16 May
LHCb discovers two excited states for the Λb beauty particle
The new excited states show clear signals at masses of 5912 MeV/c2 and 5920 MeV/c2 (Image: LHCb collaboration)
The Large Hadron Collider beauty (LHCb) experiment at CERN today announced that it has observed two new excited states of the Λb beauty baryon. Though the Standard Model of particle physics predicts the existence of these new states, this is the first time they have been confirmed in an experiment.
Baryons are subatomic particles whose mass is equal to or greater than that of a proton. Like protons and neutrons, the Λb beauty baryon is composed of three quarks. In Λb these are up, down and beauty quarks.
LHCb physicists found the signals for the Λb particlesin a sample of about 60 trillion proton—proton collisions which were delivered by the LHC operating at a centre-of-mass energy of 7 TeV in 2011. They measured the masses of the new excited states as 5912 MeV/c2 and 5920 MeV/c2 respectively - over five times greater than the mass of a proton or neutron.
The result adds to a growing list of discoveries at CERN in recent months. Last month the Compact Muon Solenoid (CMS) experiment observed a new excited state for the Ξb beauty baryon, and back in December 2011 ATLAS detected a new "quarkonium state" containing a beauty quark bound with its antiquark.
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LHCb result
Other recent discoveries
16 May
AMS celebrates one year in space and 16 billion cosmic-ray events
Physicists monitor the AMS-02 detector from the Payload Operation Control Center at CERN (Image: CERN)
On 16 May last year Space Shuttle Endeavour made its final flight, carrying the Alpha Magnetic Spectrometer (AMS-02) to the International Space Station (ISS). AMS-02 is a space-based particle-physics detector that operates as an external module on the ISS. By detecting and analyzing cosmic rays, AMS-02 is addressing some of the mysteries of modern physics, such as the questions of dark matter and antimatter.
Experts from the AMS collaboration operate the detector round the clock from the Payload Operation Control Center, a facility on the CERN site with a direct link to the ISS. Since its launch, AMS-02 has recorded over 16 billion cosmic-ray events at energies exceeding 10 TeV.
The crew of STS134 – the Space-Shuttle mission that brought AMS to space – will visit CERN on 25 July this year.