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Subthreshold rho-0 Photoproduction on 2H, 3He and 12C  [PDF]
G. J. Lolos
Physics , 2001,
Abstract: The rho-0 has been photoproduced using tagged photon energies in the 700-1120 MeV region on 2H, 3He and 12C by utilizing the Fermi momentum of the bound nucleons to produce the rho-0. These energies lie mostly below the production threshold on the free proton. Large mass modifications are indicated from the analysis, together with large polarizations of the produced rho-0 mesons with helicity zero, unlike the case of coherent rho-0 production on nuclei.
Helicity Signatures in Subthreshold rho Production on Nuclei  [PDF]
G. J. Lolos,G. M. Huber,A. Shinozaki,Z. Papandreou,E. J. Brash,K. Hossain,M. Iurescu,D. Nordin,G. Garino,K. Maruyama,K. Maeda,T. Suda,A. Toyofuku,A. Sasaki,H. Yamashita
Physics , 2001,
Abstract: We report a helicity analysis of subthreshold rho production on 2H and 12C nuclei at low photoproduction energies and large |t|. The results are indicative of a large longitudinal rho polarization (l=1, m=0) and are consistent with a strong helicity-flip mechanism of rho production. The analysis is model-independent and supports the large mass shift reported from the earlier 3He experiments.
Pion emission in 2H, 12C, 27Al, gamma pi+ reactions at threshold  [PDF]
P. Golubev,V. Avdeichikov,K. G. Fissum,B. Jakobsson,I. A. Pshenichnov,W. J. Briscoe,G. V. O'Rielly,J. Annand,K. Hansen,L. Isaksson,H. Jaederstrom,M. Karlsson,M. Lundin,B. Schroeder,L. Westerberg
Physics , 2008, DOI: 10.1016/j.nuclphysa.2008.02.308
Abstract: The first data from MAX-lab in Lund, Sweden on pion production in photonuclear reactions at threshold energies, is presented. The decrease of the total yield of pi+ in gamma + 12C, 27Al reactions below 200 MeV as well as differential, dsigma/dOmega, cross sections follow essentially predictions from an intranuclear cascade model with an attractive potential for pion-nucleus interaction in its simplest form. Double differential, d2sigma/dOmegadT, cross sections at 176 MeV show, however, deviations from the model, which call for refinements of nuclear and Coulomb potentials and possibly also for coherent pion production mechanisms.
Subthreshold rho^0 photoproduction on 3He  [PDF]
TAGX Collaboration,M. A. Kagarlis,Z. Papandreou,G. M. Huber,G. J. Lolos,A. Shinozaki,E. J. Brash,F. Farzanpay,M. Iurescu,A. Weinerman,G. Garino,K. Maruyama,O. Konno,K. Maeda,T. Terasawa,H. Yamazaki,T. Emura,H. Hirosawa,K. Niwa,H. Yamashita,S. Endo,K. Miyamoto,Y. Sumi,A. Leone,R. Perrino,T. Maki,A. Sasaki,J. C. Kim
Physics , 1998, DOI: 10.1103/PhysRevC.60.025203
Abstract: A large reduction of the rho^0 mass in the nuclear medium is reported, inferred from dipion photoproduction spectra in the 1 GeV region, for the reaction 3He(gamma,pi+ pi-)X with a 10% duty factor tagged-photon beam and the TAGX multi-particle spectrometer. The energy range covered (800 < E(gamma) < 1120 MeV) lies mostly below the free rho^0 production threshold, a region which is believed sensitive to modifications of light vector-meson properties at nuclear-matter densities. The rho^0 masses extracted from the MC fitting of the data, m*(rho^0) = 642 +/- 40, 669 +/- 32, and 682 +/- 56 MeV/c^2 for E(gamma) in the 800-880, 880-960, and 960-1040 MeV regions respectively, are independently corroborated by a measured, assumption-free, kinematical observable. This mass shift, far exceeding current mean-field driven theoretical predictions, may be suggestive of rho^0 decay within the range of the nucleonic field.
Pion Absorption Cross Section for ^2H and ^3He in the Delta-Isobar Region: A Phenomenological Connection  [PDF]
H. Kamada,M. P. Locher,T. -S. H. Lee,J. Golak,V. E. Markushin,W. Gl?ckle,H. Witala
Physics , 1996, DOI: 10.1103/PhysRevC.55.2563
Abstract: The absorption of \pi^+ on ^3He in the $\Delta$-region is evaluated with exact inclusion of the final state interaction among the three emerging protons. The absorption is described by a $\pi N \to \Delta$ vertex and a $N\Delta - NN$ transition t-matrix which are calculated from a phenomenological model for NN and \pi d reactions. In a calculation where the initial pion scattering effects are neglected, the predicted peaks of the pion absorption cross sections for ^2H and ^3He lie too high in energy in relation to the data. The effect of the final state three-nucleon interaction turns out to be too small for changing the magnitude and shifting the peak position of the total absorption cross section for ^3He. We demonstrate that the adjustment of the peak position for the deuteron cross section by small modifications of the $\Delta$-parameters, automatically leads to the correct peak position in ^3He.
