High Energy Particle Collisions Research Articles

Tau Lepton Identification With Graph Neural Networks at Future Electron–Positron Colliders

Efficient and accurate reconstruction and identification of tau lepton decays plays a crucial role in the program of measurements and searches under the study for the future high-energy particle colliders. Leveraging recent advances in machine learning algorithms, which have dramatically improved the state of the art in visual object recognition, we have developed novel tau identification methods that are able to classify tau decays in leptons and hadrons and to discriminate them against QCD jets. We present the methodology and the results of the application at the interesting use case of the IDEA dual-readout calorimeter detector concept proposed for the future FCC-ee electron–positron collider.

Measurement of splittings along a jet shower in $\sqrt{s} = 200$ GeV pp collisions at STAR

Jets are algorithmic proxies of hard scattered partons, i.e. quarks and gluons, in high energy particle collisions. The STAR collaboration presents the first measurements of substructure observables at the first, second and third splits in the jet clustering tree via the iterative SoftDrop procedure. For each of these splits, we measure the fully corrected groomed shared momentum fraction (z_gg) and groomed jet radius (R_gg). We discuss the evolution of jet substructure in both the angular and momentum scales which allows for a self-similarity test of the DGLAP splitting function. We compare the fully corrected data to Monte Carlo models, providing stringent constraints on model parameters related to the parton shower and non-perturbative effects such as hadronization.

The performance regulation optimization and engineering application of a domestic helium liquefier

<p indent="0mm">The superconducting magnets and the superconducting cavities are the key devices of large-scale scientific facilities, such as the HL-LHC in the CERN, the ITER, the EAST, the CiADS, and so on. A stable and reliable cold source such as the liquid helium (–269°C) is required to keep the superconducting magnets and the superconducting cavities working. Therefore, a helium liquefier or a helium refrigerator working at <sc>4.5 K</sc> is necessary for them. Research on high-field-strength superconducting dipole magnets used in future high-energy particle colliders is developed in the Institute of High Energy Physics of the Chinese Academy of Sciences. High-field-strength superconducting dipole magnets have large thermal loads and long test durations, which need large amount of liquid helium for their performance tests. Therefore, the long-term operating economy, stability, and reliability of the refrigeration system are highly required. The engineering application of using a helium liquefier for producing liquid helium to cool down superconducting dipole magnets has not been realized in China yet. Meanwhile, the price of the imported helium liquefiers is usually too high and the supply cycles are too long. Fortunately, a domestic helium liquefier has been developed by the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences. This paper will realize the engineering application of the domestic helium liquefier applied to the superconducting dipole magnet test platform for the first time. In order to meet the test requirements of high-field-strength superconducting dipole magnets, a performance regulation and optimization of the first domestic helium liquefier is studied. It realizes the optimal control of the cold-box cooling process and the Dewar cooling process, saves the power consumption of the compressor by 12.3% and 25.2% respectively, and significantly improves the economy of the helium liquefier. After the commissioning of the liquefier, the helium liquefier realizes the automatic control adjustment function to adapt to variable loads in different operating conditions. And the specific energy consumption of the helium liquefier under each load state is analyzed. Without considering the consumption of liquid nitrogen, the minimum specific energy consumption of the helium liquefier is <sc>2.4 kW h/L</sc> when the liquefier works with the full load. Through control optimization and experimental testing, the helium liquefier successfully realizes the joint operation with the user-end superconducting dipole magnet test platform, and passed the long-term operation reliability test. At present, the helium liquefier has run stably for more than two months, produced more than <sc>35000 L</sc> of liquid helium, promoting the first domestic accelerator high-field superconducting dipole magnet to achieve a breakthrough in the new index of the magnetic field strength of <sc>12.47 T.</sc> It’s the first time for the domestic helium liquefier applying to the superconducting dipole magnet test platform, and this engineering application can be further promoted in future.

General analysis for observing quantum interference at colliders

Despite their inextricable quantum mechanical nature, events at a high energy particle collider experiment typically have very few unambiguous quantum signatures, due the type of data and the manner in which they are collected. We present a general analysis of one feature of quantum mechanics, interference between two orthogonal states on Hilbert space, projected onto the basis of states that span a collider experiment observable space. Identification of quantum interference can be considered as a binary discrimination between a pure state and a mixed state, and we introduce several statistical measures that quantify the amplitude of interference in a pure state with respect to a mixed state that exhibits no interference. Two explicit examples from particle physics are provided to demonstrate features of the general formalism.

