Q.No:1 CSIR Dec-2014
Consider the four processes
(i) \(p^{+}\to n+e^{+}+v_{e}\)
(ii) \(\Gamma^{0}\to p^{+}+e^{+}+v_{e}\)
(iii) \(\pi^{+}\to e^{+}+v_{e}\)
(iv) \(\pi^{0}\to \gamma+\gamma\)
Which of the above is/are forbidden for free particles?
(1)
only (ii)
(2)
(ii) and (iv)
(3)
(i) and (iv)
(4)
(i) and (ii)
Check Answer
Option 4
Q.No:2 CSIR June-2015
The charm quark is assigned a charm quantum number C = 1. How should the Gellmann-Nishijima formula for electric charge be modified for four flavours of quarks?
(1)
\(I_{3} + \frac{1}{2}(B - S - C)\)
(2)
\(I_{3} + \frac{1}{2}(B - S + C)\)
(3)
\(I_{3} + \frac{1}{2}(B + S - C)\)
(4)
\(I_{3} + \frac{1}{2}(B + S + C)\)
Check Answer
Option 4
Q.No:3 CSIR June-2015
The reaction \({ }_{1}^{2} \mathrm{D}+{ }_{1}^{2} \mathrm{D} \rightarrow{ }_{2}^{4} \mathrm{He}+\pi^{0}\) cannot proceed via strong interactions because it violates the conservation of
(1)
angular momentum
(2)
electric charge
(3)
baryon number
(4)
isospin
Check Answer
Option 4
Q.No:4 CSIR Dec-2015
Consider the following processes involving free particles
(i) \(\bar{n}\to \bar{p}+e^+ +\bar{v}_e\)
(ii) \(\bar{p}+n\to \pi^-\)
(iii) \(p+n\to \pi^+ +\pi^0+\pi^0\)
(iv) \(p+\bar{v}_e\to n+e^+\)
Which of the following statements is true?
(1)
Process (i) obeys all conservation laws
(2)
Process (ii) conserves baryon number, but violates energy-momentum conservation
(3)
Process (iii) is not allowed by strong interactions, but is allowed by weak interactions
(4)
Process (iv) conserves baryon number, but violates lepton number conservation
Check Answer
Option 2
Q.No:5 CSIR Dec-2016
Which of the following reaction(s) is/are allowed by the conservation laws?
(i)
\(\pi^+ +n\to \Lambda^0+K^+\)
(ii)
\(\pi^- +p\to \Lambda^0+K^0\)
(1)
both (i) and (ii)
(2)
only (i)
(3)
only (ii)
(4)
neither (i) nor (ii)
Check Answer
Option 1
Q.No:6 CSIR Dec-2016
A particle, which is a composite state of three quarks \(u, d\) and \(s\), has electric charge, spin and strangeness respectively, equal to
(1)
\(1, \frac{1}{2}, -1\)
(2)
\(0, 0, -1\)
(3)
\(0, \frac{1}{2}, -1\)
(4)
\(-1, -\frac{1}{2}, +1\)
Check Answer
Option 3
Q.No:7 CSIR June-2017
A baryon \(X\) decays by strong interaction as \(X\to \Sigma^{+}+\pi^{-}+\pi^0\), where \(\Sigma^{+}\) is a member of the isotriplet \((\Sigma^{+}, \Sigma^{0}, \Sigma^{-})\). The third component \(I_3\) of the isospin of \(X\) is
(1)
\(0\)
(2)
\(1/2\)
(3)
\(1\)
(4)
\(3/2\)
Check Answer
Option 1
Q.No:8 CSIR Dec-2017
Which of the following processes is not allowed by the strong interaction but is allowed by the weak interaction?
(1)
\(K^{0}+\pi^{0}\to \bar{K}^{0}+\pi^{+}+\pi^{-}\)
(2)
\(p+n\to d+p+\bar{p}\)
(3)
\(\Delta^{+}+K^{0}\to p+n\)
(4)
\(p+\Delta^{+}\to \bar{n}+\Delta^{++}\)
Check Answer
Option 1
Q.No:9 CSIR June-2018
Which of the following elementary particle processes does not conserve strangeness?
