High Energy Hadron Research Articles

Measurement of inclusive jet spectra in pp, p–Pb, and Pb–Pb collisions with the ALICE detector

Highly energetic jets are sensitive probes of the kinematic properties and the topology of high energy hadron collisions. Jets are collimated sprays of charged and neutral particles, which are produced in fragmentation of hard scattered partons from an early stage of the collision. In ALICE, jets have been measured in pp, p–Pb, and Pb–Pb collisions at several collision energies. While analyses of Pb–Pb events unveil properties of the hot and dense medium formed in heavy-ion collisions, pp and p–Pb collisions can shed light on hadronization and cold nuclear matter effects in jet production. Additionally, pp and p–Pb collisions serve as a baseline for disentangling hot and cold nuclear matter effects. A possible modification of the initial state is tested in p–Pb analyses. For the extraction of a jet signal, the exact evaluation of the background from the underlying event is an especially important ingredient. Due to the different nature of underlying events, each collision system requires a different analysis technique for removing the effect of the background on the jet sample. The focus of this publication is on the ALICE measurements of nuclear modification factors connecting p–Pb and Pb–Pb events to pp collisions. Furthermore, the radial jet structure is explored by comparing jet spectra reconstructed with different resolution parameters.

The gluon condensation at high energy hadron collisions

We report that the saturation/CGC model of gluon distribution is unstable under action of the chaotic solution in a nonlinear QCD evolution equation, and it evolves to the distribution with a sharp peak at the critical momentum. We find that this gluon condensation is caused by a new kind of shadowing–antishadowing effects, and it leads to a series of unexpected effects in high energy hadron collisions including astrophysical events. For example, the extremely intense fluctuations in the transverse-momentum and rapidity distributions of the gluon jets present the gluon-jet bursts; a sudden increase of the proton–proton cross sections may fill the GZK suppression; the blocking QCD evolution will restrict the maximum available energy of the hadron–hadron colliders.

Initial conditions in AA and pA collisions

A full understanding of the spacetime evolution of the QCD matter created in a heavy ion collision requires understanding the properties of the initial stages. In the weak coupling picture these are dominated by classical gluon fields, whose properties can also be studied via the scattering of dilute probes off a high energy hadron or nucleus. A particular challenge is understanding small systems, where LHC data is also showing signs of collective behavior. We discuss some recent results of on the initial matter production and thermalization in heavy ion collisions, in particular in the gluon saturation framework.

Progress on the TRIPOLI-4®-Geant4 coupling

The capability to simulate the transport of charged and/or high-energy hadrons (especially protons) is indispensable for a number of applications. This includes, among others, simulation studies concerned with radiation protection and decommissioning around accelerators and high-intensity laser facilities, as well as beam characterisation in spallation neutron sources. In the context of Monte-Carlo particle transport codes, solving these problems often requires the use of advanced variance-reduction techniques. TRIPOLI-4® is a reference Monte-Carlo particle transport code for the simulation of low-energy (≲ 20 MeV) neutrons and photons and offers a wide range of sophisticated variance-reduction schemes; however, it cannot be applied to the problems mentioned above because it lacks the capability to transport charged, high-energy hadrons.This limitation can be circumvented by coupling TRIPOLI-4r with the Geant4 particle-transport toolkit. We present here the first results of this coupling.

Detection of high energy electromagnetic and hadron components of air-shower cores in the new hybrid experiment “Pamir-XXI”

In the Chacaltaya hybrid experiment we have shown that the observed characteristics of the events accompanying atmospheric families (a bundle of high energy particles in the air-shower core) can not be well described by current simulations. The atmospheric families detected so far by emulsion chambers (sandwiches of X-ray films and lead plates) are key ingredients in the analysis. But the number of analyzed events with atmospheric family is still small due to the limited size of the experiment. Now a new very large hybrid experiment “PAMIR-XXI” is proposed to be constructed at the Pamirs. The notable feature of the experiment is to construct large hadron calorimeters at the center of air-shower arrays to study the air-shower core in detail. We study the possibility to analyze high energy air-shower cores in the “Pamir-XXI” experiment by using the burst density of scintillation detectors instead of using the family data of emulsion chambers. It is shown that the unusual characteristics of the events observed by the Chacaltaya hybrid experiment can be well seen in the hybrid experiment “PAMIR-XXI” too.

