Zhen-Jun Xiao
The NLO contributions to some two-body charmless hadronic B meson decays, such as those from the QCD vertex corrections, the quark loops and the chromo-magnetic penguins, have been calculated in the pQCD factorization approach.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
继续探索
The matrix element of B^0 -\bar B^0 mixing is evaluated from QCD sum rules for three-point correlators with next-to-leading order accuracy in pQCD.
By employing the perturbative QCD(pQCD) factorization approach, we calculated the partial next-to-leading order (NLO) contributions to $B_s \to P P$ decays ($P= π, K, \etap $), coming from the QCD vertex corrections, the quark-loops and the chromo-magnetic penguins. we found numerically that (a) for three measured decays $\bar{B}_s \to K^+ π^-, K^+K^-$ and $π^+π^-$, the consistency between the pQCD predictions and the measured values are improved effectively by the inclusion of the NLO contributions; (b) for $\bar{B}_s \to K^0\etap$ and $K^0π^0$ decays, the NLO enhancements to the branching ra…
We present a generally applicable reduction formalism which makes it possible to express an arbitrary tensor and scalar one-loop Feynman integral, with N external lines and massless propagators, in terms of a basic set of eight fundamental scalar Feynman integrals with 2, 3, and 4 external lines, for arbitrary external kinematics. The formalism is particularly suitable for the NLO calculations of exclusive processes at large momentum transfer in pQCD, where all previously developed reduction methods fail due to the presence of collinear external on-shell lines.
By employing the perturbative QCD (pQCD) factorization approach, we calculated some important next-to-leading-order(NLO) contributions to the two-body charmless hadronic decays $B^+ \to ρ^+ η^{(\prime)}$ and $B^0 \to ρ^0(ω, ϕ) η^{(\prime)}$, induced by the vertex QCD corrections, the quark-loops as well as the chromo-magnetic penguins. From the numerical results and phenomenological analysis we find that (a) for $B^\pm \to ρ^\pm \etap$ decays, the partial NLO contributions to branching ratios are small in magnitude; (b) for $B^0 \to ρ^0(ω,ϕ) \etap$ decays, the NLO contributions can provide sig…
In many years ago, Isgur and Llewellyn Smith addressed that PQCD is inapplicable to exclusive processes, such as the pion form factor.The main problem is that the asymptotic of PQCD is only about one fourth of the experimental value. We reexamine this PQCD deep problem. By including NLO power corrections to the pion form factor, we may arrive at a perturbative explanation for the data. The key realization is that we need to interprete that the strong interaction coupling constant involved in the PQCD result should be taken as an effective coupling constant under nonperturbative QCD vaccum. Thi…
We calculate the important next-to-leading-order (NLO) contributions to the $B \to K K^*$ decays from the vertex corrections, the quark loops, and the magnetic penguins in the perturbative QCD (pQCD) factorization approach. The pQCD predictions for the CP-averaged branching ratios are $Br(B^+ \to K^+ \bar{K}^{*0}) \approx 3.2\times 10^{-7}$, $Br(B^+ \to \bar{K}^0 {K}^{*+}) \approx 2.1\times 10^{-7}$, $Br(B^0/\ov{B}^0 \to K^0\bar{K}^{*0}+\bar{K}^0 K^{*0}) \approx 8.5\times 10^{-7}$, $Br(B^0/\ov{B}^0 \to K^+K^{*-} + K^-K^{*+}) \approx 1.3\times 10^{-7}$, which agree well with both the experiment…
We calculate the branching ratios and CP violating asymmetries of the four $B \to K \etap$ decays in the perturbative QCD (pQCD) factorization approach. Besides the full leading order contributions, the partial next-to-leading order (NLO) contributions from the QCD vertex corrections, the quark loops, and the chromo-magnetic penguins are also taken into account. The NLO pQCD predictions for the CP-averaged branching ratios are $Br(B^+ \to K^+ η) \approx 3.2 \times 10^{-6}$, $Br(B^\pm \to K^\pm \etar) \approx 51.0 \times 10^{-6}$, $Br(B^0 \to K^0 η) \approx 2.1 \times 10^{-6}$, and $Br(B^0 \to …
