Neutrinos and Anti-neutrinos

Yi-Zen Chu; Yiren Qu

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no, scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Hi everyone\n\nIs it true that it is still an open question whether neutrinos are their\nown anti-particles? (More generally, does our theories tell us anything\nabout why or whether a given particle is its own anti-particle?)\n\nI read in D.J. Griffiths\' Introduction To Elementary Particles that\nDavis and Harmer did an experiment in the late 50\'s to compare the two\nreactions\n\nnu + n -> p + e_minus\nnu_bar + n -> p + e_minus\n\nand it was found that the latter does not occur, thereby proving that\nanti-neutrinos are not their own anti-particles. What is our current\nview / interpretation of this experiment?\n\nThanks!\n\nYi-Zen\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>Hi everyone

Is it true that it is still an open question whether neutrinos are their
own anti-particles? (More generally, does our theories tell us anything
about why or whether a given particle is its own anti-particle?)

I read in D.J. Griffiths' Introduction To Elementary Particles that
Davis and Harmer did an experiment in the late 50's to compare the two
reactions

[tex]\nu + n -> p + e_{minus}\nu_bar + n -> p + e_{minus}[/tex]

and it was found that the latter does not occur, thereby proving that
anti-neutrinos are not their own anti-particles. What is our current
view / interpretation of this experiment?

Thanks!

Yi-Zen

Ulmo

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no, scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"Yi-Zen Chu; Yiren Qu" <y#i#-#z#e#n#.#c#h#u#@#y#a#l#e#.#e#d#u> wrote in message news:<c81g8m\\$lao\\$1@news.wss.yale.edu>...\n> Hi everyone\n>\n> Is it true that it is still an open question whether neutrinos are their\n> own anti-particles? (More generally, does our theories tell us anything\n> about why or whether a given particle is its own anti-particle?)\n>\n> I read in D.J. Griffiths\' Introduction To Elementary Particles that\n> Davis and Harmer did an experiment in the late 50\'s to compare the two\n> reactions\n>\n> nu + n -> p + e_minus\n> nu_bar + n -> p + e_minus\n>\n> and it was found that the latter does not occur, thereby proving that\n> anti-neutrinos are not their own anti-particles. What is our current\n> view / interpretation of this experiment?\n>\n> Thanks!\n\nMaybe some people thought that when some people thought the neutrino was massless.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Yi-Zen Chu; Yiren Qu" <y#i#-#z#e#n#.#c#h#u#@#y#a#l#e#.#e#d#u> wrote in message news:<c81g8m$lao$1@news.wss.yale.edu>...
> Hi everyone
>
> Is it true that it is still an open question whether neutrinos are their
> own anti-particles? (More generally, does our theories tell us anything
> about why or whether a given particle is its own anti-particle?)
>
> I read in D.J. Griffiths' Introduction To Elementary Particles that
> Davis and Harmer did an experiment in the late 50's to compare the two
> reactions
>
> [itex]\nu + n -> p + e_{minus}[/itex]
> [itex]\nu_bar + n -> p + e_{minus}[/itex]
>
> and it was found that the latter does not occur, thereby proving that
> anti-neutrinos are not their own anti-particles. What is our current
> view / interpretation of this experiment?
>
> Thanks!

Maybe some people thought that when some people thought the neutrino was massless.

