LHCb
Encyclopedia
LHCb is one of six particle physics detector experiments collecting data at the Large Hadron Collider accelerator at CERN
CERN
The European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...
. LHCb is a specialized b-physics experiment, that is measuring the parameters of CP violation
CP violation
In particle physics, CP violation is a violation of the postulated CP-symmetry: the combination of C-symmetry and P-symmetry . CP-symmetry states that the laws of physics should be the same if a particle were interchanged with its antiparticle , and left and right were swapped...
in the interactions of b-hadron
Hadron
In particle physics, a hadron is a composite particle made of quarks held together by the strong force...
s (heavy particles containing a bottom quark
Bottom quark
The bottom quark, also known as the beauty quark, is a third-generation quark with a charge of − e. Although all quarks are described in a similar way by the quantum chromodynamics, the bottom quark's large bare mass , combined with low values of the CKM matrix elements Vub and Vcb, gives it a...
). Such studies can help to explain the Matter-Antimatter asymmetry
Baryon asymmetry
The baryon asymmetry problem in physics refers to the apparent fact that there is an imbalance in baryonic matter and antibaryonic matter in the universe. Neither the standard model of particle physics, nor the theory of general relativity provide an obvious explanation for why this should be so;...
of the Universe. The detector is also able to perform measurements of production cross sections and electroweak
Electroweak interaction
In particle physics, the electroweak interaction is the unified description of two of the four known fundamental interactions of nature: electromagnetism and the weak interaction. Although these two forces appear very different at everyday low energies, the theory models them as two different...
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
Ferney-Voltaire
Ferney-Voltaire is a commune in the Ain department in eastern France.It lies between the Jura mountains and the Swiss border and forms part of the metropolitan area of Geneva.-History:...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
just over the border from Geneva. The (small) MoEDAL
MoEDAL experiment
The Monopole and Exotics Detector At the LHC is an international research collaboration whose spokesperson is the University of Alberta’s James Pinfold. MoEDAL is the seventh experiment at the LHC; it was approved and sanctioned by the CERN research board on May of 2010, and started its first test...
experiment will share the same cavern.
Physics goals
The experiment has wide physics program covering many important aspects of Heavy flavor, Electroweak and QCDQuantum chromodynamics
In theoretical physics, quantum chromodynamics is a theory of the strong interaction , a fundamental force describing the interactions of the quarks and gluons making up hadrons . It is the study of the SU Yang–Mills theory of color-charged fermions...
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 Bs → μ+ μ- decay.
- Measuring the forward-backward asymmetry of the muon pair in the flavour changing neutral currentFlavor changing neutral currentIn theoretical physics, flavor-changing neutral currents are expressions that change the flavor of a fermion current without altering its electric charge. If they occur in the Lagrangian, they may induce processes that have not been observed in experiment...
Bd → K* mu+ mu- decay. Such a flavour changing neutral current cannot occur at tree-level in the Standard ModelStandard ModelThe Standard Model of particle physics is a theory concerning the electromagnetic, weak, and strong nuclear interactions, which mediate the dynamics of the known subatomic particles. Developed throughout the mid to late 20th century, the current formulation was finalized in the mid 1970s upon...
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 violatingCP violationIn particle physics, CP violation is a violation of the postulated CP-symmetry: the combination of C-symmetry and P-symmetry . CP-symmetry states that the laws of physics should be the same if a particle were interchanged with its antiparticle , and left and right were swapped...
phase in the decay Bs → J/ψ φ, caused by interference between the decays with and without Bs oscillations. This phase is one of the CP observables with the smallest theoretical uncertainty in the Standard ModelStandard ModelThe Standard Model of particle physics is a theory concerning the electromagnetic, weak, and strong nuclear interactions, which mediate the dynamics of the known subatomic particles. Developed throughout the mid to late 20th century, the current formulation was finalized in the mid 1970s upon...
