Physics Goals Research Articles

Measurements of muon neutrino charged-current interactions by the MicroBooNE experiment

MicroBooNE is a 170 ton Liquid Argon Time Projection Chamber (LArTPC) experiment located at Fermi National Accelerator Laboratory. It has been operating in the Booster neutrino beam since October 2015 and is already demonstrating the superb imaging capabilities of LArTPC detectors. MicroBooNE is the first large LArTPC detector to be exposed to a high-intensity neutrino beam. Among its primary physics goals are precise measurements of muon neutrino charged-current (CC) interactions on argon. In order to analyse its high-statistics data, a suite of fully automated techniques have been developed that reconstruct the LArTPC images and separate muon neutrino CC interactions from their cosmic-ray and neutral current backgrounds. These proceedings will describe the reconstruction and selection of muon neutrino CC event candidates, and present measured distributions of the observed events based on 5e19 protons on target from the first MicroBooNE data-taking period.

Physics capabilities of the SNO+ experiment

SNO+ will soon enter its first phase of physics data-taking. The Canadian-based detector forms part of the SNOLAB underground facility, in a Sudbury nickel mine; its location providing more than two kilometres of rock overburden. We present an overview of the SNO+ experiment and its physics capabilities. Our primary goal is the search for neutrinoless double-beta decay, where our expected sensitivity would place an upper limit of 1.9 × 1026 y, at 90% CL, on the half-life of neutrinoless double-beta decay in 130Te. We also intend to build on the success of SNO by studying the solar neutrino spectrum. In the unloaded scintillator phase SNO+ has the ability to make precision measurements of the fluxes of low-energy pep neutrinos and neutrinos from the CNO cycle. Other physics goals include: determining the spectrum of reactor antineutrinos, to further constrain ; detecting neutrinos produced by a galactic supernova and investigating certain modes of nucleon decay.

Calibration of the SNO+ experiment

The main goal of the SNO+ experiment is to perform a low-background and high-isotope-mass search for neutrinoless double-beta decay, employing 780 tonnes of liquid scintillator loaded with tellurium, in its initial phase at 0.5% by mass for a total mass of 1330 kg of 130Te. The SNO+ physics program includes also measurements of geo- and reactor neutrinos, supernova and solar neutrinos. Calibrations are an essential component of the SNO+ data-taking and analysis plan. The achievement of the physics goals requires both an extensive and regular calibration. This serves several goals: the measurement of several detector parameters, the validation of the simulation model and the constraint of systematic uncertainties on the reconstruction and particle identification algorithms.SNO+ faces stringent radiopurity requirements which, in turn, largely determine the materials selection, sealing and overall design of both the sources and deployment systems. In fact, to avoid frequent access to the inner volume of the detector, several permanent optical calibration systems have been developed and installed outside that volume. At the same time, the calibration source internal deployment system was re-designed as a fully sealed system, with more stringent material selection, but following the same working principle as the system used in SNO. This poster described the overall SNO+ calibration strategy, discussed the several new and innovative sources, both optical and radioactive, and covered the developments on source deployment systems.

The design of the JUNO veto system

The Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose 20 kton liquid scintillator detector. The detector will be built in a 700 m deep underground laboratory, and its primary physics goal will be to determine the neutrino mass hierarchy. Due to the low background requirement of the experiment, a multi-veto system for cosmic muon detection and background reduction is designed. The volume outside the central detector is filled with pure water and equipped with 2000 MCP-PMTs (20 inches) to form a water Cherenkov detector for muon tagging. A Top Tracker system will be built by re-using the Target Tracker plastic scintillator modules of the OPERA experiment and will cover half of the top area. This will provide valuable information for cosmic muon induced 9Li/8He study.

Determination of the rigidity scale of the Alpha Magnetic Spectrometer

The Alpha Magnetic Spectrometer (AMS) experiment aboard the International Space Station has been collecting data since May 2011. The AMS silicon tracker accurately determines the trajectory of charged particles. Together with the magnet, it measures the rigidity (momentum per unit charge) of cosmic rays in the range from ∼0.5 GV to several TV. The precise knowledge of the rigidity scale is of critical importance to the physics goals of the experiment. The method to establish the tracker rigidity scale by using electron and positron events is presented. It allowed validation of the tracker alignment and estimation of the potential rigidity scale shifts. Using 5 years of AMS data, the tracker rigidity scale was measured with an accuracy of ±0.030(stat)±0.017(sys) TV−1, limited mostly by available positron statistics.

