Siew Yan Hoh

This document a outlines a set of simplified models for dark matter and its interactions with Standard Model particles. It is intended to summarize the main characteristics that these simplified models have when applied to dark matter searches at the LHC, and to provide a number of useful expressions for reference. The list of models includes both s-channel and t-channel scenarios. For s-channel, spin-0 and spin-1 mediations are discussed, and also realizations where the Higgs particle provides a portal between the dark and visible sectors. The guiding principles underpinning the proposed simplified models are spelled out, and some suggestions for implementation are presented.

This document is the final report of the ATLAS-CMS Dark Matter Forum, a forum organized by the ATLAS and CMS collaborations with the participation of experts on theories of Dark Matter, to select a minimal basis set of dark matter simplified models that should support the design of the early LHC Run-2 searches. A prioritized, compact set of benchmark models is proposed, accompanied by studies of the parameter space of these models and a repository of generator implementations. This report also addresses how to apply the Effective Field Theory formalism for collider searches and present the results of such interpretations.

We show that the wakefield driven by fast electrons inside the nanowire when irradiated with an ultra-short relativistic laser pulse strips atoms to a higher charge state. Using particle-in-cell simulations, we demonstrate that the charge state agrees with the barrier suppression threshold of the wakefield and reaches a higher value via collision. The ionisation of gold nanowires occurs only via a collisional-damped wakefield. We found that the collisional ionisation of high-Z nanowires depends on the onset of the z-pinch. These results suggest a different ionisation mechanism of the structured target in the subfemtosecond regime.

The muon collider represents one of the most promising solutions for a future machine exploring the high energy frontier, but several challenges due to the 2.2 $\mu$sec muon lifetime at rest have to be carefully considered. The LEMMA project is investigating the possibility of producing low emittance muon/antimuon pairs from the e$^+$e$^-$ annihilation process at threshold energy, resulting in small transverse emittance beams without any additional beam cooling. However most of the measurements available are performed at higher $\sqrt{s}$ values. It is therefore necessary to measure muons production in positron annihilation at threshold energy and compare the experimental results with the predictions in this specific energy regime. Apart from being a topic of physical interest by itself, these near to threshold measurements can have a sizeable impact on the estimation of the ultimate luminosity achievable in a muon collider with the LEMMA injection scheme.

Dark Matter is a hypothetical particle proposed to explain the missing matter expected from the cosmological observation. The motivation of Dark Matter is overwhelming however as it is mainly deduced from its gravitational interaction, for it does little to pinpoint what Dark Matter really is. In WIMPs Miracle, weakly interactive massive particle being the Dark Matter candidate is correctly producing the current thermal relic density at weak scale, implying the possibility of producing and detecting it in Large Hadron Collider. Assuming WIMPs being the maverick particle within collider, it is expected to be pair produced in association with a Standard Model particle. The presence of the WIMPs pair is inferred from the Missing Transverse Energy (MET) which is the vector sum of the imbalance in the transverse momentum plane recoils a Standard Model Particle. The collider is able to produce light mass Dark Matter which the traditional detection fail to detect due to the small momentum transfer involved in the interaction; on the other hand, the traditional detection is robust in detecting a higher Dark matter masses but the collider is suffered from the parton distribution function suppression. Topologically the processes are similar to the scattering processes in the direct detection thus complementary to the traditional Dark Matter detection. The collider searches are strongly motivated as the results are usually translated to the annihilation and scattering rates at more traditional Dark Matter-oriented experiments, thus a concordance approach is adapted. An overview of Dark Matter searches at the Large Hadron Collider will be covered in this paper.

The derivation of Srinivasan and Aiken (1988) for the mass transfer coefficient of carbon dioxide absorption into water droplets formed by controlled breakup of capillary jet was based on turbulent flow equations. This derivation was re-examined, taking into account the fact that the data used were in fact in the laminar flow regime. An alternative derivation and correlation is presented.

This work introduces an experimental test of the new proposal for a low–emittance muon accelerator (LEMMA). A low–emittance muon beam is obtained from the e$^+$ e$^-$ → μ$^+$ μ$^-$ annihilation process at the threshold energy of 45 GeV eliminating the need for a dedicated muon cooling system. A series of two testbeam campaigns were carried out at CERN to validate this concept. The experimental setup is presented together with first preliminary results from the obtained data.