Learning to simulate high energy particle collisions from unlabeled data

In many scientific fields which rely on statistical inference, simulations are often used to map from theoretical models to experimental data, allowing scientists to test model predictions against experimental results. Experimental data is often reconstructed from indirect measurements causing the aggregate transformation from theoretical models to experimental data to be poorly-described analytically. Instead, numerical simulations are used at great computational cost. We introduce Optimal-Transport-based Unfolding and Simulation (OTUS), a fast simulator based on unsupervised machine-learning that is capable of predicting experimental data from theoretical models. Without the aid of current simulation information, OTUS trains a probabilistic autoencoder to transform directly between theoretical models and experimental data. Identifying the probabilistic autoencoder’s latent space with the space of theoretical models causes the decoder network to become a fast, predictive simulator with the potential to replace current, computationally-costly simulators. Here, we provide proof-of-principle results on two particle physics examples, Z-boson and top-quark decays, but stress that OTUS can be widely applied to other fields.

Explainable machine learning of the underlying physics of high-energy particle collisions

We present an implementation of an explainable and physics-aware machine learning model capable of inferring the underlying physics of high-energy particle collisions using the information encoded in the energy-momentum four-vectors of the final state particles. We demonstrate the proof-of-concept of our White Box AI approach using a Generative Adversarial Network (GAN) which learns from a DGLAP-based parton shower Monte Carlo event generator. The constrained generator network architecture mimics the structure of a parton shower exhibiting similarities with Recurrent Neural Networks (RNNs). We show, for the first time, that our approach leads to a network that is able to learn not only the final distribution of particles, but also the underlying parton branching mechanism, i.e. the Altarelli-Parisi splitting function, the ordering variable of the shower, and the scaling behavior. While the current work is focused on perturbative physics of the parton shower, we foresee a broad range of applications of our framework to areas that are currently difficult to address from first principles in QCD. Examples include nonperturbative and collective effects, factorization breaking and the modification of the parton shower in heavy-ion, and electron-nucleus collisions.

Notes on Extraction of Energy from an~Extremal Kerr–Newman Black Hole via Charged Particle Collisions

The so-called BSW effect is an idealised scenario for high-energy test particle collisions in the vicinity of black holes; if the black hole is extremal and one of the particles fine-tuned, the centre-of-mass collision energy can be arbitrarily high. It has been recently shown that the energy of escaping particles produced in this process can also be arbitrarily high in the given approximation, as long as both the black hole and the escaping particles are charged, regardless of how small the black-hole charge might be. We revisit these results and show that they are also compatible with properties of microscopic particles for the case of motion in the equatorial plane of an extremal Kerr-Newman black hole.

Quantum imprints of gravitational shockwaves

Gravitational shockwaves are simple exact solutions of Einstein equations representing the fields of ultrarelativistic sources and idealized gravitational waves (shocks). Historically, much work has focused on shockwaves in the context of possible black hole formation in high energy particle collisions, yet they remain at the forefront of research even today. Representing hard modes in the bulk, shocks give rise to the gravitational memory effect at the classical level and implant supertranslation (BMS) hair onto a classical spacetime at the quantum level. The aim of this paper is to further our understanding of the ‘information content’ of such supertranslations. Namely, we show that, contrary to the several claims in the literature, a gravitational shockwave does leave a quantum imprint on the vacuum state of a test quantum field and that this imprint is accessible to local observers carrying Unruh-DeWitt (UDW) detectors in this spacetime.

Color confinement, dark matter and the missing anti-matter

Quantum chromodynamics is the fundamental theory to describe strong interaction, where quarks and gluons have the color degrees of freedom. However, a single quark or gluon cannot be separated out and all observable particles are color singlet states. Color confinement or quark confinement conjecture can be proved by considering not only the strong interaction but also the electroweak interaction, which is the SU(3) c invariant. Any measurable state that has to be a color singlet is the direct consequence of the common symmetry of the standard model. Color non-singlet objects are created from the big bang when the interaction breaks SU(3) c symmetry based on the non-local Lagrangian. There is nearly no interaction between colored objects and the color singlet Universe when the momentum transfer is not large enough. Colored objects are reasonable candidates of dark matter and the missing anti-matter in the Universe can also be easily explained. Dark matter can be produced in a laboratory, which can be tested by measuring the energy loss and baryon number change in the extremely high energy collisions of particles and anti-particles.

