Physics Studies for the LBNF Graphite Target Design
Physics Studies for the LBNF Graphite Target Design
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DOI：
10.18429/jacow-ipac2021-wepab212
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发表时间：
2021-08
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通讯作者：
J. Back
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作者：
J. Back
本文介绍了长基线中微子设施（LBNF）石墨靶的模拟物理性能，该靶是由RAL高功率靶组为深地下中微子实验（DUNE）设计的。我们首先比较了三种概念圆柱形靶设计方案，作为靶长度（最高2.2米）的函数：下游支撑，两个单独的靶和上游支撑的悬臂。选择悬臂设计作为基准，我们展示了加宽第一聚焦角上游内导体的效果，为支撑目标提供了额外的空间。我们还给出了1.5米原型和1.8米生产悬臂目标的预期性能估计。此外，我们还展示了自DUNE TDR以来对其他两个聚焦喇叭进行的主要工程更新的影响。美国费米实验室（Fermilab）的LBNF将向DUNE近、远探测器[1]发射世界上最强烈的沿轴中微子束，目的是发现中微子在（三）种味态之间振荡时电荷宇称（CP）违逆导致的物质-反物质不对称性，这可能有助于解释早期宇宙中物质的主导地位。LBNF束线[2]将把120 GeV， 1.2 MW的质子束（可升级到2.4 MW）碰撞到石墨靶上，产生二次带电的介子，这些介子在衰变前通过π+→μνμ和π−→μν ？μ，产生强烈的μ子中微子或反中微子流向DUNE探测器。本文利用Geant4[3]软件和QGSP_BERT强子模型，对3喇叭聚焦系统的概念目标、原型目标和生产目标的物理性能进行了仿真。卢瑟福实验室（RAL）大功率靶标组正在设计并将建造LBNF靶标。氦冷却圆柱形石墨靶考虑了三种概念设计，即一个由下游（DS）框架支撑的长（最长2.2米）靶，两个有自己支撑的靶（第一个总是1米长），以及一个上游支撑的悬臂。在每种情况下，靶完全插入第一个2.2 m长的聚焦角“A”（24 cm外导体半径）内，石墨芯靶半径固定为8 mm，等于3（高斯）质子束宽度。每个目标都在一个1毫米厚的锥形圆柱形钛容器内（半径3.7厘米至2.7厘米），容器内充满氦气冷却气体，周围是氮气大气。* J.J.Back@warwick.ac.uk图1显示了三个选项的CP灵敏度σ作为目标长度的函数，其中三个聚焦角没有改变，每个聚焦角的内外导体之间的方向磁场B = 0.02I/r T，串联电流I =±293 kA（反中微子为负）和半径r （cm）。灵敏度σ等于测量cp违背的最小值√Δχ2，该值满足±180°之间75%的中微子振荡相位δCP值。√Δχ(δCP)分布使用GLoBES软件[4]（假设正常质量顺序）与Geant4模拟的中微子通量谱，每个中微子和反中微子以1.2 MW运行3.5年，对应于1.1 × 1021个质子每运行年（204.5日历日），位于南达科他州Sanford地下研究设施1297公里（美国）[5]的40 kt液态氩远探测器。1.2 1.4 1.6 1.82 2.2目标长度(m) 1.76 1.78 1.8 1.82 1.84 1.86 1.88 1.9 1.92 1.94
We present the simulated physics performance of the Long-Baseline Neutrino Facility (LBNF) graphite target that is being designed by the RAL High Power Targets Group for the Deep Underground Neutrino Experiment (DUNE). We first compare three conceptual cylindrical target design options as a function of target length (up to 2.2 m): downstream supported, two individual targets and an upstreamsupported cantilever. Choosing the cantilever design as the baseline, we show the effect of widening the upstream inner conductor of the first focusing horn to provide extra space for supporting the target. We also give estimates of the expected performance of the 1.5 m prototype and 1.8 m production cantilevered targets. Furthermore, we show the effects of the main engineering updates made to the other two focusing horns since the DUNE TDR. INTRODUCTION The LBNF at Fermilab (USA) will deliver the world’s most intense on-axis neutrino beam to the DUNE near and far detectors [1], with the aim of discovering matter-antimatter asymmetries from charge-parity (CP) violation when neutrinos oscillate between (three) flavour states, which could help explain the dominance of matter in the early universe. The LBNF beamline [2] will collide a 120 GeV, 1.2 MW proton beam (upgradable to 2.4 MW) onto a graphite target, creating secondary charged pions which are focused by three magnetic horns before they decay, via π+ → μνμ and π− → μ?̄?μ, to produce an intense flux of muon neutrinos or antineutrinos towards the DUNE detectors. Here, we show the simulated physics performance of conceptual, prototype and production targets for the 3-horn focusing system, using Geant4 [3] software with the QGSP_BERT hadronic model. CONCEPTUAL TARGET DESIGNS The Rutherford Lab (RAL) High Power Targets Group is designing, and will build, the LBNF target. Three conceptual designs were considered for the helium-cooled cylindrical graphite target, namely a long (up to 2.2 m) target supported by a downstream (DS) frame, two targets (where the first one is always 1 m long) with their own supports, and an upstream-supported cantilever. For each case, the target is fully inserted inside the first 2.2 m-long focusing horn “A” (24 cm outer conductor radius), and the graphite core target radius is fixed at 8 mm, equal to 3 (Gaussian) proton beam widths. Each target is inside a 1 mm-thick tapered cylindrical titanium container (3.7 cm to 2.7 cm radius) filled with helium cooling gas, surrounded by a nitrogen atmosphere. ∗ J.J.Back@warwick.ac.uk Figure 1 shows the CP sensitivity σ as a function of target length for the three options, with no changes made to the 3 focusing horns, which each have an azimuthal magnetic field B = 0.02I/r T between their inner and outer conductors, for series current I = ±293 kA (negative for antineutrinos) and radius r (cm). The sensitivity σ is equal to the minimum value of √Δχ2 for measuring CP-violation that is satisfied by 75% of the neutrino oscillation phase δCP values between ±180∘. The √Δχ(δCP) distribution is found using GLoBES software [4] (assuming normal mass ordering) with neutrino flux spectra from the Geant4 simulations, for 3.5 years each of neutrino then antineutrino running at 1.2 MW, corresponding to 1.1 × 1021 protons-on-target per run year (204.5 calendar days), with a 40 kt liquid argon far detector located 1297 km downstream at the Sanford Underground Research Facility in South Dakota (USA) [5]. 1.2 1.4 1.6 1.8 2 2.2 Target length (m) 1.76 1.78 1.8 1.82 1.84 1.86 1.88 1.9 1.92 1.94