Thu·Feb 4, 2016Thursday·February 4, 2016

1. 01*

   Nonextensive statistics in spin precession

   Matthew J. Bales🇺🇸 · Peter Fierlinger🇩🇪 · Robert Golub🇺🇸

   Many experiments utilize the precession of trapped particles in magnetic fields to perform high precision measurements. It had been presumed that after free precession, initially polarized particles will form a Gaussian phase distribution in the plane of precession. We show that trapped particles in the presence of magnetic field gradients and electric fields will often form a non-Gaussian distribution with power-law tails which are consistent with nonextensive statistics. As the exact shape of the distribution depends upon many experimental parameters, it provides a potential new technique to directly measure them.

   nucl-exphysics.atom-phEPL(2016)·3 citations
2. 02*

   Anisotropic flow of charged particles in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV

   ALICE Collaboration

   We report the first results of elliptic ($v_2$), triangular ($v_3$) and quadrangular flow ($v_4$) of charged particles in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector at the CERN Large Hadron Collider. The measurements are performed in the central pseudorapidity region $|\eta |<0.8$ and for the transverse momentum range $0.2<p_{\mathrm{T}}<5$ GeV/$c$. The anisotropic flow is measured using two-particle correlations with a pseudorapidity gap greater than one unit and with the multi-particle cumulant method. Compared to results from Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV, the anisotropic flow coefficients $v_2$, $v_3$ and $v_4$ are found to increase by ($3.0\pm 0.6$)%, ($4.3\pm 1.4$)% and ($10.2\pm 3.8$)%, respectively, in the centrality range 0-50%. This increase can be attributed mostly to an increase of the average transverse momentum between the two energies. The measurements are found to be compatible with hydrodynamic model calculations. This comparison provides a unique opportunity to test the validity of the hydrodynamic picture and the power to further discriminate between various possibilities for the temperature dependence of shear viscosity to entropy density ratio of the produced matter in heavy-ion collisions at the highest energies.

   nucl-exhep-exPRL(2016)·340 citations
3. 03*

   Rapidity and centrality dependence of particle production for identified hadrons in Cu+Cu collisions at $\sqrt{s_{NN}}=200$ GeV

   BRAHMS Collaboration: I. C. Arsene🇳🇴 · I. G. Bearden🇩🇰 · D. Beavis🇺🇸 · S. Bekele🇺🇸 · C. Besliu🇷🇴 · B. Budick🇺🇸 · H. Bøggild🇩🇰 · C. Chasman🇺🇸 · C. H. Christensen🇩🇰 · P. Christiansen🇸🇪 · H. H. Dalsgaard🇩🇰 · R. Debbe🇺🇸 and 31 other authors

   The BRAHMS collaboration has measured transverse momentum spectra of pions, kaons, protons and antiprotons at rapidities 0 and 3 for Cu+Cu collisions at $\sqrt{s_{NN}}=200$ GeV. As the collisions become more central the collective radial flow increases while the temperature of kinetic freeze-out decreases. The temperature is lower and the radial flow weaker at forward rapidity. Pion and kaon yields with transverse momenta between 1.5 and 2.5 GeV/c are suppressed for central collisions relative to scaled $p+p$ collisions. This suppression, which increases as the collisions become more central is consistent with jet quenching models and is also present with comparable magnitude at forward rapidity. At such rapidities initial state effects may also be present and persistence of the meson suppression to high rapidity may reflect a combination of jet quenching and nuclear shadowing. The ratio of protons to mesons increases as the collisions become more central and is largest at forward rapidities.

   nucl-exPRC(2016)·27 citations
4. 04*

   Efficient formulas for efficiency correction of cumulants

   Masakiyo Kitazawa🇯🇵

   We derive formulas which connect cumulants of particle numbers observed with efficiency losses with the original ones based on the binomial model. These formulas can describe the case with multiple efficiencies in a compact form. Compared with the presently suggested ones based on factorial moments, these formulas would drastically reduce the numerical cost for efficiency corrections when the order of the cumulant and the number of different efficiencies are large. The efficiency correction with realistic $p_T$-dependent efficiency would be carried out with the aid of these formulas.

   ↳ nucl-thhep-phnucl-exPRC(2016)·38 citations
5. 05*

   Particle identification in ALICE: a Bayesian approach

   ALICE Collaboration

   We present a Bayesian approach to particle identification (PID) within the ALICE experiment. The aim is to more effectively combine the particle identification capabilities of its various detectors. After a brief explanation of the adopted methodology and formalism, the performance of the Bayesian PID approach for charged pions, kaons and protons in the central barrel of ALICE is studied. PID is performed via measurements of specific energy loss ($\mathrm{d}E/\mathrm{d}x$) and time-of-flight. PID efficiencies and misidentification probabilities are extracted and compared with Monte Carlo simulations using high-purity samples of identified particles in the decay channels ${\mathrm{K}}_S^0\to {\pi }^{-}{\pi }^{+}$, $\varphi \to {\mathrm{K}}^{-}{\mathrm{K}}^{+}$, and $\Lambda \to \mathrm{p}{\pi }^{-}$ in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. In order to thoroughly assess the validity of the Bayesian approach, this methodology was used to obtain corrected $p_{\mathrm{T}}$ spectra of pions, kaons, protons, and D${}^0$ mesons in pp collisions at $\sqrt{s}=7$ TeV. In all cases, the results using Bayesian PID were found to be consistent with previous measurements performed by ALICE using a standard PID approach. For the measurement of D${}^0\to {\mathrm{K}}^{-}{\pi }^{+}$, it was found that a Bayesian PID approach gave a higher signal-to-background ratio and a similar or larger statistical significance when compared with standard PID selections, despite a reduced identification efficiency. Finally, we present an exploratory study of the measurement of ${\Lambda }_{\mathrm{c}}^{+}\to \mathrm{p}{\mathrm{K}}^{-}{\pi }^{+}$ in pp collisions at $\sqrt{s}=7$ TeV, using the Bayesian approach for the identification of its decay products.

   ↳ physics.data-anhep-exnucl-exEur.Phys.J.Plus(2016)·66 citations
6. 06*

   Time-of-flight Fourier UCN spectrometer

   G.V. Kulin · A.I. Frank · S.V. Goryunov · D.V. Kustov · P. Geltenbort🇫🇷 · M. Jentschel🇫🇷 · B.Lauss🇨🇭 · Ph. Schmidt-Wellenburg🇨🇭

   We describe a new time-of-flight Fourier spectrometer for investigation of UCN diffraction by a moving grating. The device operates in the regime of a discrete set of modulation frequencies. The results of the first experiments show that the spectrometer may be used for obtaining UCN energy spectra in the energy range of 60$÷$200 neV with a resolution of about 5 neV. The accuracy of determination of the line position was estimated to be several units of $10^{-10}$ eV

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2016)·5 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.