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CKM unitarity problem:CKM unitarity problem:results from NA48 results from NA48

experimentexperiment

Evgueni Goudzovski (JINR)Evgueni Goudzovski (JINR)

JINR Scientific CouncilJINR Scientific CouncilJanuary 20, 2005January 20, 2005

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The CKM matrix The Cabibbo-Kobayashi-Maskawa matrix connects

the eigenstates d’,s’,b’ of weak interaction with the quark flavour eigenstates d,s,b:

Vud Vus Vub

Vcd Vcs Vcb

Vtd Vts Vtb

d

s

b

d’

s’

b’

=

Conservation of probability: CKM matrix has to be unitary: VCKMVCKM

+=I

If unitary not fulfilled: New Physics (e.g. 4th quark generation)

E. Goudzovski JINR SC January 20, 2005

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CKM unitarity problem CKM unitarity requires for the 1st row:

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

Particle Data Group (PDG)(PDG) 2004 review: |Vub|=(3.67 ± 0.47)∙10-3

[negligible contribution into unitarity relation, ~10-5] |Vud|=0.9738 ± 0.0005

[well measured, e.g. neutron lifetime] |Vus|= 0.2200 ± 0.0026 (≈sinCabibbo)

[old measurements: semileptonic kaon decays]

|Vud|2+|Vus|2+|Vub|2 = 1(4.3±1.9)∙10-3

(2.2 deviation from unitarity)

E. Goudzovski JINR SC January 20, 2005

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CKM unitarity: |Vus| measurement

Best way to determine |Vus|: semileptonic (neutral and charged) kaon decays Ke (Ke3);

A few recent measurements of BR(Ke3) lead to |Vus| values significantly above PDG 2004 values;

New measurements of |Vus| are desirable.

E. Goudzovski JINR SC January 20, 2005

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Determination of |Vus| from BR(Ke3)

where• Br(Ke3()) experimentally measured value;• K kaon lifetime, measured by other experiments;• f+(0) form-factor, evaluated theoretically;• SEW=1.0232 short distance enhancement factor;• IK phase space integral;• C2=1 for K0, C2=1/2 for K.

|Vus|=1283Br(Ke3())/K

C2GF2MK

5SEWIK

1f+

K(0)

f+K0+(0) = 0.981

0.010f+

K+0(0) = 1.002 0.010

Form-factor calculation(Cirigliano, Neufeld, Pichl, EPJC35,53,2004)

(evaluated with 1% precision)

PrecisionsKaon lifetimes:

• (KL)/(KL)=0.8%;• (K)/(K)=0.2%;

Desirable BR(Ke3) precision:• BR/BR<1%

E. Goudzovski JINR SC January 20, 2005

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NA48 experiment at CERN SPS

Main detector components:

• Magnetic spectrometer (4 DCHs) redundancy high efficiency; Δp/p = 0.5% + 0.009%*p [GeV/c].

• Hodoscope high granularity multiplicity trigger; precise time measurement (150ps).

• Liquid Krypton EM calorimeter (LKr) High granularity, quasi-homogenious; ΔE/E = 3.2%/√E + 9%/E + 0.42%; electron/pion discrimination; registration.

E. Goudzovski JINR SC January 20, 2005

DCH

LKrHOD

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|Vus| measurements by NA48

NA48/2NA48/2: Semileptonic K± decays: K±0e (Ke3) Data: 90k events in 8 hours of low intensity run 2003; Loose hodoscope trigger (1 charged track);

NA48NA48: Semileptonic KL decays: KLe (Ke3) Data: 6.8 mln events in 2 days of special run 1999; Trigger on 2 charged particles in DCH or hodoscope;

NA48/1NA48/1: Semileptonic 0 decays: 0+e Data: whole high intensity run 2002 (6.2k events); Approach different to the one for kaon decays; These preliminary results are not discussed in this

talk.

E. Goudzovski JINR SC January 20, 2005

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Measurement method: normalize Ke3 events to K0 events (Br=0.21130.0014);

Signal practically background free; Statistics selected from the minimum bias run:

Br(K0e) measurement

Decay Statistics

K++e 59∙103

Ke 33∙103

K++0 468∙103

K0 260∙103

E. Goudzovski JINR SC January 20, 2005

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K0e: Data/MC comparison

Without radiative corrections With radiative corrections

E. Goudzovski JINR SC January 20, 2005

Data/MCData/MC Data/MCData/MC

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Br(K0e): result

Br

Detector acceptance 0.038%

Trigger efficiency 0.004%

BR (K0) 0.034%

Radiative events 0.006%

MC statistics 0.022%

Total systematics 0.056%

Statistic uncertainty 0.017%

Preliminary NA48/2 result:

Br(K0e) = (5.140.02stat0.06syst)%

Main systematics:

PDG 2004

NA48/2BNLE865

K+

K K

… confirms the deviation from PDG observed by BNL E865!… the most precise measurement of Br(Ke3)!

