Recent results of the na48 2 experiment
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Recent results of the NA48/2 experiment. Mauro Raggi LNF On behalf of the NA48/2 Collaboration PHI PSI 08 International Workshop on e + e - collisions Laboratori Nazionali di Frascati, Italy 7-10 April 2008. Outline. NA48 history and detector NA48/2 recent results in charged Kaon decays

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Recent results of the NA48/2 experiment

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Recent results of the na48 2 experiment

Recent results of the NA48/2 experiment

Mauro Raggi LNF

On behalf of the NA48/2 CollaborationPHIPSI 08International Workshop on e+e- collisions Laboratori Nazionali di Frascati, Italy7-10 April 2008


Outline

Outline

  • NA48 history and detector

  • NA48/2 recent results in charged Kaon decays

    • BR and FF in K±→p±e+e- (New preliminary)

    • BR and kinematics in K±→p±gg (New preliminary)

    • Measurement of K±→p±e+e-g (New Final)

    • Lepton universality in RK=Ke2/Km2

  • NA62 prospects for RK

PHI PSI 08, LNF 7-10 April 2008


10 years of history

NA62

2007 Ke2/K2 run

10 years of History

  • NA48(1997-2001):Direct CP-Violation in neutral K

    • Re(ε’/ε) = (14.7 ±2.2)·10-4

      NA48/1(2002):Rare KS decays and hyperons

      NA48/2(2003-2004):Direct CP-Violation in charged K

    • Ag(K±→π±π+π-) = (-1.5±2.2)·10-4

    • Ag(K±→π±π0π0) = (1.8 ± 1.8)·10-4

      NA62(2007-?):

    • RK(Ke2/Ke2)

PHI PSI 08, LNF 7-10 April 2008


Simultaneous k beam

PK = 60±3 GeV/c

Width ~ 5 mm

K+/K-~ 1 mm

54 60 66

Simultaneous K±Beam

~71011

p/spill

400 GeV/c

Simultaneous K+ and K- beams:

Flux ratio:K+/K– ~ 1.8

largecharge symmetrizationof experimental conditions

PHI PSI 08, LNF 7-10 April 2008


Na48 detector layout

LKr EM calorimeter

Spectrometer

- 4 Drift Chambers- Magnet

Trigger Hodoscope

NA48 detector layout

PHI PSI 08, LNF 7-10 April 2008


K l l theoretical framework

K±→l+l– Theoretical framework

K  *  l+l–:suppressed FCNC process Usefull test for cPT

dee/dz ~ P(z)·|W(z)|2

z=(Mee/MK)2, P(z) is a phase space factor

Form-factor models:

(2) D’Ambrosio et al. JHEP 8 (1998) 4, (3) Dubnickova et al. hep-ph/0611175

(1) polynomial:W(z) = GFMK2∙f0∙(1+z)

(2) ChPT O(p6):W(z) = GFMK2∙(a++b+z) + W(z)

(3)Dubna ChPT:W(z) = W(Ma, Mρ, z)

(f0,) or (a+,b+) or (Ma,Mρ) determine a model-dependent BR

PHI PSI 08, LNF 7-10 April 2008


Measurement technique and goals

Measurement technique and goals

  • The BR is measured normalizing to K0D

  • To reject K0D background a Kinematic cut has been applied: Mee>140 MeV

  • This cut suppress the low Mee region (z<0.08), most interesting for model dependent BR determination

  • NA48/2 analysis goals

  • Model-independent BR(z>0.08) in visible kinematic range

  • Model’s parameters and BRs in full kinematic range

PHI PSI 08, LNF 7-10 April 2008


Na48 2 k p e e data sample

NA48/2 K±→p±e+e- data sample

Kaon decay flux (2003+2004):K=1.701011

FlaviaNet ‘08BR(K2) used

K±→p±e+e-

K±→p±p0D

7146 events (Mee>140 MeV)Background = 0.6% (K0DK0De + particle misID)

12.23 mln events

Background = 0.15% (K0D)

PHI PSI 08, LNF 7-10 April 2008


Raw fit results preliminary

Raw fit results (preliminary)

polynomial:W(z) = GFMK2∙f0∙(1+z)

ChPT O(p6):W(z) = GFMK2∙(a++b+z) + W(z)

Dubna ChPT:W(z) = W(Ma, Mρ, z)

(1)

(2)

Analysis cut:z>0.08, or Mee>140MeV/c2

(3)

Available data set unable to distinguish among models

Model-Independent BRMI(z>0.08) can be computed by integrating dG/dz

PHI PSI 08, LNF 7-10 April 2008


Preliminary br results

Preliminary BR results

(1)

(2)

(3)

Including uncertainty due to the model dependence, (full z range)

BR=(3.080.04stat0.04syst0.08ext 0.07model)10–7=(3.080.12)10–7

CPV parameter (first measurement! correlated K+/K– uncertainties excluded):

(K±ee) = (BR+–BR–) / (BR++BR–) = (–2.1±1.5stat±0.3syst)%

PHI PSI 08, LNF 7-10 April 2008


Results comparison

BR(10-7)

NA48/2

NA48/2

New “naïve” WA

‘08

‘92

‘75

‘99

‘08

‘99

‘00

‘92

VMD models [PRD60 (1999) 053007]

