h mass measurement with the
3g final state

B. Di Micco
Università degli Studi di Roma Tre

Phi radiative Working Group Meeting

18 July 2005

The method

f ® hg

gg

E1

E2

E3

Kinematic fit constraints:

Pxtot, Pytot, Pztot, Etot

t-r/c of clusters

do the job

improve z

resolution

We have 3 energies, 6 angles and 4 constraints. The energies are over determined by the cluster angles, no matter what is the cluster energy, no matter what is the energy scale of the calorimeter.

The knowledge of the total momentum is the crucial point.

Using kinematic fit we can constraint the photon energies.

f ® p0 g

gg

Very simple selection

At least 3 prompt clusters on barrel

50° < qg < 130° |t-r/c| < min(5st ,2ns)

Kinematic fit on the photon combinations;

Inputs to the kinematic fit.

3 x clusters information x,y,z,t

f momentum from BMOM

I.P. position from BPOS

Kinematic fit output.

All the inputs.

the combination with the smallest c2 is taken.

c2 distribution

cut

2001 DATA

Huge background

Dalitz plot

The photons are sorted according the energy.

Dalitz plot

E1 < E2 < E3

p0

h

no c2 cut

c2/n.d.f < 5

p0

h

Background that doesn't close the kinematic.

gg(g)

e+ e- (g)

clean region

Selection in the dalitz to reject background.

accepted region

before cut

after cut

negligible background

DATA analyzed

1	17874-20600	03/01 – 07/01 5	24451-25350 06/02-07/02

2	20601-22200	07/01-11/01	6 25351-26050 07/02-08/02

3	22201-	23133	11/01-12/01 7	26051-26600 08/02-09/02

4	23201-24450	02/02-06/02	8 26601-27137 09/02

period	run-range time-range

2001+2002 DATA are divided in 8 periods of 50 pb-1.

Absolute scale (p0 mass)

Period 1

Double gaussian fit

with the same mean

core gaussian

p0 mass

rescaling the error by

the factor sqrt(c2)

m(p0) = 134978 ± 10 KeV

m(p0)PDG= 134976.6 ± 0.6 KeV

Absolute scale known @10 KeV

Fit result.

Single gaussian fit.

Fit to the h mass.

Mean 547.703 ± 0.018 MeV

Sigma 2.146 ± 0.012 MeV

c2/n.d.f = 0.91

Results.

The systematic is taken into account by doing the rms of all measurements .

Comparison with previous measurement.

NA48 compatibility 1.2s

PDG recomputation

PDG 2004

2004+GEM

2004+GEM+KLOE

547.75 ± 0.12 MeV

547.51 ± 0.18 MeV

547.61 ± 0.13 MeV

(includes NA48)

New situation with KLOE.

average

scale factor 5.5

Conclusions

For the prelimiary blessing (September)

Linearity response with MC toy.

Stability versus cuts choice.

For final blessing

Full simulation with 3 different values of h mass.

The KLOE calorimeter is able (alone) to do high precision measurements;

the absolute scale of the method is well checked using p0 mass;

the main systematic come from the sqrt(s) knowledge.

2005-07-13T16:07:12