Recent results of the NA48/2 experiment

Recent results of the NA48/2 experiment

Mauro Raggi LNFOn behalf of the NA48/2 Collaboration

PHI PSI 08International Workshop on e+e-

collisions Laboratori Nazionali di Frascati, Italy

7-10 April 2008

Mauro Raggi PHI PSI 08, LNF 7-10 April 2008 2

Outline

o NA48 history and detectoro NA48/2 recent results in charged Kaon

decays oBR and FF in K±→±ee (New preliminary)

oBR and kinematics in K±→±(New preliminary)

oMeasurement of K±→±e+e-(New Final)

oLepton universality in RK=Ke2/K2

o NA62 prospects for RK


10 years of HistoryNA48(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± → πππ) = (-1.5±2.2)·10-4

>Ag(K± → ππ0π0) = (1.8 ± 1.8)·10-

4

NA62(2007-?):

>RK(Ke2/Ke2)2007 K

e2/K2 runNA62


Simultaneous K± Beam

PK = 60±3 GeV/c

54 60 66

~71011

p/spill400

GeV/c

Simultaneous K+ and K- beams:

Flux ratio: K+/K– ~ 1.8large charge

symmetrization of experimental conditions

Width ~ 5 mm

K+/K- ~ 1 mm


NA48 detector layout

Spectrometer

- 4 Drift Chambers- Magnet

)(044.0.%1)(

GeVpp

p

mmyxVTX 2~,

%5.01.0%2.3)(

EEE

ELKr EM calorimeter

mmyx 3.1,

Trigger Hodoscopepst 150


K±→l+l– Theoretical framework

(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)

dee/dz ~ P(z)·|W(z)|2

Form-factor models:

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

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

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

K * l+l–: suppressed FCNC process

Usefull test for PT


Measurement technique and goals

o The BR is measured normalizing to K0D

o To reject K0D background a Kinematic cut has been

applied: Mee>140 MeV

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

NA48/2 analysis goals1. Model-independent BR(z>0.08) in visible kinematic

range2. Model’s parameters and BRs in full kinematic range

Previous Measurements Sample BR

Bloch et al., PL 56 (1975) B201 41 (K+)(2.700.50)·10-7

Alliegro et al., PRL 68 (1992) 278 500 (K+)(2.750.26)·10-7

Appel et al. [E865], PRL 83 (1999) 4482

10,300 (K+)

(2.940.15 )·10-7


NA48/2 K±→±e+e- data sample

7146 events (Mee>140 MeV)Background = 0.6% (K0

D

K0De + particle misID)

12.23 mln eventsBackground = 0.15% (K0

D)

Kaon decay flux (2003+2004): K=1.701011FlaviaNet ‘08BR(K2) used

K±→DK±→e+e-


Raw fit results (preliminary)

= 2.420.15f0 = 0.5290.012

ρ(, f0) = –0.963

a+ = –0.5760.012

b+ = –0.8300.053

ρ(a+, b+) = –0.913

Ma = (0.9510.028) GeV

Mρ = (0.7050.010) GeV

ρ(Ma, Mρ) = 0.998

(1)

(2)

(3)

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)

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

Available data set unable to distinguish among models

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


Preliminary BR resultsBRMI

=2.26 0.03stat 0.03syst 0.06ext = (2.26 0.08) 10-7

z>0.08

= 2.35 0.15stat 0.09syst = 2.35 0.18

f0 = 0.532 0.012stat 0.008syst 0.007ext = 0.532 0.016

BR1= 3.02 0.04stat 0.04syst 0.08ext = (3.02 0.10) 10-7

a+ = –0.579 0.012stat 0.008syst 0.007ext = –0.579

0.016

b+ = –0.798 0.053stat 0.037syst 0.017ext = –0.798

0.067

BR2= 3.11 0.04stat 0.04syst 0.08ext = (3.11 0.10) 10-7

Ma = 0.965 0.028stat 0.018syst 0.002ext = 0.965 0.033 [GeV/c]

Mρ = 0.711 0.010stat 0.007syst 0.002ext = 0.711 0.013 [GeV/c]

BR3= 3.15 0.04stat 0.04syst 0.08ext = (3.15 0.10) 10-7 BR=(3.080.04stat0.04syst0.08ext 0.07model)10–7=(3.080.12)10–7

