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用ATLAS探测器对高质量$ZZ$和$WW$末态离壳希格斯玻色子信号强度的约束

Constraints on the off-shell Higgs boson signal strength in the high-mass $ZZ$ and $WW$ final states with the ATLAS detector

ATLAS Collaboration

备注：
34 pages plus author list + cover pages (50 pages total), 12 figures, 6 tables, submited to The European Physical Journal C, All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2014-10/
发表信息：
Eur. Phys. J. C (2015) 75:335
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摘要：

在高于$2m_Z$和$2m_W$阈值的质量范围内测量$ZZ$和$WW$终态提供了测量希格斯玻色子的离壳耦合强度的独特机会。本文介绍了在$ZZ \to 4\ell$、$ZZ\to2\ell2ν$和$WW\to eνμν$最终状态下对离壳希格斯玻色子事件产量归一化到标准模型预测（信号强度）的约束。结果是基于在大型强子对撞机上ATLAS实验收集的$pp$碰撞数据，对应于在$\sqrt{s}$ =8 TeV的碰撞能量下$20.3$ fb $^\text{-1}$的积分光度。使用$CL_s$方法，观察到的离壳信号强度的95%置信水平（CL）上限在5.1-8.6范围内，预期范围为6.7-11.0。在每种情况下，范围是通过改变未知的$gg\to ZZ$和$gg\to WW$背景K因子从高阶QCD校正之间的一半和两倍的已知信号K因子的值。假设相关的希格斯玻色子耦合与希格斯粒子产生的能量尺度无关，结合壳层上的测量，使用相同的背景K因子变化，得到$Γ_H/Γ_H^{\mathrm{SM}}$的观测（预期）95\% CL上限在4.5- 7.5（6.5- 11.2）范围内。假设未知的$gg\rightarrow VV$背景K因子等于信号K因子，这转化为观察到的（预期的）希格斯玻色子玻色子总宽度的95%CL上限为22.7（33.0）MeV。

英文摘要：

Measurements of the $ZZ$ and $WW$ final states in the mass range above the $2m_Z$ and $2m_W$ thresholds provide a unique opportunity to measure the off-shell coupling strength of the Higgs boson. This paper presents constraints on the off-shell Higgs boson event yields normalised to the Standard Model prediction (signal strength) in the $ZZ \to 4\ell$, $ZZ\to2\ell2ν$ and $WW\to eνμν$ final states. The result is based on $pp$ collision data collected by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of $20.3$ fb$^\text{-1}$ at a collision energy of $\sqrt{s}$=8 TeV. Using the $CL_s$ method, the observed 95% confidence level (CL) upper limit on the off-shell signal strength is in the range 5.1-8.6, with an expected range of 6.7-11.0. In each case the range is determined by varying the unknown $gg\to ZZ$ and $gg\to WW$ background K-factor from higher-order QCD corrections between half and twice the value of the known signal K-factor. Assuming the relevant Higgs boson couplings are independent of the energy scale of the Higgs production, a combination with the on-shell measurements yields an observed (expected) 95\% CL upper limit on $Γ_H/Γ_H^{\mathrm{SM}}$ in the range 4.5- -7.5 (6.5- -11.2) using the same variations of the background K-factor. Assuming that the unknown $gg\rightarrow VV$ background K-factor is equal to the signal K-factor,this translates into an observed (expected) 95% CL upper limit on the Higgs boson total width of 22.7 (33.0) MeV.

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