Luminosity Frontier Research Articles

Simulation of the response of a diamond-based radiation detector to ultra-short and intense high-energy electron pulses

Single-crystal synthetic diamond sensors have been widely used in radiation dosimetry and beam diagnostics. The foreseen harsh radiation environment in electron-positron colliders at the luminosity frontier requires a thorough investigation of diamond’s response to large radiation bursts, in particular, to intense high-energy electron pulses. In this article, a two-step numerical simulation approach (Sentaurus + LTspice) is proposed to explore this topic. The time response of the diamond detector is simulated using TCAD-Sentaurus while the transmission effect of the electronic circuit is taken into account using LTspice. Good agreement is observed between results of the numerical simulation and preliminary experimental data from detector’s exposure to high-energy sub-picosecond electron pulses, on both the amplitude and the shape of the induced signals. This simulation combination is a novel approach to designing and optimizing diamond detectors for radiation and beam loss monitoring in particle physics experiments.

Charming charm, beautiful bottom and quark–gluon plasma in the Large Hadron Collider era

After a few microseconds of the creation of our Universe through the Big Bang, the primordial matter was believed to be a soup of the fundamental constituents of matter -- quarks and gluons. This is expected to be created in the laboratory by colliding heavy nuclei at ultra-relativistic speeds. A plasma of quarks and gluons, called Quark-Gluon Plasma (QGP) can be created at the energy and luminosity frontiers in the Relativistic Heavy Ion Collider (RHIC), at Brookhaven National Laboratory, New York, USA, and the Large Hadron Collider (LHC) at CERN, Geneva, Switzerland. Heavy quarks, namely the charm and bottom quarks, are considered as novel probes to characterize QGP, and hence the produced Quantum Chromodynamics (QCD) matter. Heavy quark transport coefficients play a significant role in understanding the properties of QGP. Experimental measurements of nuclear suppression factor and elliptic flow can constrain the heavy quark transport coefficients, which are key ingredients for phenomenological studies, and they help to disentangle different energy loss mechanisms. We give a general perspective of the heavy quark drag and diffusion coefficients in QGP and discuss their potentials as probes to disentangle different hadronization mechanisms, as well as to probe the initial electromagnetic fields produced in non-central heavy-ion collisions. Experimental perspectives on future measurements are discussed with special emphasis on heavy-flavors as next-generation probes in view of new technological developments.

Performance of the Unified Readout System of Belle II

The Belle II experiment at the SuperKEKB collider at KEK, Tsukuba, Japan has successfully started taking data with the full detector in March 2019. Belle II is a luminosity frontier experiment of the new generation to search for physics beyond the Standard Model of elementary particles, from precision measurements of a huge number of B and charm mesons and tau leptons. In order to read out the events at a high rate from the seven subdetectors of Belle II, we adopt a highly unified readout system, including a unified trigger timing distribution system (TTD), a unified high speed data link system (Belle2link), and a common backend system to receive Belle2link data. Each subdetector frontend readout system has a field-programmable gate array (FPGA) in which unified firmware components of the TTD receiver and Belle2link transmitter are embedded. The system is designed for data taking at a trigger rate up to 30 kHz with a dead-time fraction of about 1% in the frontend readout system. The trigger rate is still much lower than our design. However, the background level is already high due to the initial vacuum condition and other accelerator parameters, and it is the most limiting factor of the accelerator and detector operation. Hence the occupancy and radiation effects to the frontend electronics are rather severe, and they cause various kind of instabilities. We present the performance of the system, including the achieved trigger rate, dead-time fraction, stability, and discuss the experience gained during the operation.

Beam induced vacuum effects in the future circular hadron collider beam vacuum chamber

EuroCirCol is a conceptual design study of a post-LHC, Future Circular Hadron Collider (FCC-hh) with 50 TeV of beam energy and 100 km long, which aims to expand the current energy and luminosity frontiers. The vacuum chamber of the FCC-hh will have to cope with unprecedented levels of synchrotron radiation power for proton colliders, dealing simultaneously with a tighter magnet aperture. Considering that the high radiation power and photon flux will release larger amounts of gas into the system, the difficulty to meet the vacuum specifications increases substantially compared with the LHC. This paper presents a study on the beam induced vacuum effects for the FCC-hh novel conditions, the different phenomena which, owing to the presence of the beam, have an impact on the accelerator's vacuum level. It is concluded that thanks to the adopted mitigation measures the proposed vacuum system shall be adequate, allowing us to reach $\ensuremath{\le}1\ifmmode\times\else\texttimes\fi{}{10}^{15}\text{ }\text{ }{\mathrm{H}}_{2\text{ }eq}/{\mathrm{m}}^{3}$ with baseline beam parameters within the first months of conditioning.

