We study magnetic dipole (M1) transitions between two quarkonia in the framework of nonrelativistic effective field theories of QCD. Relativistic corrections of relative order v 2 are investigated in a systematic fashion. Nonperturbative corrections due to color-octet effects are considered for the first time and shown to vanish at relative order v 2 . Exact, all order expressions for the relevant 1=m and 1=m 2 magnetic operators are derived. The results allow us to scrutinize several potential model claims. In particular, we show that QCD excludes both contributions to the anomalous magnetic moment of the quarkonium induced by low-energy fluctuations and contributions to the magnetic dipole operators of the type induced by a scalar potential. Finally, we apply our results to the transitions J= ! c ,, and b2 1P ! h b 1P by assuming these quarkonium states in the weak-coupling regime. Our analysis shows that the J= ! c width is consistent with a weak-coupling treatment of the charmonium ground state, while such a treatment for the hindered transition 2S ! b appears difficult to accommodate within the CLEO III upper limit.

This paper explores a new mechanism for B production in which a b quark combines with a light parton from the hard-scattering process before hadronizing into the B hadron. This recombination mechanism can be calculated within perturbative QCD up to a few nonperturbative constants. Though suppressed at large transverse momentum by a factor Λ QCD m b /p 2 ⊥ relative to b fragmentation production, it can be important at large rapidities. A signature for this heavy-quark recombination mechanism in pp colliders is the presence of rapidity asymmetries in B cross sections. Given reasonable assumptions about the size of nonperturbative parameters entering the calculation, we find that the asymmetries are only significant for rapidities larger than those currently probed by collider experiments.

The leading particle effect in charm hadroproduction is an enhancement of the cross section for a charmed hadron D in the forward direction of the beam when the beam hadron has a valence parton in common with the D. The large D(+)/D(-) asymmetry observed by the E791 experiment is an example of this phenomenon. We show that the heavy-quark recombination mechanism provides an economical expla-nation for this effect. In particular, the D(+)/D(-) asymmetry can be fit reasonably well using a single parameter whose value is consistent with a recent determination from charm photoproduction.

Recently a new family of Cr-based A 2 Cr 3 As 3 (A = K, Rb, Cs) superconductors were reported, which own a rare quasi-one-dimensional (Q1D) crystal structure with infinite (Cr 3 As 3 ) 2chains and exhibit intriguing superconducting characteristics possibly derived from spin-triplet electron pairing. The crystal structure of A 2 Cr 3 As 3 is actually a slight variation of the hexagonal TlFe 3 Te 3 prototype although they have different lattice symmetry. Here we report superconductivity in a 133-type KCr 3 As 3 compound that belongs to the latter structure. The single crystals of KCr 3 As 3 were prepared by the deintercalation of K ions from K 2 Cr 3 As 3 crystals which were grown from a high-temperature solution growth method, and it owns a centrosymmetric lattice in contrast to the non-centrosymmetric K 2 Cr 3 As 3 .After annealing at a moderate temperature, the KCr 3 As 3 crystals show bulk superconductivity at 5 K revealed by electrical resistivity, magnetic susceptibility and heat capacity measurements. The discovery of this KCr 3 As 3 superconductor provides a different structural instance to study the exotic superconductivity in these Q1D Cr-based superconductors.

Unlike the bewildering situation in the γγ * → π form factor, a widespread view is that perturbative QCD can decently account for the recent BaBar measurement of γγ * → ηc transition form factor. The next-to-next-to-leading order (NNLO) perturbative correction to the γγ * → η c,b form factor, is investigated in the NRQCD factorization framework for the first time. As a byproduct, we obtain by far the most precise order-α 2 s NRQCD matching coefficient for the η c,b → γγ process. After including the substantial negative order-α 2 s correction, the good agreement between NRQCD prediction and the measured γγ * → ηc form factor is completely ruined over a wide range of momentum transfer squared. This eminent discrepancy casts some doubts on the applicability of NRQCD approach to hard exclusive reactions involving charmonium.

