The Large Hadron–Electron Collider (LHeC) is designed to move the field of deep inelastic scattering (DIS) to the energy and intensity frontier of particle physics. Exploiting energy-recovery technology, it collides a novel, intense electron beam with a proton or ion beam from the High-Luminosity Large Hadron Collider (HL-LHC). The accelerator and interaction region are designed for concurrent electron–proton and proton–proton operations. This report represents an update to the LHeC’s conceptual design report (CDR), published in 2012. It comprises new results on the parton structure of the proton and heavier nuclei, QCD dynamics, and electroweak and top-quark physics. It is shown how the LHeC will open a new chapter of nuclear particle physics by extending the accessible kinematic range of lepton–nucleus scattering by several orders of magnitude. Due to its enhanced luminosity and large energy and the cleanliness of the final hadronic states, the LHeC has a strong Higgs physics programme and its own discovery potential for new physics. Building on the 2012 CDR, this report contains a detailed updated design for the energy-recovery electron linac (ERL), including a new lattice, magnet and superconducting radio-frequency technology, and further components. Challenges of energy recovery are described, and the lower-energy, high-current, three-turn ERL facility, PERLE at Orsay, is presented, which uses the LHeC characteristics serving as a development facility for the design and operation of the LHeC. An updated detector design is presented corresponding to the acceptance, resolution, and calibration goals that arise from the Higgs and parton-density-function physics programmes. This paper also presents novel results for the Future Circular Collider in electron–hadron (FCC-eh) mode, which utilises the same ERL technology to further extend the reach of DIS to even higher centre-of-mass energies.

Given the fact that the relatively light Higgsino mass $\mu$ favored in natural supersymmetry usually results in a sizable scattering cross section between the neutralino dark matter and the nucleon, we study the impact of the recently updated direct detection bounds from LUX experiment, including both Spin Independent (SI) and Spin Dependent (SD) measurements, on the parameter space of natural Next-to-Minimal Supersymmetric Standard Model (nNMSSM). Different from the common impression that the SI bound is stronger than the SD one, we find that the SD bound is complementary to the SI bound and in some cases much more powerful than the latter in limiting the nNMSSM scenarios. After considering the LUX results, nNMSSM is severely limited, e.g. for the peculiar scenarios of the NMSSM where the next-to-lightest CP-even Higgs corresponds to the $125 {\rm GeV}$ Higgs boson discovered at the LHC, the samples obtained in our random scan are excluded by more than $85\%$. By contrast, the monojet search at the LHC Run-I can not exclude any sample of nNMSSM. We also investigate the current status of nNMSSM and conclude that, although the parameter points with low fine tuning are still attainable, they are distributed in some isolated parameter islands which are difficult to get. Future dark matter direct search experiments such as XENON-1T will provide a better test of nNMSSM.Comment: 20 pages, 10 figures, meet JHEP published versio

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Abstract:We investigate the impact of the direct searches for SUSY at LHC Run I on the naturalness of the Next-to-Minimal Supersymmetric Standard Model (NMSSM). For this end, we first scan the vast parameter space of the NMSSM to get the region where the fine tuning measures ∆ Z and ∆ h at the electroweak scale are less than about 50, then we implement by simulations the constraints of the direct searches on the parameter points in the region. Our results indicate that although the direct search experiments are effective in excluding the points, the parameter intervals for the region and also the minimum reaches of ∆ Z and ∆ h are scarcely changed by the constraints, which implies that the fine tuning of the NMSSM does not get worse after LHC Run I. Moreover, based on the results we propose a natural NMSSM scenario where the lightest neutralinoχ 0 1 as the dark matter (DM) candidate is Higgsino-dominated. In this scenario, ∆ Z and ∆ h may be as low as 2 without conflicting with any experimental constraints, and intriguinglyχ 0 1 can easily reach the measured DM relic density due to its significant Singlino component. We exhibit the features of the scenario which distinguish it from the other natural SUSY scenario, including the properties of its neutralino-chargino sector and scalar top quark sector. We emphasize that the scenario can be tested either through searching for 3l + E miss T signal at 14 TeV LHC or through future DM direct detection experiments.

Recently the ATLAS collaboration reported a 3σ excess in the leptonic-Z + jets + E miss T channel. This may be interpreted in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) by gluino pair production with the decay chaing → qqχ 0 2 → qqZχ 0 1 , whereχ 0 1 andχ 0 2 denote the lightest and the next-to-lightest neutralinos with singlino and bino as their dominant components respectively. After exploring the relevant parameter space of the NMSSM by considering the constraints from the ATLAS searches for jets + E miss T signals, we conclude that the NMSSM is able to explain the excess at 1σ level with the number of the signal events reaching its measured central value in optimal cases, and the best explanation comes from a compressed spectrum such as mg 650 GeV, mχ0 2 565 GeV and mχ0 1 465 GeV. We also check the consistency of the ATLAS results with the null result of the CMS on-Z search. We find that under the CMS limits at 95% C.L., the event number of the ATLAS on-Z signal can still reach 11 in our scenario, which is about 1.2σ away from the measured central value.

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We explore the explanation of the Fermi Galactic Center excess (GCE) in the next-to-minimal supersymmetric Standard Model. We systematically consider various experimental constraints including the dark matter (DM) relic density, DM direct detection results, and indirect searches from dwarf galaxies. We find that, for DM with mass ranging from 30 to 40 GeV, the GCE can be explained by the annihilation XX a* bb only when the CP-odd scalar satisfies ma -2mx, and in order to obtain the measured DM relic density, a sizable Z-mediated contribution to DM annihilation must intervene in the early universe. As a result, the Higgsino mass p is upper bounded by about 350 GeV. Detailed Monte Carlo simulations on the + E f'ss signal from neutralino/chargino associated production at 14-TeV LHC indicate that the explanation can be mostly (completely) excluded at 95% C.L. with an integrated luminosity of 100(200) fb~'. We also discuss the implication of possible large Z coupling to DM for the DM-nucleon spin dependent (SD) scattering cross section, and find that although the current experimental bounds on o f is less stringent than the spin independent results, the future XENON-IT and LZ data may be capable of testing most parts of the GCE-favored parameter region.

In the light dark matter (DM) scenario of the MSSM, the DM relic density puts non-trivial requirements on the spectrum of supersymmetric particles. As a result, the direct search for multi-lepton signals at the LHC has great impact on the scenario. In this work, we concentrate on the searches for sleptons and electroweak-inos at the LHC, investigate their constraints on the light DM scenario with the 8 TeV LHC data, and also study their capability to test the scenario at the 14 TeV LHC. For this purpose, we first get the samples of the scenario by scanning the vast parameter space of the MSSM with various available constraints considered. Then for the surviving samples, we simulate the 2l +E miss T signal from slepton pair production process and the 2l + E miss T and 3l + E miss T signals from chargino and neutralino associated production processes at both the 8 TeV LHC and the 14 TeV LHC. Our simulations indicate that the 8 TeV LHC data have excluded a sizable portion of the samples, and the capability of the 14 TeV LHC will be much more powerful in testing the scenario. For example, in case that no excess of the multi-lepton signals is observed at the 14 TeV LHC, most samples of the light DM scenario will be excluded, especially a lower limit on the lightest neutralino mass will be set at 42 GeV and 44 GeV with 30 fb −1 and 100 fb −1 data respectively, and this limit can be further pushed up to 55 GeV with 300 fb −1 data.