Mon·Aug 6, 2018Monday·August 6, 2018

1. 01*

   Spin alignment measurements using vector mesons with ALICE detector at the LHC

   Ranbir Singh (for the ALICE Collaboration)🇮🇳

   We present new measurements related to spin alignment of ${\mathrm{K}}^{\ast 0}$ vector mesons at mid-rapidity for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 and 5.02 TeV. The spin alignment measurements are carried out with respect to production plane and second order event plane. At low $p_{\mathrm{T}}$ the spin density matrix element ${\rho }_{00}$ for ${\mathrm{K}}^{\ast 0}$ is found to have values slightly below 1/3, while it is consistent with 1/3, i.e. no spin alignment, at high $p_{\mathrm{T}}$. Similar values of ${\rho }_{00}$ are observed w.r.t. both production plane and event plane. Within statistical and systematic uncertainties, ${\rho }_{00}$ values are also found to be independent of $\sqrt{s_{\mathrm{NN}}}$. ${\rho }_{00}$ also shows centrality dependence with maximum deviation from 1/3 for mid-central collisions w.r.t. both the kinematic planes. The measurements for ${\mathrm{K}}^{\ast 0}$ in pp collisions at $\sqrt{s}$ = 13 TeV and for ${\mathrm{K}}_{\mathrm{S}}^0$ (a spin 0 hadron) in 20-40% central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV are consistent with no spin alignment.

   ↳ hep-exnucl-exNPA(2019)·9 citations
2. 02*

   Photoproduction of $K^{+}{K}^{-}$ meson pairs on the proton

   S. Lombardo · M. Battaglieri · A. Celentano · A. D'Angelo · R. De Vita · A. Filippi · D. Glazier · S. M. Hughes · V. Mathieu · A. Rizzo · E. Santopinto · I. Stankovic and 4 other authors

   The exclusive reaction $\gamma p\to p{K}^{+}{K}^{-}$ was studied in the photon energy range $3.0-3.8\text{mbox}GeV$ and momentum transfer range $0.6<-t<1.3\text{mbox}{GeV}^2$. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. In this kinematic range the integrated luminosity was approximately 20 pb${}^{-1}$. The reaction was isolated by detecting the $K^{+}$ and the proton in CLAS, and reconstructing the $K^{-}$ via the missing-mass technique. Moments of the di-kaon decay angular distributions were extracted from the experimental data. Besides the dominant contribution of the $\varphi$ meson in the $P$-wave, evidence for $S-P$ interference was found. The differential production cross sections $d\sigma /dt$ for individual waves in the mass range of the $\varphi$ resonance were extracted and compared to predictions of a Regge-inspired model. This is the first time the $t$-dependent cross section of the $S$-wave contribution to the elastic $K^{+}{K}^{-}$ photoproduction has been measured.

   ↳ hep-exnucl-exPRD(2018)·8 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.