charm quark

charm quark
Name	Charm quark
Generation	Second
Charge	+2/3 e
Mass	~1.27 GeV/c^2
Spin	1/2
Color	red/green/blue

charm quark The charm quark is a second-generation elementary particle in the Standard Model associated with a +2/3 electric charge and spin 1/2. It participates in strong, weak, and electromagnetic interactions and contributes to the structure of hadrons such as charmed mesons and charmed baryons. Studies of the charm quark have intersected with experiments at facilities like the Stanford Linear Accelerator Center, CERN, and Fermilab and with theoretical work by physicists including Sheldon Glashow, Steven Weinberg, and Makoto Kobayashi.

Overview

The charm quark was postulated to resolve anomalies in weak interactions and to implement the Glashow–Iliopoulos–Maiani mechanism, motivating links with Glashow–Iliopoulos–Maiani and predictions tested at accelerators including CERN, SLAC National Accelerator Laboratory, and Fermi National Accelerator Laboratory. Its existence influenced research by theorists such as Sheldon Glashow, John Iliopoulos, and Makoto Kobayashi and experimental efforts culminating in discoveries credited to collaborations at Brookhaven National Laboratory and Stanford Linear Accelerator Center. The charm quark contributes to the composition of particles observed in detectors like those used by the ATLAS experiment, CMS experiment, LHCb, and historic detectors such as CLEO and BESIII.

Properties

The charm quark carries color charge and transforms under Quantum chromodynamics color SU(3), affecting bound states studied in lattice QCD by groups at CERN and Brookhaven National Laboratory. Its mass scale, determined by collaborations including Particle Data Group analyses and lattice computations from RIKEN and Fermilab groups, sits between the up/down and bottom/top sectors, informing decays measured by experiments such as BaBar and Belle. Flavor-changing processes involving the charm quark are governed by the Cabibbo–Kobayashi–Maskawa matrix, connecting its weak transitions to quarks in measurements performed at KEK and SLAC. Radiative and hadronic decays probe CP symmetry and are studied in contexts involving CP violation searches and rare processes constrained by results from LHCb and Belle II.

Production and Detection

Charm quarks are produced in high-energy collisions at machines like the Large Hadron Collider, Tevatron, and fixed-target facilities such as CERN SPS and Fermilab Main Injector. Experimental signatures include displaced vertices from weakly decaying charmed hadrons observed in vertex detectors developed by collaborations at CMS experiment, ATLAS experiment, and LHCb. Reconstruction methods rely on tracking systems and calorimeters pioneered at SLAC National Accelerator Laboratory and DESY, with analysis techniques refined by research groups at Princeton University, California Institute of Technology, and Massachusetts Institute of Technology. Production channels exploited by experiments include deep inelastic scattering at HERA and e+e− annihilation at facilities like BEPCII and KEK B.

Role in Particle Physics and the Standard Model

Within the Standard Model framework established by Steven Weinberg and Abdus Salam, the charm quark provides essential cancellations in loop diagrams via the Glashow–Iliopoulos–Maiani mechanism, affecting predictions for flavor-changing neutral currents tested by experiments at CLEO-c and LHCb. Precision measurements of charm-sector observables feed global fits maintained by the Particle Data Group and inform searches for physics beyond the Standard Model pursued by collaborations at CERN and Fermilab. The interplay between charm quark phenomenology and theoretical frameworks—such as heavy quark effective theory advanced by researchers at Universität Mainz and Harvard University—constrains models including supersymmetry investigated by groups at CERN and string-inspired proposals explored at Institute for Advanced Study.

Experimental Discoveries and History

The discovery of charmonium states, notably the J/ψ particle detected in independent experiments at Brookhaven National Laboratory and Stanford Linear Accelerator Center in 1974, provided compelling evidence for the charm quark and spurred the "November Revolution" in particle physics involving teams at SLAC and BNL. Subsequent spectroscopy of charmed mesons by collaborations such as CLEO, BaBar, and Belle mapped out states predicted by quark models developed by physicists including Murray Gell-Mann and George Zweig. Landmark experimental programs at CERN (including the NA experiments), Fermilab (including the E791 experiment), and later at the Large Hadron Collider expanded knowledge of charm production, lifetimes, and decay modes.

Applications and Related Phenomena

Studies of the charm quark impact areas including heavy-flavor tagging techniques used by the ATLAS experiment and CMS experiment in searches for the Higgs boson and beyond-Standard-Model signatures pursued at CERN. Charm physics informs neutrino experiments at FNAL and cosmological constraints relevant to models explored by theorists at CERN Theory Division and Perimeter Institute. Observations of exotic states such as tetraquarks and pentaquarks reported by LHCb and analyzed by groups at University of Oxford and University of Cambridge demonstrate how charm-containing hadrons broaden hadron spectroscopy developed under the influence of Murray Gell-Mann and Enrico Fermi.

Category:Quarks