Wed·Sep 14, 2016Wednesday·September 14, 2016

1. 01*

   Vector boson and charmonia measurements in $p$+Pb collisions with ATLAS

   Markus K. Koehler (for the ATLAS Collaboration)🇮🇱

   The production of electroweak bosons ($Z,\gamma$ and $W$) and charmonia is sensitive to the initial-state geometry of heavy-ion collisions and to the parton distribution function with its potential nuclear modification. Since their leptonic decay products do not interact strongly, their kinematics are unmodified by the strongly interacting medium, which can be created in a heavy-ion collision. We report on the latest results of the ATLAS Collaboration on electroweak boson and charmonia production in $p$+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. Production yields of $Z$ and $W$ bosons are presented as a function of (pseudo-)rapidity in different centrality bins. The forward-backward ratio of J/$\psi$ is shown as a function of transverse momentum and center-of-mass rapidity.

   nucl-exPoS(2016)·0 citations
2. 02*

   Search for the decay of nature's rarest isotope ${}^{180m}$Ta

   Björn Lehnert🇩🇪 · Mikael Hult🇧🇪 · Guillaume Lutter🇧🇪 · Kai Zuber🇩🇪

   ${}^{180m}$Ta is the rarest naturally occurring quasi-stable isotope and the longest lived metastable state which is known. Its possible decay via the ${\beta }^{-}$ or the electron capture channel has never been observed. This article presents a search for the decay of ${}^{180m}$Ta with an ultra low background Sandwich HPGe gamma spectrometry setup in the HADES underground laboratory. No signal is observed and improved lower partial half-life limits are set with a Bayesian analysis to $5.8\cdot 10^{16}$ yr for the ${\beta }^{-}$ channel and $2.0\cdot 10^{17}$ yr for the electron capture channel (90% credibility). The total half-life of ${}^{180m}$Ta is longer than $4.5\cdot 10^{16}$ yr. This is more than a factor of two improvement compared to previous searches.

   nucl-exPRC(2017)·27 citations
3. 03*

   Di-Jet Imbalance Measurements at $\sqrt{s_{NN}}=200$ GeV at STAR

   STAR Collaboration: L. Adamczyk · J. K. Adkins · G. Agakishiev · M. M. Aggarwal · Z. Ahammed · I. Alekseev · D. M. Anderson · R. Aoyama · A. Aparin · D. Arkhipkin · E. C. Aschenauer · M. U. Ashraf and 332 other authors

   We report the first di-jet transverse momentum asymmetry measurements from Au+Au and p+p collisions at RHIC. The two highest-energy back-to-back jets reconstructed from fragments with transverse momenta above 2 GeV/c display a significantly stronger momentum imbalance in heavy-ion collisions than in the p+p reference. When re-examined with correlated soft particles included, we observe that these di-jets then exhibit a unique new feature -- momentum balance is restored to that observed in p+p for a jet resolution parameter of R=0.4, while re-balancing is not attained with a smaller value of R=0.2.

   nucl-exPRL(2017)·76 citations
4. 04*

   Measurement of electrons from beauty-hadron decays in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV

   ALICE Collaboration

   The production of beauty hadrons was measured via semi-leptonic decays at mid-rapidity with the ALICE detector at the LHC in the transverse momentum interval $1<p_{\mathrm{T}}<8$ GeV/$c$ in minimum-bias p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV and in $1.3<p_{\mathrm{T}}<8$ GeV/$c$ in the 20% most central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV. The pp reference spectra at $\sqrt{s}=5.02$ TeV and $\sqrt{s}=2.76$ TeV, needed for the calculation of the nuclear modification factors $R_{\mathrm{pPb}}$ and $R_{\mathrm{PbPb}}$, were obtained by a pQCD-driven scaling of the cross section of electrons from beauty-hadron decays measured at $\sqrt{s}=7$ TeV. In the $p_{\mathrm{T}}$ interval $3<p_{\mathrm{T}}<8$ GeV/$c$ a suppression of the yield of electrons from beauty-hadron decays is observed in Pb-Pb compared to pp collisions. Towards lower $p_{\mathrm{T}}$, the $R_{\mathrm{PbPb}}$ values increase with large systematic uncertainties. The $R_{\mathrm{pPb}}$ is consistent with unity within systematic uncertainties and is well described by theoretical calculations that include cold nuclear matter effects in p-Pb collisions. The measured $R_{\mathrm{pPb}}$ and these calculations indicate that cold nuclear matter effects are small at high transverse momentum also in Pb-Pb collisions. Therefore, the observed reduction of $R_{\mathrm{PbPb}}$ below unity at high $p_{\mathrm{T}}$ may be ascribed to an effect of the hot and dense medium formed in Pb-Pb collisions.

   nucl-exhep-exJHEP(2017)·58 citations
5. 05*

   Commissioning of the COBRA demonstrator and investigation of surface events as its main background

   Jan Tebrügge🇩🇪

   The COBRA collaboration investigates 0{\nu}\beta\beta-decays (neutrinoless double beta-decays). Therefore, a demonstrator setup using coplanar-grid CdZnTe detectors is operated at the LNGS underground laboratory. In this work, the demonstrator was commissioned and completed, which is discussed extensively. The demonstrator works reliably and collects low-background physics data. One result of the analysis of the data is that surface events are the dominating background component. To better understand and possibly discriminate this background, surface events were studied in detail. This was done mainly using laboratory measurements. For a better interpretation of these measurements, simulations of particle trajectories and ranges were done. The surface sensitivity tests showed large differences between the individual detectors. Often, a dead-layer was determined, especially at the surfaces where the non-collecting anode (NCA) is the outermost anode rail. Due to this, the sensitivity of the surfaces where the collecting anode (CA) is adjacent was typically about a factor of three larger than the NCA sensitivity. A comparison of the pulse shape analysis methods LSE and A/E was done. Laboratory measurements indicate, that the latter performs better. Alpha scanning measurements were done to spatially investigate the surface sensitivity. Plausible variations were measured. However, no hints were found how to improve the surface event recognition. The instrumentation of the guard ring, which surrounds the anode structure, was tested and improved the surface event discrimination significantly. The fraction of surviving alpha events was at a per-mill level. Important steps for a future large-scale COBRA experiment are discussed briefly, mainly the use of an integrated read-out system. Overall, the results indicate a large potential in background reduction for the COBRA experiment.

