\boldmath Search for heavy neutrinos\\ mixing with tau neutrinos
P.~Astier
We report on a search for heavy neutrinos ($\nus$) produced in the decay $D_s\to \tau \nus$ at the SPS proton target followed by the decay $\nudecay$ in the NOMAD detector.\ Both decays are expected to occur if $\nus$ is a component of $\nu_{\tau}$.\ From the analysis of the data collected during the 1996-1998 runs with $4.1\times10^{19}$ protons on target, a single candidate event consistent with background expectations was found.\ %No evidence for this decay chain has been found This allows to derive an upper limit on the mixing strength between the heavy neutrino and the tau neutrino in the $\nus$ mass range from 10 to 190 $MeV$.\ Windows between the SN1987a and Big Bang Nucleosynthesis lower limits and our result are still open for future experimental searches.\ The results obtained are used to constrain an interpretation of the time anomaly observed in the KARMEN1 detector.\
paperplb.tex
\documentclass{elsart}
\usepackage{epsfig}
\usepackage{rotate}
% following line is from elsevier; I don't know what it does -BC
% \usepackage{natbib}
\usepackage{amssymb}
\usepackage{amsmath}

%%%%%%%%%%%%My definitions

\newcommand\pair{e^+ e^-}
\newcommand\x{\nu_i}
\newcommand\nudecay{\nu_4 \rightarrow \nu_\tau e^+  e^-}
\newcommand\direct{1-cos\Theta_{\nu e^+  e^-}}
\newcommand\nus{\nu_4}

\newcommand\cc{{\rm CC}}
\newcommand\nutau{{\nu_\tau}}
\newcommand\anutau{\bar\nu_\tau}
\newcommand\numu{{\nu_\mu}}
\newcommand\anumu{\bar\nu_\mu}
\newcommand\nue{{\nu_e}}
\newcommand\anue{\bar\nu_e}
\newcommand\Eetot{E_{\rm e}^{\rm tot}} 
\newcommand\evis{E_{\rm vis}}
\newcommand\qlep{Q_{\rm Lep}}
\newcommand\enunu{e^- \anue \nu_\tau}
\newcommand\mununu{\mu^- \anumu \nu_\tau}
\newcommand\taue{\tau^- \to \enunu}
\newcommand\taumu{\tau^- \to \mununu}
\newcommand\tauonepr{\tau^- \to h^- (n\pi^0) \nutau}
\newcommand\taupi{\tau^- \to \pi^- \nutau}
\newcommand\taurho{\tau^- \to \rho^- \nutau}
\newcommand\threepi{\pi^-\pi^+\pi^-}
\newcommand\tauthreepi{\tau^- \to \threepi \nutau}
\newcommand\tauthreepr{\tau^- \to \threepi (n\pi^0) \nutau}
\newcommand\tauplusthreepi{\tau^+ \to \pi^+\pi^-\pi^+ \anutau}
\newcommand\numunutau{\numu \to \nutau}
\newcommand\anumunutau{\anumu \to \anutau}
\newcommand\epsmu{\epsilon_\mu}
\newcommand\epstau{\epsilon_\tau}
\newcommand\pt{p_T}
\newcommand\xvis{\tau_{\rm V}}
\newcommand\vpxvis{\vec p^{\,\xvis}}
\newcommand\jet{H}                    %symbol for hadronic jet
\newcommand\C{\mathcal C}
\newcommand\mpigamgam{M_{\pi\gamma\gamma}} %was M_{\rho} in original draft
\newcommand\mthreepi{M_{3\pi}}

\newcommand\Nmuobs{N_\mu^{\rm obs}}
\newcommand\ee{e^+e^-}
\newcommand\ntaumax{N_\tau^{\rm max}}

\newcommand\liknc{\mathcal{L}_{e1}} 
\newcommand\liknue{\mathcal{L}_{e2}}

\newcommand\ratnc{\ln\lambda_{e1}} 
\newcommand\ratnue{\ln\lambda_{e2}}

\newcommand\qtrat{R_T}
\newcommand\LikThreePi{\lambda_{3\pi}}
\newcommand\RatThreePi{\ln\lambda_{3\pi}}
\newcommand\ratpimu{\ln\lambda_{h\mu}}
\newcommand\ratpikin{\ln\lambda_{h{\rm kin}}}

