MICE: the Muon Ionization Cooling Experiment. Step I: First Measurement of Emittance with Particle Physics Detectors

The Muon Ionization Cooling Experiment (MICE) is a strategic R&D project intended to demonstrate the only practical solution to providing high brilliance beams necessary for a neutrino factory or muon collider. MICE is under development at the Rutherford Appleton Laboratory (RAL) in the United Kingdom. It comprises a dedicated beamline to generate a range of input muon emittances and momenta, with time-of-flight and Cherenkov detectors to ensure a pure muon beam. The emittance of the incoming beam will be measured in the upstream magnetic spectrometer with a scintillating fiber tracker. A cooling cell will then follow, alternating energy loss in Liquid Hydrogen (LH2) absorbers to RF cavity acceleration. A second spectrometer, identical to the first, and a second muon identification system will measure the outgoing emittance. In the 2010 run at RAL the muon beamline and most detectors were fully commissioned and a first measurement of the emittance of the muon beam with particle physics (time-of-flight) detectors was performed. The analysis of these data was recently completed and is discussed in this paper. Future steps for MICE, where beam emittance and emittance reduction (cooling) are to be measured with greater accuracy, are also presented

Nuclear Alpha-Particle Condensates

The $\alpha$-particle condensate in nuclei is a novel state described by a product state of $\alpha$'s, all with their c.o.m. in the lowest 0S orbit. We demonstrate that a typical $\alpha$-particle condensate is the Hoyle state ($E_{x}=7.65$ MeV, $0^+_2$ state in $^{12}$C), which plays a crucial role for the synthesis of $^{12}$C in the universe. The influence of antisymmentrization in the Hoyle state on the bosonic character of the $\alpha$ particle is discussed in detail. It is shown to be weak. The bosonic aspects in the Hoyle state, therefore, are predominant. It is conjectured that $\alpha$-particle condensate states also exist in heavier $n\alpha$ nuclei, like $^{16}$O, $^{20}$Ne, etc. For instance the $0^+_6$ state of $^{16}$O at $E_{x}=15.1$ MeV is identified from a theoretical analysis as being a strong candidate of a $4\alpha$ condensate. The calculated small width (34 keV) of $0^+_6$, consistent with data, lends credit to the existence of heavier Hoyle-analogue states. In non-self-conjugated nuclei such as $^{11}$B and $^{13}$C, we discuss candidates for the product states of clusters, composed of $\alpha$'s, triton's, and neutrons etc. The relationship of $\alpha$-particle condensation in finite nuclei to quartetting in symmetric nuclear matter is investigated with the help of an in-medium modified four-nucleon equation. A nonlinear order parameter equation for quartet condensation is derived and solved for $\alpha$ particle condensation in infinite nuclear matter. The strong qualitative difference with the pairing case is pointed out.Comment: 71 pages, 41 figures, review article, to be published in "Cluster in Nuclei (Lecture Notes in Physics) - Vol.2 -", ed. by C. Beck, (Springer-Verlag, Berlin, 2011

Lifetime measurements of N ≃ 20 phosphorus isotopes using the AGATA γ-ray tracking spectrometer

International audienceLifetimes of excited states of the phosphorus isotopes 1533,34,35,36P have been measured by using the differential recoil-distance method. The isotopes of phosphorus were populated in binary grazing reactions initiated by a beam of S36 ions of energy 225 MeV incident on a thin Pb208 target mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA γ-ray tracking array was used to detect γ rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were made within the range from about 1 to 100 ps. The number of states for which lifetime measurements were possible was limited by statistics. For P33, lifetime limits were determined for the first 3/2+ and 5/2+ states at 1431 and 1848 keV, respectively; the results are compared with previous published lifetime values. The lifetime of the first 2+ state of P34 at 429 keV was determined and compared with earlier measurements. For P35, the states for which lifetimes, or lifetime limits, were determined were those at 2386, 3860, 4101, and 4493 keV, with Jπ values of 3/2+, 5/2+, 7/21−, and 7/22−, respectively. There have been no previous published lifetimes for states in this nucleus. A lifetime was measured for the stretched π(1f7/2)⊗ν(1f7/2)Jπ=(7+) state of P36 at 5212 keV and a lifetime limit was established for the stretched π(1d3/2)⊗ν(1f7/2)Jπ=(5−) state at 2030 keV. There are no previously published lifetimes for states of P36. Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF effective interaction. In addition, measured branching ratios, published mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. In general, there is good agreement between experiment and the shell model; however there is evidence that the shell-model values of the M1 transition rates for the 3/21+→1/2+ (ground state) and 5/21+→3/21+ transitions in P33 underestimate the experimental values by a factor between 5 and 10. In P35 there are some disagreements between experimental and shell-model values of branching ratios for the first and second excited 7/2− states. In particular, there is a serious disagreement for the decay characteristics of the second 7/2− state at 4493 keV, for which the shell-model counterpart lies at 4754 keV. In this case, the shell-model competing electromagnetic decay branches are dominated by E1 and M1 transitions