Detection of high energy electromagnetic and hadron components of air-shower cores in the new hybrid experiment “Pamir-XXI”

In the Chacaltaya hybrid experiment we have shown that the observed characteristics of the events accompanying atmospheric families (a bundle of high energy particles in the air-shower core) can not be well described by current simulations. The atmospheric families detected so far by emulsion chambers (sandwiches of X-ray films and lead plates) are key ingredients in the analysis. But the number of analyzed events with atmospheric family is still small due to the limited size of the experiment. Now a new very large hybrid experiment “PAMIR-XXI” is proposed to be constructed at the Pamirs. The notable feature of the experiment is to construct large hadron calorimeters at the center of air-shower arrays to study the air-shower core in detail. We study the possibility to analyze high energy air-shower cores in the “Pamir-XXI” experiment by using the burst density of scintillation detectors instead of using the family data of emulsion chambers. It is shown that the unusual characteristics of the events observed by the Chacaltaya hybrid experiment can be well seen in the hybrid experiment “PAMIR-XXI” too.

Calibration system of the LHCb hadronic calorimeter

The Hadron Calorimeter of LHCb (HCAL) is one of the four sub-detectors of the experiment calorimetric system, which also includes: Scintillator Pad Detector (SPD), Pre-Shower Detector (PS), and electromagnetic (ECAL) calorimeter. The main purpose of HCAL is to provide data for Level-0 trigger for selection events with high transverse energy hadrons. It is important to have a precise and reliable calibration system which produces result immediately after the calibration run. LHCb HCAL is equipped with a calibration system based on 137Cs radioactive source embedded into the calorimeter structure. It allows to obtain absolute calibration with good precision and monitor technical condition of the detector.

The Kaon identification system of the NA62 experiment

The main goal of the NA62 experiment at the CERN SPS is to measure the branching ratio of the ultra-rare decay with 10% accuracy. This can be achieved by detecting about 100 Standard Model events with 10% background in 2 - 3 years of data taking. NA62 is exposed to a 750 MHz high-energy unseparated charged hadron beam, with a 6% kaons component, and uses kaon decay-in-flight technique. Precise timing matching of the incident kaon and of the downstream charged track is essential to reject accidental coincidences when working in such a high rate environment. This is achieved by the kaon tagging system KTAG, which identifies kaons with an efficiency higher than 95% and provides precise time information with a resolution better than 100 ps. KTAG re-uses the Cherenkov radiator and optics of a CEDAR, a ring-focusing Cherenkov detector designed for MHz beam intensity in the 1970s. To reach the required performance, KTAG is equipped with new photon detectors, electronics readout, mechanics, cooling and safety systems.

Hadron tomography studies by generalized parton distributions and distribution amplitudes

We discuss hadron-tomography studies for the nucleon and exotic hadrons by high-energy hadron reactions. First, the constituent-counting rule is explained for determining internal quark configurations of exotic-hadron candidates by scaling properties of high-energy exclusive cross sections. Next, possibilities are discussed for investigating the generalized parton distributions (GPDs) of the nucleon and exotic hadrons at J-PARC. In particular, we study hadronic $2 \to 3$ process $p+p \to N+\pi+B$, exclusive Drell-Yan process, and exotic-hadron GPDs. For determining three-dimensional structure of unstable exotic hadrons, we consider $s$-$t$ crossed quantities of the GPDs called generalized distribution amplitudes (GDAs), which can be investigated at KEKB. We explain possible studies of the GDAs by two-photon processes.

Confronting lepton flavor universality violation in B decays with high- p T tau lepton searches at LHC

We confront the indications of lepton flavor universality (LFU) violation observed in semi-tauonic $B$ meson decays with new physics (NP) searches using high $p_T$ tau leptons at the LHC. Using effective field theory arguments we correlate possible non-standard contributions to semi-tauonic charged currents with the $\tau^+ \tau^-$ signature at high energy hadron colliders. Several representative standard model extensions put forward to explain the anomaly are examined in detail: (i) weak triplet of color-neutral vector resonances, (ii) second Higgs doublet and (iii) scalar or (iv) vector leptoquark. We find that, in general, $\tau^+ \tau^-$ searches pose a serious challenge to NP explanations of the LFU anomaly. Recasting existing 8 TeV and 13 TeV LHC analyses, stringent limits are set on all considered simplified models. Future projections of the $\tau^+ \tau^-$ constraints as well as caveats in interpreting them within more elaborate models are also discussed.

