arXiv subjects

K. Rybicki

Publications and source records attributed to K. Rybicki.

62 records · Page 4Linked to original sources

arXiv2015

Total eclipse of the heart: The AM CVn Gaia14aae / ASSASN-14cn

We report the discovery and characterisation of a deeply eclipsing AM CVn-system, Gaia14aae (= ASSASN-14cn). Gaia14aae was identified independently by the All-Sky Automated Survey for Supernovae (ASAS-SN; Shappee et al. 2014) and by the Gaia Science Alerts project, during two separate outbursts. A third outburst is seen in archival Pan-STARRS-1 (PS1; Schlafly et al. 2012; Tonry et al. 2012; Magnier et al. 2013) and ASAS-SN data. Spectroscopy reveals a hot, hydrogen-deficient spectrum with clear double-peaked emission lines, consistent with an accreting double degenerate classification. We use follow-up photometry to constrain the orbital parameters of the system. We find an orbital period of 49.71 min, which places Gaia14aae at the long period extremum of the outbursting AM CVn period distribution. Gaia14aae is dominated by the light from its accreting white dwarf. Assuming an orbital inclination of 90 degrees for the binary system, the contact phases of the white dwarf lead to lower limits of 0.78 M solar and 0.015 M solar on the masses of the accretor and donor respectively and a lower limit on the mass ratio of 0.019. Gaia14aae is only the third eclipsing AM CVn star known, and the first in which the WD is totally eclipsed. Using a helium WD model, we estimate the accretor's effective temperature to be 12900+-200 K. The three out-burst events occurred within 4 months of each other, while no other outburst activity is seen in the previous 8 years of Catalina Real-time Transient Survey (CRTS; Drake et al. 2009), Pan-STARRS-1 and ASAS-SN data. This suggests that these events might be rebrightenings of the first outburst rather than individual events.

astro-ph.SR↗

arXiv2002

A New Analysis of the pi+pi- and pi0pi0 Data

A joint analysis of the pi+pi- and pi0pi0 S-wave amplitudes including results of three experiments has been performed. Using our theoretical model of the pion-pion production in which not only the pion exchange but also the a1(1260) meson exchange were taken into account we have obtained a unique solution (called "down-flat") for the scalar-isoscalar phase shifts. Thus a long-standing problem of ambiguities in the S-wave isoscalar amplitude has been finally resolved and the second ("up-flat") solution was eliminated.

hep-ph↗

arXiv2001

Comment on `Analysis of O(p^2) Corrections to <2pi|Q_{7,8}|K>'

We extend in several respects our earlier work on O(p^2) corrections to matrix elements of the electroweak penguin operator O_{ewp}. First, to facilitate comparison with certain lattice studies we calculate O(p^2) corrections to in the SU(3) limit of equal light quark masses. Next, we demonstrate how an apparent disagreement in the literature regarding whether higher order chiral contributions increase or decrease <2pi_{I=2}|O_{ewp}|K> is simply a consequence of how the leading order chiral amplitude is defined. Finally, we address an aspect of the epsilon'/epsilon problem by estimating O(p^2) corrections to recent determinations of <2pi_{I=2}|Q_{7,8}|K> which were carried out in the chiral limit.

hep-ph↗

arXiv2000

Theoretical constraints on interaction amplitudes of light mesons

We impose unitarity constraints on the S-wave isoscalar pion-pion amplitudes extracted from the analysis of the pi- p ---> pi+ pi- n data which have been measured by the CERN-Cracow-Munich collaboration on a transversely polarized target at 17.2 GeV/c pi- momentum. Two "steep" solutions contain a narrow S-wave f0(750) resonance under the rho(770) and exhibit a considerable inelasticity eta which is in disagreement with the four pion production data below the KKbar threshold. We impose eta= 1 for all data points and examine four sets of solutions for the S-wave isoscalar phase-shifts. The "down-flat" and "up-flat" solutions easily pass the eta=1 constraint but the remaining "down-steep" and "up-steep" are eliminated. We conclude that the 17.2 GeV data cannot be described by a relatively narrow f0(750).

hep-ph↗

arXiv1999

Further study of the pi-pi S-wave isoscalar amplitude below the K - Kbar threshold

