Ρπ Decay Research Articles

The Mass and Decay Properties of the 1−+ Light Hybrid Meson

We calculate the complete form of the dimension-8 condensate contributions in the two-point correlator of the (1−+,0++) light hybrid current considering the operator mixing under renormalization. We find the inclusion these higher power corrections as well as the update of 〈g3G3〉 increase the QCD sum rule mass prediction for the 1−+ light hybrid. The obtained conservative mass range 1.72–2.60 GeV does not favor the π1(1400) and the π1(1600) to be pure hybrid states and suggests the π1(2015) observed by E852 is more likely to have much of a hybrid constituent. We also study the b1π and ρπ decay patterns of the 1−+ light hybrid with light-cone QCD sum rules. We obtain a relatively large partial decay width of the b1π mode, which is consistent with the predictions from the flux tube models and lattice QCD. More interestingly, using the tensor interpolating current we find the partial decay width of the ρπ mode is very small due to the lack of the leading twist contribution in the light-cone expansion of the correlation function.

The width of the ω meson in the nuclear medium

We evaluate the width of the ω meson in nuclear matter. We consider the free decay mode of the ω into three pions, which is dominated by ρπ decay, and replace the ρ and π propagators by their medium-modified ones. We also take into account the quasielastic and inelastic processes induced by a vector-baryon interaction dominated by vector meson exchange, as well as the contributions coming from the $ \omega\rightarrow K\bar{K}$ mechanism with medium-modified K , $ \bar{K}$ propagators. We obtain a substantial increase of the ω width in the medium, reaching a value of 121 ± 10 MeV at normal nuclear matter density for an ω at rest, which comes mainly from ωN → ππN, ωNN → πNN processes associated to the dominant ω → ρπ decay mode. The value of the width increases moderately with momentum, reaching values of around 200MeV at 600MeV/c.

LIGHT MESON DECAY IN THE ${\rm C}\,{}^{3}\!P_{0}$ MODEL

Having its origin in a successful mapping technique, the Fock–Tani formalism, the corrected [Formula: see text] model [Formula: see text] retains the basic aspects of the [Formula: see text] predictions with the inclusion of bound-state corrections. Evaluation of the decay amplitudes has been performed for open-flavor strong decays in the light meson sector. The bound-state corrections introduce a fine-tuning for the former [Formula: see text] model, in particular, the adjustment of the D/S ratios in b1→ωπ, a1→ρπ and h1→ρπ decays.

NEW PHYSICS SIGNALS THROUGH CP VIOLATION IN B→ρπ

We describe here a method for detecting physics beyond the standard model via CP violation in B→ρπ decays. Using a Dalitz-plot analysis to obtain α, along with an analytical extraction of the various tree (T) and penguin (P) amplitudes, we obtain a criterion for the absence of new physics (NP). This criterion involves the comparison of the measured |P/T| ratio with its value as predicted by QCD factorization. We show that the detection of NP via this method has a good efficiency when compared with the corresponding technique using B→ππ decays.

Radial excitations of pseudoscalar mesons

The η(1440) seems to be split into two components, an η(1410) and an η(1470). The splitting might signal a node in the η(1440) wave function suggesting that the η(1440) is a radial excitation. The partial width of the η(1440) for the ϱγ decay leaves a little room for an exotic interpretation of the η(1440). The production rate of the η(1440) in p̄p annihilation is similar to that of the π(1300) which was observed in its ϱπ decay. No evidence was observed for the η(1295). If the latter exists its production must be much weaker than that of the π(1300) by about a factor 100. If the latter is assigned to the 2 1 S 0 nonet, the η(1295) cannot belong to this nonet. Then a new pseudoscalar nonet emerges consisting of π(1300), η(1440), η(1760) and K(1460).

Study of [formula omitted] annihilations into five pions

The preliminary analysis of four high statistic 5π data sets taken with the Crystal Barrel detector shows that at least two scalar states are needed to describe the data, the f 0(1370) with m = 1395 ± 40 Me V/ c 2, Γ = 275 ± 55 Me V/ c 2 and the f 0(1500) with mass and width compatible with previous findings. The first one decays dominantely into σσ and ϱϱ, the second one into σσ and π ∗(1300)π . In addition to the dominant scalar intensity the π ∗(1300) plays an important role in the 5π-dynamics. We found a mass of m = 1375 ± 40 Me V/ c 2 and a width of Γ = 268 ± 50 Me V/ c 2 with a dominat decay into ϱπ. The ( ππ) s π decay of the π ∗(1300) is less than 15% of its ϱπ decay as expected for a radial excitation of the π.

