Status of KLOE

1
Status of KLOE experiment _at_ DA?NE
B.
Valeriani Institut für Experimentelle
Kernphysik-Universität Karlsruhe
2
KLOE DA?NE

• DA?NE and KLOE have been
• conceived with the primary goal of
• studying CP and CPT violation in the
• neutral kaon system
• Two different methods are used
• to investigate these symmetries
• ? Double Ratio as _at_ fixed target
• experiments
• Quantum Interferometry, unique
• feature _at_ a ? factory, since
• kaon pairs are collinear and
• monochromatic

DA?NE facility e - e- collider working at the
? mass ?s 1.02 GeV Design
philosophy ? L(single bunch) 5x1030 cm-2s-1
(? LVEPP-2M) high collision frequency
(up to 120 bunches) ? two independent beam lines
to avoid beam-beam interaction
Maximum achieved Luminosity L 3 ?
1031 cm-2s-1
3
(No Transcript)
4
KLOE detector
Superconducting Coil B0.6 T
Be beam pipe (0.5 mm thickness) permanent Quads
instrumentation Pb / Scintillating Fibers
Iron Yoke
Cylindrical Drift Chamber 4 m ?, 3.3 m length 90
Helium, 10 Isobutane all stereo wires
Electromagnetic Calorimeter Pb / Scintillating
Fibers Endcap - Barrel - Modules
5
KLOE performances EmC DC
6
Ks decays studies with 2000 data
KL interacting in EMC (KLCRASH)
The KS is tagged by a KL in the EmC. The
measurement of BR(Ks ? ??-)/BR(Ks ? ?0?0) is
already competitive
PDG 2000 Ratio 2.197 ? 1 1.2 ? 10-2
(stat) 0.6? 10-2 (syst) KLOE 2000 Ratio
2.23 ? 1 0.35 ? 10-2 (stat) 1.5 ? 10-2
(syst) preliminary
systematics under study
7
Ks decays studies with 2000 data
Ks ? ?e? decay
Emiss-Pmiss
PDG2000 (CMD2) BR(KS? ?e? ) 7.2 1.2 ? 10-4
KLOE preliminary result BR(KS? ?e? ) 7.47
0.51(stat) ? 10-4 (systematics under evaluation)
8
? radiative decays studies with 2000 data
Scalar sector BR(? ? f0? ? ?0?0?) 7.9 ? 0.2
(stat) ? 10-5 BR(? ? a0? ? ??0?) 5.8 ? 0.5
(stat) ? 10-5 (? ? ??) BR(? ? a0? ? ??0?)
6.7 ? 0.9 (stat) ? 10-5 (? ? ?????0) Assuming
BR(? ? f0?) ? 3 ? BR(? ? f0? ? ?0?0?) and BR(? ?
a0?) ? BR(? ? a0? ? ??0?) BR(? ? f0?) / BR(? ?
a0?) 4.1 ? 0.4 (stat) Pseudoscalar
sector BR(? ? ??) / BR(? ? ??) 5.3 ? 0.6 ?
10-3 M? 958.0 ? 0.6 MeV/c2 BR(? ? ??)
6.8 ? 0.8 ? 10-5 (PDG2000 BR 6.7 ? 1.5 ?
10-5 ) ?mix 401.71.5o (flavour basis)
-14.71.71.5o (singlet-octet
basis) In both cases the analysis is going on to
evaluate systematic errors
9
? ? ?????0
0.3M events
3 contributions to Dalitz plot
Preliminary
E0 m?o GeV

