At high energies, the cross section of a hard exclusive process at finite scattering angle falls off as a negative power of the center-of-mass energy $\sqrt{s}$. If all involved quark-gluon compositions undergo hard momentum transfers, the scaling of the fall-off is determined by the underlying valence structures of the initial and final states, known as the constituent counting rules. It was argued in the literature that the counting rules are a powerful tool to determine the valence degrees of freedom inside multiquark states when applied to exclusive production processes. However, we demonstrate that for hadrons with hidden flavors the naive application of the constituent counting rules is problematic, since it is not mandatory for all components to participate the hard scattering at the scale $\sqrt{s}$. The correct scaling rules can be obtained easily by using effective field theory. A few examples involving the $Z_c(3900)^\pm$ and $X(3872)$ are discussed.
We propose to increase the factual reliability of descriptions of exotic multiquark hadrons utilizing the approach to bound states of strongly interacting constituents known as QCD sum rules, by allowing exclusively all contributions that potentially bear some relevance for multiquark states to enter the correlation functions that form the main ingredient of this framework. The route to this goal is illustrated for the (presumably least involved) special case of tetraquark states.
We assume that the two hidden charm pentaquark discovered at $LHCb$ are built by the three light quarks and the $c \bar{c}$ pair, both colour octets. in relative P-wave for the $\frac{5}{2}^+$ state and by the eigenvectors of the chromomagnetic interaction for the five constituents in S-wave for the four $\frac{3}{2}^-$ state with masses $4360$, $4410$, $4490$ and $4560$ MeV . The "open channel" $p $ $J/ψ$ has large components along the two first states and so appear as the $4380$ resonance and the $Λ_c$ $ \bar{D}^{0*}$ and $Σ_c$ $\bar{D}^*$ are "open channels" for the lower and higher resonan…
We propose a novel approach to construction of hadron spectroscopy. The case of light nonstrange mesons is considered. By assumption, all such mesons above 1 GeV appear due to creation of constituent quark-antiquark pairs inside the pi or rho (omega) mesons. These spin-singlet or triplet pairs dictate the quantum numbers of formed resonance. The resulting classification of light mesons turns out to be in a better agreement with the experimental observations than the standard quark model classification. It is argued that the total energy of quark components should be proportional to the hadron …
If connecting properties of a multiquark hadron with those exhibited by its constituents, QCD sum rules inferred along the routes of traditional wisdom necessarily involve contributions not related at all to and thus not presenting information about multiquarks. Realizing this deficiency, we propose to increase, for the example of tetraquarks, the predictive power of the QCD sum-rule formalism by disposal of all of the unwanted contributions from the very beginning; this move is easily accomplished by subjecting the contributions to our perspicuous selection criterion.
The constituent counting rules, i.e., the scaling behavior of amplitudes (in terms of the number of fundamental constituents) for exclusive processes when high energy scales are present, have been known for decades, and have been borne out in a number of experiments. Such scaling would be sensitive, in particular, to possible exotic multiquark content. Here we examine how one may use the rules to test for pentaquarks in electroproduction, or for tetraquarks in e^+ e^- annihilation. An interesting new type of scaling (separate Mandelstam s and t behavior) arises in the forward scattering direct…
Hard exclusive baryon-antibaryon production in 2-$γ$ collisions
本文将重子看作夸克-双夸克系统，用微扰方法计算了双光子碰撞中重子对的产生，即$γγ\to B \bar{B}$。我们的方法占成分的质量效应在一个系统的方式。从前面研究的其他电子和光子诱导重子反应的双夸克模型参数，我们的结果与最近的大动量转移数据的$p\bar{p}$，$Λ\barΛ$，和$Σ^0\barΣ^0$通道吻合得很好。
QCD constituent counting rules define the scaling behavior of exclusive hadronic scattering and electromagnetic scattering amplitudes at high momentum transfer in terms of the total number of fundamental constituents in the initial and final states participating in the hard subprocess. The scaling laws reflect the twist of the leading Fock state for each hadron and hence the leading operator that creates the composite state from the vacuum. Thus, the constituent counting scaling laws can be used to identify the twist of exotic hadronic candidates such as tetraquarks and pentaquarks. Effective …
We show that an endpoint overlap model can explain the scaling laws observed in exclusive hadronic reactions at large momentum transfer. The model assumes one of the valence quarks carries most of the hadron momentum. Hadron form factors and fixed angle scattering are related directly to the quark wave function, which can be directly extracted from experimental data. A universal linear endpoint behavior explains the proton electromagnetic form factor, proton-proton fixed angle scattering, and the t-dependence of proton-proton scattering at large s>>t. Endpoint constituent counting rules relate…
With an appropriate hard scale, exclusive hadronic processes could provide novel information of the internal quark-gluon configurations of hadrons. The availability of 10-20 GeV secondary meson beam in the coming high-momentum beam line of Hadron Hall at J-PARC offers an unique opportunity to carry out the measurements of the exclusive hard processes. We address this interesting approach by two possibilities: (a) $π^- p \to K^0 Λ(1405)$ for the constituent quark structure of $Λ(1405)$, and (b) exclusive pion-induced Drell-Yan process $π^- p \to γ^* n \to l^+ l^- n$ for the generalized parton d…
The constituent counting ruling (CCR) has been found to hold for numerous hard, exclusive processes. It predicts the differential cross section at high energies and fixed $\cos θ_{c.m.}$ should follow $\frac{d σ}{dt} \sim \frac{1}{s^{n-2}}$, where $n$ is the minimal number of constituents involved in the reaction. Here we provide an in-depth analysis of the reaction $γp \rightarrow ωp$ at $θ_{c.m.}\sim 90^\circ$ using CLAS data with an energy range of $s = 5 - 8$ GeV$^2$, where the CCR has been shown to work in other reactions. We argue for a stringent method to select data to test the CCR and…
Three-dimensional imaging of hadrons with hard exclusive reactions: advances in experiment, theory, phenomenology, and lattice QCD
NRC “Kurchatov Institute” - PNPI（库尔恰托夫国家研究中心 - 彼得堡核物理研究所）；INFN Laboratori Nazionali di Frascati（意大利国家核物理研究所弗拉斯卡蒂实验室）；Virginia Tech（弗吉尼亚理工大学）；Thomas Jefferson National Accelerator Facility（托马斯·杰斐逊国家加速器设施）；Temple University（天普大学）；Department of Physics, Kyungpook National University（庆北国立大学物理系）；BenGurion（本古里安大学）；IRB（意大利国家核物理研究所）；INFN（意大利国家核物理研究所）
