latest results on kaon physics a.antonelli lnf-infn - qcd@work conversano june 2005 latest results...

Latest results on kaon physics A.Antonelli LNF-INFN - QCD@WORK Conversano June 2005

Latest results on kaon physics

Vus

KS rare and “semi” rare decays

CP violation in charged kaonscattering lengthFuture programsOutlook & Conclusions

In spite of a long history the K system is still a laboratory for interesting physics: flavour physics, CP violation. It can be a sensitive probe for NP. Most of the recent results come from KLOE, KTEV, NA48


Unitarity test of CKM: Vus Saga

|Vud|2 + |Vus|2 + |Vub|2 = 1

Unitarity (or lack thereof) of CKM matrix tests existence of further quark generations and possible new physics (eg. Supersymmetry)

Vud2 = 0.9482±0.0010 (nuclear decays)

Vus2 = 0.0484±0.0011 ( from e.g. K+0e+e )

Vub2 = 0.000011±0.000003 ( B meson decays)

Most precise test of unitarity possible at present comes from 1st row:

2|Vud|dVud = 0.0010

2|Vus|dVus = 0.0011 PDG

2004|Vud|2 + |Vus|2 + |Vub|2 = 0 9972±0.0015 (~ 2 deviation)


Vus from Kl3 decays

• I() phase space integral, Sew short distance corrections (1.0232)

|Vus| is extracted from Kl3 partial decay widths

where i runs over the four modes K±,0(e3), K±,0(3)

G2M5

Ki • Ni = C2

i [Ci=1(2-½) for neutral (charged kaon decays)] 1923

Ii () ) phase space electromagnetic correction

• f+K0-(0) form factor at zero momentum transfer: pure theory calculation (PT, lattice)

i SU(2) ,e2p2 form factor correction due to isospin breaking (strong and electromagnetic)

few 10-2

slopes (momentum dependence of the vector and scalar form factors)



2003: First hint: BNL E865

Br(K+→π0e+ν) =(5.13±0.02stat±0.10sys)% PDG(<2004): (4.87±0.06)%

Vus consistent with unitarity but 2.7σ above existing Br(K ± →π0e±ν) value.

Key issue is systematic control of the Branching Ratio.Detector not optimized for photons (designed for π+μ-e+)Require: π0 e+e-γ in signal and normalization ( K+→+π0)

2004: KLOE KTEV, NA48 experiments measure Kl3 branching ratio for Ks and KL , lifetime and form factors with different techniques


KKLL “crash”“crash”= 0.22 (TOF)= 0.22 (TOF)

KKSS ee

KS tagged by KL interaction in EmCEfficiency ~ 30%KS momentum resolution ~ 1 MeV

KKSS

KKLL 2 2

KL tagged by KS+-

Efficiency ~ 70%KL momentum resolution ~ 1 MeV

KLOE:Tagging of neutral kaons


KLOE:Measurement of KL BR’s

)(/)()()(

1

N

N i)BR(K

tag

iL allii tagtagLFVrec

Reconstruction efficiencies: KL , e (rec) 55% KL (rec) 40% KL (rec) 100%

Integral over the fiducial volume: ε (FV, L) 26%, depends on L

Tagging efficiency

Trigger required on the KS side

Tagging Precisely measure absolute branching ratios


KLOE:KL30

KS

At least 3 neutral clustersNeutral vertex reconstructed along KL direction using TofEfficiency close to 100%, bkg 1%


KLOE:KLcharged

KS

2 tracks forming a vertex along the KL direction.Vertex and tracking efficiency 55% for Kl3 and 40% for 3

P-E() (MeV)

Events counted by fitting missing momentum minus missing energy in the pion-muon hypothesis


KLOE: KLchargedPmiss - Emiss distribution very sensitive to radiation and momentum resolutionCheck data/MC agreement via independent PIDRadiative corrections properly included in the Monte Carlo generators (IR-finite treatment of radiative effects (no energy cutoff))

KL econtrol sample KL control sample


KLOE: Absolute BR's results

BR(KLe) = 0.4049 0.0010 0.0031 ~8105 events

BR(KL) = 0.2726 0.0008 0.0022 ~ 5105 events

BR(KL 3) = 0.2018 0.0004 0.0026 ~ 7105 events

BR(KL) = 0.1276 0.0006 0.0016 ~ 2105 events

• Absolute BR results with (KL

= 51.54 ns):

¾ of 2001-2002 data has been used for efficiency evaluation and

¼ for BR measurement corresponding to 13106 tagged KL.

