Future Electron-positron Colliders Research Articles

NLO QCD corrections forJ/ψ+c+c¯production in photon-photon collision

The $\ensuremath{\gamma}+\ensuremath{\gamma}\ensuremath{\rightarrow}J/\ensuremath{\psi}+c+\overline{c}$ inclusive process is an extremely important subprocess in $J/\ensuremath{\psi}$ production via photon-photon scattering, like at LEPII or various types of future electron-positron colliders. In this work we perform the next-to-leading order (NLO) QCD corrections to this process in the framework of nonrelativistic QCD (NRQCD) factorization formalism, the first NLO calculation for two projectiles to the 3-body quarkonium inclusive production process. By setting the center-of-mass energy at LEPII, the $\sqrt{s}=197\text{ }\text{ }\mathrm{GeV}$, we conduct analyses of the ${p}_{t}^{2}$ distribution and total cross section of this process at the NLO accuracy. It turns out that the total cross section is moderately enhanced by the NLO correction with a $K$ factor of about 1.46, and hence the predicted $J/\ensuremath{\psi}$ inclusive productivity is increased while the DELPHI data still overshoot the theoretical prediction. At the future Circular Electron-Positron Collider, the NLO corrections are found to be more significant, with a $K$ factor of about 1.76.

Bounds on the Electromagnetic Dipole Moments through the Single Top Production at the CLIC

We obtain bounds on the anomalous magnetic and electric dipole moments of thet-quark from a future high-energy and high-luminosity linear electron positron collider, as the CLIC, with polarized and unpolarized electron beams which are powerful tools for determining new physics. We consider the processesγe-→t¯bνe(γis the Compton backscattering photon) ande+e-→e-γ⁎e+→t¯bνee+(γ⁎is the Weizsacker-Williams photon) as they are one of the most important sources of single top quark production. For systematic uncertainties ofδsys=0% (5%),b-tagging efficiency=0.8, center-of-mass energy ofs=3 TeV, and integrated luminosity ofL=2ab-1the futuree+e-collider may put bounds on the electromagnetic dipole momentsa^Vanda^Aof the top quark of the order ofO(10-2–10-1)at the2σ (3σ)level, which are competitive with those recently reported in previous studies at hadron colliders and the ILC.

Interference Effects in a Very Precise Measurement of the Muon Charge Asymmetry at FCC-ee

At the future high luminosity electron-positron collider FCC-ee proposed for CERN, the precise measurement of the charge asymmetry in $e^+ e^- \to \mu^+ \mu^-$ near the Z resonance is of special interest. In particular, such a measurement at $M_Z \pm 3.5$ GeV may provide a very precise measurement of the electromagnetic coupling at the scale $\sim M_Z$, a fundamental constant of the Standard Model. However, this charge asymmetry is plagued by a large trivial contribution from the interference of photon emission from initial state electrons and final state muons. We address the question whether this interference can be reliably calculated and subtracted with the help of a resummed QED calculation.

JINR LHEP photoinjector prototype

A photoinjector prototype for future electron–positron colliders and free-electron lasers (FEL) is being developed at the Joint Institute for Nuclear Research (JINR). A 30-keV photogun stand, transmission (backside irradiated) photocathode concept, and stand investigations of such cathodes in collaboration with Institute of Electrical Engineering (IEE SAS) (Bratislava, the Slovak Republic) are described. A progress report on creating the photoinjector at an electron energy of up to 400 keV with a unique 10-ps laser driver is given.

Single and double production of the Higgs boson at hadron and lepton colliders in minimal composite Higgs models

In the composite Higgs models, originally proposed by Georgi and Kaplan, the Higgs boson is a pseudo Nambu-Goldstone boson (pNGB) of spontaneous breaking of a global symmetry. In the minimal version of such models, global SO(5) symmetry is spontaneously broken to SO(4), and the pNGBs form an isospin doublet field, which corresponds to the Higgs doublet in the Standard Model (SM). Predicted coupling constants of the Higgs boson can in general deviate from the SM predictions, depending on the compositeness parameter. The deviation pattern is determined also by the detail of the matter sector. We comprehensively study how the model can be tested via measuring single and double production processes of the Higgs boson at LHC and future electron-positron colliders. The possibility to distinguish the matter sector among the minimal composite Higgs models is also discussed. In addition, we point out differences in the cross section of double Higgs boson production from the prediction in other new physics models.

