arXiv subjects

Zhao Li

Publications and source records attributed to Zhao Li.

At least 145 records · Page 8Linked to original sources

arXiv2012

Discovery and Identification of W' and Z' in SU(2) x SU(2) x U(1) Models at the LHC

We explore the discovery potential of W' and Z' boson searches for various SU(2) x SU(2) x U(1) models at the Large Hadron Collider (LHC), after taking into account the constraints from low energy precision measurements and direct searches at both the Tevatron (1.96 TeV) and the LHC (7 TeV). In such models, the W' and Z' bosons emerge after the electroweak symmetry is spontaneously broken. Two patterns of the symmetry breaking are considered in this work: one is SU(2)_L x SU(2)_2 x U(1)_X to SU(2)_L x U(1)_Y (BP-I), another is SU(2)_1 x SU(2)_2 x U(1)_Y to SU(2)_L x U(1)_Y (BP-II). Examining the single production channel of W' and Z' with their subsequent leptonic decays, we find that the probability of detecting W' and Z' bosons in the considered models at the LHC (with 14 TeV) is highly limited by the low energy precision data constraints. We show that observing Z' alone, without seeing a W', does not rule out new physics models with non-Abelian gauge extension, such as the phobic models in BP-I. Models in BP-II would predict the discovery of degenerate W' and Z' bosons at the LHC.

hep-ph↗

arXiv2012

Progress in CTEQ-TEA PDF analysis

Recent developments in the CTEQ-TEA global QCD analysis are presented. The parton distribution functions CT10-NNLO are described, constructed by comparing data from many experiments to NNLO approximations of QCD.

hep-ph↗

arXiv2012

One-way information reconciliation schemes of quantum key distribution

Information reconciliation(IR) is a basic step of quantum key distribution (QKD). Classical message interaction is necessary in a practical IR scheme, and the communication complexity has become a bottleneck of QKD's development. Here we propose a concatenated method of IR scheme which requires only one time one-way communication to achieve any given error rate level. A QKD scheme with the concatenated IR can work without the special interaction of error rate estimation.

quant-ph↗

arXiv2011

QCD resummation for jet substructures

We provide a novel development in jet physics by predicting the energy profiles of light-quark and gluon jets in the framework of perturbative QCD. Resumming large logarithmic contributions to all orders in the coupling constant, our predictions are shown to agree well with Tevatron CDF and Large-Hadron-Collider CMS data. We also extend our resummation formalism to the invariant mass distributions of light-quark and gluon jets produced in hadron collisions. The predicted peak positions and heights in jet mass distributions are consistent with CDF data within uncertainties induced by parton distribution functions.

hep-ph↗

arXiv2011

Improved Predictions for Higgs Q_T at the Tevatron and the LHC

The search for the Higgs boson at the Tevatron and the LHC relies on detailed calculations of the kinematics of Higgs boson production and decay. In this paper, we improve the calculation of the distribution in transverse momentum, $Q_T$, of the Higgs boson in the gluon fusion production process, $gg\to H$, by matching the resummed distribution at small $Q_T$ with the ${\cal O}(α_{s}^4)$ fixed-order perturbative calculation at high $Q_T$ in the ResBos Monte Carlo program. The distribution is higher at large $Q_T$ than with the old ${\cal O}(α_{s}^3)$ fixed-order perturbative calculation, and the matching with the resummed calculation is much smoother. The total cross section is also increased, more in line with next-to-next-to-leading-order calculations. We also study the effect of the new calculation on the distribution of $Δϕ_{\ell\ell}$ in the overall process $gg\to H\to W^{+} W^{-}\to\ell^{+}\ell^{-}ν\barν$, and the effect of PDF uncertainties on the distributions at the Tevatron and the LHC.

hep-ph↗

arXiv2010

New parton distributions for collider physics

We extract new parton distribution functions (PDFs) of the proton by global analysis of hard scattering data in the general-mass framework of perturbative quantum chromodynamics. Our analysis includes new theoretical developments together with the most recent collider data from deep-inelastic scattering, vector boson production, and single-inclusive jet production. Due to the difficulty in fitting both the DO Run-II W lepton asymmetry data and some fixed-target DIS data, we present two families of PDFs, CT10 and CT10W, without and with these high-luminosity W lepton asymmetry data included in the global analysis. With both sets of PDFs, we study theoretical predictions and uncertainties for a diverse selection of processes at the Fermilab Tevatron and the CERN Large Hadron Collider.

hep-ph↗

arXiv2010

Uncertainty induced by QCD coupling in the CTEQ global analysis of parton distributions