This perturbative Quantum Chromo Dynamics (pQCD) analysis attempts to present a simultaneous determination of parton distribution functions (PDFs) and the strong coupling $α_s(M^2_Z)$ from inclusion of inclusive H1 and ZEUS jet, DiJets and TriJets production cross sections data on the HERA I and II combined data, as the central data sets for probing the internal structure of proton. To present an accurate pQCD analysis, we separate the role and influence of inclusion jet production cross sections data from inclusion of the strong coupling $α_s(M^2_Z)$ as an extra fit parameter parameter on the…
We study the effect from a sequential fourth generation quark on penguin-dominated two-body nonleptonic B meson decays in the next-to-leading order perturbative QCD formalism. With an enhancement of the color-suppressed tree amplitude and possibility of a new CP phase in the electroweak penguin, we can account better for A_{CP}(B^0 -> K^+ pi^-)-A_{CP}(B^+ -> K^+ pi^0). Taking |V_{t's}V_{t'b}| \sim 0.02 with phase just below 90^\circ, which are consistent with the b -> s l^+ l^- rate and the B_s mixing parameter Δm_{B_s}, we find a downward shift in the mixing-induced CP asymmetries of B^0 -> K…
Using repeated Laplace transform techniques, along with newly-developed accurate numerical inverse Laplace transform algorithms, we transform the coupled, integral-differential NLO singlet DGLAP equations first into coupled differential equations, then into coupled algebraic equations, which we can solve iteratively. After Laplace inverting the algebraic solution analytically, we numerically invert the solutions of the decoupled differential equations. Finally, we arrive at the decoupled NLO evolved solutions F_s(x,Q^2)=calF_s(F_{s0}(x),G_0(x)) and G(x,Q^2)=calG(F_{s0}(x),G_0(x)), where calF_s…
We present the first NLO pQCD study of coherent exclusive $J/ψ$ photoproduction in ultraperipheral heavy-ion collisions (UPCs) at the LHC. Taking the generalized parton distributions (GPDs) in their forward limit, as parton distribution functions (PDFs), we quantify the NLO contributions in the rapidity-differential cross section, show that the real part of the amplitude must not be neglected, study the gluon and quark contributions, chart the scale-choice and PDF uncertainties, and compare the NLO results with LHC and HERA data. We show that the scale dependence is significant but a scale cho…
In this paper, we calculated the branching ratios and direct CP violation of the four $B\to Kπ$ decays with the inclusion of all currently known next-to-leading order (NLO) contributions by employing the perturbative QCD (pQCD) factorization approach. We found that (a) Besides the 10% enhancement from the NLO vertex corrections, the quark-loops and magnetic penguins, the NLO contributions to the form factors can provide an additional $\sim 15%$ enhancement to the branching ratios, and lead to a very good agreement with the data; (b) The NLO pQCD predictions are $\acp^{dir}(B^0\to K^+π^-)=(-6.5…
Enhanced Quark-Loop Contribution to Pure Annihilation Nonleptonic B-meson decays in PQCD approach
本研究在PQCD框架下考虑次领头阶夸克圈贡献，发现该贡献虽不影响纯湮灭B介子衰变分支比，但作为重要强相位来源，显著增强了直接与混合诱导的CP不对称性。
In this paper we perform a comprehensive study of the four $B \to K \etap$ decays in the pQCD factorization approach. We calculate the CP-averaged branching ratios and CP-violating asymmetries of $B \to K\etap$ decays in the ordinary $η$-$\etar$, the $η$-$\etar$-$G$, and the $η$-$\etar$-$G$-$η_c$ mixing schemes. Besides the full LO contributions, all currently known NLO contributions to $B \to K \etap$ decays in the pQCD approach are taken into account. From our calculations and phenomenological analysis, we find the following. (a) The NLO contributions in general can provide significant enhan…
