Talk:CP violation

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Requested move[edit]

The following is a closed discussion of the proposal. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the proposal was Move Parsecboy (talk) 00:20, 28 January 2009 (UTC)

Why is this term hyphenated? Surely as a noun, "CP violation" should not be hyphenated. As an adjective "CP-violating" should be. The same of course applies to "T violation", "CPT violation" etc. Does an expert in English language want to comment? Paulfharrison 07:57, 29 May 2007 (UTC). Note that none of the section headings has "CP violation" hyphenated, and neither do the books of the same title in the references at the bottom.Paulfharrison 08:54, 30 May 2007 (UTC)

You are entirely correct; the hyphen, and the one in "CP symmetry", are unnecessary. Can someone move this? (talk) 01:03, 29 February 2008 (UTC)
I third this; the hyphen is utterly ridiuculous. ΤΕΡΡΑΣΙΔΙΩΣ(Ταλκ) 03:45, 26 August 2008 (UTC)
Fourthed.Headbomb {ταλκκοντριβςWP Physics} 07:25, 22 January 2009 (UTC)
  • Support move. There is no reason to have a hyphen in this term. •Life of Riley (talk) 04:38, 23 January 2009 (UTC)
  • Support move The hyphen makes no sense to me. Dauto (talk) 03:08, 24 January 2009 (UTC)

Pictogram voting info.svg Administrator note:{{editprotected}} template has been removed, as this template is not appropriate for page moves. This page move has been listed at WP:Requested moves, and an admin will evaluate this discussion once that listing is 5 days old. Please be patient.--Aervanath (talk) 10:06, 25 January 2009 (UTC)

The above discussion is preserved as an archive of the proposal. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.


'CP-symmetry was violated and only a much stronger version of the symmetry existed, CPT-symmetry'

Is this correct terminology? I would say that if some symmetry is violated a stronger one is also violated (a strong condition or property implies a weaker one). I would say that CPT-symmetry is neither stronger nor weaker than CP-symmetry (CPT-symmetry would however be weaker than CP- and T-symmetry together). Patrick 12:11 Nov 24, 2002 (UTC)
I understand now that 'strong version' in this context means 'more universally true'. Some clarification in the articles would be useful, as what in logic would be a weak condition/property would be strong in this sense. Patrick 13:02 Nov 24, 2002 (UTC)
  • Cleaned up by Voyajer 12/2/05

To merge "Strong CP problem" here[edit]

  • I say yes, it is better to handle a thing at one place, and 'Strong CP problem" is a stub anyway. Also, CP-symmetry is redirected to here, it makes even more sense. Hidaspal 19:02, 28 April 2006 (UTC)
  • Done. Hidaspal 20:39, 28 April 2006 (UTC)

OK, well, don't go to crazy merging. Someday, someone might want to write a long article for the strong CP problem, and there won't be room for that here. But whatever, this was not a bad choice. linas 05:38, 29 April 2006 (UTC)

In fact, there should be a long article on the strong CP problem. There's really no excuse other than laziness for it not existing right now. On a related note, tho, the name of this article should really be CP-symmetry, not CP-violation, to match all the other symmetries in the CPT family. -- Xerxes 19:24, 29 April 2006 (UTC)

Relation to standard model[edit]

I just edited this, see [1]. Since I'm not a physicist, someone should probably check me. Especially the bit where I link to Planck Mass is shaky. I think it's meaningful (why is CP violation relatively livelier on the experimental side, when theorists wouldn't a priori focus there to extend the Standard Model?) but clearly leaping over the Higgs mass to the Planck mass is a giant step. If someone knows an honest way not to make that leap then please fix it. --Homunq 11:53, 13 August 2006 (UTC)

Matter vs. Anti matter?[edit]

The Standard Model contains only two ways to break CP symmetry. The first of these, discussed above, is the QCD lagrangian; but one would expect this to lead to either no CP violation or a CP violation that is many, many orders of magnitude too large. The second of these, involving the weak force, can account for a small portion of CP-violation, but it is predicted to be sufficient for a net mass of matter equivalent to only a single galaxy in the known universe.

What about mass of neutrinos? Since they change type, they experience time, and so have mass; since they are their own anti-particle, this is a way for equal amounts of particle and anti-particle to have mass. Or am I completely off base? Keybounce 06:45, 14 November 2006 (UTC)

I'm no expert, but I changed the article to say "normal matter" because you may be right. Of course, the phrase "net matter" could be interpreted to mean "matter minus antimatter" which would exclude particles like neutrinos. --Homunq 15:37, 14 November 2006 (UTC)


I'm not a physicist, physics student, or that "up" on physics news for the most part... But I saw that recently some evidence for the existnce of axions seems to have come out. Can one of you more knowledgeable types take a better look at it and see what relevance it might have to this article? 22:52, 6 December 2006 (UTC)

This is mentioned on the Axion page.

