Post on 31-Jan-2016
description
Studies of the Branching Ratio for ηµ+µ- decay
Frascati, Phi Decay Meeting 5.02.2008 Jarosław Zdebik
PLAN
1. Physics motivation, previous experiments and results.
2. Simulation studies for the signal and background with Geanfi.
Physic motivation
1. The dilepton pair production decays can serve to study the structure of decaying hadrons (Form Factor shape)
2. These decays gives a chance to study the physics beyond the Standard Model (searching a candidate for the dark matter particle)
3. Recent BR value measured by SATURNE is equal to 1.3±0.2 (~20% ,~100 events) times the unitarity bound (4.3*10-6) [calculated with VDM]
4. Rare decay - BR= 5.8 * 10-6
Previous measurements of the BR(ηµ+µ- )
1968 – BROOKHAVEN
upper bound for ..%901020 6 LC
1969 – CERN The first observation of this decay.
anythingnp
B
610923
1980 (published) – SERPUKHOV [Institute for High Energy Physics, USSR]
6101.25.6 BMeasured result is:
Phys. Rev. Lett. V70, N7
Phys. Lett. B V. 97, Pages 471-472
np 27±8 events
ηµ+µ-
Previous measurements of the BR(ηµ+µ- ) (2)
66.07.0 10.5.0.6.5
syststatB
1993 (published) - SATURNE
Measured 100 events of and 8 events of background
1994 (published) – SATURNE IIPhys. Rev. D 50, 92-103
Measured 114 events of and 14 events of background
67.07.0 10.5.0.7.5
syststatB
3Hepd
3Hepd
How many events for we expect?
KLOE data = 100 000 000 η mesons (L=2.5 fb-1)
BR(ηµ+µ-) = 5.8 * 10-6 PDG(2008)
If reconstruction efficiency=100%
Number of reactions = 100 000 000 * 5.8 * 10-6 = 580 events (reactions) (5 x Saturne events)
Need to perform efficiency studies in order to estimate how many events we should see.
Very important background rejection (especially from e+e-u+u-)
The value in PDG 2008, Was calculated as the
average forSerpukhov and Saturne II
results
SERPUKHOV [Institute for High Energy
Physics, USSR] near Moscov
CEA at Saclay, near Paris, SATURNE synchrotron
Reaction mechanism
η
l+
l-
γ*
γ*
Dominant mechanism within the Standard Model: second order electromagnetic process,
F(q12,q2
2)arXiv:0711.3531v3
F(q12,q2
2)
C parity: +1 -1
η γ
Expected background channels for
ϕ ηγ 1.304% ηµ+µ- 5.8 *10-
6 e+e-µ+µ-γ e+e-µ+µ- e+e- ??
e+e-e+e- e+e- γ ??e+e-π+π-γ e+e-π+π- π0 π+π-γ γ e+e- e+e-γ ??
phi decays:
collision:
eta decays: ηπ+π- π0π+π-γ γ 22.73%
ηπ+π-γ 4.6% ηe+e-γ 6.8
*10-3ηµ+µ-γ 3.1 *10-4
η π+π- 1.3 *10-5
ϕe+e- 2.97 *10-4 ??ϕµ+µ- 2.86 *10-4
ϕ π+π- 7.3 *10-5
Signature of signal:One neutral cluster in calorimeter,
Two charged tracks in Drift Chamber
ϕ π+π- γ 4.1 *10-5
ϕµ+µ- γ 1.4 *10-5
Simulations
Signal:simulated with the standard GEANFI package,
(stand alone simulation)
Background :
GEANFI + phokara generator
Reconstruction and production prod2ntu.hbook was performed
using standard kloe „datarec.exe” program
(e+e-µ+µ-γ)
Geanfi studies [NTMC - KINE]
Cut:541.0 < Inv mass µ+µ- < 554.0
50 000 events
ηµ+µ-e+e-µ+µ-γ
ηµ+µ-
e+e-µ+µ-γ
GeanFi studies [NTV – tracks connected with vertex]
50 000 eventsCut:
541.0 < Inv mass µ+µ- < 554.0 eV
σ(e+e-µ+µ-γ) ~ 30.7 [nb]
σ(e+e- ϕ η γ µ+µ- γ) ~ 3.1 *10-6 * 1.304 *10-2 * 5.8 *10-6
= 2.3 *10-4 [nb]
Ratio S/B~10-5 before any cut.
