Future Hadron Colliders Research Articles

Flavor-changing decay h \u2192 \u03c4 \u03bc at super hadron colliders

We study the flavor-changing decay h → τ μ with τ = τ− +τ+ and μ = μ− +μ+ of a Higgs boson at future hadron colliders, namely: a) High Luminosity Large Hadron Collider, b) High Energy Large Hadron Collider and c) Future hadron-hadron Circular Collider. The theoretical framework adopted is the Two-Higgs-Doublet Model type III. The free model parameters involved in the calculation are constrained through Higgs boson data, Lepton Flavor Violating processes and the muon anomalous magnetic dipole moment; later they are used to analyze the branching ratio of the decay h → τ μ and to evaluate the gg → h production cross section. We find that at the Large Hadron Collider is not possible to claim for evidence of the decay h → τ μ achieving a signal significance about of 1.46σ by considering its final integrated luminosity, 300 fb−1. More promising results arise at the High Luminosity Large Hadron Collider in which a prediction of 4.6σ when an integrated luminosity of 3 ab−1 and tan β = 8 are achieved. Meanwhile, at the High Energy Large Hadron Collider (Future hadron-hadron Circular Collider) a potential discovery could be claimed with a signal significance around 5.04σ (5.43σ) for an integrated luminosity of 3 ab−1 and tan β = 8 (5 ab−1 and tan β = 4).

Light yield and uniformity measurements of different scintillator tiles with silicon photomultipliers

We present light yield and uniformity measurements of square and hexagonal tiles read out with silicon photomultipliers via a Y11 wavelength-shifting fiber or directly from the side or from the center at the top face. All tiles are 3 mm thick and have an area of 9 cm2. The sides are wrapped with two layers of Teflon tape while top and bottom faces are covered with two layers of Tyvec paper. We further show the first light yield and uniformity measurements of ATLAS Tile Calorimeter (TileCal) tiles with MPPC readout. This study has been motivated by looking into a possible phase 3 upgrade for the ATLAS hadron calorimeter and for hadron calorimeters at future hadron colliders.

3D Detectors on Hydrogenated Amorphous Silicon for particle tracking in high radiation environment

The vertex detectors for the future hadronic colliders will operate under proton fluencies above 1016 p/cm2. Crystalline Silicon detector technology, up to now, has kept the pace of the increasing fluencies in the LHC era and it is still the prevalent vertex detector material for the present and for the immediate future. Looking ahead in time, an alternative solution for such a detector has to be found because for the future there is no guarantee that Crystalline Silicon will hold this challenge. For this reason the development of hydrogenated amorphous silicon vertex detectors based on 3D-technology have been proposed and the technological solutions in order to build these detectors are described in this paper.

Power meets precision to explore the symmetric Higgs portal

We perform a comprehensive study of collider aspects of a Higgs portal scenario that is protected by an unbroken Z2 symmetry. If the mass of the Higgs portal scalar is larger than half the Higgs mass, this scenario becomes very difficult to detect. We provide a detailed investigation of the model's parameter space based on analyses of the direct collider sensitivity at the LHC as well as at future lepton and hadron collider concepts and analyse the importance of these searches for this scenario in the context of expected precision Higgs and electroweak measurements. In particular we also consider the associated electroweak oblique corrections that we obtain in a first dedicated two-loop calculation for comparisons with the potential of, e.g., GigaZ. The currently available collider projections corroborate an FCC-hh 100 TeV as a very sensitive tool to search for such a weakly-coupled Higgs sector extension, driven by small statistical uncertainties over a large range of energy coverage. Crucially, however, this requires good theoretical control. Alternatively, Higgs signal-strength measurements at an optimal FCC-ee sensitivity level could yield comparable constraints.

