studies of the branching ratio for η µ + µ - decay

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