Lepton-hadron Collisions Research Articles

Muon ring and FCC-ee/CEPC based antimuon-electron colliders

Recently, the construction of an antimuon-electron collider, μTRISTAN, at KEK has been proposed. We argue that the construction of a similar muon ring tangential to FCC-ee and CEPC will give an opportunity to realize antimuon-electron collisions at higher center-of-mass energies. Moreover, the same ring may be used later to realize energy-frontier antimuon-proton colliders based on FCC-pp and SppC. Similarly, the change of the electron ring in the μTRISTAN project into the proton ring will give the opportunity to investigate lepton-hadron collisions at ∼2 TeV center-of-mass energies. In this paper the main parameters of the proposed colliders have been studied. It is shown that sufficiently high luminosities can be achieved for all proposals under consideration.

A POWHEG generator for deep inelastic scattering

We present a new event generator for the simulation of both neutral- and charged-current deep inelastic scattering (DIS) at next-to-leading order in QCD matched to parton showers using the POWHEG method. Our implementation builds on the existing POWHEG BOX framework originally designed for hadron-hadron collisions, supplemented by considerable extensions to account for the genuinely different kinematics inherent to lepton-hadron collisions. In particular, we present new momentum mappings that conserve the special kinematics found in DIS, which we use to modify the POWHEG BOX implementation of the Frixione-Kunszt-Signer subtraction mechanism. We compare our predictions to fixed-order and resummed predictions, as well as to data from the HERA ep collider. Finally we study a few representative distributions for the upcoming Electron Ion Collider.

Revisiting NLO QCD corrections to total inclusive J/ψ and ϒ photoproduction cross sections in lepton-proton collisions

We revisit inclusive J/ψ and ϒ photoproduction at lepton-hadron colliders, namely in the limit when the exchanged photon is quasi real. Our computation includes the next-to-leading-order (NLO) αs corrections to the leading-order contributions in v. Similarly to the case of NLO charmonium-hadroproduction processes, the resulting cross sections obtained in the MS‾ factorisation scheme are sometimes found to be negative. We show that the scale-fixing criterion which we derived in a previous study of ηc production successfully solves this problem from the EicC all the way up to the FCC-eh energies. We then elaborate on how to study a scale uncertainty akin to that derived by scale variations when one fixes a scale. In turn, we investigate where both J/ψ and ϒ photoproduction could be used to improve our knowledge of gluon content of the proton at scales as low as a couple of GeV.

Electron-Hadron Colliders: EIC, LHeC and FCC-eh

Electron-hadron colliders are the ultimate tool for high-precision quantum chromodynamics studies and provide the ultimate microscope for probing the internal structure of hadrons. The electron is an ideal probe of the proton structure because it provides the unmatched precision of the electromagnetic interaction, as the virtual photon or vector bosons probe the proton structure in a clean environment, the kinematics of which is uniquely determined by the electron beam and the scattered lepton, or the hadronic final state accounting appropriately for radiation. The Hadron Electron Ring Accelerator HERA (DESY, Hamburg, Germany) was the only electron-hadron collider ever operated (1991–2007) and advanced the knowledge of quantum chromodynamics and the proton structure, with implications for the physics studied in RHIC (BNL, Upton, NY) and the LHC (CERN, Geneva, Switzerland). Recent technological advances in the field of particle accelerators pave the way to realize next-generation electron-hadron colliders that deliver higher luminosity and enable collisions in a much broader range of energies and beam types than HERA. Electron-hadron colliders combine challenges from both electron and hadron machines besides facing their own distinct challenges derived from their intrinsic asymmetry. This review paper will discuss the major features and milestones of HERA and will examine the electron-hadron collider designs of the Electron-Ion Collider (EIC) currently under construction at BNL, the CERN’s Large Hadron electron Collider (LHeC), at an advanced stage of design and awaiting approval, and the Future Circular lepton-hadron Collider (FCC-eh).

Factorized approach to radiative corrections for inelastic lepton-hadron collisions

We propose a factorized approach to QED radiative corrections for inclusive and semi-inclusive deep-inelastic scattering to systematically account for QED and QCD radiation contributions to both processes on equal footing. This is achieved by utilizing factorization to resum logarithmically enhanced QED radiation into universal lepton distribution and fragmentation (or jet) functions. Numerical simulations suggest that the QED effects induced by the rotational distortion of the hadron transverse momentum, arising from the mismatch between the experimental Breit frame and the true photon-hadron frame, can be as large as 50\% for moderate $Q$, and become increasingly important for large transverse momenta. Our framework provides a uniform treatment of radiative effects for extracting three-dimensional hadron structure from high-energy lepton-hadron scattering at current and future facilities, such as the Electron-Ion Collider.

