# ${{\boldsymbol X}{(1835)}}$ MASS INSPIRE search

VALUE (MeV) EVTS DOCUMENT ID TECN  COMMENT
$\bf{ 1826.5 {}^{+13.0}_{-3.4}}$ OUR AVERAGE
$1825.3$ $\pm2.4$ ${}^{+17.3}_{-2.4}$ 1
 2016 J
BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \eta}^{\,'}}$
$1844$ $\pm9$ ${}^{+16}_{-25}$
 2015 T
BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit K}_S^0}$ ${{\mathit K}_S^0}$ ${{\mathit \eta}}$
• • • We do not use the following data for averages, fits, limits, etc. • • •
$1839$ $\pm26$ $\pm26$ 2
 2018 I
BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \gamma}}{{\mathit \phi}{(1020)}}$
$1909.5$ $\pm15.9$ ${}^{+9.4}_{-27.5}$ 3
 2016 J
BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \eta}^{\,'}}$
$1842.2$ $\pm4.2$ ${}^{+7.1}_{-2.6}$ 0.6k
 2013 U
BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}$3 ( ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$)
$1832$ ${}^{+19}_{-5}$ $\pm26$ 4
 2012 D
BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit p}}{{\overline{\mathit p}}}$
$1836.5$ $\pm3.0$ ${}^{+5.6}_{-2.1}$ 4265 5
 2011 C
BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \eta}^{\,'}}$
$1877.3$ $\pm6.3$ ${}^{+3.4}_{-7.4}$ 6
 2011 J
BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \omega}}$ ( ${{\mathit \eta}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ )
$1837$ ${}^{+10}_{-12}$ ${}^{+9}_{-7}$ 231 7, 8
 2010
CLEO ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit p}}{{\overline{\mathit p}}}$
$1833.7$ $\pm6.1$ $\pm2.7$ 264
 2005 R
BES2 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \eta}^{\,'}}$
$1831$ $\pm7$ 9, 8
 2005 R
BES2 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit p}}{{\overline{\mathit p}}}$
$1859$ ${}^{+3}_{-10}$ ${}^{+5}_{-25}$ 8
 2003 F
BES2 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit p}}{{\overline{\mathit p}}}$
1  From a fit of the measured ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \eta}^{\,'}}$ lineshape that accounts for the abrupt distortion observed at the ${{\mathit p}}{{\overline{\mathit p}}}$ threshold through interference with a second previously unseen narrow resonance near 1870 MeV. The fit uses Breit-Wigner functions for the signal shapes and includes known backgrounds and contributors.
2  From a fit to ${{\mathit \gamma}}{{\mathit \phi}}$ invariant mass. Angular analysis consistent with $\mathit J{}^{PC} = 0{}^{-+}$. Other $\mathit J{}^{PC}$ not excluded.
3  Pole mass from a fit of the measured ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \eta}^{\,'}}$ lineshape to a Flatte formula that accounts for the abrupt distortion observed at the ${{\mathit p}}{{\overline{\mathit p}}}$ threshold; the fit also includes known backgrounds and contributors, as well as an $\mathit ad~hoc$ Breit-Wigner function (M $\approx{}$ 1919 MeV; $\Gamma$ $\approx{}$ 51 MeV) that is required for a good fit.
4  From the fit including final state interaction effects in isospin 0 ${\mathit S}{\mathrm -wave}$ according to SIBIRTSEV 2005A. Supersedes ABLIKIM 2010G.
5  From a fit of the ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \eta}^{\,'}}$ mass distribution to a combination of ${{\mathit \gamma}}{{\mathit f}_{{1}}{(1510)}}$ , ${{\mathit \gamma}}{{\mathit X}{(1835)}}$ , and two unconfirmed states ${{\mathit \gamma}}{{\mathit X}{(2120)}}$ , and ${{\mathit \gamma}}{{\mathit X}{(2370)}}$ , for ${{\mathit M}}$( ${{\mathit p}}{{\overline{\mathit p}}}$ ) $<$ 2.8 GeV, and accounting for backgrounds from non-${{\mathit \eta}^{\,'}}$ events and ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \eta}^{\,'}}$ .
6  The selected process is ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \omega}}{{\mathit a}_{{0}}{(980)}}{{\mathit \pi}}$ . This state may be due also to ${{\mathit \eta}_{{2}}{(1870)}}$ or to a combination of ${{\mathit X}{(1835)}}$ and ${{\mathit \eta}_{{2}}{(1870)}}$.
