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\Title{LHCb Status and Plans}

\bigskip\bigskip

%+\addtocontents{toc}{{\it D. Reggiano}}
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\begin{raggedright}  

{\it Roger Forty\footnote{On behalf of the LHCb collaboration.}\index{Forty, R.}\\
CERN\\
CH-1211 Geneva, SWITZERLAND}
\bigskip\bigskip
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\section{Introduction}

LHCb is the dedicated flavour physics experiment at the LHC. While ATLAS and CMS
search for the direct production of new states, LHCb is designed to see their
indirect effect on charm and beauty decays, via virtual production in loop
diagrams. Such an indirect approach can be very powerful: e.g.\ the discovery of
$B^0$--$\overline{B}^0$ mixing~\cite{argus} demonstrated that the top quark was
unexpectedly heavy: $m(t) > 50\, {\rm GeV/}c^2$, before it had been directly
observed.  Key topics for LHCb include the study of CP violation---is it due to
a single phase in the quark mixing (CKM) matrix, as in the Standard Model?---and
the study of rare decays: flavour-changing neutral current decays (e.g.\ $B^0_s
\rightarrow \mu^+\mu^-$) are strongly suppressed in the Standard Model, but may
be enhanced by Supersymmetry or other new physics.

Since $b$-hadron production is strongly forward-peaked at the LHC, LHCb is a
forward spectrometer covering the angular region from 10--300\,mrad from the
beam axis (but operating in collider mode), as shown in Fig.~\ref{fig1}.
The $b\overline{b}$ cross-section is large: it has been measured to be $284 \pm
53\,\mu$b at the LHC (at $\sqrt{s} = 7\,{\rm TeV})$ ~\cite{sigmabb} which results in
about 100,000 $b\overline{b}$ pairs being produced per second at LHCb ($\sim
10^4 \times$ the B factories).  Charm production is a factor $\sim 20$ higher~\cite{sigmacc}, so the
LHC is an excellent environment for the precision study of flavour physics.

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There are other advantages of flavour physics at the LHC. All $b$-hadron species
are produced at high energy, and $B^0_s$ physics is rich and little explored
until now. The enormous production rate has allowed LHCb to overtake the B
factories even for $B^0$ and $B^+$ decays.  For example, the recent measurement
BR$(B^+ \rightarrow \pi^+\mu^+\mu^-) = (2.4 \pm 0.6 \pm 0.2) \times
10^{-8}$~\cite{rarest} is the rarest $B$ decay ever observed.  The previous best
limit (from Belle) was $< 6.9 \times 10^{-8}$~\cite{belle}.  With the large
boost at LHCb $B$ decay lengths are of order 1\,cm, allowing excellent
decay-time determination. Finally, the forward pseudorapidity coverage $2 < \eta
< 5$ is complementary to the central detectors for other physics, including
electroweak, QCD, and the search for exotics.

The LHCb detector is described in Ref.~\cite{LHCb-det}.  It features a precise
silicon vertex detector (VELO) that approaches to within 8\,mm of the beams,
and a high-performance particle identification system based on RICH detectors.
The trigger of the experiment is designed to be efficient for fully hadronic
final states, as well as those containing leptons or photons, and the output data
rate to storage is a few kHz. 

\section{LHCb status}

LHCb has run successfully over the last three years, taking data with high
efficiency (greater than 90\%), and with all subdetectors working as designed.  In 2011
an integrated luminosity of 1\,fb$^{-1}$ was recorded, which has been used for a
wide variety of physics analyses, with 58 published papers to date and an even
larger number of preliminary results sent to conferences.  In 2012 the detector
continues to run well, at a luminosity that is levelled at $4\times
10^{32}$\,cm$^{-2}$s$^{-1}$.

The physics results are reviewed in many contributions to this conference, and just a few
highlights are mentioned here.  $B^0_s$--$\overline{B}^0_s$ oscillations have been measured with the
world's best precision, see Fig.~\ref{fig2}\,(a).  Radiative $B$ decays have
been studied, Fig.~\ref{fig2}\,(b), and the ratio of $B^0_s\rightarrow
\phi\gamma$ and $B^0\rightarrow K^*\gamma$ branching fractions determined, as
well as the CP asymmetry for $K^*\gamma$. For the rare decay
$B^0_s\rightarrow\mu^+\mu^-$ LHCb has set the most stringent limit on the
branching ratio, $< 4.5\times 10^{-9}$ at 95\% CL.  A few candidates are seen,
as shown in Fig.~\ref{fig2}\,(c), compatible with the Standard Model expectation, but not
enough to yield a significant observation.  The limit on the branching ratio
gives strong constraints on new physics models.  The $B^0\rightarrow
K^{*0}\mu^+\mu^-$ decay is another mode that is very sensitive to new physics,
and different angular distributions have been studied, including the
forward-backward asymmetry shown in Fig.~\ref{fig2}\,(d), for which the
zero-crossing point has been measured for the first time and found to be in
agreement with the Standard Model expectation.

