Status report on KLOE physics
description
Transcript of Status report on KLOE physics
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Outline:•Published papers•Neutral kaons•Charged kaons• decays•Hadronic cross section•Conclusions
Outline:•Published papers•Neutral kaons•Charged kaons• decays•Hadronic cross section•Conclusions
Status report on KLOE physics
Camilla Di Donato
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KLOE integrated luminosity
KLOE integrated luminosity
1999 run: 2.5 pb-1 machine and detector studies
2000 run: 25 pb-1 7.5 x 107 published results
2001 run: 190 pb-1 5.7 x 108 2002 run: 300 pb-1 9 x 108
analysis in progress
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Published results: 2000 data
•Measurement of branching fraction for the decay KS -> e (Phys. Lett. B 535 (2002) 37)
BR(KS -> e) = (6.91±0.37)x10-4
•Study of the decay -> 0 0 with the KLOE detector (Phys. Lett. B537 (2002) 21)
BR(-> f0 ) = (4.47±0.21)x10-4 and f0 shape
•Study of the decay -> 0 with the KLOE detector (Phys. Lett. B536 (2002) 209)
BR(-> a0 ) = (7.4 ±0.7) x 10-5 and a0 shape
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Published results: 2000 data
•Measurement of (KS -> +- ()) / (KS -> 0 0)
(Phys. Lett. B 538 (2002) 21-26)
(KS -> +- ()) / (KS -> 0 0)=(2.236 0.003
0.015)
•Measurement of (-> ' ) / (-> ) and the
pseudoscalar
mixing angle (Phys. Lett. B 541 (2002) 45-51)
BR( -> ' ) = (6.10±0.61±0.43)x10-5
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KS -> eThe method already used for 2000 data (PLB 535, 37(2002)) has been used to analyze 90 pb-1 out of the 2001 data set
Ne N
= BR(KS -> e)BR(KS -> )
e
x
eboost
KS
KL
‘Kcrash’ cluster
•Events tagged by a ‘Kcrash’ cluster
•2 tracks and 1 vertex close to the IP
•Reject events with invariant mass M close to the K0 mass
•Use time information from calorimeter clusters to perform PID for charged tracks
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/e identification
• Time of flight e/identification (t = 2 ns) :
t(m) = tcluster – t.o.f. calculated with mass hypothesis m
• Sign of the charge is determined
-> semileptonic asymmetry accessible
t(me2)-t(m1)
t(m
e1)-t
(m2
)
e
e
AS,L =
S,LS,L
S,L
S,L
6 ns
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N(e± N(e±
Charge independent fit compatible with the sum: N(e±
EmissESEeE
PmissPSp1pES,PS from KL direction and momentum
Charge identified yields
Preliminary result on the asimmetry has an overall error of 3% and is consistent with 0.We expect 1% error with full 500 pb-1 data set
Preliminary result on the asimmetry has an overall error of 3% and is consistent with 0.We expect 1% error with full 500 pb-1 data set
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Long distance contribution to the rare KL decay
Relative uncertainty on BR(KL ) 1.3%
Motivations:
Common preselection, essentially:•KLtag•Neutral vertex•Fiducial volume
preselection, essentially:
•E> 100 MeV•Photons angular separation in the plane transverse to KL momentum > 150o
BR(KL->)/BR(KL->3)
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Mafter preselection
Two discriminating variables exploiting the fixed kinematics in KL center of mass system:
E*E*
KL-> selection
M after E* cutM after E* cutM after cutM after cut
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The three pions sample is trivially selected with minimal requirements on photon energies. To limit systematics due to photon splitting/merging inclusive selection is done with N
Data quality and stability with different data taking conditions is very good
KLOE: L = 51.6 ± 0.8 ns
PDG: L = 51.7 ± 0.4 ns
KLOE: L = 51.6 ± 0.8 ns
PDG: L = 51.7 ± 0.4 ns ‘01 data
KL-> selection
KLOE preliminary: R = (2.80 ± 0.03stat ± 0.03
syst)10-3
NA48 (2002): R = (2.81 ± 0.01stat ± 0.02
syst)10-3
KLOE preliminary: R = (2.80 ± 0.03stat ± 0.03
syst)10-3
NA48 (2002): R = (2.81 ± 0.01stat ± 0.02
syst)10-3
2001+2002 data2001+2002 data(143 + 169) pb-1
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Neutral kaons produced in a pure quantum state (JPC = 1- - ) :
pppp ,,,,2
1SLSL KKKKi
Time evolution for
)cos(2|)(| 2/|)|(||||2 tmeeetA ttt LSSL
No simultaneous events: same final state + antisymmetric initial state
L ~ 280 pb-1
Peak position sensitive to m value
KL regeneration on the pipe
t|/s
A first glance at interference
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Many improvements have been introduced for charged kaons in the reconstruction – classification – analysis chain, in order to cope with the peculiar features of these events at KLOE:
•Improved energy loss treatment in track fit•Refined treatment of multiple scattering correlation matrix•Improved merging of split kaon tracks•Realistic drift chamber noise simulation from data•T0 global finding•Kaon time of flight corrections•Single arm tagging method in event classification
•Improved energy loss treatment in track fit•Refined treatment of multiple scattering correlation matrix•Improved merging of split kaon tracks•Realistic drift chamber noise simulation from data•T0 global finding•Kaon time of flight corrections•Single arm tagging method in event classification
Charged kaons
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Good statistical power few % accuracy with 1 pb-1
Exploits the K0 TAG K counting insensitive to Kaon BR’s and reconstruction efficiencies
Good statistical power few % accuracy with 1 pb-1
Exploits the K0 TAG K counting insensitive to Kaon BR’s and reconstruction efficiencies
+
KK+
K+
+
N2 = number of ev with 2 triggering 0 tags
N1 = number of ev with 1 triggering 0 tag
The number of K+K- events Nkk is function of N1, N2 and geometrical acceptances (or ,and ), but not of the Tag efficiency (id ) !!