rho -> pi pi decay in nuclear medium  [PDF]
Wojciech Broniowski,Wojciech Florkowski,Brigitte Hiller
Physics , 2001, DOI: 10.1016/S0375-9474(01)01146-0
Abstract: We calculate the medium modifications of the rho pi pi vertex in a relativistic hadronic framework, incorporating nucleons and Delta(1232) isobars. We find a substantial increase of the rho pi pi coupling, dominated by processes where the Delta is excited. The coupling depends significantly on the virtuality of the rho, which is related to analytic properties of the vertex function. We analyze the general case of a non-zero three-momentum of the rho with respect to the nuclear medium, and evaluate the resulting widths and spectral strength in the transverse and longitudinal channels for the rho -> pi pi decay. These widths are used to obtain the dilepton yields from rho decays in relativistic heavy-ion collisions.
The omega to rho pi transition and omega to rho 3 pi decay  [PDF]
J. L Lucio,M. Napsuciale,M. D. Scadron,V. M. Villanueva
Physics , 1999,
Abstract: We evaluate the omega to rho pi transition and the omega to 3 pi decay using a Quark Level Linear Sigma Model ($QL\sigma M$). We obtain $g^{QL\sigma M}_{\omega\rho\pi}= (10.33 - 14.75) GeV^{-1}$ to be compared with other model dependent estimates averaging to $g_{\omega\rho\pi} = 16 GeV^{-1}$. We show that in the $QL\sigma M$ a contact term is generated for the $\omega \to 3 \pi$ decay. Although the contact contribution by itself is small, the interference effects turn out to be important.
Measurement of alpha/phi2 in Bo --> pi pi, rho pi and rho rho  [PDF]
J. Dalseno
Physics , 2011,
Abstract: We present a summary of the measurements of the CKM angle, alpha (phi2), performed by the BaBar and Belle experiments which collect BBbar pairs at the Y(4S) resonance produced in asymmetric e+ e- collisions. We discuss the measurements of the branching fractions and CP asymmetries in the B --> pi pi, rho pi and rho rho final states that lead to constraints on alpha (phi2).
Direct CP violation in $\bar{B}^0 \to \rho^0(\omega)\rho^0(\omega) \to \pi^+\pi^-\pi^+\pi^-$
Guo, X. -H.;Zhang, Z. -H.
High Energy Physics - Phenomenology , 2007, DOI: 10.1103/PhysRevD.75.074028
Abstract: We study the direct CP violation in $\bar{B}^0 \to \rho^0(\omega)\rho^0(\omega) \to \pi^+\pi^-\pi^+\pi^-$ (with unpolarized $\rho^0(\omega)$) via the $\rho-\omega$ mixing mechanism which causes a large strong phase difference and consequently a large CP violating asymmetry when the masses of the $\pi^+\pi^-$ pairs are in the vicinity of the $\omega$ resonance. Since there are two $\rho (\omega)$ mesons in the intermediate state $\rho-\omega$ mixing contributes twice to the first order of isospin violation, leading to an even larger CP violating asymmetry (could be 30% -- 50% larger) than in the case where only one $\rho (\omega)$ meson is involved. The CP violating asymmetry depends on the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements and the hadronic matrix elements. The factorization approach is applied in the calculation of the hadronic matrix elements with the nonfactorizable effects being included effectively in an effective parameter, $N_c$. We give the constraint on the range of $N_c$ from the latest experimental data for the branching ratios for $\bar{B}^0 \to\rho^0\rho^0$ and $\bar{B}^0 \to\rho^+\rho^-$. We find that the CP violating asymmetry could be very large (even more than 90% for some values of $N_c$). It is shown that the sensitivity of the CP violating asymmetry to $N_c$ is large compared with its smaller sensitivity to the CKM matrix elements. We also discuss the possibility to remove the mod $(\pi)$ ambiguity in the determination of the CP violating phase angle $\alpha$ through the measurement of the CP violating asymmetry in the decay $\bar{B}^0\to \rho^0(\omega)\rho^0(\omega) \to \pi^+\pi^-\pi^+\pi^-$.
B->rho pi and the unitary angle alpha  [PDF]
Aldo Deandrea
Physics , 2000,
Abstract: The role of the decay mode B->rho pi for the determination of the unitarity angle alpha is critically examined in view of the smaller than expected ratio B(B->rho+/- pi-/+)/B(B->rho0 pi+/-) found by the CLEO collaboration.
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