330 pb-1

2001-2002


KLOE: BR results

KL

= 50.72 0.140.36ns

Assuming BR(KLX) =1

independent measurement of KL

BR(KLe) = 0.4007 0.0006 0.0014

BR(KL) = 0.2698 0.0006 0.0014

BR(KL 3) = 0.1997 0.0005 0.0019

BR(KL) = 0.1263 0.0005 0.0011

BR(e ++ +3 + rare decays from PDG) = 1.0104 0.0076

KL FV acceptance depends on the lifetime :

Systematics evaluated including

full error matrix from all sources.


KLOE: KL lifetime from KL30

• Large acceptance for KL decays 0.4 high statistical accuracy•KL momentum measured from KS+-

• KL30 efficiency >99% little variation along the KL path•KL+-0 as a control sample for the estimate of efficiency, resolution and time scale

PDG) (fit) = (51.7 PDG) (fit) = (51.7 ±± 0.4) ns 0.4) ns(Vosburg, 1972) =(Vosburg, 1972) =±±ns - 0.4 Mevents ns - 0.4 Mevents L(KLOE) = (50.87 ± 0.16 ± 0.26 ) ns - 14.5 Mevents – 440 pb-1

+ data

Eve

nts

/0.3

ns

t*= LK/c (ns)

6 -26 ns (40% L)


NA48 & KTeV Measurements

BR(KLe

)BR(2 track)= 0.4978 0.0035

Using PDG-KTeV average for BR(KL 3)

BR(KLe) = 0.401

0.0045

Both experiments measures ratio of BR

They also have a preliminary measurement of BR(KL 3) = 0.19660.0035

BR(K e)=0.05140.0006

NA48 KTeV

KTeV measure 5 KL ratios

e3 / 3 , +-0/ e3 , 000/ e3

+- / e3 , 00 /

These 6 decay modes account for 99.93% of KL decays and the ratiocan be combined to extract BR

(~6 million reconstructed Ke3) (sample sizes 105-106)


BR comparison


Vus from Kl3 decays and L

hep-ph/0411097 (F. Mescia @ICHEP04)

1) Quadratic parametrization of the form factor momentum dependence:

from KTeV + ISTRA

2) KL lifetime from KLOE (average of the two measurements) :

KL

= (50.81

ns3) BRs from KLOE (setting the sum =1):

4) Form factor f+K(0) from Leutwyler-Roos: 0.961(8)

BR(KLe) = 0.4007 0.0006

0.0014

BR(KL) = 0.2698 0.0006

0.0014

2

2

2 21)0()(

m

t

m

tftf



KLOE results: |Vus

|f+

K(0) (KSe3

) = 0.2169 0.0017

|Vus

|f+

K(0) (KLe3

) = 0.2164 0.0007 |V

us|f

+K(0)(K

L3) = 0.2174 0.0009

From Unitarity: (1-|Vud

|2)1/2f+

K(0) = 0.2177 0.0028

|Vus|f+Kπ(0)


KLOE: BR(K++())

• Tag from K-- • 2002 data 175 pb-1 (2/3 is used as efficiency sample)• Background events identified by the presence of a neutral pion.

P()*(MeV)

Particle momentum in K rest frameCombining the experimental value of

(K())/(())with the ratio

fK/f obtained from lattice calculations

we can extract the ratio |Vus|/|Vud| (Marciano hep-ph/0406324)Selection

e


KLOE: BR(K++())

P()*(MeV)

• Event counting performed by fitting the P* distribution with signal and background shapes obtained from data control samples: bkg-sample selected by looking for 2 photons from neutral pion; control sample for signal shape selected by identifying the muon cluster in the Emc. •Systematics are dominated by efficiency estimate.