Large-PT inclusive photoproduction of J/ψ in electron-proton collisions at HERA and the EIC

We study the inclusive J/ψ production at large transverse momenta at lepton-hadron colliders in the limit when the exchange photon is quasi real, also referred to as photoproduction. Our computation includes the leading-PT leading-v next-to-leading αs corrections. In particular, we consider the contribution from J/ψ plus another charm quark, by employing for the first time in quarkonium photoproduction the variable-flavour-number scheme. We also include a QED-induced contribution via an off-shell photon which remained ignored in the literature and which we show to be the leading contribution at high PT within the reach of the EIC. In turn, we use our computation of J/ψ+charm to demonstrate its observability at the future EIC and the EIC sensitivity to probe the non-perturbative charm content of the proton at high x.

Charting the coming synergy between lattice QCD and high-energy phenomenology

Building upon the PDFSense framework developed in Ref. [1], we perform a comprehensive analysis of the sensitivity of present and future high-energy data to a number of quantities commonly evaluated in lattice gauge theory, with a particular focus on the integrated Mellin moments of nucleon parton distribution functions (PDFs), such as $\langle x \rangle_{u^+ - d^+}$ and $\langle x \rangle_{g}$, as well as $x$-dependent quark quasi-distributions -- in particular, that of the isovector combination. Our results demonstrate the potential for lattice calculations and phenomenological quark distributions informed by high-energy experimental data to cooperatively improve the picture of the nucleon's collinear structure. This will increasingly be the case as computational resources for lattice calculations further expand, and QCD global analyses continue to grow in sophistication. Our sensitivity analysis suggests that a future lepton-hadron collider would be especially instrumental in providing phenomenological constraints to lattice observables.

Single production of composite electrons at future SPPC-based lepton–hadron colliders

We consider the production of excited electrons with spin-1/2 at future SPPC-based electron–proton colliders with center-of-mass energies of 8.4, 11.6, 26.6, and 36.8 TeV. These exotic particles are predicted in the composite models. We calculate the production cross sections and concentrate on the photon decay channel of the excited electrons with the process of ep → e∗X → eγX. The pseudo rapidity and transverse momentum distributions of the electrons and photons in the final state have been plotted to determine the kinematical cutoffs best suited for discovery of the excited electrons. By applying these cutoffs we compute 2σ, 3σ, and 5σ contour plots of the statistical significance of the expected signal in the parameter space (L, m∗), where L denotes the integrated luminosity of the collider and m∗ is the mass of the composite electrons.

Single production of the excited electrons in the future FCC-based lepton–hadron colliders

We study the composite electron production at the FCC-based three electron–proton colliders with the center-of-mass energies of 3.46, 10 and 31.6 TeV. For the signal process of [Formula: see text], the production cross-sections and decay widths of the excited electrons have been calculated. The differences of some kinematical quantities of the final state particles between the signal and background have been analyzed. For this purpose, transverse momentum and pseudorapidity distributions of electron and photon have been obtained and the kinematical cuts for discovery of the excited electrons have been assigned. We have finally determined the mass limits of excited electrons for observation and discovery by applying these cuts. It is shown that the mass limit for discovery obtained from the collider with [Formula: see text] TeV (called PWFA-LC[Formula: see text]⊗[Formula: see text]FCC) is 22.3 TeV for the integrated luminosity [Formula: see text].

Energy-Frontier Lepton-Hadron Collisions at CERN: The LHeC and the FCC-eh

Lepton-hadron colliders that use a proton or nucleus beam of current and future hadron colliders and let it collide with an electron beam from a newly built electron accelerator bring attractive physics programs which are strong and complementary to the hadron collider physics. Machine development for Energy Recovery LINAC and physics performance studies of such electron-hadron colliders, specifically the LHeC that uses the existing LHC beam and FCC-eh that is an option of Future Circular Collider program, are ongoing and reviewed in this article.

