The history of LHCb

Abstract

In this paper, we describe the history of the LHCb experiment over the last three decades, and its remarkable successes and achievements. LHCb was conceived primarily as a \({b} \)-physics experiment, dedicated to \(CP\) violation studies and measurements of very rare \({{b}} \) decays; however, the tremendous potential for \({c} \)-physics was also clear. At first data taking, the versatility of the experiment as a general-purpose detector in the forward region also became evident, with measurements achievable such as electroweak physics, jets and new particle searches in open states. These were facilitated by the excellent capability of the detector to identify muons and to reconstruct decay vertices close to the primary \({{p}} {{p}} \)?interaction region. By the end of the LHC Run 2 in 2018, before the accelerator paused for its second long shut down, LHCb had measured the CKM quark mixing matrix elements and \(CP\) violation parameters to world-leading precision in the heavy-quark systems. The experiment had also measured many rare decays of \({b} \) ?and \({c} \) ?quark mesons and baryons to below their Standard Model expectations, some down to branching ratios of order 10\(^{-9}\). In addition, world knowledge of \({{b}} \) and \({{c}} \) spectroscopy had improved significantly through discoveries of many new resonances already anticipated in the quark model, and also adding new exotic four and five quark states. The paper describes the evolution of the LHCb detector, from conception to its operation at the present time. The authors’ subjective summary of the experiment’s important contributions is then presented, demonstrating the wide domain of successful physics measurements that have been achieved over the years.