In this study,we reanalyze the top-quark pair production at next-to-next-to-leading order(NNLO)in quantum chromodynamics(QCD)at future e^(+)e^(−)colliders using the Principle of Maximum Conformality(PMC)method.The PMC...In this study,we reanalyze the top-quark pair production at next-to-next-to-leading order(NNLO)in quantum chromodynamics(QCD)at future e^(+)e^(−)colliders using the Principle of Maximum Conformality(PMC)method.The PMC renormalization scales inαs are determined by absorbing the non-conformalβterms by recursively using the Renormalization Group Equation(RGE).Unlike the conventional scale-setting method of fixing the scale at the center-of-mass energyμ_(r)=√s,the determined PMC scale Q_(⋆)is far smaller than the √sand increases with the √s,yielding the correct physical behavior for the top-quark pair production process.Moreover,the convergence of the pQCD series for the top-quark pair production is greatly improved owing to the elimination of the renormalon divergence.For a typical collision energy of √s=500 GeV,the PMC scale is Q_(⋆)=107 GeV;the QCD correction factor K for conventional results is K∼1+0.1244+0.0102+0.0012−0.0087−0.0011+0.0184−0.0086+0.0002+0.0061−0.0003,where the first error is caused by varying the scaleμr∈[√s/2,2√s]and the second error is from the top-quark massΔm_(t)=±0.7 GeV.After applying the PMC,the renormalization scale uncertainty is eliminated,and the QCD correction factor K is improved to K∼1+0.1507_(−0.0015)^(+0.0015)−0.0057_(−0.0000)^(+0.0001),where the error is from the top-quark massΔm_(t)=±0.7 GeV.The PMC improved predictions for the top-quark pair production are helpful for detailed studies of the properties of the top-quark at future e^(+)e^(−)colliders.展开更多
By applying the Error PDF Updating Method,we analyze the impact of the absolute and normalized single differential cross-sections for top-quark pair production data from the ATLAS and CMS experiments at the Large Hadr...By applying the Error PDF Updating Method,we analyze the impact of the absolute and normalized single differential cross-sections for top-quark pair production data from the ATLAS and CMS experiments at the Large Hadron Collider,at a center-of-mass energy of √s=8TeV,on the CT14HERA2 PDFs.We find that the top quark pair single differential distributions provide minor constraints on the CT14HERA2 gluon PDF when the nominal CT14HERA2 inclusive jet production data are included in the fit.Larger constraints on the gluon distribution are present when the jet data are removed(CT14HERA2mJ)and/or when increased weights are given to the top data in the CT14HERA2 fits.The weighted$t\bar t$data provide significant constraints on the CT14HERA2mJ gluon PDF,which are comparable to those obtained from inclusive jet production data.Furthermore,we examine the top quark mass sensitivity of the top-quark pair single differential distributions.展开更多
In this study,we calculate the tt pQCD production cross-section at the NNLO and determine the top-quark pole mass from recent measurements at the LHC at the center-of-mass energy √S=13 TeV to a high precision by appl...In this study,we calculate the tt pQCD production cross-section at the NNLO and determine the top-quark pole mass from recent measurements at the LHC at the center-of-mass energy √S=13 TeV to a high precision by applying the principle of maximum conformality(PMC).The PMC provides a systematic method that rigorously eliminates QCD renormalization scale ambiguities by summing the nonconformalβcontributions into the QCD coupling constant.The PMC predictions satisfy the requirements of renormalization group invariance,including renormalization scheme independence,and the PMC scales accurately reflect the virtuality of the underlying production subprocesses.By using the PMC,an improved prediction for the tt production cross-section is obtained without scale ambiguities,which in turn provides a precise value for the top-quark pole mass.Moreover,the prediction of PMC calculations that the magnitudes of higher-order PMC predictions are well within the error bars predicted from the known lower-order has been demonstrated for the top-quark pair production.The resulting determination of the top-quark pole mass,m^(pole)_(t)=172.5±1.4 GeV,from the LHC measurement at √S=13 TeV agrees with the current world average cited by the Particle Data Group(PDG).The PMC prediction provides an important high-precision test of the consistency of pQCD and the SM at √S=13 TeV with previous LHC measurements at lower CM energies.展开更多
