The LHCb detector is a forward spectrometer at the Large Hadron Collider (LHC) at CERN. The experiment is designed for precision measurements of CP violation and rare decays of beauty and charm hadrons. In this paper the performance of the various LHCb sub-detectors and the trigger system are described, using data taken from 2010 to 2012. It is shown that the design criteria of the experiment have been met. The excellent performance of the detector has allowed the LHCb collaboration to publish a wide range of physics results, demonstrating LHCb's unique role, both as a heavy flavour experiment and as a general purpose detector in the forward region.

We present a measurement of form-factor-independent angular observables in the decay B(0)→K*(892)(0)μ(+)μ(-). The analysis is based on a data sample corresponding to an integrated luminosity of 1.0 fb(-1), collected by the LHCb experiment in pp collisions at a center-of-mass energy of 7 TeV. Four observables are measured in six bins of the dimuon invariant mass squared q² in the range 0.1

This paper presents the design of the LHCb trigger and its performance on data taken at the LHC in 2011. A principal goal of LHCb is to perform flavour physics measurements, and the trigger is designed to distinguish charm and beauty decays from the light quark background. Using a combination of lepton identification and measurements of the particles' transverse momenta the trigger selects particles originating from charm and beauty hadrons, which typically fly a finite distance before decaying. The trigger reduces the roughly 11 MHz of bunch-bunch crossings that contain at least one inelastic pp interaction to 3 kHz. This reduction takes place in two stages; the first stage is implemented in hardware and the second stage is a software application that runs on a large computer farm. A data-driven method is used to evaluate the performance of the trigger on several charm and beauty decay modes.

We propose an inclusive search for dark photons A 0 at the LHCb experiment based on both prompt and displaced dimuon resonances. Because the couplings of the dark photon are inherited from the photon via kinetic mixing, the dark photon A 0 → μ þ μ − rate can be directly inferred from the off-shell photon γ Ã → μ þ μ − rate, making this a fully data-driven search. For run 3 of the LHC, we estimate that LHCb will have sensitivity to large regions of the unexplored dark-photon parameter space, especially in the 210-520 MeV and 10-40 GeV mass ranges. This search leverages the excellent invariant-mass and vertex resolution of LHCb, along with its unique particle-identification and real-time data-analysis capabilities. DOI: 10.1103/PhysRevLett.116.251803 Dark matter-firmly established through its interactions with gravity-remains an enigma. Though there are increasingly stringent constraints on direct couplings between visible matter and dark matter, little is known about the dynamics within the dark sector itself. An intriguing possibility is that dark matter might interact via a new dark force, felt only feebly by standard model (SM) particles. This has motivated a worldwide effort to search for dark forces and other portals between the visible and dark sectors (see Ref.[1] for a review).A particularly compelling dark-force scenario is that of a dark photon A 0 which has small SM couplings via kinetic mixing with the ordinary photon through the operator ðϵ=2ÞF 0 μν F μν [2][3][4][5][6][7]. Previous beam dump [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], fixed target [22][23][24], collider [25][26][27], and rare meson decay [28][29][30][31][32][33][34][35][36][37] experiments have already played a crucial role in constraining the dark photon mass m A 0 and kinetic-mixing strength ϵ 2 . Large regions of the m A 0 − ϵ 2 plane, however, are still unexplored (see Fig. 1). Looking to the future, a wide variety of innovative experiments have been proposed to further probe the dark photon parameter space [38][39][40][41][42][43][44][45][46][47][48], though new ideas are needed to test m A 0 > 2m μ and ϵ 2 ∈ ½10 −7 ; 10 −11 .In this Letter, we propose a search for dark photons via the decayat the LHCb experiment during LHC run 3 (scheduled for 2021-2023). The potential of LHCb to discover dark photons was recently emphasized in Ref.[48], which exploits the exclusive charm decay modeHere, we consider an inclusive approach where the production mode of A 0 need not be specified. An important feature of this search is that it can be made fully data driven, since the A 0 signal rate can be inferred from measurements of the SM prompt μ þ μ − spectrum. The excellent invariant-mass and vertex resolution of the LHCb detector, along with its unique particle-identification and real-time data-analysis capabilities [50,51], make it highly sensitive to A 0 → μ þ μ − . We derive the LHCb sensitivity for both prompt and displaced A 0 decays, and show that LHCb can probe otherwise inaccessible regions of the m A 0 − ϵ 2 plane...

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