Modeling new XYZ states at JPAC

The observation of the unexpected XYZP resonances has challenged the usual heavy quarkonium framework. One of the most studied exotic states, the X(3872), happens to be copiously produced in high-energy hadron collisions. We discuss how this large prompt production cross-section, together with the comparison with light nuclei production data, disfavors a loosely-bound molecule interpretation, and calls for a new interpretation for the exotic hadron resonances. We also present the research of the Joint Physics Analysis Center in Hadron Spectroscopy.

Color fluctuations in high energy hadron- and photon-nucleus collisions

We explain that coherence of high energy QED and QCD processes implies existence of new kind of phenomena which are beyond a framework based on Regge poles (cuts). New phenomena emerge as the consequence of compositeness of the bound states and the Lorentz slowing down of interaction. We focus on the color fluctuations phenomena predicted earlier for [Formula: see text] collisions within QCD and recent evidence for this phenomenon from [Formula: see text] LHC run, significant modification of nuclear shadowing phenomenon in the diffractive photoproduction of vector mesons observed recently in the ultra peripheral collisions at LHC. We outlined briefly general properties of color fluctuations phenomena and perspectives of future studies of this phenomenon in electron (photon) collisions with nuclei.

Mass Ordering of Spectra from Fragmentation of Saturated Gluon States in High-Multiplicity Proton-Proton Collisions.

The mass ordering of mean transverse momentum ⟨p_{T}⟩ and of the Fourier harmonic coefficient v_{2}(p_{T}) of azimuthally anisotropic particle distributions in high energy hadron collisions is often interpreted as evidence for the hydrodynamic flow of the matter produced. We investigate an alternative initial state interpretation of this pattern in high-multiplicity proton-proton collisions at the LHC. The QCD Yang-Mills equations describing the dynamics of saturated gluons are solved numerically with initial conditions obtained from the color-glass-condensate-based impact-parameter-dependent glasma model. The gluons are subsequently fragmented into various hadron species employing the well established Lund string fragmentation algorithm of the pythia event generator. We find that this initial state approach reproduces characteristic features of bulk spectra, in particular, the particle mass dependence of ⟨p_{T}⟩ and v_{2}(p_{T}).

The MV model of the color glass condensate for a finite number of sources including Coulomb interactions

We modify the McLerran–Venugopalan model to include only a finite number of sources of color charge. In the effective action for such a system of a finite number of sources, there is a point-like interaction and a Coulombic interaction. The point interaction generates the standard fluctuation term in the McLerran–Venugopalan model. The Coulomb interaction generates the charge screening originating from well known evolution in x. Such a model may be useful for computing angular harmonics of flow measured in high energy hadron collisions for small systems. In this paper we provide a basic formulation of the problem on a lattice.

Towards future circular colliders

The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) presently provides proton-proton collisions at a center-of-mass (c.m.) energy of 13 TeV. The LHC design was started more than 30 years ago, and its physics program will extend through the second half of the 2030’s. The global Future Circular Collider (FCC) study is now preparing for a post-LHC project. The FCC study focuses on the design of a 100-TeV hadron collider (FCC-hh) in a new ∼100 km tunnel. It also includes the design of a high-luminosity electron-positron collider (FCCee) as a potential intermediate step, and a lepton-hadron collider option (FCC-he). The scope of the FCC study comprises accelerators, technology, infrastructure, detectors, physics, concepts for worldwide data services, international governance models, and implementation scenarios. Among the FCC core technologies figure 16-T dipole magnets, based on Nb3 S n superconductor, for the FCC-hh hadron collider, and a highly-efficient superconducting radiofrequency system for the FCC-ee lepton collider. Following the FCC concept, the Institute of High Energy Physics (IHEP) in Beijing has initiated a parallel design study for an e + e − Higgs factory in China (CEPC), which is to be succeeded by a high-energy hadron collider (SPPC). At present a tunnel circumference of 54 km and a hadron collider c.m. energy of about 70 TeV are being considered. After a brief look at the LHC, this article reports the motivation and the present status of the FCC study, some of the primary design challenges and R&D subjects, as well as the emerging global collaboration.

