Wed·Jul 29, 2015Wednesday·July 29, 2015

1. 01*

   Matching pion-nucleon Roy-Steiner equations to chiral perturbation theory

   Martin Hoferichter🇺🇸 · Jacobo Ruiz de Elvira🇩🇪 · Bastian Kubis🇩🇪 · Ulf-G. Meißner🇩🇪

   We match the results for the subthreshold parameters of pion-nucleon scattering obtained from a solution of Roy-Steiner equations to chiral perturbation theory up to next-to-next-to-next-to-leading order, to extract the pertinent low-energy constants including a comprehensive analysis of systematic uncertainties and correlations. We study the convergence of the chiral series by investigating the chiral expansion of threshold parameters up to the same order and discuss the role of the \Delta(1232) resonance in this context. Results for the low-energy constants are also presented in the counting scheme usually applied in chiral nuclear effective field theory, where they serve as crucial input to determine the long-range part of the nucleon-nucleon potential as well as three-nucleon forces.

   ↳ nucl-thhep-phnucl-exPRL(2015)·216 citations
2. 02*

   Study of cosmic ray events with high muon multiplicity using the ALICE detector at the CERN Large Hadron Collider

   ALICE Collaboration

   ALICE is one of four large experiments at the CERN Large Hadron Collider near Geneva, specially designed to study particle production in ultra-relativistic heavy-ion collisions. Located 52 meters underground with 28 meters of overburden rock, it has also been used to detect muons produced by cosmic ray interactions in the upper atmosphere. In this paper, we present the multiplicity distribution of these atmospheric muons and its comparison with Monte Carlo simulations. This analysis exploits the large size and excellent tracking capability of the ALICE Time Projection Chamber. A special emphasis is given to the study of high multiplicity events containing more than 100 reconstructed muons and corresponding to a muon areal density ${\rho }_{\mu }>5.9$m${}^{-2}$. Similar events have been studied in previous underground experiments such as ALEPH and DELPHI at LEP. While these experiments were able to reproduce the measured muon multiplicity distribution with Monte Carlo simulations at low and intermediate multiplicities, their simulations failed to describe the frequency of the highest multiplicity events. In this work we show that the high multiplicity events observed in ALICE stem from primary cosmic rays with energies above $10^{16}$ eV and that the frequency of these events can be successfully described by assuming a heavy mass composition of primary cosmic rays in this energy range. The development of the resulting air showers was simulated using the latest version of QGSJET to model hadronic interactions. This observation places significant constraints on alternative, more exotic, production mechanisms for these events.

   ↳ astro-ph.HEhep-exnucl-exJCAP(2016)·55 citations
3. 03*

   Status of the MAJORANA DEMONSTRATOR

   C. Cuesta🇺🇸 · N. Abgrall🇺🇸 · I.J. Arnquist🇺🇸 · F.T. Avignone III🇺🇸 · C.X. Baldenegro-Barrera🇺🇸 · A.S. Barabash🇷🇺 · F.E. Bertrand🇺🇸 · A.W. Bradley🇺🇸 · V. Brudanin🇷🇺 · M. Busch🇺🇸 · M. Buuck🇺🇸 · D. Byram🇺🇸 and 58 other authors

   The MAJORANA Collaboration is constructing the MAJORANA DEMONSTRATOR, an ultra-low background, modular, HPGe detector array with a mass of 44-kg (29 kg 76Ge and 15 kg natGe) to search for neutrinoless double beta decay in Ge-76. The next generation of tonne-scale Ge-based neutrinoless double beta decay searches will probe the neutrino mass scale in the inverted-hierarchy region. The MAJORANA DEMONSTRATOR is envisioned to demonstrate a path forward to achieve a background rate at or below 1 count/tonne/year in the 4 keV region of interest around the Q-value of 2039 keV. The MAJORANA DEMONSTRATOR follows a modular implementation to be easily scalable to the next generation experiment. First, the prototype module was assembled; it has been continuously taking data from July 2014 to June 2015. Second, Module 1 with more than half of the total enriched detectors and some natural detectors has been assembled and it is being commissioned. Finally, the assembly of Module 2, which will complete MAJORANA DEMONSTRATOR, is already in progress.

