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1. chinaXiv:201605.01711 [pdf]

Probing topcolor-assisted technicolor from top charge asymmetry and triple-top production at the LHC

Han, Chengcheng; Liu, Ning; Wu, Lei; Yang, Jin Min
Subjects: Physics >> The Physics of Elementary Particles and Fields

In a topcolor-assisted technicolor model (TC2) with large FCNC top quark couplings, we study its correlated contributions to the top quark forward-backward asymmetry (A(FB)) at the Tevatron, the top charge asymmetry (A(C)) and the triple-top production at the LHC. Under current constraints on the top quark from the LHC and Tevatron (such as the total and differential production rates), we scan the parameter space of such a TC2 model. We find that in the allowed parameter space the TC2 model can explain the Tevatron measured A(FB) at 2 sigma level, but meanwhile significantly enhance A(C) at the LHC. Such enhanced A(C), albeit currently allowed by the LHC measurement at 2 sigma level, will serve as a test of TC2 with the improvement of measurement precision at the LHC. Then with all the constraints (including the requirement to explain A(FB) at 2 sigma level and satisfying the current LHC measurement of A(C) at 2 sigma level), we find that the TC2 model can induce sizable triple-top production at the 14 TeV LHC (the production rate can maximally reach 16 pb). Due to the low SM backgrounds, the triple-top production can also be a good probe for TC2 model, complementary to A(C). (C) 2012 Elsevier B.V. All rights reserved.

submitted time 2016-05-14 Hits1023Downloads562 Comment 0

2. chinaXiv:201605.01709 [pdf]

Probing natural SUSY from stop pair production at the LHC

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

We consider the natural supersymmetry scenario in the framework of the R-parity conserving minimal supersymmetric standard model (called natural MSSM) and examine the observability of stop pair production at the LHC. We first scan the parameters of this scenario under various experimental constraints, including the SM-like Higgs boson mass, the indirect limits from precision electroweak data and B-decays. Then in the allowed parameter space we study the stop pair production at the LHC followed by the stop decay into a top quark plus a lightest neutralino or into a bottom quark plus a chargino. From detailed Monte Carlo simulations of the signals and backgrounds, we find the two decay modes are complementary to each other in probing the stop pair production, and the LHC with root s = 14 TeV and 100 fb(-1) luminosity is capable of discovering the stop predicted in natural MSSM up to 450 GeV. If no excess events were observed at the LHC, the 95% C.L. exclusion limits of the stop masses can reach around 537 GeV.

submitted time 2016-05-14 Hits959Downloads533 Comment 0

3. chinaXiv:201605.01154 [pdf]

Current experimental bounds on stop mass in natural SUSY

Han, Chengcheng; Hikasa, Ken-ichi; Wu, Lei; Yang, Jin Min; Zhang, Yang
Subjects: Physics >> The Physics of Elementary Particles and Fields

Motivated by the recent progress of direct search for the productions of stop pair and sbottom pair at the LHC, we examine the constraints of the search results on the stop ( (t) over tilde (1)) mass in natural SUSY. We first scan the parameter space of natural SUSY in the framework of MSSM, considering the constraints from the Higgs mass, B-physics and electroweak precision measurements. Then in the allowed parameter space we perform a Monte Carlo simulation for stop pair production followed by (t) over tilde (1). t (chi) over tilde (0)(1) or (t) over tilde (1). b (chi) over tilde (+)(1) and sbottom pair production followed by (b) over tilde (1) -> b (chi) over tilde (0)(1) or (b) over tilde (1) -> t (chi) over tilde (-)(1). Using the combined results of ATLAS with 20.1 fb(-1) from the search of l + jets + (sic)(T), hadronic t (t) over bar + (sic)(T) and 2b + (sic)(T), we find that a stop lighter than 600 GeV can be excluded at 95% CL in this scenario.

submitted time 2016-05-09 Hits1089Downloads587 Comment 0

4. chinaXiv:201605.01153 [pdf]

Two-Higgs-doublet model with a color-triplet scalar: a joint explanation for top-quark forward-backward asymmetry and Higgs decay to diphoton

Han, Chengcheng; Liu, Ning; Wu, Lei; Yang, Jin Min; Zhang, Yang
Subjects: Physics >> The Physics of Elementary Particles and Fields

The excess of top-quark forward-backward asymmetry (A(FB)(t)) reported by the Tevatron and the enhancement of the Higgs decay to diphoton observed at the LHC may point to a same origin of new physics. In this note we examined such anomalies in the two-Higgs-doublet model with a color-triplet scalar. We found that under current experimental constraints this model can simultaneously explain both anomalies at 1 sigma level. Also, we examined the Higgs decay h -> Z gamma and displayed its correlation with h -> gamma gamma. We found that unlike other models, this model predicts a special correlation between h -> Z gamma and h -> gamma gamma, i.e., the Z gamma rate is highly suppressed while the gamma gamma rate is enhanced. This behavior may help to distinguish this model in the future high luminosity run of the LHC.

submitted time 2016-05-09 Hits1097Downloads578 Comment 0

5. chinaXiv:201605.01152 [pdf]

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

Han, Chengcheng; Kobakhidze, Archil; Liu, Ning; Saavedra, Aldo; Wu, Lei; Yang, Jin Min
Subjects: 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).

submitted time 2016-05-09 Hits1001Downloads539 Comment 0

6. chinaXiv:201605.01151 [pdf]

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

Han, Chengcheng; Ji, Xuanting; Wu, Lei; Wu, Peiwen; Yang, Jin Min
Subjects: 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.

submitted time 2016-05-09 Hits956Downloads586 Comment 0

7. chinaXiv:201605.01149 [pdf]

A light SUSY dark matter after CDMS-II, LUX and LHC Higgs data

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

In SUSY, a light dark matter is usually accompanied by light scalars to achieve the correct relic density, which opens new decay channels of the SM-like Higgs boson. Under current experimental constraints including the latest LHC Higgs data and the dark matter relic density, we examine the status of a light neutralino dark matter in the framework of NMSSM and confront it with the direct detection results of CoGeNT, CDMS-II and LUX. We have the following observations: (i) A dark matter as light as 8 GeV is still allowed and its scattering cross section off the nucleon can be large enough to explain the CoGeNT/CDMS-II favored region; (ii) The LUX data can exclude a sizable part of the allowed parameter space, but still leaves a light dark matter viable; (iii) The SM-like Higgs boson can decay into the light dark matter pair with an invisible branching ratio reaching 30% under the current LHC Higgs data, which may be tested at the 14 TeV LHC experiment.

submitted time 2016-05-09 Hits757Downloads421 Comment 0

8. chinaXiv:201605.01147 [pdf]

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

Cao, Junjie; Han, Chengcheng; Wu, Lei; Yang, Jin Min; Zhang, Mengchao
Subjects: 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.

submitted time 2016-05-09 Hits799Downloads433 Comment 0

9. chinaXiv:201605.01137 [pdf]

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

Han, Chengcheng; Wu, Lei; Yang, Jin Min; Zhang, Mengchao; Zhang, Yang
Subjects: 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.

submitted time 2016-05-09 Hits817Downloads456 Comment 0

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