7  From a fit of the ${{\mathit p}}{{\overline{\mathit p}}}$ mass distribution to a combination of ${{\mathit \gamma}}{{\mathit X}{(1835)}}$ , ${{\mathit \gamma}}{{\mathit R}}$ with ${{\mathit M}}({{\mathit R}}$) = 2100 MeV and ${{\mathit \Gamma}}({{\mathit R}}$) = 160 MeV, and ${{\mathit \gamma}}{{\mathit p}}{{\overline{\mathit p}}}$ phase space, for ${{\mathit M}}$( ${{\mathit p}}{{\overline{\mathit p}}}$ ) $<$ 2.85 GeV.
8  Evidence for a threshold enhancement in the ${{\mathit p}}{{\overline{\mathit p}}}$ mass spectrum was also reported by ABE 2002K, AUBERT,B 2005L, and WANG 2005A in ${{\mathit B}^{+}}$ $\rightarrow$ ${{\mathit p}}{{\overline{\mathit p}}}{{\mathit K}^{+}}$ , WANG 2005A in ${{\mathit B}^{0}}$ $\rightarrow$ ${{\mathit p}}{{\overline{\mathit p}}}{{\mathit K}_S^0}$ , ABE 2002W in ${{\overline{\mathit B}}^{0}}$ $\rightarrow$ ${{\mathit p}}{{\overline{\mathit p}}}{{\mathit D}^{0}}$ , DEL-AMO-SANCHEZ 2012 in ${{\mathit B}}$ $\rightarrow$ ${{\mathit D}}$ (${{\mathit D}^{*}}$) ${{\mathit p}}{{\overline{\mathit p}}}$ (${{\mathit \pi}}$), and WEI 2008 in ${{\mathit B}^{+}}$ $\rightarrow$ ${{\mathit p}}{{\overline{\mathit p}}}{{\mathit \pi}^{+}}$ decays. Not seen by ATHAR 2006 in ${{\mathit \Upsilon}{(1S)}}$ $\rightarrow$ ${{\mathit p}}{{\overline{\mathit p}}}{{\mathit \gamma}}$ .
9  From the fit including final state interaction effects in isospin 0 ${\mathit S}{\mathrm -wave}$ according to SIBIRTSEV 2005A. Systematic errors not estimated.
References:
 ABLIKIM 2018I
PR D97 051101 Study of $\eta(1475)$ and $X(1835)$ in radiative $J/\psi$ decays to $\gamma \phi$
 ABLIKIM 2016J
PRL 117 042002 Observation of an Anomalous line Shape of the ${{\mathit \eta}^{\,'}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ Mass Spectrum Near the ${{\mathit p}}{{\overline{\mathit p}}}$ Mass Threshold in ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \eta}^{\,'}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$
 ABLIKIM 2015T
PRL 115 091803 Observation and Spin-Parity Determination of the ${{\mathit X}{(1835)}}$ in ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit K}_S^0}$ ${{\mathit K}_S^0}$ ${{\mathit \eta}}$
 ABLIKIM 2013U
PR D88 091502 Observation of a Structure at 1.84 GeV/$\mathit c{}^{2}$ in the 3(${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$) Mass Spectrum in ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}$3( ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$) Decays
 ABLIKIM 2012D
PRL 108 112003 Spin-Parity Analysis of ${{\mathit p}}{{\overline{\mathit p}}}$ Mass Threshold Structure in ${{\mathit J / \psi}}$ and ${{\mathit \psi}{(3686)}}$ Radiative Decays
 ABLIKIM 2011J
PRL 107 182001 ${{\mathit \eta}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ Resonant Structure Around 1.8 GeV/$\mathit c{}^{2}$ and ${{\mathit \eta}{(1405)}}$ in ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \omega}}{{\mathit \eta}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$
 ABLIKIM 2011C
PRL 106 072002 Confirmation of the ${{\mathit X}{(1835)}}$ and Observation of the Resonances ${{\mathit X}{(2120)}}$ and ${{\mathit X}{(2370)}}$ in ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \eta}^{\,'}}$
 ALEXANDER 2010
PR D82 092002 Study of ${{\mathit \psi}{(2S)}}$ Decays to ${{\mathit \gamma}}{{\mathit p}}{{\overline{\mathit p}}}$, ${{\mathit \pi}^{0}}{{\mathit p}}{{\overline{\mathit p}}}$, and ${{\mathit \eta}}{{\mathit p}}{{\overline{\mathit p}}}$, and Search for ${{\mathit p}}{{\overline{\mathit p}}}$ Threshold Enhancements
 ABLIKIM 2005R
PRL 95 262001 Observation of a Resonance ${{\mathit X}{(1835)}}$ in ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \eta}^{\,'}}$
 BAI 2003F
PRL 91 022001 Observation of a near Threshold Enhancement in the ${{\mathit p}}{{\overline{\mathit p}}}$ Mass Spectrum from Radiative ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit p}}{{\overline{\mathit p}}}$ Decays