Search

We apply a color glass condensate+nonrelativistic QCD (CGC+NRQCD) framework to compute J/ψ production in deuteron-nucleus collisions at RHIC and proton-nucleus collisions at the LHC. Our results match smoothly at high p⊥ to a next-to-leading order perturbative QCD+NRQCD computation. Excellent agreement is obtained for p⊥ spectra at the RHIC and LHC for central and forward rapidities, as well as for the normalized ratio RpA of these results to spectra in proton-proton collisions. In particular, we observe that the RpA data are strongly bounded by our computations of the same for each of the individual NRQCD channels; this result provides strong evidence that our description is robust against uncertainties in initial conditions and hadronization mechanisms. [ABSTRACT FROM AUTHOR]

We calculate the O(αs³) short-distance, QCD collinear-factorized coefficient functions for all partonic channels that include the production of a heavy quark pair at short distances. This provides the first power correction to the collinear-factorized inclusive hadronic production of heavy quarkonia at large transverse momentum, pT, including the full leading-order perturbative contributions to the production of heavy quark pairs in all color and spin states employed in NRQCD treatments of this process. We discuss the role of the first power correction in the production rates and the polarizations of heavy quarkonia in high-energy hadronic collisions. The consistency of QCD collinear factorization and nonrelativistic QCD factorization applied to heavy quarkonium production is also discussed. [ABSTRACT FROM AUTHOR]

We present a perturbative QCD factorization formalism for inclusive production of heavy quarkonia of large transverse momentum, pT at collider energies, including both leading power (LP) and next-to-leading power (NLP) behavior in pT. We demonstrate that both LP and NLP contributions can be factorized in terms of perturbatively calculable short-distance partonic coefficient functions and universal nonperturbative fragmentation functions, and derive the evolution equations that are implied by the factorization. We identify projection operators for all channels of the factorized LP and NLP infrared safe short-distance partonic hard parts, and corresponding operator definitions of fragmentation functions. For the NLP, we focus on the contributions involving the production of a heavy quark pair, a necessary condition for producing a heavy quarkonium. We evaluate the first nontrivial order of evolution kernels for all relevant fragmentation functions, and discuss the role of NLP contributions. [ABSTRACT FROM AUTHOR]

Induced by three gluons symmetry, Mandelstam variables s, t, u symmetric expressions are widely involved in collider physics, especially in heavy quarkonium physics. In this work we study the general form of s, t, u symmetric polynomials, and find that they can be expressed as polynomials where the symmetry is manifest. The general form is then used to simplify expressions which asymptotically reduces the length of original expression to one-sixth. Based on the general form, we reproduce the exact differential cross section of J/? hadron production at leading order in ν2 up to four unknown constant numbers by simple analysis. Furthermore, we prove that differential cross section at higher order in ν2 is proportional to that at leading order. This proof explains the proportion relation at next-to-leading order in ν2 found in previous work and generalizes it to all order. [ABSTRACT FROM AUTHOR]

With nonrelativistic QCD factorization, we calculate the &ggr;(1S) prompt production at hadron colliders at next-to-leading order in &agr;s. In addition to the color-singlet contribution, color-octet channels (especially the P-wave channel) up to O(&ngr;4) are all considered. Aside from direct production, the feed-down contributions from higher excited S-wave and P-wave b&bmacr; states to &ggr;(15) production are also included. We use the potential model estimates as input for color-singlet long-distance matrix elements (LDMEs). While for color-octet contributions, we find they can be approximately described by three LDMEs: 〈…(3S[8]>1)&rlang;, 〈…(1S[8]>0)&rlang; and 〈…(3S[8]>0)&rlang;. By fitting the Tevatron data we can determine some hnear combinations of these LDMEs, and then use them to predict &ggr;(1S) production at the LHC. Our predictions are consistent with the new experimental data of CMS and LHCb. [ABSTRACT FROM AUTHOR]

A complete next-to-leading-order calculation in αs for the J/ψ and ψ' prompt production at the Tevatron, LHC, and RHIC in nonrelativistic QCD is presented. We argue that the next-to-next-to-leading-order color-singlet contribution may not be so important as to resolve the large discrepancy between theory and experiment in J/ψ large PT production cross sections. Therefore, a complete next-to-leading-order calculation, including both color-singlet and color-octet contribution, is necessary and essential to give a good description for J/ψ and ψ' production. We also study the methods to fit the long-distance matrix elements using either two linear combined matrix elements or three matrix elements, and find these two methods can give consistent results. Compared with the measurements at the LHC and RHIC for prompt J/ψ and ψ' production, our predictions are found to agree with all data. In particular, the recently released large pT data (up to 60-70 GeV) at the LHC are in good agreement with our predictions. Our results imply that the universality of color-octet matrix elements holds approximately in charmonium hadroproduction, when one uses fixed-order perturbative calculation to describe data (the data in small pT region are not included). Our work may provide a new test for the universality of color-octet matrix elements, and the color-octet mechanism in general. [ABSTRACT FROM AUTHOR]

