标题： 通过半轻子衰变在压缩区域中停止搜索 显示英文标题

标题： Stop Search in the Compressed Region via Semileptonic Decays

摘要： 在标准模型的超对称扩展中，顶夸克的超对称伙伴（停夸克）在解决自然性问题中起着关键作用。 对于停夸克的直接成对产生，每个停夸克衰变为一个顶夸克和最轻中性子的情况，标准的停夸克搜索在压缩谱情况下难以找到停夸克，因为此时停夸克与最轻中性子之间的质量差接近顶夸克质量，事件看起来与大量的$t\bar{t}$背景非常相似。 随着额外的硬ISR喷注，来自停夸克衰变的两个中性子会被反方向推动，并可能产生一些缺失横向能量。 这可能用于区分停夸克衰变与背景。 在本文中，我们研究了这种信号事件在压缩质量谱下的半轻子衰变。 尽管来自$W$衰变的中微子也会产生一些缺失横向能量，但其动量可以从运动学假设和质量壳条件中重建。 然后可以将其从总缺失横向动量中减去，以得到中性子的贡献。 由于受到的背景较少，我们表明，在压缩线$m_{\tilde{t}} - m_{\tilde{\chi}}\approx m_t$上，半轻子衰变通道比完全强子衰变通道具有更好的发现能力。 在300$\text{fb}^{-1}$的条件下，13 TeV的LHC可以将停夸克的发现范围扩大到500 GeV，覆盖最自然的参数空间区域。 显示英文摘要

摘要： In supersymmetric extensions of the Standard Model, the superpartners of the top quark (stops) play the crucial role in addressing the naturalness problem. For direct pair-production of stops with each stop decaying into a top quark plus the lightest neutralino, the standard stop searches have difficulty finding the stop for a compressed spectrum where the mass difference between the stop and the lightest neutralino is close to the top quark mass, because the events look too similar to the large $t\bar{t}$ background. With an additional hard ISR jet, the two neutralinos from the stop decays are boosted in the opposite direction and they can give rise to some missing transverse energy. This may be used to distinguish the stop decays from the backgrounds. In this paper we study the semileptonic decay of such signal events for the compressed mass spectrum. Although the neutrino from the $W$ decay also produces some missing transverse energy, its momentum can be reconstructed from the kinematic assumptions and mass-shell conditions. It can then be subtracted from the total missing transverse momentum to obtain the neutralino contribution. Because it suffers from less backgrounds, we show that the semileptonic decay channel has a better discovery reach than the fully hadronic decay channel along the compressed line $m_{\tilde{t}} - m_{\tilde{\chi}}\approx m_t$. With 300 $\text{fb}^{-1}$, the 13 TeV LHC can discover the stop up to 500 GeV, covering the most natural parameter space region.