\begin{figure}[t]
\centering
\includegraphics[width=0.9\columnwidth,clip=]{Fig2.eps}
\caption{\small (a) $B^0_s$ oscillations seen in the asymmetry as a function of
  decay time for the $D^-_s \pi^+$ channel. (b) Invariant mass distribution of
  $B^0_s\rightarrow\phi\gamma$. (c) Invariant mass distribution of
  $B^0_s\rightarrow\mu^+\mu^-$ candidates. (d) Forward-backward asymmetry of
  $B^0\rightarrow K^{*0}\mu^+\mu^-$ decays, as a function of $q^2$.  }
  \label{fig2}
\end{figure}

CP asymmetries have been studied in the two-body decays of $B$ hadrons to
charmless final states, as illustrated in Figs.~\ref{fig3}\,(a) and (b).  The
$\sim\,10\%$ asymmetry between the CP-conjugated $B^0\rightarrow K\pi$ decays is
clear from the raw distributions, and remains after the small corrections for
production and detector effects.  In a related analysis the first $> 3\,\sigma$
evidence has been seen for CP violation in $B^0_s$ decays.  A precise
measurement has also been made of the CP phase of $B^0_s$ mixing ($\phi_s$),
which is expected to be small in the Standard Model.  In Fig.~\ref{fig3}\,(c)
the very clean signal for $B^0_s\rightarrow J/\psi\,\phi$ decay that is used for
this study is shown, which has a mass resolution of about 8\,MeV$/c^2$.  In
Fig.~\ref{fig3}\,(d) it can be seen that the result for $\phi_s$ is compatible
with the Standard Model, and also gives the world's best measurement of the
decay width difference in the $B^0_s$ system, $\Delta\Gamma_s$.  Important steps
have been made towards the measurement of the most poorly known angle of the
Unitarity Triangle, $\gamma$, through the observation of the suppressed modes in
$B\rightarrow DK$ decays.

The above gives a taste of the results so far from LHCb, focussing on those key
measurements that had been identified before the experiment started taking
data~\cite{roadmap}.  The results have already had a strong impact on models of
physics beyond the Standard Model, as illustrated in Fig.~\ref{fig4}\,(a).  In addition
there have been many interesting results in spectroscopy, observing new excited
states of $B$ mesons and $\Lambda_b$ baryons, new decay modes such as
$B^+_c\rightarrow J/\psi\, \pi^+\pi^+\pi^-$, and studying exotic states such as
the $X$(3872).  Numerous electroweak and QCD measurements have also been
performed.  While the majority of the results have been in good agreement with
Standard Model expectations, there have been a few surprises: evidence has been seen for CP
violation in charm decays, and for an isospin asymmetry in $B\rightarrow
K\mu^+\mu^-$ decays, which require further study with more data.  Details of all
these analyses can be found in the dedicated talks from LHCb at this conference, along
with their references.

\begin{figure}[t]
\centering
\includegraphics[width=0.99\columnwidth,clip=]{Fig3.eps}
\caption{\small (a) $K^+\pi^-$ invariant mass distribution showing signals from
  two-body $B$ decays, with the largest contribution from $B^0\rightarrow
  K^+\pi^-$. (b) $K^-\pi^+$ invariant mass distribution, with the largest
  contribution from $\overline{B}^0\rightarrow K^-\pi^+$ decays. (c) Invariant
  mass distribution of $J/\psi(\mu^+\mu^-)\,\phi(K^+K^-)$ candidates. (d) Experimental 
  constraints on the decay width difference $\Delta\Gamma_s$ and CP phase
  $\phi_s$ in $b\rightarrow c\overline{c}s$ decays~\cite{HFAG}.
} \label{fig3}
\end{figure}

\section{Plans}

By the end of the extended 2012 run, LHCb expects to have tripled its data
sample, ready for detailed analysis during the first long shutdown of the LHC
over 2013--14.  In
2015 we expect to run at 13\,TeV which will give significantly higher production
cross-sections for heavy flavours (increasing roughly linearly with
centre-of-mass energy).  In the period 2015--17 we expect to further double the
integrated luminosity, to a total of around 5--7$\rm\, fb^{-1}$.  At this point
the data-doubling time would become excessive, so it is planned to upgrade the
experiment to run at higher luminosity.