%\newcommand\epsdir{/home/jbarney/latex}
%\newcommand\epsdir{/pool/ucla1/cousins/elsevier/}
\newcommand\epsdir{.}
\newcommand\bff{\bf}

\newcommand{\fix}[1]{{\bf <<< #1 !!! }}
\begin{document}
\begin{frontmatter}
\title{\boldmath Search for heavy neutrinos\\
 mixing with tau neutrinos}
%\collab{NOMAD Collaboration}
\vspace{-0.cm}
\centerline{\bf NOMAD Collaboration}
\author[Paris]             {P.~Astier}
\author[CERN]              {D.~Autiero}
\author[Saclay]            {A.~Baldisseri}
\author[Padova]            {M.~Baldo-Ceolin}
%\author[CERN]              {G.~Ballocchi}
\author[Paris]             {M.~Banner}
\author[LAPP]              {G.~Bassompierre}
\author[Lausanne]          {K.~Benslama}
\author[Saclay]            {N.~Besson}
\author[CERN,Lausanne]     {I.~Bird}
\author[Johns Hopkins]     {B.~Blumenfeld}
\author[Padova]            {F.~Bobisut}
\author[Saclay]            {J.~Bouchez}
\author[Sydney]            {S.~Boyd}
\author[Harvard,Zuerich]   {A.~Bueno}
\author[Dubna]             {S.~Bunyatov}
\author[CERN]              {L.~Camilleri}
\author[UCLA]              {A.~Cardini}
\author[Pavia]             {P.W.~Cattaneo}
\author[Pisa]              {V.~Cavasinni}
\author[CERN,IFIC]         {A.~Cervera-Villanueva}
\author[Padova]            {G.~Collazuol}
\author[Urbino]            {G.~Conforto}
\author[Pavia]             {C.~Conta}
\author[Padova]            {M.~Contalbrigo}
\author[UCLA]              {R.~Cousins}
\author[Harvard]           {D. Daniels}
\author[Lausanne]          {H.~Degaudenzi}
\author[Pisa]              {T.~Del~Prete}
\author[CERN]              {A.~De~Santo}
\author[Harvard]           {T.~Dignan}
\author[CERN]              {L.~Di~Lella}
\author[CERN]              {E.~do~Couto~e~Silva}
%\author[ANSTO,Sydney]      {I.J.~Donnelly}
\author[Paris]             {J.~Dumarchez}
\author[Sydney]            {M.~Ellis}
\author[LAPP]              {T.~Fazio}
\author[Harvard]           {G.J.~Feldman}
\author[Pavia]             {R.~Ferrari}
\author[CERN]              {D.~Ferr\`ere}
\author[Pisa]              {V.~Flaminio}
\author[Pavia]             {M.~Fraternali}
\author[LAPP]              {J.-M.~Gaillard}
%\author[Pavia]             {A.~Gandolfo}
\author[CERN,Paris]        {E.~Gangler}
\author[Dortmund,CERN]     {A.~Geiser}
\author[Dortmund]          {D.~Geppert}
\author[Padova]            {D.~Gibin}
\author[CERN,INR]          {S.N.~Gninenko}
\author[Sydney]            {A.~Godley}
\author[IFIC]         {M.C.~Gonzalez-Garcia}
\author[CERN,IFIC]         {J.-J.~Gomez-Cadenas}
\author[Saclay]            {J.~Gosset}
\author[Dortmund]          {C.~G\"o\ss ling}
\author[LAPP]              {M.~Gouan\`ere}
\author[CERN]              {A.~Grant}
\author[Florence]          {G.~Graziani}
\author[Padova]            {A.~Guglielmi}
\author[Saclay]            {C.~Hagner}
\author[IFIC]              {J.~Hernando}
\author[Harvard]           {D.~Hubbard}
\author[Harvard]           {P.~Hurst}
\author[Melbourne]         {N.~Hyett}
\author[Florence]          {E.~Iacopini}
\author[Lausanne]          {C.~Joseph}
\author[Lausanne]          {F.~Juget}
\author[INR]               {M.M.~Kirsanov}
\author[Dubna]             {O.~Klimov}
\author[CERN]              {J.~Kokkonen}
\author[INR,Pavia]         {A.V.~Kovzelev}
\author[INR]               {N.V.~Krasnikov}
\author[LAPP,Dubna]        {A.~Krasnoperov}
\author[Padova]            {S.~Lacaprara}
\author[Paris]             {C.~Lachaud}
\author[Zagreb]            {B.~Laki\'{c}}
\author[Pavia]             {A.~Lanza}