Probing doubly and singly charged Higgs bosons at the pp collider HE-LHC

We analyse the signal sensitivity of multi-lepton final states at collider that can arise from doubly and singly charged Higgs decay in a type-II seesaw framework. We assume triplet vev to be very small and degenerate masses for both the charged Higgs states. The leptonic branching ratio of doubly and singly charged Higgs states have a large dependency on the neutrino oscillation parameters, lightest neutrino mass scale, as well as neutrino mass hierarchy. We explore this as well as the relation between the leptonic branching ratios of the singly and doubly charged Higgs states in detail. We evaluate the effect of these uncertainties on the production cross-section. Finally, we present a detailed analysis of multi-lepton final states for a future hadron collider HE-LHC, that can operate with center of mass energy $\sqrt{s}=27$ TeV.

Beam induced vacuum effects in the future circular hadron collider beam vacuum chamber

EuroCirCol is a conceptual design study of a post-LHC, Future Circular Hadron Collider (FCC-hh) with 50 TeV of beam energy and 100 km long, which aims to expand the current energy and luminosity frontiers. The vacuum chamber of the FCC-hh will have to cope with unprecedented levels of synchrotron radiation power for proton colliders, dealing simultaneously with a tighter magnet aperture. Considering that the high radiation power and photon flux will release larger amounts of gas into the system, the difficulty to meet the vacuum specifications increases substantially compared with the LHC. This paper presents a study on the beam induced vacuum effects for the FCC-hh novel conditions, the different phenomena which, owing to the presence of the beam, have an impact on the accelerator's vacuum level. It is concluded that thanks to the adopted mitigation measures the proposed vacuum system shall be adequate, allowing us to reach $\ensuremath{\le}1\ifmmode\times\else\texttimes\fi{}{10}^{15}\text{ }\text{ }{\mathrm{H}}_{2\text{ }eq}/{\mathrm{m}}^{3}$ with baseline beam parameters within the first months of conditioning.

Multi-Higgs boson production and unitarity in vector-boson fusion at future hadron colliders

We study multi-Higgs final states in vector boson fusion (VBF) processes at the LHC and at future proton-proton colliders, focusing on the prospects for measurements at 27 TeV and at 100 TeV. We use an effective Lagrangian which includes higher-dimensional operators in the mass eigenstates which are relevant to VBF processes and relate this to specific parameterizations and models for new physics in the Higgs sector. We derive theoretical constraints on the parameter space from the unitarity of $2\to n$ scattering amplitudes and apply the results to $V V \to hh$ and $h h h$ processes, where $V=W,Z$. As a result, we present constraints on differential distributions as appropriate to the study of $V V \to hh$ and $h h h$ processes.

Same-sign tetralepton signature at the Large Hadron Collider and a future pp collider

We analyze a novel signature of the type II seesaw model - same-sign tetra-lepton signal arising from the mixing of neutral Higgs bosons and their subsequent decays to singly and doubly charged Higgs bosons. For this, we consider wide ranges of the triplet vacuum expectation value (vev) and Yukawa couplings, that are consistent with the observed neutrino masses and mixing as well as the LHC search limits. We find that a doubly charged Higgs boson with mass around 250 GeV and triplet vev around $10^{-4}-10^{-2}$ GeV can give significantly large number of events through it decay to same-sign $W$ gauge bosons at High-Luminosity LHC with $3000 \text{fb}^{-1}$ of data. We also pursue the analysis for a future hadron collider with the c.m. energy of 100 TeV. Considering a heavy Higgs boson around 900 GeV and an intermediate region of the triplet vev, where both same-sign dilepton and gauge boson decays can occur, we identify a limited range of the parameters where the number of same-sign tetra-lepton events are as large as 1000.

Fast Data-Driven Simulation of Cherenkov Detectors Using Generative Adversarial Networks

The increasing luminosities of future Large Hadron Collider runs and next generation of collider experiments will require an unprecedented amount of simulated events to be produced. Such large scale productions are extremely demanding in terms of computing resources. Thus new approaches to event generation and simulation of detector responses are needed. In LHCb, the accurate simulation of Cherenkov detectors takes a sizeable fraction of CPU time. An alternative approach is described here, when one generates high-level reconstructed observables using a generative neural network to bypass low level details. This network is trained to reproduce the particle species likelihood function values based on the track kinematic parameters and detector occupancy. The fast simulation is trained using real data samples collected by LHCb during run 2. We demonstrate that this approach provides high-fidelity results.