Pseudorapidity distributions of charged particles in pp(), p(d)A and AA collisions using Tsallis thermodynamics

The pseudorapidity distributions of charged particles measured in p + p() collisions for energies ranging from GeV to 13 TeV and A + A collisions at RHIC and LHC are investigated in the fireball model with Tsallis thermodynamics. We assume that the rapidity axis is populated with fireballs following q-Gaussian distribution and the charged particles follow the Tsallis distribution in the fireball. We also extend the fireball model to asymmetric collision systems, i.e. d + Au collisions at GeV and p + Pb collisions at TeV, by taking into account the asymmetric geometry configuration. The model can fit the experimental data well for all the collision systems and centralities investigated. The collision energy and centrality dependence of the model parameters for the symmetric (asymmetric) collision system, i.e. the central position y 0 (y 0a , y 0A ) and its width σ (σ a , σ A ) of the fireball distribution, are also investigated and discussed. Our results suggest that the fireball model with Tsallis thermodynamics can be used as a universal framework for the pseudorapidity distributions of charged particles in high energy collisions at RHIC and LHC.

Towards a quantum computing algorithm for helicity amplitudes and parton showers

The interpretation of measurements of high-energy particle collisions relies heavily on the performance of full event generators. By far the largest amount of time to predict the kinematics of multi-particle final states is dedicated to the calculation of the hard process and the subsequent parton shower step. With the continuous improvement of quantum devices, dedicated algorithms are needed to exploit the potential quantum computers can provide. We propose general and extendable algorithms for quantum gate computers to facilitate calculations of helicity amplitudes and the parton shower process. The helicity amplitude calculation exploits the equivalence between spinors and qubits and the unique features of a quantum computer to compute the helicities of each particle involved simultaneously, thus fully utilising the quantum nature of the computation. This advantage over classical computers is further exploited by the simultaneous computation of s and t-channel amplitudes for a 2$\rightarrow$2 process. The parton shower algorithm simulates collinear emission for a two-step, discrete parton shower. In contrast to classical implementations, the quantum algorithm constructs a wavefunction with a superposition of all shower histories for the whole parton shower process, thus removing the need to explicitly keep track of individual shower histories. Both algorithms utilise the quantum computer's ability to remain in a quantum state throughout the computation and represent a first step towards a quantum computing algorithm to describe the full collision event at the LHC.

Artificial neural network for identification of short-lived particles in the CBM experiment

In high energy particle colliders, detectors record millions of points of data during collision events. Therefore, good data analysis depends on distinguishing collisions which produce particles of interest (signal) from those producing other particles (background). Machine learning algorithms in the current times have become popular and useful as the method of choice for such large scale data analysis. In this work, we propose and implement an artificial neural network architecture to achieve the task of identifying precisely the parent particles from all the candidates arising out of track reconstruction from collision data in the future Compressed Baryonic Matter (CBM) experiment. Our framework performs comparably to the existing computational algorithm for this task even with a simple network architecture.

New Scenarios of High-Energy Particle Collisions Near Wormholes

We suggest two new scenarios of high-energy particle collisions in the background of a wormhole. In scenario 1, the novelty consists of the fact that the effect does not require two particles coming from different mouths. Instead, all such scenarios of high energy collisions develop, when an experimenter sends particles towards a wormhole from the same side of the throat. For static wormholes, this approach leads to indefinitely large energy in the center of mass. For rotating wormholes, it makes possible the super-Penrose process (unbounded energies measured at infinity). In scenario 2, one of colliding particles oscillates near the wormhole throat from the very beginning. In this sense, scenario 2 is intermediate between the standard one and scenario 1 since the particle under discussion does not come from infinity at all.

