Study of X-ray and proton emission after muon capture in aluminium - - PowerPoint PPT Presentation

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

Physics Motivations Introduction to AlCap Muon beam and experimental setup Muon beam profile characterization and tuning Sanity checks and future analysis work

2 Argonne National Laboratory – Boston University – Brookhaven National Laboratory – Fermilab National Accelerator Laboratory – Imperial College London – INFN Lecce – INFN Pisa – Institute of High Energy Physics, China – Laboratori Nazionali di Frascati, INFN – Nanjing University – Osaka University – University College London – University of Houston – University of Washington, Seattle

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. 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.

3 SUSY loop diagram Littlest Higgs model with T-parity conservation

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

• scillations.

COMET Phase-I aims to have a per event sensitivity of to the order 3.1 x 10-15 therefore it is important to 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 SM process where the μ-to-e can occur but at a branching ratio so low current experiments can not detect it. (c.f. http: //arxiv.org/abs/1412.1406)

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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.

5 Monte carlo simulations of momentum distributions for the μN -> eN signal in red and DIO events in blue. (c.f. COMET TDR)

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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 peak.

6 c.f. arxiv.org/abs/1501.04880

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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.

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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.

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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.

9 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

年末発表 25 Dec 2015

Experimental setup

Targets used: ~2 days Al100μm, ~2 days Al50μm, ~1 day Si, ~1 day Ti. A germanium detector is placed

• utside the chamber. All components

are shielded and grounded. For each target, we optimized the muon beam momentum for highest number of captured muons.

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Si detectors target Ge detector

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. d. target is tilted 45o to the beam direction facing the Ge detector. e. a veto scintillator behind the target to count rates.

11 c.f. P. Litchfield

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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.

c.f. J. Quirk, BU 12

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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 to a 3x3mm SiPM. Currently we have a rough estimate of where the beam spot is.

13 c.f. P. Litchfield

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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.

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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.

15 c.f. V. Tishenko

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Questions & Comments

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