK Sun, JF Sun, K Sun, L Sun, R Sun, SS Sun, T Sun, WY Sun, YC Sun, YH Sun, YJ Sun, YZ Sun, ZQ Sun, ZT Sun, H Tabaharizato, CJ Tang, GY Tang, J Tang, JJ Tang, LF Tang, YA Tang, LY Tao, M Tat, JX Teng, JY Tian, WH Tian, Y Tian, ZF Tian, I Uman, E van der Smagt, B Wang, Bin Wang, Bo Wang, C Wang, Chao Wang, Cong Wang, DY Wang, HJ Wang, HR Wang, J Wang, JJ Wang, JP Wang, K Wang, LL Wang, LW Wang, M Wang, Mi Wang, NY Wang, S Wang, Shun Wang, T Wang, TJ Wang, W Wang, WP Wang, XF Wang, XL Wang, XN Wang, Xin Wang, Y Wang, YD Wang, YF Wang, YH Wang, YJ Wang, YL Wang, YN Wang, Yanning Wang, Yaqian Wang, Yi Wang, Yuan Wang, Z Wang, ZL Wang, ZQ Wang, ZY Wang, Zhi Wang, Ziyi Wang, D Wei, DH Wei, DJ Wei, HR Wei, F Weidner, SP Wen, U Wiedner, G Wilkinson, M Wolke, JF Wu, LH Wu, LJ Wu, Lianjie Wu, SG Wu, SM Wu, XW Wu, Z Wu, HL Xia, L Xia, BH Xiang, D Xiao, GY Xiao, H Xiao, YL Xiao, ZJ Xiao, C Xie, KJ Xie, Y Xie, YG Xie, YH Xie, ZP Xie, TY Xing, DB Xiong, CJ Xu, GF Xu, HY Xu, M Xu, QJ Xu, QN Xu, TD Xu, XP Xu, Y Xu, YC Xu, ZS Xu, F Yan, L Yan, WB Yan, WC Yan, WH Yan, WP Yan, XQ Yan, YY Yan, HJ Yang, HL Yang, HX Yang, JH Yang, RJ Yang, XY Yang, Y Yang, YH Yang, YM Yang, YQ Yang, YZ Yang, Youhua Yang, ZY Yang, ZP Yao, M Ye, MH Ye, ZJ Ye, Junhao Yin, ZY You, BX Yu, CX Yu, G Yu, JS Yu, LW Yu, T Yu, XD Yu, YC Yu, Yongchao Yu, CZ Yuan, H Yuan, J Yuan, Jie Yuan, L Yuan, MK Yuan, SH Yuan, Y Yuan, CX Yue, Ying Yue, AA Zafar, FR Zeng, SH Zeng, X Zeng, YJ Zeng, Yujie Zeng, YC Zhai, YH Zhan, BL Zhang, BX Zhang, DH Zhang, GY Zhang, Gengyuan Zhang, H Zhang, HC Zhang, HH Zhang, HQ Zhang, HR Zhang, HY Zhang, Han Zhang, J Zhang, JJ Zhang, JL Zhang, JQ Zhang, JS Zhang, JW Zhang, JX Zhang, JY Zhang, JZ Zhang, Jianyu Zhang, Jin Zhang, Jiyuan Zhang, LM Zhang, Lei Zhang, N Zhang, P Zhang, Q Zhang, QY Zhang, QZ Zhang, RY Zhang, SH Zhang, SN Zhang, Shulei Zhang, XM Zhang, XY Zhang, Y Zhang, YT Zhang, YH Zhang, YP Zhang, Yu Zhang, ZD Zhang, ZH Zhang, ZL Zhang, ZX Zhang, ZY Zhang, Zh Zh Zhang, Zhilong Zhang, Ziyang Zhang, Ziyu Zhang, G Zhao, J-P Zhao, JY Zhao, JZ Zhao, L Zhao, Lei Zhao, MG Zhao, RP Zhao, SJ Zhao, YB Zhao, YL Zhao, YP Zhao, YX Zhao, ZG Zhao, A Zhemchugov, B Zheng, BM Zheng, JP Zheng, WJ Zheng, WQ Zheng, XR Zheng, YH Zheng, B Zhong, C Zhong, H Zhou, JQ Zhou, S Zhou, X Zhou, XK Zhou, XR Zhou, XY Zhou, YX Zhou, YZ Zhou, AN Zhu, J Zhu, K Zhu, KJ Zhu, KS Zhu, LX Zhu, Lin Zhu, SH Zhu, TJ Zhu, WD Zhu, WJ Zhu, WZ Zhu, YC Zhu, ZA Zhu, XY Zhuang, M Zhuge, JH Zou

Branching fraction measurement of the Λ → p μ − ν ¯ μ decay

Journal of High Energy Physics Springer 2026:4 (2026) 96

Authors:

R Aaij, ASW Abdelmotteleb, C Abellan Beteta, F Abudinén, T Ackernley, AA Adefisoye, B Adeva, M Adinolfi, P Adlarson, C Agapopoulou, CA Aidala, Z Ajaltouni, S Akar, K Akiba, P Albicocco, J Albrecht, R Aleksiejunas, F Alessio, P Alvarez Cartelle, R Amalric, S Amato, JL Amey, Y Amhis, L An, L Anderlini, D Bacher

Abstract:

A measurement of the branching fraction for the decay Λ→pμ−ν¯μ is presented using pp collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV. The analysis is based on data recorded between 2016 and 2018, corresponding to an integrated luminosity of 5.4 fb−1. The result is obtained using Λ → pμ− decays as a normalisation channel. The measured branching fraction is BΛ→pμ−ν¯μ=1.462±0.016±0.100±0.011×10−4, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalisation mode branching fraction, respectively. This result improves the precision of the branching fraction measurement by a factor of two compared to the previous best measurement and sets a more stringent bound on lepton flavour universality in s → u quark transitions. It is consistent with previous measurements, and the extracted lepton flavour universality test observable, Rμe=ΓΛ→pμ−ν¯μΓΛ→pe−ν¯e=0.175±0.012, agrees with the Standard Model prediction.