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Probing light higgsinos in natural SUSY from monojet signals at the LHC

Han, Chengcheng; Kobakhidze, Archil; Liu, Ning; Saavedra, Aldo; Wu, Lei; Yang, Jin MinSubjects: Physics >> The Physics of Elementary Particles and Fields

We investigate a strategy to search for light, nearly degenerate higgsinos within the natural MSSM at the LHC. We demonstrate that the higgsino mass range mu in 100 - 160 GeV, which is preferred by the naturalness, can be probed at 3 sigma significance through the monojet search at 14TeV HL-LHC with 3000 fb(-1) luminosity. The proposed method can also probe certain region in the parameter space for the lightest neutralino with a high higgsino purity, that cannot be reached by planned direct detection experiments at XENON-1T(2017). |

Higgs pair production with SUSY QCD correction: revisited under current experimental constraints

Han, Chengcheng; Ji, Xuanting; Wu, Lei; Wu, Peiwen; Yang, Jin MinSubjects: Physics >> The Physics of Elementary Particles and Fields

We consider the current experimental constraints on the parameter space of the MSSM and NMSSM. Then in the allowed parameter space we examine the Higgs pair production at the 14TeV LHC via b (b) over bar -> hh (h is the 125GeV SM-like Higg boson) with one-loop SUSY QCD correction and compare it with the production via gg -> hh. We obtain the following observations: (i) For the MSSM the production rate of b (b) over bar -> hh can reach 50 fb and thus can be competitive with gg -> hh, while for the NMSSM b (b) over bar -> hh has a much smaller rate than gg. hh due to the suppression of the hb (b) over bar coupling; (ii) The SUSY-QCD correction to b (b) over bar -> hh is sizable, which can reach 45% for the MSSM and 15% for the NMSSM within the 1s region of the Higgs data; (iii) In the heavy SUSY limit (all soft mass parameters become heavy), the SUSY effects decouple rather slowly from the Higgs pair production (especially the gg -> hh process), which, for M S U S Y = 5TeV and m A < 1TeV, can enhance the production rate by a factor of 1.5 and 1.3 for the MSSM and NMSSM, respectively. So, the Higgs pair production may be helpful for unraveling the effects of heavy SUSY. |

Full one-loop electroweak corrections to e(+)e(-) -> ZH gamma at a Higgs factory

Liu, Ning; Ren, Jie; Wu, Lei; Wu, Peiwen; Yang, Jin MinSubjects: Physics >> The Physics of Elementary Particles and Fields

Motivated by the future precision test of the Higgs boson at an e(+)e(-) Higgs factory, we calculate the production e(+)e(-) -> ZH gamma in the Standard Model with complete next-to-leading order electroweak corrections. We find that for p s root s = 240 (350) GeV the cross section of this production is sizably reduced by the electroweak corrections, which is 1.03 (5.32) fb at leading order and 0.72 (4.79) fb at next-to-leading order. The transverse momentum distribution of the photon in the final states is also presented. |

SUSY induced top quark FCNC decay t -> ch after Run I of LHC

Cao, Junjie; Han, Chengcheng; Wu, Lei; Yang, Jin Min; Zhang, MengchaoSubjects: Physics >> The Physics of Elementary Particles and Fields

In light of the Higgs discovery and the nonobservation of sparticles at the LHC, we revisit the supersymmetric theory (SUSY) induced top quark flavor-changing decay into the Higgs boson. We perform a scan over the relevant SUSY parameter space by considering the constraints from the Higgs mass measurement, the LHC search for SUSY, the vacuum stability, the precision electroweak observables as well as B -> X-s gamma. We make the following observations: (1) In the Minimal Supersymmetric Standard Model (MSSM), the branching ratio of t -> ch can only reach 3.0 x 10(-6), which is about one order smaller than previous results obtained before the advent of the LHC. Among the considered constraints, the Higgs mass and the LHC search for sparticles are found to play an important role in limiting the prediction. (2) In the singlet extension of the MSSM, since the squark sector is less constrained by the Higgs mass, the branching ratio of t -> ch can reach the order of 10(-5) in the allowed parameter space. (3) The chiral-conserving mixings delta(LL) and delta(RR) may have remanent effects on t -> ch in the heavy SUSY limit. In the MSSM with squarks above 3 TeV and gluino above 4 TeV and meanwhile the CP-odd Higgs boson mass around 1 TeV, the branching ratio of t -> ch can still reach the order of 10(-8) under the constraints. |

