Why can a particle decay into two photons but not one?
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I recently read an old physics news about the Higgs boson where it was observed to decay into 2 photons and I was wondering why it wouldn't have decayed into a single photon with the combined energy of 2 photons?
particle-physics photons momentum conservation-laws higgs
edited 2 days ago
Ben Crowell
49.2k4153294
asked Jan 12 at 3:42
user6760user6760
2,53611738
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add a comment |
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I recently read an old physics news about the Higgs boson where it was observed to decay into 2 photons and I was wondering why it wouldn't have decayed into a single photon with the combined energy of 2 photons?
particle-physics photons momentum conservation-laws higgs
edited 2 days ago
Ben Crowell
49.2k4153294
asked Jan 12 at 3:42
user6760user6760
2,53611738
$endgroup$
$begingroup$
Related: physics.stackexchange.com/q/427466/2451 and links therein.
$endgroup$
– Qmechanic♦
2 days ago
add a comment |
$begingroup$
I recently read an old physics news about the Higgs boson where it was observed to decay into 2 photons and I was wondering why it wouldn't have decayed into a single photon with the combined energy of 2 photons?
particle-physics photons momentum conservation-laws higgs
edited 2 days ago
Ben Crowell
49.2k4153294
asked Jan 12 at 3:42
user6760user6760
2,53611738
$endgroup$
I recently read an old physics news about the Higgs boson where it was observed to decay into 2 photons and I was wondering why it wouldn't have decayed into a single photon with the combined energy of 2 photons?
particle-physics photons momentum conservation-laws higgs
particle-physics photons momentum conservation-laws higgs
edited 2 days ago
Ben Crowell
49.2k4153294
asked Jan 12 at 3:42
user6760user6760
2,53611738
edited 2 days ago
Ben Crowell
49.2k4153294
asked Jan 12 at 3:42
user6760user6760
2,53611738
edited 2 days ago
Ben Crowell
49.2k4153294
edited 2 days ago
Ben Crowell
49.2k4153294
edited 2 days ago
Ben Crowell
49.2k4153294
49.2k4153294
asked Jan 12 at 3:42
user6760user6760
2,53611738
asked Jan 12 at 3:42
user6760user6760
2,53611738
asked Jan 12 at 3:42
user6760user6760
2,53611738
2,53611738
$begingroup$
Related: physics.stackexchange.com/q/427466/2451 and links therein.
$endgroup$
– Qmechanic♦
2 days ago
add a comment |
$begingroup$
Related: physics.stackexchange.com/q/427466/2451 and links therein.
$endgroup$
– Qmechanic♦
2 days ago
$begingroup$
Related: physics.stackexchange.com/q/427466/2451 and links therein.
$endgroup$
– Qmechanic♦
2 days ago
$begingroup$
Related: physics.stackexchange.com/q/427466/2451 and links therein.
$endgroup$
– Qmechanic♦
2 days ago
add a comment |
2 Answers
2
active
oldest
votes
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No massive particle can decay into a single photon.
In its rest frame, a particle with mass $M$ has momentum $p=0$. If it decayed to a single photon, conservation of energy would require the photon energy to be $E=Mc^2$, while conservation of momentum would require the photon to maintain $p=0$. However, photons obey $E=pc$ (which is the special case of $E^2 = (pc)^2 + (mc^2)^2$ for massless particles). It's not possible to satisfy all these constraints at once. Composite particles may emit single photons, but no massive particle may decay to a photon.
answered Jan 12 at 5:37
rob♦rob
40k972165
$endgroup$
$begingroup$
Massive particle as in fermion with half integer spin right, so it have to decay into some other particles on top of a photon to conserve energy and spin momentum is this what you are saying?
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– user6760
Jan 12 at 6:04
3
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@user6760 This argument is about linear, not angular, momentum. And there are plenty of massive particles which obey Bose-Einstein statistics and have integer spins.
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– rob♦
2 days ago
add a comment |
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The Higgs boson has spin $0$. A photon has spin $1$. The total angular momentum cannot change in the decay, so a Higgs boson cannot decay into a single photon, regardless of the energy. But the total angular momentum of two photons can be zero (because their spins can be oriented in opposite directions), so this decay mode can conserve angular momentum.