Rotating dyonic black hole in , U(1)2 gauged supergravity as natural laboratory for high energy particle collisions

In the present work, we explore several gravitational aspects such as energy extraction (via the Penrose process and superradiance), particle collisions around a , U(1)2 rotating dyonic black hole (BH) in the gauged supergravity model. The influence of the rotation parameter (a) and the gauge coupling constant (g) on the behavior of the horizon and ergoregion of the BH is investigated. In comparison to the extremal Kerr BH, the gauge coupling constant, under certain constraints, can interestingly enhance the maximum efficiency of energy extraction through the Penrose process by almost twice. Under the same constraints, we can extract approximately 60.75% of the initial mass-energy from the BH which is noticeably higher and far different from that of the Kerr BH. The limit of energy extraction in terms of the local speeds of the fragments is also determined with the help of the Wald inequality. We discover an upper limit on the gauge coupling constant up to which superradiance is likely to occur. Finally, we estimate the center-of-mass energy (E CM) of two particles with the same rest mass moving in the equatorial plane of the BH. Our study also aims to sensitize E CM to the parameters a and g for both extremal and nonextremal spacetime. Especially, for the extremal case, an infinitely large amount of E CM can be achieved closer to the event horizon confirming a basic point of view that an extreme supergravity BH with dyons could serve as ultimate particle accelerators as compared to Kerr and any other generalized BHs in this family and other alternative theories of gravity. However, E CM for the nonextremal spacetime is shown to be finite and has an upper bound.

CIMBA: Fast Monte Carlo generation using cubic interpolation

Monte Carlo generation of high energy particle collisions is a critical tool for both theoretical and experimental particle physics, connecting perturbative calculations to phenomenological models, and theory predictions to full detector simulation. The generation of minimum bias events can be particularly computationally expensive, where non-perturbative effects play an important role and specific processes and fiducial regions can no longer be well defined. In particular scenarios, particle guns can be used to quickly sample kinematics for single particles produced in minimum bias events. CIMBA (Cubic Interpolation for Minimum Bias Approximation) provides a comprehensive package to smoothly sample predefined kinematic grids, from any general purpose Monte Carlo generator, for all particles produced in minimum bias events. These grids are provided for a number of beam configurations including those of the Large Hadron Collider. Program summaryProgram title: CIMBA (Cubic Interpolation for Minimum Bias Approximation)CPC Library link to program files:http://dx.doi.org/10.17632/49m44md4ph.1Licensing provisions: GPL version 2 or laterProgramming language: Python, C++Nature of problem: generation of simulated events in high energy particle physics is quickly becoming a bottleneck in analysis development for collaborations on the Large Hadron Collider (LHC). With the expected long-term continuation of the high luminosity LHC, this problem must be solved in the near future. Significant progress has been made in designing new ways to perform detector simulation, including parametric detector models and machine learning techniques, e.g. calorimeter shower evolution with generative adversarial networks. Consequently, the efficiency of generating physics events using general purpose Monte Carlo event generators, rather than just detector simulation, needs to be improved.Solution method: in many cases, single particle generation from pre-sampled phase-space distributions can be used as a fast alternative to full event generation. Phase-space distributions sampled in particle pseudorapidity and transverse momentum are sampled from large, once-off, minimum bias samples generated with Pythia 8. A novel smooth sampling of these distributions is performed using piecewise cubic Hermite interpolating polynomials. Distributions are created for all generated particles, as well as particles produced directly from hadronisation. Interpolation grid libraries are provided for a number of common collider configurations, and code is provided which can produce custom interpolation grid libraries.Restrictions: Single particle generation

Quantum algorithms for jet clustering

Identifying jets formed in high-energy particle collisions requires solving optimization problems over potentially large numbers of final-state particles. In this work, we consider the possibility of using quantum computers to speed up jet clustering algorithms. Focusing on the case of electron-positron collisions, we consider a well-known event shape called thrust whose optimum corresponds to the most jet-like separating plane among a set of particles, thereby defining two hemisphere jets. We show how to formulate thrust both as a quantum annealing problem and as a Grover search problem. A key component of our analysis is the consideration of realistic models for interfacing classical data with a quantum algorithm. With a sequential computing model, we show how to speed up the well-known O(N^3) classical algorithm to an O(N^2) quantum algorithm, including the O(N) overhead of loading classical data from N final-state particles. Along the way, we also identify a way to speed up the classical algorithm to O(N^2 log N) using a sorting strategy inspired by the SISCone jet algorithm, which has no natural quantum counterpart. With a parallel computing model, we achieve O(N log N) scaling in both the classical and quantum cases. Finally, we consider the generalization of these quantum methods to other jet algorithms more closely related to those used for proton-proton collisions at the Large Hadron Collider.

