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Register a new userPartial Wave Analysis at BESIII
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Beijiang Liu
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The BESIII experiment in Beijing takes data in $tau$-charm domain since 2009. For the moment the world largest samples of $J/psi$, $psi(3686)$, $psi(3770)$ and $psi(4040)$ data have been collected. Hadron spectroscopy is a unique way to access QCD, which is one of the most important physics goals of BESIII. Experimental search of new forms of hadrons and subsequent investigation of their properties would provide validation of and valuable input to the quantitative understanding of QCD. The key to success lies in high levels of precision during the measurement and high statistics in the recorded data set complemented with sophisticated analysis methods. Partial wave analysis (PWA) is a powerful tool to study the hadron spectroscopy, that allows one to extract the resonances spin-parity, mass, width and decay properties with high sensitivity and accuracy. In this poster, we present the working PWA framework of BESIII -- GPUPWA and the recent results of PWA of $J/psitogammaetaeta$. GPUPWA is a PWA framework for high statistics partial wave analyses harnessing the GPU parallel computing.
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At present very large data samples in the energy region of 2.0-4.6 GeV were accumulated by the BESIII detector, which is operated in the upgraded Beijing electron positron collider (BEPCII). These data samples provide an unprecedented opportunity in the study of light hadron spectra and charmonium(-like) decays. We review some experimental analyses related to isospin violations at BESIII in this proceeding, which can be classify into three categories: isospin violating processes with a $f_0(980)$ or $a^0_0(980)$ production, isospin violating processes with baryon final states, and isospin violating hadronic transitions in the charmonium system.
Based on $psi(3686)$ decays of 106 million, the 1.31 billion J/psi events and a data sample of $psi(3770)$ with $2.9~fb^{-1}$ integrated luminosity, many analyses are performed. Exclusively baryonic decays of the $psi(3770)$, the radiative transition $psi(3770)togammaeta_c(2S)$, the $psi(3770)$ transition to $chi_{cJ}$, isospin violation decay $chi_{c0,2}topi^0eta_c$, the $C-$parity violation decays $J/psitogammagamma,gammaphi$ are searched for, but no significant signals are observed, and upper limits are set for these decays. The decays of $psi(3770)togammachi_{c1}$ and $J/psitopi^0phi$ signals are observed. These measurements provide more information on the charmonium structure, and the isospin and $C$-parity violation in the charmonium decays.
A partial wave analysis of pbar-p -> eta-eta-pizero data from the Crystal Barrel experiment is made in terms of s-channel resonances. The decay channels a_0(980)-eta, f_0(1770)-pi and f_0(2105)-pi provide evidence for two I = 1 J^{PC} = 0^{-+} resonances. The first has mass M =2360 +- 25 MeV and width Gamma = 300^{+100}_{-50} MeV, and the second M =2070 pm 35 MeV, Gamma = 310^{+100}_{-50} MeV. There is also evidence for a J^{PC} = 2^{-+} state with M = 2005 +- 15 MeV and Gamma = 200 +- 40 MeV, decaying strongly to a_0(980)-pi.
Since few years, a new family of exotic states has been appearing above the open-heavy meson thresholds: the so-called $XYZ$ states. BESIII at the BEPCII $e^+e^-$ collider plays a unique role in the study of those particles in the charmonium sector. Changing the beam energy, BESIII can collect large data samples by means of scans of the resonant region, accessing directly to all vector states. As part of a larger upgrade program, BESIII has planned to increase the center of mass energy to reach $4.7$ GeV: this will allow BESIII to investigate the nature of the $Y(4660)$, that was at first observed by Belle and BaBar after Initial State Radiation only in $pipi psi(2s)$ and $Lambda_c$ $bar{Lambda}_c$ final states. The relative branching ratio seems to point toward a baryonium interpretation of the resonance, as expected in Rossi-Veneziano model. BESIII can directly measure the cross sections around the expected peak position and verify this prediction. In this presentation, the status of the $XYZ$ searches at BESIII will be presented, with a focus also on the plans for the newest data taking and for the $Y(4660)$ studies.
A combined analysis is reported of 3pizero, pizero-eta and pizero-etaprime data in the mass range 1960 to 2410 MeV. This analysis is made consistent also with eta-eta-pizero data, reported separately. The analysis requires s-channel resonances with a spectrum close to that published earlier for C = +1 states with I = 0; masses for I=1 states are lower on average by 20 MeV. Two alternative solutions are found, differing only for J^P = 2^+ and 4^+ states by small amounts in masses and widths. Both 3pizero and eta-pizero data prefer one of these two solutions. For this preferred solution, observed states have J^PC, masses and widths (M,Gamma) in MeV as follows: 4^-+: (2250+-15, 215+-25), 4^++: (2255+-40, 330 ^{+110}_{-50}) and (2005 ^{+25}_{-45}, 180+-30), 3^++: (2275+-35, 350 ^{+100}_{-50}) and (2031+-12, 150 pm 18), 2^-+: (2245+-60, 320 ^{+100}_{-40}) and (2005+-15, 200+-40, 2^++: (2255+-20, 230+-15), (2175+-40, 310^{+90}_{-45}) and (2030+-20, 205+-30), and 1^++: (2270 ^{+55}_{-40}, 305 ^{+70}_{-35}). There are indications of further 2^-+, 2^++ and 1^++ contributions just below the available mass range, and also a 0^++ state at ~2025 MeV.
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