arXiv subjects

C. Rangacharyulu

Publications and source records attributed to C. Rangacharyulu.

33 records · Page 2Linked to original sources

arXiv2008

Evidence of the Θ^+ in the γd \to K^+K^-pn reaction

The γd \to K^+K^-pn reaction has been studied to search for the evidence of the Θ^+ by detecting K^+K^- pairs at forward angles. The Fermi-motion corrected nK^+ invariant mass distribution shows a narrow peak at 1.524 +- 0.002 + 0.003 GeV/c^2. The statistical significance of the peak calculated from a shape analysis is 5.1 σ, and the differential cross-section for the γn \to K^- Θ^+ reaction is estimated to be 12 +- 2 nb/sr in the photon energy range from 2.0 GeV to 2.4 GeV in the LEPS angular range by assuming the isotropic production of the Θ^+ in the γn center-of-mass system. The obtained results support the existence of the Θ^+.

nucl-ex↗

arXiv2008

Forward coherent $ϕ$-meson photoproduction from deuterons near threshold

Differential cross sections and decay asymmetries for coherent $ϕ$-meson photoproduction from deuterons were measured for the first time at forward angles using linearly polarized photons at $E_γ$= 1.5-2.4 GeV. This reaction offers a unique way to directly access natural-parity Pomeron dynamics and gluon exchange at low energies. The cross sections at zero degrees increase with increasing photon energy. The decay asymmetries demonstrate a complete dominance of natural-parity exchange processes, showing that isovector unnatural-parity $π$-meson exchange is small. Nevertheless the deduced cross sections of $ϕ$-mesons from nucleons contributed by isoscalar t-channel exchange processes are not well described by the conventional Pomeron model.

nucl-ex↗

arXiv2007

Backward-angle photoproduction of $π^0$ mesons on the proton at $E_γ$ = 1.5--2.4 GeV

Differential cross sections and photon beam asymmetries for $π^0$ photoproduction have been measured at $E_γ$ = 1.5--2.4 GeV and at the $π^0$ scattering angles, --1 $<$ cos$Θ_{c.m.} <$ --0.6. The energy-dependent slope of differential cross sections for $u$-channel $π^0$ production has been determined. An enhancement at backward angles is found above $E_γ$ = 2.0 GeV. This is inferred to be due to the $u$-channel contribution and/or resonances. Photon beam asymmetries have been obtained for the first time at backward angles. A strong angular dependence has been found at $E_γ>$ 2.0 GeV, which may be due to the unknown high-mass resonances.

nucl-ex↗

arXiv2006

Differential cross section and photon beam asymmetry for the gamma n -> K+ Sigma- reaction at Egamma=1.5-2.4 GeV

Differential cross sections and photon beam asymmetries have been measured for the gamma n -> K+ Sigma- and gamma p -> K+ Sigma0 reactions separately using liquid deuterium and hydrogen targets with incident linearly polarized photon beams of Egamma=1.5-2.4 GeV at 0.6<cosTheta<1. The cross section ratio of sigma(K+Sigma-)/sigma(K+Sigma0), expected to be 2 on the basis of the isospin 1/2 exchange, is found to be close to 1. For the K+Sigma- reaction, large positive asymmetries are observed indicating the dominance of the K*-exchange. A large difference between the asymmetries for the K+Sigma- and K+Sigma0 reactions can not be explained by simple theoretical considerations.

hep-ex↗

arXiv2005

Measurement of K^+ \to π^0 μ^+ νγdecay using stopped kaons

The K^+ \to π^0 μ^+ νγ($K_{μ3 γ}$) decay has been measured with stopped positive kaons at the KEK 12 GeV proton synchrotron. A $K_{μ3 γ}$ sample containing 125 events was obtained. The partial branching ratio $Br(K_{μ3 γ}, E_γ>30 {\rm MeV}, θ_{μ^+ γ}>20^{\circ})$ was found to be $[2.4 \pm 0.5(stat) \pm 0.6(syst)]\times 10^{-5}$, which is in good agreement with theoretical predictions.

hep-ex↗

arXiv2005

Diffractive $ϕ$-meson photoproduction on proton near threshold

Photoproduction of $ϕ$-meson on protons was studied by means of linearly polarized photons at forward angles in the low-energy region from threshold to $E_γ$= 2.37 GeV. The differential cross sections at $t = -|t|_{min}$ do not increase smoothly as $E_γ$ increases, but show a local maximum at around 2.0 GeV. The angular distributions demonstrate that $ϕ$-mesons are photo-produced predominantly by helicity-conserving processes, and the local maximum is not likely due to unnatural-parity processes.

nucl-ex↗

arXiv2004

phi photo-production from Li, C, Al, and Cu nuclei at Egamma=1.5 - 2.4 GeV

The photo-production of $ϕ$ mesons from Li, C, Al, and Cu at forward angles has been measured at $E_gamma$=1.5--2.4 GeV. The number of events for incoherent phi photo-production is found to have a target mass number dependence of $A^{0.72\pm 0.07}$ in the kinematical region of $|t|\le 0.6$ ${\rm GeV}^2/c^2$. The total cross section of the $ϕ$-nucleon interaction, $σ_{ϕN}$, has been estimated as $35^{+17}_{-11}$ mb using the $A$-dependence of the $ϕ$ photo-production yield and a Glauber-type multiple scattering theory. This value is much larger than $σ_{ϕN}$ in free space, suggesting that the $ϕ$ properties might change in the nuclear medium.

nucl-ex↗

arXiv2004

Measurement of $K^+ \to π^0 π^0 e^+ ν$ ($K_{e4}^{00}$) decay using stopped positive kaons