Helical beam screen for the Future Circular Collider for hadrons injection kicker magnets

The Future Circular Collider for hadrons (FCC-hh) is the proposed high-energy frontier particle collider, which is expected to enable proton-proton collisions at a center-of-mass energy of 100 TeV. The specifications for the FCC-hh injection kicker system are very challenging. To provide fast magnetic field rise and fall times, and low ripple during the flat-top, ferrite loaded transmission line type magnets will be used. To limit the beam coupling impedance, a suitable beam screen will be placed in the aperture of each kicker magnet. Due to issues associated with the ``conventional'' beam screen design, used in the injection kickers magnets of the Large Hadron Collider (LHC), such as high voltage (HV) breakdowns and yoke heating problems, we have developed a novel concept of a helical beam screen. The fundamental advantage of the new design, in comparison to the conventional beam screen, is a significant reduction of the maximum voltage induced on the screen conductors, thus a greatly reduced probability of an electrical breakdown of the beam screen. In addition, the longitudinal beam coupling impedance of the helical beam screen is optimized to reduce power deposition in the kicker magnet. Furthermore, the helical beam screen allows a reduction of the maximum transverse beam coupling impedance of the kicker system. Detailed numerical simulations, theoretical studies and experimental results demonstrate that a new design is a promising solution not only for the FCC-hh, but also for existing machines.

ADS Injector-I 2 K superfluid helium cryogenic system

The Accelerator Driven Sub-critical (ADS) system is a strategic plan to solve the nuclear waste problem for nuclear power plants in China. High-energy particle accelerators and colliders contain long strings of superconducting devices, superconducting radio frequency cavities, and magnets, which may require cooling by 2 K superfluid helium (Helium II). 2 K superfluid helium cryogenic system has become a research hot spot in the field of superconducting accelerators. In this study, the ADS Injector-I 2 K cryogenic system is examined in detail. The cryogenic system scheme design, key equipment, and technology design, such as the 2 K Joule–Thomson (J–T) heat exchanger and cryomodules CM1 + CM2 design, are examined, in addition to the commissioning and operation of the cryogenic system. The ADS Injector-I 2 K cryogenic system is the first 100 W superfluid helium system designed and built independently in China. The ADS proton beam reached 10 MeV at 10 mA in July 2016 and 10 MeV at 2 mA in continuous mode in January 2017 and has been operated reliably for over 15,000 h, proving that the design of ADS Injector-I 2 K cryogenic system, the key equipment, and technology research are reasonable, reliable, and meet the requirements. The research into key technologies provides valuable engineering experience that can be helpful for future projects such as CI-ADS (China Initiative Accelerator-Driven System), SHINE (Shanghai High Repetition Rate XFEL and Extreme Light Facility), PAPS (Platform of Advanced Photon Source Technology), and CEPC (Circular Electron-Positron Collider), thereby developing national expertise in the field of superfluid helium cryogenic systems.

High energy particle collisions in static, spherically symmetric black-hole-like wormholes

A Damour-Solodukhin wormhole with a metric which is similar to a Schwarzschild black hole seems to be a black hole mimicker since it is difficult to distinguish them by practical astrophysical observations. In this paper, we investigate a center-of-mass energy for the collision of two test particles in the Damour-Solodukhin wormhole spacetime. We show that the center-of-mass energy for the head-on collision of the particles is large if the difference between the metrics of the wormhole and the black hole is small. To deeply understand the high energy particle collision, we generalize the head-on collision to static, spherically symmetric black-hole-like wormholes.

Discovery and Spectroscopy of Dark Matter and Dark Sectors with Microscopic Black Holes at Next Generation Colliders

If the length scale of possible extra dimensions is large enough, the effective Planck scale is lowered such that microscopic black holes could be produced in collisions of high-energy particles at colliders. These black holes evaporate through Hawking radiation of a handful of energetic particles drawn from the set of all kinematically and thermally allowed degrees of freedom, including dark matter. Here, we perform the first numerical black hole spectroscopic study of the dark sector. We find that if the next generation of colliders can produce microscopic black holes, then missing momentum signatures can reveal the existence of any new light (≲10 TeV) particle, regardless of the strength of its coupling to the standard model, even if there exists no such nongravitational coupling at all.