We propose a new dihedral angle observable for measuring the CP property of the interaction between the top quark and Higgs boson int\bar{t}Hproduction at the 14 TeV Large Hadron Collider(LHC).We consider two decay mo...We propose a new dihedral angle observable for measuring the CP property of the interaction between the top quark and Higgs boson int\bar{t}Hproduction at the 14 TeV Large Hadron Collider(LHC).We consider two decay modes of the Higgs boson,H→to b\b and H→γγ,and demonstrate that the dihedral angle distribution is able to distinguish between the CP-even and the CP-odd hypothesis at a 95%confidence level,with an integrated luminosity of\sim 180fb^(-1).展开更多
This paper posits that the observed resonance with 28 GeV at the LHC is the pseudoscalar top-bottom quark-antiquark composite which has the calculated mass of 27.9 GeV derived from the periodic table of elementary par...This paper posits that the observed resonance with 28 GeV at the LHC is the pseudoscalar top-bottom quark-antiquark composite which has the calculated mass of 27.9 GeV derived from the periodic table of elementary particles. The calculated mass is for the mass of?. In the periodic table of elementary particles, t quark (13.2 GeV) in the pseudoscalar top-bottom quark-antiquark composite is only a part of full t quark (175.4 GeV), so pseudoscalar?(26.4 GeV) cannot exist independently, and can exist only in the top-bottom quark-antiquark composite. As shown in the observation at the LHC, the resonance with 28 GeV weakens significantly at the higher energy collision (13 TeV), because at the higher collision energy, low-mass pseudoscalar? in the composite likely becomes independent full high-mass vector? moving out of the composite. The periodic table of elementary particles is based on the seven mass dimensional orbitals derived from the seven extra dimensions of 11 spacetime dimensional membrane. The calculated masses of hadrons are in excellent agreement with the observed masses of hadrons by using only five known constants. For examples, the calculated masses of proton, neutron, pion (π±), and pion (±0) are 938.261, 939.425, 139.540, and 134.982 MeV in excellent agreement with the observed 938.272, 939.565, 139.570, and 134.977MeV, respectively with 0.0006%, 0.01%, 0.02%, and 0.004%, respectively for the difference between the calculated and observed mass. The calculated masses of the Higgs bosons as the intermediate vector boson composites are in excellent agreements with the observed masses. In conclusion, the calculated masses of the top-bottom quark-antiquark composite (27.9 GeV), hadrons, and the Higgs bosons by the periodic table of elementary particles are in excellent agreement with the observed masses of resonance with 28 GeV at the LHC, hadrons, and the Higgs bosons, respectively.展开更多
In this review we do not try to cover all the aspects of physics besnd tile standard model （BSM）, instead our latest understanding on tile BSM will be presented： i） Tile Higgs sector is likely related to BSM, whic...In this review we do not try to cover all the aspects of physics besnd tile standard model （BSM）, instead our latest understanding on tile BSM will be presented： i） Tile Higgs sector is likely related to BSM, which can be confirmed at current running large hadron collider （LHC） or tile fllture eolliders. Furthermore we pointed out that spontaneous CP violation can be closely related to the lightness of the Higgs boson, ii） Top quark forward-backward asymmetry, which was mea.sured by Tewttron, might be the sign of BSM.2; proposed a new color-octet particle Zcr to account fi）r the observation and Z can be fllrther studied at the LHC. iii） If dark matter （DM） is utilized to accommodate astrophysical obserwtions, it ought to be observed at the high energy LttC and DM produced at colliders should be tile slnoking gun signal, iv） Lithium puzzle might also be the sign of the BSM. We briefly review tile newly proposed solution to Lithium puzzle, i.e.. the existonce of non-thermal component during the big bang nuclei-synthesis （BBN）. The possible origins of the non-thermal coinponent can be dark matter or the new accelerating mechanism of normal particles.展开更多
