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arXiv 1503.05491hep-ph
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未来轻子对撞机上重中微子对撞的展望

Prospects of Heavy Neutrino Searches at Future Lepton Colliders

Shankha Banerjee, P. S. Bhupal Dev, Alejandro Ibarra, Tanumoy Mandal, Manimala Mitra

备注：
21 pages, 19 figures, 9 tables. Minor changes. Accepted in PRD. Matches with published version
发表信息：
Phys. Rev. D 92, 075002 (2015)
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摘要：

我们讨论了在下一代轻子对撞机上寻找重中微子的前景。我们特别关注计划中的正负电子对撞机，该对撞机以两种不同的束流模式运行，即$e^+e^-$和$e^-e^-$。在$e^+e^-$束模式下，我们考虑了重中微子（$N$）的各种产生和衰变模式，发现由$e^+e^-\to Nν$产生模式产生的具有$e+2j+{E\!\!\!/}_T$的末态是最有希望的通道。然而，由于这种模式是不敏感的重中微子的Majorana性质，我们还研究了一个新的生产通道$e^+e^-\to Ne^\pm W^\mp$，它导致了相同的符号双轻子加四喷流的最终状态，从而直接探讨在$e^+e^-$对撞机轻子数违反。在$e^-e^-$束模式下，我们研究了重Majorana中微子介导的$e^-e^-\to W^-W^-$轻子数破缺过程的前景。我们使用基于切割和多变量分析技术，使相关的信号和背景事件，包括检测器的影响，一个通用的线性对撞机检测器的现实计算。我们发现，在95% C. L下，轻重中微子混合参数$|V_{eN}|^2$可以被探测到$\sim 10^{-4}$。对于重中微子质量达到$400$ GeV或在$\sqrt s=500$ GeV左右，积分光度为$100 \rm{fb}^{-1}$。对于较小的混合值，我们表明，多变量分析可以提高信号的显着性高达一个数量级。这些极限将比目前电弱精密数据的最佳极限以及$\sqrt s=14$ TeV LHC的预计极限至少好一个数量级。

英文摘要：

We discuss the future prospects of heavy neutrino searches at next generation lepton colliders. In particular, we focus on the planned electron-positron colliders, operating in two different beam modes, namely, $e^+e^-$ and $e^-e^-$. In the $e^+e^-$ beam mode, we consider various production and decay modes of the heavy neutrino ($N$), and find that the final state with $e+2j+{E\!\!\!/}_T$, arising from the $e^+e^-\to Nν$ production mode, is the most promising channel. However, since this mode is insensitive to the Majorana nature of the heavy neutrinos, we also study a new production channel $e^+e^-\to Ne^\pm W^\mp$, which leads to a same-sign dilepton plus four jet final state, thus directly probing the lepton number violation in $e^+e^-$ colliders. In the $e^-e^-$ beam mode, we study the prospects of the lepton number violating process of $e^-e^-\to W^-W^-$, mediated by a heavy Majorana neutrino. We use both cut-based and multivariate analysis techniques to make a realistic calculation of the relevant signal and background events, including detector effects for a generic linear collider detector. We find that with the cut-based analysis, the light-heavy neutrino mixing parameter $|V_{eN}|^2$ can be probed down to $\sim 10^{-4}$ at 95\% C.L. for the heavy neutrino mass up to $400$ GeV or so at $\sqrt s=500$ GeV with $100 \rm{fb}^{-1}$ of integrated luminosity. For smaller mixing values, we show that a multivariate analysis can improve the signal significance by up to an order of magnitude. These limits will be at least an order of magnitude better than the current best limits from electroweak precision data, as well as the projected limits from $\sqrt s=14$ TeV LHC.

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