Download - The CP-violation experiments NA48 at CERN

The CP-violation experiments NA48 at CERN

Manfred Jeitler

Institute of High Energy Physics

of the

Austrian Academy of Sciences

RECFA meeting

Innsbruck, 26 March 2004

Manfred Jeitler, Institute of High Energy Physics, Vienna: The NA48 experiment Innsbruck,

26 March 2004

overview

the original NA48 experiment – direct CP-violation: Re ’/

measurements in a high-intensity KS beam– KS 0 0 0

– KS 0e+e- and KS 0+-

measurements of direct CP-violation with charged kaon beams– K + -

future ?


26 March 2004

Re61/00

00

S

L

S

L

K

K

K

KR

The original aim of NA48: measuring Re ’/

KS

KS

KL

KL

’/ 0:

direct CP-violation

exists

”frequent“ ”rare“

/


26 March 2004

The neutral kaon beams of NA48


26 March 2004

The detector of the NA48 experiment at CERN

• spectrometer (consisting of 4 drift chambers and a magnet) and hadron calorimeter for measuring -decays

• electromagnetic liquid-krypton calorimeter for measuring -decays

magnet

DCH

DCH

DCH

DCH

hadron calorimeter


26 March 2004

The liquid-krypton calorimeter

• measures decays of kaons into neutral particles: K

• filled with 9 m3

of liquid krypton

• part of trigger electronics built by HEPHY, Vienna


26 March 2004

NA48

Re’/= (14.7 ± 2.2) 10-4 NA48 (all data)

Re’/: the experimental result

(15.3 ± 2.6) 10-4

Re’/= (16.6 ± 1.6) 10-4 new world average

(13.

7 ±

3.1)

1

0-4


26 March 2004

Re ’/: the shape of the theory

considering the present accuracy of calculations, there is no use to further improve measurements


26 March 2004


26 March 2004

pay one – take three:

charged kaons

charged kaons

CP-violation in K0S decays:

KS 000

KS 0e +e - and KS 0+-


26 March 2004

The high-intensity KS-beam


26 March 2004

KS 000

CP-violating decay– no CP-conserving components such as in KS +-0

counterpart to the “classical” CP-violating decay KL 0 0

– CP | 000 > = - | 000 > while

– CP | KS > ~ CP | K1

> = + | K1 >

described by parameter )3(

)3(0

0000

L

s

KA

KA


26 March 2004

KS 000 : the result

result consistent with zero with 5% probability

limit on branching fraction:

BR(KS 000) < 1.410-6 at 90% confidence level

(one order of magnitude better than previous limit)


26 March 2004

KS 000 and CPT

Bell-Steinberger relation statesfinal

fSW ii )]Im())[Re(tan1(


26 March 2004

KS 0e +e - and KS 0+-


26 March 2004

7 events found with a background of 0.15 +0.10

-0.04

KS 0e +e -


26 March 2004

KS 0+-

CP-violation in charged K decays:

K + - K 0 0


26 March 2004

measure decays of K+ and K–

direct CP-violation in K (3) :

M(u,v) 1 + gu + hu2 + kv2

Ag (g+ g– )/(g+ + g–)

measurement of the ratio

R (u) dvM+(u,v)2 dvM–(u,v)2

constant simultaneous K+ and K– beams same acceptance, alternating magnetic field

high-precision measurement of K (3)


26 March 2004

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

Bel'kov '99Shabalin '98

SUSY D'Ambrosio '99

SM

asymmetry parameter Ag in K (3)

theoreticalpredictions

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

NA48KLOE

Hyper CP

BNL

and expectedexperimental

accuracy


26 March 2004

KAon BEam Spectrometer(“Micromegas” detector)


26 March 2004

KABES: KAon BEam Spectrometer(a MICROMEGAS detector)


26 March 2004

charged Ke4 decays K+/- e

experimental observation of quark-antiquark condensate– s-wave scattering length a0