Myther et al[edit]

No person called Myther is known to the physics preprint archive or to NASA ADS. I assume the following (inserted recently by is OR or a hoax of some sort, so removed it:

Myther et al suggest that, if T-symmetry is violated, then there could be a possibility of the universe experiencing a big crunch without going through a complete replay of the history of universe. Thus, the problems associated with the reversed arrow of time posed by the laws of thermodynamics can be ignored assuming that the universe will then start experiencing a different history while moving towards the big crunch from a distinct point in future when the universe will cease to expand and gravity will take over.

(The same user inserted another reference to this under Aeon). PaddyLeahy 00:26, 27 April 2007 (UTC)

QCD Lagrangian[edit]

I see in the Strong CP Problem section, the Lagrangian has terms like

It's a picky point, and possibly beyond my knowledge, but what does the trace even mean here? As far as I'm concerned, is a trace of sorts. There are certainly no clear free indices left over which to sum. The seems redundant and, more importantly, inconsistent with other articles. Warrickball (talk) 20:54, 21 May 2008 (UTC)

usually indicates the electromagnetic strength tensor. The strong CP problem, instead, involves the "chromomagnetic" strength tensors (cfr. Quantum chromodynamics). The trace refers to the summation over the index .

Unfortunately the page is semi protected... could anyone fix the typos?

Eugenio —Preceding unsigned comment added by (talk) 18:46, 12 November 2008 (UTC)

2008 Nobel Prize in Physics, clarifying direct CP violation, etc.[edit]

The article on CP violation needs some updates and corrections. Unfortunately, it is write-protected, so a Wiki-wizard would have to do the work.

2008 NOBEL PRIZE: As acknowledged in the public announcement of the 2008 Nobel Prize in Physics by the Nobel Committee, the observation of CP violation in B mesons by the Belle and BaBar B-factories was the last (and perhaps the most important) stone that paved the way to the Kobayashi and Maskawa's Nobel Prize. So, a mention of the 2008 Nobel Prize needs to be added to the top of the page.

IMPORTANT CORRECTION: The type of CP violation discovered by the BaBar and Belle experiments in 2001 is *not* direct CP violation. It is CP violation in interference between the decays of neutral B mesons with the without B0-B0bar mixing (B0 -> J/psi K0 interfering with B0 -> B0bar -> J/psi K0). Direct CP violation in B-meson decays was discovered a few years later, so far only in the difference between the B0 -> K+pi- and B0bar -> K-pi+ decay rates (and only BaBar currently has a statistically significant single-experiment measurement, although Belle and CDF are not far behind in precision and are fully consistent). Additionally, Belle has reported a statistically significant observation of direct CP violation in B0 -> pi+pi- (BaBar's measurement is equally precise and consistent with Belle's but is not statistically significant).

REFERENCES to the most important CP violation discoveries in B mesons, in chronological order:

B. Aubert et al. (BaBar Collaboration), "Observation of CP violation in the B0 meson system," Phys. Rev. Lett. 87, 091801 (2001),

K. Abe et al. (Belle Collaboration), "Observation of Large CP Violation in the Neutral B Meson System," Phys. Rev. Lett. 87, 091802 (2001),

B. Aubert et al. (BaBar Collaboration), "Direct CP Violating Asymmetry in B0 -> K+pi- Decays," Phys.Rev.Lett. 93, 131801 (2004),

H. Ishino et al. (Belle Collaboration), "Observation of Direct CP Violation in B0 -> pi+pi- Decays and Model-Independent Constraints on phi2," Phys. Rev. Lett. 98, 211801 (2007),

B. Aubert et al. (BaBar Collaboration), "Observation of CP Violation in B0 -> K+pi- and B0 -> pi+pi-," Phys. Rev. Lett. 99, 021603 (2007), —Preceding unsigned comment added by (talk) 11:08, 9 November 2008 (UTC)

Rename to charge-parity symmetry violation[edit]

Would it make more sense to spell out the acronym and rename the article to charge-parity symmetry violation?
Apis (talk) 08:52, 1 December 2008 (UTC)

My impression is that CP violation is nearly always refered to as CP violation, so I don't think it should be moved.Headbomb {ταλκκοντριβςWP Physics} 09:58, 1 December 2008 (UTC)

Altough spelling it out in the lead would be a good idea.Headbomb {ταλκκοντριβςWP Physics} 09:59, 1 December 2008 (UTC)
Done. Bhny (talk) 05:03, 30 December 2008 (UTC)
I've taken the liberty to rewrite what you wrote. I think this is a less blunt way to explicit the names of CP symmetry. Headbomb {ταλκκοντριβςWP Physics} 12:59, 30 December 2008 (UTC)
I prefer my blunt version. it's pretty much unreadable now. anyway i'll step out of this CP edit war Bhny (talk) 23:27, 31 December 2008 (UTC)

Experiments depend on background[edit]

