Search

The VES experiment has collected high statistics of exclusive reactions with three pions in the final state: $ \pi^-\pi^-\pi^+ $ (about $43\cdot10^6$ events) and $\pi^-\pi^0\pi^0 $ (about $20\cdot10^6$ events). The $ 3\pi $ systems are produced by impinging of 28.9 GeV $\pi^-$ beam on the beryllium target. The dominant production mechanism is the Pomeron exchange between incoming beam pion and the target. At the very low momentum transfer squared $t'$ the data clearly shows coherent diffractive production on the whole nucleus which is replaced by incoherent process on the individual nucleons at higher $ 0.05 < t' < 1 $GeV$^2$. The mass-independent partial wave analysis is performed dividing data into the bins of $ m(3\pi) $ and $t'$. The comparison of results with two models of PWA: using formalism of unlimited-rank density matrix and, using rank=1 is presented. The predicted isospin relations (assuming $I=1$ of $3\pi$ systems) and observed ones for intensities in $\pi^-\pi^-\pi^+ $ and $\pi^-\pi^0\pi^0$ are shown.

The isospin violating decay $f_1(1285)\to\pi^+\pi^-\pi^0$ has been studied at VES facility. This study is based at the statistics acquired in $\pi^- Be$ interactions at 27, 36.6 and 41 GeV/c in diffractive reaction $\pi^- N \to (f_1 \pi^-) N$. The $f_1(1285) \to \pi^+\pi^-\pi^0$ decay is observed. The ratio of decay probabilities $BR(f_1(1285) \to \pi^+\pi^-\pi^0)$ to $BR(f_1(1285) \to \eta \pi^+\pi^-) \cdot BR(\eta \to \gamma\gamma)$ is $\sim\:1.4%$.

The status of spin-exotic mesons is reviewed. There is now compelling evidence for at least three π1 states between one and two GeV. Preliminary results from the reaction π−p → π+π+π−π−π0p show structure in the exotic waves corresponding to IGJPC = 0−2+−.

This Letter reports results from the partial wave analysis of the π−π−π+η final state in π−p collisions at 18 GeV /c . Strong evidence is observed for production of two mesons with exotic quantum numbers of spin, parity and charge conjugation, JPC=1−+ in the decay channel f1(1285)π−. The mass M=1709±24±41 MeV /c 2 and width Γ=403±80±115 MeV /c 2 of the first state are consistent with the parameters of the previously observed π1(1600). The second resonance with mass M=2001±30±92 MeV /c 2 and width Γ=333±52±49 MeV /c 2 agrees very well with predictions from theoretical models. In addition, the presence of π2(1900) is confirmed with mass M=2003±88±148 MeV /c 2 and width Γ=306±132±121 MeV /c 2 and a new state, a1(2096), is observed with mass M=2096±17±121 MeV /c 2 and width Γ=451±41±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.

A new measurement of the reaction pi- p -> K+ K- pi0 n has been made at a beam energy of 18 GeV. A partial wave analysis of the K+ K- pi0 system shows evidence for three pseudoscalar resonances, eta(1295), eta(1416), and eta(1485), as well as two axial vectors, f1(1285), and f1(1420). Their observed masses, widths and decay properties are reported. No signal was observed for C(1480), an IG J{PC} = 1+ 1{--} state previously reported in phi pi0 decay., Comment: 7 pages, 6 figs, to be submitted to Phys. Lett

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

Results are presented on a partial wave analysis of the Omega Eta final state produced in Pi- Proton interactions at 18 GeVc where Omega -> Pi+ Pi- Pi0, Pi0 -> 2 Gammas, and Eta -> 2 Gammas. We observe the previously unreported decay mode Omega(1650) -> Omega Eta and a new 1(+-) meson state h1(1595) with a mass M=1594(15)(+10)(-60) MeV/c^2 and a width Gamma=384(60)(+70)(-100) MeV/c^2. The h1(1595) state exhibits resonant-like phase motion relative to the Omega(1650).

New measurements of peripheral meson production are presented. The data confirm the existence of exotic mesons at 1.4 and 1.6 GeV/c2. The latter state dominates the eta'pi- decay spectrum. The data on eta pi+pi-pi- decay show large strength in several exotic (Jpc = 1- +) waves as well.

