arXiv subjects

Haiyan Gao

Publications and source records attributed to Haiyan Gao.

24 records · Page 2Linked to original sources

arXiv2012

Laboratory Search for Spin-dependent Short-range Force from Axion-Like-Particles using Optically Polarized 3He gas

The possible existence of short-range forces between unpolarized and polarized spin-1/2 particles has attracted the attention of physicists for decades. These forces are predicted in various theories and provide a possible new source for parity (P) and time reversal (T) symmetry violation. We use an ensemble of polarized 3He gas in a cell with a 250 um thickness glass window to search for a force from scalar boson exchange over a sub-millimeter ranges. This interaction would produce a NMR frequency shift as an unpolarized mass is moved near and far from the polarized ensemble. We report a new upper bound on the product g_{s}g_{p}^{n} of the scalar couplings to the fermions in the unpolarized mass, and the pseudoscalar coupling of the polarized neutron in the 3He nucleus for force ranges from 1e-4 to 1e-2 m, which corresponds to a mass range of 2e-3 to 2e-5 eV for the scalar boson.

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arXiv2004

Pion photoproduction on the nucleon

The $γn \to π^- p$ and $γp \to π^+ n$ reactions are essential probes of the transition from meson-nucleon degrees of freedom to quark-gluon degrees of freedom in exclusive processes. The cross sections of these processes are also advantageous, for the investigation of oscillatory behavior around the quark counting prediction, since they decrease relatively slower with energy compared with other photon-induced processes. In this talk, we discuss recent results on the $γp \to π^+ n$ and $γn \to π^{-}p$ processes from Jefferson Lab experiment E94-104. We also discuss a new experiment in which singles $γp \to π^+ n$ measurement from hydrogen, and coincidence $γn \to π^{-} p$ measurements at the quasifree kinematics from deuterium for center-of-mass energies between 2.3 GeV to 3.4 GeV in fine steps at a center-of-mass angle of $90^\circ$ are planned. The proposed measurement will allow a detailed investigation of the oscillatory scaling behavior in photopion production processes.

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arXiv2004

High Resolution Search for Exotic Pentaquark $Θ^{++}$, and $Θ^+$ at Jefferson Lab

Recent evidence for the existence of pentaquark $Θ^+$ particle from several experiments at several different laboratories around the world has caused great excitement and raised many unanswered questions. We discuss a new proposal on a high resolution experiment searching for pentaquark states in Hall C at Jefferson Lab using an untagged bremsstrahlung photon beam employing both the hydrogen and the deuterium targets by studying the following processes: $γp \to Θ^{++} K^-$, and $γn \to Θ^+ K^-$. This new experiment will significantly improve our current knowledge of the mass, the width of the $Θ^+$ particle if it is confirmed and provide unambiguous evidence for the existence or non-existence of the $Θ^{++}$ particle from the γp \to Θ^{++} K^-$ process.

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arXiv2004

Neutron Electromagnetic Form Factors

The nucleon electromagnetic form factors have been studied in the past extensively from unpolarized electron scattering experiments. With the development in polarized beam, recoil polarimetry, and polarized target technologies, polarization experiments have provided more precise data on these quantities. In this talk, I review recent experimental progress on this subject.

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arXiv2003

Status on nucleon electromagnetic form factors

Nucleon electromagnetic form factors are fundamental quantities related to the charge and magnetization distributions inside the nucleon. Understanding the nucleon electromagnetic structure in terms of the underlying quark and gluon degrees of freedom of quantum chromodynamics is a challenging and urgent task. The nucleon electromagnetic form factors have been studied in the past extensively from unpolarized electron scattering experiments. With the development in polarized beam, recoil polarimetry, and polarized target technologies, polarization experiments have provided more precise data on these quantities. At the same time, significant theoretical progress in areas ranging from effective field theories to lattice QCD calculations, has been made in describing these data. In this article, we review recent experimental and theoretical progress on this subject. we also provide future outlook on this topic.

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arXiv2003

Exotic Hadrons Of Minimal Pentaquark ($qqqq\Bar{Q}$) States

It is shown that the exotic non-qqq hadrons of pentaquark $qqqq\bar{q}$ states can be clearly distinguished from the conventional qqq-baryon resonances or their hybrids if the flavor of $\bar{q}$ is different from any of the other four quarks. We suggest the physical process $p(e,e'K^-)Z(uuud\bar{s})$, which can be investigated at the Thomas Jefferson National Accelerator Facility (JLab), as an ideal process to search for the existence or non-existence of the exotic hadron of minimal pentaquark state $Z(uuud\bar{s})$. (The search for the existence of $Z(uudd\bar{s})$ is also discussed in the paper. We added this sentence after the original published form of this paper.)

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