N2 = Nkk and (id BRK )2
N1 = 2 Nkk BRK id [or (1- BRK) +
BRK and (1- id)]
2
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2 4
2
N
NNN
or
andKK
measurement with K±
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Before tagging
peak peakAND taggedOr Tagged
Shapes for the pion (muon) peak are obtained from data in K±->±tagged events.
To count N1 and N2 look at the pion Momentum in the kaon rest frame p*
Kl3 background
MCMC
measurement with K± (2)
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Analysis procedure used to extract the cross section e+eK+K- at the peak on a subsample of 2002 data set:
2002 (7.0 pb-1): (1713±32stat±34lumi) nb (
2002 (7.0 pb-1): (1713±32stat±34lumi) nb (
Together with the other channels will allow the extraction of all parameters.
W dependence for the 2002 scan (± 2 MeV)
W dependence for the 2002 scan (± 2 MeV)
Preliminary results
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222
i
iAppA
AAAA
dirii
Fit function
The two main terms are :
i
ddireCaA
2
2
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2
2
2
3
1 222
)(
)()(
)(
1
k
k
k
k
kkk
k
kkkkk
q
m
mp
qpq
qimmqA
Y=(E0– M0) X=(E+ - E- )/3
->0 dynamics
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ad = 0.093 0.011 0.015
d = 2.45 0.09 0.11 rad
M(0) = 775.86 0.57 0.67 MeV
M -0.54 0.34 0.68 MeV
M = 0.45 0.39 0.67 MeV
= 145.2 1.2 1.0 MeV
ad = 0.093 0.011 0.015
d = 2.45 0.09 0.11 rad
M(0) = 775.86 0.57 0.67 MeV
M -0.54 0.34 0.68 MeV
M = 0.45 0.39 0.67 MeV
= 145.2 1.2 1.0 MeV
The (not quite) preliminary results, on 20 pb-1 (2000 data) are:
/dof = 1947(1874-8)/dof = 1947(1874-8)
->0 dynamics
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M (MeV)
Eve
nts 2001 data (140 pb-1)
2000 data
• Same selection as of 2000 • Event number scales with luminosity
5 final state5 final state
M (MeV)
Eve
nts 5 final state5 final state
->update
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• Same selection as of 2000 • Event number scales with luminosity
M (MeV)
Eve
nts
2001 data2000 data
5 final state5 final state
->update
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With the (almost) complete statistics of 2001-2002 we finally found evidence for the f0 -> decay
The amount of events in the f0 peak is already indicative of a destructive interference with FSR
With the (almost) complete statistics of 2001-2002 we finally found evidence for the f0 -> decay
The amount of events in the f0 peak is already indicative of a destructive interference with FSR
Prelim
inary
Prelim
inary
M (MeV)
2001+2002 data
980
f0 ->
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bands
region
Sidebands for bkg shape evaluation
700 evts in the peak700 evts in the peak
100 pb-1 (2001)100 pb-1 (2001)
->-> update
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The selected number of events scales with luminosity within errors as expected. Events are very clean with background <1%
300 kevents
N’/N = (2.4 ± 0.24 stat ± 0.1 bkg )·10-3N’/N = (2.4 ± 0.24 stat ± 0.1 bkg )·10-3
N’/N = (2.2 ± 0.09 stat ± 0.05 bkg )·10-3N’/N = (2.2 ± 0.09 stat ± 0.05 bkg )·10-3
Year 2000 (16.3 pb-1):
Year 2001 (preliminary) (100 pb-1):
, ratio
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E++E-2/Ndgf
->->
•2000:16 pb-1
•2001:118pb-1
•2002:223pb-1
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KLOE can improve the current PDG limit for this C violating decay
MM (MeV) (MeV) MM (MeV) (MeV)
142 pb-1
BR() < 3.5 10-5
142 pb-1
BR() < 3.5 10-5
KLOE preliminary
->
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Davier, Eidelman, Höcker, Zhang: hep-ph/0208177
1.6
3.0
hep-ex/0208001
FJ 02 (e+e- based)2.8
PRELIMIN
ARY
Disagreement between e+e- basedand based evaluations
Experiment and Theory with almost identical errors ( ± 8·10-10 ):
Hadronic cross section and a
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We measure the cross-section (e+ e- hadrons ) as function of the hadronic c.m.s energy M 2
hadrons by using the radiative return
disadvantage advantage
Requires precise calculations of ISR Data comes as by-product of standard program EVA + Phokhara MC Generator Requires good suppression (or knowledge) Systematic errors from Luminosity, s, … enter only once of FSR
d(e+ e- hadrons + )
dhadrons
Radiative Return
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550< < 1250
