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In 1977 a fifth quark, named the bottom quark, was discovered by particle physicists - Edexcel - A-Level Physics - Question 18 - 2023 - Paper 4
Question 18
In 1977 a fifth quark, named the bottom quark, was discovered by particle physicists. The table shows the particles in the standard model known at that time. (a) (i... show full transcript
Worked Solution & Example Answer:In 1977 a fifth quark, named the bottom quark, was discovered by particle physicists - Edexcel - A-Level Physics - Question 18 - 2023 - Paper 4
Step 1
Explain why the existence of a sixth quark was predicted.
Answer
The existence of a sixth quark was predicted based on the need for a complete theoretical framework known as the standard model of particle physics. Previous observations indicated anomalies in quark behavior and interactions that suggested the presence of additional particles. Theoretical models posited that if there were only five quarks, the symmetry in their representations would be violated. Hence, to maintain the symmetry and balance in the quark family, a sixth quark was hypothesized.
Step 2
Step 3
Explain the advantage of colliding beams of particles.
Answer
Colliding beams of particles are advantageous as they can produce higher-energy collisions compared to fixed-target experiments. This allows for the creation of particles that require significant energy to form, providing better conditions to observe rare particle interactions. Additionally, with both beams in motion, the center of mass frame of the collision is at rest relative to the laboratory frame, maximizing the energy available for particle production.
Step 4
Calculate the maximum kinetic energy, in joules, of a top quark produced in this experiment.
Answer
Firstly, convert the total energy to joules: 900 GeV = 900 × 1.6 × 10⁻¹³ J = 1.44 × 10⁻¹⁰ J.
The rest energy of the top quark is given as 173 GeV = 173 × 1.6 × 10⁻¹³ J = 2.77 × 10⁻¹¹ J.
The maximum kinetic energy can be calculated as follows:
Thus, the maximum kinetic energy of the top quark is approximately 1.16 × 10⁻¹⁰ J.
Step 5
Deduce whether a top quark with kinetic energy 1.2 × 10⁷ J is travelling at a relativistic speed.
Answer
To determine if a top quark with a kinetic energy of 1.2 × 10⁷ J is traveling at relativistic speeds, we compare its kinetic energy to its rest energy. The rest energy of the top quark is 173 GeV, which converts to approximately 2.77 × 10⁻¹¹ J.
Since the kinetic energy (1.2 × 10⁷ J) is significantly larger than the rest energy, it indicates that the quark is moving at speeds close to the speed of light, thereby travelling at a relativistic speed.
Step 6
Assess this suggestion.
Answer
The suggestion that top quarks could form hadrons at relativistic speeds is plausible. When traveling at such speeds, the top quarks would experience time dilation and length contraction, which could allow them short-lived interactions that might promote hadron formation. However, given their extremely short lifetime of 10⁻²⁵ s, even at relativistic speeds, they are unlikely to form stable states before decaying. Thus, while the idea remains interesting from a theoretical perspective, practical hadron formation is still doubtful.