Precision Frontier Research Articles

Alignment and Calibration of the Belle II Detector

In spring 2018 the SuperKEKB electron-positron collider at High Energy Accelerator Research Organization (KEK, Tsukuba, Japan) will deliver its first collisions to the Belle II experiment. The aim of Belle II is to collect a data sample 50 times larger than the previous generation of BFactories taking advantage of the unprecedented SuperKEKB design luminosity of 8×1035cm-2s-1. The Belle II detector will allow to conduct precise measurements in the harsh collider environment, probing for signs of physics beyond the standard model at the precision frontier. In order to deliver data suitable for physics analysis, the detector has to be properly calibrated on a regular basis. Among other calibrations the detector alignment plays a key role. For example, precise measurements of time dependent CP-violation rely on the accurate alignment of the new vertex detector, as well as on the determination of the beamspot position and size. To automate the calibration procedures and manage the large amount of data and processing power needed for detector calibration, a software framework has been developed which allows to define the complete workflow and to execute it on a computing cluster. The framework integrates the Millepede II algorithm to solve the large minimization problem emerging in the track-based alignment and calibration of the pixel and strip detector, the central drift chamber, and the muon system. The first collision data will allow to test and to further improve and tune the alignment and calibration procedures. Although the vertexing capabilities will be limited due to the installation of only a small slice of the full vertex detector, the commissioning phase will allow to test most of the alignment procedure features and to prepare for the full operation. We will present the results achieved during the first data taking, the experience gained and the plans for the first physics run with the full detector.

Applications of Machine Learning at BESIII

BESIII is an experiment at the high precision frontier of hadron physics in τ-charm region. Machine learning techniques have been used to improve the performance of BESIII software. In this proceeding, we present novel approaches with XGBoost for multi-dimensional distribution reweighting, muon identification and cluster reconstruction for CGEM (Cylindrical Gas Electron Multiplier) inner tracker.

Calibration and Alignment Framework for the Belle II detector

The Belle II experiment [1] is approaching its first physics run in 2018. Its full capability to operate at the precision frontier will need not only excellent performance of the SuperKEKB accelerator and the detector, but also advanced calibration methods combined with data quality monitoring. To deliver data in a form suitable for analysis as soon as possible, an automated Calibration Framework (CAF) has been developed. The CAF integrates various calibration algorithms and their input collection methods for event-level data. It allows execution of the calibration workflow using different backends from local machines to a computing cluster, resolution of dependencies among algorithms, management of the produced calibration constants, and database access across possible iterations. One of the main algorithms fully integrated in the framework uses Millepede II [2] to solve a large minimization problem emerging in the track-based alignment and calibration of the pixel and strip detector, the central drift chamber, and the muon system. Advanced fitting tools are used to properly describe the detector material and magnetic field and include measurements of different sub-detectors into a single global fit performed by Millepede. This talk will present the design of the calibration framework, the integration of the Millepede calibration, and its current performance.

The First Direct Detection of Gravitational Waves Opens a Vast New Frontier in Astronomy

The first direct detection of gravitational waves (GWs), announced on 11 February 2016, has opened a vast new frontier in astronomy. Albert Einstein predicted the existence of these waves about a century ago as a consequence of his general theory of relativity. Radio astronomy observations of the binary pulsar system PSR 1913 + 16 over a 20 year period beginning in 1975 provided strong observational evidence that gravitational waves carried energy away from the orbits of neutron stars at precisely the level predicted by general relativity (GR). This relentless conversion of orbital energy into gravitational wave energy causes binary orbits to decay until the objects eventually collide and merge. The frontier of precision measurement science, using laser interferometers, was pushed for more than four decades to achieve this first direct detection, marking a milestone in experimental physics and engineering. Even more significantly, this milestone also opens a new window onto our universe and a completely new kind of astronomy to explore.

Energy helps accuracy: Electroweak precision tests at hadron colliders

We show that high energy measurements of Drell–Yan at the LHC can serve as electroweak precision tests. Dimension-6 operators, from the Standard Model Effective Field Theory, modify the high energy behavior of electroweak gauge boson propagators. Existing measurements of the dilepton invariant mass spectrum, from neutral current Drell–Yan at 8 TeV, have comparable sensitivity to LEP. We propose measuring the transverse mass spectrum of charged current Drell–Yan, which can surpass LEP already with 8 TeV data. The 13 TeV LHC will elevate electroweak tests to a new precision frontier.