(1)
\(\pi^{0}+p\to K^{+}+\Lambda^{0}\)
(2)
\(\pi^{-}+p\to K^{0}+\Lambda^{0}\)
(3)
\(\Delta^{0}\to \pi^{0}+n\)
(4)
\(K^{0}\to \pi^{+}+\pi^{-}\)
Check Answer
Option 4
Q.No:10 CSIR June-2018
A deuteron \(d\) captures a charged pion \(\pi^{-}\) in the \(l=1\) state, and subsequently decays into a pair of neutrons (\(n\)) via strong interaction. Given that the intrinsic parities of \(\pi^{-}, d\) and \(n\) are \(-1, +1\) and \(+1\) respectively, the spin-wavefunction of the final state neutrons is a
(1)
linear combination of a singlet and a triplet
(2)
singlet
(3)
triplet
(4)
doublet
Check Answer
Option 2
Q.No:11 CSIR Dec-2018
Consider the decay \(A\to B+C\) of a relativistic spin-\(\frac{1}{2}\) particle \(A\). Which of the following statements is true in the rest frame of the particle \(A\)?
(1)
The spin of both \(B\) and \(C\) may be \(\frac{1}{2}\)
(2)
The sum of the masses of \(B\) and \(C\) is greater than the mass of \(A\)
(3)
The energy of \(B\) is uniquely determined by the masses of the particles
(4)
The spin of both \(B\) and \(C\) may be integral
Check Answer
Option 3
Q.No:12 CSIR Dec-2018
Assume that pion-nucleon scattering at low energies, in which isospin is conserved, is described by the effective interaction potential \(V_{\text{eff}}=F(r) \vec{I}_{\pi}\cdot \vec{I}_N\), where \(F(r)\) is a function of the radial separation \(r\) and \(\vec{I}_{\pi}\) and \(\vec{I}_N\) denote, respectively, the isospin vectors of a pion and the nucleon. The ratio \(\sigma_{I=3/2}/\sigma_{I=1/2}\) of the scattering cross-sections corresponding to total isospins \(I=3/2\) and \(1/2\), is
(1)
\(3/2\)
(2)
\(1/4\)
(3)
\(5/4\)
(4)
\(1/2\)
Check Answer
Option 2
Q.No:13 CSIR June-2019
The elastic scattering of a neutrino \(\nu_e\) by an electron \(e^{-}\), i.e. the reaction \(\nu_e+e^{-}\to \nu_e+e^{-}\), can be described by the interaction Hamiltonian
\[
H_{\text{int}}
=\frac{1}{\sqrt{2}} G_F \int d^3 \mathbf{x}(\bar{\psi}_e(\mathbf{x})\gamma^{\mu}\psi_{\nu_e}(\mathbf{x}))(\bar{\psi}_{\nu_e}(\mathbf{x})\gamma_{\mu}\psi_e(\mathbf{x}))
\]
The cross-section of the above process depends on the centre of mass energy \(E\), as
(1)
\(1/E^2\)
(2)
\(E^2\)
(3)
\(E\)
(4)
\(\sqrt{E}\)
Check Answer
Option 2
Q.No:14 CSIR June-2019
The mean life-time of the following decays: \(\rho_0\to \pi^{+}+\pi^{-}, \pi^{0}\to \gamma+\gamma, \mu^{-}\to e^{-}+\bar{\nu}_e+\nu_{\mu}\), are \(\tau_{\rho}, \tau_{\pi}\) and \(\tau_{\mu}\), respectively. They satisfy
(1)
\(\tau_{\pi}< \tau_{\rho}< \tau_{\mu}\)
(2)
\(\tau_{\mu}< \tau_{\rho}< \tau_{\pi}\)
(3)
\(\tau_{\rho}< \tau_{\pi}< \tau_{\mu}\)
(4)
\(\tau_{\rho}< \tau_{\mu}< \tau_{\pi}\)
Check Answer
Option 3
Q.No:15 CSIR Dec-2019
Which of the following decay processes is allowed?
