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Observation of a new Ξb baryon
S Chatrchyan1, V Khachatryan, A M Sirunyan
1Yerevan Physics Institute, Yerevan, Armenia.
Physical Review Letters
|September 26, 2012
Summary
Researchers observed a new b baryon particle decaying into Ξ(b)(-) and a pion. This discovery, made using data from the Large Hadron Collider
Area of Science:
- High Energy Physics
- Particle Physics
- Hadron Spectroscopy
Background:
- The Standard Model of particle physics describes fundamental particles and forces.
- Baryons are composite particles made of three quarks, with b baryons containing a bottom quark.
- Understanding baryon properties is crucial for refining quantum chromodynamics (QCD) calculations.
Purpose of the Study:
- To report the observation of a new b baryon state.
- To characterize the properties of this new particle, including its mass and quantum numbers.
- To contribute to the comprehensive understanding of the b baryon family.
Main Methods:
- Analysis of proton-proton collision data collected by the CMS experiment at the LHC.
- Reconstruction of the known Ξ(b)(-) baryon via its decay chain: Ξ(b)(-) → J/ψΞ(-) → μ(+)μ(-)Λ(0)π(-), with Λ(0) → pπ(-).
- Identification of the new b baryon through its strong decay into Ξ(b)(-)π(+) and observation of a significant mass peak.
Main Results:
- Observation of a new b baryon state with a statistical significance exceeding 5 standard deviations.
- Measurement of the mass difference of the new state as 14.84 ± 0.74(stat) ± 0.28(syst) MeV.
- The new state is likely the J(P) = 3/2(+) companion to the known Ξ(b) baryon.
Conclusions:
- The discovery of this new b baryon expands the known spectrum of heavy hadrons.
- The observed properties suggest it is the predicted spin partner of the Ξ(b) baryon.
- This finding provides valuable data for testing theoretical models of hadron structure and QCD.
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