7. The following diagram gives information on the Standard Model of fundamental particles - Scottish Highers Physics - Question 7 - 2017

The statement 'All baryons are hadrons, but not all hadrons are baryons' is correct because baryons, such as protons and neutrons, are a specific category of hadrons made from three quarks. However, hadrons also include mesons, which are made from a quark-antiquark pair. Therefore, while all baryons qualify as hadrons, not all hadrons are classified as baryons.

The charge on the strange quark can be derived from the balance of the total charge of the sigma particles. For the neutral sigma (Σ⁰) particle, which consists of one up quark (charge = rac{2}{3}e) and two down quarks (charge = -rac{1}{3}e each), the equation is:

rac{2}{3}e + 2 imes ext{-}rac{1}{3}e = 0

From this, it can be deduced that the charge of the strange quark is -rac{1}{3}e.

The force that holds the quarks together in the sigma (Σ) particle is called the strong nuclear force.

The boson associated with the strong nuclear force is known as the gluon.

To calculate the mean lifetime of the Σ⁻ particle from the perspective of an observer where it is moving at a speed of 0.9c, we utilize time dilation, given by:

t' = rac{t}{ ext{sqrt}(1 - v^2/c^2)}

Here, $t$ is the proper lifetime (1.5 × 10⁻⁸ s), so we first compute:

$1 - (0.9c)^2/c^2 = 1 - 0.81 = 0.19$

Taking the square root, we find:

$ext{sqrt}(0.19) o 0.43589$

Now, substituting back:

t' = rac{1.5 imes 10^{-8}}{0.43589} o t' ext{ (approximately) } 3.44 imes 10^{-8} ext{ s}

Thus, the mean lifetime of the Σ⁻ particle as measured by the observer is approximately $3.44 imes 10^{-8}$ s.