As emphasized in a comment, conservation of angular momentum is only a necessary condition, not a sufficient one. Please see rob's answer for clarification about this.
answered Jan 12 at 3:52
Dan YandDan Yand
8,33211234
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1
$begingroup$
I just look up spin so spin can be negative
$endgroup$
– user6760
Jan 12 at 4:14
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
No massive particle can decay into a single photon.
In its rest frame, a particle with mass $M$ has momentum $p=0$. If it decayed to a single photon, conservation of energy would require the photon energy to be $E=Mc^2$, while conservation of momentum would require the photon to maintain $p=0$. However, photons obey $E=pc$ (which is the special case of $E^2 = (pc)^2 + (mc^2)^2$ for massless particles). It's not possible to satisfy all these constraints at once. Composite particles may emit single photons, but no massive particle may decay to a photon.
answered Jan 12 at 5:37
rob♦rob
40k972165
$endgroup$
$begingroup$
Massive particle as in fermion with half integer spin right, so it have to decay into some other particles on top of a photon to conserve energy and spin momentum is this what you are saying?
$endgroup$
– user6760
Jan 12 at 6:04
3
$begingroup$
@user6760 This argument is about linear, not angular, momentum. And there are plenty of massive particles which obey Bose-Einstein statistics and have integer spins.
$endgroup$
– rob♦
2 days ago
add a comment |
$begingroup$
No massive particle can decay into a single photon.
In its rest frame, a particle with mass $M$ has momentum $p=0$. If it decayed to a single photon, conservation of energy would require the photon energy to be $E=Mc^2$, while conservation of momentum would require the photon to maintain $p=0$. However, photons obey $E=pc$ (which is the special case of $E^2 = (pc)^2 + (mc^2)^2$ for massless particles). It's not possible to satisfy all these constraints at once. Composite particles may emit single photons, but no massive particle may decay to a photon.
answered Jan 12 at 5:37
rob♦rob
40k972165
$endgroup$
$begingroup$
Massive particle as in fermion with half integer spin right, so it have to decay into some other particles on top of a photon to conserve energy and spin momentum is this what you are saying?
$endgroup$
– user6760
Jan 12 at 6:04
3
$begingroup$
@user6760 This argument is about linear, not angular, momentum. And there are plenty of massive particles which obey Bose-Einstein statistics and have integer spins.
$endgroup$
– rob♦
2 days ago
add a comment |
$begingroup$
No massive particle can decay into a single photon.
In its rest frame, a particle with mass $M$ has momentum $p=0$. If it decayed to a single photon, conservation of energy would require the photon energy to be $E=Mc^2$, while conservation of momentum would require the photon to maintain $p=0$. However, photons obey $E=pc$ (which is the special case of $E^2 = (pc)^2 + (mc^2)^2$ for massless particles). It's not possible to satisfy all these constraints at once. Composite particles may emit single photons, but no massive particle may decay to a photon.
answered Jan 12 at 5:37
rob♦rob
40k972165
$endgroup$
No massive particle can decay into a single photon.
In its rest frame, a particle with mass $M$ has momentum $p=0$. If it decayed to a single photon, conservation of energy would require the photon energy to be $E=Mc^2$, while conservation of momentum would require the photon to maintain $p=0$. However, photons obey $E=pc$ (which is the special case of $E^2 = (pc)^2 + (mc^2)^2$ for massless particles). It's not possible to satisfy all these constraints at once. Composite particles may emit single photons, but no massive particle may decay to a photon.
answered Jan 12 at 5:37
rob♦rob
40k972165
answered Jan 12 at 5:37
rob♦rob
40k972165
answered Jan 12 at 5:37
rob♦rob
40k972165
answered Jan 12 at 5:37
rob♦rob
40k972165
40k972165
$begingroup$
Massive particle as in fermion with half integer spin right, so it have to decay into some other particles on top of a photon to conserve energy and spin momentum is this what you are saying?
$endgroup$
– user6760
Jan 12 at 6:04
3
$begingroup$
@user6760 This argument is about linear, not angular, momentum. And there are plenty of massive particles which obey Bose-Einstein statistics and have integer spins.
$endgroup$
– rob♦
2 days ago
add a comment |
$begingroup$
Massive particle as in fermion with half integer spin right, so it have to decay into some other particles on top of a photon to conserve energy and spin momentum is this what you are saying?