The $K^+ \to π^0 π^0 e^+ ν$ ($K_{e4}^{00}$) decay has been measured with stopped positive kaons for a data sample of 216 events. A comparison of the observed spectra with a Monte Carlo simulation determined the $K_{e4}^{00}$ form factor. The results are compatible with the $K^+ \to π^+ π^- e^+ ν$ data, as estimated from the $ΔI=1/2$ rule. We also established that the $K_{e4}^{00}$ channel can be used to determine the $π$-$π$ scattering lengths.

hep-ex↗

arXiv2004

A new limit of T-violating transverse muon polarization in the $K^{+}\toπ^{0}μ^{+} ν$ decay

A search for T-violating transverse muon polarization ($P_T$) in the $K^{+}\to π^{0}μ^{+}ν$ decay was performed using kaon decays at rest. A new improved value, $P_T= -0.0017\pm 0.0023 (stat)\pm 0.0011 (syst)$, was obtained giving an upper limit, $| P_T | < 0.0050$. The T-violation parameter was determined to be Im$ξ= -0.0053 \pm 0.0071(stat)\pm 0.0036(syst)$ giving an upper limit, $|$Im$ξ| <0.016$.

hep-ex↗

arXiv2003

Testing quantum correlations with nuclear probes

We investigated the feasibility of quantum-correlation measurements in nuclear physics experiments. In a first approach, we measured spin correlations of singlet-spin (1S0) proton pairs, which were generated in 1H(d,2He) and 12C(d,2He) nuclear charge-exchange reactions. The experiment was optimized for a clean preparation of the 2He singlet state and offered a 2pi detection geometry for both protons in the exit channel. Our results confirm the effectiveness of the setup for theses studies, despite limitations of a small data sample recorded during the feasibility studies.

quant-ph↗

arXiv2003

Search for Narrow Nucleon Resonances below Pion Threshold in the H(e,e'pi^+)X and D(e,e'p)X Reactions

In two series of high-resolution coincidence experiments at the three-spectrometer facility at MAMI, the H(e,e'pi^+)X and D(e,e'p)X reactions were studied to search for narrow nucleon resonances below pion threshold. The missing-mass resolution was 0.6 to 1.6 MeV/c^2 (FWHM) in the proton experiment and 0.9 to 1.3 MeV/c^2 in the deuteron experiment. The experiments covered the missing-mass region from the neutron mass up to about 1050 and 1100 MeV/c^2, respectively. None of our measurements showed a signal for narrow resonances to a level of down to 10^-4 with respect to the neutron peak in the missing-mass spectra.

nucl-ex↗

arXiv2003

Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)Sigma0 reactions at Egamma=1.5-2.4 GeV

Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)sigma0 reactions are measured for the first time for Egamma=1.5-2.4 GeV and 0.6<cos(theta_cm(K+))<1.0 by using linearly polarized photons at the Laser-Electron-Photon facility at SPring-8 (LEPS). The observed asymmetries are positive and gradually increase with rising photon energy. The data are not consistent with theoretical predictions based on tree-level effective Lagrangian approaches. Including the new results in the development of the models is, therefore, crucial for understanding the reaction mechanism and to test the presence of baryon resonances which are predicted in quark models but are sofar undiscovered.

nucl-ex↗

arXiv2003

Polarization Correlations of 1S0 Proton Pairs as Tests of Bell and Wigner Inequalities

In an experiment designed to overcome the loophole of observer dependent reality and satisfying the counterfactuality condition, we measured polarization correlations of 1S0 proton pairs produced in 12C(d,2He) and 1H(d,He) reactions in one setting. The results of these measurements are used to test the Bell and Wigner inequalties against the predictions of quantum mechanics.

quant-ph↗

arXiv2002

Self energies of the pion and the delta isobar from the ^3He(e,e'pi^+)^3H reaction

In a kinematically complete experiment at the Mainz microtron MAMI, pion angular distributions of the $^3$He(e,e'$π^+)^3$H reaction have been measured in the excitation region of the $Δ$ resonance to determine the longitudinal ($L$), transverse ($T$), and the $LT$ interference part of the differential cross section. The data are described only after introducing self-energy modifications of the pion and $Δ$-isobar propagators. Using Chiral Perturbation Theory (ChPT) to extrapolate the pion self energy as inferred from the measurement on the mass shell, we deduce a reduction of the $π^+$ mass of $Δm_{π^+} = (-1.7^{+ 1.7}_{- 2.1})$ MeV/c$^2$ in the neutron-rich nuclear medium at a density of $ρ= (0.057^{+ 0.085}_{- 0.057})$ fm$^{-3}$. Our data are consistent with the $Δ$ self energy determined from measurements of $π^0$ photoproduction from $^4$He and heavier nuclei.

nucl-ex↗

arXiv1996

Studies of chaotic Dynamics in a Three-Dimensional Superconducting Microwave Billiard

We present first measurements on a superconducting three-dimensional, partly chaotic microwave billiard shaped like a small deformed cup. We analyze the statistical properties of the measured spectrum in terms of several methods originally derived for quantum systems like eigenvalue statistics and periodic orbits and obtain according to a model of Berry and Robnik a mixing parameter of about 25%. In numerical simulations of the classical motion in the cup the degree of chaoticity has been estimated. This leads to an invariant chaotic Liouville measure of about 45%. The difference between this figure and the mixing parameter is due to the limited accuracy of the statistical analysis, caused by both, the fairly small number of 286 resonances and the rather poor desymmetrization of the microwave cavity. Concerning the periodic orbits of the classical system we present a comparison with the length spectrum of the resonator and introduce a new bouncing ball formula for electromagnetic billiards.

chao-dyn↗