Source: HINDU

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Context

• Scientists presented the latest results from the NOvA collaboration at a conference in Italy on June 17.
• They said the collaboration had acquired twice as much data as it had during NOvA’s previous run, four years ago.
• The new results complemented the previous ones with greater precision.

Details

About Neutrinos

• Nature of Neutrinos:
  • Subatomic particles with no electric charge.
  • Have a small mass and are left-handed (spin opposite to motion).
  • Second-most abundant particles in the universe after photons.
• Production:
  • Produced when leptons (such as muons, electrons, and tauons) interact with matter.
  • Rarely interact with matter, making them difficult to study.

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Importance of Studying Neutrinos

• Technological Advancements: Neutrinos have the potential to revolutionize technology due to their unique properties.
• Scientific Interest: Crucial for understanding fundamental physics and the universe’s evolution.
• Communication:
  • Neutrinos can pass through most matter untouched, making them potential carriers of information across large distances.
  • Could revolutionize communication technologies, especially where electromagnetic waves are ineffective (e.g., underwater).

Challenges in Neutrino Detection

• Low Interaction Rate: Neutrinos interact with matter very rarely (e.g., a muon-neutrino interacts with an atom’s nucleus once in a million times).
• Large Detectors Required: Detectors need fine tracking capabilities and large volumes to maximize interactions.

NOvA Experiment Overview

• Acronym: NuMI Off-axis νe Appearance (NuMI Off-axis Electron Neutrino Appearance).
• Location: Minnesota, U.S and extends to northern Minnesota.
• Managed by: Fermi National Accelerator Laboratory.
• Setup: Creates a beam of neutrinos that travel 800 km to a 14,000-tonne detector.

Objectives of NOvA

• Role of Neutrinos in Cosmic Evolution:
  • Determine which neutrino type has the most mass.
  • Understanding neutrino mass could answer fundamental physics questions.
• Mechanism of Mass Acquisition: Neutrinos may gain mass through a different mechanism than other particles.
• Explore CP Violation in the Lepton Sector: Investigate whether neutrinos and antineutrinos behave differently, which could explain the matter-antimatter asymmetry in the universe.

Neutrino vs. Antineutrino

Property	Neutrino	Antineutrino
Definition	Subatomic particle with no charge and half-integer spin	Antiparticle with no charge and half-integer spin
Lepton Number	Positive lepton number (+1)	Negative lepton number (-1)
Chirality	Left-handed helicity	Right-handed helicity
Weak Isospin	+1/2	-1/2
Interactions	Weak interaction and gravity	Weak interaction and gravity
Production	Produced in beta decay and other weak interactions	Produced in beta decay and other weak interactions
Detection	Produces negatively charged electrons upon interaction	Produces positively charged positrons upon interaction

Matter vs. Antimatter

Property	Matter	Antimatter
Definition	Composed of particles such as electrons, protons, and neutrons	Composed of antiparticles such as positrons, antiprotons, and antineutrons
Charge	Particles have positive or negative charge	Antiparticles have opposite charges to their corresponding particles
Mass	Positive mass	Positive mass (same as corresponding particles)
Spin	Half-integer spin	Half-integer spin (same as corresponding particles)
Interaction	Subject to electromagnetic, weak, and strong forces	Subject to electromagnetic, weak, and strong forces (opposite charges cause different interaction behavior)
Annihilation	When matter and antimatter collide, they annihilate, producing energy (photons)	When antimatter and matter collide, they annihilate, producing energy (photons)
Examples	Electrons, protons, neutrons	Positrons, antiprotons, antineutrons

Historical Context

• Neutrino Astronomy:
  • Began with the detection of neutrinos from a supernova in 1987.
  • Neutrinos detected before the light from the explosion reached Earth.
• Mass Discovery:
  • Initially thought to be massless like photons.
  • Evidence in the late 1990s from Japan and Canada showed neutrinos have mass and can oscillate between types.

The Neutrino Mass Hierarchy

• Neutrino Oscillation: Neutrinos change types as they travel long distances.
• Mass Hierarchy Models:
  • Normal Order: One type is much heavier, and the other two have lower comparable masses.
  • Inverted Order: One type is lighter, and the other two have higher comparable masses.

