Thu·Dec 13, 2018Thursday·December 13, 2018

1. 01*

   Measurement of the Weak Axial-Vector Coupling Constant in the Decay of Free Neutrons Using a Pulsed Cold Neutron Beam

   Bastian Märkisch🇩🇪 · Holger Mest🇩🇪 · Heiko Saul🇩🇪 · Xiangzun Wang🇩🇪 · Hartmut Abele🇦🇹 · Dirk Dubbers🇩🇪 · Michael Klopf🇦🇹 · Alexander Petoukhov🇫🇷 · Christoph Roick🇩🇪 · Torsten Soldner🇫🇷 · Dominik Werder🇩🇪

   We present a precision measurement of the axial-vector coupling constant $g_A$ in the decay of polarized free neutrons. For the first time, a pulsed cold neutron beam was used for this purpose. By this method, leading sources of systematic uncertainty are suppressed. From the electron spectra we obtain $\lambda =g_A/g_V=-1.27641(45{)}_{\mathrm{stat}}(33{)}_{\mathrm{sys}}$ which confirms recent measurements with improved precision. This corresponds to a value of the parity violating beta asymmetry parameter of $A_0=-0.11985(17{)}_{\mathrm{stat}}(12{)}_{\mathrm{sys}}$. We discuss implications on the CKM matrix element $V_{ud}$ and derive a limit on left-handed tensor interaction.

   nucl-exPRL(2019)·256 citations
2. 02*

   A new investigation of half-lives for the decay modes of ${}^{50}$V

   M. Laubenstein🇮🇹 · B. Lehnert🇩🇪 · S. S. Nagorny🇮🇹 · S. Nisi🇮🇹 · K. Zuber🇩🇪

   A new search for the decay modes of the 4-fold forbidden non-unique decay of ${}^{50}$V has been performed at the Gran Sasso Underground Laboratory (LNGS). In total an exposure of 197 kg $\times$ d has been accumulated. The half-life for the electron capture into the first excited state of ${}^{50}$Ti has been measured with the highest precision to date as $2.67_{-0.18}^{+0.16}\times 10^{17}$ yr (68% C.I.) in which systematics uncertainties dominate. The search for the $\beta$-decay into the first excited state of ${}^{50}$Cr resulted in a lower limit of $1.9\times 10^{19}$ yr (90% C.I.), which is an improvement of almost one order of magnitude compared to existing results. The sensitivity of the new measurement is now in the region of theoretical predictions.

   nucl-exPRC(2019)·15 citations
3. 03*

   First determination of the $\rho$ parameter at $\sqrt{s}=13$ TeV -- probing the existence of a colourless three-gluon bound state

   TOTEM Collaboration: G. Antchev🇨🇭 · P. Aspell🇨🇭 · I. Atanassov🇵🇱 · V. Avati🇵🇱 · J. Baechler🇨🇭 · C. Baldenegro Barrera🇺🇸 · V. Berardi🇮🇹 · M. Berretti🇫🇮 · E. Bossini🇮🇹 · U. Bottigli🇮🇹 · M. Bozzo🇮🇹 · R. Bruce🇨🇭 and 83 other authors

   The TOTEM experiment at the LHC has performed the first measurement at $\sqrt{s}=13$ TeV of the $\rho$ parameter, the real to imaginary ratio of the nuclear elastic scattering amplitude at $t=0$, obtaining the following results: $\rho =0.09\pm 0.01$ and $\rho =0.10\pm 0.01$, depending on different physics assumptions and mathematical modelling. The unprecedented precision of the $\rho$ measurement, combined with the TOTEM total cross-section measurements in an energy range larger than 10 TeV (from 2.76 to 13 TeV), has implied the exclusion of all the models classified and published by COMPETE. The $\rho$ results obtained by TOTEM are compatible with the predictions, from alternative theoretical models both in the Regge-like framework and in the QCD framework, of a colourless 3-gluon bound state exchange in the $t$-channel of the proton-proton elastic scattering. On the contrary, if shown that the 3-gluon bound state $t$-channel exchange is not of importance for the description of elastic scattering, the $\rho$ value determined by TOTEM would represent a first evidence of a slowing down of the total cross-section growth at higher energies. The very low-$|t|$ reach allowed also to determine the absolute normalisation using the Coulomb amplitude for the first time at the LHC and obtain a new total proton-proton cross-section measurement ${\sigma }_{tot}=110.3\pm 3.5$ mb, completely independent from the previous TOTEM determination. Combining the two TOTEM results yields ${\sigma }_{tot}=110.5\pm 2.4$ mb.

