A partial-wave analysis of the mesons from the reaction $\pi^{-}% p\to\pi^{+}\pi^{-}\pi^{-}\pi^{0}\pi^{0}p$ has been performed. The data show $b_{1}\pi$ decay of the spin-exotic states $\pi_{1}(1600)$ and \ $\pi_{1}(2000)$. Three isovector $2^{-+}$ states were seen in the $\omega\rho^{-}$ decay channel. In addition to the well known $\pi_{2}(1670)$, signals were also observed for $\pi_{2}(1880)$ and $\pi_{2}(1970)$.

This letter reports results from the partial wave analysis of the $\pi^{-}\pi^{-}\pi^{+}\eta$ final state in $\pi^{-}p$ collisions at 18GeV/c. Strong evidence is observed for production of two mesons with exotic quantum numbers of spin, parity and charge conjugation, $J^{PC} = 1^{-+}$ in the decay channel $f_{1}(1285)\pi^{-}$. The mass $M = 1709 \pm 24 \pm 41$ MeV/c^2 and width $\Gamma = 403 \pm 80 \pm 115$ MeV/c^2 of the first state are consistent with the parameters of the previously observed $\pi_{1}(1600)$. The second resonance with mass $M = 2001 \pm 30 \pm 92$ MeV/c^2 and width $\Gamma = 333 \pm 52 \pm 49$ MeV/c^2 agrees very well with predictions from theoretical models. In addition, the presence of $\pi_{2}(1900)$ is confirmed with mass $M = 2003 \pm 88 \pm 148$ MeV/c^2 and width $\Gamma = 306 \pm 132 \pm 121$ MeV/c^2 and a new state, $a_{1}(2096)$, is observed with mass $M = 2096 \pm 17 \pm 121$ MeV/c^2 and width $\Gamma = 451 \pm 41 \pm 81$ MeV/c^2. The decay properties of these last two states are consistent with flux tube model predictions for hybrid mesons with non-exotic quantum numbers.

We discuss a coupled channel analysis of the $\eta\pi$ and $\eta'\pi$ systems produced in $\pi^-p$ interactions at 18 GeV/$c$. We show that known $Q\bar Q$ resonances, together with residual soft meson-meson rescattering, saturate the spectra including the exotic $J^{PC}=1^{-+}$ channel. A possibility of a narrow exotic resonance at a mass near 1.6 GeV/$c^2$ cannot, however, be ruled out.

A partial wave analysis (PWA) of the of the $\eta \pi ^0$ system (where $\eta \to \gamma \gamma$) produced in the charge exchange reaction $\pi ^-p\to \eta \pi ^0n$ at an incident momentum of 18 GeV$/c$ is presented as a function of ${\eta \pi ^0}$ invariant mass, $m_{\eta\pi^0}$, and momentum transfer squared, $t_{\pi^{-}\to\eta\pi}$, from the incident $\pi^-$ to the outgoing ${\eta\pi ^0}$ system. $S$, $P$ and $D$ waves were included in the PWA. The $a_0(980)$ and $a_2(1320)$ states are clearly observed in the overall ${\eta\pi ^0}$ effective mass distribution as well as in the amplitudes associated with $S$ wave and $D$ waves respectively after partial wave decomposition. The observed distributions in moments (averages of spherical harmonics) were compared to the results from the PWA and the two are consistent. The distribution in $t_{\pi^{-}\to\eta\pi}$ for individual $D$ waves associated with natural and unnatural parity exchange in the $t$-channel are consistent with Regge phenomenology. Of particular interest in this study is the $P$ wave since this leads to an exotic $J^{PC}=1^{-+}$ for the $\eta \pi$ system. A $P$ wave is present in the data, however attempts to describe the mass dependence of the amplitude and phase motion with respect to the $D$ wave as a Breit-Wigner resonance are problematic. This has implications regarding the existence of a reported exotic $J^{PC} = 1^{-+}$ meson decaying into $\eta \pi^0$ with a mass near 1.4 GeV$/c^2$.

The CERN COMPASS experiment may use 100-280 GeV pion and Kaon beams and magnetic spectrometers and calorimeters to measure Hybrid (mixed quark-gluon) meson production cross sections in the ultra-peripheral Primakoff scattering of high energy pions and Kaons from virtual photons in the Coulomb field of High-Z targets. There are strong advantages to study Hybrid mesons by the Primakoff reactions pi- gamma --> Hybrid --> rho pi, eta pi, eta' pi, pi b1, pi f1; and similar reactions with a K- beam. Such data should provide significant new input for a more complete understanding of the strong interactions of QCD. A brief description and update of this program is presented.

