measurement of the da ne luminosity with the kloe experiment federico nguyen università roma tre...
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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