LHCb

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
MoEDAL	Monopole and Exotics Detector At the LHC
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

LHCb (standing for "Large Hadron Collider beauty") is one of six particle physics detector experiments collecting data at the Large Hadron Collider accelerator at CERN. LHCb is a specialized b-physics experiment, that is measuring the parameters of CP violation in the interactions of b-hadrons (heavy particles containing a bottom quark). Such studies can help to explain the Matter-Antimatter asymmetry of the Universe. The detector is also able to perform measurements of production cross sections and electroweak physics in the forward region. Approximately 760 people from 54 scientific institutes, representing 14 countries form the collaboration who built and now operate the detector. The experiment is located at point 8 on the LHC tunnel close to Ferney-Voltaire, France just over the border from Geneva. The (small) MoEDAL experiment will share the same cavern.

Physics goals

The experiment has wide physics program covering many important aspects of Heavy flavor, Electroweak and QCD physics. Six key measurements have been identified involving B mesons and are described in a roadmap document that form the core physics program for the first high energy LHC running in 2010 - 2012. These include:

• Measuring an upper limit on the branching ratio of the rare B_s → μ⁺ μ^- decay.
• Measuring the forward-backward asymmetry of the muon pair in the flavour changing neutral current B_d → 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 → J/ψ φ, caused by interference between the decays with and without 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.
• Tree-level determination of the CKM triangle angle γ
• Charmless charged two-body B decays

The LHCb detector

The fact that the two b-hadrons are predominantly produced in the same forward cone 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 VELO

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.

The detector operates at 7 millimetres (0.28 in) from the LHC beam. This implies an enormous flux of particles; The VELO has been designed to withstand integrated fluences of more than 10¹⁴p/cm² per year for a period of about three years. The detector operates in vacuum and is cooled to approximately −25 °C (−13 °F) using a biphase CO₂ system. The data of the VELO detector are amplified and read out by the Beetle ASIC.

RICH1

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.

Main Tracker

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. The tracker consists of three subdetectors

• The Tracker Turicensis, a silicon strip detector located before the LHCb dipole magnet
• The Outer Tracker. A straw-tube based detector located after the dipole magnet covering the outer part of the detector

acceptance

• The Inner Tracker, silicon strip based detector located after the dipole magnet covering the inner part of the detector acceptance

RICH2

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

ECAL

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).

Muon System

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

See also

• CERN: European Organization for Nuclear Research
• Large Hadron Collider

External links

• LHCb Public Webpage
• LHCb section from US/LHC Website
• A. Augusto Alves Jr. et al. (LHCb Collaboration) (2008). "The LHCb Detector at the LHC". Journal of Instrumentation 3 (08): S08005. Bibcode 2008JInst...3S8005T. doi:10.1088/1748-0221/3/08/S08005. http://www.iop.org/EJ/journal/-page=extra.lhc/jinst.  (Full design documentation)