The impact of s- $\bar{s}$ asymmetry on the strange electromagnetic form factor

The existence of the strange quark asymmetry in the nucleon sea has been indicated by both the experimental and theoretical analyses. Although it is well known that the s-\(\bar{{s}}\) asymmetry is important for some processes in high-energy hadron collisions, it has also been indicated that it can be related to the strange Dirac form factor F1s. In this work, we have studied the impact of s-\( \bar{{s}}\) asymmetry and its uncertainty from various modern parton distribution functions (PDFs) on F1s and compared the obtained results with the available experimental information. As a result, we found that the uncertainty in F1s(t) due to the s(x) - \( \bar{s}\)(x) distribution is rather large so that it dominates the model uncertainty at all values of the squared momentum transfer t. However, taking into account the uncertainties, the theoretical predictions of F1s(t) are fully compatible with the estimate extracted from experiment. We concluded that the future accurate experimental data of the strange Dirac form factor might be used to put direct constraints on the strange content of the proton and reduce its uncertainty that has always been a challenge.

Embedded Detection and Correction of SEU Bursts in SRAM Memories Used as Radiation Detectors

SRAM memories are widely used as particle fluence detectors in high radiation environments, such as in the Radiation Monitoring System (RadMon) currently in operation in the CERN accelerator complex. Multiple Cell Upsets (MCUs), arising from micro-latchup events, are characterized by a large number of SEUs, ultimately affecting the measurement of particle fluxes and resulting in corrupted data and accuracy losses. A study of the generation of this type of SEU bursts was performed on an 8 Mbit 90-nm SRAM memory. Experimental tests were carried out with a focused beam of protons on target as well as in a mixed field environment dominated by high energy hadrons. A solution approach using an on-line detection and correction algorithm embedded on an FPGA was investigated and evaluated for use on a RadMon device.

Precision muon tracking detectors for high-energy hadron colliders

Small-diameter muon drift tube (sMDT) chambers with 15mm tube diameter are a cost-effective technology for high-precision muon tracking over large areas at high background rates as expected at future high-energy hadron colliders including HL-LHC. The chamber design and construction procedures have been optimised for mass production and provide sense wire positioning accuracy of better than 10μm. The rate capability of the sMDT chambers has been extensively tested at the CERN Gamma Irradiation Facility. It exceeds the one of the ATLAS muon drift tube (MDT) chambers, which are operated at unprecedentedly high background rates of neutrons and γ-rays, by an order of magnitude, which is sufficient for almost the whole of the muon detector acceptance at FCC-hh at maximum luminosity. sMDT operational and construction experience exists from ATLAS muon spectrometer upgrades which are in progress or under preparation for LHC Phase 1 and 2.

Detection of thermal neutrons with the PRISMA-YBJ array in extensive air showers selected by the ARGO-YBJ experiment

We report on a measurement of thermal neutrons, generated by the hadronic component of extensive air showers (EAS), by means of a small array of EN-detectors developed for the PRISMA project (PRImary Spectrum Measurement Array), novel devices based on a compound alloy of ZnS(Ag) and 6LiF. This array has been operated within the ARGO-YBJ experiment at the high altitude Cosmic Ray Observatory in Yangbajing (Tibet, 4300 m a.s.l.). Due to the tight correlation between the air shower hadrons and thermal neutrons, this technique can be envisaged as a simple way to estimate the number of high energy hadrons in EAS. Coincident events generated by primary cosmic rays of energies greater than 100 TeV have been selected and analyzed. The EN-detectors have been used to record simultaneously thermal neutrons and the air shower electromagnetic component. The density distributions of both components and the total number of thermal neutrons have been measured. The correlation of these data with the measurements carried out by ARGO-YBJ confirms the excellent performance of the EN-detector.

Space-Time Development of Electromagnetic and Hadronic Showers and Perspectives for Novel Calorimetric Techniques

The performance of hadronic calorimeters will be a key parameter at the next generation of High Energy Physics accelerators. A detector combining fine granularity with excellent timing information would prove beneficial for the reconstruction of both jets and electromagnetic particles with high energy resolution. In this work, the space and time structure of high energy showers is studied by means of a Geant 4-based simulation toolkit. In particular, the relevant time scales of the different physics phenomena contributing to the energy loss are investigated. A correlation between the fluctuations of the energy deposition of high energy hadrons and the time development of the showers is observed, which allows for an event-by-event correction to be computed to improve the energy resolution of the calorimeter. These studies are intended to set the basic requirements for the development of a new-concept, total absorption time-imaging calorimeter, which seems now within reach thanks to major technological advancements in the production of fast scintillating materials and compact photodetectors.