Hydrogenated amorphous silicon detectors for particle detection, beam flux monitoring and dosimetry in high-dose radiation environment

Hydrogenated amorphous silicon (a-Si:H) has remarkable radiation resistance properties and can be deposited on a lot of different substrates. A-Si:H based particle detectors have been built since mid 1980s as planar p-i-n or Schottky diode structures; the thickness of these detectors ranged from 1 to 50 μm. However MIP detection using planar structures has always been problematic due to the poor S/N ratio related to the high leakage current at high depletion voltage and the low charge collection efficiency. The usage of 3D detector architecture can be beneficial for the possibility to reduce inter-electrode distance and increase the thickness of the detector for larger charge generation compared to planar structures. Such a detector can be used for future hadron colliders for its radiation resistance and also for X-ray imaging. Furthermore the possibility of a-Si:H deposition on flexible materials (like kapton) can be exploited to build flexible and thin beam flux measurement detectors and x-ray dosimeters.

Anatomy of tthh physics at the HL-LHC

The $tthh$ production at colliders contain rich information on the nature of Higgs boson. In this article, we systematically studied its physics at High-Luminosity Large Hadron Collider (HL-LHC), using exclusive channels with multiple ($\geq 5$) $b$-jets and one lepton ($5b1\ell$), multiple ($\geq 5$) $b$-jets and opposite-sign di-lepton ($5b2\ell$), same-sign di-lepton (SS2$\ell$), multiple leptons (multi-$\ell$), and di-tau resonance ($\tau\tau$). The scenarios analyzed include: (1) the $tthh$ production in Standard Model; (2) the $tthh$ production mediated by anomalous cubic Higgs self-coupling and $tthh$ contact interaction; (3) heavy Higgs ($H$) production with $tt H \to tthh$; and (4) pair production of fermionic top partners ($T$) with $T T \to tthh$. To address the complication of event topologies and the mess of combinatorial backgrounds, a tool of Boosted-Decision-Tree was applied in the analyses. The $5b1\ell$ and SS2$\ell$ analyses define the two most promising channels, resulting in slightly different sensitivities. For non-resonant $tthh$ production, a combination of these exclusive analyses allows for its measurment in the SM with a statistical significance $\sim 0.9\sigma$ (with $S/B > 1 \%$), and may assist partially breaking the sensitivity degeneracy w.r.t. the cubic Higgs self-coupling, a difficulty usually thought to exist in gluon fusion di-Higgs analysis at HL-LHC. These sensitivities were also projected to future hadron colliders at 27 TeV and 100 TeV. For resonant $tthh$ productions, the heavy Higgs boson in type II Two-Higgs-Doublet-Model could be efficiently searched for between the mass thresholds $2 m_h < m_H < 2 m_t$ and even beyond that, for relatively small $\tan\beta$, while the fermionic top partners in composite Higgs models could be probed for up to $\sim 1.5$ TeV and $\sim 1.7$ TeV, for Br$(T\to th)=25\%$ and $50\%$, respectively.

Modeling of neutron radiation-induced defects in silicon particle detectors

Radiation damage of the silicon detectors in future hadron colliders poses a major challenge for its reliable operation. It is crucial to investigate the neutron-induced radiation damage owing to its large flux in the calorimeters and the trackers. Measurement results on irradiated detectors are complemented by modeling for getting a deep insight into the device behavior. This work presents the development of neutron-induced radiation damage model in silicon detectors using TCAD simulation. A wide spectrum of measurement results available on neutron-irradiated silicon detectors, viz. full depletion voltage, leakage current, charge collection, and effective trapping times, helps in constraining the model parameters, resulting in a robust model for neutron damage. Modeling has been performed within the phase-space of the measurements, i.e. for different initial bulk resistivities, active thicknesses and for both polarities up to the fluence values of 9 × 1014 1 MeV neq cm−2 (where, 1 MeV neq refers to the equivalent fluence for monoenergetic neutrons of energy 1 MeV) and for two measurement temperatures, 253 and 263 K. The results obtained from the devised neutron damage model show a good agreement with the measurement results.