Background from e+e-µ+µ-γ
Inv mass studies – kine MC
B/S ~ 62.5Cut:541.0 < Inv mass < 554.0
Inv mass studies – ReconTracks connected with vertex – DC signal
Cut:541.0 < Inv mass < 554.0
B/S ~ 300
Angular distributions for muons+
Angular distributions for photon
Statistic: 50000events
How we reconstructed „gamma quanta” (neutral) cluster ?
1. Extracted neutral cluster using TRACK to CLUSTER association BANK
2. Time window condition:
2
2
222
14.01000
057.05_
__
CLU
LIGHT
CLUCLU
CLUCLUCLUCLU
Ewindowtime
c
RTclutimedelta
BpzZBpyYBpxXR
If(time_window > 2.0) smaller_window = 2.0If(time_window < 2.0) smaller_window = time_window
if(delta_time_clu < smaller_window) calculate:
180arccos
MODUL
Z
CLU
CLUCLUi
p
p
R
XEp
Energy distributions for photon
Strongly correlated with the invariant mass for eta
statistic Inv mass µ+ µ-Cut: 541<inv<554
2 measured tracks
1 neutral cluster
1 neutral cluster
ECLU> 250 MeVKINE RECO
N
signal 50 000 50 000 38 401
44 225 45 847 44 276
background
50 000 357 319 41 324 43 424 6 767
Cuts efficiency studies
Conclusions and futher steps
-- perform efficiency studies in the respect to estimate a realistic number of reactions
-- good cut: invariant mass of the muons (541 < Inv mass < 554)-- additional background recjection should be given by: optimizing invariant mass of the muon (m =5 MeV)and angular cuts-- perform /mu separation
Thanks for attention
BACKUP SLIDES
TRACKS to VERTEX reconstruction
LOOP of tracks connected to the vertex, „vv”
LOOP of all reconstructed tracks, „tt”
If(trkind[tt]==trknumv[vv])
If(trtype1 == 5 mion+)If(trtype1 == 6 mion-)
Why we need this BR ?
The real part of the amplitude of ηe+e- decay can be estimated using the measured value of BR(ηµ+µ-), etc.
arXiv:0711.3531v3
Dark matter – cluster bullet
Evidence for existing Dark Matter in Universe.
Galactic gas (red color),Dark matter (blue color). Year: 2006
Analysis goals
Present measurement:16% precision on the BR
etamu+mu-
Goal of the analysis:Measurement of the BR at 8%
precision level or better.
Enhancement on respect the predicted value of 5.11 ± 0.20 is expected from the
KTevresult on
ee0
Inv mass studies – kine MC
62.5 times higher background than signal
Cut:541.0 < Inv mass < 554.0
250 times higher background than signal
Cut:541.0 < Inv mass < 554.0
Inv mass studies – ntv MCTracks connected with vertex – DC signal
Unitarity bound
Electromagnetic decays of light mesonsInstitute for High Energy Physics, Serpukhov, U.S.S.R
Physics Reports 128. No. 6 (1985) 301-376
2
22
2/12
2222
1
1ln
4
1
41
:
2
Y
m
m
where
YXPBRallP
llPllPBR
P
l
for unitarity bound:
Y and X are the imaginary (absorptive) and real (dispersive) components, respectively,of the normalized dimensionless amplitude
in Pl+l- decay
BR(ηµ+µ-)unit.= BR(ηγγ)*1.07*10-5=4.3*10-6