Pion contamination in the MICE muon beam

The international Muon Ionization Cooling Experiment (MICE) will perform a systematic investigation of ionization cooling with muon beams of momentum between 140 and 240\,MeV/c at the Rutherford Appleton Laboratory ISIS facility. The measurement of ionization cooling in MICE relies on the selection of a pure sample of muons that traverse the experiment. To make this selection, the MICE Muon Beam is designed to deliver a beam of muons with less than $\sim$1\% contamination. To make the final muon selection, MICE employs a particle-identification (PID) system upstream and downstream of the cooling cell. The PID system includes time-of-flight hodoscopes, threshold-Cherenkov counters and calorimetry. The upper limit for the pion contamination measured in this paper is $f_\pi < 1.4\%$ at 90\% C.L., including systematic uncertainties. Therefore, the MICE Muon Beam is able to meet the stringent pion-contamination requirements of the study of ionization cooling.Department of Energy and National Science Foundation (U.S.A.), the Instituto Nazionale di Fisica Nucleare (Italy), the Science and Technology Facilities Council (U.K.), the European Community under the European Commission Framework Programme 7 (AIDA project, grant agreement no. 262025, TIARA project, grant agreement no. 261905, and EuCARD), the Japan Society for the Promotion of Science and the Swiss National Science Foundation, in the framework of the SCOPES programme

170Yb Mössbauer study of the crystalline electric field and exchange interaction in YbFe2

The Mössbauer study of 170Yb in YbFe2 was performed in the temperature range 4.2-60 K. The hyperfine spectra are in agreement with an easy direction of the magnetization along [100]. The thermal variations of the hyperfine field and of the electric quadrupole coupling suggest that the crystalline field effects on the ytterbium ion are rather small and we get good least square fits with pure exchange only (μB Hex/kB = 111 ± 4 K) ; the corresponding values of the conduction electron field and of the Sternheimer shielding factor are respectively.H c = 240 ± 100 kOe and RQ = 0.22 ± 0.01. In connection with the smallness of the crystalline field, we discuss the influence of the magnetostriction on the crystalline potential seen by a rare earth ion in the RFe2 compounds.Nous avons étudié l'effet Mössbauer de 170Yb dans YbFe 2 entre 4,2 et 60 K. Les spectres hyperfins sont compatibles avec une direction de facile aimantation suivant [100]. Les variations thermiques du champ hyperfin et du couplage quadrupolaire électrique suggèrent que les effets de champ cristallin sur l'ion ytterbium sont réduits, et les courbes s'interprètent bien en le supposant seulement soumis à un champ d'échange (μB, Hex/kB = 111 ± 4K); la contribution des électrons de conduction au champ hyperfin est Hc = 240 ± 100 kOe et le facteur d'écran de Sternheimer est RQ = 0,22 ± 0,01. En relation avec la petitesse du champ cristallin, nous examinons l'influence de la magnétostriction sur le potentiel cristallin vu par un ion de terre rare dans les composés RFe2

RECENT MÖSSBAUER INVESTIGATIONS ON THE RFe2 COMPOUNDS

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Synthesis, magnetic properties and 57Fe Mössbauer study of the laves phase compound YbFe2

The cubic MgCu2-type compound YbFe2 was synthesised at 1 200 °C under 80 kbar pressure and characterized by means of X-ray diffraction. The temperature dependent magnetization exhibits a compensation point at 31 K. The Môssbauer spectra shows that at very low temperature the magnetization is parallel to a direction. As the temperature increases the magnetization probably slightly deviates from this direction.Le composé cubique YbFe2, de structure MgCu2, a été synthétisé à 1 200°C sous 80 kbar et identifié par diffraction des rayons X. La courbe d'aimantation en fonction de la température présente un point de compensation à T = 31 K. Les spectres Mössbauer indiquent qu'à très basse température l'aimantation est parallèle à une direction . Quand la température s'élève, l'aimantation semble légèrement s'écarter de cette direction

Critical field, Hc2, and critical current in YBa2Cu3O7, up to 20 Tesla

International audienc