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

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

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

(1)

(2)

(3)


Results comparison

NA48/2

VMD models [PRD60 (1999) 053007]

‘92 ‘99 ‘00 ‘08

New

“naïv

e”

WA

NA48/2

‘75 ‘92 ‘99 ‘08

BR

(10

-7)

Measurement

BR(10-7)

Bloch et al., 2.700.50

Alliegro et al. 2.750.26

Appel et al. 2.940.15

NA48/2 prel. (08) 3.080.12

Measurement Process value

Alliegro et al K++e+

e–

1.310.48

Appel et al.[E865]

K++e+

e–

2.140.20

Ma et al.[E865] K+++–

2.45+1.30–0.95

NA48/2 prel. (08) Ke+e–

2.350.18


K±→physics

O(p4) in PT: B=D=0; A loop diagrams contribution, C WZW anomaly (10%)

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

Relevant only @ low m


BR dependence on ĉBoth the BR and the m spectrum shape depend on ĉ:

The spectrum dependence will be used to extract the ĉ value


K±→ data sample

1164 candidates3.3% BG

MC O(p6), ĉ=2

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

BG mainly from (IB)

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

BR(O(p6),ĉ=2)=(1.070.04sta0.08sys)·10–6

Preliminary BR result:

Previous measurement by E787: BR=(1.10.32)·10–6

ĉ=1.8±0.6Based on 31 events 5 BG events


First observation of K±→±e+e−

Event sample:Event sample:120 candidates events with120 candidates events with6.1% Background

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

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

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

Never observed beforeLike in ĉ determines BR and mee shapeTheoretical expectation (Gabbiani 99):BR(K±→±e+e−)=(0.9-1.6)·10-8Normalization channel: Normalization channel: K±→

DKaon decay flux: K=1.48·1011

(’03-’04)

[final result published, PLB659 (2008) 493]

ĉ=0.90±0.45ĉ=0.90±0.45

Using Gabbiani ChPT O(p4) model:


Ke2/K2 measurement physics

Test of lepton universalityV-A couplings Within SM

Theoretical prediction forTheoretical prediction forRRKK=R=RKK(0)(1+(0)(1+RRKK)=(2.477±0.001)·10)=(2.477±0.001)·10-5-5

PDG average: RPDG average: RKK=(2.45±0.11)·10=(2.45±0.11)·10-5-5

Experimental error (4.5%) 100 times bigger wrt theoretical

)1())((

))((2

22

22

2

2

KK

eKeK R

mm

mm

m

m

K

eKR

112 events

534 events

404 events

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


SUSY LFV mechanism Ke2/K2

If tan=40 and MH+=500 GeV with |R31|2= 5·10-4

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

SM SUSY


Present status of NA48/2 Ke2/K2

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 - K2 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

)()()(

)()()(1

)()(

)()(

222

222

22

22

ePIDeTRe

PIDTR

BG

eBGeK KEffKEffKAcc

KEffKEffKAcc

DKNKN

KNKNR


NA62 2007 data taking Ke2/K2

Dedicated 2007 data taking:

- 4 months of data taking (excluding detectors prototype tests)- More than ~1105 Ke2 events collected- Aims to a precision better than 0.5 % on RK

Reduction of systematicsNew beam and spectrometer configuration:

Kaon momentum: (60±3) GeV/c → (75.0 ± 2.5) GeV/cPT kick from spectrometer magnet: 120 MeV/c → 263 MeV/c → improved missing mass resolution → improved Ke2 / K2 kinematic separation

Direct measurement of K2 background and electron mis-identification probability

Minimum bias 1 track trigger (as for 2004 run)


Summaryo Preliminary BRs in K→ee

oBR =(3.080.12)10–7 (including model dependence errors)

oBRmi(z>0.08)=(2.26±0.08)·10-7

o Preliminary BR of K→oBR(O(p6),ĉ=2)=(1.070.04sta0.08sys)·10–6

o Final BR and FF of K→eeoBR(±e+e−)=(1.19±0.12sta±0.04sys)·10−8

oĉ=(0.90±0.45)

o Preliminary results and prospect in Ke2/K2

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

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

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

Documents

Recent results of the NA48/2 experiment