Correlations between non-identical particles at small relative velocity probe asymmetries in the average space-time emission points at freeze-out. The origin of such asymmetries may be from long-lived resonances, bulk collective effects, or differences in the freeze-out scenario for the different particle species. STAR has extracted pion-proton correlation functions from a dataset of Au+Au collisions at $\sqrt{s_{NN}}=200$ $GeV$. We present correlation functions in the spherical harmonic decomposition representation, for different centralities and for different combinations of pions and (anti-)protons.
At the leading twist, the transversity distribution function, $h^{q}_{1}(x)$, where $x$ is the longitudinal momentum fraction of the proton carried by quark $q$, encodes the transverse spin structure of the nucleon. Extraction of it is difficult because of its chiral-odd nature. In transversely polarized proton-proton collisions ($p^\uparrow p$), $h_{1}^{q}(x)$ can be coupled with another chiral-odd partner, a spin-dependent fragmentation function (FF). The resulting asymmetries in hadron(s) azimuthal correlations directly probe $h_{1}^{q}(x)$. We report the measurement of correlation asymmetr…
First results on the longitudinal asymmetry and its effect on the pseudorapidity distributions in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV at the Large Hadron Collider are obtained with the ALICE detector. The longitudinal asymmetry arises because of an unequal number of participating nucleons from the two colliding nuclei, and is estimated for each event by measuring the energy in the forward neutron-Zero-Degree-Calorimeters (ZNs). The effect of the longitudinal asymmetry is measured on the pseudorapidity distributions of charged particles in the regions $|η| < 0.9$, $2.8 < η< …
Understanding the proton spin composition from the quarks and gluons spin polarization and their motion is important to test various kinds of sum rules and nonperturbative properties of hadrons. At the Relativistic Heavy Ion Collider (RHIC), we collide longitudinally polarized proton beams and measure the double helicity asymmetry $A_{LL}$, which is an important physical quantity for extracting the polarized parton distribution functions (PDFs) of the proton. Direct photon, jet and charged pion production are good channels to probe the gluon spin polarization inside the proton, with the abilit…
Cross section and single transverse target spin asymmetry for backward pion electroproduction
核子-介子跃迁分布振幅（TDA）是核子-介子态之间非定域三夸克算符的非对角矩阵元，它是在共线因式分解描述的介子从核子反向排斥电生过程中产生的.下面我们将讨论π介子到核子时间分辨模型的问题。我们提出了一个因式分解的四重分布与软π介子定理的输入π N TDAs的。为了满足多项式性质在其完整的形式的频谱表示补充与D-项一样的贡献，从核子交换的u-通道的反应。我们提出了我们的估计后向π介子电产生非极化截面和它的横向目标单自旋不对称性在我们的复合模型为π N TDAs。
Pion-kaon femtoscopy in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV modeled in (3+1)D hydrodynamics coupled to Therminator 2 and the effect of delayed kaon emission
We report systematic measurements of bulk properties of the system created in Au+Au collisions at $\sqrt{s_{NN}}$ = 54.4 GeV recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum spectra of $π^{\pm}$, $K^{\pm}$, and $p$($\bar{p}$) are studied at mid-rapidity $(\lvert y \rvert < 0.1)$ for different centrality classes. We also present mid-rapidity measurement of particle yields $(dN/dy)$ and particle ratios in Au+Au collisions at $\sqrt{s_{NN}}$ = 54.4 GeV. The kinetic freeze-out parameters ($T_{kin}$ and $\langle β\rangle$) are extracted from parti…
Transverse single-spin asymmetries of very forward neutral pions generated in polarized $p + p$ collisions allow us to understand the production mechanism in terms of perturbative and non-perturbative strong interactions. During 2017 the RHICf Collaboration installed an electromagnetic calorimeter in the zero-degree region of the STAR detector at the Relativistic Heavy Ion Collider (RHIC) and measured neutral pions produced at pseudorapidity larger than 6 in polarized $p$+$p$ collisions at $\sqrt{s}$ = 510 GeV. The large non-zero asymmetries increasing both in longitudinal momentum fraction $x…
In neutrino-nucleus interactions, a proton produced with a correlated pion might exhibit a left-right asymmetry relative to the lepton scattering plane even when the pion is absorbed. Absent in other proton production mechanisms, such an asymmetry measured in charged-current pionless production could reveal the details of the absorbed-pion events that are otherwise inaccessible. In this study, we demonstrate the idea of using final-state proton left-right asymmetries to quantify the absorbed-pion event fraction and underlying kinematics. This technique might provide critical information that h…
In this paper, the first femtoscopic analysis of pion-kaon correlations at the LHC is reported. The analysis was performed on the Pb-Pb collision data at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV recorded with the ALICE detector. The non-identical particle correlations probe the spatio-temporal separation between sources of different particle species as well as the average source size of the emitting system. The sizes of the pion and kaon sources increase with centrality, and pions are emitted closer to the centre of the system and/or later than kaons. This is naturally expected in a system with strong …
