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.
Highlights
LHCb is an experiment at the CERN LHC, dedicated to the study of heavy flavours with large statistics
The LHC Committee (LHCC) decision sent a strong signal to the high-energy physics community: that CERN were prepared to give their strong support to one dedicated B experiment
The background composition is dominated by photon conversions to μ+μ− in the VErtex LOcator detector (VELO), b-hadron decays where two muons are produced in the decay chain, and the low-mass tail from KS0 → π+π− decays where both pions are misidentified as muons
Summary
LHCb is an experiment at the CERN LHC, dedicated to the study of heavy flavours with large statistics. In 1985, the fixed-target WA75 hybrid experiment at the CERN SPS [10] observed in emulsions the first partially reconstructed bb pair produced by an extracted pion beam of 350 GeV/c, confirming that the production cross section at such low energies was very small To circumvent this problem, simple experiments were proposed [11] for the CERN SPS and for the planned UNK machine [12] at Serpukhov, with a brute-force approach based on a high-intensity extracted beam and a minimalist detector designed to reconstruct the B0 → J/ψKS0 decay and to provide flavour tagging (Fig. 1). These were a need of a robust and efficient tracking and a flexible trigger systems able to adapt to harsher environments than may have been expected, as well as the need to design the thinnest and lightest detector (in terms of radiation and interaction lengths)
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