TextEvolution: susyjets.tex

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%\preprint{TSL/ISV-2004-0282\\
%September 2004}

\title{Effects of jet matching in production of new heavy particles at
the LHC}
\date{\today}
\author{Johan Alwall\footnote{Research supported by the Swedish Research Council}\\ 
Stanford Linear Accelerator Center, 2575 Sand Hill Rd, Menlo Park,
CA 94025, USA\\
E-mail: \email{awall@slac.stanford.edu}}
\author{Simon de Visscher\\
Universit\'e de Louvain\\
E-mail: \email{simon.devisscher@ulouvain.be}}
\author{Fabio Maltoni\\
Universit\'e de Louvain\\
E-mail: \email{fabio.maltoni@ulouvain.be}}

%\abstract{ 
%
%}


%\keywords{Supersymmetry, Beyond the Standard Model, LHC, QCD, jet matching}


\begin{document}
%%%%%%%%%%%%%%%%%%%%%%%
\section{Introduction}
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Many models for physics beyond the Standard Model, notably
Supersymmetry, Little Higgs models, many models for extra dimensions
and many versions of technicolor models, contain new strongly
interacting particles with masses below or near the TeV scale. Such
particles, if they exist, will be copiously produced at the LHC, and
will be the first and most important sign of new physics. By analyzing
the production and decay of these particles, we might already in the
first few years of the LHC be able to determine many properties of the
new physics present in nature, including parts of the particle
spectrum, spin structure and the existance of new stable particles.

One additional difficulty in the simulation of production of heavy
particles at hadron colliders is the presence of additional QCD
radiation. This radiation, which is even more important in the
production of strongly interacting particles than for color neutral
particles, affects the event kinematics by giving transverse boosts to
the produced particle system. It also produces additional jets besides
the jets originating from the decay of the heavy particles. 

Additional jet production has traditionally been simulated using
parton shower Monte Carlo programs such as \pythia\ and \herwig, which
describe parton radiation as successive parton emissions using the
soft and collinear limit. This description is formally correct only in
the limit of soft and collinear emissions, but has been shown to give
a good description of much data also relatively far away from this
limit. However, for the production of hard and widely separated extra
jets, this description breaks down due to the lack of subleading terms
and interference. For that case, it is necessary to use the full
matrix element for the heavy particle production plus additional
jets. 

The matrix element description diverges
as jets become soft or collinear, while the parton shower description
breaks down when jets become hard and widely separated. In order to
describe both these areas in phase space, these two desriptions must
be combined, without double counting between different jet
multiplicities. An additional requirement is that this procedure gives
smooth distributions, and interpolates between the parton shower
description in the soft and collinear limits and the matrix element
description in the limit of hard and widely separated jets. Several
such procedures have been produced, including the CKKW, L\"onnblad and
Mangano schemes. These different procedures seem to all give
consistent results (see comparison).

For Standard Model processes, in particular the production of
weak vector bosons and top quark pairs plus additional jets, such
matching has been used extensively since several years.

In this paper we will argue that there are many situations in which it
is necessary to use jet matching also for the production of new heavy
particles, in order to get a sufficiently precise description. We will
study the impact of additional jet radiation on the kinematical
distributions traditionally used to determine mass scales of the new
physics, as well as extract the ...


Wishlist: Effect of additional radiation on
\begin{itemize}
\item
Variation of effect depending on masses of strong particles
\item
Variation of effect depending on type of strong particles ($\tilde
g\tilde g$, $\tilde q-\tilde q$, $\tilde q-\tilde q*$, $\tilde q-\tilde g$
\item
Variation of effect depending on masses of decay products (including
the degenerate limit)
\item
Possibility to make one tune of Pythia to describe all particle masses
\item 
$H_T$, $m_{T2}$
\item
Edges and endpoints (for mass determination)
\item
Possibility for radiation to mimic strongly decaying particles
(gluinos \gives squarks, squarks \gives gluinos)
\end{itemize}


\section{Jet matching methods}

\section{Extra jet radiation in different scenarios}

\section{Effects on inclusive observables}

\section{Mimicking of decays by extra jets}

\section{Conclusions}

\end{document}