Igor

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no, scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"Yi-Zen Chu; Yiren Qu" <y#i#-#z#e#n#.#c#h#u#@#y#a#l#e#.#e#d#u> wrote in message news:<c81g8m\\$lao\\$1@news.wss.yale.edu>...\n> Hi everyone\n>\n> Is it true that it is still an open question whether neutrinos are their\n> own anti-particles? (More generally, does our theories tell us anything\n> about why or whether a given particle is its own anti-particle?)\n>\n> I read in D.J. Griffiths\' Introduction To Elementary Particles that\n> Davis and Harmer did an experiment in the late 50\'s to compare the two\n> reactions\n>\n> nu + n -> p + e_minus\n> nu_bar + n -> p + e_minus\n>\n> and it was found that the latter does not occur, thereby proving that\n> anti-neutrinos are not their own anti-particles. What is our current\n> view / interpretation of this experiment?\n>\n> Thanks!\n>\n> Yi-Zen\n\n\nHow could they be the same when they have opposite lepton number?\nProbably a more interesting question would be whether right handed\nneutrinos (or left handed antis)exist in nature.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Yi-Zen Chu; Yiren Qu" <y#i#-#z#e#n#.#c#h#u#@#y#a#l#e#.#e#d#u> wrote in message news:<c81g8m$lao$1@news.wss.yale.edu>...
> Hi everyone
>
> Is it true that it is still an open question whether neutrinos are their
> own anti-particles? (More generally, does our theories tell us anything
> about why or whether a given particle is its own anti-particle?)
>
> I read in D.J. Griffiths' Introduction To Elementary Particles that
> Davis and Harmer did an experiment in the late 50's to compare the two
> reactions
>
> [itex]\nu + n -> p + e_{minus}[/itex]
> [itex]\nu_bar + n -> p + e_{minus}[/itex]
>
> and it was found that the latter does not occur, thereby proving that
> anti-neutrinos are not their own anti-particles. What is our current
> view / interpretation of this experiment?
>
> Thanks!
>
> Yi-Zen

How could they be the same when they have opposite lepton number?
Probably a more interesting question would be whether right handed
neutrinos (or left handed antis)exist in nature.

Gordon D. Pusch

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no, scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nulmo@cheerful.com (Ulmo) writes:\n\n> "Yi-Zen Chu; Yiren Qu" <y#i#-#z#e#n#.#c#h#u#@#y#a#l#e#.#e#d#u> wrote in\n> message news:<c81g8m\\$lao\\$1@news.wss.yale.edu>...\n>\n>> Is it true that it is still an open question whether neutrinos are their\n>> own anti-particles? (More generally, does our theories tell us anything\n>> about why or whether a given particle is its own anti-particle?)\n>>\n>> I read in D.J. Griffiths\' Introduction To Elementary Particles that\n>> Davis and Harmer did an experiment in the late 50\'s to compare the two\n>> reactions\n>>\n>> nu + n -> p + e_minus\n>> nu_bar + n -> p + e_minus\n>>\n>> and it was found that the latter does not occur, thereby proving that\n>> anti-neutrinos are not their own anti-particles. What is our current\n>> view / interpretation of this experiment?\n\nThe possibility that neutrinos might be "pure Majorana particles" (which\nhappen to also be their own antiparticles) is strongly constrained by the\nnon-observation of "neutrinoless double beta decay."\n\n\n> Maybe some people thought that when some people thought the neutrino was\n> massless.\n\nThe possibility that the neutrino sector of an "Extended Standard Model"\nmight have a _mixture_ of "Dirac" and "Majorana" mass terms has not yet\nbeen ruled out.\n\n\n-- Gordon D. Pusch\n\nperl -e \'\\$_ = "gdpusch\\@NO.xnet.SPAM.com\\n"; s/NO\\.//; s/SPAM\\.//; print;\'\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>ulmo@cheerful.com (Ulmo) writes:

> "Yi-Zen Chu; Yiren Qu" <y#i#-#z#e#n#.#c#h#u#@#y#a#l#e#.#e#d#u> wrote in
> message news:<c81g8m$lao$1@news.wss.yale.edu>...
>
>> Is it true that it is still an open question whether neutrinos are their
>> own anti-particles? (More generally, does our theories tell us anything
>> about why or whether a given particle is its own anti-particle?)
>>
>> I read in D.J. Griffiths' Introduction To Elementary Particles that
>> Davis and Harmer did an experiment in the late 50's to compare the two
>> reactions
>>
[itex]>> \nu + n -> p + e_{minus}>> \nu_bar + n -> p + e_{minus}[/itex]
>>
>> and it was found that the latter does not occur, thereby proving that
>> anti-neutrinos are not their own anti-particles. What is our current
>> view / interpretation of this experiment?

The possibility that neutrinos might be "pure Majorana particles" (which
happen to also be their own antiparticles) is strongly constrained by the
non-observation of "neutrinoless double [itex]\beta[/itex] decay."

> Maybe some people thought that when some people thought the neutrino was
> massless.

