The charge-exchange reaction π ^- Be→A ω (782)ϕ (1020) with ω→π ^+π ^-π ^0 and ϕ→ K^+K^- is studied with the upgraded VES facility (U-70, Protvino) using a 29 GeV pion beam. The distribution of the ωϕ invariant mass shows a near-threshold enhancement. Partial-wave analysis reveals that an isoscalar scalar state with J^PC=0^++ dominates in this mass region. Considering the observed signal as an f_0 resonance, and using the one-pion-exchange model, the product of the branching fractions into two channels Br(f_0→ππ ) Br(f_0→ωϕ ) is measured. Based on this value, a large partial width is found for the radiative decay of J/ψ into this state, which suggests a significant glueball component. The result is discussed under alternative assumptions concerning an identification of the observed signal as f_0(1710) or f_0(1770) .

The charge-exchange reaction π^-p → n ω(783)ϕ(1020), ω→π^+π^-π^0, ϕ→ K^+K^- is studied with the upgraded VES facility (U-70, Protvino) in the interaction of a 29 GeV pion beam with a beryllium target. The distribution over the invariant mass of the system M_ωϕ shows a near-threshold signal. A partial wave analysis reveals that the scalar state (J^PC=0^++) dominates in this mass region. The observed signal can be described with a contribution of the known resonance f_0(1710). Using OPE approximation for the reaction π^-p → n f_0(1710) the product of branching fractions is found to be: Br(f_0(1710)→ππ)· Br(f_0(1710)→ωϕ) = (4.8 ± 1.2) · 10^-3.

A complex of the new electromagnetic calorimeter (ECAL-2) for the VES setup is described. It is composed of 1592 “shashlik” type counters consisting of a set of lead−scintillator plates, high-voltage supplies based on cascade voltage multipliers for FEU-84 photomultiplier tubes, an LED-based monitoring system, a slow control system, and a pulse-height analysis system. The procedures of ECAL-2 calibration and online monitoring are described.

Preliminary results obtained by studying K − π −, K − π − π 0, and K − π − η systems in the VES experiment are presented. No statistically significant signals from possible resonances were observed in two- and three-particle mass spectra of doubly charged (sub)systems.

Studies of various processes relevant to light scalar mesons at the VES facility are reviewed.

The measurements of the Collins and Sivers asymmetries of identified hadrons produced in deep-inelastic scattering of 160 GeV/c muons on a transversely polarised 6LiD target at COMPASS are presented. The results for charged pions and charged and neutral kaons correspond to all data available, which were collected from 2002 to 2004. For all final state particles both the Collins and Sivers asymmetries turn out to be small, compatible with zero within the statistical errors, in line with the previously published results for not identified charged hadrons, and with the expected cancellation between the u- and d-quark contributions.

The semi-inclusive difference asymmetry A(h+-h-) for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002-2004 using a 160 GeV polarised muon beam scattered off a large polarised (LiD)-Li-6 target in the kinematic range 0.006 < x < 0.7 and 1 < Q(2) < 100 (GeV/C)(2). In leading order QCD (LO) the deuteron asymmetry A(h+-h-) measures the valence quark polarisation and provides an evaluation of the first moment of Delta u(v) + Delta d(v) which is found to be equal to 0.40 +/- 0.07(stat.) +/- 0.06(syst.) over the measured range of x at Q(2) = 10 (GeV/C)(2). When combined with the first moment of g(1)(d) previously measured on the same data, this result favours a non-symmetric polarisation of light quarks Delta(u) over bar = -Delta(d) over bar at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario Delta(u) over bar = Delta(d) over bar = Delta(s) over bar = Delta s. (c) 2008 Elsevier B.V. All rights reserved.

Details of the analysis of the ηπ system studied in the reaction πp → ηπp at 18 GeV/c are given. Separate analyses for the 2γ and π+π−π0 decay modes of the η are presented. An amplitude analysis of the data indicates the presence of interference between the a−2 (1320) and a J PC = 1−+ wave between 1.2 and 1.6 GeV/c2. The phase difference between these waves shows phase motion not attributable solely to the a−2 (1320). The data can be fitted by interference between the a−2 (1320) and an exotic 1−+ resonance with M = (1370 ±16 +50 −30 ) MeV/c 2 and Γ = (385 ±40 +65 −105 ) MeV/c 2. Our results are compared with those of other experiments. Typeset using REVTEX