The reaction pim p --> omega pim p, omega --> pip pim pi0 has been studied at 18 GeV/c. The omega pim mass spectrum is found to be dominated by the b1(1235). Partial Wave Analysis shows that b1 production is dominated by natural parity exchange. The S-wave and D-wave amplitudes for b1(1235) --> omega pi have been determined, and it is found that the amplitude ratio, |D/S| = 0.269 +/- (0.009)stat +/- (0.01)sys and the phase difference, phi(D-S) = 10.54 deg +/- (2.4)stat +/- (3.9)sys.

We present preliminary results of study of the ethapi-, etha'pi- and b1pi systems produced in the pi-Be-interaction at 28GeV/c. JPC=2++ and 1-+-waves resulted from the PWA have been fitted in each system separately to establish the nature of the 1-+ wave. A hypothesis of the 1-+ wave resonant nature in the ethapi- and etha'pi- has no statistically significant preference over the non-resonant one. The b1pi-system study confirms the results of the 37GeV/c beam data analysis in favor of the resonant treatment of the bump at 1.6GeV.

An understanding of the confinement mechanism in QCD requires a detailed mapping of the spectrum of hybrid mesons. Understanding confinement means understanding the role of gluons and it is in hybrid mesons that the gluonic degrees of freedom are manifest. High statistics searches for such states with pion and p beams have resulted in some tantalizing signals. There is good reason to expect beams of photons to yield hybrid mesons with J^{PC} quantum numbers not possible within the conventional picture of mesons as qqbar bound states. Meager data currently exist on the photoproduction of light quark mesons. At Jefferson Lab in Newport News, VA plans are underway to upgrade the energy of the electron accelerator to 12 GeV. Along with this energy upgrade, a hermetic detector housed in new experimental hall (Hall D) will be used to collect data on photoproduced mesons with unprecedented statistics. With 12 GeV electrons, a 9 GeV linearly polarized photon beam will be produced using the coherent bremsstrahlung technique.

An amplitude analysis of an exclusive sample of 5765 events from the reaction $\pi^{-} p \to \eta^{\prime} \pi^- p$ at 18 GeV/c is described. The $\eta^{\prime} \pi^-$ production is dominated by natural parity exchange and by three partial waves: those with $J^{PC} = 1^{-+}, 2^{++},$ and $4^{++}$. A mass-dependent analysis of the partial-wave amplitudes indicates the production of the $a_2(1320)$ meson as well as the $a_4(2040)$ meson, observed for the first time decaying to $\eta^{\prime}\pi^-$. The dominant, exotic (non-$q\bar{q}) $ $1^{-+}$ partial wave is shown to be resonant with a mass of $1.597 \pm 0.010^{+0.045}_{-0.010}$ GeV/c^2 and a width of $0.340 \pm 0.040 \pm 0.050$ GeV/c^2 . This exotic state, the $\pi_1(1600)$, is produced with a $t$ dependence which is different from that of the $a_2(1320)$ meson, indicating differences between the production mechanisms for the two states.

CERN COMPASS can investigate pion-photon interactions, to achieve a unique Primakoff Coulomb physics program, centered on pion polarizability and hybrid meson structure studies. COMPASS uses 100-280 GeV beams (muon, pion) and a virtual photon target, and magnetic spectrometers and calorimeters to measure the complete kinematics of pion-photon reactions. The COMPASS experiment is scheduled to begin data runs in 2001. Pion polarizabilities and hybrid mesons can be studied via the Primakoff reactions pion + gamma ---> pion + gamma and pion + gamma ---> Hybrid. The electric (alpha) and magnetic (beta) pion and Kaon polarizabilities characterize their deformation in an electromagnetic field, as occurs during gamma-pion Compton scattering. They depend on the rigidity of their internal structures as composite particles, and are therefore important quantities to test the validity of theoretical models. The polarizability measurement will provide an important new test of QCD chiral dynamics. The studies of quark-antiquark-gluon hybrid mesons would improve our understanding of these exotic mesons. COMPASS may improve previous Primakoff polarizability and Hybrid studies by two to three orders of magnitude. Appendixes A (Pion and Kaon Polarizabilities at COMPASS) and B (Hybrid Meson Structure at COMPASS) of this contribution include evaluations submitted to the APS DNP Town Meeting White Paper Committee. These summarize (1) the fundamental scientific issues addressed, (2) major achievements since the last DNP long range plan, (3) the short and long term U.S. outlook, (4) comparison of U.S. and global effort, (5) other issues.