Brookhaven Experiment E852 is an experiment in meson spectroscopy configured to detect final states interactions of π − p collisions in search for meson states incompatible with the constituent quark model. A description of the experimental apparatus and a general overview of the latest results is given.

The results of a partial wave analysis of 3π system produced in the reaction π − A → π + π − π − A at the momentum of 36.6 GeV/c on beryllium target are presented. Resonant signals from a ′ 1 (1750), a 3 (1860), a 4 (2050) are observed in different channels. Small bump at M ≈ 1.6GeV in the exotic wave J PC M η = 1 −+ 1 + is seen. The combined analysis of VES data on this wave in η′π, b 1 (1235) π and ϱπ channels points to the existence of a hybrid meson with M ≈ 1.6 GeV.

A partial-wave analysis of the reaction ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}p$ at $18\mathrm{GeV}/c$ has been performed on a data sample of 250 000 events obtained by Brookhaven experiment E852. The expected ${J}^{\mathrm{PC}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1}^{++}{a}_{1}(1260)$, ${2}^{++}{a}_{2}(1320)$, and ${2}^{\ensuremath{-}+}{\ensuremath{\pi}}_{2}(1670)$ resonant states are clearly observed. The exotic ${J}^{\mathrm{PC}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1}^{\ensuremath{-}+}$ wave produced in the natural parity exchange processes shows distinct resonancelike phase motion at about $1.6\mathrm{GeV}{/c}^{2}$ in the $\ensuremath{\rho}\ensuremath{\pi}$ channel. A mass-dependent fit results in a resonance mass of $1593\ifmmode\pm\else\textpm\fi{}{8}_{\ensuremath{-}47}^{+29}\mathrm{MeV}{/c}^{2}$ and a width of $168\ifmmode\pm\else\textpm\fi{}{20}_{\ensuremath{-}12}^{+150}\mathrm{MeV}{/c}^{2}$.

The {eta}{pi}{sup {minus}} system has been studied in the reaction {pi}{sup {minus}}p{r_arrow}{eta}{pi}{sup {minus}}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{sub 2}(1320) is observed in the J{sup PC}=2{sup ++} wave, as is a broad enhancement between 1.2 and 1.6 GeV/c{sup 2} in the 1{sup {minus}+} wave. The observed phase difference between these waves shows that there is phase motion in addition to that due to a{sub 2}(1320) decay. The data can be fitted by interference between the a{sub 2}(1320) and an exotic 1{sup {minus}+} resonance with M=(1370{plus_minus}16{sup +50}{sub {minus}30}) MeV/c{sup 2} and {Gamma}=(385{plus_minus}40 {sup +65}{sub {minus}105}) MeV/c{sup 2} . {copyright} {ital 1997} {ital The American Physical Society}

A partial wave analysis (PWA) of the $\pi^- \pi^- \pi^+$ and $\pi^- \pi^0 \pi^0$ systems produced in the reaction $\pi^- p \to (3\pi)^-p$ at 18 GeV/$c$ was carried out using an \emph{isobar} model assumption. This analysis is based on 3.0M $\pi^- \pi^0 \pi^0$ events and 2.6M $\pi^- \pi^-\pi^+$ events and shows production of the $a_1(1260)$, $a_2(1320)$, $\pi_2(1670)$ and $a_4(2040)$ resonances. Results of detailed studies of the stability of partial wave fits are presented. An earlier analysis of 250K $\pi^- \pi^- \pi^+$ events from the same experiment showed possible evidence for a $J^{PC}=1^{-+}$ exotic meson with a mass of $\sim$1.6 GeV/$c^2$ decaying into $\rho \pi$. In this analysis of a higher statistics sample of the $(3\pi)^-$ system in two charged modes we find no evidence of an exotic meson.

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 $\pi_{2}(1970)$.

