Status of A g measurement in NA48/2 DA NE 2004 Luca Fiorini Scuola Normale Superiore and INFN Pisa on behalf of NA48/2 collaboration: Cambridge, CERN,

Status of Ag measurement in NA48/2Status of Ag measurement in NA48/2

DANE 2004Luca Fiorini

Scuola Normale Superioreand INFN Pisa

on behalf of NA48/2 collaboration:Cambridge, CERN, Chicago, Dubna, Edinburgh, Ferrara, Firenze, Mainz, Northwestern, Perugia, Pisa, Saclay, Siegen, Torino, Vienna

Status of Direct CP violation measurement

in K±3 @NA48/2

– Search for direct CP violation in:

K± ±+-

K± ±00

– Data for present analysis:● collected from August 6 to September 7, 2003● divided in 3 supersamples (self-complete data set ~ 2

weeks period where all magnet exchange permutations have been done)

– Additional data (not included in present analysis):● 2 tracks events (K3 with lost pion)● June-July 2003 data with different systematic effects

Main Goal and Data samples

Direct CP violation @ NA48/2 2

Measurement PrinciplesKinematics Dynamics

Lorentz-invariantssi = (PK-Pi)2, i=1,2,3

s0 = (s1+s2+s3)/3u = (s3-s0)/m

2

v = (s2-s1)/m2

-1.2 < u < 1.2

Mk

p1

p2

p3

Matrix Element (K± 3)|M(u,v)|2 ~ 1 + g±u + hu2 + kv2

CP Violation:Ag = (g+-g-)/(g++g-)≠0

Charged mode is statistically favored (~4:1)but neutral mode has a larger absolute value of g:• gc = -0.2154 ± 0.0035 (K± ±+-)

• gn = 0.652 ± 0.031 (K± ±)

If acceptances are equal for K+ and K-, Ag can be extracted by a linear fit

N(u,K+,Bup) = R(u) = N(1+g+u)/(1+g-u) ~ N(1+2gAgu)

N(u,K-,Bdown)

If acceptances are equal for K+ and K-, Ag can be extracted by a linear fit

N(u,K+,Bup) = R(u) = N(1+g+u)/(1+g-u) ~ N(1+2gAgu)

N(u,K-,Bdown) Direct CP violation @ NA48/2 3

Asymmertry: Theory Vs. Experiment

Theoretical predictions for Ag:

(2~4) ·10-4 Belkov(1989-1995)(2.3± 0.6) · 10-6 Maiani (1995)~ 10-5 Scimemi (2003)A

gc=A

gn · [1+O( )] = A

½/A

3/2 ~ 1/20

Experimental Results:BNL(1970): A

gc= (-7.0±5.3) · 10-3

FNAL, HyperCP (2000): Ag

c= (2.2±1.5±3.7) · 10-3 (Choong, PhD

Thesis)

Protvino, ISTRA+: Ag

n= (-0.3±2.5) · 10-3 (Denisov, Frontier Science

2002)

NA48/2 goalA

g < 2·10-4


NA48/2 Beam Line

114m decay volume

Beams steered to coincide within <1mm at DCH1

Simultaneous K+ and K- focused beams with momentum 60±3 GeV/c

z

y

1.3·1011p/s


NA48/2 Detectors

Main detector components:

•Kabes (MicroMega TPC)1mm stripsMax rate: 2MHz/strip

X = 50 m (drift) Y = 80 m (strips) t = 0.7 ns

•Magnetic spectrometer (4 DCHs): p/p(KBS) p/p(DCH) ~ 1% (60 GeV K)

•Liquid Krypton EM calorimeter (LKr) E/E = 3.2%/E 9%/E 0.42%

•Hadron calorimeter, photon vetos, muon veto counters


NA48 Strategy for Ag

Spectrometer magnet current inversion: every 24h (every ~3h in 2004)Achromat magnet current inversoin: every 7 days

BASIC PRINCIPLE OF THE MEASUREMENT(K+,B up/down) and (K-,B down/up) acceptances are equal and cancel out in the

ratio.

Deviations from the principle

● Bup ≠B

down Imperfect field inversion Hall probes to measure magnet field

● Non inversable mag. field (Earth field and res. magn. of the beam iron pipe) Measured in spring 2003 (10-4 p

kick), corrected at software level.

● Imperfect K+ K- beams coaxiality Acceptance cut around COG position.● Since UP and DOWN conditions are realized at different time, time instability right-left asymetric of detectors or trigger is dangereus. Direct CP violation @ NA48/2 7

Track Momentum Correction● and corrections applied:

P=p(1+)(1+qbp)P – corrected track momentum

p – observed track momentum

q – charge of the track

b – sign of magnetic field

● : corrects the magnetic field by putting the value (M+

3+M3)/2 to PDG value of K mass

● : corrects the misalignment (DCHs relative movement) by putting the difference between M+

3 and M3 to zero

Day-sample

b(M3-M+

3), keV

70 mDCH shift

K±±+-


Kaon spectra and StatisticsK±±+-

Events

Events K+

K-

M3π, GeV/c2

Mass Resolution: 1.7 MeV

ALLK-K+

720

120

290

310

1120400ALL

19070SS3

450160SS2

480170SS1

Events per supersample (in 106)


Acceptance CancellationsK±±+-

Physical asymmetries:● AS → slope of ratio N(K+,B

up)/N(K-,B

down)

● AJ → slope of ratio N(K+,B

down)/N(K-,B

up)

Apparatus-induced asymmetries: ● A+ → slope of ratio N(K+,B

up)/N(K+,B

down)

● A- → slope of ratio N(K-,B

up)/N(K-,B

down) Z

axis

(beam

dir

ect

ion)

Sale

ve

Jura

X axis

Top view of the setup

ASJ = (AS+AJ)/2 physics asymmetry

A± = (A++A-)/2 = (AS-AJ)/2 asymmetry induced by experimental setup

[ many of the effects observed in A± cancel in ASJ ]


Asymmetry Stability Vs. K momentum

K±±+-

Statistical error of A : 2,7.10-4 Statistical error of Ag: 2,7.10-4

2/ndf 6/11

ASJ + offset = 0 ± 0,117.10-3

2/ndf 6,7/11

A = (0,131 ± 0,117).10-3

PK, GeV/c PK, GeV/c

AS+offsetAJ+offset

A+A-

(AS+AJ)/2 + offset

(A++A-)/2


Asymmetry Stability Vs. TimeK±±+-

2/ndf 5,6/12

2/ndf 13,5/12AS+offsetAJ+offset

A+A-

(AS+AJ)/2 + offset

(A++A-)/2

Day-sample pair Day-sample pair

Day-sample pairDay-sample pairDirect CP violation @ NA48/2 12

Conclusions

● More than109 K±±+- decays in 1 month of 2003 data taking● The statistical error of Ag at this level of analysis is 2.7·10-4

● Major sources of systematics identified, up to now the error dominated by statistics.

● About 4·107 K±±00 decays have been collected. Very early stage of analysis of the CP-violation in this mode

● The statistical error of Ag is about 5·10-4

● RUN 2004, 60 days of data taking are on progress.

● NA48/2 is NOT only direct CP violation, many other interesting analysis on progress

Ke2

, Ke3

, Ke4

,

K±±+-

K±±


Documents

Status of A g measurement in NA48/2 DA NE 2004 Luca Fiorini Scuola Normale Superiore and INFN Pisa on behalf of NA48/2 collaboration: Cambridge, CERN,