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Luo, W.

Publications and source records attributed to Luo, W..

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Measurement of the background in the CMS muon detector in ${p}{p}$-collisions at $\sqrt{s} = 13$ TeV

The CMS detector, including its muon system, has been operating at the CERN LHC in increasingly challenging conditions for about 15 years. The muon detector was designed to provide excellent triggering and track reconstruction for muons produced in proton–proton collisons at an instantaneous luminosity ($\mathcal{L}$) of 1 x 10 34 cm –2 s –1 . During the Run 2 data-taking period (2015–2018), the LHC achieved an instantaneous luminosity of twice its design value, resulting in larger background rates and making the efficient detection of muons more difficult. While some backgrounds result from natural radioactivity, cosmic rays, and interactions of the circulating protons with residual gas in the beam pipe, the dominant source of background hits in the muon system arises from proton–proton interactions themselves. Charged hadrons leaving the calorimeters produce energy deposits in the muon chambers. In addition, high-energy particles interacting in the hadron calorimeter and forward shielding elements generate thermal neutrons, which leak out of the calorimeter and shielding structures, filling the CMS cavern. We describe the method used to measure the background rates in the various muon subsystems. These rates, in conjunction with simulations, can be used to estimate the expected backgrounds in the High-Luminosity LHC. This machine will run for at least 10 years starting in 2029 reaching an instantaneous luminosity of $\mathcal{L}$ = 5 x 10 34 cm –2 s –1 and increasing ultimately to $\mathcal{L}$ = 7.5 x 10 34 cm –2 s –1 . These background estimates have been a key ingredient for the planning and design of the muon detector upgrade.

Tytgat, M. (ORCID:0000000239902074)↗
DOE OSTI2021

Spectroscopy of A=9 hyperlithium with the $(e,e^{\prime}K^{+})$ reaction

Missing mass spectroscopy with the $(e,e^{\prime}K^{+})$ reaction was performed at JLab Hall C for the neutron rich $\Lambda$ hypernucleus $^{9}_{\Lambda}{\rm Li}$. The ground state energy was obtained to be $B_{\Lambda}^{\rm g.s.}=8.84\pm0.17^{\rm stat.}\pm0.15^{\rm sys.}~{\rm MeV}$ by using shell model calculations of a cross section ratio and an energy separation of the spin doublet states ($3/2^{+}_1$ and $5/2^{+}_1$). In addition, peaks that are considered to be states of [$^{8}{\rm Li}(3^{+})\otimes s_{\Lambda}=3/2^{+}_{2}, 1/2^{+}$] and [$^{8}{\rm Li}(1^{+})\otimes s_{\Lambda}=5/2^{+}_{2}, 7/2^{+}$] were observed at $E_{\Lambda}(\#2)=1.74\pm0.27^{\rm stat.}\pm0.11^{\rm sys.}~{\rm MeV}$ and $E_{\Lambda}(\#3)=3.30\pm0.24^{\rm stat.}\pm0.11^{\rm sys.}~{\rm MeV}$, respectively. The $E_{\Lambda}(\#3)$ is larger than shell model predictions by a few hundred keV, and the difference would indicate that a ${\rm ^{5}He}+t$ structure is more developed for the $3^{+}$ state than those for the $2^{+}$ and $1^{+}$ states in a core nucleus $^{8}{\rm Li}$ as a cluster model calculation suggests.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2008

Numerical Determination of Critical Conditions for Thermal Ignition

The determination of ignition or thermal explosion in an oxidizing porous body of material, as described by a dimensionless reaction-diffusion equation of the form .tu = .2u + .e-1/u over the bounded region O, is critically reexamined from a modern perspective using numerical methodologies. First, the classic stationary model is revisited to establish the proper reference frame for the steady-state solution space, and it is demonstrated how the resulting nonlinear two-point boundary value problem can be reexpressed as an initial value problem for a system of first-order differential equations, which may be readily solved using standard algorithms. Then, the numerical procedure is implemented and thoroughly validated against previous computational results based on sophisticated path-following techniques. Next, the transient nonstationary model is attacked, and the full nonlinear form of the reaction-diffusion equation, including a generalized convective boundary condition, is discretized and expressed as a system of linear algebraic equations. The numerical methodology is implemented as a computer algorithm, and validation computations are carried out as a prelude to a broad-ranging evaluation of the assembly problem and identification of the watershed critical initial temperature conditions for thermal ignition. This numerical methodology is then used as the basis for studying the relationship between the shape of the critical initial temperature distribution and the corresponding spatial moments of its energy content integral and an attempt to forge a fundamental conjecture governing this relation. Finally, the effects of dynamic boundary conditions on the classic storage problem are investigated and the groundwork is laid for the development of an approximate solution methodology based on adaptation of the standard stationary model.

Luo, W.↗