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Atomic Nuclei: Nuclear Spin State Population Distribution01:14

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In a beam of charged particles created by a heated cathode, the particles move at different speeds. However, many applications need a beam with uniform particle speeds. An arrangement known as a velocity selector uses electric and magnetic fields to pick particles with a particular speed from the beam.
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Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10−15 meters, a nucleus is quite small compared to the radius of the entire atom, which is about 10−10 meters. Nuclei are extremely dense compared to bulk matter, averaging 1.8 × 1014 grams per cubic centimeter. If the earth’s density were equal to the average nuclear density, the earth’s radius would be only about 200 meters.
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证明B^{-}→D^{**0}τ^{-}ν_{τ}[超过 ̄]衰变的证据

R Aaij1, A S W Abdelmotteleb2, C Abellan Beteta3

  • 1Nikhef National Institute for Subatomic Physics, Amsterdam, Netherlands.

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|July 31, 2025
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概括
此摘要是机器生成的。

在LHCb实验中,观察到第一个B质子分解成D*0质子和陶质子的证据. 这一发现为B-meson衰变和高能量的粒子物理学提供了新的见解.

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科学领域:

  • 高能物理 高能物理
  • 粒子物理学 粒子物理学
  • 实验物理实验物理学

背景情况:

  • 对于测试粒子物理学的标准模型而言,B-meson衰变至关重要.
  • 了解罕见的B质子衰变可以揭示新的物理现象.
  • 之前的研究集中在涉及较轻的子的衰变上,使得子衰变的探索较少.

研究的目的:

  • 寻找并提供第一个B质子衰变的证据B^{-}→D^{**0}τ^{-}ν[over ̄]_{τ}.
  • 为了测量这种衰变模式的分支分数.
  • 为了研究离子和离子B-meson衰变的比率.

主要方法:

  • 分析了由LHCb实验在7,8和13 TeV收集的质子-质子碰撞数据.
  • D^{**0} 分子的识别,其中包括D_{1}(2420) ^{0},D_{2}^{*}(2460) ^{0}和D_{1}^{'}(2400) ^{0}状态.
  • 统计分析以确定观察到的信号的意义,并测量分支分数.

主要成果:

  • 观察到的B^{-}→D^{**0}τ^{-}ν[over ̄]_{τ}衰变的第一个证据具有3.5σ的显著性.
  • 组合分支分数 B(B^{-}→D_{1,2}^{**0}τ^{-}ν[超过 ̄]_{τ}) ×B(D_{1,2}^{**0}→D^{*+}π^{-}) 的测量值为 [0.051±0.013(stat)±0.006(syst)±0.009(ext) ]%.
  • 离子和离子衰变的比率R ((D_{1,2}^{**0}) 确定为0.13±0.03(stat)±0.01(syst)±0.02(ext).

结论:

  • 对B^{-}→D^{**0}τ^{-}ν[over ̄]_{τ}的观察为B-物理提供了重要的实验数据.
  • 测量的分支分数和比率R ((D_{1,2}^{**0}) 可以用于测试新物理学的理论模型.
  • 这一结果有助于更全面地了解涉及陶氏子的半子B-衰变.