The silicon vertex tracker for the heavy photon search experiment

P. H. Adrian
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引用次数: 5

Abstract

The Heavy Photon Search (HPS) is a new, dedicated experiment at Thomas Jefferson National Accelerator Facility (JLab) to search for a massive vector boson, the heavy photon (a.k.a. dark photon, A), in the mass range 20-500 MeV/c2 and with a weak coupling to ordinary matter. An A' can be radiated from an incoming electron as it interacts with a charged nucleus in the target, accessing a large open parameter space where the A' is relatively long-lived, leading to displaced vertices. HPS searches for these displaced A' to e+e- decays using actively cooled silicon microstrip sensors with fast readout electronics placed immediately downstream of the target and inside a dipole magnet to instrument a large acceptance with a relatively small detector. With typical particle momenta of 0.5-2 GeV/c, the low material budget of 0.7% Xo per tracking layer is key to limiting the dominant multiple scattering uncertainty and allowing efficient separation of the decay vertex from the prompt QED trident background processes. Achieving the desired low-mass acceptance requires placing the edge of the silicon only 0.5 mm from the electron beam. This results in localized hit rates above 4 MHz/mm2 and radiation levels above 1014 1 MeV neutron equivalent /cm2 dose. Hit timing at the ns level is crucial to reject out-of time hits not associated with the A' decay products from the almost continuous CEBAF accelerator beam. To avoid excessive beam-gas interactions the tracking detector is placed inside the accelerator beam vacuum envelope and is retractable to allow safe operation in case of beam motion. This contribution will discuss the design, construction and first performance results from the first data-taking period in the spring of 2015.
用于重光子搜索实验的硅顶点跟踪器
重光子搜索(HPS)是在托马斯·杰斐逊国家加速器设施(JLab)进行的一项新的、专门的实验,旨在寻找质量在20-500 MeV/c2之间、与普通物质弱耦合的大质量矢量玻色子,重光子(又名暗光子,a)。当A'与目标中的带电原子核相互作用时,它可以从进入的电子中辐射出来,进入一个大的开放参数空间,在这个空间中A'的寿命相对较长,从而导致位移的顶点。HPS使用主动冷却的硅微带传感器搜索这些位移的A'到e+e-衰变,该传感器具有快速读出电子器件,直接放置在目标下游和偶极磁铁内,用相对较小的探测器测量大的接受度。在典型的粒子动量为0.5-2 GeV/c的情况下,每层0.7% Xo的低材料预算是限制主导多重散射不确定性和有效分离衰变顶点与提示QED三叉刀背景过程的关键。实现理想的低质量接受需要将硅的边缘放置在距离电子束仅0.5毫米的地方。这导致局部命中率高于4兆赫/平方毫米,辐射水平高于10141mev中子当量/平方厘米剂量。对于拒绝与几乎连续的CEBAF加速器束产生的A′衰变产物无关的超时命中来说,ns级的命中时间至关重要。为了避免过多的光束-气体相互作用,跟踪探测器被放置在加速器束流真空包层内,并且可以伸缩,以便在束流运动的情况下安全运行。这篇文章将讨论2015年春季第一次数据采集期间的设计、建造和首次性能结果。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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