Tue·Jan 24, 2017Tuesday·January 24, 2017

1. 01*

   A study of event mixing for two-pion Bose-Einstein correlations in the {\gamma}p -> {\pi}^0 {\pi}^0 p reaction

   Q. He🇯🇵 · J. Ai🇨🇳 · T. Ishikawa🇯🇵 · T. Li🇨🇳 · L. Ma🇨🇳 · J. Ma🇨🇳 · M. Miyabe🇯🇵 · N. Muramatsu🇯🇵 · H. Shimizu🇯🇵 · Y. Tsuchikawa🇯🇵 · Y. Xiang🇨🇳 · H. Yamazaki🇯🇵 · Y. Zhang🇨🇳

   We develop an event mixing technique with a missing mass consistency (MMC) cut and a pion energy (PE) cut for the measurement of two-pion Bose-Einstein correlations (BEC) in reactions with only two identical pions produced in the final state. A multi mixing mode that allows one event to be mixed with multiple other events is proposed for the purpose of improving the statistics of mixed samples, and compared with the single mixing mode which requires one original event can be mixed only once. Numerical tests using the {\gamma}p -> {\pi}^0 {\pi}^0 p events are used to testify its ability to measure two-pion correlations. To improve the mixing speed, the optimal MMC cut window is also explored via simulations.

   nucl-exPTEP(2017)·2 citations
2. 02*

   Search for weak M1 transitions in ${}^{48}$Ca with inelastic proton scattering

   M. Mathy (1) · J. Birkhan (1) · H. Matsubara (2,3)🇯🇵 · P. von Neumann-Cosel (1)🇩🇪 · N. Pietralla (1)🇩🇪 · V.Yu. Ponomarev (1)🇩🇪 · A. Richter (1)🇩🇪 · A. Tamii (2) ((1) Institut für Kernphysik, Technische Universität Darmstadt, (2) Research Center for Nuclear Physics, Osaka University, (3) Tokyo Women's Medical University)🇯🇵

   The spinflip M1 resonance in the doubly magic nucleus ${}^{48}$Ca, dominated by a single transition, serves as a reference case for the quenching of spin-isospin modes in nuclei. The aim of the present work is a search for weak M1 transitions in ${}^{48}$Ca with a high-resolution (p,p') experiment at 295 MeV and forward angles including 0 degree and a comparison to results from a similar study using backward-angle electron scattering at low momentum transfers in order to estimate their contribution to the total B(M1) strength. M1 cross sections of individual peaks in the spectra are deduced with a multipole decomposition analysis. The corresponding reduced B(M1) transition strengths are extracted following the approach outlined in J. Birkhan et al., Phys. Rev. C 93, 041302(R) (2016). In total, 29 peaks containing a M1 contribution are found in the excitation energy region 7 - 13 MeV. The resulting B(M1) strength distribution compares well to the electron scattering results considering different factors limiting the sensitivity in both experiments and the enhanced importance of mechanisms breaking the proportionality of nuclear cross sections and electromagnetic matrix elements for weak transitions as studied here. The total strength of 1.19(6) ${\mu }_N^2$ deduced assuming a non-quenched isoscalar part of the (p,p') cross sections agrees with the (e,e') result of 1.21(13) ${\mu }_N^2$. A binwise analysis above 10 MeV provides an upper limit of 1.62(23) ${\mu }_N^2$. The present results confirm that weak transitions contribute about 25% to the total B(M1) strength in ${}^{48}$Ca and the quenching factors of GT and spin-M1 strength are comparable in fp-shell nuclei. Thus, the role of of meson exchange currents seems to be neglible, in contrast to sd-shell nuclei.

   nucl-exPRC(2017)·20 citations
3. 03*

   Measurement of $D^0$ azimuthal anisotropy at mid-rapidity in Au+Au collisions at \sNN = 200\,GeV

   STAR Collaboration: L. Adamczyk · J. K. Adkins · G. Agakishiev · M. M. Aggarwal · Z. Ahammed · N. N. Ajitanand · I. Alekseev · D. M. Anderson · R. Aoyama · A. Aparin · D. Arkhipkin · E. C. Aschenauer and 336 other authors