Emittance growth from luminosity burn-off in future hadron colliders

Future hadron colliders aim at producing larger integrated luminosities by burning-off an increased fraction of the bunch particles. This burn-off removes particles unevenly in the bunch distribution generating an emittance growth. Analytical equations are derived describing the bunch distribution suffering luminosity burn-off and cooling from synchrotron radiation damping, far from the equilibrium emittance, and possibly including transverse collision offsets. This effect is evaluated for HL-LHC [G. Apollinari et al., Report No. CERN-2017-007-M, 2017], HE-LHC [A. Abada et al., Eur. Phys. J. Spec. Top. 228, 1109 (2019)], and FCC-hh [A. Abada et al., Eur. Phys. J. Spec. Top. 228, 755 (2019).] and included into a step-by-step simulation of the physics fill, together with intrabeam scattering, to evaluate impact on performance.

Design of the future circular hadron collider beam vacuum chamber

The optimized vacuum chamber for a future higher-energy hadron collider minimizes electron cloud build-up, outgassing from synchrotron radiation, and heat leakage to the cold mass of the superconducting magnets, while maximizing pumping efficiency and ensuring mechanical stability during a magnet quench.

Thermodynamic and economic aspects of the Nelium Turbo-Brayton refrigerator development for the FCC-hh

Within the conceptual design study for the Future Circular Hadron Collider (FCC-hh) it was shown, that a large part of the total cryogenic heat load falls into the temperature range between 40 to 60 K. Thus, additional cryogenic refrigerators for this temperature level are specified for each of the 10 foreseen cryoplants. Such a cryogenic system was developed at the TU Dresden and is based on a Brayton cycle working with a neon-helium mixture as refrigerant and using multistage centrifugal compressors. The duty requirements comprise a 6.2 MW total heat load at 40 to 60 K for beam screens and shielding, additional 2.7 MW at 300 to 40 K for the pre-cooling of the helium cycle and a turndown ratio of up to 3.8. The optimisation of the referenced system was performed in order to obtain a high efficiency of the cryogenic cycle and tolerable costs for system components at the same time. An analysis of the mixture composition influence on the components and on the total gas mass was performed. Restrictions for industrially existing hardware were taken into consideration. Updated cycle parameters are subsequently described.

Probing flavor nonuniversal theories through Higgs physics at the LHC and future colliders

We explored the possibility that Higgs coupling to new physics violates flavor universality. In particular, we parameterize such models with dimension-six effective operators which modify the coupling between the first generation quarks, Higgs boson, and $Z$ boson. Through the use of boosted Higgsstrahlung events at both the HL-LHC and potential future hadron colliders, as well as existing ATLAS data for background estimates, we projected constraints on the scale of new physics as a function of the Wilson coefficient. The high energy $Zh$ process will provide unique information about these class of operators, and the sensitivity is competitive with the LEP electroweak precision measurements. We include different scenarios of the overall systematic uncertainties and the PDF uncertainties when presenting the projected sensitivities. We also discuss the constraints from FCNCs to these flavor-violating models and the complementarity of the exotic Higgs decay to the $Zh$ process.

Prospects for Lorentz invariance violation searches with top pair production at the LHC and future hadron colliders

This paper investigates the impact of hypothetical Lorentz invariance violation on the tbar{t} production at the LHC and future hadron colliders. Possible deviations from Lorentz symmetry remain poorly constrained in the top quark sector. With a dedicated analysis of tbar{t} events produced at the LHC, bounds in the top sector can be improved by up to three orders of magnitude relative to the only measurement existing so far, performed at Tevatron. The sensitivity will be even further enhanced at the HL-LHC and future colliders.

