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MyK0Analysis

Table 10: MyK0Analysis module parmaeters.

Module parameter	Description	Default value
vtxFitAlgo	name of vertexer	GeoKin
vtxFitMode	mode of vertexer	Standard
eventInfoList	EventInfoList key	Default
andCC	if true, select final state and charge conjugate	true
veeList1	input list key for vee daughter 1	GoodTracksLoose
veeList2	input list key for vee daughter 2	GoodTracksLoose
veeListName	list key for selected vees	MyVeeList
beamConstraint	if true, constrain the vee to originate from the beam spot	false
veeMassCutLo, veeMassCutHi	limits on vee invariant mass after vertexing, in GeV/$c^2$	$0.45$, $0.55$
veeDecayProbCut	minimum value of vee vertex chisquared probability	$0.01$
veePathCutLo, veePathCutHi	limits on vee decay minus production vertex position projected along momentum direction, in cm	$1.0$, $60.0$
ntupleName	name of ntuple	MyK0

This example illustrates how to select two body decays

$$A \rightarrow B + C$$ (2)

and by default, the complex conjugate decay as well. The resulting vee candidates are written to a list which is stored in the event. A simple ntuple is also written. The analysis module may be cloned, which means that an analysis chain can be created to study sequential two-body decays as well (the output lists from two clones can be input to a third clone).

Table: myK0MiniAnalysisJob.tcl snippet.

set levelOfDetail cache
set ConfigPatch "MC"
set BetaMiniTuple "hbook"
set histFileName "MyK0MiniAnalysis.hbook"
set NEvent 1000

## configure analysis module
##
module talk MyK0Analysis
    andCC set false
    beamConstraint set false
exit

## specify input collections
##
source SP-B0B0bar-Run4.tcl

sourceFoundFile BetaMiniUser/MyK0MiniAnalysis.tcl

There is no attempt in this example to adjudicate multiple vee combinations per event: multiple vee BtaCandidates within an event may share daughters. While the daughter tracks within a vee do not overlap (by construction), there is no check that the granddaughters (or descendents) within a vee do not overlap. By default, the decay $K_s^0\rightarrow \pi^+\pi^-$ is selected. The module parameters and their default values are listed in Table 10. The TCL configuration parameters are listed in Table 11. The default selection criteria are listed below.

• $\pi^+$ and $\pi^-$ from ChargedTracks list accessed in cache mode;
• $\pi^+$ and $\pi^-$ fit to a common vertex using GeoKin.
• $\pi ^+\pi ^-$ invariant mass $m$ after vertexing $0.45 \le m < 0.55$ GeV/$c^2$;
• chisquare fit probability $P(\chi^2)>1\%$;
• signed flight length sfl along momentum vector $1.0 \le {\tt\penalty0 sfl} < 60$ cm;

Details about the selection procedure can be found in the source code, MyK0Analysis.cc.

To run this example, paste the TCL snippet in Table 11 into workdir/myK0MiniAnalysisJob.tcl, add the desired input collections and tailor the TCL- and module parameters as required. Then type the command

        BetaMiniApp myK0MiniAnalysisJob.tcl

This command will produce a simple paw ntuple ($\hbox{id}=666$), containing the variables listed in Table 12.

Table 12: TCL MyK0Analysis ntuple columns.

TCL column	definition
run	run number
evt	event number
combination	combination within event
chisq	vertexing chisquare
ndf	vertexing degrees of freedom
probab	chisquared fit probability
mass	fitted vee invariant mass
momentum	fitted vee momentum
sfl	signed flight length along momentum vector
fltcos	cosine of angle between flight path and momentum vector
properTime	proper time computed using nominal vee mass
coshel	cosine of vee daughter 1 helicity angle

Figure 3: (left:) $\pi ^+\pi ^-$ invariant mass distribution for events from an SP6 Monte Carlo dataset of generic $B^0\overline {B^0}$ events satisfying the selection criteria described in the text and (right:) proper time distribution for events with $0.49 \le \ensuremath {m_{\ensuremath {K_s^0}}}< 0.51$ GeV/$c^2$.

Figure 3 (left) shows the $\pi ^+\pi ^-$ invariant mass distribution for combinations satisfying the selection criteria listed above. This distribution is fitted with a single Gaussian and quadratic polynomial PDF as shown by the solid curve. For $\pi ^+\pi ^-$ invariant masses satisfying $0.49 \le \ensuremath{m_{\pi^+\pi^-}}< 0.51$ GeV/$c^2$, the proper time distribution is shown in the right-hand plot of Figure 3. The mean of this distribution is consistent with the world average lifetime of the , $(89.34\pm0.08)$ psec.