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Large Hadron Collider
(LHC)
LHC experiments
ATLAS	A Toroidal LHC Apparatus
CMS	Compact Muon Solenoid
LHCb	LHC-beauty
ALICE	A Large Ion Collider Experiment
TOTEM	Total Cross Section, Elastic Scattering and Diffraction Dissociation
LHCf	LHC-forward
LHC preaccelerators
p and Pb	Linear accelerators for protons (Linac 2) and Lead (Linac 3)
(not marked)	Proton Synchrotron Booster
PS	Proton Synchrotron
SPS	Super Proton Synchrotron

Coordinates: 46°14′27.64″N 6°5′48.96″E / 46.2410111°N 6.0969333°E / 46.2410111; 6.0969333

The LHCb (standing for "Large Hadron Collider beauty" where "beauty" refers to the bottom quark) experiment is one of six particle physics detector experiments built on the Large Hadron Collider accelerator at CERN. LHCb is a specialized b-physics experiment, particularly aimed at measuring the parameters of CP violation in the interactions of b-hadrons (heavy particles containing a bottom quark).

[edit] The LHCb detector

The fact that both B hadrons are predominantly produced in the same forward cone as B meson production is exploited in the layout of the LHCb detector. The LHCb detector is a single arm forward spectrometer with a polar angular coverage from 10 to 300 milliradians (mrad) in the horizontal and 250 mrad in the vertical plane. The asymmetry between the horizontal and vertical plane is determined by a large dipole magnet with the main component in the vertical direction.

The vertex detector (known as the vertex locator or VELO) is built around the proton interaction region. It is used to measure the particle trajectories close to the interaction point in order to precisely separate primary and secondary vertices, e.g. for B-tagging.

The RICH-1 detector (Ring imaging Cherenkov detector) is located directly after the vertex detector. It is used for particle identification of low-momentum tracks.

The main tracking system is placed before and after the dipole magnet. It is used to reconstruct the trajectories of charged particles and to measure their momenta.

Following the tracking system is RICH-2. It allows the identification of the particle type of high-momentum tracks.

The electromagnetic and hadronic calorimeters provide measurement of the energy of electrons, photons, and hadrons. These measurements are used at trigger level to identify the particles with high transversal moment (high-Pt particles).

The muon system is used to identify and trigger on muons in the events.

[edit] LHCb Physics analyses

After the LHC starts colliding protons at a useful rate for LHCb, in early 2010, LHCb aims to make several measurements on physics phenomena involving B mesons as an early priority. These include:

Measuring an upper limit on the branching ratio of the rare $B_s \to \mu^+ \mu^-$ decay.
Measuring the forward-backward asymmetry of the muon pair in the flavour changing neutral current $B_d \to K^* \mu^+ \mu^-$ decay. Such a flavour changing neutral current cannot occur at tree-level in the Standard Model of Particle Physics, and only occurs through box and loop Feynman diagrams; properties of the decay can be strongly modified by new Physics.
Measuring the CP violating phase in the decay $B_s \to J/\psi \phi$ , caused by interference between the decays with and without $B_s-\overline{B_s}$ oscillations. This phase is one of the CP observables with the smallest theoretical uncertainty in the Standard Model, and can be significantly modified by new Physics.
Measuring properties of radiative B decays, i.e. B meson decays with photons in the final states. Specifically, these are again flavour changing neutral current decays.