Status of SuperKEKB construction

SuperKEKB is a major upgrade of the asymmetric B-factory collider, KEKB, to provide 40 times higher luminosity than that achieved at KEKB. The design of SuperKEKB adopts the nano-beam scheme for the collision of two beams, which was originally proposed for the Italian SuperB project. The nano-beam scheme is realized with low-emittance optics, a very small β-function, and a large crossing angle at the collision point. For the low-emittance design, a substantial part of the positron ring (LER) was reconstructed. All dipole magnets in the LER were replaced with longer ones. The beam pipes in the LER were redesigned to mitigate the electron cloud problem. Around the interaction point, about 300 m of both rings were completely redesigned for the new collision scheme. The commissioning of SuperKEKB is divided into three phases. Phase 1 is used for vacuum scrubbing of new beam pipes without the Belle-II detector and the final focus magnets. The final focus magnets and Belle-II are installed in Phase 2. However, the central vertex detector (VXD) of Belle-II is not installed. Phase 2 is devoted to background studies and collision tuning. After the installation of VXD, Phase 3 starts for the new luminosity frontier. The construction of SuperKEKB for Phase 1 is nearing completion. The preparation of hardware for Phase 2 and Phase 3 is in steady progress. From various aspects, the nano-beam scheme SuperKEKB is a challenging accelerator. The tolerances for the hardware to realize nano-scale beam sizes and to keep the collision are very tight. The optics design is still being optimized to maximize the dynamic aperture. It is hard to predict how the commissioning will proceed.

Detectors for collider experiments at the luminosity frontier

In experiments at the luminosity frontier, New Physics is being searched for in precision studies of rare processes. The most important example of such an effort is experiments at B factories and super B factories. While B factories have fully established the CKM quark transition matrix as the only source of CP violation in the Standard Model, the next generation of B factories, the so-called super B factories, will look for departures from the Standard Model. To collect a 50 times larger data sample, needed to reach the required sensitivity, a substantial B factory upgrade is being carried out. The SuperKEKB accelerator complex is designed for an increase in luminosity by a factor of 40. The upgraded Belle II spectrometer is being constructed to operate at considerably higher event rates, as well as higher backgrounds, accompanied by an increase in occupancy and radiation damage. Higher event rates also require substantial modifications in the trigger scheme, data acquisition system and computing. The paper discusses the detectors at B factories, the motivation for SuperKEKB/Belle II, the super B factory at KEK, as well as the requirements for the new accelerator and for the new detector. The present status of the project will be presented together with plans for the future. We will also discuss its competition, the LHCb experiment at the LHC.

High performance computing activities in hadron spectroscopy at BESIII

BESIII experiment is operated in the τ-charm threshold energy region. It has collected the world's largest data samples of J/ψ, ψ(3686), ψ(3770) and ψ(4040) decays. These data are being used to make a variety of interesting and unique studies of light hadron spectroscopy, precision charmonium physics and high-statistics measurements of D meson decays. As one of the experiments at the high luminosity frontier, data processing at BESIII is computationally very expensive for large data sets. In this presentation, we report two recent progresses in using high performance computing: a Tag-based preselection for data reduction and GPUPWA, a PWA framework harnessing the GPU parallel computing.

Observing a light dark matter beam with neutrino experiments

We consider the sensitivity of fixed-target neutrino experiments at the luminosity frontier to light stable states, such as those present in models of MeV-scale dark matter. To ensure the correct thermal relic abundance, such states must annihilate via light mediators, which in turn provide an access portal for direct production in colliders or fixed targets. Indeed, this framework endows the neutrino beams produced at fixed-target facilities with a companion `dark matter beam', which may be detected via an excess of elastic scattering events off electrons or nuclei in the (near-)detector. We study the high luminosity proton fixed-target experiments at LSND and MiniBooNE, and determine that the ensuing sensitivity to light dark matter generally surpasses that of other direct probes. For scenarios with a kinetically-mixed U(1)' vector mediator of mass m_V, we find that a large volume of parameter space is excluded for m_DM ~ 1-5 MeV, covering vector masses 2 m_DM < m_V < m_eta and a range of kinetic mixing parameters reaching as low as kappa ~ 10^{-5}. The corresponding MeV-scale dark matter scenarios motivated by an explanation of the galactic 511 keV line are thus strongly constrained.