We perform a global effective-field-theory analysis to assess the combined precision of Higgs couplings, triple gauge-boson couplings, and top-quark couplings, at future circular e＋e- colliders, with a focus on runs ...We perform a global effective-field-theory analysis to assess the combined precision of Higgs couplings, triple gauge-boson couplings, and top-quark couplings, at future circular e＋e- colliders, with a focus on runs below the tt-production threshold. Deviations in the top-quark sector entering as one-loop corrections are consistently taken into account in the Higgs and diboson processes. We find that future lepton colliders running at center-of-mass energies below the tt production threshold can still provide useful information on top-quark couplings, by measuring virtual top-quark effects. With rate and differential measurements, the indirect individual sensitivity achievable is better than at the high-luminosity LHC. However, strong correlations between the extracted top-quark and Higgs couplings are also present and lead to much weaker global constraints on top-quark couplings. This implies that a direct probe of top-quark couplings above the t~ production threshold is also helpful for the determination of Higgs and triple-gauge-boson couplings. In addition, we find that below the e＋e- -＋tth production threshold, the top-quark Yukawa coupling can be determined by its loop corrections to all Higgs production and decay channels. Degeneracy with the ggh coupling can be resolved, and even a global limit is competitive with the prospects of a linear collider above the threshold. This provides an additional means of determining the top-quark Yukawa coupling indirectly at lepton colliders.展开更多
Heavy charged gauge bosons are proposed in some theories beyond the standard model. We explore the discovery potential for W＇→tb with top quark semi-leptonic decay at the LHC. We concentrate on the new physics signa...Heavy charged gauge bosons are proposed in some theories beyond the standard model. We explore the discovery potential for W＇→tb with top quark semi-leptonic decay at the LHC. We concentrate on the new physics signal search with the deviation from the standard model prediction if the resonance peak of W＇ cannot be observed directly. Signal events with two jets plus one charged lepton and missing energy are simulated, together with the dominant standard model backgrounds. In this paper, it is found that suitable cuts on the kinematic observables can effectively suppress the standard model backgrounds mass is less than 6.6 TeV. so that it is possible to search for a W＇ signal at the LHC if its展开更多
Recently, experimental collaborations have reported 0（10） upper limits on the signal strength of fourtop production at the LHC. Surprisingly, we find that the constraining power of four-top production on the qqtt ty...Recently, experimental collaborations have reported 0（10） upper limits on the signal strength of fourtop production at the LHC. Surprisingly, we find that the constraining power of four-top production on the qqtt type of operators is already competitive with the measurements of top-pair production, even though the precision level of the latter is more than two orders of magnitude better. This is explained by the enhanced sensitivity of the four-top cross section to qqtt operators, due to multiple insertion of operators in the squared amplitude, and to the large threshold energy of four-top production. We point out that even though the dominant contribution beyond the standard model comes from the O（C^4/Λ^8） terms, the effective field theory expansion remains valid for a wide range of underlying theories. Considering the possible improvements of this measurement with higher integrated luminosity, we believe that this process will become even more crucial for probing and testing the standard model deviations in the top-quark sector, and will eventually provide valuable information about the top-quark properties,leading to significant improvements in precision top physics.展开更多
In the framework of the littlest Higgs model with T-parity, we study the top pair production at the next generation colliders like LHC and ILC. We find that the order O（αs） corrections to the standard model top pai...In the framework of the littlest Higgs model with T-parity, we study the top pair production at the next generation colliders like LHC and ILC. We find that the order O（αs） corrections to the standard model top pair production cross section at LHC can be very small and the magnitude is below 1%. However, the magnitude of corrections to the standard model top pair production rate at ILC may be over 5% for reasonable values＇of the parameters. Besides this, the corrections to the asymmetry ALR（tt） may be more sizable. Therefore, the top pair production at ILC may serve as a probe of the littlest Higgs model with T-parity, especially the asymmetry ALR（tt）.展开更多