The investigation of the energy frontier in physics requires novel concepts for future colliders. The idea of a muon collider is very appealing since it would allow to study particle collisions at up to tens of TeV energy, while offering a cleaner experimental environment with respect to hadronic colliders. One key element in the muon collider design is the low-emittance muon production. Recently,the Low EMittance Muon Accelerator (LEMMA) collaboration has explored the muon pair production close to its kinematic threshold by annihilating 45 GeV positrons with electrons in a low Z material target. In this configuration, muons are emerging from the target with a naturally low-emittance. In this paper we describe the performance of a system, to study this production mechanism, that consists in several segmented absorbers with alternating active layers composed of fast Cherenkov detectors together with a muon identification technique based on this detector. Passive layers were made of tungsten. We collected data corresponding to muon and electron beams produced at the H2 line in the North Area of the European Organization for Nuclear Research (CERN) in September 2018.

A study was undertaken to examine the esterification of FFA present in low grade feedstock - such as beef tallow - containing higher than 0.5% FFA with glycerol. The objective of this study is to investigate the feasibility of using glycerol as a pre-treatment step for low quality (high FFA content) raw material for biodiesel production and as an attempt to establish its reaction mechanism. Reaction of glycerol with triglycerides generates mono, di and tri-glycerides, which can be used in the manufacturing of biodiesel. Using these intermediate species as feedstock for biodiesel also expedites the transesterification rates. This will improve the economics of biodiesel production through the utilisation of glycerol as a low value by-product and also allow the use of low grade feedstock of high FFA content for biodiesel synthesis. Mixture of beef tallow containing known amounts of oleic acid (FFA) was reacted with glycerol in a 1.0L batch reactor with a 600rpm motorised stirrer, at 220oC for 4 hours. Experiments were conducted for beef tallow containing 15%, 25% and 50% of oleic acid by weight, and using glycerol to oil mixture molar ratios of 4, 6 and 8. Hypothetically, the esterification of FFA and the transesterification of triglycerides (beef tallow) occurs simultaneously in the reactor and it is the main objective to study these two reaction mechanisms. The FFA content in the beef tallow mixtures were successfully converted to mono-, di- and triglycerides with a maximum conversion of 93.9%. However, the presence of excess glycerol in the system did not improve the FFA conversion as expected. The transesterification reaction of triglycerides (beef tallow) was found to be competing and more favoured when an excess glycerol was employed. This has not been reported in past studies.

The muon collider represents one of the most promising solutions for a future machine exploring the high energy frontier, but several challenges due to the 2.2 $\mu$sec muon lifetime at rest have to be carefully considered. The LEMMA project is investigating the possibility of producing low emittance muon/antimuon pairs from the e$^+$e$^-$ annihilation process at threshold energy, resulting in small transverse emittance beams without any additional beam cooling. However most of the measurements available are performed at higher $\sqrt{s}$ values. It is therefore necessary to measure muons production in positron annihilation at threshold energy and compare the experimental results with the predictions in this specific energy regime. Apart from being a topic of physical interest by itself, these near to threshold measurements can have a sizeable impact on the estimation of the ultimate luminosity achievable in a muon collider with the LEMMA injection scheme.

This work introduces a new proposal for a low--emittance muon accelerator (LEMMA) in which muon beam is obtained from the e$^+$e$^-\rightarrow\mu^+\mu^-$ annihilation process with positrons at the threshold energy of 45 GeV. The experimental test beam setup implemented to validate this concept is presented together with preliminary results from the experimental data.

Dark Matter is a hypothetical particle proposed to explain the missing matter discovered from the cosmological observation. The motivation of Dark Matter is overwhelming, however those studies mainly deduced from gravitational interaction which does little to understand the underlying structure of the particle. On the other hand, the WIMP Miracle motivating dark matter production at weak scale, implying the possibility of detecting dark matter in LHC. Assuming Dark Matter is the only new particle accessible in LHC, it is expected to be pair produced in association with a Standard Model particles which can be inferred from the Transverse Missing Energy. Search for dark matter in monojet final state is a dominant channel in placing model-independent constrains on a set of effective operators coupling Dark Matter to Standard Model particle. However in the case of effective operators generated by the exchange of heavy scalar mediator, the inclusive Monojet channel is weakened due to the light quark suppression. An exclusive search on heavy quark final state such as bottom quark can improve the coupling strength of the Dark Matter process and reduce significantly the Standard Model backgrounds. A preliminary study on the search for Dark Matter produced in association with a bottom-quark is carried out as an extension to the Monojet search by requiring a b-tagged jet using the data collected by Compact Muon Solenoid detector in proton-proton collisions at center of mass energy of 8 TeV. The study shows that the data is consistent with Standard Model prediction and a limit is derived on the interaction scale and nucleon-dark matter scattering cross section.