Measurement of the DANE Luminosity with the KLOE Experiment

Federico NguyenFederico NguyenUniversità Roma TRE – INFN Roma III

February 10February 10thth 2005 2005

EURIDICE Midterm Collaboration MeetingEURIDICE Midterm Collaboration Meeting

Federico Nguyen10-02-2005 Outline

Motivations: the error on

Selection criteria of large

angle Bhabha events

Comparisons among MC codes

Main systematics of the experimental

analysis

Conclusions: how can we improve?

Federico Nguyen10-02-2005 DANE and KLOE

Electromagnetic Calorimeter

Pb / Scintillating Fibres

Endcap + Barrel = 98% (4)

DANE, e+ e colliderat s ~ 1.019 GeV ~ M

Drift Chamber

4 m , 3.3 m length

90% He, 10% i-C4H10

Superconducting Coil B=0.52 T

Federico Nguyen10-02-2005 Resolutions in KLOE

E/E = 5.4%/E(GeV)

p/p = 0.4% ( 45°)

r = 150 m , z = 2 mm

vtx ~ 3 mm

eeee e eee

EMC features:EMC features:

Drift Chamber features:Drift Chamber features:

t = 56ps /E(GeV) 133ps

Federico Nguyen10-02-2005 Selection of large angle Bhabha

angle btw the 2 most energetic clustersangle btw the 2 most energetic clusters

nr. of eventsnr. of events

eeee

ee

the luminosity is given by Bhabha events divided for a evaluated folding theory (QED rad. corrs.) with the detector simulation

2 clusters with:

eVeV

55o 125o

|1 2 180o| 9o

2 tracks with:

7.5 cm, |z| 15 cm

p400 MeV

opposite curvature

Federico Nguyen10-02-2005 The MC code BABAYAGA

BABAYAGA:

each e± can emit up to 4 photons

multiphoton emission

parameterized by structure functions

D(x,Q2), folding the Born cross section

evolution equations are solved by

the numerical method Parton Shower

the accuracy is evaluated

comparing

with the exact O() evaluation, the

authors quote 0.5% within our cuts

Pavia group has worked at an

improved version

C. M. Carloni Calame et al., Nucl. Phys., B584, 459, 2000C. M. Carloni Calame et al., Nucl. Phys., B584, 459, 2000

Federico Nguyen10-02-2005 The MC code BHWIDE

BHWIDE:

up to 100 ’s per event

complete O() corrections

exact phase space integration

collinear and infrared logarithms

accounted for to all orders

claimed precision is %

according to the LEP2

requirements

BB contains the infrared divergence due to virtual corrections

S S ((k,k,mm contains the infrared divergence due to bremsstrahlung corrections

W. Placzek et al., hep-ph/9903381, 1999W. Placzek et al., hep-ph/9903381, 1999

S. Jadach et al., Phys. Lett., B390, 298, 1997S. Jadach et al., Phys. Lett., B390, 298, 1997

Federico Nguyen10-02-2005 BHWIDE vs. BABAYAGA

we compared the 2 MC codes applying our kinematic cuts

eV

55o 125o

eV

55o 125o

|1 2 180o| 9o

we tested the differential cross sections in acollinearity, , and lost energy,

v 1Mee2/s, no significant difference has been found in the shapes

Federico Nguyen10-02-2005 Comparisons of cross sections

BHAGENF (460.8 (460.8 0.1 0.1statstat) nb) nbBABAYAGA (459.4 (459.4 0.1 0.1statstat) nb) nbBHWIDE (456.2 (456.2 0.1 0.1statstat) nb) nbMCGPJ (455.3 (455.3 0.1 0.1statstat) nb) nb

0.7 %0.1 %

0.3 %

comparing the MC codes in treating virtual ( exchange and

vacuum polarization are “switched off”), soft and hard

corrections,

the cross sections for our kinematic cuts are:

