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<!DOCTYPE HTML>
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	Benjamin Tam (benjamin.tam@queensu.ca)
	for the SNO+ Collaboration
	11 March 2023
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		<title>SNO+: Neutrinoless Double Beta Decay</title>
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									<h1>Science Programme</h1>
									<p>The SNO+ Experiment is used to investigate a large suite of physics phenomena. <br/>Find out more about our current active research interests here.</p>
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									<li><a href="0vbb.html#section" class="button primary">Neutrinoless Double Beta Decay</a></li>
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								<h2>Neutrinoless Double Beta Decay</h2>

								<p>One of the most important open questions in physics is whether the neutrino is a Majorana fermion (as opposed to a Dirac fermion like other leptons). If so, the neutrino and anti-neutrino are identical particles. Many theories predict that neutrinos are Majorana particles, as this would allow for a mechanism that naturally explains the smallness of the neutrino mass. </p>

								<p>The most promising way to discover Majorana neutrinos is through the detection of <b>neutrinoless double beta decay</b> (0νββ). The standard double beta decay process (2νββ) has been observed in a handful of nuclei, and occurs when a parent nucleus decays to a daugher nucleus via:
								<center>(A, Z) &rarr; (A, Z + 2) + 2e<sup>-</sup>&nbsp;+ 2ν̄<sub>e</sub></center>
								In 0νββ, which is forbidden in the standard model, no neutrinos are emitted and the lepton number is violated by two units:
								<center>(A, Z) &rarr; (A, Z + 2) + 2e<sup>-</sup></center>
								In the standard interpretation, where 0νββ is mediated through light Majorana neutrino exchange, the neutrino can be absorbed at the vertex, as shown here:
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  								<img src="images/feynman.png" alt="Feynman diagram of neutrinoless double beta decay" style="width:35%">
  								<!-- <figcaption>Figure 1: Feynman diagram of 0νββ decay driven by a light Majorana neutrino exchange.</figcaption> -->
  								</center>
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								The 0νββ process is distinguished from 2νββ decays because it produces events at the endpoint of the decay energy spectrum. These are rare processes and detectors require large amounts of isotope to search for double beta decay.
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								The SNO+ experiment selected <sup>130</sup>Te as its 0νββ isotope. <sup>130</sup>Te was chosen because of its high natural abundance (34%), relatively high Q-value to avoid low energy radioactive backgrounds, and because it can be loaded into scintillator while maintaining excellent optical properties.
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								Assuming an m<sub>ββ</sub> of 100 meV (which is around the level of the best current limit from KamLAND-Zen), the expected energy spectrum of the background and signal for SNO+ (after analysis cuts) is shown here:
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  								<img src="images/bkg.png" alt="SNO+ expected energy spectrum" style="width:75%">
  								<!-- <figcaption>Figure 2: SNO+ Energy spectrum.</figcaption> -->
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