Observation of exotic meson production in the reaction π−p→η′π−p \pi^{-} p \to \eta^{\prime} \pi^- p at 18 GeV/c

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.Comment: 5 pages with 4 figure

A spectroscopic analysis of the chemically peculiar star HD207561

In this paper we present a high-resolution spectroscopic analysis of the chemically peculiar star HD207561. During a survey programme to search for new roAp stars in the Northern hemisphere, Joshi et al. (2006) observed significant photometric variability on two consecutive nights in the year 2000. The amplitude spectra of the light curves obtained on these two nights showed oscillations with a frequency of 2.79 mHz [P~6-min]. However, subsequent follow-up observations could not confirm any rapid variability. In order to determine the spectroscopic nature of HD207561, high-resolution spectroscopic and spectro-polarimetric observations were carried out. A reasonable fit of the calculated Hbeta line profile to the observed one yields the effective temperature (Teff) and surface gravity (log g) as 7300 K and 3.7 dex, respectively. The derived projected rotational velocity (vsin i) for HD207561 is 74 km/sec indicative of a relatively fast rotator. The position of HD207561 in the H-R diagram implies that this is slightly evolved from the main-sequence and located well within the delta-Scuti instability strip. The abundance analysis indicates the star has slight under-abundances of Ca and Sc and mild over-abundances of iron-peak elements. The spectro-polarimetric study of HD207561 shows that the effective magnetic field is within the observational error of 100 gauss (G). The spectroscopic analysis revealed that the star has most of the characteristics similar to an Am star, rather than an Ap star, and that it lies in the delta-Scuti instability strip; hence roAp pulsations are not expected in HD207561, but low-overtone modes might be excited.Comment: 8 pages, 7 figures, 3 tables. Accepted for pubblication in MNRA

A partial wave analysis of the π0π0\pi ^0\pi ^0 system produced in π−p\pi ^-p charge exchange collisions

A partial wave analysis of the of the $\pi ^0\pi ^0$ system produced in the charge exchange reaction: $\pi ^-p\to \pi ^0\pi ^0n$ at an incident momentum of $18.3 GeV/c$ is presented as a function of ${\pi ^0\pi ^0}$ invariant mass, $m_{\pi^0\pi^0}$, and momentum transfer squared, $| {t} |$, from the incident $\pi^-$ to the outgoing ${\pi ^0\pi ^0}$ system.Comment: 24 pages total,8 pages text, 14 figures, 1 table. Submitted to Phys Rev

Partial-wave analysis of the eta pi+ pi- system produced in the reaction pi-p --> eta pi+ pi- n at 18 GeV/c

A partial-wave analysis of 9082 eta pi+ pi- n events produced in the reaction pi- p --> eta pi+ pi- 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^{PC} = 0^{-+} 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 width of 80 +- 21 MeV. Other partial waves of importance include the 1++ and the 1+- waves. Results of the partial wave analysis are combined with results of other experiments to estimate f1(1285) branching fractions. These values are considerably different from current values determined without the aid of amplitude analyses.Comment: 22 pages, 8 figure

A Study of the \eta \pi^{0} Spectrum and Search for a J^{PC} = 1^{-+} Exotic Meson

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$/c^2$.Comment: 19 pages, 29 figures, to appear in Phys. Rev.

Evidence for Exotic J^{PC}=1^{-+} Meson Production in the Reaction pi- p --> eta pi- p at 18 GeV/c

Details of the analysis of the eta pi- system studied in the reaction pi^{-} p --> eta pi^{-} p at 18 GeV/c are given. Separate analyses for the 2 gamma and pi+ pi- pi0 decay modes of the eta 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/c^2. 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 Gamma = 385 +- 40 +65 -105 MeV/c^2. Our results are compared with those of other experiments.Comment: 50 pages of text and 34 figure

First Measurement of Chiral Dynamics in \pi^- \gamma -> \pi^- \pi^- \pi^+

The COMPASS collaboration at CERN has investigated the \pi^- \gamma -> \pi^- \pi^- \pi^+ reaction at center-of-momentum energy below five pion masses, sqrt(s) < 5 m(\pi), embedded in the Primakoff reaction of 190 GeV pions impinging on a lead target. Exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, t' < 0.001 (GeV/c)^2. Using partial-wave analysis techniques, the scattering intensity of Coulomb production described in terms of chiral dynamics and its dependence on the 3\pi-invariant mass m(3\pi) = sqrt(s) were extracted. The absolute cross section was determined in seven bins of $\sqrt{s}$ with an overall precision of 20%. At leading order, the result is found to be in good agreement with the prediction of chiral perturbation theory over the whole energy range investigated.Comment: 10 pages, 5 figure

Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised proton

Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaons produced in semi-inclusive deep-inelastic scattering of high energy muons off transversely polarised protons are presented. The results were obtained using all the available COMPASS proton data, which were taken in the years 2007 and 2010. The Collins asymmetries exhibit in the valence region a non-zero signal for pions and there are hints of non-zero signal also for kaons. The Sivers asymmetries are found to be positive for positive pions and kaons and compatible with zero otherwise.Comment: 15 pages, 13 figures and 1 tabl

Measurement of the Longitudinal Spin Transfer to Lambda and Anti-Lambda Hyperons in Polarised Muon DIS

The longitudinal polarisation transfer from muons to lambda and anti-lambda hyperons, D_LL, has been studied in deep inelastic scattering off an unpolarised isoscalar target at the COMPASS experiment at CERN. The spin transfers to lambda and anti-lambda produced in the current fragmentation region exhibit different behaviours as a function of x and xF . The measured x and xF dependences of D^lambda_LL are compatible with zero, while D^anti-lambda_LL tends to increase with xF, reaching values of 0.4 - 0.5. The resulting average values are D^lambda_LL = -0.012 +- 0.047 +- 0.024 and D^anti-lambda_LL = 0.249 +- 0.056 +- 0.049. These results are discussed in the frame of recent model calculations.Comment: 13 pages, 7 figure