arXiv subjects

Xiaohui Liu

Publications and source records attributed to Xiaohui Liu.

142 records · Page 8Linked to original sources

arXiv2014

Jet vetoes for Higgs production at future hadron colliders

We study Higgs boson production in exclusive jet bins at possible future 33 and 100 TeV proton-proton colliders. We compare the cross sections obtained using fixed-order perturbation theory with those obtained by also resuming large logarithms induced by the jet-binning in the gluon-fusion and associated production channels. The central values obtained by the best-available fixed-order predictions differ by $10-20\%$ from those obtained after including resummation over the majority of phase-space regions considered. Additionally, including the resummation dramatically reduces the residual scale variation in these regions, often by a factor of two or more. We further show that in several new kinematic regimes that can be explored at these high-energy machines, the inclusion of resummation improvement is mandatory.

hep-ph↗

arXiv2014

Fast and exact implementation of 3-dimensional Tukey depth regions

Tukey depth regions are important notions in nonparametric multivariate data analysis. A $τ$-th Tukey depth region $\mathcal{D}_τ$ is the set of all points that have at least depth $τ$. While the Tukey depth regions are easily defined and interpreted as $p$-variate quantiles, their practical applications is impeded by the lack of efficient computational procedures in dimensions with $p > 2$. Feasible algorithms are available, but practically very slow. In this paper we present a new exact algorithm for 3-dimensional data. An efficient implementation is also provided. Data examples indicate that the proposed algorithm runs much faster than the existing ones.

stat.CO↗

arXiv2014

A Maximal Concurrency and Low Latency Distributed Scheduling Protocol for Wireless Sensor Networks

Existing work that schedules concurrent transmissions collision-free suffers from low channel utilization. We propose the Optimal Node Activation Multiple Access (ONAMA) protocol to achieve maximal channel spatial reuse through a distributed maximal independent set (DMIS) algorithm. To overcome DMIS's excessive delay in finding a maximal independent set, we devise a novel technique called pipelined precomputation that decouples DMIS from data transmission. We implement ONAMA on resource-constrained TelosB motes using TinyOS. Extensive measurements on two testbeds independently attest to ONAMA's superb performance compared to existing work: improving concurrency, throughput, and delay by a factor of 3.7, 3.0, and 5.3, respectively, while still maintaining reliability.

cs.NI↗

arXiv2013

Combining Resummed Higgs Predictions Across Jet Bins

Experimental analyses often use jet binning to distinguish between different kinematic regimes and separate contributions from background processes. To accurately model theoretical uncertainties in these measurements, a consistent description of the jet bins is required. We present a complete framework for the combination of resummed results for production processes in different exclusive jet bins, focusing on Higgs production in gluon fusion as an example. We extend the resummation of the Higgs + 1-jet cross section into the challenging low transverse momentum region, lowering the uncertainties considerably. We provide combined predictions with resummation for cross sections in the Higgs + 0-jet and Higgs + 1-jet bins, and give an improved theory covariance matrix for use in experimental studies. We estimate that the relevant theoretical uncertainties on the signal strength in the Higgs to WW analysis are reduced by nearly a factor of 2 compared to the current value.

hep-ph↗

arXiv2013

Polarization Controlled Ohmic to Schottky Transition at a Metal/Doped Ferroelectric Interface

Ferroelectric polar displacements have recently been observed in conducting electron-doped BaTiO3. The co-existence of a ferroelectric phase and conductivity opens the door to new functionalities which may provide a unique route for novel device applications. Using first-principles methods and electrostatic modeling we explore the effect that the switchable polarization of electron-doped BaTiO3 (n-BaTiO3) has on the electronic properties of the SrRuO3/n-BaTiO3 (001) interface. Ferroelectric polarization controls the accumulation or depletion of electron charge at the interface, and the associated bending of the n-BTO conduction band determines the transport regime across the interface. The interface exhibits a Schottky tunnel barrier for one polarization orientation, whereas an Ohmic contact is present for the opposite polarization orientation, leading to a large change in interface resistance associated with polarization reversal. Calculations reveal a large (five orders of magnitude) change in the interface resistance as a result of polarization switching.

