The nucleons (protons and neutrons) are by far the most abundant form of matter in our visible Universe; they are composite particles made of quarks and gluons, the fundamental quanta of Quantum Chromo Dynamics (QCD). The usual interpretation of the nucleon dynamics in high energy interactions is often limited to a simple one-dimensional picture of a fast moving nucleon as a collection of co-linearly moving quarks and gluons (partons), interacting accordingly to perturbative QCD rules. However, massive experimental evidence shows that, in particular when transverse spin dependent observables are involved, such a simple picture is not adequate. The intrinsic transverse motion of partons has to be taken into account; this opens the way to a new, truly 3-dimensional (3D) study of the nucleon structure. A review of the main experimental data, their interpretation and understanding in terms of new transverse momentum dependent partonic distributions, and the progress in building a 3D imaging of the nucleon is presented.
The production of vector mesons in SIDIS is a particularly interesting channel to study the polarized fragmentation and related phenomena. Preliminary COMPASS results for the first measurement of inclusive $ρ^0$ Collins and Sivers transverse-spin asymmetries are presented here for the first time. The analysis is based on the data-set collected by COMPASS in $2010$ using a $160\, \rm{GeV}/c$ $μ^+$ beam and a transversely polarized $NH_3$ target. The asymmetries are extracted as function of Bjorken-$x$, of the total transverse momentum of the oppositely charged hadron pair and of the fraction of…
Partonic Transverse Motion in Unpolarized Semi-Inclusive Deep Inelastic Scattering Processes
分析了部分子横向运动在非极化半包容深度非弹性散射（SIDIS）过程中的作用。施加适当的运动学条件，我们发现一些限制，固定的上限范围内允许的k_perp值。我们表明，应用这些额外的要求的部分子运动学，我们得到不同的结果相对于通常的唯象方法的基础上的高斯涂抹与分析积分在无限范围内的k_perp值。这些变化对某些观测值特别有意义，例如< cos phi_h >未极化SIDIS截面的方位角调制或最终检测到的强子的平均横向动量。
We survey the current phenomenological status of semi-inclusive deep inelastic scattering at moderate hard scales and in the limit of very large transverse momentum. As the transverse momentum becomes comparable to or larger than the overall hard scale, the differential cross sections should be calculable with fixed order pQCD methods, while small transverse momentum (TMD factorization) approximations should eventually break down. We find large disagreement between HERMES and COMPASS data and fixed order calculations done with modern parton densities, even in regions of kinematics where such c…
We study the semi-inclusive production of real, high-$p_T$, isolated photons in unpolarized and polarized lepton-proton collisions, $\ell p\to \ellγX$. In particular we analyze the transverse nucleon single-spin asymmetry within the collinear twist-3 formalism in perturbative QCD to leading order (LO) accuracy. We find that this spin asymmetry is generated by twist-3 dynamical quark-gluon-quark ($qgq$) correlations in the nucleon through the so-called soft-fermion and hard pole contributions. Hence, this process unprecedentedly allows for a point-by-point scan of the support of the dynamical $…
Transverse momentum dependence of the quark helicity distributions and the Cahn effect in double-spin asymmetry $A_{LL}$ in Semi Inclusive DIS
在半包含深度非弹性散射的LO QCD部分子模型$\ell N \to \ell h X$中，利用未积分的夸克分布和碎裂函数，研究了双夸克自旋不对称性$A_{LL}$对$\bfP_{hT}$的依赖性.我们包括1/Q的运动学修正，诱导方位调制的不对称性，类似于在非极化SIDIS的卡恩效应。我们表明，$A_{LL}$和加权DSA $A_{LL}^{\cosϕ_h}$的研究允许提取的横向动量依赖的未积分螺旋度分布函数$g_{1L}^q(x,k_\perp)$ [或$Δq(x, k_\perp)]$。预测，基于一些模型的未知功能，给出了正在进行的COMPASS，HERMES和JLab实验。
Jet production at hadron colliders provides constraints on the parton distribution functions (PDFs) of the proton, in particular on the gluon distribution. In the present paper, the impact on PDF of CMS inclusive differential jet cross sections at center-of-mass energy of $\sqrt s = 8$ TeV for jets with low momentum $p\mathrm{_T}$ and produced in the forward direction is investigated at next-to leading order in perturbative quantum chromodynamics (QCD). The results of the QCD global analysis are compared with theoretical predictions. The impact of low-$p\mathrm{_T}$ jet measurements on the det…
We present an extraction of unpolarized transverse-momentum-dependent parton distribution and fragmentation functions based on more than two thousands data points from several experiments for two different processes: semi-inclusive deep-inelastic scattering and Drell-Yan production of lepton pairs. The baseline analysis is performed with a Monte Carlo replica method resumming large logarithms at N3LL accuracy. The resulting description of the data is very good ($χ^2/N_{\rm dat} = 1.06$). For semi-inclusive deep-inelastic scattering, predictions for multiplicities are normalized by factors that…
Proposal for measuring new transverse momentum dependent parton distributions $g_{1T}$ and $h_{1L}^\perp$ through semi-inclusive deep inelastic scattering
Jet production at hadron colliders is a benchmark process to probe the dynamics of the strong interaction and the structure of the colliding hadrons. One of the most basic jet production observables is the single jet inclusive cross section, which is obtained by summing all jets that are observed in an event. Our recent computation of next-to-next-to-leading order (NNLO) QCD contributions to single jet inclusive observables uncovered large corrections in certain kinematical regions, which also resulted in a sizeable ambiguity on the appropriate choice of renormalization and factorization scale…
We consider semi-inclusive deep inelastic scattering (SIDIS) and Drell-Yan events within transverse momentum dependent (TMD) factorization. Based on the simultaneous fit of multiple data points, we extract the unpolarized TMD distributions and the non-perturbative evolution kernel. The high quality of the fit confirms a complete universality of TMD non-perturbative distributions. The extraction is supplemented by phenomenological analyses of various parts of the TMD factorization, such as sensitivity to non-perturbative parameterizations, perturbative orders, collinear distributions, correlati…
Motivated by recently observed tension between $O\left(α_s^2\right)$ calculations of very large transverse momentum dependence in both semi-inclusive deep inelastic scattering and Drell-Yan scattering, we repeat the details of the calculation through $O\left(α_s^2\right)$ transversely differential cross section. The results confirm earlier calculations, and provide further support to the observation that tension exists with current parton distribution and fragmentation functions.
