High Energy Particle Collisions Research Articles

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.

Flexible graphite as beam dumping material in the TDE blocks of the Large Hadron Collider

The Large Hadron Collider (LHC) is a high energy particle collider at the European Laboratory for Particle Physics (CERN) in Geneva, Switzerland. The LHC Beam Dumping System (LBDS) is composed by different equipment employed to extract and absorb the LHC circulating beam in case of need. At the end of the LBDS resides the LHC main dump (so called TDE, which stands for Target Dump External). The TDE block is constituted by several graphite blocks with different densities enclosed in a 318L stainless steel jacket. Among the different type of carbon-based materials, the flexible graphite is the one owning the lowest density (1-1.2 g/cm3). It differs from typical graphite forms such as polycrystalline and pyrolytic graphite in that no binder is added during the production process. The bonding frictional forces due to particle asperities give the typical flexibility to the material and contribute to the deformation mechanism. In order to predict the thermo-mechanical response to the proton beam-induced sudden energy deposition, the material behavior needs to be investigated in-depth in a wide range of temperature and strain-rates. In this preliminary work, the static properties of a commercial flexible graphite (Sigraflex® from SGL Carbon) have been observed at room temperature in the in-plane direction. Two sides DIC technique has been employed in order to get a reliable measurement of the strain on both front and edge specimen surfaces; the crosshead displacement-rate was varied between 0.01-10 mm/min. Finally, a discussion about the stress-strain behavior and the deformation mechanism has been given.

Landau–Khalatnikov Problem in Relativistic Fluid Dynamics

An alternative method is proposed for solving the Landau–Khalatnikov problem of the 1D expansion stage of a hot hadron matter formed during collisions of high-energy particles or atomic nuclei. The solution of relativistic fluid dynamics equations by the Riemann method gives a new representation for the Khalatnikov potential, in which the symmetry of the emerging flow to reflection in the central plane of the initial distribution of the matter is observed. New exact relations that describe the evolution of the energy density at the center of the distribution as well as the motion of boundaries between the general solution and expansion waves are derived. The energy and velocity distributions of particles, including the preexponential factors that have not been considered earlier, are obtained in the Landau approximation.

Kinematic Censorship as a Constraint on Allowed Scenarios of High-Energy Particle Collisions

In recent years, it was found that the energy $E_{c.m.}$ in the centre of mass frame of two colliding particles can be unbounded near black holes. If collision occurs exactly on the horizon, $E_{c.m.}$ is formally infinite. However, in any physically reasonable situation this is impossible. We collect different scenarios of such a kind and show why in every act of collision $E_{c.m.}$ is indeed finite (although it can be as large as one likes). The factors preventing infinite energy are diverse: the necessity of infinite proper time, infinite tidal forces, potential barrier, etc. This prompts us to formulate a general principle according to which the limits in which $E_{c.m.}$ becomes infinite are never achieved. We call this the kinematic censorship (KC). Although by itself the validity of KC is quite natural, its application allows one to forbid scenarios of collisions predicting infinite $E_{c.m.}$ without going into details. The KC is valid even in the test particle approximation, so explanation of why $E_{c.m.}$ cannot be infinite, does not require references (common in literature) to the non-linear regime, backreaction, etc. The KC remains valid not only for free moving particles but also if particles experience the action of a finite force. For an individual particle, we consider a light-like continuous limit of a time-like trajectory in which the effective mass turns into zero. We show that it cannot be accelerated to an infinite energy during a finite proper time under the action of such a force. As an example, we consider dynamics of a scalar particle interacting with a background scalar field.

FPGA implementation of a deep learning algorithm for real-time signal reconstruction in particle detectors under high pile-up conditions

The analog signals generated in the read-out electronics of particle detectors are shaped prior to the digitization in order to improve the signal to noise ratio (SNR). The real amplitude of the analog signal is then obtained using digital filters, which provides information about the energy deposited in the detector. The classical digital filters have a good performance in ideal situations with Gaussian electronic noise and no pulse shape distortion. However, high-energy particle colliders, such as the Large Hadron Collider (LHC) at CERN, can produce multiple simultaneous events, which produce signal pileup. The performance of classical digital filters deteriorates in these conditions since the signal pulse shape gets distorted. In addition, this type of experiments produces a high rate of collisions, which requires high throughput data acquisitions systems. In order to cope with these harsh requirements, new read-out electronics systems are based on high-performance FPGAs, which permit the utilization of more advanced real-time signal reconstruction algorithms. In this paper, a deep learning method is proposed for real-time signal reconstruction in high pileup particle detectors. The performance of the new method has been studied using simulated data and the results are compared with a classical FIR filter method. In particular, the signals and FIR filter used in the ATLAS Tile Calorimeter are used as benchmark. The implementation, resources usage and performance of the proposed Neural Network algorithm in FPGA are also presented.

Transverse Momentum Dependent Observables from Low to High Energy: Factorization, Evolution, and Global Analyses

Transverse momentum dependent (TMD) observables in high-energy particle collisions allow one to study the motion of hadron constituents (partons) in three dimensions. The intense theoretical, phenomenological, and experimental work over the last several decades has seen great progress in modeling and extracting TMD parton distribution functions (PDFs) and fragmentation functions (FFs) [1, 2]. The wealth of experimental data, both current and future [3–6], across various reactions and energy ranges, along with substantial progress in other approaches, such as Lattice QCD [7], has increased the demand to rigorously study the intrinsic transverse motion of hadrons. Such issues currently being addressed include factorization, evolution, and operator definitions of TMD distributions, as well as how they influence phenomenological and Lattice QCD studies. Therefore, in this special issue we attempt to further the effort of understanding TMD structure through a series of review articles that address some of the significant areas of ongoing research.

Energy Dependent Chemical Potentials of Light Particles and Quarks from Yield Ratios of Antiparticles to Particles in High Energy Collisions

We collect the yields of charged pions ( π − and π + ), charged kaons ( K − and K + ), anti-protons ( p ¯ ), and protons (p) produced in mid-rapidity interval (in most cases) in central gold–gold (Au–Au), central lead–lead (Pb–Pb), and inelastic or non-single-diffractive proton–proton ( p p ) collisions at different collision energies. The chemical potentials of light particles and quarks are extracted from the yield ratios, π − / π + , K − / K + , and p ¯ / p , of antiparticles to particles over an energy range from a few GeV to above 10 TeV. At a few GeV (∼4 GeV), the chemical potentials show, and the yield ratios do not show, different trends comparing with those at other energies, although the limiting values of the chemical potentials and the yield ratios at very high energy are 0 and 1, respectively.

Micro black holes formed in the early Universe and their cosmological implications

High energy collisions of particles may have created tiny black holes in the early Universe, which might leave stable remnants instead of fully evaporating as a result of Hawking radiation. If the reheating temperature was sufficiently close to the fundamental gravity scale, which can be different from the usual Planck scale depending of the presence and properties of spatial extra-dimensions, the formation rate could have been sufficiently high and hence such remnants could account for the entire cold dark matter of the Universe.