0 in -scattering at low energy

earlier experiments statistically and systematically limited– Rosselet et al., 1977

– Brookhaven, 2001

neutral Ke4-decay (K0L e ) was studied by the

Vienna group (Laurenz Widhalm, Heinz Dibon)


26 March 2004

SM prediction: BR(K+ → +) = 7.1 ± 1.0 × 10-

11

future plans: K+ → + so far, three events

seen at BNL (E787 and E949)

decay established but not enough statistics to check Standard Model

plans to collect ~100 events at FNAL (CKM experiment): financial difficulties

idea to use CKM’s expertise and parts of the NA48 detector at CERN

Conclusion:

NA48 has yielded an unexpectedly large amount of valuable results

.....

and may still continue to do so!

backup


26 March 2004

special interest: test of CPT invariance if CPT is conserved

– and there are no transitions to I = 3, or to nonsymmetric I = 1 states:

– A1 : I=1 amplitude

– real part fixed by CPT

– imaginary part sensitive to direct CP-violation

Bell-Steinberger relation– connects CPT violating phase with parameters via unitarity:

statesfinal

fSW ii )]Im())[Re(tan1(

KS 000

)Re(

)Im(

1

1000

A

Ai

)2

arctan(SL

SW

m


26 March 2004

KS 000 : the approach

time evolution of KL,S 000

I0 (t) ~

e-Lt + KL decay

“dilution” D is momentum dependent

look for interference term

35.0)()(

)()()(

00

00

KNKN

KNKNpD

| 000 |2 e-St + KS decay

2 D(p) (Re (000 ) cos mt – Im (000 ) sin mt) e-(S+ L)t / 2

KL – KS interference term


26 March 2004

NA48/1: preliminary result for 000


26 March 2004


26 March 2004

CP-violation: indirect / direct ?

CP-violation first seen in KL decays (1964)

KL and KS are mixtures of CP-eigenstates K1 and K2

– KL = K2 + K1

– KS = K1 + K2

mixing responsible for most of the observed CP-violation– parameter – known since long ago

– see Michele Veltri’s talk for new measurement by NA48

but longstanding question: is there “direct” CP-violation?– K2 ??

– parameter ’

small effect need high-precision measurement !


26 March 2004

the NA48 approach to measuring Re ’/

almost collinear neutral kaon beams (KL and KS )

same decay volume take all 4 modes at same time and place ! “weighting” of KL decay events with KS lifetime

– eliminate acceptance effects in first order

– reduce systematic effects at expense of statistics

distinguish KL and KS by “tagging” protons to “KS target”

“second experiment” in 2001– new drift chambers

– different spill structure and instantaneous beam intensity

– different beam energy


26 March 2004

rare decays at NA48

“KL”-beam:– KL + - e+ e- indirect CP-violation

– KL +/- e-/+ 0 form factors, – phase shifts, chiral perturbation theory

– KL 0 CP-conserving contribution in KL e+ e- 0

– KL e+ e- form factors

– KL e+ e- background for KL e+ e- 0

– KL e+e- e+e- CP-eigenvalue of KL

“KS”-beam: 0 00 mass 0 non-leptonic weak interaction 0 0 0p- transversal -polarization


26 March 2004

KS / KL 000 interference

dependence of interference on (phase of )


26 March 2004


26 March 2004

Dalitz decays: 0 e+e-

KS 0 e+e-


26 March 2004


26 March 2004

Kl3 decays and Vus

test of CKM unitarity– |Vud|2 + |Vus|2 + |Vub|2 = 0.9957 0.002 : deviation from unity

– |Vus| contributes nearly 30% of uncertainty

|Vus| calculated from (Ke3) and (K3)– K 0eand K 0– precise measurement will improve CKM unitarity test


26 March 2004

charged kaon decays: the NA48 approach

cancellation of systematic effects is essential

adapt NA48’s proven concept:

simultaneous, collinear beams

use same detector without major modifications

beam particles are charged measure their momentum !