The ηπ system has been studied in the reaction πp → ηπp at 18 GeV/c. A large asymmetry in the angular distribution is observed indicating interference between L-even and L-odd partial waves. The a2(1320) is observed in the J = 2 wave, as is a broad enhancement between 1.2 and 1.6 GeV/c in the 1 wave. The observed phase difference between these waves shows that there is phase motion in addition to that due to a2(1320) decay. The data can be fitted by interference between the a2(1320) and an exotic 1 −+ resonance with M = (1370 ±16 +50 −30 ) MeV/c and Γ = (385 ±40 +65 −105 ) MeV/c. 13.60.Le, 13.85.Fb, 14.40.Cs Typeset using REVTEX 2 The question of whether or not hadrons outside the scope of the constituent quark model exist is one whose answer speaks directly to the fullness of our understanding of quantum chromodynamics (QCD) [1]. However, non-qq mesons (or exotic mesons) have proven difficult to distinguish from the many conventional qq states which populate the various mesonic spectra. For this reason, much attention has been focused on those states with manifestly exotic J quantum numbers. A qq meson with orbital angular momentum l and total spin s must have P = (−1) and C = (−1). Thus a resonance with J = 0, 0, 1, 2, ... must be exotic. Such a state could be a gluonic excitation such as a hybrid (qqg) or glueball (2g, 3g, ...), or a multiquark (qqqq) state. In a relative P wave (L=1), the ηπ system has J = 1. Having isospin I=1, it could not be a glueball, but it could be a hybrid or a multiquark state. Production and decay properties of exotic states have been predicted using several models [2–8]. A calculation based upon the MIT bag model predicts [3] that a 1 hybrid (qqg) will have a mass near 1.4 GeV/c. On the other hand, the flux-tube model [4,5] predicts the mass of the lowest-lying hybrid state to be around 1.8 GeV/c. Characteristics of bag-model S-wave multiquark states (which would have J = 0, 1, or 2) have been predicted [7] but those for a 1 state have not. Finally, recent lattice calculations [8] of the 1 hybrid meson estimate its mass to be in the range of 1.7 to 2.1 GeV. The ηπ system has been studied in several recent experiments, with apparently inconsistent results. Alde et al. [9], in a study of πp interactions at 100 GeV/c at CERN (the GAMS experiment), claimed to observe a 1 state in the ηπ system at 1.4 GeV/c produced via unnatural parity exchange (the P0 partial wave—the naming convention is discussed below) [10]. Aoyagi et al. [11], in a πp experiment at 6.3 GeV/c at KEK, observed a rather narrow enhancement in the ηπ system at 1.3 GeV/c in the natural parity exchange 1 spectrum (P+). Beladidze et al. [12], in the VES experiment at IHEP, (π N interactions at 37 GeV/c) also reported a P+ signal in the ηπ − state, but their signal was broader and had a significantly different phase variation from that of the KEK experiment. While the 3 phase difference between the P+ and D+ waves was independent of ηπ mass in the KEK analysis, that phase difference did show significant mass dependence in the VES analysis. (Since the phase variation for the D+ wave follows a classic Breit-Wigner pattern for the a2(1320) meson, the phase difference between these waves can determine the phase variation of the unknown P+ wave.) Here we study the ηπ system in the reaction πp → ηπp at 18 GeV/c. Our data sample was collected in the first data run of E852 at the AGS at Brookhaven National Laboratory with the Multi-Particle Spectrometer (MPS) [13] using a liquid hydrogen target. The MPS, which was equipped with six drift-chamber modules [14] and three proportional wire chambers, was augmented by: a four-layer cylindrical drift chamber surrounding the target [15]; a soft-photon detector consisting of 198 blocks of thallium-doped cesium iodide [16] also surrounding the target; a window-frame lead-scintillator photon-veto counter; a large drift chamber; and a 3045-element lead-glass detector (LGD) [17] downstream of the MPS. Further details are given elsewhere [18]. A total of 47 million triggers which required one forward-going charged track, one recoil charged track, and an LGD trigger-processor signal enhancing high electromagnetic effective mass was recorded. Of these, 47,200 events were reconstructed which were consistent with the ηπp (η → 2γ) final state. These events satisfied topological and fiducial volume cuts, as well as energy/momentum conservation for production and for the η → 2γ decay with a confidence level > 10% [19]. The 2γ mass resolution at the η mass is σ = 0.03 GeV/c. The a2(1320) is the dominant feature of the ηπ − mass spectrum shown in Fig. 1a. Background has been estimated using side bands in both the 2-γ mass distribution and the missing-mass distribution, thus taking into account background from non-η sources as well as from sources due to production of other final states. The background level is approximately 7% at 1.2 GeV/c, falling to 1% at 1.3 GeV/c. The acceptance-corrected distribution of |t| = |t| − |t|min, where t is the the fourmomentum-transfer, is shown for |t| > 0.08(GeV/c) in Fig. 1b. (Our acceptance is quite low below 0.08 (GeV/c) due to a trigger requirement.) The shape of this distribution is con4 sistent with previous experiments and has been shown to be consistent with natural-parity exchange production in Regge-pole phenomenology [20,21]. The acceptance-corrected distribution of cos θ, the cosine of the angle between the η and the beam track in the Gottfried-Jackson frame [22] of the ηπ system, is shown in Fig. 2a for 1.22 < M(ηπ) < 1.42 GeV/c. There is a forward-backward asymmetry in cos θ. The asymmetry for | cos θ| < 0.8 is plotted as a function of ηπ mass in Fig. 2b. The asymmetry is large, statistically significant and mass dependent. Since the presence of only even values of L would yield a symmetric distribution in cos θ, the observed asymmetry requires that odd-L partial waves be present to describe the data. A partial-wave analysis (PWA) [23,24] based on the extended maximum likelihood method has been used to study the spin-parity structure of the ηπ system. The partial waves are parameterized in terms of the quantum numbers J as well as m, the absolute value of the angular momentum projection, and the reflectivity ǫ (which is positive (negative) for natural (unnatural) parity exchange [25]). In our naming convention, a letter indicates the angular momentum of the partial wave in standard spectroscopic notation, while a subscript of 0 means m = 0, ǫ = −1, and a subscript of +(−) means m = 1, ǫ = +1(−1). Thus, S0 denotes the partial wave having J m = 00, while P− signifies 11, D+ means 2 1, and so on. We consider partial waves with m ≤ 1, and we assume that the production spin-density matrix has rank one. The experimental acceptance is determined by a Monte Carlo method. Peripherallyproduced events are generated [26] with isotropic angular distributions in the GottfriedJackson frame. After adding detector simulation [27], the Monte Carlo event sample is subjected to the same event-selection cuts and run through the same analysis as the data. The experimental acceptance is then incorporated into the PWA by using these events to calculate normalization integrals (see ref. [23]). Goodness-of-fit is determined by calculation of a χ from comparison of the experimental moments with those predicted by the results of the PWA fit. A systematic study has been performed to determine the effect on goodness-of-fit of adding and subtracting partial waves 5 of J ≤ 2 and m ≤ 1. All such waves have been included in the final fit. We have also performed fits including partial waves with J = 3 and J = 4. Contributions from these partial waves are found to be insignificant for M(ηπ) < 1.8 GeV/c. Thus, PWA fits shown or referred to in this letter include all partial waves with J ≤ 2 and m ≤ 1 (i.e. S0, P0, P−, D0, D−, P+, and D+). The background described above was included as a non-interfering, isotropic term of fixed magnitude. The results of the PWA fit in 40 MeV/c bins for 0.98 < M(ηπ) < 1.82 GeV/c and 0.10 < |t| < 0.95 GeV are shown in Fig. 3a-c. Here, the acceptance-corrected numbers of events predicted by the PWA fit for the D+ and P+ waves and their phase difference ∆Φ(D+ − P+) are shown as a function of M(ηπ ). There are eight ambiguous solutions in the fit [24,28,29], each of which leads to the same angular distribution. We show the range of fitted values for these ambiguous solutions in the vertical rectangular bar at each mass bin, and the maximum extent of their errors is shown as the error bar. The a2(1320) is clearly observed in the D+ partial wave (Fig. 3a). A broad peak is seen in the P+ wave at about 1.4 GeV/c (Fig. 3b). ∆Φ(D+ − P+) increases through the a2(1320) region, and then decreases above about 1.5 GeV/c (Fig. 3c). The intensities for the waves of negative reflectivity (not shown) are generally small and are all consistent with zero above about 1.3 GeV/c. These results are quite consistent with the VES results [12]. In particular, the shape of the phase difference is virtually identical to that reported by VES. (The magnitude of the phase difference is shifted by about 20 relative to that of VES.) Consistency checks and tests of the data have been carried out to determine whether the observation of the structure in the P+ wave could be an artifact due to assumptions made in the analysis or to acceptance problems. These include: fitting the data in restricted ranges of the decay angle; inclusion of higher angular momentum states; fitting the data with various t cuts; fitting the data using different parametrizations of the background; making cuts on other kinematic variables such as the πp or the ηp effective masses; and fitting data using events with η → πππ decays (with rather different acceptance from the 2γ events). The results are very stable and, in particular, the behavior of ∆Φ(D+ − P+) does not change in 6 any of these checks. Fits were also carri

