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Register a new userFirst measurement of the temperature dependence of muon transfer rate from muonic hydrogen atoms to oxygen
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Emiliano Mocchiutti
Publication date
2019
fields
Physics
and research's language is
English
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We report the first measurement of the temperature dependence of muon transfer rate from $mu$p atoms to oxygen between 100 and 300 K. Data were obtained from the X-ray spectra of delayed events in gaseous target H$_2$/O$_2$ exposed to a muon beam. Based on the data, we determined the muon transfer energy dependence up to 0.1 eV, showing an 8-fold increase in contrast with the predictions of constant rate in the low energy limit. This work set constraints on theoretical models of muon transfer, and is of fundamental importance for the measurement of the hyperfine splitting of $mu$p by the FAMU collaboration.
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The first measurement of the temperature dependence of the muon transfer rate from muonic hydrogen to oxygen was performed by the FAMU collaboration in 2016. The results provide evidence that the transfer rate rises with the temperature in the range 104-300 K. This paper presents the results of the experiment done in 2018 to extend the measurements towards lower (70 K) and higher (336 K) temperatures. The 2018 results confirm the temperature dependence of the muon transfer rate observed in 2016 and sets firm ground for comparison with the theoretical predictions.
Background: The rate lambda_ppmu characterizes the formation of ppmu molecules in collisions of muonic pmu atoms with hydrogen. In measurements of the basic weak muon capture reaction on the proton to determine the pseudoscalar coupling g_P, capture occurs from both atomic and molecular states. Thus knowledge of lambda_ppmu is required for a correct interpretation of these experiments. Purpose: Recently the MuCap experiment has measured the capture rate Lambda_S from the singlet pmu atom, employing a low density active target to suppress ppmu formation (PRL 110, 12504 (2013)). Nevertheless, given the unprecedented precision of this experiment, the existing experimental knowledge in lambda_ppmu had to be improved. Method: The MuCap experiment derived the weak capture rate from the muon disappearance rate in ultra-pure hydrogen. By doping the hydrogen with 20 ppm of argon, a competing process to ppmu formation was introduced, which allowed the extraction of lambda_ppmu from the observed time distribution of decay electrons. Results: The ppmu formation rate was measured as lambda_ppmu = (2.01 +- 0.06(stat) +- 0.03(sys)) 10^6 s^-1. This result updates the lambda_ppmu value used in the above mentioned MuCap publication. Conclusions: The 2.5x higher precision compared to earlier experiments and the fact that the measurement was performed at nearly identical conditions to the main data taking, reduces the uncertainty induced by lambda_ppmu to a minor contribution to the overall uncertainty of Lambda_S and g_P, as determined in MuCap. Our final value for lambda_ppmu shifts Lambda_S and g_P by less than one tenth of their respective uncertainties compared to our results published earlier.
The FAMU experiment aims to accurately measure the hyperfine splitting of the ground state of the muonic hydrogen atom. A measurement of the transfer rate of muons from hydrogen to heavier gases is necessary for this purpose. In June 2014, within a preliminary experiment, a pressurized gas-target was exposed to the pulsed low-energy muon beam at the RIKEN RAL muon facility (Rutherford Appleton Laboratory, UK). The main goal of the test was the characterization of both the noise induced by the pulsed beam and the X-ray detectors. The apparatus, to some extent rudimental, has served admirably to this task. Technical results have been published that prove the validity of the choices made and pave the way for the next steps. This paper presents the results of physical relevance of measurements of the muon transfer rate to carbon dioxide, oxygen, and argon from non-thermalized excited mu-p atoms. The analysis methodology and the approach to the systematics errors are useful for the subsequent study of the transfer rate as function of the kinetic energy of the mu-p currently under way.
This paper reports the first measurement using the NOvA detectors of $ u_mu$ disappearance in a $ u_mu$ beam. The analysis uses a 14 kton-equivalent exposure of $2.74 times 10^{20}$ protons-on-target from the Fermilab NuMI beam. Assuming the normal neutrino mass hierarchy, we measure $Delta m^{2}_{32}=(2.52^{+0.20}_{-0.18})times 10^{-3}$ eV$^{2}$ and $sin^2theta_{23}$ in the range 0.38-0.65, both at the 68% confidence level, with two statistically-degenerate best fit points at $sin^2theta_{23} = $ 0.43 and 0.60. Results for the inverted mass hierarchy are also presented.
Studies of muonic hydrogen atoms and molecules have been performed traditionally in bulk targets of gas, liquid or solid. At TRIUMF, Canadas meson facility, we have developed a new type of target system using multilayer thin films of solid hydrogen, which provides a beam of muonic hydrogen atoms in vacuum. Using the time-of-flight of the muonic atoms, the energy-dependent information of muonic reactions are obtained in direct manner. We discuss some unique measurements enabled by the new technique, with emphasis on processes relevant to muon catalyzed fusion.
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