BR(K+ + = 0.6366 ± 0.0009 (stat.) ± 0.0012 (syst.)

Chiang = 0.6324 PDG fit = 0.6343


• fK /f =1.210±0.014 (MILC Coll. hep-lat/0407028)

Following the method from Marciano hep-ph/0406324 :

Vus=0.2223±0.0025

• Vud=0.9740±0.0005 (superallowed -decays)

Vus from K++()


(MK0 MK0) (MK0 MK0)

SM prediction: S000

= L000|+000|2 BR(KS 30) = 1.9 x 109

Best limit from: direct search SND ’99 : BR(KS 30) < 1.4 x 105

interference NA48 ’05: BR(KS 30) < 7.4 x 107

Uncertainty on KS 30 amplitude limits precision of CPT test:

_ _

from unitarity

S,L = (1 + i tanSW)Re f A*(KSf) A(KLf)/S = (i + tanSW) Im

MK MK

2 10 8 10 MK/MPlanck = 4 10-20)

Observation of KS 30 signals CP violation in mixing and/or in decay:

A limit on BR(KS 30) at 107 level translates into a 2.5-fold improvement on the accuracy of Im , i.e.

KS 000 – test of CP and CPT


Signal selection

•KS’s tagged by of Kcrash

•6 photons clusters, no tracks from IP

•Kinematic fit to improve cluster

parameter Background rejection

KS + 2 fake ’s •Signal box in plane

pairing of 6 clusters with better 0 mass estimates

pairing of 4’s out of 6: 0 masses, E(KS), P(KS), c.m. angle between 0’s

•Final cut on residual Ks energy: E(Ks )- E

DataMC 30 BR 10-5

0

20

40

80

60

4010 20 30

KLOE: : Search for KS 000


KS 000 – Final Results

KLOE: 450 pb-1 ’01+’02 data

Nsel(data) = 2 events selected as signal

= 24.5%

Nsel(bkg) = 3.130.82stat0.37sys

bkg events expected from MC

N2BR(KS 000) = BR(KS 00) < 1.2 10-7,

N3

Normalize signal counts to KS 00 count in the same data set:

Can state: N3 < 3.45 with a 90% CL


Using PDG value and our limit we obtain:

@ 90% CL

A(KS 000)

A(KL 000)

Accepted for publicationUL will decrease by ~ 10

•Increased statistics: x 6.5 improvement•Increased background rejection

2 fb-1 Prospect

|000| = < 1.8 10-2

NA48

KLOE

KLOE: : KS 000 – Final Results


Sensitivity to CPT violating effects through charge asymmetry:

Sensitivity to CP violation in K0-K0 mixing:

AS = 2Re (CPT symmetry assumed)

_

AS never measured before

If CPT holds, AS=AL

ASAL signals CPT violation in mixing and/or decay with SQ

(KS,L -e+) (KS,L +e-)

(KS,L -e+) (KS,L +e-)

_

_AS,L =

Can extract |Vus| via measurement of BR(KS e)

Test of the S = Q rule, (KS e)/(KL e) = 1 + 4 Re(x)

KS e decays – Physics issues


KS e decays: Results

•Further rejection of KS background from TOF identification

•Obtain number of signal events from a constrained likelihood fit to multiple data distributions

•Normalize to KS in the same data set

Use BR(KS ) to calculate BR(KS e)

• Kinematic closure: use KL to obtain KS momentum PK and test for presence of neutrino:

Emiss = MK2 + PK

2 – E– Ee

Pmiss = |PK – P– Pe |

Data

— MC sig + bkg

EmisscPmiss(MeV)



Dependence of efficiencies on charge mainly due to TOF effects, estimated using data control sample of KL e

AS = (2 9stat 5syst) 10-3

BR(KS e+) = (3.54 0.06stat 0.04syst) 10-4

BR(KS e-) = (3.55 0.05stat 0.02syst) 10-4

AL = (3.322 0.058 0.047) 10-3 [KTeV 2002]

