## Neutrinos and Anti-neutrinos

<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 -&gt; p + e_minus\nnu_bar + n -&gt; 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">&nbsp;&nbsp;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

$$\nu + n -> p + e_{minus}\nu_bar + n -> p + e_{minus}$$

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

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"Yi-Zen Chu; Yiren Qu" wrote in message news:... > 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 > > $\nu + n -> p + e_{minus}$ > $\nu_bar + n -> p + e_{minus}$ > > 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.



"Yi-Zen Chu; Yiren Qu" wrote in message news:... > 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 > > $\nu + n -> p + e_{minus}$ > $\nu_bar + n -> p + e_{minus}$ > > 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.

## Neutrinos and Anti-neutrinos

<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&gt; "Yi-Zen Chu; Yiren Qu" &lt;y#i#-#z#e#n#.#c#h#u#@#y#a#l#e#.#e#d#u&gt; wrote in\n&gt; message news:&lt;c81g8m\\$lao\\$1@news.wss.yale.edu&gt;...\n&gt;\n&gt;&gt; Is it true that it is still an open question whether neutrinos are their\n&gt;&gt; own anti-particles? (More generally, does our theories tell us anything\n&gt;&gt; about why or whether a given particle is its own anti-particle?)\n&gt;&gt;\n&gt;&gt; I read in D.J. Griffiths\' Introduction To Elementary Particles that\n&gt;&gt; Davis and Harmer did an experiment in the late 50\'s to compare the two\n&gt;&gt; reactions\n&gt;&gt;\n&gt;&gt; nu + n -&gt; p + e_minus\n&gt;&gt; nu_bar + n -&gt; p + e_minus\n&gt;&gt;\n&gt;&gt; and it was found that the latter does not occur, thereby proving that\n&gt;&gt; anti-neutrinos are not their own anti-particles. What is our current\n&gt;&gt; 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&gt; Maybe some people thought that when some people thought the neutrino was\n&gt; 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">&nbsp;&nbsp;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 >> $>> \nu + n -> p + e_{minus}>> \nu_bar + n -> p + e_{minus}$ >> >> 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 $\beta$ 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 $-e '_ = "gdpusch\@NO.xnet.SPAM.com\n$"$; s/NO\$.$//; s/SPAM\$.//; print;'  "Yi-Zen Chu; Yiren Qu" 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 > > $\nu + n -> p + e_{minus}$ > $\nu_bar + n -> p + e_{minus}$ > > 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 $\beta$ 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 $\beta$ decay (GNO i think?) Mike Crowe