I think it should be mentioned on this page that parity experiments are not so clear cut since the results always depend on the background. The space is filled with radiation and this radiation is certainly not uniform, it is quite possible that in Solar System some kind of background field favors one decay over the other. Enemyunknown (talk) 15:28, 23 January 2009 (UTC)

First Figure and explanation is wrong[edit]

The figure with the CP operation on the spin-up electron to the spin-down positron is wrong in the sense that the CP operation (the parity operation part) does _not_ change the direction of the spin since the spin is an axial vector. Axial vectors do not change sign under the parity operation. Actually the electron (which becomes the positron by C) changes the chirality (physics), i.e., the relative direction of the spin with respect to the momentum of the particle. This is due to the fact that the momentum is a vector and thus it changes sign under P. (talk) 13:50, 5 June 2009 (UTC)

Possible undetected vandalism[edit]

This diff [2] is an edit by an IP whose other edits are 100% vandalism, often very subtle and insidious (on another page, changing cosec to cos in a formula). Given the user's history, I suspect it's wrong, but I don't know anything about the topic, so I can't be sure. Can someone check this and see if this is indeed vandalism? Mokele (talk) 03:52, 27 February 2011 (UTC)

CP Symmetry And Gravity[edit]

Well, CP vollation nicely explains the existence of universe as we perceive it today. Still the Origin of matter, antimatter, spacetime and the fundamental forces that form the universe remains unsolved. I,hope oneday the answer will be found on the basis of CP voilation or some other consistent theory. Wajid Ansari (talk) 15:31, 7 June 2011 (UTC) JUNE,07 2011 9:00 PM

Antiparticle confusion[edit]

The article says: "C for charge conjugation, which transforms a particle into its antiparticle". This seems technically inaccurate. The page here on "antiparticles" says: "quantum states of a particle and an antiparticle can be interchanged by applying the charge conjugation (C), parity (P), and time reversal (T) operators". (talk) 20:24, 17 June 2011 (UTC)

Its not inaccurate. Charge conjugation transforms a particle into its anti-particle and vice verse. However, because parity is not a conserved quantity, you must also simultaneously apply the parity operator P in order to get an anti-particle in a equivalent state. Turns out that even CP is proximately violate so the equivalence between those states is not exact. To get an exact relationship you must apply CPT parity. Dauto (talk) 16:41, 19 June 2011 (UTC)
What you wrote makes no sense. "because parity is not a conserved quantity, you must also simultaneously apply the parity operator P". There are many quantities that are not conserved, and yet you wouldn't argue that their respective operators have to be applied in the context of matter-antimatter symmetry. "To get an exact relationship you must apply CPT parity." That is exactly what meant by his/her question: C does not transform a particle into its antiparticle (nor does CP), CPT does. Hence the article is inaccurate. -- (talk) 11:43, 11 January 2012 (UTC)

CP violation requiring a complex phase[edit]

I think it would be useful for someone to add an explanation as to why CP violation is linked to complex phases. Right now it's just stated without explanation. — Preceding unsigned comment added by Certain (talkcontribs) 15:06, 22 March 2012 (UTC)

Done! Reg (talk) 17:58, 2 August 2012 (UTC)
I'm trying to follow your explanation of why there must be a complex phase in the CKM matrix if there is CP-violation. My main stumbling block is understanding where the two different routes of going from comes from. Also, why does having this complex phase require there to be 3 generation of quarks (i.e. a 3x3 CKM matrix)? Can you please explain? I will try clarifying that part afterwards. --Omni-impotent (talk) 05:59, 14 January 2013 (UTC)
Hi, sorry for the ridiculously late answer, but I'll post in case someone else is still searching. "Two different routes" refers to intermediate particle states (e.g. a->c->b vs. a->d->b). The "3 quark generations" requirement isn't related to this derivation, but comes from the fact that the phase of the quark fields themselves can be freely redefined. If we assign each parameter of the matrix a phase, in the 2x2 case they can be "absorbed" by quark field redefinitions, but in the 3x3 case, you will always be left with at least one remaining. I'll edit the article to make these points more clear. (talk) 15:10, 7 February 2014 (UTC)

Change heading from "What is CP?" to "What is CP-symmetry?" ?[edit]

The first heading is currently titled "What is CP?", but as far as I understand it explains CP-symmetry. Wouldn't "What is CP-symmetry?" be a better name for that heading? Tony Mach (talk) 13:51, 4 August 2012 (UTC)

The titles used to be "What is CP?", "Indirect CP violation", "Direct CP violation", "Strong CP Problem", and the like. It made me expect a photo of Chris Hansen to appear. (talk) 07:38, 21 January 2014 (UTC)

Quantum Number?[edit]

Is there a quantum number associated with CP-symmetry? — Preceding unsigned comment added by (talk) 01:26, 14 February 2016 (UTC)

C and P. Headbomb {talk / contribs / physics / books} 01:56, 14 February 2016 (UTC)

merge duplicates[edit] same as — Preceding unsigned comment added by Learningtakessteps (talkcontribs) 22:23, 14 January 2017 (UTC)