Experimental Setup

• Neutrino Beam: Utilizes the NuMI (Neutrinos at the Main Injector) beam, which is one of the most intense neutrino beams in the world.
• Detectors: Consists of two detectors:
  • Near Detector: Located at Fermilab, it measures the unoscillated neutrino beam composition.
  • Far Detector: Located 810 kilometers away in Ash River, Minnesota, it detects the oscillated beam and identifies electron neutrino appearances

Key Technologies and Methods

• Liquid Scintillator Detectors: Both detectors use liquid scintillator technology to detect interactions by producing light when neutrinos interact with the detector material.
• Deep Learning and Data Analysis: NOvA employs advanced machine learning techniques to improve event classification and data analysis, significantly enhancing sensitivity to oscillation parameters​.

Subatomic Particles

• Subatomic particles are the fundamental constituents of matter, and they fall into two main categories: elementary particles and composite particles.

Elementary Particles

• These particles are not composed of other particles. They include quarks, leptons, and gauge bosons.

Category	Particle	Symbol	Charge	Mass (MeV/c²)	Spin	Generation	Interactions
Quarks	Up Quark	u	+2/3 e	2.2	1/2	1	Strong, Weak, EM
	Down Quark	d	-1/3 e	4.7	1/2	1	Strong, Weak, EM
	Charm Quark	c	+2/3 e	1,280	1/2	2	Strong, Weak, EM
	Strange Quark	s	-1/3 e	96	1/2	2	Strong, Weak, EM
	Top Quark	t	+2/3 e	173,000	1/2	3	Strong, Weak, EM
	Bottom Quark	b	-1/3 e	4,180	1/2	3	Strong, Weak, EM
Leptons	Electron	e⁻	-1 e	0.511	1/2	1	Weak, EM
	Electron Neutrino	νₑ	0	<0.0000022	1/2	1	Weak
	Muon	μ⁻	-1 e	105.66	1/2	2	Weak, EM
	Muon Neutrino	νμ	0	<0.17	1/2	2	Weak
	Tau	τ⁻	-1 e	1,776.86	1/2	3	Weak, EM
	Tau Neutrino	ντ	0	<18.2	1/2	3	Weak
Gauge Bosons	Photon	γ	0	0	1	-	EM
	Gluon	g	0	0	1	-	Strong
	W Boson	W⁺, W⁻	±1 e	80,379	1	-	Weak
	Z Boson	Z⁰	0	91,188	1	-	Weak
	Higgs Boson	H⁰	0	125,100	0	-	-

Composite Particles

• These particles are composed of quarks held together by the strong force. They include baryons and mesons.

Category	Particle	Symbol	Charge	Mass (MeV/c²)	Spin	Quark Composition	Interactions
Baryons	Proton	p	+1 e	938.27	1/2	uud	Strong, Weak, EM
	Neutron	n	0	939.57	1/2	udd	Strong, Weak
Mesons	Pion	π⁺, π⁻, π⁰	±1 e, 0	139.57, 135.0	0	u anti-d, d anti-u, (u anti-u or d anti-d)	Strong, Weak
	Kaon	K⁺, K⁻, K⁰	±1 e, 0	493.67	0	u anti-s, s anti-u	Strong, Weak

Fundamental Forces and Their Mediators

Force	Mediator	Symbol	Relative Strength	Range
Gravitational	Graviton*	G	Weakest	Infinite
Electromagnetic	Photon	γ	10³⁶ times gravity	Infinite
Weak Nuclear	W and Z Bosons	W⁺, W⁻, Z⁰	10²⁵ times gravity	Very short (~10⁻¹⁸ m)
Strong Nuclear	Gluon	g	10³⁸ times gravity	Very short (~10⁻¹⁵ m)

*Graviton is hypothetical and has not yet been observed.

Explanation of Terms

• Charge: Represents the electric charge of the particle.
• Mass (MeV/c²): The mass of the particle in mega-electronvolts per speed of light squared.
• Spin: Intrinsic form of angular momentum carried by particles.
• Generation: Refers to the different families of quarks and leptons based on their mass and interaction strength.
• Interactions: Types of fundamental forces the particle participates in.

Global Efforts in Neutrino Research

Must Read Articles:

Classification of Elementary Particles

W-Boson 

Higgs Boson

Sources:

HINDU

PRACTICE QUESTION Q: Consider the following statements about subatomic particles: Quarks are the fundamental constituents of protons and neutrons. Electrons are leptons and are not made up of smaller particles. The Higgs boson is responsible for providing mass to other particles. Which of the statements given above is/are correct? (a) 1 and 2 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2, and 3 Answer: (d)