We present the first model independent determination of S- and P-wave helicity amplitudes from CERN measurements of pi(-)p -> pi(-)pi(+)n on polarized target at small t and dipion masses 580-1080 MeV. The purely analytical determination of the helicity amplitudes is made possible by our finding analytical solution for relative phase omega_ij between S-wave amplitudes S_d and S_u of opposite transversity for each set of solutions for transversity amplitudes A_u(i), A_d(j),i,j=1,2. Of the six possible solutions for omega_ij only the solution with omega_ij=pi yields physical helicity amplitudes. Assigning rho^0(770) phase to the dominant P-wave helicity flip amplitude L_1(ij) necessitates a phase of the S-wave helicity flip amplitude S_1(ij) that is near to the rho^0(770) phase.These two amplitudes are consistent with rho^0(770)-f_0(980) mixing. The relative phases omega_ij=pi satisfy certain selfconsistency relation that must be satisfied in order for the four sets of solutions A_u(i),A_d(j),i,j=1,2 to be all physical solutions that can be identified with coevolution amplitudes describing the interaction of the pion creation process with a quantum environment. This test on phases omega_ij provides a new test of Kraus representation of the mixed final state density matrix. We show that the probabilities p_ij determining the final state rho_f in terms of solution states rho_f(ij) can be determined in measurements of recoil hyperon polarization in pi(-)p->pi(-)K(+)Lambda0 on polarized target.
This paper presents an update to the MK model, which was developed to describe single pion production in neutrino-nucleon interactions. Originally the MK model used the helicity amplitudes and the hadronic current form-factors of the Rein and Sehgal model. The update includes a new definition for the helicity amplitudes in the first and second resonance regions, and new vector-current form factors. Fits to electron-proton scattering data were used to determine these vector-current form factors, and to assign errors to the constrained free parameters of the model.
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…
The generalized parton distributions (GPDs) offer a window on three-dimensional imaging of the nucleon, providing understanding of how the fundamental properties of the nucleon, such as its mass and spin, arise from the underlying quark and gluon degrees of freedom. In this work, we present the first lattice calculation of the nucleon isovector helicity GPD at physical pion mass, using an $a \approx 0.09$ fm lattice ensemble with 2+1+1 flavors of highly improved staggered quarks generated by MILC Collaboration. We perform the GPD calculation in Breit frame using averaged nucleon boost momentum…
We present results for pion polarizabilities predicted using dispersion relations from our earlier Amplitude Analysis of world data on two photon production of meson pairs. The helicity-zero polarizabilities are rather stable and insensitive to uncertainties in cross-channel exchanges. The need is first to confirm the recent result on $(α_1-β_1)$ for the charged pion by COMPASS at CERN to an accuracy of 10\% by measuring the $γγ\toπ^+π^-$ cross-section to an uncertainty of ~1\%. Then the same polarizability, but for the $π^0$, is fixed to be $(α_1-β_1)_{π^0}=(-0.9\pm0.2)\times 10^{-4}$ fm$^{3}…
We present a state-of-the-art calculation of the isovector quark helicity Bjorken-$x$ distribution in the proton using lattice-QCD ensembles at the physical pion mass. We compute quasi-distributions at proton momenta $P_z \in \{2.2, 2.6, 3.0\}$~GeV on the lattice, and match them systematically to the physical parton distribution using large-momentum effective theory (LaMET). We reach an unprecedented precision through high statistics in simulations, large-momentum proton matrix elements, and control of excited-state contamination. The resulting distribution with combined statistical and system…
Beam-helicity asymmetry in photon and pion electroproduction in the Delta(1232) resonance region at Q^2= 0.35 (GeV/c)^2
