Jonathon Langford

The discovery of the Higgs boson in 2012, by the ATLAS and CMS experiments, was a success achieved with only a percent of the entire dataset foreseen for the LHC. It opened a landscape of possibilities in the study of Higgs boson properties, Electroweak Symmetry breaking and the Standard Model in general, as well as new avenues in probing new physics beyond the Standard Model. Six years after the discovery, with a conspicuously larger dataset collected during LHC Run 2 at a 13 TeV centre-of-mass energy, the theory and experimental particle physics communities have started a meticulous exploration of the potential for precision measurements of its properties. This includes studies of Higgs boson production and decays processes, the search for rare decays and production modes, high energy observables, and searches for an extended electroweak symmetry breaking sector. This report summarises the potential reach and opportunities in Higgs physics during the High Luminosity phase of the LHC, with an expected dataset of pp collisions at 14 TeV, corresponding to an integrated luminosity of 3 ab$^{-1}$. These studies are performed in light of the most recent analyses from LHC collaborations and the latest theoretical developments. The potential of an LHC upgrade, colliding protons at a centre-of-mass energy of 27 TeV and producing a dataset corresponding to an integrated luminosity of 15 ab$^{-1}$, is also discussed.

Recent experiments on the Tokamak Fusion Test Reactor have afforded an opportunity to measure the retention of tritium in a graphite limiter that is subject to erosion, codeposition, and high neutron flux. The tritium was injected by both gas puff and neutral beams. The isotopic mix of hydrogenic recycling was measured spectroscopically and the tritium fraction T/(H+D+T) transiently increased to as high as 75%. Some tritium was pumped out during the experimental run and some removed in a subsequent campaign using various clean-up techniques. While the short term retention of tritium was high, various conditioning techniques were successful in removing ≊8000 Ci and restoring the tritium inventory to a level well below the administrative limit.

The Tokamak Fusion Test Reactor (TFTR) has been operating safely and routinely with deuterium-tritium fuel for more than two years. In this time, TFTR has produced a number of record breaking results including core fusion power, ∼ 2 MW/m3, comparable to that expected for ITER. Advances in wall conditioning via lithium pellet injection have played an essential role in achieving these results. Deuterium-tritium operation has also provided a special opportunity to address the two years of operation was approximately 40%. Recently the in-torus tritium inventory was reduced by half through a combination of glow discharge cleaning, moist-air soaks, and plasma discharge cleaning. The tritium inventory is not a constraint in continued operations. Recent results from TFTR in the context of plasma wall interactions and deuterium-tritium issues are presented.

A measurement of the Higgs boson Yukawa coupling to the top quark is presented using proton-proton collision data at $\sqrt{s} =$ 13 TeV, corresponding to an integrated luminosity of 137 fb$^{-1}$, recorded with the CMS detector. The coupling strength with respect to the standard model value, $Y_\mathrm{t}$, is determined from kinematic distributions in $\mathrm{t\bar{t}}$ final states containing ee, $μμ$, or e$μ$ pairs. Variations of the Yukawa coupling strength lead to modified distributions for $\mathrm{t\bar{t}}$ production. In particular, the distributions of the mass of the $\mathrm{t\bar{t}}$ system and the rapidity difference of the top quark and antiquark are sensitive to the value of $Y_\mathrm{t}$. The measurement yields a best fit value of $Y_\mathrm{t} =$ 1.16 $^{+0.24}_{-0.35}$, bounding $Y_\mathrm{t}$ $\lt$ 1.54 at a 95% confidence level.

A search for exclusive two-photon production via photon exchange in proton-proton collisions, pp $\to$ p$γγ$p with intact protons, is presented. The data correspond to an integrated luminosity of 9.4 fb$^{-1}$ collected in 2016 using the CMS and TOTEM detectors at a center-of-mass energy of 13 TeV at the LHC. Events are selected with a diphoton invariant mass above 350 GeV and with both protons intact in the final state, to reduce backgrounds from strong interactions. The events of interest are those where the invariant mass and rapidity calculated from the momentum losses of the forward-moving protons matches the mass and rapidity of the central, two-photon system. No events are found that satisfy this condition. Interpreting this result in an effective dimension-8 extension of the standard model, the first limits are set on the two anomalous four-photon coupling parameters. If the other parameter is constrained to its standard model value, the limits at 95% CL are $\lvertζ_1\rvert$ $\lt$ 2.9 $\times$ 10$^{-13}$ GeV$^{-4}$ and $\lvertζ_2\rvert$ $\lt$ 6.0 $\times$ 10$^{-13}$ GeV$^{-4}$.