We analytically calculate the cross sections of double charmonium production in e+e- → J/ψ(ψ(2S))χcJ (J = 0, 1, 2) at next-to-leading order (NLO) in αs in nonrelativistic QCD, and confirm factorization of these processes. In contrast to χc0 production, for which the NLO correction is large and positive, the NLO corrections for χc1,2 production can be negative, resulting in decreased K factors of 0.91 and 0.78 for J = 1 and 2, respectively, when μ = 2mc. Consequently, the NLO QCD corrections markedly enlarge the difference between cross sections of χc0 and χc1,2. This may explain why e+e- → J/ψ(ψ(2S))χc0 but not e+e- → J/ψ(ψ(2S))χc1,2 is observed experimentally. Moreover, for J/ψ(ψ(2S))χc1,2, the NLO QCD corrections substantially reduce the μ dependence and lead to predictions with small theoretical uncertainties. [ABSTRACT FROM AUTHOR]

χcJ (J=0, 1, 2) production associated with a charm quark pair in hadron collisions is calculated in the framework of nonrelativistic QCD at the Tevatron and LHC. It is found that the color-singlet contribution is small and the color-octet contribution may be dominant in the large pT region. The differential cross section of pp¯ →χc+cc¯ is at least 1 order of magnitude smaller than the next-to-leading order result of χcJ inclusive production pp¯ → χc+X; therefore χcJ production in pp¯ → χc+cc¯ may have negligible influence on the ratio Rχc=σχc2/σχc1 measured by CDF Collaboration at the Tevatron. The feed-down contribution from χcJ+c+c¯ to J/Ψ+c+c¯ is found to be large compared with J/Ψ direct production and may have important influence on the measurement of J/Ψ+c+c¯. The validity of fragmentation approximation for the process is also discussed. [ABSTRACT FROM AUTHOR]

We study O(αsv2) corrections to decays of 1S0 heavy quarkonium into light hadrons and two photons within the framework of nonrelativistic QCD and find these O(αsv2) corrections to have significant contributions especially for the decay into light hadrons. With these new results, experimental measurements of the hadronic width and the γγ width of ηc can be described more consistently. By fitting experimental data, we find the long-distance matrix elements of ηc to be ∣Rηc(0)∣2=0.834-0.197+0.281??GeV3 and «v2»ηc=0.232-0.098+0.121. Moreover, ηc(2S) is also discussed and the γγ decay width is predicted to be 3.34-2.10+2.06??KeV. [ABSTRACT FROM AUTHOR]

To clarify the outstanding problem in charmonium production that existing theories cannot explain the observed cross sections of χcJ(J=0,1,2) and ratio Rχc=σ c2/σ c1≈0.75 (in contrast to the spin counting value 5/3) at the Tevatron, we study the complete next-to-leading order radiative corrections in nonrelativistic QCD, and find next-to-leading order contributions of 3PJ[1] are more important than leading order at high pT, and 3P1[1] decreases slower than 3P2[1], implying a natural explanation for the Rχc puzzle. By fitting Rχc, the predicted cross sections of χcJ are found to agree with data. The result indicates color-octet contribution is crucially needed, thus providing a unique test for heavy quarkonium production mechanisms. Feed-down contributions of χcJ to prompt J/ψ production are estimated to be substantial, about 30%-40% at pT=20??GeV. Production of χcJ(J=0,1,2) at the LHC is also predicted. [ABSTRACT FROM AUTHOR]

By simulating the finite temperature magnetized background at the Relativistic Heavy Ion Collider and LHC energies, we systematically study the characteristics of the thermal width and potential of heavy quarkonia. It is found that the magnetic field has less influence on the real potential but has a significant influence on the imaginary potential, especially in the low deconfined temperature. Extracted from the effect of thermal worldsheet fluctuations about the classical configuration, the thermal width of Υ(1S) at the finite temperature magnetized background is investigated. It is found that at the low deconfined temperature the magnetic field can generate a significant thermal fluctuation of the thermal width of Υ(1S), but with the increase of temperature, the effect of magnetic field on the thermal width becomes less important, which means the effect of high temperature completely exceeds that of magnetic field and magnetic field becomes less important at high temperature. The thermal width decreases with the increasing rapidity at the finite temperature magnetized background. It is also observed that the effect of the magnetic field on the thermal width when the dipole is moving perpendicular to the magnetic field is larger than that moving parallel to the magnetic field at Tc2Tc, the effect of magnetic field on the thermal fluctuation is almost the same whether dipole moving perpendicular or parallel to the magnetic field. [ABSTRACT FROM AUTHOR]

