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rnn_bachelor_thesis / Report / New Version / detector.tex
  1. \section{Detector and simulation}
  2. \label{sec:Detector}
  3.  
  4.  
  5.  
  6.  
  7. The \lhcb detector~\cite{Alves:2008zz,LHCb-DP-2014-002} is a single-arm forward
  8. spectrometer covering the \mbox{pseudorapidity} range $2<\eta <5$,
  9. designed for the study of particles containing \bquark or \cquark
  10. quarks. The detector includes a high-precision tracking system
  11. consisting of a silicon-strip vertex detector surrounding the $pp$
  12. interaction region~\cite{LHCb-DP-2014-001}\verb!*!, a large-area silicon-strip detector located
  13. upstream of a dipole magnet with a bending power of about
  14. $4{\mathrm{\,Tm}}$, and three stations of silicon-strip detectors and straw
  15. drift tubes~\cite{LHCb-DP-2013-003}\verb!*! placed downstream of the magnet.
  16. The tracking system provides a measurement of momentum, \ptot, of charged particles with
  17. a relative uncertainty that varies from 0.5\% at low momentum to 1.0\% at 200\gevc.
  18. The minimum distance of a track to a primary vertex (PV), the impact parameter (IP),
  19. is measured with a resolution of $(15+29/\pt)\mum$,
  20. where \pt is the component of the momentum transverse to the beam, in\,\gevc.
  21. Different types of charged hadrons are distinguished using information
  22. from two ring-imaging Cherenkov detectors~\cite{LHCb-DP-2012-003}\verb!*!.
  23. Photons, electrons and hadrons are identified by a calorimeter system consisting of
  24. scintillating-pad and preshower detectors, an electromagnetic
  25. calorimeter and a hadronic calorimeter. Muons are identified by a
  26. system composed of alternating layers of iron and multiwire
  27. proportional chambers~\cite{LHCb-DP-2012-002}\verb!*!.
  28. The online event selection is performed by a trigger~\cite{LHCb-DP-2012-004}\verb!*!,
  29. which consists of a hardware stage, based on information from the calorimeter and muon
  30. systems, followed by a software stage, which applies a full event
  31. reconstruction.
  32.  
  33. A more detailed description of the 'full event reconstruction' could be:
  34. \begin{itemize}
  35. \item
  36. The trigger~\cite{LHCb-DP-2012-004}\verb!*! consists of a
  37. hardware stage, based on information from the calorimeter and muon
  38. systems, followed by a software stage, in which all charged particles
  39. with $\pt>500\,(300)\mev$ are reconstructed for 2011\,(2012) data.
  40. For triggers that require neutral particles,
  41. energy deposits in the electromagnetic calorimeter are
  42. analysed to reconstruct \piz and $\gamma$ candidates.
  43. \end{itemize}
  44.  
  45. The trigger description has to be specific for the analysis in
  46. question. In general, you should not attempt to describe the full
  47. trigger system. Below are a few variations that inspiration can be
  48. taken from. First from a hadronic analysis, and second from an
  49. analysis with muons in the final state. In case you have to look
  50. up specifics of a certain trigger, a detailed description of the trigger
  51. conditions for Run 1 is available in Ref.~\cite{LHCb-PUB-2014-046}.
  52. {\bf Never cite this note in a PAPER or CONF-note.}
  53.  
  54.  
  55. \begin{itemize}
  56. \item At the hardware trigger stage, events are required to have a muon with high \pt or a
  57. hadron, photon or electron with high transverse energy in the calorimeters. For hadrons,
  58. the transverse energy threshold is 3.5\gev.
  59. The software trigger requires a two-, three- or four-track
  60. secondary vertex with a significant displacement from any primary
  61. $pp$ interaction vertex. At least one charged particle
  62. must have a transverse momentum $\pt > 1.6\gevc$ and be
  63. inconsistent with originating from a PV.
  64. A multivariate algorithm~\cite{BBDT} is used for
  65. the identification of secondary vertices consistent with the decay
  66. of a \bquark hadron.
  67. %\item The software trigger requires a two-, three- or four-track
  68. % secondary vertex with a large sum of the transverse momentum, \pt, of
  69. % the tracks and a significant displacement from the primary $pp$
  70. % interaction vertices~(PVs). At least one track should have $\pt >
  71. % 1.7\gevc$ and \chisqip with respect to any
  72. % primary interaction greater than 16, where \chisqip is defined as the
  73. % difference in \chisq of a given PV reconstructed with and
  74. % without the considered track.\footnote{If this sentence is used to define \chisqip
  75. % for a composite particle instead of for a single track, replace ``track'' by ``particle'' or ``candidate''}
  76. % A multivariate algorithm~\cite{BBDT} is used for
  77. % the identification of secondary vertices consistent with the decay
  78. % of a \bquark hadron.
  79. \item The $\decay{\Bd}{\Kstarz\mumu}$ signal candidates are first required
  80. to pass the hardware trigger, which selects events containing at least
  81. one muon with transverse momentum $\pt>1.48\gevc$ in the 7\tev data or
  82. $\pt>1.76\gevc$ in the 8\tev data. In the subsequent software
  83. trigger, at least one of the final-state particles is required to
  84. have $\pt>1.7\gevc$ in the 7\tev data or $\pt>1.6\gevc$ in the 8\tev
  85. data, unless the particle is identified as a muon in which case
  86. $\pt>1.0\gevc$ is required. The final-state particles that
  87. satisfy these transverse momentum criteria are also required
  88. to have an impact parameter larger than $100\mum$ with respect
  89. to all PVs in the event. Finally, the tracks of two or more of
  90. the final-state particles are required to form a vertex that is
  91. significantly displaced from the PVs."
  92.  
  93. % Candidate events are first required to pass the hardware trigger,
  94. % which selects muons with a transverse momentum $\pt>1.48\gevc$
  95. % in the 7\tev data or $\pt>1.76\gevc$ in the 8\tev data.
  96. % In the subsequent software trigger, at least
  97. % one of the final-state particles is required to have both
  98. % $\pt>0.8\gevc$ and impact parameter larger than $100\mum$ with respect to all
  99. % of the primary $pp$ interaction vertices~(PVs) in the
  100. % event. Finally, the tracks of two or more of the final-state
  101. % particles are required to form a vertex that is significantly
  102. % displaced from the PVs.
  103. \end{itemize}
  104.  
  105.