The perturbative QCD (PQCD) approach based on $k_T$ factorization has made a great achievement for the QCD calculation of the hadronic B decays. Regulating the endpoint divergence by the transverse momentum of quarks in the propagators, one can do the perturbation calculation for kinds of diagrams including the annihilation type diagrams. In this paper, we review the current status of PQCD factorization calculation of two-body charmless $B\to PP, PV, VV$ decays up to the next-to-leading order (NLO) QCD corrections. two new power suppressed terms in decaying amplitudes are also taken into accou…
By employing the perturbative QCD (PQCD) factorization approach, we calculated the branching ratios, CP-violating asymmetries, the longitudinal and transverse polarization fractions and other physical observables of the thirteen charmless hadronic $\bar{B}^0_s \to V V $ decays with the inclusion of all currently known next-to-leading order (NLO) contributions. We focused on the examination of the effects of all those currently known NLO contributions and found that: (a) for the measured decays $\bar{ B}_s^0 \to ϕϕ, K^{*0} ϕ,\bar K^{*0} K^{*0}$ and $ρ^0 ϕ$, the NLO contributions can provide $\s…
Exclusive quarkonium photoproduction in $A$+$A$ UPCs at the LHC in NLO pQCD
本文首次在NLO pQCD共线因子化框架下研究LHC上UPCs中$J/ψ$和$Υ$的相干排他光生过程，给出Pb和O束流的NLO预言，并分析标度、核PDFs及GPDs差异的影响，表明夸克对$J/ψ$重要而胶子主导$Υ$，同时探讨了通过截面比值和HERA等数据改进预言的方法。
In this paper we first calculate the form factors of $B \to (π,K)$ and $B_s \to K $ transitions by employing the perturbative QCD (pQCD) factorization approach with the inclusion of the next-to-leading-order(NLO) corrections, and then we calculate the branching ratios of the corresponding semileptonic decays $B/B_s \to (π, K)(l^+l^-,lν,ν\barν)$ (here $l$ denotes $e, μ$ and $τ$). Based on the numerical calculations and phenomenological analysis, we found the following results: (a) For $B \to (π, K)$ and $B_s \to K$ transition form factors $F_{0,+,\rmt}(q^2)$, the NLO pQCD predictions for the va…
We study the penguin-dominated B -> PV decays, with P (V) representing a pseudo-scalar (vector) meson, in the next-to-leading-order (NLO) perturbative QCD (PQCD) formalism, concentrating on the B -> K phi, pi K^*, rho K, and omega K modes. It is found that the NLO corrections dramatically enhance the B -> rho K, omega K branching ratios, which were estimated to be small under the naive factorization assumption. The patterns of the direct CP asymmetries A_{CP}(B^0 -> rho^\mp K^\pm) \approx A_{CP}(B^\pm -> rho^0 K^\pm) and |A_{CP}(B^0 -> pi^\mp K^{*\pm})| > |A_{CP}(B^\pm -> pi^0 K^{*\pm})| are p…
In this paper we perform a systematic study for the three $B \to (π^+π^-,π^+π^0,π^0π^0)$ decays in the perturbative QCD (pQCD) factorization approach with the inclusion of all currently known next-to-leading order (NLO) contributions from various sources. We found that (a) for the CP-averaged decay rates $Br(B^0\to π^+π^-)$ and $Br(B^+\to π^+π^0)$, the NLO pQCD predictions agree with the data within one standard dviation; (b) for $Br(B^0\to π^0π^0)$, however, although the NLO contributions can provide a $\sim 100\%$ enhancement to the leading order (LO) result, it is still not large enough to …
In this talk I report on the results of a recent calculation of the α_s corrections to a three-point correlation function at the three-loop level in QCD perturbation theory, which allows one to extract the matrix element of B^0 -\bar B^0 mixing with next-to-leading order accuracy. The evaluation of mixing parameter at NLO allows for a consistent analysis of B^0 -\bar B^0 mixing since the coefficient functions of the effective Hamiltonian for this process are known with the necessary accuracy.
