年末発表 25 Dec 2015 Study of X-ray and proton emission after muon capture in aluminium in the AlCap experiment Mark Wong 久野研
年末発表 25 Dec 2015 Contents Argonne National Laboratory – Boston University – Brookhaven National Laboratory – Fermilab National Accelerator Laboratory – Imperial Physics Motivations College London – INFN Lecce – INFN Pisa – Institute of High Energy Physics, China – Laboratori Nazionali di Frascati, INFN – Nanjing University – Osaka University – University College London – Introduction to AlCap University of Houston – University of Washington, Seattle Muon beam and experimental setup Muon beam profile characterization and tuning Sanity checks and future analysis work 2
年末発表 25 Dec 2015 Physics motivations COMET and the mu2e experiments aim to look for neutrinoless muon to electron conversion in the vicinity of a nucleus. SUSY loop diagram Several Beyond the Standard Model (BSM) theories allow for such processes. Discovery of the μ-to-e process will provide hints as to which BSM theories are viable. Littlest Higgs model with T-parity conservation 3
年末発表 25 Dec 2015 Physics Motivations The Standard Model (SM) μ-to-e branching ratio is on the order of 10 -54 which is possible via neutrino oscillations. SM process where the μ-to-e can occur COMET Phase-I aims to have a per event sensitivity of but at a branching ratio so low current experiments can not detect it. (c.f. http: to the order 3.1 x 10 -15 therefore it is important to //arxiv.org/abs/1412.1406) understand and reduce the background rates. The main processes that contribute to this background is the muon decays in orbit (DIO) and nucleon emission after muon capture. 4
年末発表 25 Dec 2015 Background events - Muon decay in orbit This is the most dominant background source. These muons are bound in a muonic atom under the Coulomb potential of the Al nucleus. Nuclear recoil can boost the decay electron to energies close to the conversion signal. Monte carlo simulations of momentum distributions for the μN -> eN signal in red and DIO events in blue. (c.f. COMET TDR) 5
年末発表 25 Dec 2015 Background events - Nucleon emission After muon capture the nucleus is excited and may emit gammas, neutrons and charged particles like protons, deuterons and maybe some tritons and alphas. These background events can be removed if we understand their momentum spectrum near the signal c.f. arxiv.org/abs/1501.04880 peak. 6
年末発表 25 Dec 2015 Introduction to AlCap The Aluminium Capture (AlCap) experiment aims to determine the proton and neutron muon capture rates which are the major contributors to the background of COMET and Mu2e. AlCap website: http://muon.npl.washington.edu/exp/AlCap/index.html The recently concluded AlCap run in Nov 2015 was the third run. The second was in this summer and the first in 2013. 7
年末発表 25 Dec 2015 Aim Recent run 2015b was from 04 Nov to 23 Nov. WP1: Charged Particle Emission after Muon Capture. Protons emitted after nuclear muon capture in the stopping target dominate the single-hit rates in the tracking chambers for both the Mu2e and COMET Phase-I experiments. We plan to measure both the total rate and the energy spectrum to a precision of 5% down to proton energies of 2.5 MeV. WP2: Gamma and X-ray Emission after Muon Capture. A Ge detector will be used to measure X-rays from the muonic atomic cascade, in order to provide the muon-capture normalization for WP1, and is essential for very thin stopping targets. It is also the primary method proposed for calibrating the number of muon stops in the Mu2e and COMET experiments. Two additional calibration techniques will also be explored; (1) detection of delayed gamma rays from nuclei activated during nuclear muon capture, and (2) measurement of the rate of photons produced in radiative muon decay. WP3: Neutron Emission after Muon Capture. Neutron rates and spectra after capture in Al and Ti are not well known. In particular, the low energy region below 10 MeV is important for determining backgrounds in the Mu2e/COMET detectors and veto counters as well as evaluating the radiation damage to electronic components. Carefully calibrated liquid scintillation detectors, employing neutron-gamma discrimination and spectrum unfolding techniques, will measure these spectra. The measurement will attempt to obtain spectra as low or lower than 1 MeV up to 10 MeV. 8
年末発表 25 Dec 2015 Muon beam We used the beam are πE1 in PSI Experimental hall. The πE1 beam line supplies high intensity pion and muon beams with momenta ranging from 10 to 500 MeV/c. Outdated (1997) layout of the πE1 beamline indicating quadrupole and dipole magnets used to steer and focus the muon beam - PSI This proton accelerator delivers a proton beam of 590 MeV energy at a current up to 2 mA - PSI 9
年末発表 25 Dec 2015 Si detectors Experimental setup Targets used: ~2 days Al100μm, ~2 days Al50μm, ~1 day Si, ~1 day Ti. A germanium detector is placed outside the chamber. All components are shielded and grounded. Ge detector For each target, we optimized the muon beam momentum for highest number of captured muons. target 10
年末発表 25 Dec 2015 Experimental setup On each side are a set of three silicon detectors, a. thin detector, 65um b. 2 x 2 segmented Si detector c. thick detector, 1.5mm. c.f. P. Litchfield target is tilted 45 o to the beam direction facing the Ge detector. d. e. a veto scintillator behind the target to count rates. 11
年末発表 25 Dec 2015 Muon beam tuning We first did an energy calibration for the Ge detector using Eu-152 in the target position. X-rays/gammas emitted from de-excited captured muons are detected by this detector. We determined the best beam momentum for highest number of x-rays emitted which was for example for the Al 0.1 mm target, p=1.035*25.3946 MeV. 12 c.f. J. Quirk, BU
年末発表 25 Dec 2015 Beam profile characterization One of the problems of previously done analysis was that the position of the beam spot was unknown. We built a remote controlled beam two dimensional scanner connected c.f. P. Litchfield to a 3x3mm SiPM. Currently we have a rough estimate of where the beam spot is. 13
年末発表 25 Dec 2015 Plots for sanity checks It is ideal to know if muons are being captured during beam time, or if we have any muons being focused on the target. Top plot shows a sample readout from a silicon detector. This plot shows the pulse heights of electron and muons hitting this detector as a target. Bottom plot shows part of the x-ray spectrum recorded by the germanium detector. They are used for the Ge detector energy calibration. Here marked in red is the 1.137MeV peak, the second one is a 1.333MeV peak. 14
年末発表 25 Dec 2015 Early analysis and future work Plot is a ΔE-E plot of particles, with about 2100 captured protons. No time cut was applied so this also includes particles emitted by muon capture from other nuclei existing in the chamber. Currently for future analysis work, We need to compile a run summary and decide on the tasks important for analysis. c.f. V. Tishenko 15
年末発表 25 Dec 2015 Questions & Comments 16
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