, 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 currentFlavor changing neutral currentIn theoretical physics, flavor-changing neutral currents are expressions that change the flavor of a fermion current without altering its electric charge. If they occur in the Lagrangian, they may induce processes that have not been observed in experiment...
decays. - Tree-level determination of the CKMCabibbo-Kobayashi-Maskawa matrixIn the Standard Model of particle physics, the Cabibbo–Kobayashi–Maskawa matrix is a unitary matrix which contains information on the strength of flavour-changing weak decays...
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 asymmetryAsymmetry
Asymmetry is the absence of, or a violation of, symmetry.-In organisms:Due to how cells divide in organisms, asymmetry in organisms is fairly usual in at least one dimension, with biological symmetry also being common in at least one dimension....
between the horizontal and vertical plane is determined by a large dipole magnet
Dipole magnet
A dipole magnet, in particle accelerators, is a magnet constructed to create a homogeneous magnetic field over some distance. Particle motion in that field will be circular in a plane perpendicular to the field and collinear to the direction of particle motion and free in the direction orthogonal...
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, e.g. for B-taggingB-tagging
b-tagging is an example of a jet flavor tagging method used in modern high-energy particle physics experiments. It is the identification of jets originating from bottom quarks .-Importance:...
.
The detector operates at 7 millimetre (0.275590551181102 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
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
and is cooled to approximately -25 C using a biphase CO2
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
system. The data of the VELO detector are amplified and read out by the Beetle ASIC
Beetle (ASIC)
The Beetle ASIC is an analog readout chip. It is developed for the LHCb experiment at CERN.-Overview:The chip integrates 128 channels with low-noise charge-sensitive pre-amplifiers and shapers. The pulse shape can be chosen such that it complies with LHCb specifications: a peaking time of...
.
RICH1
The RICH-1 detector (Ring imaging Cherenkov detectorRing imaging Cherenkov detector
A Ring Imaging Cherenkov detector is a particle detector that can determine the velocity, v , of a charged particle. This is done by an indirect measurement of the Cherenkov angle, \theta_c , i.e. the angle between the emitted Čerenkov radiation and the particle path...
) is located directly after the vertex detector. It is used for particle identification
Particle identification
Particle identification is the process of using information left by a particle passing through a particle detector to identify the type of particle. Particle identification reduces backgrounds and improves measurement resolutions, and is essential to many analyses at particle detectors.-Charged...
of low-momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
tracks.
Main Tracker
The main tracking system is placed before and after the dipole magnet. It is used to reconstructEvent reconstruction
In a particle detector experiment, event reconstruction is the process of interpreting the electronic signals produced by the detector to determine the original particles that passed through, their momenta, directions, and the primary vertex of the event...
the trajectories of charged
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
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 electromagneticElectromagnetism
Electromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...
and hadron
Hadron
In particle physics, a hadron is a composite particle made of quarks held together by the strong force...
ic calorimeters provide measurement of the energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
of electrons, photons, and hadrons. These measurements are used at trigger level
Trigger (particle physics)
In particle physics, a trigger is a system that uses simple criteria to rapidly decide which events in a particle detector to keep when only a small fraction of the total can be recorded. Trigger systems are necessary due to real-world limitations in data storage capacity and rates...
to identify the particles with high transversal moment (high-Pt particles).
Muon System
The muon system is used to identify and triggerTrigger (particle physics)
In particle physics, a trigger is a system that uses simple criteria to rapidly decide which events in a particle detector to keep when only a small fraction of the total can be recorded. Trigger systems are necessary due to real-world limitations in data storage capacity and rates...
on muons in the events.
See also
- CERN: European Organization for Nuclear ResearchCERNThe European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...
- Large Hadron ColliderLarge Hadron ColliderThe Large Hadron Collider is the world's largest and highest-energy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature....
External links
- LHCb Public Webpage
- LHCb section from US/LHC Website (Full design documentation)