在$Q^2=$ 0.35（GeV/c）$^2$的$Δ(1232)$共振区同时测量了反应（ep \to ep γ）和（ep \to ep π^0）的束流螺旋度不对称性.该实验是在MAMI进行的，使用纵向偏振光束和质子的面外探测。计算结果进行了比较的基础上的色散关系的虚拟康普顿散射和π电生产的MAID模型。实验结果与理论计算结果基本吻合。其余的差异可能归因于某些$γ^{(*)} N \to πN$多极的参数化不完善，主要导致非共振背景。两个通道（$γ$和$π^0$）中的光束螺旋度不对称性对这些多极子显示出良好的灵敏度，并且应该允许将来在其参数化中进行改进。
Evidence for evolution from pure states to mixed states in pion creation process pi(-) p -> pi(-)pi(+) n on polarized target and its physical interpretation
The double-charm tetraquark meson $T_{cc}^+(3875)$ can be produced in high-energy proton-proton collisions by the creation of the charm mesons $D^{*+} D^0$ at short distances followed by their binding into $T_{cc}^+$. The $T_{cc}^+$ can also be produced by the creation of $D^{*+} D^{*+}$ at short distances followed by their rescattering into $T_{cc}^+ π^+$. A charm-meson triangle singularity produces a narrow peak in the $T_{cc}^+ π^+$ invariant mass distribution 6.1 MeV above the threshold with a width of about 1 MeV. Well beyond the peak, the differential cross section decreases with the inv…
To measure the helicity of a spin-1 meson from the triple vector product of the three-momenta of its decay products, one needs information about the strong phase of the decay amplitude. In this paper, taking $a_1(1260)$ meson as an example, we present a method to extract information about the strong phase from the triple vector product of the pion momenta in $W \to ντ(\to νa_1(\toπ^\mp π^\mp π^\pm))$ process, where the $a_1$ helicity is known a priori from electroweak theory. This process is advantageous in that highly-boosted $a_1^-$ mesons from $τ_L^-$ decays have nearly maximal helicity asy…
If the $X(3872)$ is a weakly bound charm-meson molecule, it can be produced by the creation of $D^{*0} \bar{D}^0$ or $D^{0} \bar{D}^{*0}$ at short distances followed by the formation of the bound state from the charm-meson pairs. It can also be produced by the creation of $D^{*} \bar{D}^*$ at short distances followed by the rescattering of the charm mesons into $X π$. We use results of a previous isospin analysis of $B$ meson decays into $K D^{(*)} \bar D^{(*)}$ to estimate the short-distance amplitudes for creating $D^* \bar D^*$. We use an effective field theory for charm mesons and pions ca…
How to extract the P_{33}(1232) resonance contributions from the amplitudes M_{1+}^{3/2},E_{1+}^{3/2},S_{1+}^{3/2} of pion electroproduction on nucleons
Previous Lattice QCD calculations of nucleon transverse momentum-dependent parton distributions (TMDs) focused on the case of transversely polarized nucleons, and thus did not encompass two leading-twist TMDs associated with longitudinal polarization, namely, the helicity TMD and the worm-gear TMD corresponding to transversely polarized quarks in a longitudinally polarized nucleon. Based on a definition of TMDs via hadronic matrix elements of quark bilocal operators containing staple-shaped gauge connections, TMD observables characterizing the aforementioned two TMDs are evaluated, utilizing a…
We present the first exploratory lattice quantum chromodynamics (QCD) calculation of the polarized gluon Ioffe-time pseudo-distribution in the nucleon. The Ioffe-time pseudo-distribution provides a frame-independent and gauge-invariant framework to determine the gluon helicity in the nucleon from first principles. We employ a high-statistics computation using a $32^3\times 64$ lattice ensemble characterized by a $358$ MeV pion mass and a $0.094$ fm lattice spacing. We establish the pseudo-distribution approach as a feasible method to address the proton spin puzzle with successive improvements …
We apply the Braun-Manashov technique to improve the description of $γ^*(q_1) γ(q_2) \to M(p_1) M(p_2)$ amplitudes at large $Q^2=-q_1^2$ and small $s=(q_1+q_2)^2$. We derive the kinematical higher-twist contributions of order $s/Q^2$ and $m^2/Q^2$ to the helicity amplitudes and estimate their sizes in the kinematics accessible at Belle and Belle II.Since pion GPDs cannot be directly measured by experiment, $ππ$ GDAs are the best way to investigate the energy-momentum tensor form factors for pions.