   We report the first measurement of the elliptic anisotropy ($v_2$) of the charm meson $D^0$ at mid-rapidity ($|y|$\,$<$\,1) in Au+Au collisions at \sNN = 200\,GeV. The measurement was conducted by the STAR experiment at RHIC utilizing a new high-resolution silicon tracker. The measured $D^0$ $v_2$ in 0--80\% centrality Au+Au collisions can be described by a viscous hydrodynamic calculation for transverse momentum ($p_{\mathrm{T}}$) less than 4\,GeV/$c$. The $D^0$ $v_2$ as a function of transverse kinetic energy ($m_{\mathrm{T}}-m_0$, where $m_{\mathrm{T}}=\sqrt{p_{\mathrm{T}}^2+m_0^2}$) is consistent with that of light mesons in 10--40\% centrality Au+Au collisions. These results suggest that charm quarks have achieved local thermal equilibrium with the medium created in such collisions. Several theoretical models, with the temperature--dependent, dimensionless charm spatial diffusion coefficient ($2\pi T{D}_s$) in the range of $\sim$2--12, are able to simultaneously reproduce our $D^0$ $v_2$ result and our previously published results for the $D^0$ nuclear modification factor.

   nucl-exPRL(2017)·242 citations
4. 04*

   Is there a narrow $N(1685)$?

   A.V. Anisovich🇩🇪 · V. Burkert🇺🇸 · E. Klempt🇩🇪 · V.A. Nikonov🇩🇪 · A.V. Sarantsev🇩🇪 · U. Thoma🇩🇪

   The helicity-dependent observable $E$ for the reaction $\gamma d\to \eta n(p)$ with a spectator proton was recently measured by the A2 Collaboration at MAMI in Mainz. The data were interpreted as further evidence for a narrow resonance with spin and parity $J^P=1/2^{+}$ ($P_{11}$ wave). However, a full partial wave analysis without any narrow resonance leads to an excellent description of the data, imposing a narrow resonance with the properties suggested by the A2 Collaboration leads to a significant deterioration of the fit quality: there is no need for a narrow resonance.

   nucl-exPRC(2017)·17 citations
5. 05*

   Harmonic decomposition of three-particle azimuthal correlations at RHIC

   STAR Collaboration: L. Adamczyk · J. K. Adkins · G. Agakishiev · M. M. Aggarwal · Z. Ahammed · N. N. Ajitanand · I. Alekseev · D. M. Anderson · R. Aoyama · A. Aparin · D. Arkhipkin · E. C. Aschenauer and 336 other authors

   We present measurements of three-particle correlations for various harmonics in Au+Au collisions at energies ranging from $\sqrt{s_{\mathrm{NN}}}=7.7$ to 200 GeV using the STAR detector. The quantity $⟨\cos (m{\varphi }_1+n{\varphi }_2-(m+n){\varphi }_3)⟩$ is evaluated as a function of $\sqrt{s_{\mathrm{NN}}}$, collision centrality, transverse momentum, $p_T$, pseudo-rapidity difference, $\Delta \eta$, and harmonics ($m$ and $n$). These data provide detailed information on global event properties like the three-dimensional structure of the initial overlap region, the expansion dynamics of the matter produced in the collisions, and the transport properties of the medium. A strong dependence on $\Delta \eta$ is observed for most harmonic combinations consistent with breaking of longitudinal boost invariance. Data reveal changes with energy in the two-particle correlation functions relative to the second-harmonic event-plane and provide ways to constrain models of heavy-ion collisions over a wide range of collision energies.

   nucl-exnucl-thPRC(2018)·60 citations
6. 06*

   Constraining the initial conditions and temperature dependent transport with three-particle correlations in Au+Au collisions

   STAR Collaboration: L. Adamczyk · J. K. Adkins · G. Agakishiev · M. M. Aggarwal · Z. Ahammed · N. N. Ajitanand · I. Alekseev · D. M. Anderson · R. Aoyama · A. Aparin · D. Arkhipkin · E. C. Aschenauer and 336 other authors

   We present three-particle mixed-harmonic correlations $\text{la}\cos (m{\varphi }_a+n{\varphi }_b-(m+n){\varphi }_c)\text{ra}$ for harmonics $m,n=1-3$ for charged particles in $\sqrt{s_{NN}}=$200 GeV Au+Au collisions at RHIC. These measurements provide information on the three-dimensional structure of the initial collision zone and are important for constraining models of a subsequent low-viscosity quark-gluon plasma expansion phase. We investigate correlations between the first, second and third harmonics predicted as a consequence of fluctuations in the initial state. The dependence of the correlations on the pseudorapidity separation between particles show hints of a breaking of longitudinal invariance. We compare our results to a number of state-of-the art hydrodynamic calculations with different initial states and temperature dependent viscosities. These measurements provide important steps towards constraining the temperature dependent transport and the longitudinal structure of the initial state at RHIC.

   nucl-exnucl-thPLB(2019)·14 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.