Lambda baryon

Lambda baryon
Name	Lambda baryon
Type	Baryon
Generation	First, Second, Third
Quark content	uds, udc, udb
Spin	1/2
Mass	1115.683 MeV/c^2 (Λ^0)
Lifetime	2.632×10^−10 s (Λ^0)

Lambda baryon The Lambda baryon is a family of neutral and charged baryons first observed in cosmic-ray and accelerator experiments and studied at laboratories such as CERN, Fermilab, SLAC National Accelerator Laboratory, DESY and KEK. It plays a crucial role in investigations by collaborations including ATLAS Experiment, CMS Experiment, LHCb, Belle Experiment and BaBar and appears in theoretical work by researchers at institutions like Stanford University, Massachusetts Institute of Technology, University of Cambridge and Princeton University. Lambda baryons connect to major discoveries such as the quark model by Murray Gell-Mann and George Zweig and measurements tied to facilities like the Large Hadron Collider and the Tevatron.

Introduction

Lambda baryons were recognized after analyses at observatories including the Cosmic Ray Laboratory and experiments at Brookhaven National Laboratory and CERN Intersecting Storage Rings. The neutral Λ^0 (uds) provided early evidence for strange particle production studied by groups at University of Chicago, Columbia University, University of California, Berkeley and University of Oxford. Subsequent charged and heavy-flavor variants such as Λ_c^+ and Λ_b^0 were produced in experiments at SLAC, KEK-B, HERA, RHIC and later at the LHC. Their study involved theorists from Caltech, Imperial College London and Yale University.

Properties

Measured properties of the Λ^0 include mass, lifetime, magnetic moment and parity studied by collaborations like NA48 experiment, WA65 experiment and HyperCP experiment. Heavy-flavor partners Λ_c^+ and Λ_b^0 have masses and lifetimes measured at CDF, DØ, LHCb and Belle II. Precision determinations relate to particle-data summaries compiled by groups at Particle Data Group and to theoretical frameworks developed at CERN Theory Division and IHEP. Observables such as spin alignment, polarization and form factors are compared across results from ALICE experiment, PHENIX experiment and STAR experiment.

Quark composition and classifications

Lambda baryons are classified in flavor SU(3) multiplets following work by Murray Gell-Mann and the classification schemes used in texts from Niels Bohr Institute and Institute for Advanced Study. The light Λ^0 has quark content uds, while charmed and bottomed partners involve udc and udb. This classification links to studies by Yoichiro Nambu, Harald Fritzsch and Heinrich Leutwyler and to lattice QCD computations performed at Riken, Brookhaven National Laboratory and CERN. Multiplet patterns are contrasted with those of nucleons studied at Jefferson Lab and with strange baryons in hypernuclear experiments at J-PARC.

Production and decay modes

Production mechanisms for Λ baryons include fragmentation in e+e− annihilation at LEP and PEP-II, hadronization in pp collisions at LHC, and associated production in pA collisions at SPS and AGS. Decay channels such as Λ^0 → p π−, Λ_c^+ → p K− π+, and Λ_b^0 → J/ψ Λ are measured by collaborations including OPAL, ALEPH, CLEO and SELEX. Weak decays probe CKM matrix elements studied by groups at CERN, Fermilab and KEK, and rare or CP-violating modes are searched for by LHCb, Belle II and BaBar in analyses connecting to work by Kobayashi Takashi and Maskawa Makoto.

Experimental detection and measurements

Detection techniques rely on tracking detectors and vertexing using devices from CERN and SLAC including silicon trackers developed by teams at Lawrence Berkeley National Laboratory. Experiments such as NA61/SHINE, HADES, COMPASS and LHCb use particle identification systems from CERN and DESY to isolate Λ signals via displaced vertices and invariant-mass reconstruction. Historical measurements originated with cloud-chamber studies at University of Manchester and bubble-chamber programs at CERN and Brookhaven. Precision lifetime and branching-fraction results derive from combined analyses by Particle Data Group, LHCb, Belle and CDF.

Theoretical significance and models

Lambda baryons test nonperturbative QCD approaches developed by groups at Princeton University, Institute for Advanced Study, University of Oxford and École Normale Supérieure. Models include constituent quark models advanced by Isgur Nathan and Karl George, heavy-quark effective theory elaborated at Cornell University and chiral perturbation theory by researchers at University of Bonn and University of Washington. Lattice QCD computations from collaborations at Riken, Fermilab, BNL and CERN compare masses and form factors. Studies of Λ polarization in polarized proton collisions involve RHIC programs and theoretical work by Duke University and MIT.

Category:Baryons