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MyDstarAnalysis

Table 8: MyDstarAnalysis module parmaeters.

Module parameter	Description	Default value
vtxFitAlgo	name of vertexer	GeoKin
vtxFitMode	mode of vertexer	Standard
eventInfoList	EventInfoList key	Default
pionList	input list key for pion from decay	GoodTracksLoose
kaonList	input list key for kaon from decay	GoodTracksLoose
slowPionList	input list key for slow pion from decay	ChargedTracks
DstarCandList	list key for selected	ChargedTracks
slowPiMomLo	minimum for slow pion, in GeV/$c$	$0.05$
slowPiMomHi	maximum for slow pion, in GeV/$c$	$1.0$
slowPiRdocaMax	maximum doca of slow pion track before fit, in cm	$0.2$
slowPiZdocaMax	maximum $\vert\hbox{poca}_Z$ of slow pion track before fit, in cm	$3.0$
slowPiSvtHit	minimum number of SVT hits on slow pion track	$6$
slowPiDchHit	minimum number of DCH hits on slow pion track	$6$
d0MassCutLo, d0MassCutHi	limits on $K\pi$ invariant mass after vertexing daughters, in GeV/$c^2$	$1.7745$, $1.9745$
deltaMassCutLo, deltaMassCutHi	limits on after vertexing, in GeV/$c^2$	$0.143$, $0.148$
pStarCut	center of mass momentum minimum value, GeV/$c$	$2.2$
ntupleName	name of ntuple	MyDstar

Run in cache mode by default, this example illustrates how to select and vertex events of the type

$$D^{*+}\rightarrow D^0\pi^+, D^0\rightarrow K^-\pi^+ + c.c.$$ (1)

This example uses the TreeFitter vertexing algorithm to vertex the $D^0$ and $D^{*+}$. The other available vertexing algorithms are found in VtxBase/VtxAbsAlgorithm.hh. The default selection criteria are listed below.

• slow pion selection criteria:
  • pion from ChargedTracks list;
  • transverse laboratory momentum : $0.05 \le\ensuremath{p_t}< 1.0$ GeV/$c$;
  • $\ge 6$ Svt hits;
  • $\ge 6$ Dch hits;
  • Point of closest approach (poca) distance to the $z$ axis $\le 0.2$ cm;
  • $\vert\hbox{poca}_Z\vert\le 3$ cm;
• $D^0$ selection criteria:
  • kaon and pion from GoodTracksLoose list;
  • oppositely charged kaon and pion candidates fit to a common vertex using TreeFitter algorithm;
  • $D^0$ invariant mass $m_{D^0}$ after vertexing $1.7745 \le m_{D^0}< 1.9945$ GeV/$c^2$
• $D^{*+}$ selection criteria:
  • slow pion and $D^0$ fit to a common vertex using TreeFitter algorithm, and imposing a beam constraint on the vertex position to improve the slow pion trajectory
  • $\ensuremath{\Delta m}\equiv m_{D^{*+}}-m_{D^0}$: $0.143 \le \ensuremath{\Delta m}< 0.148$ GeV/$c^2$;
  • $D^{*+}$ center of mass momentum $\ensuremath{p^*}> 2.2$ GeV/$c$.

Details about the selection procedure can be found in BetaMiniUser/MyDstarAnalysis.cc. Table 9 lists the TCL- and module parmaeters needed to configure MyDstarAnalysis example.

Table 9: Snippet file myDstarMiniAnalysisJob.tcl

set BetaMiniReadPersistence "Kan"
set levelOfDetail "cache"
set ConfigPatch "MC"
set BetaMiniTuple "hbook"
set histFileName "MyDstarMiniAnalysis.hbk"
set NEvent 2000

## specify collections here
##
source ccbar_Dstar+_D0pi_D0Kpi.tcl

## specify job-dependent module parameters here
##
module talk MyDstarAnalysis
    vtxFitAlgo set TreeFitter	
exit

sourceFoundFile BetaMiniUser/MyDstarMiniAnalysis.tcl

To run the MyDstarAnalysis example, paste the TCL snippet in Table 9 into workdir/myDstarMiniAnalysisJob.tcl, replace the file ccbar_Dstar+_D0pi_D0Kpi.tcl with your list of collections, set the TCL- and module parameters, then type the command

        BetaMiniApp myDstarMiniAnalysisJob.tcl

This command will produce a histogram file in paw format. The histograms produced by this module will appear in the MYDSTARANALYSIS subdirectory of the histogram file.

Figure 2: Left figure: $D^{*+}-D^0$ delta mass distributions before and right figure: after performing a beam constrained fit to the $D^{*+}$ vertex. A probability density function to model the signal and background is fitted to the data and is decribed in the text.

From a sample of 2000 signal Monte Carlo events generated in release 14.4.0c corresponding to decay 1, the $D^{*+}-D^0$ delta mass distribtions obtained before and after the beam-constrained $D^{*+}$ vertex fit are displayed in the left- and right plots, respectively, of Figure 2. Each distribution is fitted with a double Gaussian to model the signal, and a quadratic polynomial to describe the combinatorial background. As can be seen from the width parameter P6 of the primary Gaussian, the width of the delta mass distribtion decreases by about a factor of two after constraining the $D^{*+}$ vertex to originate from the beam spot.