(1)
\(K^{0}\to \mu^{+}+\mu^{-}\)
(2)
\(\mu^{-}\to e^{-}+\gamma\)
(3)
\(n\to p+\pi^{-}\)
(4)
\(n\to \pi^{+}+\pi^{-}\)
Check Answer
Option 1
Q.No:16 CSIR Dec-2019
The strong nuclear force between a neutron and a proton in a zero orbital angular momentum state is denoted by \(F_{np}(r)\), where \(r\) is the separation between them. Similarly, \(F_{nn}(r)\) and \(F_{pp}(r)\) denote the forces between a pair of neutrons and protons, respectively, in zero orbital momentum state. Which of the following is true on average if the inter-nucleon distance is \(0.2 fm<r<2 fm\)?
(1)
\(F_{np}\) is attractive for triplet spin state, and \(F_{nn}, F_{pp}\) are always repulsive
(2)
\(F_{nn}\) and \(F_{np}\) are always attractive and \(F_{pp}\) is repulsive in the triplet spin state
(3)
\(F_{pp}\) and \(F_{np}\) are always attractive and \(F_{nn}\) is always repulsive
(4)
All three forces are always attractive
Check Answer
Option 2
Q.No:17 Assam CSIR Dec-2019
The probability of the decay of \(\pi^{-}\to \mu^{-}+\bar{\nu}_{\mu}\) is much higher than that of \(\pi^{-}\to e^{-}+\bar{\nu}_e\) because
(1)
the decay to \(e^{-}+\bar{\nu}_e\) does not conserve baryon number
(2)
pions have zero electron number but a non-zero muon number
(3)
the decay to \(e^{-}+\bar{\nu}_e\) is suppressed by energy-momentum conservation
(4)
the decay to \(e^{-}+\bar{\nu}_e\) is suppressed by helicity conservation
Check Answer
Option 4
Q.No:18 CSIR June-2020
(4)
Charged pions \(\pi^{-}\) decay to muons \(\mu^{-}\) and anti-muon neutrinos \(\vec{\nu}_{\mu}; \pi^{-}\to \mu^{-}+\vec{\nu}_{\mu}\). Take the rest masses of a muon and a pion to be \(105 MeV\) and \(140 MeV\), respectively. The probability that the measurement of the muon spin along the direction of its momentum is positive, is closest to
(a)
\(0.5\)
(b)
\(0.75\)
(c)
\(1\)
(d)
\(0\)
Check Answer
Option c
Q.No:19 CSIR Feb-2022
A particle of mass 1Ge\(V/c^2\) and its antiparticle, both moving with the same speed \(v\) ,
produce new particle \(x\) of mass 10Ge\(V/c^2\) in a head on collision. The minimum value of \(v\)
required for this process is closest to
(1)
\(0.83\) c
(2)
\(0.93\) c
(3)
\(0.98\) c
(4)
\(0.88\) c
Check Answer
Option 3
Q.No:20 CSIR Feb-2022
In the reaction \(p+n\rightarrow p+K^++X\) mediated by strong interaction, the baryon number \(B\) ,strangeness \(S\) and the third component of isospin 3\(I_3\) of the particle \(X\) are, respectively
(1)
\(-1,-1\) and \(-1\)
(2)
\(+1,-1\) and \(-1\)
(3)
\(+1,-2\) and \(-\frac{1}{2}\)
(4)
\(-1,-1\) and \(0\)
Check Answer
Option 2
Q.No:21 CSIR Sep-2022
The elastic scattering process \(\pi^- p \rightarrow \pi^- p\) may be treated as hard sphere scattering. The mass of \(\pi^-\), \(m_\pi \approx m_p/6\) where \(m_p \approx 938MeV/c^2\) is the mass of the proton. The total scattering cross-section is closest to
(1)
0.01 milli-barn
(2)
1 milli-barn
(3)
0.1 barn
(4)
10 barn
Check Answer
Option 3
Q.No:22 CSIR June-2023
A neural particle \(X^0\) is produced in \(\pi^-+p\rightarrow X^0+n\) by s-wave scattering. The branching ratios of the decay of \(X^0\) to \(2\gamma\), \(3\pi\) and \(2\pi\) are \(0.38\), \(0.30\) and less than \(10^{-3}\), respectively. The quantum numbers \(J^{CP}\) of \(X^0\) are
1) \(0^{-+}\)
2) \(0^{+-}\)
3) \(1^{-+}\)
4) \(1^{+-}\)
Check Answer
Option 2
Q.No:23 CSIR Dec-2023
Atmospheric neutrinos are produced from the cascading decays of cosmic pions (\(\pi^{\pm}\)) to stable particles. Ignoring all other neutrino sources, the ratio of muon neutrino (\(\nu_{\mu} + \bar{\nu}_{\mu}\)) flux to electron neutrino (\(\nu_{e} + \bar{\nu}_{e}\)) flux in atmosphere is expected to be closest to
1) 2:3
2) 1:1
3) 1:2
4) 2:1
Check Answer
Option 4
Q.No:24 CSIR June-2024
The \( \Delta^{++} \) can be produced by colliding a pion beam onto a \( H_2 \) target, in a reaction
\[
\pi^+ + p \rightarrow \Delta^{++} \rightarrow \pi^+ + p.