A partial wave analysis of the ${\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ system produced in the charge exchange reaction ${\ensuremath{\pi}}^{\ensuremath{-}}\stackrel{\ensuremath{\rightarrow}}{p}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}n$ at an incident momentum of 18.3 $\mathrm{GeV}/c$ is presented as a function of the ${\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ invariant mass ${m}_{{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}}$ and momentum transfer squared $|t|$ from the incident ${\ensuremath{\pi}}^{\ensuremath{-}}$ to the outgoing ${\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ system. For small values of $|t|,$ the S-wave intensity shows a broad enhancement at low ${m}_{{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}}$ with a sharp dip in the vicinity of the ${f}_{0}(980).$ A dip is also observed in the vicinity of the ${f}_{0}(1500).$ There is a rapid variation of the S to ${D}_{0}$ relative phase difference in these mass regions. For large values of $|t|,$ the ${f}_{0}(980)$ appears as a bump. The ${f}_{2}(1270),$ observed in D waves, is produced dominantly by $\ensuremath{\pi}$ exchange at low values of $|t|$ and ${a}_{2}$ exchange at higher values of $|t|.$

A partial-wave analysis of 9082 {eta}{pi}{sup +}{pi}{sup -}n events produced in the reaction {pi}{sup -}p{yields}{eta}{pi}{sup +}{pi}{sup -}n at 18.3 GeV/c has been carried out using data from experiment 852 at Brookhaven National Laboratory. The data are dominated by J{sup PC}=0{sup -+} partial waves consistent with observation of the {eta}(1295) and the {eta}(1440). The mass and width of the {eta}(1295) were determined to be 1282{+-}5 MeV and 66{+-}13 MeV, respectively, while the {eta}(1440) was observed with a mass of 1404{+-}6 MeV and a width of 80{+-}21 MeV. Other partial waves of importance include the 1{sup ++} and the 1{sup +-} waves. Results of the partial wave analysis are combined with results of other experiments to estimate f{sub 1}(1285) branching fractions. These values are considerably different from current values determined without the aid of amplitude analyses. (c) 2000 The American Physical Society.

Details of the analysis of the $\ensuremath{\eta}{\ensuremath{\pi}}^{\ensuremath{-}}$ system studied in the reaction ${\ensuremath{\pi}}^{\ensuremath{-}}\stackrel{\ensuremath{\rightarrow}}{p}\ensuremath{\eta}{\ensuremath{\pi}}^{\ensuremath{-}}p$ at $18\mathrm{GeV}/c$ are given. Separate analyses for the 2\ensuremath{\gamma} and ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ decay modes of the \ensuremath{\eta} are presented. An amplitude analysis of the data indicates the presence of interference between the ${a}_{2}^{\ensuremath{-}}(1320)$ and a ${J}^{\mathrm{PC}}{=1}^{\ensuremath{-}+}$ wave between 1.2 and $1.6 \mathrm{GeV}{/c}^{2}.$ The phase difference between these waves shows a phase motion not attributable solely to the ${a}_{2}^{\ensuremath{-}}(1320).$ The data can be fitted by interference between the ${a}_{2}^{\ensuremath{-}}(1320)$ and an exotic ${1}^{\ensuremath{-}+}$ resonance with $M=(1370\ifmmode\pm\else\textpm\fi{}{16}_{\ensuremath{-}30}^{+50})\mathrm{MeV}{/c}^{2}$ and $\ensuremath{\Gamma}=(385\ifmmode\pm\else\textpm\fi{}{40}_{\ensuremath{-}105}^{+65})\mathrm{MeV}{/c}^{2}.$ Our results are compared with those of other experiments.

Events of the type {pi}{sup {minus}}p{r_arrow}n{eta}{pi}{sup +}{pi}{sup {minus}} and {pi}{sup {minus}}p{r_arrow}n{eta}{pi}{sup 0} at 18thinspGeV/c are analyzed. The mass and width of the neutral and charged a{sub 0}(980) were determined. The neutral a{sub 0} is found to have a mass of (0.991{plus_minus}0.0025)thinspGeV/c{sup 2} and a width of (0.069{plus_minus}0.011)thinspGeV/c{sup 2}. A partial wave analysis technique yields (0.9983{plus_minus}0.0040) and (0.072{plus_minus}0.010)thinspGeV/c{sup 2} for the mass and width of the charged a{sub 0}. {copyright} {ital 1998} {ital The American Physical Society}