\author[Calabria]          {L.~La Rotonda}
\author[Padova]            {M.~Laveder}
\author[Paris]             {A.~Letessier-Selvon}
\author[Paris]             {J.-M.~Levy}
\author[CERN]              {L.~Linssen}
\author[Zagreb]            {A.~Ljubi\v{c}i\'{c}}
\author[Johns Hopkins]     {J.~Long}
\author[Florence]          {A.~Lupi}
%\author[LAPP]              {E.~Manola-Poggioli}
\author[Florence]          {A.~Marchionni}
\author[Urbino]            {F.~Martelli}
\author[Saclay]            {X.~M\'echain}
\author[LAPP]              {J.-P.~Mendiburu}
\author[Saclay]            {J.-P.~Meyer}
\author[Padova]            {M.~Mezzetto}
\author[Harvard,SouthC]    {S.R.~Mishra}
\author[Melbourne]         {G.F.~Moorhead}
%\author[LAPP]              {L.~Mossuz}
\author[Dubna]             {D.~Naumov}
\author[LAPP]              {P.~N\'ed\'elec}
\author[Dubna]             {Yu.~Nefedov}
\author[Lausanne]          {C.~Nguyen-Mau}
\author[Rome]              {D.~Orestano}
\author[Rome]              {F.~Pastore}
\author[Sydney]            {L.S.~Peak}
\author[Urbino]            {E.~Pennacchio}
\author[LAPP]              {H.~Pessard}
\author[CERN,Pavia]        {R.~Petti}
\author[CERN]              {A.~Placci}
%\author[Saclay]            {A.~Pluquet}
\author[Pavia]             {G.~Polesello}
\author[Dortmund]          {D.~Pollmann}
\author[INR]               {A.~Polyarush}
\author[Dubna,Paris]       {B.~Popov}
\author[Melbourne]         {C.~Poulsen}
\author[Saclay]            {P.~Rathouit}
%\author[Pisa]              {R.~Ren\`o}
%\author[Pisa]              {G.~Renzoni}
\author[Zuerich]           {J.~Rico}
\author[CERN,Pisa]         {C.~Roda}
\author[CERN,Zuerich]      {A.~Rubbia}
\author[Pavia]             {F.~Salvatore}
\author[Paris]             {K.~Schahmaneche}
\author[Dortmund,CERN]     {B.~Schmidt}
%\author[Pisa]              {G.~Segneri}
\author[Melbourne]         {M.~Sevior}
\author[LAPP]              {D.~Sillou}
\author[CERN,Sydney]       {F.J.P.~Soler}
\author[Lausanne]          {G.~Sozzi}
\author[Johns Hopkins,Lausanne]  {D.~Steele}
%\author[Lausanne]          {M.~Steininger}
\author[CERN]              {U.~Stiegler}
\author[Zagreb]            {M.~Stip\v{c}evi\'{c}}
\author[Saclay]            {Th.~Stolarczyk}
\author[Lausanne]          {M.~Tareb-Reyes}
\author[Melbourne]         {G.N.~Taylor}
\author[Dubna]             {V.~Tereshchenko}
\author[INR]               {A.N.~Toropin}
\author[Paris]             {A.-M.~Touchard}
\author[Melbourne]         {S.N.~Tovey}
\author[Lausanne]          {M.-T.~Tran}
\author[CERN]              {E.~Tsesmelis}
\author[Sydney]            {J.~Ulrichs}
%\author[Paris]             {V.~Uros}
\author[Lausanne]          {L.~Vacavant}
\author[Calabria,Perugia]  {M.~Valdata-Nappi}
%{M.~Valdata-Nappi\thanksref{Perugia}}
\author[Dubna,UCLA]        {V.~Valuev}
\author[Paris]             {F.~Vannucci}
\author[Sydney]            {K.E.~Varvell}
\author[Urbino]            {M.~Veltri}
\author[Pavia]             {V.~Vercesi}
%\author[LAPP]              {D.~Verkindt}
\author[CERN,IFIC]         {G.~Vidal-Sitjes}
\author[Lausanne]          {J.-M.~Vieira}
\author[UCLA]              {T.~Vinogradova}
%\author[Saclay]            {M.-K.~Vo}
\author[Harvard,CERN]      {F.V.~Weber}
\author[Dortmund]          {T.~Weisse}
\author[CERN]              {F.F.~Wilson}
\author[Melbourne]         {L.J.~Winton}
\author[Sydney]            {B.D.~Yabsley}
\author[Saclay]            {H.~Zaccone}
\author[Dortmund]          {K.~Zuber}
\author[Padova]            {P.~Zuccon}

