Tue·Aug 21, 2018Tuesday·August 21, 2018

1. 01*

   FAMU: study of the energy dependent transfer rate ${\Lambda }_{\mu p\to \mu O}$

   FAMU Collaboration: E. Mocchiutti (1)🇮🇹 · V. Bonvicini (1)🇮🇹 · M. Danailov (1 and 2)🇮🇹 · E. Furlanetto (1 and 3)🇮🇹 · K. S. Gadedjisso-Tossou (1,4 and 5)🇮🇹 · D. Guffanti (1 and 6)🇮🇹 · C. Pizzolotto (1)🇮🇹 · A. Rachevski (1)🇮🇹 · L. Stoychev (1 and 4)🇮🇹 · E. Vallazza (1)🇮🇹 · G. Zampa (1)🇮🇹 · J. Niemela (4)🇮🇹 and 43 other authors

   The main goal of the FAMU experiment is the measurement of the hyperfine splitting (hfs) in the 1S state of muonic hydrogen $\Delta E_{hfs}({\mu }^{-}p)1S$. The physical process behind this experiment is the following: $\mu p$ are formed in a mixture of hydrogen and a higher-Z gas. When absorbing a photon at resonance-energy $\Delta E_{hfs}\approx 0.182$~eV, in subsequent collisions with the surrounding $H_2$ molecules, the $\mu p$ is quickly de-excited and accelerated by $\sim 2/3$ of the excitation energy. The observable is the time distribution of the K-lines X-rays emitted from the $\mu Z$ formed by muon transfer $(\mu p)+Z\to (\mu Z{)}^{\ast }+p$, a reaction whose rate depends on the $\mu p$ kinetic energy. The maximal response, to the tuned laser wavelength, of the time distribution of X-ray from K-lines of the $(\mu Z{)}^{\ast }$ cascade indicate the resonance. During the preparatory phase of the FAMU experiment, several measurements have been performed both to validate the methodology and to prepare the best configuration of target and detectors for the spectroscopic measurement. We present here the crucial study of the energy dependence of the transfer rate from muonic hydrogen to oxygen (${\Lambda }_{\mu p\to \mu O}$), precisely measured for the first time.

   nucl-exphysics.data-anphysics.ins-detJ.Phys.Conf.Ser.(2018)·2 citations
2. 02*

   Revisiting the proton-radius problem using constrained Gaussian processes

   Shuang Zhou🇺🇸 · P. Giuliani🇺🇸 · J. Piekarewicz🇺🇸 · Anirban Bhattacharya🇺🇸 · Debdeep Pati🇺🇸

   Background: The "proton radius puzzle" refers to an eight-year old problem that highlights major inconsistencies in the extraction of the charge radius of the proton from muonic Lamb-shift experiments as compared against experiments using elastic electron scattering. For the latter, the determination of the charge radius involves an extrapolation of the experimental form factor to zero momentum transfer. Purpose: To estimate the proton radius by introducing a novel non-parametric approach to model the electric form factor of the proton. Methods: Within a Bayesian paradigm, we develop a model flexible enough to fit the data without any parametric assumptions on the form factor. The Bayesian estimation is guided by imposing only two physical constraints on the form factor: (a) its value at zero momentum transfer (normalization) and (b) its overall shape, assumed to be a monotonically decreasing function of the momentum transfer. Variants of these assumptions are explored to assess the impact of these constraints. Results: So far our results are inconclusive in regard to the proton puzzle, as they depend on both, the assumed constrains and the range of experimental data used. For example, if only low momentum-transfer data is used, adopting only the normalization constraint provides a value compatible with the smaller muonic result, while imposing only the shape constraint favors the larger electronic value. Conclusions: We have presented a novel technique to estimate the proton radius from electron scattering data based on a non-parametric Gaussian process. We have shown the impact of the physical constraints imposed on the form factor and of the range of experimental data used. In this regard, we are hopeful that as this technique is refined and with the anticipated new results from the PRad experiment, we will get closer to resolve of the puzzle.

   ↳ nucl-thnucl-exstat.APPRC(2019)·25 citations
3. 03*

   Search for sub-GeV dark matter by annual modulation using XMASS-I detector

   M. Kobayashi🇯🇵 · K. Abe🇯🇵 · K. Hiraide🇯🇵 · K. Ichimura🇯🇵 · Y. Kishimoto🇯🇵 · K. Kobayashi🇯🇵 · S. Moriyama🇯🇵 · M. Nakahata🇯🇵 · H. Ogawa🇯🇵 · K. Sato🇯🇵 · H. Sekiya🇯🇵 · T. Suzuki🇯🇵 and 24 other authors

   A search for dark matter (DM) with mass in the sub-GeV region (0.32-1 GeV) was conducted by looking for an annual modulation signal in XMASS, a single-phase liquid xenon detector. Inelastic nuclear scattering accompanied by bremsstrahlung emission was used to search down to an electron equivalent energy of 1 keV. The data used had a live time of 2.8 years (3.5 years in calendar time), resulting in a total exposure of 2.38 ton-years. No significant modulation signal was observed and 90% confidence level upper limits of $1.6\times 10^{-33}$ cm${}^2$ at 0.5 GeV was set for the DM-nucleon cross section. This is the first experimental result of a search for DM mediated by the bremsstrahlung effect. In addition, a search for DM with mass in the multi-GeV region (4-20 GeV) was conducted with a lower energy threshold than previous analysis of XMASS. Elastic nuclear scattering was used to search down to a nuclear recoil equivalent energy of 2.3 keV, and upper limits of 2.9 $\times$10${}^{-42}$ cm${}^2$ at 8 GeV was obtained.

   ↳ astro-ph.COhep-exnucl-exphysics.ins-detPLB(2019)·35 citations
4. 04*

   The cumulants of the baryon number from central Au+Au collision at $E_{lab}$= 1.23 GeV$/$nucleon reveal the nuclear mean-field potentials

   Yunxiao Ye🇨🇳 · Yongjia Wang🇨🇳 · Jan Steinheimer🇩🇪 · Yasushi Nara🇯🇵 · Hao-jie Xu🇨🇳 · Pengcheng Li🇨🇳 · Dinghui Lu🇨🇳 · Qingfeng Li🇨🇳 · Horst Stoecker🇩🇪

   Fluctuations of the baryon number in relativistic heavy-ion collisions are a promising observable to explore the structure of the QCD phase diagram. The cumulant ratios in heavy ion collisions at intermediate energies ($\sqrt{s_{\text{NN}}}<7$ GeV) have not been studied to date. We investigate the effects of mean field potential and clustering on the cumulant ratios of baryon and proton number distributions in Au+Au collisions at beam energy of 1.23 GeV$/$nucleon as measured by the HADES Collaboration at GSI. Ultrarelativistic Quantum Molecular Dynamics (UrQMD) and the JAM model are used to calculate the cumulants with different mean field potentials. It is found that the cumulant ratios are strongly time dependent. At the early stage, the effects of the potentials on the fluctuations of the particle multiplicity in momentum space are relatively weak. The mean fields enhance the fluctuations during the expansion stage, especially for small rapidity acceptance windows. The enhancement of cumulant ratios for free protons is strongly suppressed as compared to that for all baryons. The mean field potentials and the clustering play an important role for the measured cumulant ratios at intermediate energy.

   ↳ nucl-thnucl-exPRC(2018)·16 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.