The topcolor-assisted technicolor （TC2） model predicts a number of neutral scalars like the top-pion （πt^0） and the top-Higgs （ht^0）. These scalars have flavor-changing neutral-current （FCNC） top quark coupli...The topcolor-assisted technicolor （TC2） model predicts a number of neutral scalars like the top-pion （πt^0） and the top-Higgs （ht^0）. These scalars have flavor-changing neutral-current （FCNC） top quark couplings, among which the top-charm transition couplings may be sizable. Such FCNC couplings induce single top productions associated with a neutral scalar at the CERN Large Hadron Collider （LHC） through the parton processes cg→ tπt^0 and cg→ tht^0. In this paper we examine these productions and find their production rates can exceed the 3σ sensitivity of the LHC in a large part of parameter space. Since in the Standard Model and the minimal supersymmetric model such rare productions have unobservably small production rates at the LHC, these rare processes will serve as a good probe for the TC2 model.展开更多
We propose to study the flavor properties of the top quark at the future Circular Electron Positron Collider(CEPC) in China.We systematically consider the full set of 56 real parameters that characterize the flavor-ch...We propose to study the flavor properties of the top quark at the future Circular Electron Positron Collider(CEPC) in China.We systematically consider the full set of 56 real parameters that characterize the flavor-changing neutral interactions of the top quark,which can be tested at CEPC in the single top production channel.Compared with the current bounds from the LEP2 data and the projected limits at the high-luminosity LHC,we find that CEPC could improve the limits of the four-fermion flavor-changing coefficients by one to two orders of magnitude,and would also provide similar sensitivity for the two-fermion flavor-changing coefficients.Overall,CEPC could explore a large fraction of currently allowed parameter space that will not be covered by the LHC upgrade.We show that the c-jet tagging capacity at CEPC could further improve its sensitivity to top-charm flavor-changing couplings.If a signal is observed,the kinematic distribution as well as the c-jet tagging could be exploited to pinpoint the various flavor-changing couplings,providing valuable information about the flavor properties of the top quark.展开更多
Given the null results of searches for new physics at the LHC,we investigate the one-loop effects SUSY QCD in the process e^+e^-→tg at the ILC in Minimal Supersymmetric Standard Model(MSSM).We find that the relativ...Given the null results of searches for new physics at the LHC,we investigate the one-loop effects SUSY QCD in the process e^+e^-→tg at the ILC in Minimal Supersymmetric Standard Model(MSSM).We find that the relative SUSY-QCD corrections to the cross section of e^+e^-→ tg can maximally reach 6.5%(3.2%) at the ILC with (1/2)s= 1000 GeV when m__1= 313.4 GeV and m_g =500(1500) GeV.展开更多
We investigate new physics effects on the Wtb effective couplings in a model-independent framework. The new physics effects can be parametrized by four independent couplings, f1^L, f1^R, f2^L and f2^R. We further intr...We investigate new physics effects on the Wtb effective couplings in a model-independent framework. The new physics effects can be parametrized by four independent couplings, f1^L, f1^R, f2^L and f2^R. We further introduce a set of parameters x0, xm, xp and x5 which exhibit a linear relation to the single top production cross sections. Using recent data for the t-channel single top production cross section at, tW associated production cross section crtw, s-channel single top production cross section δs, and W-helicity fractions F0, FL and FR collected at the 8 TeV LHC and Tevatron, we perform a global fit to impose constraints on the top quark effective couplings. Our globM fitting results show that the top quark effective couplings are strongly correlated. We show that （i） improving the measurements of δt and δtw is important in constraining the correlation of （f1^R, f2^R） and （f2^L,f2^R）; （ii） f1^L and f2^R are anti-correlated, and are sensitive to all the four experiments; （iii） f1^R and f2^L are also anti-correlated, and are sensitive to the F0 and FL measurements; （iv） the correlation between f2^L and f2^R is sensitive to the precision of the δt, δtw and F0 measurements. The effective Wtb couplings are studied in three kinds of new physics models： the G（221） = SU（2）1 SU（2）2 U（1）x models, the vector-like quark models and the Littlest Higgs model with and without T-parity. We show that the Wtb couplings in the left-right model and the un-unified model are sensitive to the ratio of gauge couplings when the new heavy gauge boson＇s mass （Mw,） is less than several hundred GeV, but the constraint is loose if Mw^t 〉 1 TeV. Fhrthermore, the Wtb couplings in vector-like quark models and the Littlest Higgs models are sensitive to the mixing angles of new heavy particles and SM particles.展开更多