\address[LAPP]           {LAPP, Annecy, France}
\address[Johns Hopkins]  {Johns Hopkins Univ., Baltimore, MD, USA}
\address[Harvard]        {Harvard Univ., Cambridge, MA, USA}
\address[Calabria]       {Univ. of Calabria and INFN, Cosenza, Italy}
\address[Dortmund]       {Dortmund Univ., Dortmund, Germany}
\address[Dubna]          {JINR, Dubna, Russia}
\address[Florence]       {Univ. of Florence and INFN,  Florence, Italy}
\address[CERN]           {CERN, Geneva, Switzerland}
\address[Lausanne]       {University of Lausanne, Lausanne, Switzerland}
\address[UCLA]           {UCLA, Los Angeles, CA, USA}
\address[Melbourne]      {University of Melbourne, Melbourne, Australia}
\address[INR]            {Inst. Nucl. Research, INR Moscow, Russia}
\address[Padova]         {Univ. of Padova and INFN, Padova, Italy}
\address[Paris]          {LPNHE, Univ. of Paris VI and VII, Paris, France}
\address[Pavia]          {Univ. of Pavia and INFN, Pavia, Italy}
\address[Perugia]        {Univ. of Perugia and INFN, Perugia, Italy}
\address[Pisa]           {Univ. of Pisa and INFN, Pisa, Italy}
\address[Rome]           {Roma Tre University and INFN, Rome, Italy}
\address[Saclay]         {DAPNIA, CEA Saclay, France}
%\address[ANSTO]          {ANSTO Sydney, Menai, Australia}
\address[SouthC]         {Univ. of South Carolina, Columbia, SC, USA}
\address[Sydney]         {Univ. of Sydney, Sydney, Australia}
\address[Urbino]         {Univ. of Urbino, Urbino, and INFN Florence, Italy}
\address[IFIC]           {IFIC, Valencia, Spain}
\address[Zagreb]         {Rudjer Bo\v{s}kovi\'{c} Institute, Zagreb, Croatia}
\address[Zuerich]        {ETH Z\"urich, Z\"urich, Switzerland}

%\thanks[Perugia]         {Now at Univ. of Perugia and INFN, Perugia, Italy}

\clearpage
\begin{abstract}
We report on a search for heavy neutrinos ($\nus$) produced in
the decay $D_s\to \tau \nus$ at the SPS proton target followed by the 
decay $\nudecay$ in the NOMAD detector.\ Both decays are expected to occur
if $\nus$ is a component of $\nu_{\tau}$.\ 
 From the analysis of the data collected during the 1996-1998 runs
 with $4.1\times10^{19}$ protons on target, a single
 candidate event consistent with background expectations was found.\
%No evidence for this decay chain has been found 
This allows to derive  an upper limit on the mixing strength 
between the heavy neutrino and the tau neutrino  
in the $\nus$ mass range from 10 to 190 $\rm MeV$.\ Windows between the SN1987a 
and  Big Bang Nucleosynthesis lower limits and our result are 
still open for 
future experimental searches.\  The results obtained are used to 
constrain an interpretation of the time anomaly observed in the KARMEN1
detector.\
\end{abstract}
\begin{keyword} 
neutrino mixing, neutrino decay
\end{keyword}
\end{frontmatter}