Results comparison

PHI PSI 08, LNF 7-10 April 2008


K p gg physics

Relevant only @ low mgg

K±→p±gg physics

O(p4) in cPT:B=D=0;Aloop diagrams contribution, C WZW anomaly (10%)

O(p6) in cPT: unitarity corrections can increase the BR by 30-40 %[G. D’Ambrosio and J. Portoles, Nucl.,Phys. B386 (1996), 403]

PHI PSI 08, LNF 7-10 April 2008


Br dependence on

BR dependence on ĉ

Both the BR and the mgg spectrum shape depend on ĉ:

The spectrum dependence will be used to extract the ĉ value

PHI PSI 08, LNF 7-10 April 2008


K p gg data sample

K±→p±gg data sample

Previous measurement by E787:BR=(1.10.32)·10–6 ĉ=1.8±0.6Based on 31 events 5 BG events

1164 candidates3.3% BG

1164 events in 40% of the full data ~40 times larger wrt to world sample

BG mainly from ppg(IB)

good agreement with MC O(p6), ĉ=2measurement of ĉ is ongoing

Preliminary BR result:

MC O(p6), ĉ=2

BR(O(p6),ĉ=2)=(1.070.04sta0.08sys)·10–6

PHI PSI 08, LNF 7-10 April 2008


First observation of k p e e g

First observation of K±→p±e+e−g

Never observed before

Like in gg ĉ determines BR and meeg shape

Theoretical expectation (Gabbiani 99):BR(K±→p±e+e−g)=(0.9-1.6)·10-8

Normalization channel: K±→ p±p0DKaon decay flux: K=1.48·1011 (’03-’04)

  • Event sample:

    • 120 candidates events with

    • 6.1% Background

Model-independent BR(Mgee>260MeV/c2):

BR(±e+e−g)=(1.19±0.12stat±0.04sys)·10−8

Using Gabbiani ChPT O(p4) model:

ĉ=0.90±0.45

[final result published, PLB659 (2008) 493]

PHI PSI 08, LNF 7-10 April 2008


K e2 k m 2 measurement physics

404 events

534 events

112 events

Ke2/Km2 measurement physics

Test of lepton universality

V-A couplings

Within SM

Theoretical prediction for

RK=RK(0)(1+dRK)=(2.477±0.001)·10-5

PDG average: RK=(2.45±0.11)·10-5

Experimental error (4.5%) 100 times bigger wrt theoretical

[V. Cirigliano and I Rosell, Phys.Rev.Lett.99:231801,2007]

PHI PSI 08, LNF 7-10 April 2008


Susy lfv mechanism k e2 k m 2

SUSY LFV mechanism Ke2/Km2

SM

SUSY

If tanb=40 and MH+=500 GeV with |DR31|2= 5·10-4

The effect can be as high as 2% and therefore measurablePR D74 (2006) 011701 (A. Masiero, P. Paradisi, R. Petronzio)

PHI PSI 08, LNF 7-10 April 2008


Present status of na48 2 k e2 k m 2

Present status of NA48/2 Ke2/Km2

2003 data taking:- 1 month of data taking with downscaled trigger - trigger efficiency

2004 data taking:- 56 hours of dedicated run with minimum bias trigger - K2 background subtraction in Ke2 sample

2 new preliminary result by Na48/2:NA48/2 (‘03 data 4670 ev): RK=(2.416±0.043sta±0.024sys)·10−5

NA48/2 (‘04 data 3407 ev): RK=(2.455±0.045sta±0.041sys)·10−5

PHI PSI 08, LNF 7-10 April 2008


Na62 2007 data taking k e2 k m 2

NA62 2007 data taking Ke2/Km2

  • Dedicated2007 data taking:

  • 4 months of data taking (excluding detectors prototype tests)- More than ~1105 Ke2 events collected- Aims to a precision better than 0.5 % on RK

  • Reduction of systematics

    • New beam and spectrometer configuration:

      • Kaon momentum: (60±3) GeV/c→(75.0 ± 2.5) GeV/c

      • PT kick from spectrometer magnet: 120 MeV/c→263 MeV/c

      • → improved missing mass resolution

      • → improved Ke2 / K2 kinematic separation

    • Direct measurement of K2 background and electron mis-identification probability

    • Minimum bias 1 track trigger (as for 2004 run)

PHI PSI 08, LNF 7-10 April 2008


Summary

Summary

  • Preliminary BRs in K→pee

    • BR=(3.080.12)10–7 (including model dependence errors)

    • BRmi(z>0.08)=(2.26±0.08)·10-7

  • Preliminary BR of K→pgg

    • BR(O(p6),ĉ=2)=(1.070.04sta0.08sys)·10–6

  • Final BR and FF of K→peeg

    • BR(±e+e−g)=(1.19±0.12sta±0.04sys)·10−8

    • ĉ=(0.90±0.45)

  • Preliminary results and prospect in Ke2/Km2

    • 2003 preliminary: RK=(2.416±0.043sta±0.024sys)·10−5

    • 2004 preliminary: RK=(2.455±0.045sta±0.041sys)·10−5

    • More than 110K Ke2 events collected in 2007 dRK/RK~0.5%

PHI PSI 08, LNF 7-10 April 2008


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