\]
In the rest frame of \( \Delta^{++} \), the energy and momentum of the pion in the final state (in MeV) are closest to (assume \( c = 1 \), and \( m_\pi \approx 140 \) MeV, \( m_p \approx 1 \) GeV, \( m_{\Delta^{++}} \approx 1.2 \) GeV):
1) \( 210, 156 \)
2) \( 230, 182 \)
3) \( 175, 105 \)
4) \( 190, 130 \)
Check Answer
Option 4
Q.No:25 CSIR June-2024
The \(\pi^-\) has spin 0 and negative intrinsic parity. In a reaction, a deuteron in its ground state (\(J = 1\), parity is +1) captures a \(\pi^-\) in \(p\)-wave to produce a pair of neutrons (intrinsic parity is +1). The neutrons will be produced in a state with
1) \( l = 1, S = 0 \)
2) \( l = 0, S = 1 \)
3) \( l = 1, S = 1 \)
4) \( l = 0, S = 0 \)
Check Answer
Option 4
Q.No:26 CSIR Dec-2024
A particle of rest mass \(m_{0}\) and energy \(E\) collides with another particle at rest, with the same rest mass. What is the minimum value of \(E\) so that after the collision, there may be four particles of rest mass \(m_{0}\)?
1) \(4 m_{0} c^{2}\)
2) \(3 m_{0} c^{2}\)
3) \(7 m_{0} c^{2}\)
4) \(16 m_{0} c^{2}\)
Check Answer
Option 3
Q.No:27 CSIR Dec-2024
For the decay of the \(\Delta\)-baryons, the ratio of the decay rates
\[
\frac{\Gamma(\Delta^{-} \rightarrow n \pi^{-})}{\Gamma(\Delta^{0} \rightarrow p \pi^{-})}
\]
is best approximated by
1) \(\frac{3}{2}\)
2) \(3\)
3) \(1\)
4) \(\frac{2}{3}\)
Check Answer
Option 2
Q.No:28 CSIR June-2025
The \(\rho\)-mesons are \(J^{P} = 1^{-}\) particles that decay strongly into pions. The ratio of the particle decay widths
\[
\frac{\Gamma(\rho^{0} \rightarrow \pi^{0}\pi^{0})}{\Gamma(\rho^{+} \rightarrow \pi^{+}\pi^{0})}
\]
is closest to
1) \(1\)
2) \(\frac{1}{2}\)
3) \(0\)
4) \(2\)
Check Answer
Option 3
Q.No:1 JEST-2013
A \(K\) meson (with a rest mass of \(494 MeV\)) at rest decays into a muon (with a rest mass of \(106 MeV\)) and a neutrino. The energy of the neutrino, which can be taken to be massless, is approximately
(a)
\(120 MeV\)
(b)
\(236 MeV\)
(c)
\(300 MeV\)
(d)
\(388 MeV\)
Check Answer
Option b
Q.No:2 JEST-2015
The reaction \(e^{+}+e^{-}\to \gamma\) is forbidden because,
(a)
lepton number is not conserved
(b)
linear momentum is not conserved
(c)
angular momentum is not conserved
(d)
charge is not conserved