In this paper, we calculated the $B \to (\jpsi, η_c) K$ decays in the perturbative QCD approach with the inclusion of the partial next-to-leading order (NLO) contributions. We found that (a) when the large enhancements from the known NLO contributions are taken into account, the NLO pQCD predictions for the branching ratios are the following: $Br(B^0 \to \jpsi K^0) = 5.2^{+3.5}_{-2.8}\times 10^{-4}$, $Br(B^+ \to \jpsi K^+) = 5.6^{+3.7}_{-2.9}\times 10^{-4}$, $Br(B^0 \to η_c K^0) = 5.5^{+2.3}_{-2.0}\times 10^{-4}$, $Br(B^+ \to η_c K^+) = 5.9^{+2.5}_{-2.1}\times 10^{-4}$, which are roughly 40% s…
Two body $B$ meson decays involving the radially excited meson $ψ(2S)/η_c(2S)$ in the final states are studied by using the perturbative QCD (pQCD) approach. We find that: (a) The branching ratios for the decays involving $K$ meson are predicted as $Br(B^+\toψ(2S)K^+)=(5.37^{+1.85}_{-2.22})\times10^{-4}, Br(B^0\toψ(2S)K^0)=(4.98^{+1.71}_{-2.06})\times10^{-4}, Br(B^+\toη_c(2S)K^+)=(3.54^{+3.18}_{-3.09})\times10^{-4}$, which are consistent well with the present data when including the next-to-leading-order (NLO) effects. Here the NLO effects are from the vertex corrections and the NLO Wilson coe…
Back-to-back dihadron spectra in high-energy heavy-ion collisions are studied within the next-to-leading order (NLO) perturbative QCD parton model with jet quenching incorporated via modified jet fragmentation functions due to radiative parton energy loss in dense medium. The experimentally observed appearance of back-to-back dihadrons at high $p_T$ is found to originate mainly from jet pairs produced close and tangential to the surface of the dense matter. However, a substantial fraction of observed high $p_T$ dihadrons also comes from jets produced at the center of the medium after losing fi…
By employing the perturbative QCD (PQCD) factorization approach, we made a systematic investigation for the CP-averaged branching ratios and the CP-violating asymmetries of the thirteen $\bar{B}^0_s \to PP $ decays ( here $P=(π,K, η, η^{\prime})$) with the inclusion of all currently known next-to-leading order (NLO) contributions, and compared our results with the measured values or the theoretical predictions from other different approaches. We focused on the examination of the effects of the NLO contributions and found the following points: (a) for $\bar{B}_s^0 \to (K^0 \bar{K}^0, K^+ K^-, η…
We study the effects of supersymmetric contribution on both the B_d -> phi K^0 and B^\pm -> phi K^\pm modes using the perturbative QCD approach. We estimate the deviation of mixing-induced and direct CP asymmetries and discuss the strong-phase dependence of them.
