Question

Which of the following particles has a lepton number of \(+1\)?

• A. \(H^+\)
• B. \(\mu^-\)
• C. \(e^+\)
• D. \(p\)

Hint:

Leptons like \(e^-\), \(\mu^-\), \(\tau^-\), and neutrinos have lepton number \(+1\). Their antiparticles have lepton number \(-1\).

Answer 1

The Correct Option is B

Concept:
Lepton number is a quantum number assigned to leptons and anti-leptons. Leptons have lepton number: \[ L=+1 \] Anti-leptons have lepton number: \[ L=-1 \] Particles that are not leptons have lepton number: \[ L=0 \]

Step 1: Recall examples of leptons.
Common leptons are: \[ e^-,\ \mu^-,\ \tau^- \] and their corresponding neutrinos: \[ \nu_e,\ \nu_\mu,\ \nu_\tau \] All of these have: \[ L=+1 \]

Step 2: Recall examples of anti-leptons.
Anti-leptons include: \[ e^+,\ \mu^+,\ \tau^+ \] and anti-neutrinos. They have: \[ L=-1 \]

Step 3: Check each option.
Option (A) \(H^+\) is a proton or hydrogen ion. It is not a lepton, so: \[ L=0 \] Option (B) \(\mu^-\) is a muon. It is a lepton, so: \[ L=+1 \] Option (C) \(e^+\) is a positron. It is an anti-lepton, so: \[ L=-1 \] Option (D) \(p\) is a proton. It is a baryon, not a lepton, so: \[ L=0 \]

Step 4: Select the particle with lepton number \(+1\).
The only particle among the options with lepton number \(+1\) is: \[ \mu^- \] Hence, the correct answer is: \[ \boxed{(B)\ \mu^-} \]