AL = (3.317 0.070 0.072) 10-3 [NA48 2003]

Published result: (6.91 0.34stat 0.15syst) 10-4, KLOE ’02

BR(KS e) = (7.09 0.08stat 0.05syst) 10-4

Uncertainty in charge asymmetry still dominated by statistics

With data for an integrated luminosity of 2.5 fb, AS 3 10Re



Re(x) = (2.7 3.0stat 1.8syst) 10

Use BR(KL e±KTeV04]

Re(x) = (.1 3.2stat 1.8syst) 10

Use BR(KL e±KLOE05

Use average of KTeV and NA48 measurement of the KS lifetime: S = (89.62 0.05) ps

Use new measurement of the KL lifetime: L = (50.89 0.23) ns KLOE ’05

Compare (KS e) with (KL e): test of the S Q rule

4Re(x) = (KS e)/(KL e)1

KTeV04

KLOE05

PDG04

KLOE KS

Most precise measurement of Re(x) (in CPT conserving transitions): compare with CPLEAR99, Re(x) = 6 x 10


Direct CP-violation in K3

• Matrix elementparameterized in terms of slopes

• Kinematics

• Measured quantity sensitive to direct CP violation:

Charged kaon: direct CP violation only

|M(u,v)|2 ~ 1 + gu + hu2 + kv2

Ag = (g+-g-)/(g+

+g-)≠0

u = (s3-s0)/m2 =2mK∙(mK/3-Eodd)/m

2;

v = (s2-s1)/m2= 2mK∙(E1-E2)/m

2

si = (PK-Pi)2, i=1,2,3 (3=odd );

s0 = (s1+s2+s3)/3.

BR(K±±+)=5.57%; BR(K±±00)=1.73%.


10-6

|Ag|

Experimental precisions by 2005:Experimental precisions by 2005:

10-5

10-4

10-3

10-2

SMSM SUSYSUSYNewNew

physicsphysics

Ford et al. (1970)

HyperCP prelim. (2000)

TNF prelim. (2002)“neutral” mode

NA48/2proposal

• SM estimates vary within an order of magnitude

(few 10-6… 8×10-5)

• Models beyond SM predict substantial enhancement partially within the reach of NA48/2

• Asymmetry in decay widths expected to be smaller than in Dalitz slopes

(SM: ~10-7… 10-6)

[[AAgg~10~10-3-3]]

“charged”“neutral”

Theory

Theoretical expectations


NA48/2 goals and methodM.S. Sozzi

• Primary NA48/2 goals:Primary NA48/2 goals:– Measure slope asymmetries in “charged” and “neutral”

modes with accuracies δAg<2.2∙10-4, and δAg0<3.5∙10-4,

respectively. Requires >2∙109 decays in “charged” mode and >108 in “neutral” mode.

• NA48/2 method:NA48/2 method:– Two simultaneous K+ and K– beams, superimposed in

space, with narrow momentum spectra;– Detect asymmetry exclusively considering slopes of ratios

of normalized U distributions. If acceptance is equal for K+ and K–, R(u) = N+(u)/N–(u) ≈

≈ n∙(1+g+u)/(1+g–u) ≈ ≈ n∙(1+2gu)

– Equalize K+ and K– acceptances by frequently alternating polarities of relevant magnets.

Δg = 2g∙Ag


M.S. Sozzi

|V|

Data-taking 2003: 1.61x101.61x1099 events selected

KK+ + : 1.03x10: 1.03x109 9 eventsevents

MM=1.7 MeV/c=1.7 MeV/c22

Events

M(3) GeV/c2

UAg = (0.5±2.4stat.±2.1stat.(trig.)±2.1syst.)x10-

4 = (0.5±3.8)x10-4

NA48/2:Selected statistics 2003


Cusp-like effect in K++00

Interference generate a cusp in the spectrum next to threshold, not seen earlier by lower precision experiments