基金the Natural Science Foundation of China(12175025,12147102,12265011)by the Projects of Guizhou Provincial Department(YQK[2023]016,ZK[2023]141,[2020]1Y027,GZMUZK[2022]PT01)。
文摘In this study,we reanalyze the top-quark pair production at next-to-next-to-leading order(NNLO)in quantum chromodynamics(QCD)at future e^(+)e^(−)colliders using the Principle of Maximum Conformality(PMC)method.The PMC renormalization scales inαs are determined by absorbing the non-conformalβterms by recursively using the Renormalization Group Equation(RGE).Unlike the conventional scale-setting method of fixing the scale at the center-of-mass energyμ_(r)=√s,the determined PMC scale Q_(⋆)is far smaller than the √sand increases with the √s,yielding the correct physical behavior for the top-quark pair production process.Moreover,the convergence of the pQCD series for the top-quark pair production is greatly improved owing to the elimination of the renormalon divergence.For a typical collision energy of √s=500 GeV,the PMC scale is Q_(⋆)=107 GeV;the QCD correction factor K for conventional results is K∼1+0.1244+0.0102+0.0012−0.0087−0.0011+0.0184−0.0086+0.0002+0.0061−0.0003,where the first error is caused by varying the scaleμr∈[√s/2,2√s]and the second error is from the top-quark massΔm_(t)=±0.7 GeV.After applying the PMC,the renormalization scale uncertainty is eliminated,and the QCD correction factor K is improved to K∼1+0.1507_(−0.0015)^(+0.0015)−0.0057_(−0.0000)^(+0.0001),where the error is from the top-quark massΔm_(t)=±0.7 GeV.The PMC improved predictions for the top-quark pair production are helpful for detailed studies of the properties of the top-quark at future e^(+)e^(−)colliders.
基金The work of S.Dulat was supported by the National Natural Science Foundation of China(11965020,11847160)。
文摘By applying the Error PDF Updating Method,we analyze the impact of the absolute and normalized single differential cross-sections for top-quark pair production data from the ATLAS and CMS experiments at the Large Hadron Collider,at a center-of-mass energy of √s=8TeV,on the CT14HERA2 PDFs.We find that the top quark pair single differential distributions provide minor constraints on the CT14HERA2 gluon PDF when the nominal CT14HERA2 inclusive jet production data are included in the fit.Larger constraints on the gluon distribution are present when the jet data are removed(CT14HERA2mJ)and/or when increased weights are given to the top data in the CT14HERA2 fits.The weighted$t\bar t$data provide significant constraints on the CT14HERA2mJ gluon PDF,which are comparable to those obtained from inclusive jet production data.Furthermore,we examine the top quark mass sensitivity of the top-quark pair single differential distributions.
基金Supported in part by the Natural Science Foundation of China (11625520, 11705033, 11905056, 11947406)the Project of Guizhou Provincial Department(KY[2021]003)the Department of Energy Contract (DE-AC02-76SF00515. SLAC-PUB-17567)
文摘In this study,we calculate the tt pQCD production cross-section at the NNLO and determine the top-quark pole mass from recent measurements at the LHC at the center-of-mass energy √S=13 TeV to a high precision by applying the principle of maximum conformality(PMC).The PMC provides a systematic method that rigorously eliminates QCD renormalization scale ambiguities by summing the nonconformalβcontributions into the QCD coupling constant.The PMC predictions satisfy the requirements of renormalization group invariance,including renormalization scheme independence,and the PMC scales accurately reflect the virtuality of the underlying production subprocesses.By using the PMC,an improved prediction for the tt production cross-section is obtained without scale ambiguities,which in turn provides a precise value for the top-quark pole mass.Moreover,the prediction of PMC calculations that the magnitudes of higher-order PMC predictions are well within the error bars predicted from the known lower-order has been demonstrated for the top-quark pair production.The resulting determination of the top-quark pole mass,m^(pole)_(t)=172.5±1.4 GeV,from the LHC measurement at √S=13 TeV agrees with the current world average cited by the Particle Data Group(PDG).The PMC prediction provides an important high-precision test of the consistency of pQCD and the SM at √S=13 TeV with previous LHC measurements at lower CM energies.