   ↳ hep-exhep-phnucl-exEPJC(2019)·247 citations
4. 04*

   Identified particle production in Xe+Xe collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.44 TeV using a multiphase transport model

   Rutuparna Rath🇮🇳 · Sushanta Tripathy🇮🇳 · Raghunath Sahoo🇮🇳 · Sudipan De🇮🇳 · Mohammed Younus🇿🇦

   Xe+Xe collisions at relativistic energies provide us with an opportunity to study a possible system with deconfined quarks and gluons, whose size is in between those produced by p+p and Pb+Pb collisions. In the present work, we have used AMPT transport model with nuclear deformation to study the identified particle production such as (${\pi }^{+}+{\pi }^{-}$), (K${}^{+}$+K${}^{-}$), ${\mathrm{K}}_{\mathrm{s}}^0$, (p+$\bar{\mathrm{p}}$), $\varphi$ and ($\Lambda +\bar{\Lambda }$) in Xe+Xe collisions at $\sqrt{s_{\mathrm{NN}}}$=5.44 TeV. We study the $p{}_{\mathrm{T}}$-spectra, integrated yield, $p{}_{\mathrm{T}}$-differential and $p{}_{\mathrm{T}}$-integrated particle ratios to (${\pi }^{+}+{\pi }^{-}$) and (K${}^{+}$+K${}^{-}$) as a function of collision centrality. The particle ratios are focused on strange to non-strange ratios and baryon to meson ratios. The effect of deformations has also been highlighted by comparing our results to non-deformation case. We have also compared the results from AMPT string melting and AMPT default version to explore possible effects of coalescence mechanism. We observe that the differential particle ratios show strong dependence with centrality while the integrated particle ratios show no centrality dependence.We give thermal model estimation of chemical freeze-out temperature and the Boltzmann-Gibbs Blast Wave analysis of kinetic freeze-out temperature and collective radial flow in Xe+Xe collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.44 TeV.

   ↳ hep-phhep-exnucl-exnucl-thPRC(2019)·10 citations
5. 05*

   Sorting out quenched jets

   Jasmine Brewer🇺🇸 · José Guilherme Milhano🇵🇹 · Jesse Thaler🇺🇸

   We introduce a new 'quantile' analysis strategy to study the modification of jets as they traverse through a droplet of quark-gluon plasma. To date, most jet modification studies have been based on comparing the jet properties measured in heavy-ion collisions to a proton-proton baseline at the same reconstructed jet transverse momentum ($p_T$). It is well known, however, that the quenching of jets from their interaction with the medium leads to a migration of jets from higher to lower $p_T$, making it challenging to directly infer the degree and mechanism of jet energy loss. Our proposed quantile matching procedure is inspired by (but not reliant on) the approximate monotonicity of energy loss in the jet $p_T$. In this strategy, jets in heavy-ion collisions ordered by $p_T$ are viewed as modified versions of the same number of highest-energy jets in proton-proton collisions, and the fractional energy loss as a function of jet $p_T$ is a natural observable ($Q_{\mathrm{AA}}$). Furthermore, despite non-monotonic fluctuations in the energy loss, we use an event generator to validate the strong correlation between the $p_T$ of the parton that initiates a heavy-ion jet and the $p_T$ of the vacuum jet which corresponds to it via the quantile procedure ($p_T^{\mathrm{quant}}$). We demonstrate that this strategy both provides a complementary way to study jet modification and mitigates the effect of $p_T$ migration in heavy-ion collisions.

   ↳ hep-phhep-exnucl-exnucl-thPRL(2019)·50 citations
6. 06*

   Bias-Variance Trade-off and Model Selection for Proton Radius Extractions

   Douglas W. Higinbotham🇺🇸 · Pablo Giuliani🇺🇸 · Randall E. McClellan🇺🇸 · Simon Sirca🇸🇮 · Xuefei Yan🇺🇸

   Intuitively, a scientist might assume that a more complex regression model will necessarily yield a better predictive model of experimental data. Herein, we disprove this notion in the context of extracting the proton charge radius from charge form factor data. Using a Monte Carlo study, we show that a simpler regression model can in certain cases be the better predictive model. This is especially true with noisy data where the complex model will fit the noise instead of the physical signal. Thus, in order to select the appropriate regression model to employ, a clear technique should be used such as the Akaike information criterion or Bayesian information criterion, and ideally selected previous to seeing the results. Also, to ensure a reasonable fit, the scientist should also make regression quality plots, such as residual plots, and not just rely on a single criterion such as reduced chi2. When we apply these techniques to low four-momentum transfer cross section data, we find a proton radius that is consistent with the muonic Lamb shift results. While presented for the case of proton radius extraction, these concepts are applicable in general and can be used to illustrate the necessity of balancing bias and variance when building a regression model and validating results, ideas that are at the heart of modern machine learning algorithms.

   ↳ physics.data-annucl-ex8 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.