New high precision measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarised 6LiD target are presented. The data were taken in 2003 and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. Both the Collins and Sivers asymmetries turn out to be compatible with zero, within the present statistical errors, which are more than a factor of 2 smaller than those of the published COMPASS results from the 2002 data. The final results from the 2002, 2003 and 2004 runs are compared with naive expectations and with existing model calculations.

We present a precise measurement of the deuteron longitudinal spin asymmetry A_1^d and of the deuteron spin-dependent structure function g_1^d at Q^2 < 1 GeV^2 and 4*10^-5 < x < 2.5*10^-2 based on the data collected by the COMPASS experiment at CERN during the years 2002 and 2003. The statistical precision is tenfold better than that of the previous measurement in this region. The measured A_1^d and g_1^d are found to be consistent with zero in the whole range of x.

The longitudinal double spin asymmetry A_1^rho for exclusive leptoproduction of rho^0 mesons, mu + N -> mu + N + rho, is studied using the COMPASS 2002 and 2003 data. The measured reaction is incoherent exclusive rho^0 production on polarised deuterons. The Q^2 and x dependence of A_1^rho is presented in a wide kinematical range: 3x10^-3 < Q^2 < 7 (GeV/c)^2 and 5x10^-5 < x < 0.05. The presented results are the first measurements of A_1^rho at small Q2 (Q2 < 0.1 (GeV/c)^2) and small x (x < 3x10^-3). The asymmetry is in general compatible with zero in the whole kinematical range.