基金QHC and RZ are supported in part by the National Science Foundation of China(11725520,11675002,11635001)KPX is supported by grant(NRF-2019RICIC1010050)+1 种基金HZ is supported by Institute of High Energy Physics,Chinese Academy of Science(Y6515580U1)Innovation Grant(Y4545171Y2)。
文摘We propose a new dihedral angle observable for measuring the CP property of the interaction between the top quark and Higgs boson int\bar{t}Hproduction at the 14 TeV Large Hadron Collider(LHC).We consider two decay modes of the Higgs boson,H→to b\b and H→γγ,and demonstrate that the dihedral angle distribution is able to distinguish between the CP-even and the CP-odd hypothesis at a 95%confidence level,with an integrated luminosity of\sim 180fb^(-1).
文摘This paper posits that the observed resonance with 28 GeV at the LHC is the pseudoscalar top-bottom quark-antiquark composite which has the calculated mass of 27.9 GeV derived from the periodic table of elementary particles. The calculated mass is for the mass of?. In the periodic table of elementary particles, t quark (13.2 GeV) in the pseudoscalar top-bottom quark-antiquark composite is only a part of full t quark (175.4 GeV), so pseudoscalar?(26.4 GeV) cannot exist independently, and can exist only in the top-bottom quark-antiquark composite. As shown in the observation at the LHC, the resonance with 28 GeV weakens significantly at the higher energy collision (13 TeV), because at the higher collision energy, low-mass pseudoscalar? in the composite likely becomes independent full high-mass vector? moving out of the composite. The periodic table of elementary particles is based on the seven mass dimensional orbitals derived from the seven extra dimensions of 11 spacetime dimensional membrane. The calculated masses of hadrons are in excellent agreement with the observed masses of hadrons by using only five known constants. For examples, the calculated masses of proton, neutron, pion (π±), and pion (±0) are 938.261, 939.425, 139.540, and 134.982 MeV in excellent agreement with the observed 938.272, 939.565, 139.570, and 134.977MeV, respectively with 0.0006%, 0.01%, 0.02%, and 0.004%, respectively for the difference between the calculated and observed mass. The calculated masses of the Higgs bosons as the intermediate vector boson composites are in excellent agreements with the observed masses. In conclusion, the calculated masses of the top-bottom quark-antiquark composite (27.9 GeV), hadrons, and the Higgs bosons by the periodic table of elementary particles are in excellent agreement with the observed masses of resonance with 28 GeV at the LHC, hadrons, and the Higgs bosons, respectively.
文摘In this review we do not try to cover all the aspects of physics besnd tile standard model （BSM）, instead our latest understanding on tile BSM will be presented： i） Tile Higgs sector is likely related to BSM, which can be confirmed at current running large hadron collider （LHC） or tile fllture eolliders. Furthermore we pointed out that spontaneous CP violation can be closely related to the lightness of the Higgs boson, ii） Top quark forward-backward asymmetry, which was mea.sured by Tewttron, might be the sign of BSM.2; proposed a new color-octet particle Zcr to account fi）r the observation and Z can be fllrther studied at the LHC. iii） If dark matter （DM） is utilized to accommodate astrophysical obserwtions, it ought to be observed at the high energy LttC and DM produced at colliders should be tile slnoking gun signal, iv） Lithium puzzle might also be the sign of the BSM. We briefly review tile newly proposed solution to Lithium puzzle, i.e.. the existonce of non-thermal component during the big bang nuclei-synthesis （BBN）. The possible origins of the non-thermal coinponent can be dark matter or the new accelerating mechanism of normal particles.
