Observation of a new ηπ0π0 resonance at 1900 MeV/c2 in two-photon scattering

Abstract

Using the Crystal Ball detector at the DORIS II e+e-storage ring, we measure the TIn°n ° mass spectrum in the reaction e+e-*e+e-Tln°n°-~e+e-6T from the "qn°n ° threshold to about 2500 MeV/c 2. The spectrum is dominated by the 11' , for which we determine/'w0]')BR (q' ~6y) = 0.36 +_ 0.02 + 0.03 keV. In addition, we observe an enhancement in the cross section near 1900 MeV/c 2 which we attribute to the two-photon production of a new resonance X (1900). The angular distributions and the invariant mass distribution of the Tin ° subsystem are consistent with those expected for the hypothetical ~12 meson with jec= 2-+. For this je assignment the resonance parameters are M(X) = 1876 + 35 + 50 MeV/c 2, /'tot(X) =228 + 90_+ 34 MeV/c 2 and Frr(X)BR(X-,Ilnn) =0.9+0.2+0.3 keV.

A direct determination of the number of light neutrino families from at LEP

“…Another source of background comes from twophoton processes, e+e --,e+e-X, where X is a n °, rl, rf, a2, f2 or a recently-reported high-mass resonance [ 16 ] decaying into qn°n °, when the scattered e -+ both escape undetected down the beam pipe and only one photon is observed from the final state X. Generation of events was carried out using a Monte Carlo implementation [ 17] of the cross section formulae found in ref.…”

On D-wave meson spectroscopy and the (1410)- (1680) problem

“…Let us now extract the matrix elements of the spin-spin, spin-orbit, and tensor interaction in our model. As follows from (18)- (20) and the above relations for the masses of the I = 1, 1/2 mesons,…”

“…By expressing the ratio n/s in four different ways, viz., directly from (16), (17) and dividing the expressions (18)- (20) for the I = 1/2 and I = 1 mesons by each other, one obtains the three relations,…”

“…Since the ρ and ρ 3 states are mass near-degenerate, ρ ≈ ρ 3 (their masses are 1700±20 MeV and 1691 ± 5 MeV, respectively [4]), it then follows from (24) that either ρ 2 ≈ ρ ≈ ρ 3 , or K * ≈ K * 3 . The first possibility leads, through the relations (19), (20) applied to the I = 1 mesons, to b ≈ c ≈ 0, which would in turn, from the same relations for the I = 1/2 mesons, imply K * ≈ K 2A ≈ K * 3 . Although this case may not be excluded on the basis of current experimental data on the meson masses, we consider simultaneous disappearance of both the spin-orbit and tensor terms as dubious.…”

“…There exists an experimental candidate for the η 2 (1860) but it was omitted from the recent Meson Summary Table as "needs confirmation". This state indicated in PDG as the η 2 (1870) [4] has been seen by the Crystal Ball collaboration in the final state ηπ 0 π 0 of a γγ reaction as a resonant structure having mass and width 1881 ± 32 ± 40 MeV, 221 ± 92 ± 44 MeV, respectively [20], and as a similar structure in γγ → ηπ + π − by the CELLO collaboration, with mass and width 1850 ± 50 MeV, ∼ 360 MeV, respectively [21]. The masses of the remaining isoscalar nn states of the four nonets may be calculated by assuming that all four nonets are ideally mixed and using the Sakurai mass formula for an ideally mixed nonet [22], M 2 (I = 1) + M 2 (I = 0, nn) + 2M 2 (I = 0, ss) = 4M 2 (I = 1/2).…”