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arXiv 1902.03028hep-phhep-ex
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自旋1共振衰变中轻子能量分布的临界点

A critical point in the distribution of lepton energies from the decay of a spin-1 resonance

Lorenzo Bianchini, Gigi Rolandi

摘要:

考虑了自旋- $1$共振在任意速度谱下衰变为一对无质量轻子,并在实验室坐标系下研究了轻子能量的概率密度函数.质子-质子碰撞中产生的$W$玻色子是一种特殊情况,在这种情况下,可以足够精确地测量衰变的$W$产生的带电轻子的能量,以便高精度地测量$M_W$。我们发现共振质量的一半是轻子能量的一个特殊值,因为在这一点上的概率密度函数对于窄宽度共振一般不是解析的。特别是,密度函数的高阶导数很可能会产生奇点,如尖点或极点。共振的有限宽度恢复规律性,例如通过将尖点和极点涂抹到局部静止点中。对这些点的探索提供了一个估计共振质量的方法,大大减少了对共振的基本产生和衰减动力学的依赖。

英文摘要:

We consider a spin-$1$ resonance produced with an arbitrary spectrum of velocities and decaying into a pair of massless leptons, and we study the probability density function of the energy of the leptons in the laboratory frame. A special case is represented by the production of $W$ bosons in proton-proton collisions, for which the energy of the charged lepton from the decaying $W$ can be measured with sufficient accuracy for a high-precision measurement of $M_W$. We find that half of the resonance mass is a special value of the lepton energy, since the probability density function at this point is in general not analytic for a narrow-width resonance. In particular, the higher-order derivatives of the density function are likely to develop singularities, such as cusps or poles. A finite width of the resonance restores the regularity, for example by smearing cusps and poles into local stationary points. The quest for such points offers a handle to estimate the resonance mass with much reduced dependence on the underlying production and decay dynamics of the resonance.

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