We examine the dependence of parton distribution functions (PDFs) on the value of the QCD coupling strength $α_{s}(M_{Z})$. We explain a simple method that is rigorously valid in the quadratic approximation normally applied in PDF fitting, and fully reproduces the correlated dependence of theoretical cross sections on $α_s$ and PDF parameters. This method is based on a statistical relation that allows one to add the uncertainty produced by $α_s$, computed with some special PDF sets, in quadrature with the PDF uncertainty obtained for the fixed $α_s$ value (such as the CTEQ6.6 PDF set). A series of four CTEQ6.6AS PDFs realizing this approach, for $α_s$ values in the interval $0.116 \leq α_{s}(M_{Z}) \leq 0.120$, is presented. Using these PDFs, the combined $α_{s}$ and PDF uncertainty is assessed for theoretical predictions at the Fermilab Tevatron and Large Hadron Collider.

hep-ph↗

arXiv2009

A Dark Matter Model with Non-Abelian Gauge Symmetry

We propose a dark matter model in which the dark sector is gauged under a new SU(2) group. The dark sector consists of SU(2) dark gauge fields, two triplet dark Higgs fields, and two dark fermion doublets (dark matter candidates in this model). The dark sector interacts with the SM sector through kinetic and mass mixing operators. The model explains both PAMELA and Fermi LAT data very well and also satisfies constraints from both the DM relic density and Standard Model precision observables. The phenomenology of the model at the LHC is also explored.

hep-ph↗

arXiv2009

Nonperturbative Effect in Threshold Resummation

We show that the conventional threshold resummation calculation cannot describe well the low energy Drell-Yan (DY) data without including the non-perturbative correction terms which are deduced from analyzing the asymptotic behavior of the resummation formalism. It is demonstrated that the non-perturbative correction is generally small for the large invariant mass DY pairs produced at the Tevatron and the LHC.

hep-ph↗

arXiv2009

Threshold Resummation Effects in Neutral Higgs Boson Production by Bottom Quark Fusion at the CERN Large Hadron Collider

We investigate the QCD effects in the production of neutral Higgs bosons via bottom quark fusion in both the standard model and the minimal supersymmetric standard model at the CERN Large Hadron Collider. We include the next-to-leading order (NLO) QCD corrections (including supersymmetric QCD) and the threshold resummation effects. We use the soft-collinear effective theory to resum the large logarithms near threshold from soft gluon emission. Our results show that the resummation effects can enhance the total cross sections by about 5% compared with the NLO results.

hep-ph↗

arXiv2009

Next-to-leading order QCD corrections to the top quark decay via model-independent FCNC couplings

D0 and CDF collaborations at the Fermilab Tevatron have searched for non-standard-model single top-quark production and set upper limits on the anomalous top quark flavor-changing neutral current (FCNC) couplings $κ^g_{tc}/Λ$ and $κ^g_{tu}/Λ$ using the measurement of total cross section calculated at the next-to-leading order (NLO) in QCD. In this Letter, we report on the effect of anomalous FCNC couplings to various decay branching ratios of the top quark, calculated at the NLO. This result is not only mandatory for a consistent treatment of both the top quark production and decay via FCNC couplings by D0 and CDF at the Tevatron but is also important for the study of ATLAS and CMS sensitivity to these anomalous couplings at the CERN LHC. We find that the NLO corrections to the partial decay widths of the three decay channels $ t\to q + g$, $ t\to q + γ$ and $ t\to q + Z$ are at the order of 10% in magnitude and modify their branching ratios by about 20%, 0.4% and 2%, respectively, as compared to their leading order predictions.

hep-ph↗

arXiv2008

Same-sign top pair production in an extra-dimension model of flavor at the CERN Large Hadron Collider

We study the same-sign top pair production mediated by the first Kluza-Klein (KK) excitation of the gluon in the Randall-Sundrum (RS) model with flavor violation at the Large Hadron Collider (LHC), in which the nonuniversal couplings between fermions and KK gauge bosons will lead to observable tree level flavor-changing neutral current (FCNC) effects. We find that the same-sign top quarks produced in our case have property of high energy and high transverse momentum, and lead to an observable signal in the same-sign dilepton channel even when the mass of the KK gluon reach up to 3 TeV. We further investigate the potential of the LHC to probe the flavor violating parameters and find that the LHC can probe their values down to 0.06.

hep-ph↗

arXiv2007

Next-to-leading order QCD effects in associated charged Higgs and W boson production in the MSSM at the CERN Large Hadron Collider