The TPS is a hydrogen isotope separation system put into operation within the Tokamak Fusion Test Reactor (TFTR) tritium systems. The TPS extracts and purifies tritium from TFTR plasma exhausts, then returns it for reuse as plasma fueling. The TPS operates in two stages: separation of hydrogen isotopes from the TFTR plasma waste effluents via a Pd/Ag diffuser; and separation of hydrogen isotopes via a multi-stage cryogenic distillation system. TPS interfaces with the Gas Holding Tanks (GHTs), the Torus Cleanup System (TCS), the plant stack via the Tritiated Vent System, the Tritium Storage and Delivery System, and the Tritium Storage and Delivery Cleanup System (TSDCS). Commissioning of TPS included: operational testing at CFFTP and at Princeton, thorough helium and tritium leak checks a trial run with a limited tritium inventory (1000 Ci), and a 10000 Ci integrated systems test.

A new experiment to quantitatively measure neutrons induced by cosmic-ray muons in selected high-Z materials is introduced. The design of the Muon-Induced Neutron Indirect Detection EXperiment, MINIDEX, and the results from its first data taking period are presented as well as future plans. Neutron production in high-Z materials is of particular interest as such materials are used for shielding in low-background experiments. The design of next-generation large-scale experiments searching for neutrinoless double beta decay or direct interactions of dark matter requires reliable Monte Carlo simulations of background induced by muon interactions. The first five months of operation already provided a valuable data set on neutron production and neutron transport in lead. A first round of comparisons between MINIDEX data and Monte Carlo predictions obtained with a GEANT4-based package for two different sets of physics models of relevance for neutron production by muons is presented. The rate of muon-induced events is overall a factor three to four higher in data than predicted by the Monte Carlo packages. In addition, the time evolution of the muon-induced signal is not well described by the simulations.

Results from the most recent statistical combinations of Higgs boson measurements across decay channels by the ATLAS and CMS experiments are presented.Both analyses use LHC proton-proton collision data recorded at √ = 13 TeV with the respective detectors, where the ATLAS (CMS) analysis combines measurements with integrated luminosities ranging from 24.5-79.8(35.9-137) fb -1 depending on the decay channel.Measurements of cross sections, signal strengths and coupling modifiers are reported, alongside an interpretation using effective field theory.

A search for long-lived particles (LLPs) produced in association with a Z boson is presented. The study is performed using data from proton-proton collisions with a center-of-mass energy of 13 TeV recorded by the CMS experiment during 2016-2018, corresponding to an integrated luminosity of 117 fb$^{-1}$. The LLPs are assumed to decay to a pair of standard model quarks that are identified as displaced jets within the CMS tracker system. Triggers and selections based on Z boson decays to electron or muon pairs improve the sensitivity to light LLPs (down to 15 GeV). This search provides sensitivity to beyond the standard model scenarios which predict LLPs produced in association with a Z boson. In particular, the results are interpreted in the context of exotic decays of the Higgs boson to a pair of scalar LLPs (H $\to$ SS). The Higgs boson decay branching fraction is constrained to values less than 6% for proper decay lengths of 10-100 mm and for LLP masses between 40 and 55 GeV. In the case of low-mass ($\approx$15 GeV) scalar particles that subsequently decay to a pair of b quarks, the search is sensitive to branching fractions $\mathcal{B}$(H $\to$ SS) $\lt$ 20% for proper decay lengths of 10-50 mm. The use of associated production with a Z boson increases the sensitivity to low-mass LLPs of this analysis with respect to gluon fusion searches. In the case of 15 GeV scalar LLPs, the improvement corresponds to a factor of 2 at a proper decay length of 30 mm.

A measurement of inclusive four-jet production in proton-proton collisions at a center-of-mass energy of 13\TeV is presented. The transverse momenta of jets within $\lvert\eta\rvert \lt$ 4.7 reach down to 35, 30, 25, and 20 GeV for the first-, second-, third-, and fourth-leading jet, respectively. Differential cross sections are measured as functions of the jet transverse momentum, jet pseudorapidity, and several other observables that describe the angular correlations between the jets. The measured distributions show sensitivity to different aspects of the underlying event, parton shower, and matrix element calculations. In particular, the interplay between angular correlations caused by parton shower and double-parton scattering contributions is shown to be important. The double-parton scattering contribution is extracted by means of a template fit to the data, using distributions for single-parton scattering obtained from Monte Carlo event generators and a double-parton scattering distribution constructed from inclusive single-jet events in data. The effective double-parton scattering cross section is calculated and discussed in view of previous measurements and of its dependence on the models used to describe the single-parton scattering background.

