Particle physics or high-energy physics is the study of fundamental particles and forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the scale of protons and neutrons,while the study of combination of protons and neutrons is called nuclear physics.
In nuclear physics and particle physics,the weak interaction,which is also often called the weak force or weak nuclear force,is one of the four known fundamental interactions,with the others being electromagnetism,the strong interaction,and gravitation. It is the mechanism of interaction between subatomic particles that is responsible for the radioactive decay of atoms:The weak interaction participates in nuclear fission and nuclear fusion. The theory describing its behaviour and effects is sometimes called quantum flavourdynamics (QFD);however,the term QFD is rarely used,because the weak force is better understood by electroweak theory (EWT).
In particle physics,a pion is any of three subatomic particles:
π0
,
π+
,and
π−
. Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and,more generally,the lightest hadrons. They are unstable,with the charged pions
π+
and
π−
decaying after a mean lifetime of 26.033 nanoseconds,and the neutral pion
π0
decaying after a much shorter lifetime of 85 attoseconds. Charged pions most often decay into muons and muon neutrinos,while neutral pions generally decay into gamma rays.
The Standard Model of particle physics is the theory describing three of the four known fundamental forces in the universe and classifying all known elementary particles. It was developed in stages throughout the latter half of the 20th century,through the work of many scientists worldwide,with the current formulation being finalized in the mid-1970s upon experimental confirmation of the existence of quarks. Since then,proof of the top quark (1995),the tau neutrino (2000),and the Higgs boson (2012) have added further credence to the Standard Model. In addition,the Standard Model has predicted various properties of weak neutral currents and the W and Z bosons with great accuracy.
In physics,a subatomic particle is a particle smaller than an atom. According to the Standard Model of particle physics,a subatomic particle can be either a composite particle,which is composed of other particles,or an elementary particle,which is not composed of other particles. Particle physics and nuclear physics study these particles and how they interact. Most force carrying particles like photons or gluons are called bosons and,although they have discrete quanta of energy,do not have rest mass or discrete diameters and are unlike the former particles that have rest mass and cannot overlap or combine which are called fermions.
The charm quark,charmed quark,or c quark is an elementary particle found in composite subatomic particles called hadrons such as the J/psi meson and the charmed baryons created in particle accelerator collisions. Several bosons,including the W and Z bosons and the Higgs boson,can decay into charm quarks. All charm quarks carry charm,a quantum number. This second generation is the third-most-massive quark with a mass of 1.27±0.02 GeV/c2 as measured in 2022 and a charge of +2/3e.
The top quark,sometimes also referred to as the truth quark,is the most massive of all observed elementary particles. It derives its mass from its coupling to the Higgs Boson. This coupling is very close to unity;in the Standard Model of particle physics,it is the largest (strongest) coupling at the scale of the weak interactions and above. The top quark was discovered in 1995 by the CDF and DØexperiments at Fermilab.
The bottom quark,beauty quark,or b quark,is an elementary particle of the third generation. It is a heavy quark with a charge of −1/3 e.
In particle physics,the baryon number is a strictly conserved additive quantum number of a system. It is defined as
In particle physics,a kaon,also called a K meson and denoted
K
,is any of a group of four mesons distinguished by a quantum number called strangeness. In the quark model they are understood to be bound states of a strange quark and an up or down antiquark.
In particle physics,the W and Z bosons are vector bosons that are together known as the weak bosons or more generally as the intermediate vector bosons. These elementary particles mediate the weak interaction;the respective symbols are
W+
,
W−
,and
Z0
. The
W±
bosons have either a positive or negative electric charge of 1 elementary charge and are each other's antiparticles. The
Z0
boson is electrically neutral and is its own antiparticle. The three particles each have a spin of 1. The
W±
bosons have a magnetic moment,but the
Z0
has none. All three of these particles are very short-lived,with a half-life of about 3×10−25 s. Their experimental discovery was pivotal in establishing what is now called the Standard Model of particle physics.
In physical cosmology,baryogenesis is the physical process that is hypothesized to have taken place during the early universe to produce baryonic asymmetry,i.e. the imbalance of matter (baryons) and antimatter (antibaryons) in the observed universe.
Jack Steinberger was a German-born American physicist noted for his work with neutrinos,the subatomic particles considered to be elementary constituents of matter. He was a recipient of the 1988 Nobel Prize in Physics,along with Leon M. Lederman and Melvin Schwartz,for the discovery of the muon neutrino. Through his career as an experimental particle physicist,he held positions at the University of California,Berkeley,Columbia University (1950–68),and the CERN (1968–86). He was also a recipient of the United States National Medal of Science in 1988,and the Matteucci Medal from the Italian Academy of Sciences in 1990.
The LHCb experiment is a particle physics detector experiment collecting data at the Large Hadron Collider at CERN. LHCb is a specialized b-physics experiment,designed primarily to measure the parameters of CP violation in the interactions of b-hadrons. 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,exotic hadron spectroscopy,charm physics and electroweak physics in the forward region. The LHCb collaboration,who built,operate and analyse data from the experiment,is composed of approximately 1260 people from 74 scientific institutes,representing 16 countries. Chris Parkes succeeded on July 1,2020 as spokesperson for the collaboration from Giovanni Passaleva. 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 shares the same cavern.
In particle physics,preons are hypothetical point particles,conceived of as sub-components of quarks and leptons. The word was coined by Jogesh Pati and Abdus Salam,in 1974. Interest in preon models peaked in the 1980s but has slowed,as the Standard Model of particle physics continues to describe physics mostly successfully,and no direct experimental evidence for lepton and quark compositeness has been found. Preons come in four varieties:plus,anti-plus,zero,and anti-zero. W bosons have six preons,and quarks and leptons have only three.
The DØexperiment was a worldwide collaboration of scientists conducting research on the fundamental nature of matter. DØwas one of two major experiments located at the Tevatron Collider at Fermilab in Batavia,Illinois. The Tevatron was the world's highest-energy accelerator from 1983 until 2009,when its energy was surpassed by the Large Hadron Collider. The DØexperiment stopped taking data in 2011,when the Tevatron shut down,but data analysis is still ongoing. The DØdetector is preserved in Fermilab's DØAssembly Building as part of a historical exhibit for public tours.
The timeline of particle physics lists the sequence of particle physics theories and discoveries in chronological order. The most modern developments follow the scientific development of the discipline of particle physics.
The idea that matter consists of smaller particles and that there exists a limited number of sorts of primary,smallest particles in nature has existed in natural philosophy at least since the 6th century BC. Such ideas gained physical credibility beginning in the 19th century,but the concept of "elementary particle" underwent some changes in its meaning:notably,modern physics no longer deems elementary particles indestructible. Even elementary particles can decay or collide destructively;they can cease to exist and create (other) particles in result.
NA31 is a CERN experiment which was proposed in 1982 as a "Measurement of |η00 /η+-|2 by the CERN-Edinburgh-Mainz-Pisa-Siegen collaboration. It took data between 1986 and 1989,using a proton beam from the SPS through the K4 neutral beam-line. Its aim was to experimentally prove direct CP-violation.
