"Figure 10 (Exclusion contours)" of "Search for new particles decaying to a jet and an emerging jet"

A search is performed for events consistent with the pair production of a new heavy particle that acts as a mediator between a dark sector and normal matter, and that decays to a light quark and a new fermion called a dark quark. The search is based on data corresponding to an integrated luminosity of 16.1 fb$^{-1}$ from proton-proton collisions at $\sqrt{s}=13$ TeV collected by the CMS experiment at the LHC in 2016. The dark quark is charged only under a new quantum-chromodynamics-like force, and forms an ``emerging jet'' via a parton shower, containing long-lived dark hadrons that give rise to displaced vertices when decaying to standard model hadrons. The data are consistent with the expectation from standard model processes. Limits are set at 95% confidence level excluding dark pion decay lengths between 5 and 225 mm for dark mediators with masses between 400 and 1250 GeV. Decay lengths smaller than 5 and greater than 225 mm are also excluded in the lower part of this mass range. The dependence of the limit on the dark pion mass is weak for masses between 1 and 10 GeV. This analysis is the first dedicated search for the pair production of a new particle that decays to a jet and an emerging jet.

本研究针对与新型重粒子成对产生相符的事例开展搜寻，该重粒子作为暗扇区（dark sector）与普通物质间的媒介粒子，可衰变至轻夸克与一种被称为暗夸克（dark quark）的新型费米子。本次搜寻基于2016年大型强子对撞机（Large Hadron Collider, LHC）上的CMS实验采集的质子-质子对撞数据，其对应积分亮度为16.1 fb⁻¹，质心系能量为√s=13 TeV。暗夸克仅与一种类量子色动力学的新型相互作用荷电，并通过部分子簇射（parton shower）形成“涌现喷注（emerging jet）”；该喷注包含长寿命暗强子，这类暗强子衰变至标准模型（Standard Model）强子时会产生位移顶点。观测数据与标准模型过程的理论预期相符。本分析在95%置信水平下设置排除界限：对于质量介于400 GeV至1250 GeV之间的暗媒介子（dark mediator），其暗π介子（dark pion）的衰变长度处于5 mm至225 mm区间的情况均被排除。在该质量区间的低端，衰变长度小于5 mm与大于225 mm的情况同样被排除。当暗π介子质量介于1 GeV至10 GeV之间时，排除界限对暗π介子质量的依赖性较弱。本分析是首个专门搜寻衰变至一个普通喷注与一个涌现喷注的新型粒子成对产生过程的研究。