Simplified Template Cross Sections (STXS) have been adopted by the LHC experiments as a common framework for Higgs measurements. Their purpose is to reduce the theoretical uncertainties that are directly folded into the measurements as much as possible, while at the same time allowing for the combination of the measurements between different decay channels as well as between experiments. We report the complete, revised definition of the STXS kinematic bins (stage 1.1), which are to be used for the upcoming measurements by the ATLAS and CMS experiments using the full LHC Run 2 datasets. The main focus is on the three dominant Higgs production processes, namely gluon-fusion, vector-boson fusion, and in association with a vector boson. We also comment briefly on the treatment of other production modes.

Simplified Template Cross Sections (STXS) have been adopted by the LHC experiments as a common framework for Higgs measurements. Their purpose is to reduce the theoretical uncertainties that are directly folded into the measurements as much as possible, while at the same time allowing for the combination of the measurements between different decay channels as well as between experiments. We report the complete, revised definition of the STXS kinematic bins (stage 1.1), which are to be used for the upcoming measurements by the ATLAS and CMS experiments using the full LHC Run 2 datasets. The main focus is on the three dominant Higgs production processes, namely gluon-fusion, vector-boson fusion, and in association with a vector boson. We also comment briefly on the treatment of other production modes.

The Tokamak Fusion Test Reactor (TFTR) was supplied over 7.5/spl times/10/sup 5/ Curies combined through the vacuum vessel and Neutral Beam (NB) tritium gas injectors. Out of this quantity approximately 29,530 Curies (Ci) has entered the vacuum vessel as neutral atoms, including cold streaming gas and 20,270 Ci as direct vessel injection. TFTR has had two short term outages during DT operations Outage 1('95) and 2('96), plus the final shutdown, Outage 3 ('97), after DT operations in which tritium held up in the vessel and NB's has been actively recovered. The respective recovery values are: Outage (No.1) 8,257 Ci, (No.2) 4,668 Ci and (No.3 final shutdown) 3965 Ci. The methods for recovering this included: 1. Vessel baking to 150/spl deg/C during Deuterium Glow Discharge Cleaning (DGDC), 2. Helium/Oxygen GDC (HeOGDC), 3. Pulse Discharge Cleaning (PDC), 4. Continuous moist air purges and 5. Dry air, moist air (40% RH), and deuterium vent/soak/pump. The processes showing equivalent efficiency are the GDC, HeOGDC, and moist air purges at elevated temperatures. A small amount of tritium is introduced in the vessel at high energy through the NE /spl sim/3% relative to that supplied to the beam lines and /spl sim/1/2 of this is essentially buried in the carbon composite tiles and has a longer time constant for removal than the direct vessel injected tritium. Data shows that the bulk of surface tritium is removed by active cleaning methods and in the presence of moist air purges (room air at /spl sim/40% relative humidity) combined with elevated temperatures which accelerates its removal. Continuous outgassing at low levels in the presence of moist air (750 Torr) follows the active tritium removal processes and moist air purges. The TFTR tritium removal processes and their corresponding removal rates and quantities are reported. An ion chamber is used to measure the tritium accumulated in the Gas Holding Tanks (GHT) from the vessel throughout all the active and passive processes. The ion chamber compensation for varying gas mixtures was found to be critical in accurate measurement of this recovery and is discussed.

The Tokamak Fusion Test Reactor which is the progenitor for full D-T operating tokamaks has successfully processed > 81 grams of tritium in a safe and efficient fashion. Many of the fundamental operational techniques associated with the safe movement of tritium through the TFTR facility were developed over the course of many years at DOE tritium facilities (LANL, LLNL, SRS, Mound). In the mid 1980's The Tritium Systems Test Assembly (TSTA) at LANL began reporting operational techniques for the safe handling of tritium, and became a major conduit for the transfer of safe tritium handling technology from DOE weapons laboratories to non-weapon facilities. TFTR has built on many of the TSTA operational techniques and has had the opportunity of performing and enhancing these techniques at America's first operational D-T fusion reactor. This paper will discuss negative pressure employing “elephant trunks” in the control and mitigation of tritium contamination at the TFTR facility, and the interaction between contaminated line operations and Δ pressure control. In addition the strategy employed in managing the movement of tritium through TFTR while maintaining an active tritium inventory of < 50,000 Ci will be discussed.