E. Goudzovski JINR SC January 20, 2005

Bra

nch

ing

rati

oB

ranch

ing

rati

o

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Measurement method: Use minimum bias trigger to collect KL2-track

events; Normalization to Br(2-track) = 1.0048 Br(30)

Best input precision: ΔBr(2-track)/Br(2-track)<0.9%

Exactly the same selection for signal (Ke3) and normalization events, but electron identified by energy deposit in the LKr calorimeter;

Measured quantity:

Br(KLe) measurement

R=(KLe)

(KL all two-track) =N(Ke3)/acceptance(Ke3)

N(2-track)/acceptance(2-track)

E. Goudzovski JINR SC January 20, 2005

Phys.Lett. B602 (2004) 41Phys.Lett. B602 (2004) 41

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Data sample: ~80 million 2-track triggers taken during 2 days

of minimum bias run with pure KL beam;

Selection criteria: Conditions on track geometry and kinematics; Leave a sample of 12.6 million 2-track events;

Additional criterion for Ke3: Electron ID: E(LKr)/P>0.93

for 1 track; 6.8 mln candidates selected.

Data sample and selection

E. Goudzovski JINR SC January 20, 2005

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Background to Ke3 sample: K3/K3 with ± misidentified as e±

Estimated from Ke3 data with identified e± (E/p>1):

Prob(e)=5.8·10-3

Electron/pion separation

E. Goudzovski JINR SC January 20, 2005

Quality of electron ID can be estimated from the data itself!

Inefficiency of electron ID: Estimated from data with

identified ± (0.3<E/p<0.7):

Prob(e)=4.9·10-3

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Monte Carlo simulation To determine acceptances, Monte Carlo simulation of 5

significant 2-track modes involved (radiative corr. included):

Decay channel

BR (PDG04) Acceptance

KLe 38.8% 0.2599

KL 27.2% 0.2849

KL+-0 12.6% 0.0975

KL+- 2.1·10-3 0.5229

KL000D 7.6·10-3 0.0001 For average 2-track acceptance use ratios of BR: averages from PDG +

KTeV (B3/Be3, B3/Be3, …) Absolute BR’s are not used!

Acceptance(2-track events) = 0.2412 0.0004 Small normalization uncertainty: ΔA/A=0.16%

E. Goudzovski JINR SC January 20, 2005

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Errors on R=(Ke3)/(2-track)

Statistical errors are negligible; Dominating systematic uncertainty: due to

inexact knowledge of beam energy spectrum;

Summary of systematic errors:R/R, %

Energy spectrum 0.67

Normalization (input BR) 0.16

E/P cut (electron ID) 0.05

Trigger efficiency 0.05

DCH overflows 0.05

Magnet polarity 0.07

E. Goudzovski JINR SC January 20, 2005

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Data/Monte Carlo comparison

Profiles at drift chamberKaon energy spectrum: major uncertainty

E. Goudzovski JINR SC January 20, 2005

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Br(KLe): result Experimental result:

R =(KLe)

(KL all two-track) = 0.4978 0.0035

To compute Br(KLe) we use Br(KL30):

PDG 04: 0.21050.0023

KTeV 04 prel.:

0.19450.0018Br(KL30)=0.19920.0070

Result on Ke3 branching ratio:

Br(KLe) = 0.4010 0.0028(exp) 0.0035(norm)

= 0.4010 0.0045

(inconsistent data; scale factor applied to error)

E. Goudzovski JINR SC January 20, 2005

Phys.Lett. B602 (2004) 41Phys.Lett. B602 (2004) 41

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From BR’s to unitarity test

Br(K) = (5.14 0.06)% Br(KL) = 0.4010 0.0045

K: f+(0)|Vus| = 0.2245 0.0013 KL: f+(0)|Vus| = 0.2146 0.0016

K: |Vus| = 0.2241 0.0026 KL: |Vus| = 0.2187 0.0028

(PDG: 0.2200 0.0026)

|Vus|∙f+(0) ~

Br(Ke3)/K

[accuracy 1.1%]

[1.1%]

[0.6%][0.7%]

[1.3%][1.2%]

E. Goudzovski JINR SC January 20, 2005

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Results on |Vus|·f+(0)

0.2 0.21 0.22 0.23 0.24 0.25 0.26|Vus|

·f+(0)

NA48: KL

NA48/2: K± (preliminary)

(2003)

E. Goudzovski JINR SC January 20, 2005

PL B602 (2004) 41

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Conclusions Values of |Vus| obtained by experiments before

2003 are in poor agreement with CKM unitarity;

Recent NA48 measurements of |Vus|: From K:

In agreement with new BNL result and CKM unitarity; In disagreement with the old measurements;

From KL: In agreement with new KTeV and KLOE measurements; In better agreement with CKM unitarity than the old

measurements.

More precise calculations of f+(0) are desirable.

E. Goudzovski JINR SC January 20, 2005