   ↳ physics.ins-detnucl-ex3 citations
6. 06*

   Exclusive photoproduction of a $\gamma \rho$ pair with a large invariant mass

   R. Boussarie🇫🇷 · B. Pire🇫🇷 · L. Szymanowski🇵🇱 · S. Wallon🇫🇷

   Exclusive photoproduction of a $\gamma \rho$ pair in the kinematics where the pair has a large invariant mass and the final nucleon has a small transverse momentum is described in the collinear factorization framework. The scattering amplitude is calculated at leading order in ${\alpha }_s$ and the differential cross sections for the process where the $\rho -$meson is either longitudinally or transversely polarized are estimated in the kinematics of the JLab 12-GeV experiments.

   ↳ hep-phhep-exnucl-exnucl-thJHEP(2017)·78 citations
7. 07*

   New results related to QGP-like effects in small systems with ALICE

   Vytautas Vislavicius (for the ALICE collaboration)🇸🇪

   Results on the production of ${\pi }^{\pm }$, ${\text{K}}^{\pm }$, $\text{p}(\bar{\text{p}})$, $\Lambda (\bar{\Lambda })$, ${\Xi }^{-}\left({\bar{\Xi }}^{+}\right)$ and ${\Omega }^{-}\left({\bar{\Omega }}^{+}\right)$ at midrapidity ($|y|<0.5$) as a function of multiplicity in $\sqrt{s}=7\text{TeV}$ pp collisions are reported. Transverse momentum distributions and integrated yields are compared to expectations from statistical hadronization models along with results from different colliding systems and center-of-mass energies. The evolution of spectral shapes with multiplicity show similar patterns to those seen in p-Pb and Pb-Pb collisions. The $p_{\text{T}}$-integrated baryon yields relative to pions exhibit a significant strangeness-related enhancement in both pp and p-Pb collisions.

   ↳ hep-exnucl-exPoS(2016)·1 citation
8. 08*

   Extraction of $t$-slopes from experimental $\gamma p\to K^{+}\Lambda$ and $\gamma p\to K^{+}{\Sigma }_0$ cross section data

   Adam Freese🇺🇸 · Daniel Puentes🇺🇸 · Shankar Adhikari🇺🇸 · Rafael Badui🇺🇸 · Lei Guo🇺🇸 · Brian Raue🇺🇸

   We analyze recent $K^{+}$ meson photoproduction data from the CLAS collaboration for the reactions $\gamma p\to K^{+}\Lambda$ and $\gamma p\to K^{+}{\Sigma }_0$, fitting measured forward-angle differential cross sections to the form $A{e}^{Bt}$. We develop a quantitative scheme for determining the kinematic region where the fit is to be done, and, from the extracted $t$-slope $B$, determine whether single-Reggeon exchange can explain the production mechanism. We find that, in the region $5<s<8.1$ GeV${}^2$, production of the $K^{+}\Lambda$ channel can be explained by single $K^{+}$ Reggeon exchange, but the $K^{+}{\Sigma }_0$ production channel cannot. We verify these conclusions by fitting the data to a differential cross section produced by the interfering sum of two exponential amplitudes.

   ↳ hep-phnucl-exPRC(2017)·1 citation
9. 09*

   A high-resolution CMOS imaging detector for the search of neutrinoless double $\beta$ decay in ${}^{82}$Se

   A.E. Chavarria🇺🇸 · C. Galbiati🇺🇸 · X. Li🇺🇸 · J.A. Rowlands🇨🇦

   We introduce high-resolution solid-state imaging detectors for the search of neutrinoless double $\beta$ decay. Based on the present literature, imaging devices from amorphous ${}^{82}$Se evaporated on a complementary metal-oxide-semiconductor (CMOS) active pixel array could have the energy and spatial resolution to produce two-dimensional images of ionizing tracks of utmost quality, effectively akin to an electronic bubble chamber in the double $\beta$ decay energy regime. Still to be experimentally demonstrated, a detector consisting of a large array of these devices could have very low backgrounds, possibly reaching $10^{-7}$/(kg y) in the neutrinoless decay region of interest (ROI), as it may be required for the full exploration of the neutrinoless double $\beta$ decay parameter space in the most unfavorable condition of a strongly quenched nucleon axial coupling constant.

   ↳ physics.ins-dethep-exhep-phnucl-exJINST(2017)·17 citations
10. 10*

    The 5 MeV bump - a nuclear whodunit mystery

    Patrick Huber🇺🇸

    We perform a combined analysis of recent NEOS and Daya Bay data on the reactor antineutrino spectrum. This analysis includes approximately 1.5 million antineutrino events, which is the largest neutrino event sample analyzed to date. We use a double ratio which cancels flux model dependence and related uncertainties as well as the effects of the detector response model. We find at 3-4 standard deviation significance level, that plutonium-239 and plutonium-241 are disfavored as the single source for the the so-called 5 MeV bump. This analysis method has general applicability and in particular with higher statistics data sets will be able to shed significant light on the issue of the bump. With some caveat this also should allow to improve the sensitivity for sterile neutrino searches in NEOS.

    ↳ hep-phhep-exnucl-exnucl-thPRL(2017)·88 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.