In April of 1993 PPPL embarked upon the tritium operations phase of the TFTR project. Four years later, in the early morning of April 4, 1997, TFTR pulsed with tritium for the last time. In those four years, approximately 1 mega Curie of tritium was processed, and a Tritium Purification System (TPS) was commissioned. During this period >1,000 invasive (line break) operations were performed with <425 Cl of tritium released to the environment. The highly successful operation of the TFTR tritium systems was due to a corporate culture which stressed the importance of safe operations and the commitment by the TFTR staff to conduct nuclear operations in an efficient and safe fashion. The operation of TFTR as a nuclear facility employed 1,096 detailed operations procedures which were adhered to by all nuclear operations personnel and included a clear chain of command for nuclear operations.

The strong Coulomb field created in ultrarelativistic heavy ion collisions is expected to produce a rapidity-dependent difference ($\Delta v_2$) in the second Fourier coefficient of the azimuthal distribution (elliptic flow, $v_2$) between $\mathrm{D}^0$ ($\mathrm{\bar{u}c}$) and $\overline{\mathrm{D}}^0$ ($\mathrm{u\bar{c}}$) mesons. Motivated by the search for evidence of this field, the CMS detector at the LHC is used to perform the first measurement of $\Delta v_2$. The rapidity-averaged value is found to be $\langle\Delta v_2 \rangle =$ 0.001 $\pm$ 0.001 (stat) $\pm$ 0.003 (syst) in PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV. In addition, the influence of the collision geometry is explored by measuring the $\mathrm{D}^0$ and $\overline{\mathrm{D}}^0$ mesons $v_2$ and triangular flow coefficient ($v_3$) as functions of rapidity, transverse momentum ($p_\mathrm{T}$), and event centrality (a measure of the overlap of the two Pb nuclei). A clear centrality dependence of prompt $\mathrm{D}^0$ meson $v_2$ values is observed, while the $v_3$ is largely independent of centrality. These trends are consistent with expectations of flow driven by the initial-state geometry.

The Tritium Purification System (TPS) is a hydrogen isotope separation system put into operation within the Tokamak Fusion Test Reactor (TFTR) Tritium Systems. The TPS operates in two stages: extraction of hydrogen isotopes from the TFTR plasma waste effluents via a Palladium/Silver diffuser; and separation of hydrogen isotopes via a multiple-stage cryogenic distillation system.Commissioning of TPS included: Operational testing at Canadian Fusion Fuels Technology Project (CFFTP) and at Princeton, thorough helium and tritium leakchecks, trial run with a limited tritium inventory (1 kCi), and an integrated systems test using 10 kCi of tritium. The integrated systems test, which was started in April of 1995 took approximately eight months to perform. Several “infant mortality” failures, requiring numerous line breaks into highly contaminated piping, were safely performed. On December 18, 1995 the TPS delivered its first batch of purified tritium product.This paper provides a brief overview of the TPS design and theory of operation. The focus of this paper is the commissioning, operation, performance and maintenance of the device. Lessons learned in maintenance and repair of the TPS are also addressed.

Abstract : The report discusses the addition of the existing magnetic model suspension system to the 12- by 12-in. hypersonic Tunnel E. The addition requires an unusually long test section for studying undisturbed model wake. With the magnetic suspension system, the model can be positioned in any axial direction, and the model angle of incidence can be changed in either positive or negative direction. The proposed model positioning sensor system will consist of a gamma or X-ray source and ion detectors that will allow the model position to be controlled without need for optical ports in the tunnel wall. The instrumentation for and overall test capabilities with this magnetic suspension system in Tunnel E are discussed, and proposals for future improvements in the capabilities of the system are made.

Measurements of the inclusive and differential fiducial cross sections of the Higgs boson are presented, using the $\tau$ lepton decay channel. The differential cross sections are measured as functions of the Higgs boson transverse momentum, jet multiplicity, and transverse momentum of the leading jet in the event if any. The analysis is performed using proton-proton data collected with the CMS detector at the LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb$^{-1}$. These are the first differential measurements of the Higgs boson cross section in the final state of two $\tau$ leptons, and they constitute a significant improvement over measurements in other final states in events with a large jet multiplicity or with a Lorentz-boosted Higgs boson.

The associated production of a W and a Z boson is studied in final states with multiple leptons produced in proton-proton (pp) collisions at a centre-of-mass energy of 13 TeV using 137 fb$^{-1}$ of data collected with the CMS detector at the LHC. A measurement of the total inclusive production cross section yields $\sigma_{\text{tot}}$(pp $\to$ WZ) = 50.6 $\pm$ 0.8 (stat) $\pm$ 1.5 (syst) $\pm$ 1.1 (lum) $\pm$ 0.5 (thy) pb. Measurements of the fiducial and differential cross sections for several key observables are also performed in all the final-state lepton flavour and charge compositions with a total of three charged leptons, which can be electrons or muons. All results are compared with theoretical predictions computed up to next-to-next-to-leading order in quantum chromodynamics plus next-to-leading order in electroweak theory and for various sets of parton distribution functions. The results include direct measurements of the charge asymmetry and the W and Z vector boson polarization. The first observation of longitudinally polarized W bosons in WZ production is reported. Anomalous gauge couplings are searched for, leading to new constraints on beyond-the-standard-model contributions to the WZ triple gauge coupling.