cond-mat.mtrl-sci↗

arXiv2013

The 1-Jettiness event shape for DIS with NNLL resummation

We propose the use of 1-jettiness, a global event shape, for exclusive single jet production in lepton-nucleus deep inelastic scattering (DIS). We derive a factorization formula, using the Soft-Collinear Effective Theory, differential in the transverse momentum and rapidity of the jet and the 1-jettiness event shape. It provides a quantitative measure of the shape of the final-state QCD radiation in the presence of the hard jet, providing a useful powerful probe of QCD and nuclear physics. For example, one expects differences in the observed pattern of QCD radiation between large and small nuclei and these can be quantified by the 1-jettiness event shape. Numerical results are given for this new DIS event shape at leading twist with resummation at the next-to-next-to-leading logarithmic (NNLL) level of accuracy, for a variety of nuclear targets. Such studies would be ideal at a future EIC or LHeC electron-ion collider, where a range of nuclear targets are planned.

hep-ph↗

arXiv2013

Reducing theoretical uncertainties for exclusive Higgs plus one-jet production at the LHC

We resum a class of large Sudakov logarithms affecting Higgs boson production in the exclusive one-jet bin at the LHC. We extend previous results by calculating the full one-loop soft function for this process, which extends the accuracy of the resummation to include the leading three logarithmic corrections at each order in the QCD coupling constant. We match this result to the next-to-leading order cross section and present a detailed numerical study assuming realistic LHC cuts. Careful attention is paid to the matching procedure, and to the theoretical uncertainties induced by residual scale variation. We find that the matched NLL'+ NLO cross section has significantly smaller uncertainties than the fixed-order result, and can be used to alleviate the theoretical errors hindering current Higgs analyses at the LHC.

hep-ph↗

arXiv2012

Resummation of jet-veto logarithms in hadronic processes containing jets

We derive a factorization theorem for production of an arbitrary number of color-singlet particles accompanied by a fixed number of jets at the LHC. The jets are defined with the standard anti-$k_T$ algorithm, and the fixed number of jets is obtained by imposing a veto on additional radiation in the final state. The formalism presented here is useful for current Higgs boson analyses using exclusive jet bins, and for other studies using a similar strategy. The derivation uses the soft-collinear effective theory and assumes that the transverse momenta of the hard jets are larger than the veto scale. We resum the large Sudakov logarithms $α_s^n \log^{2n-m}(p_T^{J}/p_T^{veto})$ up to the next-to-leading-logarithmic accuracy, and present numerical results for Higgs boson production in association with a jet at the LHC. We comment on the experimentally-interesting parameter region in which we expect our factorization formula to hold.

hep-ph↗

arXiv2012

Ferroelectric Instability under Screened Coulomb Interactions

We explore the effect of charge carrier doping on ferroelectricity using density functional calculations and phenomenological modeling. By considering a prototypical ferroelectric material, BaTiO3, we demonstrate that ferroelectric displacements are sustained up to the critical concentration of 0.11 electron per unit cell volume. This result is consistent with experimental observations and reveals that the ferroelectric phase and conductivity can coexist. Our investigations show that the ferroelectric instability requires only a short-range portion of the Coulomb force with an interaction range of the order of the lattice constant. These results provide a new insight into the origin of ferroelectricity in displacive ferroelectrics and open opportunities for using doped ferroelectrics in novel electronic devices.

cond-mat.mtrl-sci↗

arXiv2012

A General Theory for Direct Quantitative Analysis of Antigen

A theory for direct quantitative analysis of an antigen is proposed. It is based on a potential homogenous immunoreaction system. It establishes an equation to describe the concentration change of the antigen and antibody complex. A maximum point is found in the concentration profile of the complex which can be used to calculate the concentration of the antigen. An experimental scheme was designed for a commercial time-resolved fluoroimmunoassay kit for HBsAg, which is based heterogeneous immunoreaction. The results showed that the theory is practically applicable.