New approach for detecting a compressed bino/wino at the LHC

Han, Chengcheng; Wu, Lei; Yang, Jin Min; Zhang, Mengchao; Zhang, YangSubjects: Physics >> The Physics of Elementary Particles and Fields

In some supersymmetric models like split supersymmetry or models with nonuniversal gaugino mass, 'bino [lightest sparticle (LSP)] and wino [next-to-lightest sparticle (NLSP)] may have rather small mass splitting in order to provide the correct dark matter relic density through bino/wino coannihilation. Such a scenario with the compressed bino/wino is difficult to explore at the LHC. In this work we propose to probe this scenario from pp -> j (chi) over tilde (0)(2)(chi) over tilde (+/-)(1) followed by (chi) over tilde (0)(2) -> gamma(chi) over tilde (0)(1) and (chi) over tilde (+/-)(1) -> W*(chi) over tilde (0)(1) -> l(+/-)nu(chi) over tilde (0)(1) (this method is also applicable to the compressed bino/Higgsino scenario). Through a detailed Monte Carlo simulation for both the signal and the backgrounds, we find that for a mass splitting Delta M similar to 10-15 GeV between bino (LSP) and wino (NLSP), the 14 TeV LHC with a luminosity of 1000 fb(-1) can probe the wino up to 150 GeV (the sensitivity can reach 3.4 sigma for Delta M = 10 GeV and 2 sigma for Delta M = 15 GeV). We also investigate the dark matter detection sensitivities for this scenario and find that the planned XENON-1T (2017) cannot fully cover the parameter space with a wino below 150 GeV allowed by relic density and the LUX limits. |

Higgs self-coupling in the MSSM and NMSSM after the LHC Run 1

Wu, Lei; Yang, Jin Min; Yuan, C. -P.; Zhang, MengchaoSubjects: Physics >> The Physics of Elementary Particles and Fields

Measuring the Higgs self-coupling is one of the crucial physics goals at the LHC Run-2 and other future colliders. In this work, we attempt to figure out the size of SUSY effects on the trilinear self-coupling of the 125 GeV Higgs boson in the MSSM and NMSSM after the LHC Run-1. Taking account of current experimental constraints, such as the Higgs data, flavor constraints, electroweak precision observables and dark matter detections, we obtain the observations: (1) In the MSSM, the ratio lambda(MSSM)(3h)/lambda(SM)(3h) has been tightly constrained by the LHC data, which can be only slightly smaller than 1 and minimally reach 97%; (2) In the NMSSM with lambda < 0.7, a sizable reduction of lambda(MSSM)(3h2)/lambda(SM)(3h2) can occur and minimally reach 10% when the lightest CP-even Higgs boson mass m(h1)., is close to the SM-like Higgs boson m(h2), due to the large mixing angle between the singlet and doublet Higgs bosons; (3) In the NMSSM with lambda > 0.7, a large enhancement or reduction -1.1 < lambda(MSSM)(3h1)/lambda(SM)(3h1) < 2 can occur, which is accompanied by a sizable change of h(1)tau(+)tau(-) coupling. The future colliders, such as the HL-LHC and ILC, will have the capacity to test these large deviations in the NMSSM. (C) 2015 The Authors. Published by Elsevier B.V. |

ATLAS Z-peaked excess in the MSSM with a light sbottom or stop

Kobakhidze, Archil; Liu, Ning; Wu, Lei; Yang, Jin MinSubjects: Physics >> The Physics of Elementary Particles and Fields

We attempt to explain the recent ATLAS 3 sigma excess of dilepton events with an invariant mass near Z peak through the gluino-mediated sbottom production in a simplified scenario inspired by the minimal supersymmetric Standard Model. The additional Z bosons can be produced through the cascade decay chain (g) over tilde -> b (b) over tilde1(dagger) -> b (b) over bar(chi) over tilde (0)(2,3) -> b (b) over bar(chi) over tilde (0)(1)Z, in which (b) over tilde (1) is the right-handed sbottom, (chi) over tilde (0)(1) is the bino-like lightest supersymmetric particle (LSP) and (chi) over tilde (0)(2,3) are two nearly degenerate Higgsino-like next-to LSPs. Taking into account the constraint from the LHC search for the gluino-mediated sbottom production in the final states with the missing transverse energy and at least three b-jets, we find that the ATLAS on-Z excess can only be marginally explained at the 2 sigma level. We also note that within the scenario where the gluino predominantly decays to the right-handed stop instead of the sbottom, the excess can hardly be explained, since the Z-boson is not produced in the stop dominant decay channel, (t) over tilde (1) -> b (chi) over tilde (+)(1). |

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