Some problems of the perturbative quantum chromodynamics (pQCD) jet calculus are discussed. The first one is related to the terminology of the order of calculation. Due to cancelation of LO and NLO terms in the ratio of mean multiplicities in gluon and quark jets $r$ the nowadays obtained results about it should be called as 4NLO approximation. The second problem reveals itself in calculations where corrections to some values (in particular, to $r'$) are larger at present energies than lower order terms. Some characteristics which do not suffer from this deficiency are proposed. Next problem l…
We discuss $\btorho$ form factors within the framework of perturbative QCD, including the higher twist contributions and study the validity of such an approach in calculating quantities such as form factors, which in principle and quite generally are thought to be completely non-perturbative objects and are expected to receive large contributions from the non-perturbative regime in the calculations. It is shown that including the Sudakov and threshold resummation effects, the general expectations of the pQCD approach are clearly met and the form factors do indeed receive most of the contributi…
The pion electromagnetic form factor with leading and next-to-leading twist corrections are studied in the framework of pQCD approach. We find that, at small momentum transfer regions, Sudakov effects cannot provide a strong enough suppression of the non-perturbative contributions coming from large transverse separations, but at large momentum transfer region, non-perturbative contributions can be effectively suppressed. So pQCD approach can be applied at large momentum transfer region. At the energy region where experiment can access so far, i.e. Q < 4GeV, pQCD prediction can not be precise b…
We point out that the B -> rho rho data have seriously constrained the possibility of resolving the B -> pi pi puzzle from the large observed B^0 -> pi^0 pi^0 branching ratio in the available theoretical approaches. The next-to-leading-order (NLO) contributions from the vertex corrections, the quark loops, and the magnetic penguin evaluated in the perturbative QCD (PQCD) approach have saturated the experimental upper bound of the B^0 -> rho^0 rho^0 branching ratio, and do not help. The NLO PQCD predictions for the B^0 -> rho^\mp rho^\pm and B^\pm -> rho^\pm rho^0 branching ratios are consisten…
Within the next-to-leading order (NLO) perturbative QCD (pQCD) parton model, suppression of away-side hadron spectra associated with a high $p_{T}$ photon due to parton energy loss is shown to provide a complete tomographic picture of the dense matter formed in high-energy heavy-ion collisions at RHIC. Dictated by the shape of the $γ$-triggered jet spectrum in NLO pQCD, hadron spectra at large $z_T=p_T^{h}/p_T^γ \stackrel{>}{\sim} 1$ are more susceptible to parton energy loss and therefore are dominated by surface emission of $γ$-triggered jets, whereas small $z_{T}$ hadrons mainly come from f…
Conventional perturbative QCD calculations on the production of a heavy quark ``$H$'' consist of two contrasting approaches: the usual QCD parton formalism uses the zero-mass approximation ($m_H=0$) once above threshold, and treats $H$ just like the other light partons; on the other hand, most recent ``NLO'' heavy quark calculations treat $m_H$ as a % large parameter and always consider $H$ as a heavy particle, never as a parton, irrespective of the energy scale of the physical process. By their very nature, both these approaches are limited in their regions of applicability. This dichotomy ca…
We present the analytical calculation of the contribution of order m_q^2 α_s^4 n_f^2 to the absorptive part of the vacuum polarization function of vector currents. This term constitutes an important gauge-invariant part of the full O(m_q^2 alpha_s^4) correction to the total cross-section of e^+ e^- annihilation into hadrons. The results are compared to predictions following from various optimization schemes.
In this paper, we will make systematic calculations for the branching ratios and the CP-violating asymmetries of the twenty one $\bar{B}^0_s \to PV $ decays by employing the perturbative QCD (PQCD) factorization approach. Besides the full leading-order (LO) contributions, all currently known next-to-leading order (NLO) contributions are taken into account. We found numerically that: (a) the NLO contributions can provide $\sim 40\%$ enhancement to the LO PQCD predictions for ${\cal B}(\bar{B}_s^0 \to K^0 \bar{K}^{*0})$ and $ {\cal B}(\bar{B}_s^0 \to K^{\pm}K^{*\mp})$, or a $\sim 37\% $ reductio…
In this paper, we calculate the branching ratios and CP violating asymmetries of the five $\bar{B}^0_s \to (π^0η^{(*)},η^{(*)}η^{(*)})$ decays, by employing the perturbative QCD (pQCD) factorization approach and with the inclusion of all currently known next-to-leading order (NLO) contributions. We find that (a) the NLO contributions can provide about 100% enhancements to the LO pQCD predictions for the decay rates of $\bar{B}_s^0 \to ηη^\prime$ and $η^\prime η^\prime$ decays, but result in small changes to $Br(\bar{B}_s \to π^0 η^{(*)})$ and $Br(\bar{B}_s \to ηη)$; (b) the newly known NLO twi…
