Progress on F with the KLOE

experiment (untagged)

Federico NguyenFederico NguyenUniversità Roma TRE

February 27February 27thth 2006 2006

Federico Nguyen

27-02-2006

Outline

Present situation

Selection criteria: the “small angle” analysis

Particle discrimination

Preliminary estimates of the background

processes

Conclusions

Federico Nguyen

27-02-2006

Available KLOE data sets

in 2001, the veto of cosmic events

(hardware) caused nonnegligible

inefficiency in events and made

the measurement of events not

feasible, from 2002 on, this effect is

taken out

Federico Nguyen

27-02-2006

KLOE: performances for the analysis

Electromagnetic Calorimeter

Pb / Scintillating Fibres

Endcap + Barrel = 98% (4)

Drift Chamber

4 m , 3.3 m length

90% He, 10% i-C4H10

the whole structure is surroundedby a superconducting coil B=0.52 T

the whole structure is surroundedby a superconducting coil B=0.52 T

p/p = 0.4% ( 45°)

r = 150 m , z = 2 mm

vtx ~ 3 mm, M ~ 1 MeV

eeee e eee

E/E = 5.4%/E(GeV)

Federico Nguyen

27-02-2006

Fiducial volume

)pp(pp miss

no photon tagging:

high statistics for ISR (~ ) low relative FSR contribution suppressed wrt the signal the threshold region is not covered

high statistics for ISR (~ ) low relative FSR contribution suppressed wrt the signal the threshold region is not covered

a) 1 and only 1 vertex ( |z| 7 cm )

connected to 2 tracks

b) each track with 50o < track < 130o

c) small angle ( )

Federico Nguyen

27-02-2006

Benefits of the selected region

MM22 (GeV (GeV22))

[%]

[%]

KLOE result (140 pbKLOE result (140 pb-1-1 of 2001) : of 2001) :

Phys. Lett., B606 (2005) 12 Phys. Lett., B606 (2005) 12 KLOE result (140 pbKLOE result (140 pb-1-1 of 2001) : of 2001) :

Phys. Lett., B606 (2005) 12 Phys. Lett., B606 (2005) 12

)pp(pp missπ0

in the selected region LO-FSR, and yields are

small, from which the published result is based on:

FSR-LO / QED /

Federico Nguyen

27-02-2006

Normalization to events

benefits from normalizing to events,

in the limit of neglecting FSR effects:

′′′′

′′

)(/

/)( s

sdd

sdds Born

obs

obsBorn

Luminosity: 0.5%Luminosity: 0.5%theory theory 0.3% 0.3%exp., Bhabhaexp., Bhabha

most of the theoretical systematic effects cancel out

Federico Nguyen

27-02-2006

Statistical error

M2 = 0.01

GeV2

L = 240 pb-1 , = 50% flat in s′, in both channels

contrary to the luminosity

normalization, statistics is

an issue, however it is a

good cross check of the

region intriguing because of

the difference with data

estimate performedwith PHOKHARA-4

H. Czyż et al.,H. Czyż et al.,

Eur.Phys.J.C39 (2005) 411Eur.Phys.J.C39 (2005) 411

Federico Nguyen

27-02-2006

Discrimination vs. e: time and energy

time of flight: for low p values e ~ 1electrons deposit mostly in

the first plane and negligible amount in the rest

pions deposit ~ 40 MeV in each

plane

/e separation is performed using a particle ID function based on time and quantity and shape of the energy released in the calorimeter

Federico Nguyen

27-02-2006

Improvements wrt the published result

mmiss, defined by the 4-

momentum conservation under

the

hypothesis of e+eX

improved selectionimproved selection

• enlarged mtrk acceptance, from 90

MeV to 80 MeV

• only 1/1000 of events with mmiss >

120 MeV

• more efficient reconstruction filter:

from 95% to 98.5%

2X

2Xmiss pEm

mtrk, defined by 4-momentum

conservation under the hypothesis

of 2 equal mass tracks and a

0)( 221

222

222

1 ppmpmps trktrk

Federico Nguyen

27-02-2006

Discrimination efficiencies for and

1) the procedure is tested

2) the event is selected if at least one of the 2 tracks is not identified to be an electron

it leads to a rejection power ~ 97% for e+ e e+ e events while keeping a selection efficiency 99.8% for

e+ e + + events

Log L/Le (per track)

electronselectrons

muons or pionsmuons or pionsbefore particle ID

after particle ID

mtrk (MeV)

