1. Salvatore Fiore Università di Roma “La Sapienza”
MonteCarlo studies of
Salvatore Fiore
Università di Roma “La Sapienza”
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

2. Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006
: can we see KLOE?
How is it identified by EVCL?
What kind of cuts should we apply?
What kind of efficiency and mass resolution?
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

3. Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006
The MC generator
Signal generation: Phokhara5
Original Phokhara5 has many decay modes for e+e- collisions with ISR:
generates pions, kaons, muons, nucleons and one or two ISR-FSR photons
process not included: added as a new decay mode in
stand-alone Phokara5
Phokhara5 in Geanfi
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

4. Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006
f0 - a0 model
Achasov Model:
Implemented simpler model
hp: negligible mass dependence of the kaon loop term
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

5. Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006
Stand-alone Phokhara5
Invariant mass mKK
Polar and azimuthal angles of the K0
K (rad)
K (rad)
mKK(MeV)
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

6. Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006
Stand-alone Phokhara5
P(K0) vs invariant mass mKK: distribution determined by the decay model
PK0(MeV/c)
mKK(MeV)
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

7. Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006
Stand-alone Phokhara5
Energy of the emitted photon
Polar and azimuthal angle of the photon
Warning: ISR-like angle generation!
Eg(MeV)
g (rad)
fg (rad)
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

8. Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006
Phokhara5 in Geanfi
Phokhara in Geanfi:
Same modifications as for stand-alone
plus two Ks generated instead of KsKl
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

9. Tracking and vertexing:
First generation
10000 events of with KS decaying only in π+π-
π± tracks reconstructed by Geanfi
KS mass from π± (reco) tracks
mKK invariant mass from (reco) KS
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

10. Reconstruction mistakes
Vertex reconstruction: sometimes Geanfi fails in associating π± to the correct vertex, or takes a μ± track, from πμν decay, together with a π± track
Mis-reconstruction probability: under study
Effect: wrong mass reconstruction
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

11. Signal selection: the cuts
Trigger requirement
EVCL
2 Vertices in a fiducial region
Two tracks per vertex
Invariant masses of the KS
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

12. Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006
Trigger & EVCL cut
Trigger: required second level EMC or DC
EVCL: selected events are in the KSKL stream
(Check: selecting events from ANY stream  see dashed line)
All events
Trigger OK
EVCL OK
100
94.9
64.6
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

13. Vertex position & tracks attached to vertex
y(cm)
Vertices position cut
Two vertices inside a fiducial volume of 10cm radius and ±20cm in z
All events
Trigger OK
100
EVCL OK
94.9
x(cm)
Vertices OK
z(cm)
2 tracks OK
64.6
Number of tracks:
two tracks attached to each vertex are required
51.0
50.8
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

14. “The final cut”: π+ π - invariant masses
m2(MeV)
π+π- invariant masses:
reconstructed after previous cuts
6 MeV circle cut applied around KS mass in m1 vs m2 plane
All events
m1(MeV)
Trigger OK
100
EVCL OK
94.9
Vertices OK
2 tracks OK
64.6
51,0
50,8
KS Invariant mass OK
31.1
mK(MeV)
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

15. f0 /a0 invariant mass: efficiency and resolution
MC truth before (solid) and after (dashed) the cuts
MC true – rec invariant mass
selection efficiency
DmKK(MeV)
mKK(MeV)
mKK(MeV)
s1MeV
mKK(MeV)
DmKK(MeV)
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

16. “On the warning on ISR-like photon generation “
Efficiency vs photon polar angle
g (rad)
< eSEL > =31.1%
g (rad)
Applying the cut 0.2< g <3.0  the efficiency becomes eSEL=31.2%
The selection efficiency does not depend on the photon polar angle
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

17. Conclusions A simple generator for process has been inserted in GEANFI
The selection efficiency, for KS  π+π-, is %
Therefore, with Achasov estimation of the cross section for
this process,
the number of expected events with 2fb-1 is
N(KS  π+π-, KS  π+π- , 2fb-1 = 6  20
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006

18. Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006
Work in progress
Generator:
Check the photon angle distribution
Include kaon loop matrix element
Check the invariant mass reconstruction errors
Background contamination:
First check looking at four pions final state
Then try on the events in KsKL stream
Salvatore Fiore – MC studies of K0 K0  – LNF, feb. 16, 2006