The Beam Energy Scan at the Relativistic Heavy Ion Collider

The Beam Energy Scan (BES) at the Relativistic Heavy Ion Collider (RHIC) is based on Au + Au collision data acquired between 2010 and 2014 at beam energies of = 7.7, 11.5, 14.5, 19.6, 27 and 39 GeV. These measurements constitute Phase-I of BES (also known as BES-I), and along with higher-energy data at 62.4 and 200 GeV, they allow the phase diagram of QCD matter to be probed. BES-I has three physics goals: investigation of a turning-off of the Quark-Gluon Plasma (QGP) signatures that are by now well established at higher energies, the search for a possible first-order phase transition between hadronic and QGP phases, and the search for a possible critical point. Several promising signals have been reported, but since RHIC luminosity decreases steeply as the beam energy is scanned down, statistical errors are excessively large at the lower BES-I energies where potentially novel phenomena are observed. In 2019 and 2020, BES-II will take data with large improvements in both RHIC luminosity and in detector performance.

Nanoscale superconducting memory based on the kinetic inductance of asymmetric nanowire loops

The demand for low-dissipation nanoscale memory devices is as strong as ever. As Moore’s law is staggering, and the demand for a low-power-consuming supercomputer is high, the goal of making information processing circuits out of superconductors is one of the central goals of modern technology and physics. So far, digital superconducting circuits could not demonstrate their immense potential. One important reason for this is that a dense superconducting memory technology is not yet available. Miniaturization of traditional superconducting quantum interference devices is difficult below a few micrometers because their operation relies on the geometric inductance of the superconducting loop. Magnetic memories do allow nanometer-scale miniaturization, but they are not purely superconducting (Baek et al 2014 Nat. Commun. 5 3888). Our approach is to make nanometer scale memory cells based on the kinetic inductance (and not geometric inductance) of superconducting nanowire loops, which have already shown many fascinating properties (Aprili 2006 Nat. Nanotechnol. 1 15; Hopkins et al 2005 Science 308 1762). This allows much smaller devices and naturally eliminates magnetic-field cross-talk. We demonstrate that the vorticity, i.e., the winding number of the order parameter, of a closed superconducting loop can be used for realizing a nanoscale nonvolatile memory device. We demonstrate how to alter the vorticity in a controlled fashion by applying calibrated current pulses. A reliable read-out of the memory is also demonstrated. We present arguments that such memory can be developed to operate without energy dissipation.

Preface: Special Topic on Frontiers in Molecular Scale Electronics

The electronic, mechanical, and thermoelectric properties of molecular scale devices have fascinated scientists across several disciplines in natural sciences and engineering. The interest is partially technological, driven by the fast miniaturization of integrated circuits that now have reached characteristic features at the nanometer scale. Equally important, a very strong incentive also exists to elucidate the fundamental aspects of structure-function relations for nanoscale devices, which utilize molecular building blocks as functional units. Thus motivated, a rich research field has established itself, broadly termed “Molecular Electronics,” that hosts a plethora of activities devoted to this goal in chemistry, physics, and electrical engineering. This Special Topic on Frontiers of Molecular Scale Electronics captures recent theoretical and experimental advances in the field.

Self-assembly of knots and links

Guiding the self-assembly of identical building blocks towards complex three-dimensional structures with a set of desired properties is a major goal in material science, chemistry and physics. A particularly challenging problem, especially explored in synthetic chemistry, is that of self-assembling closed structures with a target topology starting by simple geometrical templates. Here we overview and revisit recent advancements, based on stochastic simulations, where the geometry of rigid helical templates with functionalised sticky ends has been designed for self-assembling efficiently and reproducibly into a wide range of three-dimensional closed structures. Notably, these include non trivial topologies of links and knots, including the 819 knot that we had predicted to be highly encodable and that has only recently been obtained experimentally. By appropriately tuning the parameters that define the template shape, we show that, for fixed concentration of templates, the assembly process can be directed towards the formation of specific knotted and linked structures such as the trefoils, pentafoil knots, Hopf and Solomon links. More exotic and unexpected knots and links are also found. Our results should be relevant to the design of new protocols that can both increase and broaden the population of synthetise molecular knots and catenanes.

Emergent fuzzy geometry and fuzzy physics in four dimensions

A detailed Monte Carlo calculation of the phase diagram of bosonic mass-deformed IKKT Yang–Mills matrix models in three and six dimensions with quartic mass deformations is given. Background emergent fuzzy geometries in two and four dimensions are observed with a fluctuation given by a noncommutative U(1) gauge theory very weakly coupled to normal scalar fields. The geometry, which is determined dynamically, is given by the fuzzy spheres SN2 and SN2×SN2 respectively. The three and six matrix models are effectively in the same universality class. For example, in two dimensions the geometry is completely stable, whereas in four dimensions the geometry is stable only in the limit M⟶∞, where M is the mass of the normal fluctuations. The behaviors of the eigenvalue distribution in the two theories are also different. We also sketch how we can obtain a stable fuzzy four-sphere SN2×SN2 in the large N limit for all values of M as well as models of topology change in which the transition between spheres of different dimensions is observed. The stable fuzzy spheres in two and four dimensions act precisely as regulators which is the original goal of fuzzy geometry and fuzzy physics. Fuzzy physics and fuzzy field theory on these spaces are briefly discussed.