q-bio.QM↗

arXiv2012

Gauge-boson production with multiple jets near threshold

Signatures of new physics beyond the Standard Model are often characterized by large missing transverse energy ($\not E_T$) produced in association with multiple jets. The dominant Standard Model background to such processes comes from gauge-boson production in association with jets. A standard search strategy involves looking for an excess in the $m_{eff}$ distribution, where $m_{eff}= \not E_T +\sum_{J} p^T_J$ and $p^T_J$ denotes the transverse momentum of the $J$-th jet. The region of large $m_{eff}$ is dominated by jet production near threshold, giving rise to large Sudakov logarithms that can change the magnitude and shape of the $m_{eff}$ distribution. We present an effective theory framework for the resummation of such threshold logarithms. We perform an analysis for exclusive jet production using the N-jettiness global event shape, which allows theoretical control to also be maintained over large logarithms induced by vetoing additional jets. As a first step, we give explicit numerical results with next-to-leading-log (NLL) resummation for $pp \to γ+ 2$ jets in the large $m_{eff}$ region.

hep-ph↗

arXiv2011

Exactly computing bivariate projection depth contours and median

Among their competitors, projection depth and its induced estimators are very favorable because they can enjoy very high breakdown point robustness without having to pay the price of low efficiency, meanwhile providing a promising center-outward ordering of multi-dimensional data. However, their further applications have been severely hindered due to their computational challenge in practice. In this paper, we derive a simple form of the projection depth function, when (μ, σ) = (Med, MAD). This simple form enables us to extend the existing result of point-wise exact computation of projection depth (PD) of Zuo and Lai (2011) to depth contours and median for bivariate data.

stat.CO↗

arXiv2010

SCET approach to top quark decay

In this work we study QCD corrections to the top quark doubly decay rate with a detected $B$ hadron containing a $b$ quark. We focus on the regime among which the emitted $W$ boson nearly carries its maxim energy. The tool that we use here is the soft-collinear effective theory (SCET). The factorization theorem based on SCET indicates a novel fragmenting jet function. We calculate this function to next-to-leading order in $α_s$. Large logarithms due to several well separated scale are summed up using the renormalization group equation (RGE). Finally we reach an analytic formula for the distribution which could easily be generalized to other heavy hadron decay.

hep-ph↗

arXiv2010

Color-Octet $\jpsi$ Production in $Υ$ Decay near the Kinematic Limit

Recent experiments by the CLEO III detector at CESR indicate that the $\jpsi$ spectrum produced in $Υ$ decay is in conflict with Non-Relativistic QCD (NRQCD) calculations. The measured $\jpsi$ momentum distribution is much softer than predicted by the color-octet mechanisms. The expected peak at the kinematic limit is not observed in the data. However it has recent been pointed out that NRQCD calculations break down near the kinematic endpoint due to large perturbative and non-perturbative corrections. In this paper we combine NRQCD with soft collinear effective theory to study the color-octet contribution to the $Υ\to \jpsi + X$ decay in this region of phase space. We obtain a spectrum that is significantly softened when including the correct degrees of freedom in the endpoint region, giving better agreement with the data than previous predictions.

hep-ph↗

arXiv2009

QED Contribution to the Color-Singlet $\jpsi$ Production in $Υ$ Decay Near the Endpoint

A recent study indicates that the $α^2α_s^2$ order QED processes of $Υ\to \jpsi + X$ decay are compatible with those of QCD processes. However, in the endpoint region, the Non-relativistic QED (NRQED) calculation breaks down since the collinear degrees of freedom are missing under the framework of this effective theory. In this paper we apply the soft collinear effective theory (SCET) to study the color-singlet QED process at the kinematic limit. Within this approach we are able to sum the kinematic logarithms by running operators using the renormalization group equations of SCET, which will lead to a dramatic change in the momentum distribution near the endpoint and the spectrum shape consistent with the experimental results.

hep-ph↗

arXiv2007

The color-singlet contribution to e^+ e^- ->J/psi + X at the endpoint

Recent observations of the J/psi spectrum produced in e^+e^- collisions at the Upsilon(4S) resonance are in conflict with fixed-order calculations using Non-Relativsitic QCD effective theory (NRQCD). One problem is an enhancement in the cross section when the J/psi has maximal energy, due to large perturbative corrections (Sudakov logarithms). In a recent paper, the Sudakov logarithms in the color-octet contribution were summed by combining NRQCD with the Soft-Collinear Effective Theory. However to be consistent, the color-singlet contributions must also be summed in the endpoint region which was not done in that paper. In this paper, we sum the leading and next-to-leading logarithms in the color-singlet contribution to the J/psi production cross section. We find that the color-singlet cross section is suppressed near endpoint compared to the fixed order NRQCD prediction.

hep-ph↗