The KEKB accelerator: pioneer of the luminosity frontier

The KEKB accelerator: pioneer of the luminosity frontier

Exploring portals to a hidden sector through fixed targets

We discuss the sensitivity of neutrino experiments at the luminosity frontier to generic hidden sectors containing new (sub)-GeV neutral states. The weak interaction of these states with the Standard Model can be efficiently probed through all of the allowed renormalizable `portals' (in the Higgs, vector, and neutrino sectors) at fixed target proton beam facilities, with complementary sensitivity to colliders. We concentrate on the kinetic-mixing vector portal, and show that certain regions of the parameter space for a new secluded U(1) gauge sector with long-lived sub-GeV mass states decaying to Standard Model leptons are already severely constrained by the datasets at LSND, MiniBooNE, and NuMI/MINOS. Furthermore, scenarios in which portals allow access to stable neutral particles, such as MeV-scale dark matter, generally predict that the neutrino beam is accompanied by a `dark matter beam', observable through neutral-current-like interactions in the detector. As a consequence, we show that the LSND electron recoil event sample currently provides the most stringent direct constraint on MeV-scale dark matter models.

Lepton colliders at the energy and luminosity frontiers: Linear colliders & SuperB factories

After a brief review of the performance of the various Lepton Colliders presently in operation at the energy and luminosity frontiers, the article describes their possible evolution and the envisaged new projects to improve their performances. Beauty Factories have the potential to extend the present luminosity frontier of Lepton Colliders by two orders of magnitude into the 1036 cm-2 sec-1 range. Linear Colliders have the potential to extend the present energy frontier of Lepton Colliders by one order of magnitude into the Multi-TeV energy range. The ideas and challenges to boost these frontiers in the next future are described as well as the R&D plans to demonstrate their feasibility and/or to prepare projects proposals through engineering design optimisation and industrialisation. Technically driven schedule for their possible fabrication and installation are presented.

Accelerating Applications of RF Superconductivity—Success Stories

RF superconductivity has become an important technology for accelerators at the energy and luminosity frontiers as well as at the cutting edge of nuclear physics and basic materials science. Nearly one kilometer of superconducting cavities have been installed in accelerators to provide more than 5 gigavolts of acceleration. Superconducting cavities support beam currents above one ampere, and deliver up to 380 kW of beam power. Steady advances in science and technology are responsible for spectacular increases in performance since the large installations of CEBAF (Jefferson Lab) and LEP-II (CERN) during the 1990's. The gradient of niobium cavities has more than tripled over the last decade, spurring new accelerators. The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory switched to superconducting technology in 2000. The X-ray Free Electron Laser at DESY will provide angstrom-wavelength beams of unprecedented brilliance. Recently an International Technology Recommendation Panel selected the superconducting option for the International Linear Collider. The 500 GeV collider will require 20,000 superconducting cavities, each about one meter long, operating at 2 K. Energy Recovery Linac (ERL) studies are flowering for a variety of applications: ultra-fast, high brilliance light sources as well as electron beams for cooling or colliding with ions in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Lab. Designs for the nuclear Rare Isotope Accelerator (RIA) demand high performance cavities. With many years of operating experience at major accelerators demonstrating a robust technology, SRF is ready to launch major initiatives.

European perspectives for electron-nucleon scattering at the luminosity frontier

European perspectives are discussed on fixed-target electron or positron scattering experiments using polarized and unpolarized beams and targets in various combinations. The goal envisioned is a deep and complete understanding of the momentum and spin structure of hadrons in the context of Quantum Chromo Dynamics, based on measurements at moderate and low photon virtualities. This program can be realized by performing electron-nucleon experiments with high resolution and high luminosity, at beam energies of at least 25–30 GeV.