χ b (3P) -Meson

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χ b1 (3P) -Meson

classification
Boson
Hadron
Meson
properties
electric charge neutral
Resting energy (10512.1 ± 2.3)  MeV
Spin parity 1 +
Isospin 0
Quark
composition 		Bottom - anti-bottom

The χ b (3P) meson is a meson from the Bottomonia family . It was found by the ATLAS collaboration and breaks down radiatively into Υ (1S) + γ or Υ (2S) + γ or Υ (3S) + γ.

The χ mesons, like the η mesons and the Ypsilon mesons, are quark- antiquark combinations. While the two quarks in the η form an S orbital ( orbital angular momentum L = 0) with spin 0 and in the Ypsilon to an S orbital with spin 1, the χ meson is a P orbital combination of the two quarks, d. i.e. it has an orbital angular momentum of L = 1. The index b expresses that the quarks are a bottom quark and an anti-bottom quark, the number 3 stands for the main quantum number n .

It is the first particle that was discovered at the Large Hadron Collider . In addition to the two χ b (nP) states with principal quantum numbers n = 1 and n = 2 at 9.90 and 10.26 GeV, a peak at 10.52 GeV was observed for the first time, with the theoretical mass for the n = 3 state matches. The particle is not perceived directly, but after its decay into a Υ meson and gamma radiation, the Υ meson is observed through its decay into a μ + μ pair and the gamma radiation in the electromagnetic calorimeter .

The mass originally determined by ATLAS was an overlay of min. two or three different spin states. The mass of the particle with spin 1, so-called χ b1 (3P) , could be determined from the more recent measurement results of the LHCb from 2015 . It is assumed that the particle with spin 2, called χ b2 (3P) , has a mass that is approx. 10 MeV greater. A final confirmation is still pending.

Web links

Individual evidence

  1. ↑ The information on the particle properties (info box) are, unless otherwise stated, taken from: KA Olive et al. ( Particle Data Group ): 2015 Review of Particle Physics. In: Chin. Phys. C, Vol. 38, 090001 (2014) and 2015 update. Particle Data Group, accessed May 7, 2018 .
  2. ↑ a b ATLAS collaboration: Observation of a new state in radiative transitions to Y (1S) and Y (2S) at ATLAS . In: Phys. Rev. Lett. 108, 152001 . April 9, 2012, doi : 10.1103 / PhysRevLett.108.152001 , arxiv : 1112.5154 (English, aps.org [accessed November 4, 2012]).
  3. ↑ Astropage.eu: Chi-b (3P): ATLAS experiment discovers new particle at the LHC. December 23, 2011, accessed November 4, 2012 .