Federico Nguyen

27-02-2006

Definition of and events (I)

MeV mtrkand inside the area, are

mtrk MeV are

M2 [0.37,0.42] GeV2

mtrk (MeV)

no

man

’s la

nd

no

man

’s la

nd

(MC)

DATA

Federico Nguyen

27-02-2006

Definition of and events (II)

M2 [0.57,0.62] GeV2

M2 [0.87,0.92] GeV2

mtrk (MeV)

mtrk (MeV)

ee contamination @ high

M

can be neglected to 1st

order

Federico Nguyen

27-02-2006

Tracking efficiencies for events

evaluated from data samples of and events, and from a MC sample of events, and compared

the agreement is on the level of 0.5-0.6%, at maximum,

preliminary

Federico Nguyen

27-02-2006

Background for the selection

background yields are

estimated using MC

distributions after the

whole selection,

normalized to the

luminosity of the

selected data sample

for data and 2

background sources:

22vis

MΔ

N1

dM

dσ

L

MC

M2 (GeV2)

dd v

isvis/d

M/d

M22 (

nb/G

eV (

nb/G

eV22 ))

preliminary

data

MC

Federico Nguyen

27-02-2006

The “raw” spectrum

M2 (GeV2)

dd

/dM

/dM

22 (ev

ents

/0.0

1 G

eV (

even

ts/0

.01

GeV

22 ))

MM22 = 0.01 GeV = 0.01 GeV22, L = 242 pb, L = 242 pb-1-1

of data taken in 2002of data taken in 2002

a) pion with 50o < track <

130o

b) small angle ( )

c) mtrk > 130 MeV and inside

the area (mtrk vs M)

d) at least 1 track not to be

identified as an electron

preliminary

Federico Nguyen

27-02-2006

Background for the selection

background yields are

estimated using MC

distributions after the

whole selection,

normalized to the

luminosity of the

selected data sample

for data and 2

background sources:

22vis

MΔ

N1

dM

dσ

L

M2 (GeV2)

dd v

isvis/d

M/d

M22 (

nb/G

eV (

nb/G

eV22 ))

MC

preliminary

MC

data

Federico Nguyen

27-02-2006

The “raw” spectrum

MM22 = 0.01 GeV = 0.01 GeV22, L = 242 pb, L = 242 pb-1-1

of data taken in 2002of data taken in 2002

dd

/dM

/dM

22 (ev

ents

/0.0

1 G

eV (

even

ts/0

.01

GeV

22 ))

M2 (GeV2)

a) muon with 50o < track <

130o

b) small angle ( )

c) mtrk < 115 MeV

d) at least 1 track not to be

identified as an electron

preliminary

Federico Nguyen

27-02-2006

the extraction of F, from both the absolute

measurement of events and from the ratio of to

events, is in an advanced state,

these methods have different systematics,

we are finalizing the estimate of the corrections and of

the systematic uncertainties,

good control of //e discrimination,

even on the theory side some improvements are

expected

Conclusions and perspectives

Results will come soon…

Please, stay tuned

Federico Nguyen

27-02-2006

Comparison among available data sets

a (10-10 )

KLOE,

SND,

CMD-2 EPS (‘05),

CMD-2,

MM22 (GeV (GeV22))

/

KL

OE

- 1

• CMD-2 (‘04) and KLOE agree @ high M

• disagreement btw KLOE and CMD-2/SND

around the peak

• fair agreement btw CMD-2 (‘04) and KLOE• difference at about 1btw KLOE and SND due to the peak and above

interpolation ofKLOE 60 data points

from 0.35 to 0.95 GeV2

a

4 ptsndf

P4 pts

SND: Achasov et al., hep-ex/0506076