A search for new long-lived particles decaying to leptons using proton-proton collision data produced by the CERN LHC at $\sqrt{s}$ = 13 TeV is presented. Events are selected with two leptons (an electron and a muon, two electrons, or two muons) that both have transverse impact parameter values between 0.01 and 10 cm and are not required to form a common vertex. Data used for the analysis were collected with the CMS detector in 2016, 2017, and 2018, and correspond to an integrated luminosity of 118 (113) fb$^{-1}$ in the ee channel (e$\mu$ and $\mu\mu$ channels). The search is designed to be sensitive to a wide range of models with displaced e$\mu$, ee, and $\mu\mu$ final states. The results constrain several well-motivated models involving new long-lived particles that decay to displaced leptons. For some areas of the available phase space, these are the most stringent constraints to date.

The CMS experiment at the LHC has measured the differential cross sections of Z bosons decaying to pairs of leptons, as functions of transverse momentum and rapidity, in lead-lead collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The measured Z boson elliptic azimuthal anisotropy coefficient is compatible with zero, showing that Z bosons do not experience significant final-state interactions in the medium produced in the collision. Yields of Z bosons are compared to Glauber model predictions and are found to deviate from these expectations in peripheral collisions, indicating the presence of initial collision geometry and centrality selection effects. The precision of the measurement allows, for the first time, for a data-driven determination of the nucleon-nucleon integrated luminosity as a function of lead-lead centrality, thereby eliminating the need for its estimation based on a Glauber model.

Measurements of differential and double-differential cross sections of top quark pair ($\text{t}\overline{\text{t}}$) production are presented in the lepton+jets channels with a single electron or muon and jets in the final state. The analysis combines for the first time signatures of top quarks with low transverse momentum $p_\text{T}$, where the top quark decay products can be identified as separated jets and isolated leptons, and with high $p_\text{T}$, where the decay products are collimated and overlap. The measurements are based on proton-proton collision data at $\sqrt{s} = $ 13 TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 137 fb$^{-1}$. The cross sections are presented at the parton and particle levels, where the latter minimizes extrapolations based on theoretical assumptions. Most of the measured differential cross sections are well described by standard model predictions with the exception of some double-differential distributions. The inclusive $\text{t}\overline{\text{t}}$ production cross section is measured to be $\sigma_{\text{t}\overline{\text{t}}} = $ 791 $\pm$ 25 pb, which constitutes the most precise measurement in the lepton+jets channel to date.

In the summer/fall of 1996 after nearly three years of D-T operations, TFTR underwent an extended outage during which large port covers were removed from the vacuum vessel in order to complete upgrades to the tokamak. Following the venting of the torus, a three tier system was developed for the outage in order to reduce and control the free tritium in the vacuum vessel so as to minimize the exposure to personnel during port cover removal and reinstallation. The first phase of the program to reduce the free tritium consisted of direct flowthrough of room air through the vacuum vessel to the molecular sieve beds using the Torus Cleanup System. Real time measurements of the effluent tritium concentration were used to derive the amount of tritium removed from the torus. Once the free tritium in the vessel had been reduced to approximately 50 Ci, a second phase was initiated using a 55 Gallon Drum Bubbler System for the direct processing of the vacuum vessel to further lower the tritium level in the torus. Tritium oxide is absorbed by the bubbler system with the exhaust vented to one of the tritium monitored HVAC ventilation stacks. To preclude the release of tritium to the Test Cell location of TFTR and to minimize the exposure of workers, a variable flow exhaust system was employed in order to maintain a negative pressure in the vacuum vessel between 0.05" and 1.5" w.c. during the removal of port covers ranging in size from approximately 5 to 1000 in(superscript2). These systems were completely successful in reducing and controlling the free tritium in TFTR and were instrumental in maintaining ALARA (As Low As Reasonably Achievable) exposures to tritium during the 1996 outage. These systems are again being utilized during the safe shutdown and decommissioning of TFTR which commenced in April of 1997. This paper describes in detail the configuration of these systems and the data obtained during the outage and safe shutdown of TFTR.