Heavy neutrino impact on the triple Higgs coupling

We present the first calculation of the one-loop corrections to the triple Higgs coupling in the framework of a simplified 3+1 Dirac neutrino model, that is three light neutrinos plus one heavy neutrino embedded in the Standard Model (SM). The triple Higgs coupling is a key parameter of the scalar potential triggering the electroweak symmetry-breaking mechanism in the SM. The impact of the heavy neutrino can be as large as $+20\%$ to $+30\%$ for parameter points allowed by the current experimental constraints depending on the tightness of the perturbative bound. This can be probed at the high-luminosity LHC, at future electron-positron colliders and at the Future Circular Collider in hadron-hadron mode, an envisioned 100 TeV $pp$ machine. Our calculation, being done in the mass basis, can be extended to any model using the neutrino portal. In addition, the effects that we have calculated are expected to be enhanced if additional heavy fermions with large Yukawa couplings are included, as in low-scale seesaw mechanisms.

Measuring the trilinear neutral Higgs boson couplings in the minimal supersymmetric standard model at e+e− colliders in the light of the discovery of a Higgs boson

We consider the measurement of the trilinear couplings of the neutral Higgs bosons in the minimal supersymmetric standard model (MSSM) at a high energy [Formula: see text] linear collider in the light of the discovery of a Higgs boson at the CERN Large Hadron Collider (LHC). We identify the state observed at the LHC with the lightest Higgs boson [Formula: see text] of the MSSM, and impose the constraints following from this identification, as well as other experimental constraints on the MSSM parameter space. In order to measure trilinear neutral Higgs couplings, we consider different processes where the heavier Higgs boson [Formula: see text] of the MSSM is produced in electron–positron collisions, which subsequently decays into a pair of lighter Higgs boson. We identify the regions of the MSSM parameter space where it may be possible to measure the trilinear couplings of the Higgs boson at a future electron–positron collider. A measurement of the trilinear Higgs couplings is a crucial step in the construction of the Higgs potential, and hence in establishing the phenomena of spontaneous symmetry breaking in gauge theories.

Studies on GEM modules for a Large Prototype TPC for the ILC

The International Linear Collider (ILC) is a future electron–positron collider with centre of mass energy of 500–1000GeV. The International Large Detector (ILD) is one of two detector concepts at the ILC. Its high precision tracking system consists of Silicon sub-detectors and a Time Projection Chamber (TPC) equipped with micro-pattern gas detectors (MPGDs). Within the framework of the LCTPC collaboration, a Large Prototype (LP) TPC has been built as a demonstrator. This prototype has been equipped with Gas Electron Multiplier (GEM) modules and studied with electron beams of energies 1–6GeV at the DESY test beam facility. The performance of the prototype detector and the extrapolation to the ILD TPC is presented here. In addition, ongoing optimisation studies and R&D activities in order to prepare the next GEM module iteration are discussed.

Study of the performance of a compact sandwich calorimeter for the instrumentation of the very forward region of a future linear collider detector

The FCAL collaboration is preparing large scale prototypes of special calorimeters to be used in the very forward region at a future linear electron positron collider for a precise and fast luminosity measurement and beam-tuning. These calorimeters are designed as sensor-tungsten calorimeters with very thin sensor planes to keep the Moliere radius small and dedicated FE electronics to match the timing and dynamic range requirements. A partially instrumented prototype was investigated in the CERN PS T9 beam in 2014 and at the DESY-II Synchrotron in 2015. It was operated in a mixed particle beam (electrons, muons and hadrons) of 5GeV from PS facilities and with secondary electrons of 5GeV energy from DESY-II. The results demonstrated a very good performance of the full readout chain. The high statistics data were used to study the response to different particles, perform sensor alignment and measure the longitudinal shower development in the sandwich. In addition, Geant4 MC simulations were done, and compared to the data.