Scalar meson nonet in the gauged chiral model

The scalar meson nonet arising from fluctuations around quark condensates is incorporated into the gauged chiral model. We find its widths are more or less correctly given by the minimal model which, however, must be modified to produce the correct g ϱππ coupling and the large A 1 → ϱπ decay rate found in recent τ decay measurements. This suggests that the scalar meson resonances at 1 GeV may be the particles associated with dynamical symmetry breaking.

New limits on Primakoff production of hybrid mesons

I discuss constraints on properties of isoscalarJ PC =1−+ exotic hybrid mesons, assuming their dominant decay mode is ηπ. This work expands on a similar study by the Rochester-Minnesota-Fermilab collaboration, which excluded ϱπ as the dominant decay channel for such hybrids. The experimental limits are based on Primakoff production of such states and on a VDM argument relating their radiative widths to their ϱπ decay modes. Using data on coherent production of ηπ+ systems in π+ collisions with nuclei, I obtain few percent limits on the ϱπ branching ratios for hybrid masses ≲1.5 GeV.

A new upper limit for the decay rate Γ(f′ → ππ)

Data from an experiment on π − p → K S 0K S 0n are used to compare the K K D-wave at the f′(1516) mass with that at the f(1270) mass. The ratio yields an upper limit for f′ production by ππ scattering followed by decay into K K . This limit can be expressed by Γ( f′ → ππ) Γ( f′ → all) ⪅ 1% or Γ( f′ → ππ) Γ(f → ππ) ≤ 1/400 ; this indeicate a suppression of the two-pion decay of the f′, stronger than the well-known suppression of the φ(1019) → ϱπ decay.

The budding pomeron in the tree approximation to ππ inelastic channels

To study how the budding pomeron is produced in meson-meson scattering the first inelastic channels to couple strongly to π +π + are investigated. The π + π + → ϱ + ϱ + and π + π + → π +A 1 + cross sections are calculated in the tree graph approximation - with the ratio of A 1 → ϱπ decay rates computed on the way. It is concluded that either the pubescent pomeron is not precocious in ππ scattering or factorisation is not fulfilled.

Production and decay of the A 2 meson in 7 GeV/ cπ−p interactions

The production and decay of the A 2 meson has been studied in a 3.3 events/μb, 7 GeV/ cπ −p bubble chamber experiment. The cross section for π −p→A 2 −p was found to be 120±25 μb. The reaction π −p→A 2 − π 0p was also observed. The alignment of the A 2 − is consistent with the hypothesis that the production is due mainly to ϱ-exchange. The ϱπ decay distributions favour a 2 + spin parity assignment for both the lower and upper parts of the A 2. The ηπ decay distributions for the whole A 2 region are also consistent with J P =2 +.

Parameters of the A 1 → ϖπ decay

Combining the superconvergent sum rules for the A 1 ϱ → A 1 ϱ amplitude with the current algebraic “hard-pion” calculations of the related vertices given by Schnitzer and Weinberg, the solution δ = 0 has been found, implying a purely S-wave A 1 → ϱπ decay. The closely connected π N ϱA 1 and A 1 ϱA 1 couplings have also been calculated in this model. Predictions of the adopted “saturation hypothesis” are compared with other theoretical results and available experimental data.

Evidence for narrow 3π effects near 960 MeV in K − P interaction at 4.6 and 5.0 GeV/c

In an investigation of the final states K −π −π +π Op and K −π −π +π +n produced in K −p interactions at 4.6 and 5.0 GeV/ c we have observed narrow enhancements near 960 MeV in both the π +π −π O and π +π +π − distributions. These structures are strongly associated with the Δ(1236). Also, there is evidence for a possible ϱπ decay for these effects.

Approximate saturation of ρ-π superconvergence relations

The supercovergent, double spin-flip, sum rule for ρ-π scattering is saturated att=0, together with its first derivative att=0. The particles corresponding to the two lowest multiplets of the rest symmetryU6⊗U6⊗O3 are used in the saturation. Where possible, experimental values for masses and coupling constants are inserted. A bound is obtained for the ratio ofd-wave tos-wave coupling for the A1→ρπ decay. The effect of higher resonances is considered briefly, and the consistency of the saturation with the related current algebra sum rules is discussed.

Superconvergence sum rules for radiative decays of meson resonances

We consider the process γπ→ρп for which three sum rules are derived from high-energy behaviour hypothesis. Combining these sum rules with the analogous ones for the process ρπ→ρπ we determine the electromagnetic widths of the ω, A1, A2 resonances, and theS-wave/D-wave ratio for the A1→ρπ decay. We discuss some features of gauge invariance and superconvergence requirements: in particular, we derive some already known low-energy theorem consequences,e.g. the sum rule obtained byHarari for Compton scattering. This last one and the Cabibbo and Radicati sum rule are used to select the best values of the ω, A1, A2 electromagnetic widths.