One loop calculation: cusp located at m = 2m+ N. Cabibbo hep-ph/0405001

Recent two loops calculation: d/(dm)2 F (a0 -a2 , a2 , g, h, m) allows to extract

scattering lengths a0 -a2 from m spectrum N. Cabibbo ,G. Isidori hep-ph/0502130

To be compared to precise (2%) PT prediction

M0 = 1+gu/2 M1 (a0 -a2)

d/dm |M0 + M1|2

Two diagram contribute: direct emission, re-scattering


Cusp-like effect in K++00

Best fit obtained with 2 loops and a smallcontribution from pionium fixed to:BR(K pionium)/ BR(K3) 0.8 10-5

(a0 -a2)·m= 0.281 ± 0.007 (stat.) ±0.014 (syst.) ± 0.014 (theor.) NA48/2 prel

NA48/2 2x108 K++00

4x109 K++ –+2003-2004

50 days-2003

m2


Rare Kaon decays mediated by Flavor Changing Neutral Currents are the main experimental tool to probe the flavour structure of physics beyond the SM independent from B mesons.

• No SM tree-level contribution

• Strong suppression within the SM because

of CKM hierarchy

• Predicted with high precision within the SM

if dominated by short-distance dynamics G. Isidori

(holy grail)

|Vtd|

* 2 5t

2

20

s

2

5

4

td

4

0 0 10

10

10

11

( ):

( ) 1.8 10 ( )

4.1 10 3.0

( ) 1.0 10

Standard Mode =I l

0.6 10

I mV Vm A

I

=

mB

B

t

t

tL

Buras

x X x

x A

x A

x

K

K

2 117.8 1.2 10x

Rare Kaon Decays and the SM


Status & Future programs•K0

L –Upper limit is 4 order of magnitude from the SM prediction, KTEV@FNAL

–Expect results from data collected by E391a@KEK (proposed SES~3 10-

10)

–Next experiment KOPIO@ BNL (>100 signal events), JPARC (180 signal events)

•K+ –3 clean events are published (in agreement with SM)

–Next experiment: NA48/3@CERN (O(100 ) signal events), JPARC (> 50 signal events)

–Move from stopped to in flight experiments (increased acceptance)


Outlook & Conclusions

• In spite of a long history the K system is still a laboratory for interesting physics: flavour physics, CP violation etc..

• “Unitarity Crisis” in first row of CKM matrix seems resolved.

• In the next year we will have new results on KL and KS K decays from KLOE ( 2fb-1 will be collected by the end of 2005) and NA48.

• Many experiment proposed (not yet approoved) on rare kaon decays will probe the flavour structure of physics beyond the SM

Is kaon physics still interesting???

Answer is YES!!!


20 200 04060 40

Data— MC sig + bkg

60 80

Emiss–Pmiss(MeV)

BR(KS e) = (7.09 0.07stat 0.08syst) 10-4

KS semileptonic decay

•Selected using Tof technique•Event counting obtained by fitting the E(e)-P distribution•The two charge modes are measured independently• selected ~104 signal events per charge in the 2001-2002 data sample.


W = m

(1019.4 MeV)

Ldesign

51032 cm-2 s-1

DANE2002:270 pb-1

2001: 170 pb-1

2000: 20 pb-1

2004 best Lpeak 1.2×1032 cm-2s-1

2004 avg L ~6×1031cm-2s-1

Collected 770 pb-1 since May 2004


Conclusion

•The dominant KL BR’s with 0.5% accuracy• The KL lifetime with 0.6% accuracy• BR(KS e) with 1% accuracy• BR(K+ +) with 0.2% accuracy • All BR’s are inclusive of the radiation

With the data collected in the year 2001-2002 KLOE has measured:

A large number of K semileptonic decays has been collected and identified

will allow us to measure all the BR’s with better than 1% accuracy

KLOE is now measuring:• K± lifetime• Kl3 form factor• KS BRComing soon the update of (KS+-())/(KS00) measurement We expect to collect 2fb-1 for the end of December 2005

Final papers are under review by the Collaboration



EXP: Need to measure BR, lifetime, and slopes with good accuracy TH : Need to improve estimate on f(0)