Helicity and nuclear β decay correlations

We present simple derivations of nuclear β-decay correlations with an emphasis on the special role of helicity. This topic provides a good opportunity to teach students about helicity and chirality in particle physics with exercises that use simple aspects of quantum mechanics. In addition, this paper serves as an introduction to nuclear β-decay correlations from both a theoretical and experimental perspective. This article can be used to introduce students to ongoing experiments searching for hints of new physics in the low-energy precision frontier.

Sensitivity to light weakly-coupled new physics at the precision frontier

Precision measurements of rare particle physics phenomena (flavor oscillations and decays, electric dipole moments, etc.) are often sensitive to the effects of new physics encoded in higher-dimensional operators with Wilson coefficients given by $\mathrm{C}/({\mathrm{\ensuremath{\Lambda}}}_{\mathrm{NP}}{)}^{n}$, where C is dimensionless, $n\ensuremath{\ge}1$, and ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{NP}}$ is an energy scale. Many extensions of the Standard Model predict that ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{NP}}$ should be at the electroweak scale or above, and the search for new short-distance physics is often stated as the primary goal of experiments at the precision frontier. In rather general terms, we investigate the alternative possibility---$\mathrm{C}\ensuremath{\ll}1$, and ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{NP}}\ensuremath{\ll}{m}_{W}$---to identify classes of precision measurements sensitive to light new physics (hidden sectors) that do not require an ultraviolet completion with additional states at or above the electroweak scale. We find that hadronic electric dipole moments, lepton number and flavor violation, nonuniversality, as well as lepton $g\ensuremath{-}2$ can be induced at interesting levels by hidden sectors with light degrees of freedom. In contrast, many hadronic flavor- and baryon number-violating observables, and precision probes of charged currents, typically require new physics with ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{NP}}\ensuremath{\gtrsim}{m}_{W}$. Among the leptonic observables, we find that a nonzero electron electric dipole moment near the current level of sensitivity would point to the existence of new physics at or above the electroweak scale.

Probing primordial non-Gaussianity via iSW measurements with SKA continuum surveys

The Planck CMB experiment has delivered the best constraints so far on primordial non-Gaussianity, ruling out early-Universe models of inflation that generate large non-Gaussianity. Although small improvements in the CMB constraints are expected, the next frontier of precision will come from future large-scale surveys of the galaxy distribution. The advantage of such surveys is that they can measure many more modes than the CMB—in particular, forthcoming radio surveys with the Square Kilometre Array will cover huge volumes. Radio continuum surveys deliver the largest volumes, but with the disadvantage of no redshift information. In order to mitigate this, we use two additional observables. First, the integrated Sachs-Wolfe effect—the cross-correlation of the radio number counts with the CMB temperature anisotropies—helps to reduce systematics on the large scales that are sensitive to non-Gaussianity. Second, optical data allows for cross-identification in order to gain some redshift information. We show that, while the single redshift bin case can provide a σ(fNL) ∼ 20, and is therefore not competitive with current and future constraints on non-Gaussianity, a tomographic analysis could improve the constraints by an order of magnitude, even with only two redshift bins. A huge improvement is provided by the addition of high-redshift sources, so having cross-ID for high-z galaxies and an even higher-z radio tail is key to enabling very precise measurements of fNL. We use Fisher matrix forecasts to predict the constraining power in the case of no redshift information and the case where cross-ID allows a tomographic analysis, and we show that the constraints do not improve much with 3 or more bins. Our results show that SKA continuum surveys could provide constraints competitive with CMB and forthcoming optical surveys, potentially allowing a measurement of σ(fNL) ∼ 1 to be made. Moreover, these measurements would act as a useful check of results obtained with other probes at other redshift ranges with other methods.

Precision frontier in semileptonic weak interactions: theory

Recent advances in experimental physics have opened a new frontier for the precision measurements in low energy weak interactions. In this note we discuss the theoretical basis for the analysis of such experiments and their implications for the standard model.

Status of Belle II and SuperKEKB

The second generation B-factory project at KEK, Belle II/SuperKEKB, to explore new physics at the precision frontier, is now under construction. In this paper, the present status of SuperKEKB accelerator components as well as the Belle II detector upgrade is described.