We describe a pion physics program attainable with the CERN COMPASS spectrometer, involving tracking detectors and an electromagnetic calorimeter. COMPASS can realize state-of-the-art pion beam hybrid meson and meson radiative transition studies. We review here the physics motivation for this program. We describe the beam, detector, trigger requirements, and hardware/software requirements for this program. The triggers for all this hybrid meson physics can be implemented for simultaneous data taking. We will investigate hybrid meson production via pion-photon Primakoff and pion-Pomeron diffractive interactions. We will determine new properties of quark-antiquark-gluon hybrid mesons, using unique production methods, to improve our understanding of these exotic mesons. The CERN COMPASS experiment uses 100-280 GeV beams (muon, pion), and magnetic spectrometers and calorimeters, to measure the complete kinematics of pion-photon and pion-Pomeron reactions. The COMPASS experiment is currently under construction, and scheduled to begin data runs in 2001. We carry outsimulation studies to optimize the beam, detector, trigger, and hardware/software for achieving high statistics data with low systematic uncertainties in the hybrid meson component of this program. We will improve previous Primakoff Hybrid studies by three orders of magnitude. We implement special detectors and triggers for hybrid meson production reactions. We propose to prepare for these COMPASS pion beam hybrid studies by setting up with muon beam tests.

BES data on $J/\psi \to \gamma (K^{\pm} K_S^0 \pi^{\mp})$ are presented. There is a strong peak due to $\eta(1440)/\iota$, which is fitted with a Breit-Wigner amplitude with $s$-dependent widths for decays to $K^*K$, $\kappa K$, $\eta \pi\pi$ and $\rho\rho$; $\kappa$ refers to the $K\pi$ S-wave. At a $K\bar{K}\pi$ mass of $\sim 2040$ MeV, there is a second peak with width $\sim 400$ MeV; $J^P = 0^-$ is preferred over $1^+$ and $2^-$ respectively by 5.2 and 6.8 standard deviations. It is a possible candidate for a $0^-$ $s\bar sg$ hybrid partner of $\pi(1800)$.

The moment expressions for the boson resonances X with spin-parity J_X^{P_XC}=0^{++}, 1^{-+}, 1^{++}, and 2^{++} possibly produced in the process $J/\psi\to\rho X$, $X\to b_1(1235)\pi$, $b_1\to \omega \pi$ are given in terms of the generalized moment analysis method. The resonance with J_X^{P_XC}=1^{-+} can be distinguished from other resonances by means of these moments except for some rather special cases. The suggestion that the search for the hybrid with I^G(J^{PC})=1^-(1^{-+}) can be performed in the decay channel $J/\psi\to\rho\omega\pi\pi$ at upgraded BEPC/BES is presented.

A partial-wave analysis of the reaction pi - p(right-arrow) pi + pi - pi - p at 18 GeV/c has been performed on a data sample of 250 000 events obtained by Brookhaven experiment E852. The expected JPC = 1 + + a1(1260) , 2 + + a2(1320) , and 2 - + pi 2(1670) resonant states are clearly observed. The exotic JPC = 1 - + wave produced in the natural parity exchange processes shows distinct resonancelike phase motion at about 1.6 GeV/c2 in the rho pi channel. A mass-dependent fit results in a resonance mass of 1593 ± 8[sup +29][sub -47] MeV /c2 and a width of 168 ± 20[sup +150][sub -12] MeV /c2 .

The results of patial wave analysis of the omega pi- pi0 system, produced in the reaction pi- Be --> pi+ 2pi- 2pi0 Be at beam momentum of 37 GeV are presented. An indication of the resonant type structure with mass near 1.74 GeV and JpMetha=0-0+ in the omega rho- system was found. The decay branching ratio of a2(1320)- to omega pi- pi0 was measured. A wave with JpMetha=2+1+ shows a broad bump at M near 1.7 GeV. The decays pi2(1670)- --> omega rho- and a4(2040)- --> omega rho- were observed for the first time. The bump in the b1(1235)pi wave with exotic quantum numbers Jpc=1-+ at M near 1.7 GeV was observed.

The $\eta \pi^{-}$ system has been studied in the reaction $\pi^{-} p \to \eta \pi^{-} p$ at 18 GeV/c. A large asymmetry in the angular distribution is observed indicating interference between L-even and L-odd partial waves. The $a_{2}(1320)$ is observed in the $J^{PC}$ = $2^{++}$ wave, as is a broad enhancement between 1.2 and 1.6 GeV/c^{2} in the $J^{PC} = 1^{-+}$ wave. The observed phase difference between these waves shows that there is phase motion in addition to that due to $a_{2}(1320)$ decay. The data can be fitted by interference between the $a_{2}(1320)$ and an exotic $1^{-+}$ resonance with $M = (1370 \pm 16 {+50}\atop{-30}$) MeV/c^2 and $\Gamma =(385 \pm 40 {+65}\atop{-105}$) MeV/c^2.