Status report on KLOE physics

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1 Outline : •Published papers •Neutral kaons •Charged kaons decays •Hadronic cross section •Conclusions Status report on KLOE physics Camilla Di Donato

description

Status report on KLOE physics. Outline : Published papers Neutral kaons Charged kaons f decays Hadronic cross section Conclusions. Camilla Di Donato. KLOE integrated luminosity. KLOE integrated luminosity. 1999 run: 2.5 pb -1 machine and detector studies 2000 run: 25 pb -1 - PowerPoint PPT Presentation

Transcript of Status report on KLOE physics

Page 1: 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

221

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

23

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