The possibility that the neutrino sector of an "Extended Standard Model"
might have a _mixture_ of "Dirac" and "Majorana" mass terms has not yet
been ruled out.

-- Gordon D. Pusch

perl [itex]-e '$_ = "gdpusch\@NO.xnet.SPAM.com\n[/itex]"[itex]; s/NO\[/itex].[itex]//; s/SPAM\[/itex].//; print;'

Mike Crowe

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no, scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n"Yi-Zen Chu; Yiren Qu" <y#i#-#z#e#n#.#c#h#u#@#y#a#l#e#.#e#d#u> wrote in\nmessage news:c81g8m\\$lao\\$1@news.wss.yale.edu...\n> Hi everyone\n>\n> Is it true that it is still an open question whether neutrinos are their\n> own anti-particles? (More generally, does our theories tell us anything\n> about why or whether a given particle is its own anti-particle?)\n>\n> I read in D.J. Griffiths\' Introduction To Elementary Particles that\n> Davis and Harmer did an experiment in the late 50\'s to compare the two\n> reactions\n>\n> nu + n -> p + e_minus\n> nu_bar + n -> p + e_minus\n>\n> and it was found that the latter does not occur, thereby proving that\n> anti-neutrinos are not their own anti-particles. What is our current\n> view / interpretation of this experiment?\n>\n> Thanks!\n>\n> Yi-Zen\n>\n\nAt the moment the verdict is still out on this, but I will confess I am not\nparticularly clear on all the subtleties of the theory.\n\nThere are basically three different considered models for neutrinos:\nWeyl\nThis is the ultrarelatavistic approximation to the Dirac equation, and\nso applies exactly were the neutrino is massless.\nDirac\nWould be the "normal" way the particles should be have, the mass being\ngiven by the coupling between left and right as per usual\nMajorana\nHere, the particle can be thought of as its own antiparticle, but it is\nachieved by a linear combination of left and right. For the majorana set up\nneutrino-less double beta decay should be possible, since it allows two\nneutrino\'s to annihilate each other. However, I believe it is the\nfundemental particle states that are Majorana, and not neccisarily the\nflavour eigenstates, which would be the explanation for the above reaction\nnot working. Personally though I\'m scepticle of the Majorana model, but\ndon\'t really know enough about it in detail to pass too much judgement. They\nare still looking for the double beta decay (GNO i think?)\n\nMike Crowe\n\n\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Yi-Zen Chu; Yiren Qu" <y#i#-#z#e#n#.#c#h#u#@#y#a#l#e#.#e#d#u> wrote in
message news:c81g8m$lao$1@news.wss.yale.edu...
> Hi everyone
>
> Is it true that it is still an open question whether neutrinos are their
> own anti-particles? (More generally, does our theories tell us anything
> about why or whether a given particle is its own anti-particle?)
>
> I read in D.J. Griffiths' Introduction To Elementary Particles that
> Davis and Harmer did an experiment in the late 50's to compare the two
> reactions
>
> [itex]\nu + n -> p + e_{minus}[/itex]
> [itex]\nu_bar + n -> p + e_{minus}[/itex]
>
> and it was found that the latter does not occur, thereby proving that
> anti-neutrinos are not their own anti-particles. What is our current
> view / interpretation of this experiment?
>
> Thanks!
>
> Yi-Zen
>

At the moment the verdict is still out on this, but I will confess I am not
particularly clear on all the subtleties of the theory.

There are basically three different considered models for neutrinos:
Weyl
This is the ultrarelatavistic approximation to the Dirac equation, and
so applies exactly were the neutrino is massless.
Dirac
Would be the "normal" way the particles should be have, the mass being
given by the coupling between left and right as per usual
Majorana
Here, the particle can be thought of as its own antiparticle, but it is
achieved by a linear combination of left and right. For the majorana set up
neutrino-less double [itex]\beta[/itex] decay should be possible, since it allows two
neutrino's to annihilate each other. However, I believe it is the
fundemental particle states that are Majorana, and not neccisarily the
flavour eigenstates, which would be the explanation for the above reaction
not working. Personally though I'm scepticle of the Majorana model, but
don't really know enough about it in detail to pass too much judgement. They
are still looking for the double [itex]\beta[/itex] decay (GNO i think?)

Mike Crowe

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