We continue the analysis of S-wave production amplitudes for the reaction pi- p -> pi+ pi- n involving the data obtained by the CERN--Cracow-Munich collaboration on a transversely polarized target at 17.2 GeV/c pi- momentum. This study deals with the region below the K - Kbar threshold. In particular, we study the "up-steep" solution containing a narrow S-wave resonance under the rho(770). This solution exhibits a considerable inelasticity (eta) which does not have any physical interpretation. Assuming that this inelasticity behaviour represents an unlikely fluctuation we impose eta = 1 for all data points. This leads to non-physical results in one third of the pi+pi- effective mass bins and in the remaining mass bins some parameters behave in a queer way. The situation is even worse for the "down-steep" solution. We conclude that the 17.2 GeV data cannot be described by a relatively narrow f0(750). The "down-flat" and "up-steep" solutions which easily pass the eta = 1 constraint exhibit a slow increase of phase shifts in the rho(770) mass range.

hep-ph↗

arXiv1997

New Solutions for Scalar-Isoscalar pi-pi Phase Shifts

The scalar-isoscalar pi-pi phase shifts are calculated in the pi-pi energy range from 600 MeV to 1600 MeV. We use results of the CERN-Cracow-Munich collaboration for the reaction pi^- p --> pi^+ pi^- n on a transversely polarized target at 17.2 GeV/c pi^- momentum. Energy-independent separation of the S-wave pseudoscalar amplitude (pi exchange) from the pseudovector amplitude (a_1 exchange) is carried out. Below the KK threshold we find two solutions for the pi-pi phase shifts, for which the phases increase slower with the effective pi-pi mass than the P-wave phases ("flat" solutions) and two solutions for which the phases increase faster than the P-wave phases ("steep" solutions). Above 1420 MeV both sets of phase shifts increase with energy faster than in the experiment on an unpolarized target. This fact can be related to a presence of the scalar resonance f_0(1500).

hep-ph↗

arXiv1997

Separation of S- wave pseudoscalar and pseudovector amplitudes in pi^- p---> pi^+ pi^- n reaction on polarized target

A new analysis of S-wave production amplitudes for the reaction $π^- p_{\uparrow} \rightarrow π^+ π^- n$ on a transversely polarized target is performed. It is based on the results obtained by the CERN-Cracow -Munich collaboration in the pion-pion energy range from 600 MeV to 1600 MeV at 17.2 GeV/c $π^-$ momentum. Energy-independent separation of the S-wave pseudoscalar amplitude ($π$ exchange) from the pseudovector amplitude ($a_{1}$ exchange) is carried out using assumptions much weaker than those in all previous analyses. We show that, especially around 1000 MeV and around 1500 MeV, the $a_{1}$ exchange amplitude cannot be neglected. The scalar-isoscalar $ππ$ phase shifts are calculated using fairly weak assumptions. Below the $K\overline{K}$ threshold we find two solutions for the $π-π$ phase shifts, for which the phases increase slower with the effective $π-π$ mass than the P-wave phases. Both solutions are consistent with a broad $f_{0}(500)$ but only one is similar to the well-known "down" solution. We find also the third solution (with a somewhat puzzling behavior of inelasticity) which exhibits a narrow $f_{0}(750)$ claimed by Svec. All the solutions undergo a rapid change at the $K\overline{K}$ threshold. Above 1420 MeV the phase shifts increase with energy faster than those obtained without the polarized-target data. This phase behavior as well as an increase of the modulus of the $a_{1}$-exchange amplitude can be due to the presence of the $f_{0}(1500)$.

hep-ph↗

arXiv1995

Momentum Correlations of Charmed Pairs Produced in $π^{-}-Cu$ Interactions at 230 GeV/c

We study the production characteristics of 557 pairs of charmed hadrons produced in $π^{-}-Cu$\ interactions at 230~GeV/c using a momentum estimator for charmed hadrons with missing decay products. We find, the mean value of the transverse momentum squared of the charmed pairs is $<$\pts$>=(1.98\pm 0.11\pm 0.09)\;$ GeV$^2$/c$^2$, the mean rapidity difference is $<|$\yd$|>=0.54\pm 0.02\pm 0.24$, and the mean effective mass is $<$\mef$>=(4.45\pm 0.03\pm 0.13)\;$ GeV/c$^2$. Comparing these results with the next-to-leading order QCD predictions we find an agreement for the \yd\ and \mef, whilst the measured mean value of \pts\ is significantly larger than the predicted value.

hep-ex↗