< 150 > 1650
Two fiducial volumes are currently studied:
Pion tracks are measured at angles 40o< <140o
large angle: 55o<<125o
–Allows a tagging of the radiative photon
small angle: < 15o and > 165o
–Photon cannot be detected efficiently with EmC, untagged measurement in which we cut on the missing momentum
The two kinematical regions differ for:• cross section (SA: 24 nb; LA: 3 nb)• M2
spectrum shape• background contamination• relative contribution of FSR
Signal selection
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M2(GeV)
Ni/0.01GeV2Performed on 73 pb-1 of 2001 data set
after selection: about 106 events
statistical error/bin < 1% for M
2>0.45 GeV2
after selection: about 106 events
statistical error/bin < 1% for M
2>0.45 GeV2
d
dM 2
Nobs N bkg
M2
1
Select.
1
L
Background Signal
Selection efficiency Luminosity
30000
20000
10000
Small angle analysis
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DATA is compared with the MC generator PHOKHARA (NLO) whose output is expected to be accurate at 0.5% level and has been interfaced with the detector simulation program (GEANFI).
MC events are generated with the SA fiducial volume cuts: M2
(GeV2)
d/dM2(nb/GeV2)
MC• DATA
Preliminary results
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Pion form factor (prelim.) Data points have been fitted with the Gounaris-Sakurai-Parametrization
m, , are free parameters
of the fit, while mm are fixed to CMD-2 values
M=775.14 MeV = 147.05 MeV
=(-0.08) •10-3
= 2.893•10-3
124.80
(Stat. Errors only)
(G.J. Gounaris and J.J. Sakurai, Phys.Rev. Lett. 21 (1968), 244)
1
1 2GS'
GS BW)BWm
s(BW
)s(F
|F|2
=CMD2
=KLOE
M2+ -
(GeV2)
KLOEPRELIMINARY
Pion form factor (prelim.):
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•Experimental and Theoretical groups are in close contact to improve the measurement and to allow an interpretation for the evaluation of the hadronic contribution to a.•Work is in progress in order to refine the analysis with all the statistics of 2001 (~170 pb-1 )•Short term goal: a paper in beginning 2003 with:
• a measurement of d(e+e-->)/dM2for SA cuts
based on full 2001 statistics with a precision of 2 % • a derivation of (e+e-->)obtained by dividing d(e+e-->)/dM2
for the radiation function
• a fit of the pion form factor
conclusions & outlook
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•The increased performances of DAFNE are giving us the chance to investigate deeper and deeper the unique KLOE physics program.
•All previously performed analyses are obtaining significantly improved results, and many new ones are coming to a definitively sound status. Precision measurements are on arrival also for relatively rare processes…
…we are ready for the fb-1 era…!
Conclusions
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Tra
ckm
ass
M2
This background contamination is more significant at small M2
values and affects
mainly the LA region
The signal is further selected by performing a cut in the so called trackmass variable in order to reduce background
background (Mtrack104 MeV)rejected by a cut on Mtrack =120 MeV
Remaining contamination estimated from MC:below 1% for SA region
Background
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NN
AS = NN
To get the asymmetry, one has to correct the e and e event yields using the charge dependent efficiencies…
Efficiencies are determined on data using several control samples and currently read:
e = (21.7 ± 0.5)% e= (21.0 ± 0.5)%
Quoted errors depend mainly on the statistics of the KL->econtrol sample and determine the overall systematic uncertainty (2%)Preliminary result on the asimmetry has an overall error of 3% and is consistent with 0. We expect 1% error with full 500 pb-1 data set.
Preliminary result on the asimmetry has an overall error of 3% and is consistent with 0. We expect 1% error with full 500 pb-1 data set.
Charge asymmetry
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In the S.M., in a completely independent way from hadronic matrix elements and related uncertainties one has:
with
Currently:Rx = (-1.8 ± 6.1)·10-3 from CPLEAR (1998) With 2 fb-1 KLOE can improve the accuracy by a factor ten
)10(1 41 )3(/)3( 6 OxKK LS
AL AS R(CPT)
AS,L =
S,LS,L
S,L
S,L
AS not yet measured. Need 20 fb-1 to measure with 30% accuracy
SQ)
KS e : motivations