Silicon pixel R&D for CLIC

Challenging detector requirements are imposed by the physics goals at the future multi-TeV e+ e− Compact Linear Collider (CLIC). A single point resolution of 3 μm for the vertex detector and 7 μm for the tracker is required. Moreover, the CLIC vertex detector and tracker need to be extremely light weighted with a material budget of 0.2% X0 per layer in the vertex detector and 1–2% X0 in the tracker. A fast time slicing of 10 ns is further required to suppress background from beam-beam interactions. A wide range of sensor and readout ASIC technologies are investigated within the CLIC silicon pixel R&D effort. Various hybrid planar sensor assemblies with a pixel size of 25×25 μm2 and 55×55 μm2 have been produced and characterised by laboratory measurements and during test-beam campaigns. Experimental and simulation results for thin (50 μm–500 μm) slim edge and active-edge planar, and High-Voltage CMOS sensors hybridised to various readout ASICs (Timepix, Timepix3, CLICpix) are presented.

Results from the RHIC Beam Energy Scan

The first phase of the Beam Energy Scan (BES-I) program at the Relativistic Heavy Ion Collider (RHIC) is based on Au+Au collision data collected between 2010 and 2014 at center-of-mass energies sNN = 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV. The BES-I program has four physics goals: search for the turning off of the signatures of the Quark Gluon Plasma (QGP), the search for the possible first-order phase transition between hadronic gas and QGP, the search for the possible critical end point and the study of the transport properties of the strongly interacting matter as a function of the temperature T and baryon chemical potential μB . In this article, we briefly review and discuss the main results and their understanding from the BES-I program and future plans for the BES-II program (2019-2020).

FPGA-Based Tracklet Approach to Level-1 Track Finding at CMS for the HL-LHC

During the High Luminosity LHC, the CMS detector will need charged particle tracking at the hardware trigger level to maintain a manageable trigger rate and achieve its physics goals. The tracklet approach is a track-finding algorithm based on a road-search algorithm that has been implemented on commercially available FPGA technology. The tracklet algorithm has achieved high performance in track-finding and completes tracking within 3.4 $\mu$s on a Xilinx Virtex-7 FPGA. An overview of the algorithm and its implementation on an FPGA is given, results are shown from a demonstrator test stand and system performance studies are presented.

Recent progress of high-coherence ultrafast electron sources

Microscopic dynamic process of material structure which determines the inherent property of substance takes place on a molecular and atomic scale. Understanding the underlying mechanisms of the various fundamental processes has always been the goal of chemistry, physics, biology and materials science. With Ahmed Zewail's pioneering work in the field of femtoscience, the time-resolved electron diffraction, combining the pump-probe and electron diffraction technique, has become an excellent tool with sufficient temporal precision to directly deliver insights into ultrafast phenomena on an atomic level. Central to this method is the ultrashort electron pulses generated from a metal photocathode. However, up to now, owing to the initial size, effective temperature, energy dispersion and inherent coulomb repulsion of electron source, the state-of-the-art transverse coherence of conventional planar cathode photoemission source is still insufficient to resolve the complex chemical and biological organic molecules. Hence, in recent years, many efforts have focused on developing high-coherence ultrashort electron sources. The main methods include minimizing the initial beam size, weakening the space charge, reducing the effective temperature, and matching the photon energy of laser with the work function of cathode material. In this review, we firstly summarize the history and advantages of the electron probe, secondly sketch out the figure of merit of the electron source. And then taking coherence as the main line, we review recent progress in common planar photoemission sources, and discuss the latest development of tip-based electron sources and cold atom electron sources in terms of their generation mechanisms, unique properties and research progress. Finally, the development and future applications of the diffraction technique are prospected. In general, the high-coherence length of photoelectric surface source is often at the expense of the current. The needle source can obtain the highest coherence length, but it is similar to femtosecond single-electron pulse, which must be less than one electron per pulse to eliminate the electron-electron coulomb interaction. Thus, a diffraction pattern can only be formed by accumulating millions of shots. The cold atom electron source, which has a transverse coherence greater than 15 nm and a peak brightness similar to conventional electron source's, is sufficient for some molecular systems in biochemistry. In short, with the improvement of coherence and the emergence of new electron sources, it is possible to reveal complex organic and inorganic structures, especially the dynamic behaviors of protein, and promote the understanding of nanoscale energy transport, solid-liquid and solid-gas interfacial dynamics and chemical reaction and so on. High-coherence electron sources not only serve in the diffraction experiments, but also play a key role in developing ultrafast electron microscopy, coherent diffraction imaging and ptychography.