NNLO QCD + NLO EW with Matrix+OpenLoops: precise predictions for vector-boson pair production

We present the first combination of NNLO QCD and NLO EW corrections for vector-boson pair production at the LHC. We consider all final states with two, three and four charged leptons, including resonant and non-resonant diagrams, spin correlations and off-shell effects. Detailed predictions are discussed for three representative channels corresponding to W+W−, W±Z and Z Z production. Both QCD and EW corrections are very significant, and the details of their combination can play a crucial role to achieve the level of precision demanded by experimental analyses. In this context we point out nontrivial issues that arise at large transverse momenta, where the EW corrections are strongly enhanced by Sudakov logarithms and the QCD corrections can feature so-called giant K -factors. Our calculations have been carried out in the Matrix+OpenLoops framework and can be extended to the production of an arbitrary colour singlet in hadronic collisions, provided that the required two-loop QCD amplitudes are available. Combined NNLO QCD and NLO EW predictions for the full set of massive diboson processes will be made publicly available in the next release of Matrix and will be instrumental in advancing precision diboson studies and new-physics searches at the LHC and future hadron colliders.

Sensitivity on anomalous neutral triple gauge couplings via ZZ production at FCC-hh

We study the sensitivity of anomalous neutral triple gauge couplings (aNTGC) via pp rightarrow ZZ production in the 4ell channel at 100 TeV center of mass energy of future circular hadron collider, FCC-hh. The analysis including the realistic detector effects is performed in the mode where both Z bosons decay into same-flavor, oppositely charged lepton pairs. The sensitivities to the charge–parity (CP)-conserving couplings C_{{tilde{B}}W} / Lambda ^{4} and CP-violating couplings C_{WW} / Lambda ^{4}, C_{BW} / Lambda ^{4} and C_{BB} / Lambda ^{4} obtained at 95% Confidence Level using the invariant mass distribution of the 4ell system reconstructing the leading and sub-leading Z boson candidates are [-,0.09, ,, +,0.09], [-,0.21, ,, +,0.21], [-,0.26, ,, +,0.26], and [-,0.10, ,, +,0.10] in units of hbox {TeV}^{-4}, respectively.

The Acts project: track reconstruction software for HL-LHC and beyond

The reconstruction of trajectories of the charged particles in the tracking detectors of high energy physics (HEP) experiments is one of the most difficult and complex tasks of event reconstruction at particle colliders. As pattern recognition algorithms exhibit combinatorial scaling to high track multiplicities, they become the largest contributor to the CPU consumption within event reconstruction, particularly at current and future hadron colliders such as the LHC, HL-LHC and FCC-hh. Current algorithms provide an extremely high standard of physics and computing performance and have been tested on billions of simulated and recorded data events. However, most algorithms date back to more than 20 years ago and maintaining them has become increasingly challenging. In addition, they are challenging to adapt to modern programming paradigms and parallel architectures. Acts is based on the well-tested and highly functioning components of LHC track reconstruction algorithms, implemented with modern software concepts and inherently designed for parallel architectures. Multithreading becomes increasingly important to balance the memory usage per CPU core. However, a fully multithreaded event processing framework blurs the clear border between events, which has in the past often been used as a clearly defined validity boundary for event conditions. Acts is equipped with a full contextual conditions concept that allows to run concurrent track reconstruction even in case of multiple detector alignments, conditions or varying magnetic field being processed at the same time. It provides an experiment and, in particular, framework-independent software toolkit and light-weight, highly optimised event data model for track reconstruction. Particular care is given to thread safety and data locality. It is designed as a toolbox that allows to implement and extend widely known pattern recognition algorithms, and in addition suitable for algorithm templating and R&amp;D. Acts has been used as the fast simulation engine for the Tracking Machine Learning (TrackML) Challenge, and will provide reference implementation of several submitted solution programs of the two phases of the challenge.