The widely used nonrelativistic QCD (NRQCD) factorization theory now encounters some notable difficulties in describing quarkonium production. This may be due to the inadequate treatment of soft hadrons emitted in the hadronization process, which causes bad convergence of velocity expansion in NRQCD. In this paper, starting from QCD we propose a rigorously defined factorization approach, soft gluon factorization (SGF), to better deal with the effects of soft hadrons. After a careful velocity expansion, the SGF can be as simple as the NRQCD factorization in phenomenological studies, but has a much better convergence. The SGF may provide a new insight to understand the mechanisms of quarkonium production and decay. [ABSTRACT FROM AUTHOR]

High-order calculation at the semihard scale in high-energy collisions is very important, but a satisfactory calculation framework is still missing. We propose a systematic method to regularize the rapidity divergence in color glass condensate (CGC) factorization, which makes higher-order calculation rigorous and straightforward. By applying this method to the single hadron production in the pA collision, we find the kinematic constraint effect introduced by hand in previous works comes out automatically, but with different values. The difference is crucial for our next-to-leading-order result to have a smaller theoretical uncertainty compared with leading-order result, which makes the high-order calculation in CGC factorization be useful. As a byproduct, the negativity problem found in the literature can also be overcome in our framework by properly choosing the factorization scale. [ABSTRACT FROM AUTHOR]

High-order calculation at the semihard scale in high-energy collisions is very important, but a satisfactory calculation framework is still missing. We propose a systematic method to regularize the rapidity divergence in color glass condensate (CGC) factorization, which makes higher-order calculation rigorous and straightforward. By applying this method to the single hadron production in the pA collision, we find the kinematic constraint effect introduced by hand in previous works comes out automatically, but with different values. The difference is crucial for our next-to-leading-order result to have a smaller theoretical uncertainty compared with leading-order result, which makes the high-order calculation in CGC factorization be useful. As a byproduct, the negativity problem found in the literature can also be overcome in our framework by properly choosing the factorization scale. [ABSTRACT FROM AUTHOR]

By introducing an auxiliary parameter, we find a new representation for Feynman integrals, which defines a Feynman integral by analytical continuation of a series containing only vacuum integrals. The new representation therefore conceptually translates the problem of computing Feynman integrals to the problem of performing analytical continuations. As an application of the new representation, we use it to construct a novel reduction method for multiloop Feynman integrals, which is expected to be more efficient than the known integration-by-parts reduction method. Using the new method, we successfully reduced all complicated two-loop integrals in the gg → HH process and gg → ggg process. [ABSTRACT FROM AUTHOR]

Heavy flavor measurements in high multiplicity proton-proton and proton-nucleus collisions at collider energies enable unique insights into their production and hadronization mechanism because experimental and theoretical uncertainties cancel in ratios of their cross sections relative to minimum bias events. We explore such event engineering using the color glass condensate (CGC) effective field theory to compute short-distance charmonium cross sections. The CGC is combined with heavy-quark fragmentation functions to compute D-meson cross sections; for the J/ψ, hadronization is described employing nonrelativistic QCD (NRQCD) and an improved color evaporation model. Excellent agreement is found between the CGC computations and the LHC heavy flavor data in high multiplicity events. Event engineering in this CGC+NRQCD framework reveals a very rapid growth in the fragmentation of the ³S[8]1 state in rare events relative to minimum bias events. [ABSTRACT FROM AUTHOR]

Parton distribution functions (PDFs) are nonperturbative quantities describing the relation between a hadron and the quarks and gluons within it. We propose to extract PDFs from QCD global analysis of "data" generated by lattice QCD calculations of good "lattice cross sections," which are basically single-hadron matrix elements that are lattice QCD calculable and perturbative QCD factorizable into the PDFs. To demonstrate the existence of good "lattice cross sections," we take quasiquark distribution introduced by Ji [Phys. Rev. Lett. 110, 262002 (2013)] as a case study to show that it could be factorized into the PDFs to all orders in perturbation theory if it can be multiplicatively renormalized. We calculate the factorized coefficients at the next-to-leading order in αs. [ABSTRACT FROM AUTHOR]

Fragmentation is the dominant mechanism for hadron production with high transverse momentum. For spin-triplet S-wave heavy quarkonium production, contribution of gluon fragmenting to color-singlet channel has been numerically calculated since 1993. However, there is still no analytic expression available up to now because of its complexity. In this paper, we calculate both polarization-summed and polarized fragmentation functions of gluon fragmenting to a heavy quark-antiquark pair with quantum number ³S1[1]. Our calculations are performed in two different frameworks. One is the widely used nonrelativistic QCD factorization, and the other is the newly proposed soft gluon factorization. In either case, we calculate at both leading order and next-to-leading order in velocity expansion. All of our final results are presented in terms of compact analytic expressions. [ABSTRACT FROM AUTHOR]

