W and Z bosons
During these processes, the W± boson charge induces electron or positron emission or absorption, thus causing nuclear transmutation.The Z boson mediates the transfer of momentum, spin and energy when neutrinos scatter elastically from matter (a process which conserves charge).Whenever an electron is observed as a new free particle, suddenly moving with kinetic energy, it is inferred to be a result of a neutrino interacting with the electron (with the momentum transfer via the Z boson) since this behavior happens more often when the neutrino beam is present.With masses of 80.4 GeV/c2 and 91.2 GeV/c2, respectively, the W and Z bosons are almost 80 times as massive as the proton – heavier, even, than entire iron atoms.(Although gluons are also presumed to have zero mass, the range of the strong nuclear force is limited for different reasons; see Color confinement.)The emission or absorption of a Z0 boson can only change the spin, momentum, and energy of the other particle.At the most fundamental level, then, the weak force changes the flavour of a single quark: which is immediately followed by decay of the W− itself: The Z0 boson is its own antiparticle.[c] Weak neutral currents via Z boson exchange were confirmed shortly thereafter (also in 1973), in a neutrino experiment in the Gargamelle bubble chamber at CERN.[8] Following the success of quantum electrodynamics in the 1950s, attempts were undertaken to formulate a similar theory of the weak nuclear force.This culminated around 1968 in a unified theory of electromagnetism and weak interactions by Sheldon Glashow, Steven Weinberg, and Abdus Salam, for which they shared the 1979 Nobel Prize in Physics.The fact that the W and Z bosons have mass while photons are massless was a major obstacle in developing electroweak theory.The Higgs mechanism, first put forward by the 1964 PRL symmetry breaking papers, fulfills this role.It requires the existence of another particle, the Higgs boson, which has since been found at the Large Hadron Collider.Today it is widely accepted as one of the pillars of the Standard Model of particle physics, particularly given the 2012 discovery of the Higgs boson by the CMS and ATLAS experiments.This is a hallmark of a neutral current interaction and is interpreted as a neutrino exchanging an unseen Z boson with a proton or neutron in the bubble chamber.The neutrino is otherwise undetectable, so the only observable effect is the momentum imparted to the proton or neutron by the interaction.The first such machine that became available was the Super Proton Synchrotron, where unambiguous signals of W bosons were seen in January 1983 during a series of experiments made possible by Carlo Rubbia and Simon van der Meer.Van der Meer was the driving force on the accelerator end (stochastic cooling).In May 2024, the Particle Data Group estimated the World Average mass for the W boson to be 80369.2 ± 13.3 MeV, based on experiments to date.[11] As of 2021, experimental measurements of the W boson mass had been similarly assessed to converge around 80379±12 MeV,[12] all consistent with one another and with the Standard Model.Fermilab Deputy Director Joseph Lykken reiterated that "... the (new) measurement needs to be confirmed by another experiment before it can be interpreted fully."[15][16] In 2023, an improved ATLAS experiment measured the W boson mass at 80360±16 MeV, aligning with predictions from the Standard Model.Neglecting phase space effects and higher order corrections, simple estimates of their branching fractions can be calculated from the coupling constants.The decay width of the W boson to a quark–antiquark pair is proportional to the corresponding squared CKM matrix element and the number of quark colours, NC = 3 .The decay widths for the W+ boson are then proportional to: Here, e+, μ+, τ+ denote the three flavours of leptons (more exactly, the positive charged antileptons).The hadronic branching ratio is dominated by the CKM-favored ud and cs final states.The relative strengths of each coupling can be estimated by considering that the decay rates include the square of these factors, and all possible diagrams (e.g. sum over quark families, and left and right contributions).The results tabulated below are just estimates, since they only include tree-level interaction diagrams in the Fermi theory.In 2018, the CMS collaboration observed the first exclusive decay of the Z boson to a ψ meson and a lepton–antilepton pair.
W −
boson
W
bosons. This is one of the leading terms contributing to neutral Kaon oscillation.
Elementary particleStatisticsBosonicGauge bosonInteractionsWeak interactionGlashowWeinbergDecay widthElectric chargeWeak isospinWeak hyperchargeStandard Modelparticle physicsElementary particlesQuantum field theoryGauge theorySpontaneous symmetry breakingHiggs mechanismElectroweak interactionQuantum chromodynamicsCKM matrixStandard Model mathematicsStrong CP problemHierarchy problemNeutrino oscillationsPhysics beyond the Standard ModelRutherfordThomsonChadwickSudarshanDavis JrAndersonFeynmanRubbiaGell-MannKendallTaylorFriedmanPowellIliopoulosLedermanMaianiChamberlainCabibboSchwartzMajoranaKobayashiMaskawaYukawa't HooftVeltmanPolitzerReinesSchwingerWilczekCroninEnglertGuralnikKibblede MayoloLattesvector bosonsmediateelectric chargeelementary chargeantiparticlesneutralhalf-lifephysicistSteven Weinbergneutrinonuclear transmutationelasticallybubble chambersmassesprotonphotonforce carrierelectromagnetismgravitongluonsstrong nuclear forceColor confinementparticle spinstrange quarkup quarkchargesstrangenessbaryon numberWeak neutral currentFeynman diagramnuclear decaybeta decaycobalt-606027Co6028Ninucleusbeta particledown quarksflavourits own antiparticleflavour quantum numbersneutral currentmomentumneutrinoselastic scatteringGargamellebubble chamberquantum electrodynamicsSheldon GlashowAbdus SalamNobel Prize in Physicselectroweak theory1964 PRL symmetry breaking papersHiggs bosonLarge Hadron ColliderGoldstone bosonGlashow–Weinberg–Salam modelvacuum expectation valueparticle acceleratorsparticle detectorshigh-energy physicsSuper Proton SynchrotronCarlo RubbiaSimon van der Meer