基金supported by IHEP(Y7515540U1)supported by a Marie Sk lodowska-Curie Individual Fellowship of the European Commission’s Horizon 2020 Programme(704187)
文摘We perform a global effective-field-theory analysis to assess the combined precision of Higgs couplings, triple gauge-boson couplings, and top-quark couplings, at future circular e＋e- colliders, with a focus on runs below the tt-production threshold. Deviations in the top-quark sector entering as one-loop corrections are consistently taken into account in the Higgs and diboson processes. We find that future lepton colliders running at center-of-mass energies below the tt production threshold can still provide useful information on top-quark couplings, by measuring virtual top-quark effects. With rate and differential measurements, the indirect individual sensitivity achievable is better than at the high-luminosity LHC. However, strong correlations between the extracted top-quark and Higgs couplings are also present and lead to much weaker global constraints on top-quark couplings. This implies that a direct probe of top-quark couplings above the t~ production threshold is also helpful for the determination of Higgs and triple-gauge-boson couplings. In addition, we find that below the e＋e- -＋tth production threshold, the top-quark Yukawa coupling can be determined by its loop corrections to all Higgs production and decay channels. Degeneracy with the ggh coupling can be resolved, and even a global limit is competitive with the prospects of a linear collider above the threshold. This provides an additional means of determining the top-quark Yukawa coupling indirectly at lepton colliders.
基金Supported by the National Natural Science Foundation of China(NSFC)(11325525,11635009,11775130,11447009,11305049)Natural Science Foundation of Shandong Province(ZR2017JL006,ZR2017MA002)
文摘Heavy charged gauge bosons are proposed in some theories beyond the standard model. We explore the discovery potential for W＇→tb with top quark semi-leptonic decay at the LHC. We concentrate on the new physics signal search with the deviation from the standard model prediction if the resonance peak of W＇ cannot be observed directly. Signal events with two jets plus one charged lepton and missing energy are simulated, together with the dominant standard model backgrounds. In this paper, it is found that suitable cuts on the kinematic observables can effectively suppress the standard model backgrounds mass is less than 6.6 TeV. so that it is possible to search for a W＇ signal at the LHC if its
基金Supported by the 100-talent project of Chinese Academy of Sciences
文摘Recently, experimental collaborations have reported 0（10） upper limits on the signal strength of fourtop production at the LHC. Surprisingly, we find that the constraining power of four-top production on the qqtt type of operators is already competitive with the measurements of top-pair production, even though the precision level of the latter is more than two orders of magnitude better. This is explained by the enhanced sensitivity of the four-top cross section to qqtt operators, due to multiple insertion of operators in the squared amplitude, and to the large threshold energy of four-top production. We point out that even though the dominant contribution beyond the standard model comes from the O（C^4/Λ^8） terms, the effective field theory expansion remains valid for a wide range of underlying theories. Considering the possible improvements of this measurement with higher integrated luminosity, we believe that this process will become even more crucial for probing and testing the standard model deviations in the top-quark sector, and will eventually provide valuable information about the top-quark properties,leading to significant improvements in precision top physics.
文摘In the framework of the littlest Higgs model with T-parity, we study the top pair production at the next generation colliders like LHC and ILC. We find that the order O（αs） corrections to the standard model top pair production cross section at LHC can be very small and the magnitude is below 1%. However, the magnitude of corrections to the standard model top pair production rate at ILC may be over 5% for reasonable values＇of the parameters. Besides this, the corrections to the asymmetry ALR（tt） may be more sizable. Therefore, the top pair production at ILC may serve as a probe of the littlest Higgs model with T-parity, especially the asymmetry ALR（tt）.
