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Studies of the Branching Ratio for ηµ+µ- decay
Frascati, Phi Decay Meeting 5.02.2008 Jarosław Zdebik
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PLAN
1. Physics motivation, previous experiments and results.
2. Simulation studies for the signal and background with Geanfi.
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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
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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-
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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
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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-)
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The value in PDG 2008, Was calculated as the
average forSerpukhov and Saturne II
results
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SERPUKHOV [Institute for High Energy
Physics, USSR] near Moscov
CEA at Saclay, near Paris, SATURNE synchrotron
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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
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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
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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)
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Geanfi studies [NTMC - KINE]
Cut:541.0 < Inv mass µ+µ- < 554.0
50 000 events
ηµ+µ-e+e-µ+µ-γ
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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
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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
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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
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Angular distributions for muons+
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Angular distributions for photon
Statistic: 50000events
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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
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Energy distributions for photon
Strongly correlated with the invariant mass for eta
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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
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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
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Thanks for attention
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BACKUP SLIDES
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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-)
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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
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Dark matter – cluster bullet
Evidence for existing Dark Matter in Universe.
Galactic gas (red color),Dark matter (blue color). Year: 2006
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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
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Inv mass studies – kine MC
62.5 times higher background than signal
Cut:541.0 < Inv mass < 554.0
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250 times higher background than signal
Cut:541.0 < Inv mass < 554.0
Inv mass studies – ntv MCTracks connected with vertex – DC signal
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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