We present the calculations of the next-to-leading order (NLO) QCD corrections to the inclusive total cross sections for the associated production of the $W^{\pm}H^{\mp}$ through $b\bar{b}$ annihilation in the Minimal Supersymmetric Standard Model at the CERN Large Hadron Collider. The NLO QCD corrections can either enhance or reduce the total cross sections, but they generally efficiently reduce the dependence of the total cross sections on the renormalization/factorization scale. The magnitude of the NLO QCD corrections is about 10% in most of the parameter space and can reach 15% in some parameter regions. We also show the Monte Carlo simulation results for the $2j+τ_{jet}+\not{p}_{T}$ signature from the $W^{\pm}$ and the $H^{\mp}$ decays including the NLO QCD effects, and find an observable signal at a $5σ$ level in some parameter region of the minimal supergravity model.

hep-ph↗

arXiv2007

Contributions from SUSY-FCNC couplings to the interpretation of the HyperCP events for the decay Σ^+ \to p μ^+ μ^-

The observation of three events for the decay $Σ^+ \to p μ^+ μ^-$ with a dimuon invariant mass of $214.3\pm0.5$MeV by the HyperCP collaboration imply that a new particle X may be needed to explain the observed dimuon invariant mass distribution. We show that there are regions in the SUSY-FCNC parameter space where the $A^0_1$ in the NMSSM can be used to explain the HyperCP events without contradicting all the existing constraints from the measurements of the kaon decays, and the constraints from the $K^0-\bar{K}^0$ mixing are automatically satisfied once the constraints from kaon decays are satisfied.

hep-ph↗

arXiv2007

Threshold Resummation Effects in the Associated Production of Chargino and Neutralino at Hadron Colliders

We investigate the QCD effects in the associated production of the chargino and the neutralino, $\tildeχ^\pm_{1}$ and $\tildeχ^0_{2}$, in the Minimal Supersymmetric Standard Model (MSSM) at both the Fermilab Tevatron and the CERN Large Hadron Collider (LHC). We include the next-to-leading order (NLO) QCD corrections (including supersymmetric QCD) and the threshold resummation effects. Our results show that, compared to the NLO predictions, the threshold resummation effects can increase the total cross sections by 3.6% and 3.9% for the associated production of $\tildeχ^+_{1}\tildeχ^0_{2}$ and $\tildeχ^-_{1}\tildeχ^0_{2}$ at the LHC, respectively, and by 4.7% for those of $\tildeχ^\pm_{1}\tildeχ^0_{2}$ at the Tevatron. In the invariant mass distributions the resummation effects are significant for large invariant mass. The threshold resummation reduces the dependence of the total cross sections at the LHC (Tevatron) on the renormalization/factorization scales to 5% (4%) from up to 7% (11%) at NLO.

hep-ph↗

arXiv2007

Unparticle Physics and Supersymmetry Phenomenology

We show a natural form of the interaction between unparticle and supersymmetry. Using the couplings of unparticle to supersymmetry presented, as examples, we calculate the differential decay rates for the processes ${\it {\tilde f}}\to {\it f}+{\cal U}_{3/2}$, ${\it {\tilde χ}}^0\to{\it γ}+{\cal U}_{3/2}$, ${\it {\tilde χ}}^\pm\to W^\pm+{\cal U}_{3/2}$ and ${\it {\tilde χ}}^0\to Z^0+{\cal U}_{3/2}$. Finally, we discuss the phenomenological implication of our results and give some comments.

hep-ph↗

arXiv2007

Supersymmetric QCD corrections to single top quark production at hadron colliders

We present the calculations of the supersymmetric QCD corrections to the total cross sections for single top production at the Fermilab Tevatron and the CERN Large Hadron Collider in the minimal supersymmetric standard model. Our results show that for the s-channel and t-channel, the supersymmetric QCD corrections are at most about 1%, but for the associated production process, the supersymmetric QCD corrections increase the total cross sections significantly, which can reach about 6% for most values of the parameters, and the supersymmetric QCD corrections should be taken into consideration in the future high precision experimental analysis for top physics.

hep-ph↗

arXiv2006

Associated Production of Neutral Higgs Boson with Squark Pair in the Minimal Supersymmetric Standard Model with Explicit CP Violation at the CERN LHC

We investigate the associated production of neutral Higgs boson with squark pair in the minimal supersymmetric standard model with and without explicit CP violation, respectively. We show that the dominant productions in both cases are always ones of the lightest neutral Higgs boson associated with the lightest stop pair, which can reach a few pb, in the ranges of parameters allowed by constraints from the electric dipole moment experiments. In most of the parameter space, the total cross sections in the case with explicit CP violation are significantly enhanced, compared with ones without explicit CP violation. For some special parameters, several orders of magnitude enhancement can be obtained.

hep-ph↗