We calculate the time-like pion electromagnetic form factor in the $k_T$ factorization formalism with the inclusion of the next-to-leading-order(NLO) corrections to the leading-twist and sub-leading-twist contributions. It's found that the total NLO correction can enhance (reduce) the magnitude (strong phase) of the leading order form factor by $20\% - 30\%$ ( $< 15^o$) in the considered invariant mass squared $q^2 > 5$ GeV$^2$, and the NLO twist-3 correction play the key role to narrow the gap between the pQCD predictions and the measured values for the time-like pion electromagnetic form fac…
We apply the renormalization group optimized perturbation theory (RGOPT) to evaluate the quark contribution to the QCD pressure at finite temperatures and baryonic densities, at next-to-leading order (NLO). Our results are compared to NLO and state-of-the-art higher orders of standard perturbative QCD (pQCD) and hard thermal loop perturbation theory (HTLpt). The RGOPT resummation provides a nonperturbative approximation, exhibiting a drastically better remnant renormalization scale dependence than pQCD, thanks to built-in renormalization group invariance consistency. At NLO, upon simply adding…
The leptonic radiative decay $B \to γlν$ is of great importance in the determination of $B$ meson wave functions, and evaluating the form factors $ F_{V,A}$ are the essential problem on the study of this channel. We computed next-to-leading power corrections to the form factors within the framework of PQCD approach, including the power suppressed hard kernel, the contribution from a complete set of three-particle $B$ meson wave functions up to twist-4 and two-particle off light-cone wave functions, the $1/m_b$ corrections in heavy quark effective theory, and the contribution from hadronic stru…
By employing the perturbative QCD (PQCD) factorization approach, we studied the sixteen $B/B_s \to η_c (π, K, η^{(\prime)},ρ,K^*,ω,ϕ)$ decays with the inclusion of the currently known next-to-leading order (NLO) contributions. We found the following main points: (a) for the five measured $B \to η_c (K,K^*)$ and $B_s\to η_cϕ$ decays, the NLO contributions can provide $ (80-180)\%$ enhancements to the leading order (LO) PQCD predictions of their branching ratios, which play an important role to help us to interpret the data; (b) for the seven ratios $R_{1,\cdots,7}$ of the branching ratios defin…
Considering the $B$ mesonic distribution amplitude $ϕ_{B2}$, we reinvestigated the $B$ ${\to}$ $PP$ (where $P$ $=$ $π$ and $K$) decays with the perturbative QCD (pQCD) approach based on the $k_{T}$ factorization for three scenarios. It is found that the contributions of $ϕ_{B2}$ to formfactors $F_{0}^{B{\to}P}(0)$ and branching ratios are comparable with those from the NLO corrections. The $B$ ${\to}$ $Kπ$ decays could be well explained by considering the $ϕ_{B2}$. Hence, when the nonleptonic $B$ decays are studied withe the pQCD approach, the $ϕ_{B2}$ should be taken into account seriously.
By employing the perturbative QCD(pQCD) factorization approach, we calculate the branching ratios and CP violating asymmetries of the four $\bar{B}_s^0 \to Kπ$ and $K K $ decays, with the inclusion of all known next-to-leading order (NLO) contributions. We find numerically that (a) the NLO contribution can interfere with the LO part constructively or destructively for different decay modes; (b) the NLO contribution leads to a $22\%$ decrease for $Br(\bar{B}^0_s \to K^+ π^-)$, but $\sim 50\%$ enhancements to other three considered $\bar{B}_s$ decays, and therefore play an important role in inte…
We present a leading-order pQCD calculation of the helicity-flip $Δ\to Nγ^*$ matrix element $G_0$ (Coulomb quadrupole amplitude $C2$), taking into account the transverse momenta of the quarks and the contribution from the gluons. In the large $Q^2$ limit, its scaling behavior acquires a double-logarithmic correction $\log^2{(Q^2/Λ^2)}$ compared with the standard scaling analysis, due to the contribution from the orbital motion of the small-$x$ partons. Based on this and on the latest JLab experimental results of the $C2-M1$ ratio $R_{SM}$ at $Q^2$ = 3 $\sim$ 4 GeV$^2$, we make a phenomenologic…
We discuss central exclusive production of $W^+W^-$ pairs in proton-proton collisions at LHC. Predictions for the total cross section and differential distributions in transverse momentum of $W^{\pm}$ and $WW$ invariant mass are presented. We discuss both $γγ\to W^+ W^-$ mechanism as well as a new mechanism of exclusive diffractive production. The amplitude for the latter process is calculated in the Durham model. We compare the two (QED and QCD) types of contributions. The diffractive contribution is only a small fraction of fb compared to the $γγ$ contribution which is of the order of 100 fb…