• ? r ?,0 p 0, ?
• f ? p p -p 0 (direct)
• ee- ? wp 0

in the fit the mass and width of the ?, the
?M(??,?0) and the direct decay contribution are
left free
(E - E-)/?3 GeV
A1 (?10-2) f1 (deg) M(r,-)
M(r0) G DM(,-)
KLOE 8.5 ? 0.5 88 ? 9 775.3 ?0.4 773.0
?0.6 149.1 ? 1.0 0.4 ? 0.3 () PDG
-15 ?11 (CMD-2) 776.0 ? 0.9 ()
150.2 ? 0.8 - () CPT test at lt 5
x 10-4 () mixed charges (t decay and ee-)
average M(r0) - M(r,-) 0.4 ?0.8 Efficiency
(X,Y) from Montecarlo fine tuning in progress
to reduce systematic effects on M(r0) (now at 2
MeV level)
10
Measurement of ?(ee? ? ????) _at_ ?slt1 GeV
KLOE measures hadronic
cross-section as a function of the ?? center of
mass energy M2?? in the fixed energy environment
of DA?NE by using the RADIATIVE RETURN METHOD.
A hard photon radiated in the initial state
(Initial State Radiation, ISR) lowers the
available energy, allowing to exploit the full
energy range 4m2? lt M2?? lt 1 GeV2, without any
energy scan.
?
?
M2?? M2? - 2M? E?
Why are we interested in measuring ?(ee? ? ???)
_at_ ?slt1 GeV? A precise measurement of ?(ee? ?
???) as a function of M2?? in this energy range
is relevant for the theoretical estimation of the
hadronical contribution both to the muon
anomalous magnetic moment a? and to the fine
structure constant at the Z mass ?(M2Z).
11
?(e?e? ? ????) a?
The reduction of the present error on
the hadronical contribution to a? becomes
extremely important with the new results of the
BNL g-2 experiment
Reducing ?a?had allows to isolate possible new
physics contributions!
12
KLOE contribution to the measurement
a? can be expressed in terms of
?(e?e? ? hadrons) via the dispersion integral
Since low energy contributions are enhanced in
the dispersion integral, ca. 77 of a?had comes
in the energy region 2m? lt M?? lt 1.4 GeV. 61
of a?had is covered by the ? resonance
0.28 GeV lt M?? lt 0.81 GeV
An accuracy of 1 in ?(e?e? ? hadrons) up to 1.4
GeV results in
?a? ? 7 ? 10-10 The same accuracy in the
measurement of ?(e?e? ? hadrons) up to 3.1
GeV would result in ?a? ? 1.5 ?
10-10
13
The ?? ?? ? final state

• Three processes contribute to the ?? ?? ? final
  state
• ? Initial State Radiation (ISR)
• ? Final State Radiation (FSR)
• ? ? ? f0? ? ?????
• The relative contribution of the three processes
  depends strongly on
• the photon polar angle and on the two pions
  invariant mass value
• ? ISR contribution is peaked at small photon
  polar angle
• ? FSR and ? direct decay contributions are mainly
  concentrated in the
• high M?? region (M2?? gt 0.8 GeV2)

S. Binner, J.H. Kühn, K. Melnikov, Phys. Lett. B
459, 1999
14
(No Transcript)
15
Fiducial volume definition

• Two fiducial volumes are currently studied
• small angle?? lt21o ? ??gt169o
• highest cross section small background from ???
  small
• contribution from FSR no photon tagging
  required
• large angle 60olt??lt120o
• large background from ???, especially at low
  M2?? photon detected in the EmC
• The pions must be central (55o-125o)
• to cut down the background (e?e? ?,
• ???? ?)

16
Signal selection1
Bhabha events are rejected with
a likelihood function based on the TOF and the
shape of the energy deposit in the EmC
eff. on pions
? ????? ?????0 ? e?e?? 450MeVlt Ptrlt500MeV
eff. on electrons
log(Relative Likelihood)
Track momentum
? ??? and radiative bhabhas are used as control
samples ? different likelihood functions are
defined for each track momentum range (50 MeV
bin)
17
Signal selection2
25lt qg lt 155, 50lt qp lt130
Before Likelihood ( Rad. Bhabhas )
After Likelihood
mmg
pp-p0
18
e?e? ? ????? cross-section
Integrated luminosity
? ?acc??trg??sel
? the acceptance eacc is evaluated from MC (large
angle small angle) ? the global selection
efficiency esel is evaluated from DATAMC ? the
trigger efficiency etrig is evaluated from DATA
? the Luminosity is measured using the Bhabha
scattering at large angles
19
Pion form factor
F?(M2??)2
? large angle ? small angle
?Ldt 16.5 pb-1
M??
Z. Phys. C48 (1990) 445
20
Pion polar angle asymmetry
FSR parametrization in the MC has
been checked by looking at the pion pair
asymmetry in the polar angle distribution
small angle
large angle
Asymmetry ()
? DATA ? MC
Asymmetry ()
? DATA ? MC
??
??
21
Conclusion
? KLOE has collected 25pb-1 by the end of
year 2000 ? Preliminary studies show the good
performances of the detector ? Competitive
results have already been achieved on the
analysis of KS decays (BR(KS ? ??-)/BR(KS ?
?0?0), KS semileptonic decays) and of ? radiative
decays (BR(? ? ?S), ?-? mixing) ? KLOE is
expected to collect 200 pb-1 by the end of 2001
? With these statistics a measurement of ?(ee?
? ????) _at_ ?slt1 GeV at 1 level can be performed
? This result would play an important role
in the reduction of the present error on
the hadronical contribution to a? ? First
results obtained from the analysis of the 2000
statistics (16.5 pb-1) look promising
? In parallel a theoretical work is going on
(Kühn and collaborators) in order to
evaluate the radiative corrections to the process
to the NLO (hep-ph/0106132)