BHAGENF features:

complete O() corrections

corrections due to e+ e→ e+ e

authors quote O(0.5%) accuracy

E. Drago and G. Venanzoni, Report INFN-AE-97-48, 1997E. Drago and G. Venanzoni, Report INFN-AE-97-48, 1997

F. Berends and R. Kleiss, Nucl. Phys., B228, 537, 1983F. Berends and R. Kleiss, Nucl. Phys., B228, 537, 1983 Monte Carlo Generator with Photon Jets:

use of structure functions

complete O() corrections

authors quote O(0.2%) accuracy

A. Arbuzov et al., Report Budker INP-2004-70, 2004A. Arbuzov et al., Report Budker INP-2004-70, 2004

A. Arbuzov et al., JHEP 9710:001, 1997A. Arbuzov et al., JHEP 9710:001, 1997

Federico Nguyen10-02-2005 Momentum and comparisons

we checked that the MC code folded with the detector simulationreproduces the kinematic variables, especially at the borders

dn

/dp

[

(0.5

MeV

)d

n/d

p

[(0

.5 M

eV)-1-1

]]

++ DataData

- Babayaga (MC)Babayaga (MC)

- Bhagenf (MC)Bhagenf (MC)

MC• data

perfect agreement in the acollinearity distributions very good agreement near p ~ 400 MeV

p 400 MeV

Federico Nguyen10-02-2005 Polar angle systematics

global agreement is very

good

but the cut occurs in a steep

region of the distributions

estimate of border

mismatches

after normalizing MC to

make it coincide with data in

the region , we

estimate as a systematic

error:

MC• data

Federico Nguyen10-02-2005 Background estimate (I)

A0A1

events/3 MeV

events/3 MeV

DATA

MC

other than Bhabha, there are events with mtrk ~ 137 MeV,

ee

around mtrk ~ [100,170] MeV the exponential is subtracted from

data )%004.0541.0( TOT

bkg

N

N

mtrk: 4-mom. conserv. under the hypothesis of 2 equal mass tracks and a

Federico Nguyen10-02-2005

a second method consists in discr. eat least one track identified as

an average of background content of 0.55% and a systematic

error of 0.10% are estimated

Background estimate (II)

)%015.0623.0( TOT

bkg

N

N

E (first plane) (MeV)

E (

last

pla

ne)

(M

eV)

E (first plane) (MeV)

E (

last

pla

ne)

(M

eV)

pions deposit ~ 40 MeV in each

plane

electrons deposit mostly in the first plane and negligible

amount in the rest

ee

Federico Nguyen10-02-2005 Dependence on sqrt(s)

since the cross section is

evaluated at the nominal value

of s1/2= 1019.5 MeV, we corrected

for DANE variations of s1/2 in

time

L/L =

is parameterized as a function

of s1/2, from Monte Carlo:

35 1.0195)(x102.497

1.0195)(x4.228σ

Δσ

Federico Nguyen10-02-2005 List of systematics

(theory)(theory)

(experiment)(experiment) = =

(total error) (total error)

due tos

putting all together:

BHAGENF: eff = ( 430.7 ± 0.3stat ) nb

BABAYAGA: eff = ( 431.0 ± 0.3stat ) nb

both groups of authors claim 0.5%both groups of authors claim 0.5%

summing in summing in quadraturequadrature

Federico Nguyen10-02-2005

the measurement of the luminosity is performed using

large angle Bhabha events, detected in KLOE in 2001 the major source of uncertainty is from theory we are going to use the improved version of BABAYAGA,

and also BHWIDE and MCGPJ to pin down the 0.5% factor what about implementing recent 2 loop evaluations?

from the experimental side we are going to analyse the

2002 data, and we are going to look at the process e+e→

as an independent luminometer reaction, which is the

precision of radiative corrections in this channel?

Conclusions and perspectives

A. A. Penin, hep-ph/0501120A. A. Penin, hep-ph/0501120

R. Bonciani et al., hep-ph/0411321R. Bonciani et al., hep-ph/0411321

M. Czakon et al., hep-ph/0412164M. Czakon et al., hep-ph/0412164

Federico Nguyen10-02-2005 Loss of cosmic events

at the trigger level, events are rejected because they have characteristics similar to cosmic rays (amount of energy released at the outer planes of the

EMC)

genuine cosmic event Bhabha event rejected because taken as cosmic

a fraction of 0.41% large angle Bhabha events are lost because of

this