   ↳ physics.ins-detnucl-exAIP Conf.Proc.(2015)·6 citations
4. 04*

   Reply to "Comment on `Lattice determination of Sigma - Lambda mixing' "

   R. Horsley🇬🇧 · J. Najjar🇩🇪 · Y. Nakamura🇯🇵 · H. Perlt🇩🇪 · D. Pleiter🇩🇪 · P.E.L. Rakow🇬🇧 · G. Schierholz🇩🇪 · A. Schiller🇩🇪 · H. Stüben🇩🇪 · J.M. Zanotti🇦🇺

   In this Reply, we respond to the above Comment. Our computation [Phys. Rev. D 91 (2015) 074512] only took into account pure QCD effects, arising from quark mass differences, so it is not surprising that there are discrepancies in isospin splittings and in the Sigma - Lambda mixing angle. We expect that these discrepancies will be smaller in a full calculation incorporating QED effects.

   ↳ hep-lathep-phnucl-exnucl-thPRD(2015)·11 citations
5. 05*

   Measurement of longitudinal single-spin asymmetries for $W^{\pm }$ boson production in polarized $p+p$ collisions at $\sqrt{s}=510$ GeV at STAR

   Devika Gunarathne (for the STAR collaboration)🇺🇸

   $W^{\pm }$ boson production in longitudinally polarized $p+p$ collisions provides unique and clean access to the individual helicity polarizations of $u$ / $d$ quarks and anti-quarks. Due to the maximal violation of parity in the coupling, $W$ bosons couple to left-handed quarks and right-handed anti-quarks and hence offer direct probes of their respective helicity distributions in the nucleon. These can be extracted from measured parity-violating longitudinal single-spin asymmetries, $A_L$, for $W^{+(-)}$ boson production as a function of the decay lepton (positron) pseudo-rapidity $\eta$. The STAR experiment is well equipped to measure $A_L$ for $W^{\pm }$ boson production for $|\eta |<1$. The published STAR $A_L$ results (2011 and 2012 data combined) have been used by several theoretical analyses suggesting a significant impact in constraining the helicity distributions of anti-$u$ and anti-$d$ quarks. In 2013 the STAR experiment has collected a large data sample of $\sim$250 pb${}^{-1}$ which is more than 3 times larger than the total integrated luminosity in 2012, at $\sqrt{s}=510$ GeV with an average beam polarization of $\sim$54\%, comparable to run 2012. The status of the 2013 $A_L$ analysis will be discussed along with an overview of future plans.

   ↳ hep-exnucl-exPoS(2015)·0 citations
6. 06*

   Constraining Sea Quark Distributions Through $W^{\pm }$ Cross Section Ratios Measured at STAR

   M. Posik (for the STAR Collaboration)🇺🇸

   Over the past several years the STAR experiment at RHIC has been contributing to our understanding of the proton structure. Through its instrumentation, STAR is well equipped to measure $W\to \nu +e$ in $\sqrt{s}$ = 500/510 GeV proton-proton collisions at mid-rapidity (-1.1 $\le \eta \le$ 1.1) . The $W$ cross section ratio ($W^{+}/W^{-}$) is sensitive to unpolarized $u$, $d$, $\bar{u}$, and $\bar{d}$ quark distributions. At these kinematics, STAR is able to measure the quark distributions near Bjorken-$x$ values of 0.1. The RHIC runs in 2011, 2012 and 2013 at $\sqrt{s}$ = 500/510 GeV saw a significant increase in delivered luminosity from previous years. This resulted in a total data sample being collected of about 352 pb${}^{-1}$ of integrated luminosity. The increased statistics will lead to a higher precision measurement of the $W^{+}/W^{-}$ cross section ratio than was previously measured by STAR's 2009 run, as well as allow for a measurement of its $\eta$ dependence at mid-rapidity. Presented here is an update of the $W$ cross section ratio analysis from the STAR 2011, 2012 and 2013 runs.

   ↳ hep-exnucl-exPoS(2015)·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.