\input motivation

\input nomad

\input method

\input analysis

\input background

\input result_p

\input karmen1

\input conclusion

\input bibliography


%\input table
\newpage
  \begin{figure}
 \begin{center}
   \mbox{\hspace{-1.8cm}\epsfig{file=karmen2_setup.eps,width=120mm}}
\end{center}
    \centering
\vspace{0.5cm}
    \caption{\em Schematic illustration of the production of $\nus$ and 
its detection via the $\nudecay$ decay.\ Because of its short lifetime
the $D_s$ decays immediately at the production point.}
%  \label{figure 1:}
\end{figure}

  \begin{figure}
.\vspace{-3.5cm}
   \mbox{\hspace{3.0 cm}\epsfig{file=prod_p.eps,height=120mm}}
.\vspace{-6.5cm}
 \mbox{\hspace{3.0 cm}\epsfig{file=decay_p.eps,height=120mm}}
    \centering
    \caption{\em Feynman diagrams illustrating a) $\nus$ production  from 
 $D_s(\overline{D}_s)$ decay  and b) the decay of an isosinglet neutrino
$\nus$.}
  \label{figure 1:}
\end{figure}


\newpage
  \begin{figure}
 \begin{center}
   \mbox{\epsfig{file=tauspctr.eps, height=160mm,width=160mm}}
\vspace{0.5cm}
    \centering
    \caption{\em Combined energy spectra of tau neutrinos 
 pointing towards the NOMAD fiducial area from the 
proton target and from the beam dump a) originating directly from  $D_s(\overline{D}_s)$ decays;
b) originating 
from the decays of $\tau^{\pm}$ produced in $D_s(\overline{D}_s)$ decays; 
c) the sum of the two.\ The spectra 
are calculated for $10^{11}$ protons on target ({\em pot}).}
  \end{center}
  \label{figure 1:}
\end{figure}


\newpage
  \begin{figure}
 \begin{center}
   \mbox{\hspace{-1.5cm}\epsfig{file=polar_33mev.eps,height=80mm}}
\end{center}
    \centering
    \caption{\em Energy distribution  of $e^+e^-$ pairs
 from  decays of a $\nus$ with 33.9 $\rm MeV$  mass 
for different $\nu_4$ helicities. The average $e^+e^-$ pair energies are 
 $<E>_{+1}=16.4~\rm GeV$ and $<E>_{-1}=14.1~\rm GeV$ for helicities +1 and -1,
respectively.} 
  \label{figure 1:}
\end{figure}

  \begin{figure}
 \begin{center}
   \mbox{\epsfig{file=result2.eps,height=80mm,width=120mm}}
    \centering
    \caption{\em The final (1 - $cos\Theta_{\nu e^+ e^-)}$ distribution  
for the data and MC.\ The  dashed histogram represents the distribution 
expected from signal events.}
\end{center}
  \label{figure 1:}
\end{figure}

\newpage
  \begin{figure}
 \begin{center}
   \mbox{\epsfig{file=direct1.eps,height=80mm,width=120mm}}
    \centering
    \caption{\em The (1 - $cos\Theta_{e^+ e^-}$) distribution  
for $\pair$ pairs from photons converted in the DC target at large distances 
from the primary vertex for the data and MC.}
\end{center}
  \label{figure 1:}
\end{figure}


  \begin{figure}
 \begin{center}
   \mbox{\epsfig{file=limit_p.eps,height=90mm,
width=120mm}}
\end{center}
%\vspace{2.cm}
    \centering
    \caption{\em  The NOMAD  90\% $CL$ upper limit, and the 
SN1987a and  Big Bang Nucleosynthesis lower limits 
 for the mixing strength 
$|U_{\tau 4}|^2$ as a function of the heavy neutrino mass.\ The SN1987a and 
BBN limits are reproduced from ref. \cite{dolgov1}. Note that  upper
limits of $|U_{\tau 4}|^2\lesssim 10^{-8}$ from SN1987a and 
$|U_{\tau 4}|^2\lesssim 10^{-10} \div 10^{-12}$ from BBN arguments have also been
derived for the corresponding mass ranges shown, respectively. 
For more details see ref. \cite{dolgov1}.}
  \label{figure 1:}
\end{figure}

\end{document}