Announcement for the replacement of the PACIAE 2.1 and PACIAE 2.2 series

We replace the old PACIAE 2.1 and PACIAE 2.2 program series with new ones, respectively. In the new program series, the method of creation of the partonic initial state is changed, an option for calling PYEVNT or PYEVNW in PYTHIA is added, and the few bugs in the calculation for the reduction of strange quark suppression are corrected. New version program summaryProgram Title: PACIAE version 2.1 & 2.2Program Files doi:http://dx.doi.org/10.17632/w3g68dj4d9.1Licensing provisions: CC By 4.0Programming language: FORTRAN 77Journal reference of previous version: Comput. Phys. Comm. 184 (2013) 1476, 193 (2015) 89.Does the new version supersede the previous version?: YesNature of problem: PYEVNT is the subroutine in PYTHIA to administer the generation of a high-pT event via calls a number of subroutines. PYEVNW is the new subroutine in PYTHIA to administer the generation of an event for new multiple interactions scenario. In previous PACIAE versions only PYEVNT is called, while both PYEVNT and PYEVNW can be called in this new version.Solution method: There has been added a parameter of mstp81 in PACIAE programs and input files of usux.dat (for 21a or 22a) and usu.dat (for 21b, 21c ,22b and 22c). The PACIAE will call PYEVNT when mstp81=1( default) and call PYEVNW when mstp81=21.Reasons for the new version: The method of creation of the partonic initial state is changed, an option for calling PYEVNT or PYEVNW in PYTHIA is added, and the few bugs in the calculation for the reduction of strange quark suppression are corrected in the new version.Summary of revisions: The PACIAE model [1] is a parton and hadron cascade model based on PYTHIA [2]. PACIAE model consists of four stages of the parton initiation, the parton evolution (rescattering), the hadronization, and the hadron evolution (rescattering). The stage of parton initiation is just by means of PYTHIA model and the rest are modeled by us [1]. PYTHIA model is for the high energy elementary particle collisions such as hadron–hadron and lepton–hadron collisions, but PACIAE model is also for high energy lepton–nucleus, hadron–nucleus and nucleus–nucleus collisions.So far, the PACIAE model has three series of PACIAE 2.0 (catalogue identifier: AEKI_v1_0) [1], PACIAE 2.1 (AEKI_v2_0) [3], and PACIAE 2.2 (AEKI_v2_2) [4]. The discrepancy between PACIAE 2.0 and PACIAE 2.1 is just the sampling of momentum x and y components at fixed pT. In the PACIAE 2.0 it is sampled on the circle with radius of pT, but on the circumference of ellipse with half major and minor axes of pT(1+δp) and pT(1−δp), respectively in PACIAE 2.1. Including the reaction of lepton–nucleon and lepton–nucleus is the distinction of PACIAE 2.2 series from the PACIAE 2.1. Each series of PACIAE 2.0, PACIAE 2.1 and PACIAE 2.2 consists of a, b, and c packages. The package of PACIAE 2.1a, for instance, is for the high energy elementary collisions, while the PACIAE 2.1b as well as PACIAE 2.1c for the high energy hadron–nucleus and nucleus–nucleus collisions. We refer to [1] for the difference between PACIAE 2.0b and PACIAE 2.0c (PACIAE 2.1b and PACIAE 2.1c as well as PACIAE 2.2b and PACIAE 2.2c).In this replacement the modifications are as follows: 1.The method of creation of a partonic initial state is changed from setting mstj(1)=0 (or mstp(111)=0) before “CALL PYINIT” to adding a “RETURN” statement before the statement of “CALL PYEXEC” in subroutine PYEVNT (PYEVNW) in p21b.f.2.Correcting the mistakes in the calculation for the mechanism of reduction of strange quark suppression.3.Calling PYEVNT or PYEVNW is controlled by mstp(81) (=1 or 21) instead of calling PYEVNT only originally.

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.

Invisible Higgs decay at the Large Hadron-Electron Collider

The possibility that the 125 GeV Higgs boson may decay into invisible non-standard-model (non-SM) particles is theoretically and phenomenologically intriguing. In this letter we investigate the sensitivity of the Large Hadron Electron Collider (LHeC) to an invisibly decaying Higgs, in its proposed high luminosity running mode. We focus on the neutral current Higgs production channel which offers more kinematical handles than its charged current counterpart. The signal contains one electron, one jet and large missing energy. With a cut-based parton level analysis, we estimate that if the $hZZ$ coupling is at its standard model (SM) value, then assuming an integrated luminosity of $1\,\mbox{ab}^{-1}$ the LHeC with the proposed 60 GeV electron beam (with $-0.9$ polarization) and 7 TeV proton beam is capable of probing $\mathrm{Br}(h\rightarrow E\!\!\!\!/_T)=6\%$ at $2\sigma$ level. Good lepton veto performance (especially hadronic $\tau$ veto) in the forward region is crucial to the suppression of the dominant $Wje$ background. We also explicitly point out the important role that may be played by the LHeC in probing a wide class of exotic Higgs decay processes and emphasize the general function of lepton-hadron colliders in precision study of new resonances after their discovery in hadron-hadron collisions.

