Azimuthal distributions of pions inside a jet in hadronic collisions
Umberto D'Alesio, Francesco Murgia, Cristian Pisano
备注:
6 pages, 3 figures, to appear in the proceedings of Third International Workshop on Transverse Polarization Phenomena in Hard Scattering (Transversity 2011), Veli Lošinj (Croatia), 29 August-2 September 2011
Using a generalized parton model approach including spin and intrinsic parton motion effects, and assuming the validity of factorization for large pT jet production in hadronic collisions, we study the azimuthal distribution around the jet axis of leading pions, produced in the jet fragmentation process. We identify the observable leading-twist azimuthal asymmetries, which are generated by all the physically allowed combinations of transverse momentum dependent (TMD) parton distribution and fragmentation functions. In particular, we show how one can isolate the Collins and Sivers contributions, and suggest a test of the process dependence of the Sivers function by considering the effect of color-gauge invariant initial and final state interactions.
Restrictions on the Hadronic Contribution to the Muon $(g-2)$-factor and to the Pion Electromagnetic Formfactor from Analytical Properties of the Pion Electromagnetic Formfactor
A sizable $\cos 4ϕ$ azimuthal asymmetry in exclusive di-pion production near $ρ^0$ resonance peak in ultraperipheral heavy ion collisions recently has been reported by STAR collaboration. We show that both elliptic gluon Wigner distribution and final state soft photon radiation can give rise to this azimuthal asymmetry. The fact that the QED effect alone severely underestimates the observed asymmetry might signal the existence of the nontrivial correlation in quantum phase distribution of gluons.
The largest error in the theoretical determination of the muon anomalous magnetic moment is due to the low-energy hadronic vacuum polarization, which cannot be calculated by perturbative QCD and requires nonperturbative techniques. Recently, an accurate determination of the low-energy two-pion contribution to muon $g-2$ has been obtained by a parametrization-free analytic continuation of the pion vector form factor from other kinematical regions. In this work we compare the results of the analytic continuation with direct determinations at low momenta from experiment and lattice QCD. We also e…
In this paper, we investigate the influence of coherent pion emission on long-range azimuthal correlations in relativistic proton-proton collisions. We study the pion momentum distribution for a coherent source with both transverse and Bjorken longitudinal expansions, and calculate the two-particle correlation function $C(Δη,Δϕ)$. A "ridge" structure is observed in the correlation function $C(Δη,Δϕ)$ of the coherent pion emission, whether the coherent source is expanding or static. The onset of this long-range azimuthal correlation can be traced back to the asymmetric initial transverse profil…
The inclusive production at the LHC of a charged light hadron and of a jet, featuring a wide separation in rapidity, is suggested as a new probe process for the investigation of the BFKL mechanism of resummation of energy logarithms in the QCD perturbative series. We present some predictions, tailored on the CMS and CASTOR acceptances, for the cross section averaged over the azimuthal angle between the identified jet and hadron and for azimuthal correlations.
Soft-Fermion-Pole Mechanism to Single Spin Asymmetry in Hadronic Pion Production
单自旋不对称性(SSA)是在共线因式分解方法中可观察到的扭曲-3。给出了一个与RHIC实验相关的pp碰撞中π介子产生的扭曲3单自旋相关截面公式p^ \uparrow p \to πX.特别地,我们从夸克-胶子关联函数计算了软费米子极(SFP)对散射截面的贡献。我们表明,它的效果可以作为大的软胶子极(SGP)的贡献,由于大SFP部分子硬截面,即使衍生物的SFP功能不参与的截面。
We study the $\sin2ϕ_h$ azimuthal asymmetry of charged and neutral pion productions off the longitudinally polarized nucleon targets in semi-inclusive deeply inelastic scattering (SIDIS) process within the transverse momentum dependent~(TMD) factorization. The asymmetry is contributed by the convolution of the TMD distribution $h_{1L}^{\perp}$ and the Collins fragmentation function $H_{1}^\perp$. We adopt the Wandzura-Wilczek-type~(WW-type) approximation for $h_{1L}^{\perp}$ and two different parametrizations on the nonperturbative part of TMD evolution for $h_{1L}^{\perp}$ and $H_{1}^\perp$. …
We propose a model-independent parametrization for the one-pion-to-vacuum matrix elements of the vector and axial vector hadronic currents in the presence of an external uniform magnetic field. It is shown that, in general, these hadronic matrix elements can be written in terms of several gauge covariant Lorentz structures and form factors. Within this framework we obtain a general expression for the weak decay $π^- \to l\,\barν_l$ and discuss the corresponding limits of strong and weak external magnetic fields.