$endgroup$
– user6760
Jan 12 at 6:04
3
$begingroup$
@user6760 This argument is about linear, not angular, momentum. And there are plenty of massive particles which obey Bose-Einstein statistics and have integer spins.
$endgroup$
– rob♦
2 days ago
$begingroup$
Massive particle as in fermion with half integer spin right, so it have to decay into some other particles on top of a photon to conserve energy and spin momentum is this what you are saying?
$endgroup$
– user6760
Jan 12 at 6:04
$begingroup$
Massive particle as in fermion with half integer spin right, so it have to decay into some other particles on top of a photon to conserve energy and spin momentum is this what you are saying?
$endgroup$
– user6760
Jan 12 at 6:04
3
3
$begingroup$
@user6760 This argument is about linear, not angular, momentum. And there are plenty of massive particles which obey Bose-Einstein statistics and have integer spins.
$endgroup$
– rob♦
2 days ago
$begingroup$
@user6760 This argument is about linear, not angular, momentum. And there are plenty of massive particles which obey Bose-Einstein statistics and have integer spins.
$endgroup$
– rob♦
2 days ago
add a comment |
$begingroup$
The Higgs boson has spin $0$. A photon has spin $1$. The total angular momentum cannot change in the decay, so a Higgs boson cannot decay into a single photon, regardless of the energy. But the total angular momentum of two photons can be zero (because their spins can be oriented in opposite directions), so this decay mode can conserve angular momentum.
As emphasized in a comment, conservation of angular momentum is only a necessary condition, not a sufficient one. Please see rob's answer for clarification about this.
answered Jan 12 at 3:52
Dan YandDan Yand
8,33211234
$endgroup$
1
$begingroup$
I just look up spin so spin can be negative
$endgroup$
– user6760
Jan 12 at 4:14
add a comment |
$begingroup$
The Higgs boson has spin $0$. A photon has spin $1$. The total angular momentum cannot change in the decay, so a Higgs boson cannot decay into a single photon, regardless of the energy. But the total angular momentum of two photons can be zero (because their spins can be oriented in opposite directions), so this decay mode can conserve angular momentum.
As emphasized in a comment, conservation of angular momentum is only a necessary condition, not a sufficient one. Please see rob's answer for clarification about this.
answered Jan 12 at 3:52
Dan YandDan Yand
8,33211234
$endgroup$
1
$begingroup$
I just look up spin so spin can be negative
$endgroup$
– user6760
Jan 12 at 4:14
add a comment |
$begingroup$
The Higgs boson has spin $0$. A photon has spin $1$. The total angular momentum cannot change in the decay, so a Higgs boson cannot decay into a single photon, regardless of the energy. But the total angular momentum of two photons can be zero (because their spins can be oriented in opposite directions), so this decay mode can conserve angular momentum.
As emphasized in a comment, conservation of angular momentum is only a necessary condition, not a sufficient one. Please see rob's answer for clarification about this.
answered Jan 12 at 3:52
Dan YandDan Yand
8,33211234
$endgroup$
The Higgs boson has spin $0$. A photon has spin $1$. The total angular momentum cannot change in the decay, so a Higgs boson cannot decay into a single photon, regardless of the energy. But the total angular momentum of two photons can be zero (because their spins can be oriented in opposite directions), so this decay mode can conserve angular momentum.
As emphasized in a comment, conservation of angular momentum is only a necessary condition, not a sufficient one. Please see rob's answer for clarification about this.
answered Jan 12 at 3:52
Dan YandDan Yand
8,33211234
edited 2 days ago
answered Jan 12 at 3:52
Dan YandDan Yand
8,33211234
answered Jan 12 at 3:52
Dan YandDan Yand
8,33211234
answered Jan 12 at 3:52
Dan YandDan Yand
8,33211234
8,33211234
1
$begingroup$
I just look up spin so spin can be negative
$endgroup$
– user6760
Jan 12 at 4:14
add a comment |
1
$begingroup$
I just look up spin so spin can be negative
$endgroup$
– user6760
Jan 12 at 4:14
1
1
$begingroup$
I just look up spin so spin can be negative
$endgroup$
– user6760
Jan 12 at 4:14
$begingroup$
I just look up spin so spin can be negative
$endgroup$
– user6760
Jan 12 at 4:14
add a comment |
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Related: physics.stackexchange.com/q/427466/2451 and links therein.
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– Qmechanic♦
2 days ago