We compute the next-to-next-to-leading order (NNLO) QCD corrections to the hadronic decay rates of the pseudoscalar quarkonia, at the lowest order in velocity expansion. The validity of NRQCD factorization for inclusive quarkonium decay process, for the first time, is verified to relative order α 2 s . As a byproduct, the renormalization group equation (RGE) of the leading NRQCD 4-fermion operator O1( 1 S0) is also deduced to this perturbative order. By incorporating this new piece of correction together with available relativistic corrections, we find that there exists severe tension between the state-of-the-art NRQCD predictions and the measured ηc hadronic width, and in particular the branching fraction of ηc → γγ. NRQCD appears to be capable of accounting for η b hadronic decay to a satisfactory degree, and our most refined prediction is Br(η b → γγ) = (4.8 ± 0.7) × 10 −5 . Heavy quarkonium decay has historically played a preeminent role in establishing asymptotic freedom of QCD [1,2]. Due to the nonrelativistic nature of heavy quark inside a quarkonium, the decay rates are traditionally expressed as the squared bound-state wave function at the origin multiplying the short-distance quarkantiquark annihilation decay rates. With the advent of the modern effective-field-theory approach, the nonrelativistic QCD (NRQCD), this factorization picture has been put on a firmer ground, and one is allowed to systematically include the QCD radiative and relativistic corrections when tackling various quarkonium decay and production processes [3].

In a typical exclusive quarkonium production process, when the center-of-mass energy, √ s, is much greater than the heavy quark mass m, large kinematic logarithms of s/m 2 will unavoidably arise at each order of perturbative expansion in the short-distance coefficients of the nonrelativistic QCD (NRQCD) factorization formalism, which may potentially harm the perturbative expansion.This symptom reflects that the hard regime in NRQCD factorization is too coarse and should be further factorized. We suggest that this regime can be further separated into "hard" and "collinear" degrees of freedom, so that the familiar light-cone approach can be employed to reproduce the NRQCD matching coefficients at the zeroth order of m 2 /s and order by order in α s . Taking two simple processes, exclusive η b + γ production in e + e − annihilation and Higgs boson radiative decay into Υ, as examples, we illustrate how the leading logarithms of s/m 2 in the NRQCD matching coefficients are identified and summed to all orders in α s with the aid of Brodsky-Lepage evolution equation.Introduction. One of the classical applications of perturbative Quantum Choromodynamics (QCD) is the successful description of many exclusive processes with large momentum transfer using collinear factorization, that allows one to express the scattering amplitude as the convolution of perturbatively calculable short-distance parts and the nonperturbative but universal light-cone distribution amplitudes (LCDA) [1,2]. In describing hard exclusive processes involving heavy quarkonium, i.e., a nonrelativistic bound state made of a heavy quark and a heavy antiquark, however, there also exists another widely-accepted theoretical framework, the nonrelativistic QCD (NRQCD) factorization formalism [3]. In this approach, the amplitude can also be put in a factorized form, that is, an infinite sum of products of short-distance coefficients and nonperturbative, albeit universal, NRQCD matrix elements.In recent years, considerable amount of efforts have been spent to understand exclusive charmonium production mechanisms from both NRQCD and light-cone perspectives.This endeavor is perhaps largely propelled by a somewhat unexpected finding, that the lowest-order NRQCD calculation of double charmonium production rate for the process e + e − → J/ψη c [4] fell short by about one order-of-magnitude of the Belle measurement [5].The validity of applying NRQCD to charmonia was soon questioned by some authors, who advocated that if charmonium is treated as light meson, the light-cone approach instead could satisfactorily accommodate the Belle data [6,7,8]. However, a careful reexamination [9] suspected that these optimistic assertions are premature and it was argued that a "consistent" light-cone analysis would in fact yield a result not much different from NRQCD, so that the situation has not truly improved.In reviewing this episode, one may get the impression that the light-cone and NRQCD approaches are two drastically different, and, competing, theoretical frameworks. Indeed, t...

Within the nonrelativistic QCD (NRQCD) factorization framework, we investigate the inclusive production of the h c meson associated with either light hadrons or charmed hadrons at B factory energy √ s = 10.58 GeV. Both the leading color-singlet and color-octet channels are included. For the h c production associated with light hadrons, the total production rate is dominated by the color-octet channel, thus the future measurement of this process may impose useful constraint on the value of the color-octet matrix element O hc 8 ( 1 S 0 ) ; for the h c production associated with charmed hadrons, the total production rate is about one order of magnitude smaller, and dominated by the color-singlet channel.