Cut moments and a generalization of DGLAP equations

We elaborate a cut (truncated) Mellin moments (CMM) approach that is constructed to study deep inelastic scattering in lepton-hadron collisions at the natural kinematic constraints. We show that generalized CMM obtained by multiple integrations of the original parton distribution $f(x,\mu^2)$ as well as ones obtained by multiple differentiations of this $f(x,\mu^2)$ also satisfy the DGLAP equations with the correspondingly transformed evolution kernel $P(z)$. Appropriate classes of CMM for the available experimental kinematic range are suggested and analyzed. Similar relations can be obtained for the structure functions $F(x)$, being the Mellin convolution $F= C \ast f$, where $C$ is the coefficient function of the process.

F2andFLat smallxusing a collinearly improved BFKL resummation

We present a detailed description of the ${Q}^{2}$ and $x$ dependence of the structure functions ${F}_{2}$ and ${F}_{L}$ as extracted from the deep inelastic scattering data at HERA in the small Bjorken $x$ region. Making use of a collinearly improved Balitsky-Fadin-Kuraev-Lipatov equation at next-to-leading order and a treatment of the running of the coupling using non-Abelian physical renormalization together with the Brodsky-Lepage-Mackenzie scale choice allows us to reach low values of ${Q}^{2}$. We also provide some predictions for future lepton-hadron colliders.

Longitudinally polarized photoproduction of heavy flavors at next-to-leading order of QCD

We present a phenomenological study of charm quark photoproduction in longitudinally polarized lepton–hadron collisions at next-to-leading order accuracy of QCD. Our results are based on a recently developed, flexible parton-level Monte Carlo program for spin-dependent heavy flavor hadroproduction, which we extend to deal also with both direct and resolved photon contributions. The subsequent hadronization into charmed mesons is modeled in our calculations, which allows us to compare with data on double-spin asymmetries for D 0 meson production taken by the COMPASS collaboration. In general, next-to-leading order QCD corrections are found to be very significant and do not cancel in spin asymmetries. We elucidate the role of the individual hard scattering subprocesses and determine the range of parton momentum fractions predominantly probed for charm production at COMPASS. Theoretical uncertainties are estimated by varying renormalization and factorization scales and parameters controlling the hadronization of the charm quarks.

Structure function method of QED radiative corrections calculation for processes on lepton-hadron, lepton-photon, and lepton-lepton colliders

Structure function method of QED radiative corrections calculation for processes on lepton-hadron, lepton-photon, and lepton-lepton colliders

Photoproduction of single inclusive jets at futureepcolliders in next-to-leading order QCD

A next-to-leading order QCD calculation for single-inclusive jet photoproduction in unpolarized and longitudinally polarized lepton-hadron collisions is presented which consistently includes ``direct'' and ``resolved'' photon contributions. The computation is performed within the ``small-cone approximation'' in a largely analytical form. Phenomenological aspects of jet production at future $ep$ colliders such as the CERN Large Hadron electron Collider and the polarized Brookhaven National Laboratory eRHIC are discussed, placing particular emphasis on the perturbative stability of the predictions and the possibility to constrain the parton content of the photon.

Possibility of searching for fourth generation neutrino at future ep colliders

We investigate the production of fourth generation neutrino in the context of a new eν4W magnetic dipole moment type interaction in ep collisions at future lepton–hadron colliders. We have obtained the mass limits of 700 GeV for THERA (S=1 TeV) and 2.8 TeV for LC⊗LHC (S=3.74 TeV).

A UNIFIED APPROACH TO NNLO SOFT AND VIRTUAL CORRECTIONS IN ELECTROWEAK, HIGGS, QCD, AND SUSY PROCESSES

I present a unified approach to calculating the next-to-next-to-leading order (NNLO) soft and virtual QCD corrections to cross-sections for electroweak, Higgs, QCD, and SUSY processes. I derive master formulas that can be used for any of these processes in hadron–hadron and lepton–hadron collisions. The formulas are based on a unified threshold resummation formalism and can be applied to both total and differential cross-sections for processes with either simple or complex color flows and for various factorization schemes and kinematics. As a test of the formalism, I rederive known NNLO results for Drell–Yan and Higgs production, deep inelastic scattering, and W+γ production, and I obtain expressions for several two-loop anomalous dimensions and other quantities needed in next-to-next-to-leading-logarithm (NNLL) resummations. I also present new results for the production of supersymmetric charged Higgs bosons; massive electroweak vector bosons; photons; heavy quarks in lepton–hadron and hadron–hadron collisions and in flavor-changing neutral current processes; jets; and squarks and gluinos. The NNLO soft and virtual corrections are often dominant, especially near threshold, and they reduce the scale dependence of the cross-section. Thus, a unified approach to these corrections is important in the search for new physics at present and future colliders.