Higgs Phenomenology of the Supersymmetric Grand Unification with the Hosotani Mechanism

The supersymmetric S U(5) grand unified theory with the gauge symmetry broken by the Hosotani mechanism naturally solves the mass hierarchy problem between the colored Higgs triplet and the electroweak Higgs doublet, and predicts the existence of adjoint chiral superfields with masses of the order of the supersymmetry breaking scale as a byproduct. In addition to the two SU(2)L Higgs doublets of the minimal supersymmetric standard model, the Higgs sector is extended by an SU(2)L triplet chiral supermultiplet with hypercharge zero and a neutral singlet one. Such new triplet and singlet chiral supermultiplets deviate the standard model-like Higgs boson couplings and the additional Higgs boson masses from their Standard Model predictions. We show that this model can be distinguished from other new physics models using by precisely measuring such Higgs couplings and masses, and that our model is a good example of grand unification testable at the luminosity up-graded Large Hadron Collider and future electron-positron colliders.

Higgs Physics at CLIC

The Compact Linear Collider (CLIC) is an attractive option for a future multi-TeV linear electron-positron collider, offering the potential for a rich precision physics programme, combined with sensitivity to a wide range of new phenomena. The physics reach of CLIC has been studied in the context of three distinct centre-of-mass energies, s=350 GeV, 1.4 TeV and 3.0 TeV. This staged scenario provides an excellent environment for precise studies of the properties of the 126 GeV Higgs boson. Operation at s=350 GeV allows, on the one hand, for a determination of the couplings and width of the Higgs boson in a model-independent manner through the study of the Higgsstrahlung process, and on the other hand, for a study of Higgs bosons produced in W+W− fusion for the most common Higgs decay modes. Operation at higher centre-of-mass energies, s1.4 TeV and 3 TeV, provides high statistics W+W− fusion samples allowing for high precision measurements of many Higgs couplings and a study of rare Higgs decay modes, Higgs boson samples produced in ZZ fusion, and the potential to study the top Yukawa coupling as well as the Higgs boson self-coupling. We explore the potential of the CLIC Higgs physics programme based on full simulation studies of a wide range of final states. The evolution of the physics sensitivity as a function of the centre-of-mass energy is presented in terms of combined fits to all measurements and their respective statistical uncertainty.

Probing the fermionic Higgs portal at lepton colliders

We study the sensitivity of future electron-positron colliders to UV completions of the fermionic Higgs portal operator $H^\dagger H \bar \chi \chi$. Measurements of precision electroweak $S$ and $T$ parameters and the $e^+e^- \to Zh$ cross section at the CEPC, FCC-ee, and ILC are considered. The scalar completion of the fermionic Higgs portal is closely related to the scalar Higgs portal, and we summarize existing results. We devote the bulk of our analysis to a singlet-doublet fermion completion. Assuming the doublet is sufficiently heavy, we construct the effective field theory (EFT) at dimension-6 in order to compute contributions to the observables. We also provide full one-loop results for $S$ and $T$ in the general mass parameter space. In both completions, future precision measurements can probe the new states at the (multi-)TeV scale, beyond the direct reach of the LHC.

Phenomenology of the Georgi-Machacek model at future electron-positron colliders

We study the phenomenology of the exotic Higgs bosons in the Georgi-Machacek model at future electron-positron colliders such as the International Linear Collider (ILC), assuming the collision energies of 500 GeV and 1 TeV. We show that the existence of the neutral and singly charged Higgs bosons in the 5-plet representation under the custodial $SU(2{)}_{V}$ symmetry can be readily identified by studying various energy and invariant mass distributions of the ${W}^{+}{W}^{\ensuremath{-}}Z$ final state. Moreover, their masses can be determined with sufficiently high precision to test the mass degeneracy, a feature due to the custodial symmetry of the model. A synergy between such searches at the ILC and the doubly charged Higgs search at the LHC will make the 5-plet Higgs boson study more comprehensive.

A calibration system for Compton polarimetry at e+e− linear colliders

Polarimetry with permille-level precision is essential for future electron-positron linear colliders. Compton polarimeters can reach negligible statistical uncertainties within seconds of measurement time. The dominating systematic uncertainties originate from the response and alignment of the detector which records the Compton scattered electrons. The robust baseline technology for the Compton polarimeters foreseen at future linear colliders is based on an array of gas Cherenkov detectors read out by photomultipliers. In this paper, we will present a calibration method which promises to monitor nonlinearities in the response of such a detector at the level of a few permille. This method has been implemented in an LED-based calibration system which matches the existing prototype detector. The performance of this calibration system is sufficient to control the corresponding contribution to the total uncertainty on the extracted polarisation to better than 0.1%.