Twentieth-Century Length: The Origins, Use, and Formalization of Electromagnetic Standards

There was a fundamental change in our standards of length during the twentieth century, as the metal bars that had served for so long gave way to standards based on the wavelength, and then velocity, of light. This article describes those changes with particular emphasis on the standards-in-use of practitioners at the frontier of precision: spectroscopists, industrialists, geodesists, and astronomers. It reveals a multiplicity of de facto standards that supported their various innovations in practical electromagnetic measurement techniques. These de facto standards often came before, and guided the adoption of, the more visible new de jure standards that have been the subject of greater historical attention. I also offer a new explanation of the processes of change in our standards of length, based not simply on the search for better precision but more on concepts of mutual grounding and coherence.

The ‘nec plus ultra’ of precision measurement: Geodesy and the forgotten purpose of the Metre Convention

Geodesy—the determination of the size and shape of the earth—has often been the science operating at the frontier of precision in the measurement of length. Its contribution to the technologies and standards of length measurement has, however, been underestimated in the literature. That, instead, places emphasis on the on the creation and international acceptance of the metric system as a whole. By new research into the standards-in-use of the community of geodesists, I rediscover the original purpose of the Metre Convention of 1875, and show for the first time the significant influence of geodesy on the standardisation of length measurement thereafter. I emphasise the role of the coherence of the web of measurement in the context of change and improvement in standards.

High power cryogenic targets

The development of high power cryogenic targets for use in parity violating electron scattering has been a crucial ingredient in the success of those experiments. As we chase the precision frontier, the demands and requirements for these targets have grown accordingly. We discuss the state of the art, and describe recent developments and strategies in the design of the next generation of these targets.

Flavour Physics in SUSY extensions of the SM in the LHC era

The coming years will witness tremendous progress at the “high energy frontier” accomplished primarily at the LHC. Important advances are also expected at the “high precision frontier” through the improved B s -physics experiments at the Tevatron and in particular LHCb at CERN. After summarizing the status of various tensions in the present Unitarity Triangle (UT) analyses, we consider a number of Supersymmetric models showing their capability to solve these tensions. Moreover, we show how the characteristic patterns of correlations among flavour observables allow to distinguish between these different SUSY scenarios. We propose a “DNA-Flavour Test” of NP models, with the aim of showing a tool to distinguish between these NP scenarios, once additional data on flavour changing processes become available.

Charmless two-body B-meson decays in QCD

The coming years will witness tremendous progress at the ''high energy frontier'' accomplished primarily at the LHC. Important advances are also expected at the ''high precision frontier'' through the improved B_s-physics experiments at the Tevatr on and in particular LHCb at CERN. After summarizing the status of various tensions in the present Unitarity Triangle (UT) analyses, we consider a number of Supersymmetric models showing their capability to solve these tensions. Moreover, we show how the characteristic patterns of correlations among flavour observables allow to distinguish between these different SUSY scenarios. We propose a ''DNA-Flavour Test'' of NP models, with the aim of showing a tool to distinguish between these NP scenarios, once a dditional data on flavour changing processes become available.

B MESON FACTORIES

Particle physics makes progress in three Frontiers: (1) High Energy Frontier, (2) High Intensity Frontier, and (3) High Precision Frontier. Category (1) will be dominated by the SSC and LHC experiments in the next decade and (3) by precise measurements of the (g−2)μ and sin2θw. In category (2) there will be a new round of intense “factories” constructed for rare K decays, [τ charm] studies, ϕ Factories and B Factories. Each of these Factories provide new physics possibilities as illustrated in Table 1. Note that the High Intensity Frontier is sometimes the same as the High Precision Frontier since high statistics are usually needed for high precision. In this brief note we describe some of the current possibilities for B Meson Factories.

Excited weak vector bosons facing the high energy and high precision frontier

If the recently discovered weak bosons W ± and Z were manifestations of a composite structure of the weak interactions rather than the commonly assumed gauge bosons of a fundamental gauge symmetry one is naturally led to expect a corresponding spectrum of excited weak vector bosons. Experiments at LEP I/SLC and LEP II may be uniquely suited to shed light on this question with their power to perform high precision tests of the standard model.