Spiral Wave Law Is Involved in the Unification of Four Fundamental Forces and the Origin and the Evolution of the Universe

A long-term goal of theoretical physics is to develop a single simple theory or model that would unify the four known fundamental forces (or interactions) and give explanations for the origin and the evolution of the Universe. Here a “spiral wave law” has been proposed based on the previous studies that a consistent universe field presents various forms of spiral (helical) wave motions at the speed of light (c), and therefore, a mathematical equation for the relationship between the radius of a spiral wave motion (r) and its wave length (λ) is derived including a simplified formula ( or ), which could provide a novel explanation for the origin and the evolution of the Universe, and the space-time relationships. This model may give a new way for the unification of four fundamental forces and determine the moving properties of galaxies and basic particles, and the propagation characteristics of electromagnetic waves at the large or small scale.

Recent results from the NA61/SHINE strong interaction physics programme

The main physics goals of the NA61/SHINE programme on strong interactions are the study of the properties of the onset of deconfinement and the search for signatures of the critical point of strongly interacting matter. For this purpose a scan of the two dimensional phase diagram ($T$-$\mu_{B}$) is being performed at the SPS by measurements of hadron production in nucleus-nucleus collisions as a function of collision energy and system size. This contribution presents intriguing results on the energy dependence of hadron spectra and yields in inelastic p+p and centrality selected Be+Be and Ar+Sc collisions. In particular, the energy dependence of the signals of deconfinement, the "horn", "step" and "kink", and new results on fluctuations and correlations are shown and compared with the corresponding data of other experiments and model predictions.

Alignment calibration and performance study of the STAR PXL detector

We report in this paper the alignment calibration of the STAR pixel detector (PXL) prototype for the RHIC 2013 run and performance study of the full PXL detector installed and commissioned in the RHIC 2014 run. PXL detector is the innermost two silicon layers of the STAR heavy flavor tracker aiming at high-precision reconstruction of secondary decay vertex of heavy flavor particles. To achieve the physics goals, the calibration work was done on the detector with high precision. A histogram-based method was successfully applied for the alignment calibration, and the detector efficiency after alignment was studied using both \(p+p\) collision data and cosmic ray data.

Operational experience with the CMS pixel detector in LHC Run II

The CMS pixel detector was repaired successfully, calibrated and commissioned for the second run of Large Hadron Collider during the first long shutdown between 2013 and 2015. The replaced pixel modules were calibrated separately and show the expected behavior of an un-irradiated detector. In 2015, the system performed very well with an even improved spatial resolution compared to 2012. During this time, the operational team faced various challenges including the loss of a sector in one half shell which was only partially recovered. In 2016, the detector is expected to withstand instantaneous luminosities beyond the design limits and will need a combined effort of both online and offline teams in order to provide the high quality data that is required to reach the physics goals of CMS. We present the operational experience gained during the second run of the LHC and show the latest performance results of the CMS pixel detector.

Efficient time-sampling method in Coulomb-corrected strong-field approximation.

One of the main goals of strong-field physics is to understand the complex structures formed in the momentum plane of the photoelectron. For this purpose, different semiclassical methods have been developed to seek an intuitive picture of the underlying mechanism. The most popular ones are the quantum trajectory Monte Carlo (QTMC) method and the Coulomb-corrected strong-field approximation (CCSFA), both of which take the classical action into consideration and can describe the interference effect. The CCSFA is more widely applicable in a large range of laser parameters due to its nonadiabatic nature in treating the initial tunneling dynamics. However, the CCSFA is much more time consuming than the QTMC method because of the numerical solution to the saddle-point equations. In the present work, we present a time-sampling method to overcome this disadvantage. Our method is as efficient as the fast QTMC method and as accurate as the original treatment in CCSFA. The performance of our method is verified by comparing the results of these methods with that of the exact solution to the time-dependent Schrödinger equation.

Conceptual design studies for a CEPC detector

The physics potential of the Circular Electron Positron Collider (CEPC) can be significantly strengthened by two detectors with complementary designs. A promising detector approach based on the Silicon Detector (SiD) designed for the International Linear Collider (ILC) is presented. Several simplifications of this detector for the lower energies expected at the CEPC are proposed. A number of cost optimizations of this detector are illustrated using full detector simulations. We show that the proposed changes will enable one to reach the physics goals at the CEPC.