Energy reconstruction in a highly granularity semi-digital hadronic calorimeter

The Semi-Digital Hadronic CALorimeter(SDHCAL) using Glass Resistive Plate Chambers (GRPCs) is one of the calorimeters proposed for particle physics experiments at the future electron-positron collider. It is a high granularity calorimeter which is required for the application of the particle flow algorithm in order to improve the jet energy resolution as one of the goals of this experiments. We discuss the energy reconstruction, based on digital and semi-Digital methods, to study the effect on the improvement of the single particle energy resolution and the linearity of the detecor response. This study was performed with the GEANT4 simulation. Results on the energy resolution and linearity, for negative pions over an energy range from 1 to 100 GeV are presented and compared with different energy reconstruction methods including Artificial Neural Networks.

Indirect reach of heavy MSSM Higgs bosons by precision measurements at future lepton colliders

In the Minimal Supersymmetric Standard Model (MSSM), the bottom Yukawa coupling of the Higgs boson can considerably deviate from its Standard Model prediction due to nondecoupling effects. We point out that the ratio of the Higgs boson decay branching fraction to a bottom quark pair and that to a W-boson pair from the same production channel is particularly sensitive to large additional MSSM Higgs boson mass regions at future electron–positron colliders. Based on this precision measurement, we explicitly show the indirect discovery reach of the additional Higgs bosons according to planned programs of the International Linear Collider.

Anomalous Higgs-top coupling pollution of the triple Higgs coupling extraction at a future high-luminosity electron-positron collider

One of the most challenging tasks for future high-luminosity electron-positron colliders is to extract Higgs triple coupling. It was proposed that this can be carried out via the precisely measuring the cross section of ZH associated production up to $0.4\%$. In this paper, we example the possible heavy pollution from Higgs-top anomalous coupling. Our numerical results show that the pollution is small for $\sqrt{s}_{e^+e^-}= 240 GeV$. However for the higher energy collider, pollution is sizable, which should be taken into account. We further explored the possibility to measure CP-violated Higgs top coupling, via the forward-backward asymmetry $A_{FB}$ for the process $e^+e^- \rightarrow ZH$. The asymmetry can reach $0.7\%$ which is comparable to the precision of cross section measurement.

DEPFET detectors for future electron-positron colliders

The DEPFET Collaboration develops highly granular, ultra-thin pixel detectors for outstanding vertex reconstruction at future electron-positron collider experiments. A DEPFET sensor, by the integration of a field effect transistor on a fully depleted silicon bulk, provides simultaneous position sensitive detector capabilities and in pixel amplification. The characterization of the latest DEPFET prototypes has proven that a adequate signal-to-noise ratio and excellent single point resolution can be achieved for a sensor thickness of 50 micrometers. The close to final auxiliary ASICs have been produced and found to operate a DEPFET pixel detector of the latest generation with the required read-out speed. A complete detector concept is being developed for the Belle II experiment at the new Japanese super flavor factory. DEPFET is not only the technology of choice for the Belle II vertex detector, but also a prime candidate for the ILC. Therefore, in this contribution, the status of DEPFET R&D project is reviewed in the light of the requirements of the vertex detector at a future electron-positron collider.

Probing HZγ and Hγγ anomalous couplings in the process e+e−→ Hγ**Supported by National Science Foundation of China (11275009)

We propose to measure the HZγ and Hγγ anomalous couplings in the process e+e− → Hγ with the sequential decay of H → bb̄. The discovery potential of observing the anomalous couplings are explored in detail. Our study shows that future electron-positron colliders have great potential to test the HZγ and Hγγ couplings. Conservative bounds on the two anomalous couplings are also derived when no new physics signal is detected on top of the SM backgrounds.

Beam dump experiment at future electron–positron colliders

We propose a new beam dump experiment at future colliders with electron (e−) and positron (e+) beams, BDee, which will provide a new possibility to search for hidden particles, like hidden photon. If a particle detector is installed behind the beam dump, it can detect the signal of in-flight decay of the hidden particles produced by the scatterings of e± beams off materials for dumping. We show that, compared to past experiments, BDee (in particular BDee at e+e− linear collider) significantly enlarges the parameter region where the signal of the hidden particle can be discovered.