文摘The topcolor-assisted technicolor （TC2） model predicts a number of neutral scalars like the top-pion （πt^0） and the top-Higgs （ht^0）. These scalars have flavor-changing neutral-current （FCNC） top quark couplings, among which the top-charm transition couplings may be sizable. Such FCNC couplings induce single top productions associated with a neutral scalar at the CERN Large Hadron Collider （LHC） through the parton processes cg→ tπt^0 and cg→ tht^0. In this paper we examine these productions and find their production rates can exceed the 3σ sensitivity of the LHC in a large part of parameter space. Since in the Standard Model and the minimal supersymmetric model such rare productions have unobservably small production rates at the LHC, these rare processes will serve as a good probe for the TC2 model.
基金Supported by CNRS via the LIA FCPPL,by the CEPC theory study grant,and by IHEP(Y7515540U1)
文摘We propose to study the flavor properties of the top quark at the future Circular Electron Positron Collider(CEPC) in China.We systematically consider the full set of 56 real parameters that characterize the flavor-changing neutral interactions of the top quark,which can be tested at CEPC in the single top production channel.Compared with the current bounds from the LEP2 data and the projected limits at the high-luminosity LHC,we find that CEPC could improve the limits of the four-fermion flavor-changing coefficients by one to two orders of magnitude,and would also provide similar sensitivity for the two-fermion flavor-changing coefficients.Overall,CEPC could explore a large fraction of currently allowed parameter space that will not be covered by the LHC upgrade.We show that the c-jet tagging capacity at CEPC could further improve its sensitivity to top-charm flavor-changing couplings.If a signal is observed,the kinematic distribution as well as the c-jet tagging could be exploited to pinpoint the various flavor-changing couplings,providing valuable information about the flavor properties of the top quark.
基金Supported by the National Natural Science Foundation of China(NNSFC)under Grant Nos.11305049,11275057,and 11405047Specialized Research Fund for the Doctoral Program of Higher Education under Grant No.20134104120002the Startup Foundation for Doctors of Henan Normal University under Grant No.11112
文摘Given the null results of searches for new physics at the LHC,we investigate the one-loop effects SUSY QCD in the process e^+e^-→tg at the ILC in Minimal Supersymmetric Standard Model(MSSM).We find that the relative SUSY-QCD corrections to the cross section of e^+e^-→ tg can maximally reach 6.5%(3.2%) at the ILC with (1/2)s= 1000 GeV when m__1= 313.4 GeV and m_g =500(1500) GeV.
基金Supported by National Science Foundation of China(11275009,11675002,11635001)National Science Foundation(PHY-1315983,PHY-1316033)DOE(DE-SC0011095)
文摘We investigate new physics effects on the Wtb effective couplings in a model-independent framework. The new physics effects can be parametrized by four independent couplings, f1^L, f1^R, f2^L and f2^R. We further introduce a set of parameters x0, xm, xp and x5 which exhibit a linear relation to the single top production cross sections. Using recent data for the t-channel single top production cross section at, tW associated production cross section crtw, s-channel single top production cross section δs, and W-helicity fractions F0, FL and FR collected at the 8 TeV LHC and Tevatron, we perform a global fit to impose constraints on the top quark effective couplings. Our globM fitting results show that the top quark effective couplings are strongly correlated. We show that （i） improving the measurements of δt and δtw is important in constraining the correlation of （f1^R, f2^R） and （f2^L,f2^R）; （ii） f1^L and f2^R are anti-correlated, and are sensitive to all the four experiments; （iii） f1^R and f2^L are also anti-correlated, and are sensitive to the F0 and FL measurements; （iv） the correlation between f2^L and f2^R is sensitive to the precision of the δt, δtw and F0 measurements. The effective Wtb couplings are studied in three kinds of new physics models： the G（221） = SU（2）1 SU（2）2 U（1）x models, the vector-like quark models and the Littlest Higgs model with and without T-parity. We show that the Wtb couplings in the left-right model and the un-unified model are sensitive to the ratio of gauge couplings when the new heavy gauge boson＇s mass （Mw,） is less than several hundred GeV, but the constraint is loose if Mw^t 〉 1 TeV. Fhrthermore, the Wtb couplings in vector-like quark models and the Littlest Higgs models are sensitive to the mixing angles of new heavy particles and SM particles.
