相关实验视频
Updated: Jul 12, 2025

07:46
Setting Limits on Supersymmetry Using Simplified Models
Published on: November 15, 2013
8.6K
使用ATLAS探测器观测Pb+Pb碰撞中的γγ→ττ过程以及对t-Lepton异常磁矩的约束
G Aad1, B Abbott2, D C Abbott3
1CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille, France.
Physical review letters
|October 28, 2023
概括
研究人员观察到-碰撞中-对的产生. 这项研究还为-勒普顿异常磁矩提供了新的约束,这是这个基本粒子的一个关键性质.
科学领域:
- 高能粒子物理学 高能粒子物理学
- 量子电动力学 量子电动力学
- 标准模型物理学的物理.
背景情况:
- 超外围碰撞 (UPC) 提供了一个独特的环境来研究重离子之间的电磁相互作用.
- 通过光子-光子融合 (γγ→ττ) 产生-子对 (ττ) 是基础物理学的敏感探测器.
- -子 (aτ) 的异常磁矩是标准模型预测的关键参数.
研究的目的:
- 报告了在极端外围的与碰撞中第一个t-lepton对产生的观察.
- 使用实验数据来限制t-lepton异常磁矩 (aτ).
- 在一个新的碰撞系统中测试量子电力学预测.
主要方法:
- 来自ATLAS实验的1.44nb-1的Pb+Pb碰撞数据在√sNN = 5.02 TeV的分析.
- 选择具有特定衰变特征的事件:一个子和一个电子/来自 τ 衰变的带电轨道.
- 模板适合子横向动量分布,使用子控制样本来限制不确定性.
主要成果:
- 在Pb+Pb碰撞中观察γγ→ττ过程,显著度大于5个标准偏差.
- 测量信号强度 μττ = 1.03+0.06−0.05,与标准模型预测一致.
- 观察到的aτ的95%置信级间隔: -0.057 < aτ < 0.024.
结论:
- 在UPC中观察t-lepton对的产生得到证实.
- 该测量为t-lepton异常磁矩提供了迄今为止最严格的约束.
- 结果验证了理论预测,并为重离子碰撞的精度测量开辟了新的途径.
相关概念视频
Thomson's e/m Experiment
3.8K
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.
A particle with charge q, speed v, and mass m enters an area from the top, where the magnetic and electric fields are perpendicular both to the particle's motion and to one another. The...
A particle with charge q, speed v, and mass m enters an area from the top, where the magnetic and electric fields are perpendicular both to the particle's motion and to one another. The...
3.8K
Atomic Nuclei: Nuclear Magnetic Moment
1.1K
All atomic nuclei are positively charged. When they have a nonzero spin, they behave like rotating charges. As a consequence of their charge and spin, these nuclei generate a magnetic field (B). This, in turn, gives rise to a magnetic moment (μ), which is randomly oriented in the absence of an external magnetic field. When an external magnetic field (B0) is applied, the magnetic moment vectors can align with the field or against it in 2 + 1 orientations. A hydrogen nucleus, which is just a...
1.1K
Atomic Nuclei: Nuclear Relaxation Processes
660
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis, the precessing magnetic moments are randomly oriented around the z-axis.
660
Atomic Nuclei: Magnetic Resonance
666
The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
666
Magnetic Moment of an Electron
1.4K
Electrons revolving around a nucleus are analogous to a circular current carrying loop. This current produces a magnetic dipole moment proportional to the electron's orbital angular momentum. Since the orbital angular momentum is quantized in terms of the reduced Planck's constant, the dipole moment is quantized in the Bohr Magneton. The value of the Bohr magneton is 9.27 x 10-24 Am2. Electrons also have an intrinsic spin angular momentum, and the associated spin magnetic moment is...
1.4K
Potential Due to a Magnetized Object
297
Magnetic dipoles in magnetic materials are aligned when placed under an external magnetic field. For paramagnets and ferromagnets, dipole alignment occurs in the direction of the magnetic field. However, the dipoles align opposite to the field in the case of diamagnets. This state of magnetic polarization due to the external field is called magnetization. Magnetization is defined as the dipole moment per unit volume. It plays a similar role to polarization in electrostatics.
The vector...
The vector...
297