Quasiparton distribution functions have received a lot of attention in both the perturbative QCD and lattice QCD communities in recent years because they not only carry good information on the parton distribution functions but also could be evaluated by lattice QCD simulations. However, unlike the parton distribution functions, the quasiparton distribution functions have perturbative ultraviolet power divergences because they are not defined by twist-2 operators. In this paper, we identify all sources of ultraviolet divergences for the quasiparton distribution functions in coordinate space and demonstrate that power divergences as well as all logarithmic divergences can be renormalized multiplicatively to all orders in QCD perturbation theory. [ABSTRACT FROM AUTHOR]

We propose an improved version of the color evaporation model to describe heavy quarkonium production. In contrast to the traditional color evaporation model, we impose the constraint that the invariant mass of the intermediate heavy quark-antiquark pair be larger than the mass of produced quarkonium. We also introduce a momentum shift between the heavy quark-antiquark pair and the quarkonium. Numerical calculations show that our model can describe the charmonium yields as well as the ratio of ψ ′ over J / ψ better than the traditional color evaporation model. [ABSTRACT FROM AUTHOR]

Using the guage/gravity correspondence, we study the free energy, entropy, binding energy, and internal energy of a heavy quarkonium in the rotating quark-gluon plasma (QGP). First, we extend the static black hole with planar horizon to the spinning case, which is dual to the rotating matter. Subsequently, we use the Wilson loop to get the free energy of heavy quarkonium. Entropy, binding energy, and internal energy are naturally given by the thermodynamic relationship. It is found that angular velocity will suppress the dissociation temperature of heavy quarkonium and change the system from confined to deconfined phase with the increase of angular velocity. Thus, the heavy quarkonium will dissolve at a certain separating distance in the deconfined phase. We also compare these thermodynamic quantities of the quark-antiquark pair in the direction parallel and transverse to the rotation direction. At last, the free energy, entropy, and internal energy of a single quark are discussed. It is found that these quantities are decreasing functions of temperature. [ABSTRACT FROM AUTHOR]

We study the effect of magnetic field on heavy quark-antiquark pair in both Einstein-Maxwell (EM) and Einstein-Maxwell-dilaton (EMD) model. The interquark distance, free energy, entropy, binding energy, and internal energy of the heavy quarkonium are calculated. It is found that the free energy suppresses and the entropy increases quickly with the increase of the magnetic field B. The binding energy vanishes at smaller distance when increasing the magnetic field, which indicates the quark-antiquark pair dissociates at smaller distance. The internal energy which consists of free energy and entropy will increase at large separating distance for a nonvanishing magnetic field. These conclusions are consistent both in the EM and EMD model. Moreover, we also find that the quarkonium will dissociate easier in the parallel direction than that in the transverse direction for EMD model, but the conclusion is opposite in EM model. Lattice results are in favor of EMD model. Besides, a Coulomb-plus-linear potential (Cornell potential) can be realized only in EMD model. Thus, a dilaton field is proved to be important in holographic model. Finally, we also show that the free energy, entropy, and internal energy of a single quark in EMD model with the presence of magnetic field. [ABSTRACT FROM AUTHOR]

With the QCD sum rules approach, we study the newly discovered doubly heavy baryon Ξcc++. We analytically calculate the next-to-leading-order (NLO) contribution to the perturbative part of the JP = 1/2+ baryon current with two identical heavy quarks, and then reanalyze the mass of Ξcc++ at the NLO level. We find that the NLO correction significantly improves both scheme dependence and scale dependence, whereas it is hard to control these theoretical uncertainties at leading order. With the NLO contribution, the baryon mass is estimated to be mΞcc++ = 3.66-0.10+0.08 GeV, which is consistent with the LHCb measurement. [ABSTRACT FROM AUTHOR]

We extract the pion valence quark distribution qπv(x) from lattice QCD (LQCD) calculated matrix elements of spacelike correlations of one vector and one axial vector current analyzed in terms of QCD collinear factorization, using a new short-distance matching coefficient calculated to one-loop accuracy. We derive the Ioffe time distribution of the two-current correlations in the physical limit by investigating the finite lattice spacing, volume, quark mass, and higher-twist dependencies in a simultaneous fit of matrix elements computed on four gauge ensembles. We find remarkable consistency between our extracted qvπ(x) and that obtained from experimental data across the entire x range. Further, we demonstrate that the one-loop matching coefficient relating the LQCD matrix computed in position space to the qvπ(x) in momentum space has well-controlled behavior with Ioffe time. This justifies that LQCD-calculated current-current correlations are good observables for extracting partonic structures by using QCD factorization, which complements to the global effort to extract partonic structure from experimental data. [ABSTRACT FROM AUTHOR]