We calculate the cross section of diffractive dijet photoproduction in $ep$ scattering at next-to-leading order (NLO) of perturbative QCD (pQCD), which we supplement by a model of factorization breaking for the resolved-photon contribution. In this model, the suppression depends on the flavor and momentum fraction of the partons in the photon. We show that within experimental and theoretical uncertainties, the resulting approach provides a good description of the available HERA data in most of the bins. Hence, taken together with the observation that NLO pQCD explains well the data on diffract…
It has been observed that conventional renormalization scheme and scale ambiguities for the pQCD predictions can be eliminated by using the principle of maximum conformality (PMC). However, being the intrinsic nature of any perturbative theory, there are still two types of residual scale dependences due to uncalculated higher-order terms. In the paper, as a step forward of our previous work [Phys.Rev.D {\bf 89},116001(2014)], we reanalyze the electroweak $ρ$ parameter by using the PMC single-scale approach. Using the PMC conformal series and the Pad$\acute{e}$ approximation approach, we observ…
In this paper, by employing the $k_{T}$ factorization theorem, we calculate firstly the next-to-leading-order (NLO) twist-3 contributions to the pion electromagnetic form factors in the $πγ^* \to π$ process. From the analytical and numerical calculations we find the following points: (a) For the leading order (LO) twist-2, twist-3 and the NLO twist-2 contributions, our results agree very well with those obtained in previous works; (b) We extract out two factors $F^{(1)}_{\rm T3}(x_i,t,Q^2)$ and $\ov{F}^{(1)}_{\rm T3}(x_i,t,Q^2)$, which describe directly the NLO twist-3 contributions to the pio…
New physics contributions to B decays often arise through chromo-magnetic penguin operators. To look for new physics effects in B decays, it is useful to be able to estimate the hadronic matrix elements for the chromo-magnetic operator. We compute this contribution to B ->phi K decays using PQCD methods. It is shown that, if the Wilson coefficient of the new physics is same order of magnitude as that of the Standard Model, this operator gives a non-negligible contribution compared to that of the Standard Model (about 30%). We also investigate the value of q^2, which is the momentum transferred…
In this paper, we calculate the next-to-leading-order (NLO) twist-3 contribution to the form factors of $B \to π$ transitions by employing the $k_{T}$ factorization theorem. All the infrared divergences regulated by the logarithms $\ln(k_{iT}^{2})$ cancel between those from the quark diagrams and from the effective diagrams for the initial $B$ meson wave function and the final pion meson wave function. An infrared finite NLO hard kernel is therefore obtained, which confirms the application of the $k_{T}$ factorization theorem to $B$ meson semileptonic decays at twist-3 level. From our analytic…
We study the effects of the MSSM contribution on B -> phi K decays using the perturbative QCD approach. In this approach, strong phases can be calculated, so that we can predict the values of CP asymmetries with the MSSM contribution. We predict a large relative strong phase between the penguin amplitude and the chromomagnetic penguin amplitude. If there is a new CP violating phase in the chromomagnetic penguin amplitude, then the CP asymmetries may change significantly from the SM prediction. We parametrize the new physics contributions that appear in the Wilson coefficients. We maximize the …
We present a study of central exclusive production of $W^+W^-$ pairs in proton-proton collisions at the LHC. We compare the contribution of the $γγ\to W^+ W^-$ mechanism with a new mechanism of exclusive diffractive production through the $gg \to W^+ W^-$ subprocess with intermediate virtual Higgs boson and quark box diagrams. The amplitude for the latter process is expressed in terms of the off-diagonal unintegrated gluon distribution functions. Several observables related to this process are calculated. The phase space integrated diffractive contribution when separated is only a small fracti…
Details of the calculation of the non-forward BFKL kernel at next-to-leading order (NLO) are offered. Specifically we show the calculation of the two-gluon production contribution. This contribution was the last missing part of the kernel. Together with the NLO gluon Regge trajectory, the NLO contribution of one-gluon production and the contribution of quark-antiquark production which were found before it defines the kernel completely for any colour state in the $t$-channel, in particular the Pomeron kernel presented recently.