The present detector could run at luminosities $\sim\,10^{33}~\rm cm^{-2}s^{-1}$
once the machine reaches its nominal number of bunches, corresponding to 25\,ns
spacing.  However, it is currently limited to a read-out rate of 1\,MHz.  To
trigger at an increased event rate requires a substantial change in the LHCb
read-out architecture.  The present first level trigger is implemented in
hardware~\cite{LHCb-det}.  Trigger selections are made at the 40~MHz beam
crossing rate using either the calorimeters or the Muon system. Criteria are
based on the deposit of several GeV of transverse energy, $E_{\rm T}$, by
charged hadrons, muons, electrons or photons. While this provides high
efficiencies on dimuon events, it typically removes half of the fully hadronic
signal decays. In these hadronic decays the $E_{\rm T}$ threshold required to
reduce the rate of triggered events to an acceptable level is already a
significant fraction of the $B$ meson mass. Any further increase in the rate
requires an increase of this threshold, which then removes a substantial
fraction of signal decays. The trigger yield therefore saturates for hadronic
channels with increasing luminosity, as shown in Fig.~\ref{fig4}\,(b).

\begin{figure}[t]
\vspace*{-2cm}
\centering
\hspace*{-3.5cm}\includegraphics[width=1.2\columnwidth,clip=]{Fig4.eps}
\vspace*{-4.5cm}
\caption{\small (a) Parameter space of various models for physics beyond the Standard Model,
  in the plane of BR$(B^0_s\rightarrow\mu^+\mu^-)$ {\em vs.}~the $B^0_s$ mixing phase
  $S_{\psi\phi} = \phi_s$, taken from \cite{straub}; the Standard Model point is shown with
  a star, and the constraints from LHCb are shown by the dashed
  box. (b)~Trigger yield for different $B$ decays 
  normalized to the trigger yield expected in nominal conditions at a luminosity
  of $2\times 10^{32}\rm~ cm^{-2}s^{-1}$; the hadronic yields saturate, while
  the muon triggers continue to gain with increased luminosity.  
} \label{fig4}
\end{figure}

The most effective way of upgrading the trigger is to supply the full event
information, including whether tracks originate from the displaced vertex that
is characteristic of heavy flavour decays, at each level of the trigger. This
requires reading out the whole detector at 40\,MHz and then analysing each event
in a trigger system implemented in software.  A bigger CPU farm, more disk
storage and more computing power will be needed to swallow a factor 5--10 more
events at the output of the software trigger.  The upgraded detector will be
able to collect at least 5\,fb$^{-1}$ per year, for a total of 50\,fb$^{-1}$
over lifetime of the upgrade.  The annual signal yields will be higher by a
factor of around ten for muonic $B$~decays and twenty or more for heavy-flavour
decays to hadronic final states, compared to those obtained by LHCb in 2011.

The detailed physics case for the LHCb upgrade was presented in
Ref.~\cite{bib:LOI}. Following endorsement of the physics case by the LHCC, the
experiment was encouraged to prepare Technical Design Reports (TDRs), and a
Framework TDR has been submitted in May 2012~\cite{FTDR} giving an overview of
the schedule, cost and participating institutes. After the current period of
R\&D it is planned to submit TDRs for the subsystems next year, to be ready for
installation of the upgraded detector during the second long shutdown of the LHC in
2018. An exciting future lies ahead for the experiment, searching for signs of
physics beyond the Standard Model in the flavour sector and beyond.

\begin{thebibliography}{99}

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\bibitem{argus} ARGUS collaboration, Phys.\ Lett.\ {\bf B 192} 245.
\bibitem{sigmabb} LHCb collaboration, Phys.\ Lett.\ {\bf B 694} 209.
\bibitem{sigmacc} LHCb collaboration, LHCb-CONF-2010-013.
\bibitem{rarest} LHCb collaboration, LHCb-CONF-2012-006.
\bibitem{belle} LHCb collaboration, Phys.\ Rev. {\bf D 78} 011101.

\bibitem{LHCb-det} LHCb collaboration, JINST {\bf 3} S08005.

\bibitem{HFAG} Heavy Flavour Averaging Group, [arXiv:1207.1158], 
updated results available at {\tt http://www.slac.stanford.edu/xorg/hfag/}.

\bibitem{roadmap} LHCb collaboration, [arXiv:0912.4179].

\bibitem{straub} D.\ Straub, [arXiv:1107.0266].
\bibitem{bib:LOI} LHCb collaboration, CERN-LHCC-2011-001, March 2011.

\bibitem{FTDR} LHCb collaboration, CERN-LHCC-2012-007, May 2012.

\end{thebibliography}

\end{document}