0

0

30

1

20

1

2

1

BR

BR

2

1

0

0

f

f

V

V

us

us

exp th

0.3 % 0.4% 0.3% 0.8%K0 e0.6% 0.1% 0.3% 0.8%K e

0.5% 0.4% 0.8% 0.8%K0 0.6%

0.9% 0.1% 1.5% 0.8%K 0.2%


The KLOE detector

CalorimeterCalorimeter

(E)/E = 5.7%/E(GeV) (t) = 54 ps/E(GeV) 100 ps

p/p0.4 % (tracks with > 45°)x

hit150 m (xy), 2 mm (z)x

vertex ~ 1 mm(M) ~ 1 MeV


Radiative corrections

IR-finite treatment of radiative effects in MC (no energy cutoff)The E-P shape is checked using Ke3/K3 enriched samples obtained from an independent calorimetric selection: Tof, E/p, and cluster centroid position.The Ke3 BR changes by 2% neglecting the radiative tail.

P-E() (MeV)P-E(e) (MeV)


Semileptonic decays of K±

Absolute BR measurement.

K±, decays used to tag the events. Kl3 selection: kaon decay vertex in FV Reject two-body decays: P*() 195

MeV Cut on missing momentum to reject decays.

0 search: 2 neutral clusters in EmC, prompt wrt the K vertex.

Spectrum of charged daughter mass, m2, from TOF measurement.

m2=p2 [(cT/L)2-1]

Ratio of data and MC efficiency is used to correct MC acceptance.

KK

KK

ee


Semileptonic decays of K±

K++0 Tag

Tag K+2 Tag K+2 Tag K-2 Tag K-2

NKe3 67 022 331 26 774 215 71 188 345 25 942 211

NK3 42 096 282 16 586 179 44 925 293 16 465 180

ml2=pTRK

2 [(c(tl-t)/LTRK )2-1]


Tagging of charged kaons

• Tag performed selecting K± ±, ±0 decays (85% of K±) by measuring the charged particle momentum in the K rest frame (P*).• In the following analyses the trigger is required on the tag side.


Generators for radiative K decays

12

b

o M

EbA

dE

d

Motivation: acceptance evaluation with accuracy better than 1%, shape of kinematic variables (e.g. Emiss-pmiss spectrum)

New MC generators for and Kl3 decays including radiated photon, without any cutoff on the energy. The fraction of events in the tail is in agreement with present experimental knowledge:

2

2

2

1093.0

1093.0

10)015.0908.0(

)(

)2030,(

MC

aletBijnens

kTeV

eKBR

MeVEeKBR

L

eL

310)07.059.2()(

)50,(

S

S

KBR

MeVEKBR E731 (2.560.09)10-3

MC 2.6 10-3



KLOE results: |Vus

|f+

K(0) (KSe3

) = 0.2169 0.0017

|Vus

|f+

K(0) (KLe3

) = 0.2164 0.0007 |V

us|f

+K(0)(K

L3) = 0.2174 0.0009

From Unitarity: (1-|Vud

|2)1/2f+

K(0) = 0.2181 0.0022 New Vud

|Vus|f+Kπ(0)

New Vud



1-|Vud

|2)1/2f+

K(0) = 0.2181 0.0022

new vud=0.9739(3) old vud 0.9740(5) new vus 0.2269(13) old vus 0.2265(22)


Kaons at KLOE

K+K- 1.5 106/pb-1

KLKS 106/pb-1

• The decays at rest allow us to select monochromatic (p ~ 110 MeV/c) pure beams of

Kaons • Observation of KL,S signals presence of KS,L

• KS decays near IP: S ~ 0.6 cm• ~50% of KL decays inside the detector: L ~ 340 cm• ± ~ 95 cm• Events per pb-1:

KS(+)

KL(-)

~4 m


Kaon Rare Decays and the SM(holy grail)

Kaons provide quantitative tests of SM independentfrom B mesons…

…and a large windowof opportunity exists!

G. Isidori

Im t = A2 5 Re t = A2 5

Vtd

latest results on kaon physics a.antonelli lnf-infn - qcd@work conversano june 2005 latest results...

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