We present the tree-level and next-to-leading order (NLO) electroweak (EW) contributions to squark-squark production at the Large Hadron Collider (LHC) within the framework of the Minimal Supersymmetric Standard Model (MSSM).
The most general QCD-NLO Anomalous-Dimension Matrix of all four-fermion dimension six Delta F=2 operators is presented. Two applications of this Anomalous-Dimension Matrix to the study of SUSY contribution to K- Kbar mixing are also discussed.
Electroweak one-loop calculations for production of top-quark pairs at colliders are completed by providing the missing QED type contributions from real and virtual photons, where also effects from interference between QED and QCD contributions have to be taken into account. Moreover, photon-induced $t \bar{t}$ production is included as another partonic channel.
Electrons from semileptonic decays of heavy-flavor mesons (D and B) allow to study the energy loss of heavy-quarks in nuclear collisions at sqrt(s) = 200 GeV at RHIC. Since pQCD calculations have shown that the crossing point where bottom decay electrons start to dominate over charm decay electrons is largely unknown, an urgent need arises to access the relative contributions independently. A correlation method is proposed to identify and separate charm and bottom production processes on a statistical basis through tagging of their decay electrons and open charmed mesons. The feasibility for t…
Presented are complete next-to-leading order electroweak (NLO EW) corrections to top-squark pair production at the Large Hadron Collider (LHC) within the Minimal Supersymmetric Standard Model (MSSM). At this order, also effects from the interference of EW and QCD contributions have to be taken into account. Moreover, photon-induced top-squark production is considered as an additional partonic channel, which arises from the non-zero photon density in the proton.
In this short review, we present the current status about the theoretical and experimental studies for some important semileptonic decays of $B/B_s$ mesons. We firstly gave a brief introduction for the experimental measurements for $B/B_s \to P (l^+l^-, l^-\barν_l, ν\barν)$ decays, the BaBar's $R(D)$ and $R(D^*)$ anomaly, the $P_5^\prime$ deviation for $B^0 \to K^{*0} μ^+ μ^-$ decay. We then made a careful discussion about the evaluations for the relevant form factors in the light-cone QCD sum rule (LCSRs), the heavy quark effective theory, and the perturbative QCD factorization approach. By u…
We show that the conventional prescription used for DGLAP parton evolution at NLO has an inconsistent treatment of the contribution from the infrared (IR) region. We illustrate the problem by studying the simple example of QED evolution, treating the electron and photon as partons. The deficiency is not present in a physical approach which removes the IR divergency and allows calculation in the normal 4-dimensional space.
We calculate the full $\mathcal{O}(α_s^2α)$ corrections to the process of gluino pair production at hadron colliders in the framework of the real MSSM. We show that these contributions can be neglected at the LHC performing a scan over a wide region of the parameter space. The impact of these corrections in the parameter range investigated at the Tevatron is small.
We present a next-to-leading order calculation of single-top production interfaced to Shower Monte Carlo programs, implemented according to the POWHEG method. A detailed comparison with MC@NLO and PYTHIA is carried out for several observables, for the Tevatron and LHC colliders.
扫码添加微信好友，提出您的宝贵建议 👇
💡 备注请填写：网站反馈
发表机构由 AI 从论文文本抽取，如发现错误，欢迎反馈修正建议。