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, Chicago, Dubna, Edinburgh, Ferrara, Firenze, Mainz, Northwestern, Perugia, Pisa, Saclay, Siegen, Torino, Vienna Status of Direct CP violation measurement in K ±  3

– Search for direct CP violation in: K ±  ±  +  - K ±  ±  0  0 – 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 ( K  3  with lost pion) ● June-July 2003 data with different systematic effects Main Goal and Data samples Direct CP NA48/22

Measurement Principles Kinematics Dynamics Lorentz-invariants s i = (P K -P  i ) 2, i=1,2,3 s 0 = (s 1 +s 2 +s 3 )/3 u = (s 3 -s 0 )/m  2 v = (s 2 -s 1 )/m  < u < 1.2 MkMk p1p1 p2p2 p3p3 Matrix Element (K ±  3  ) |M(u,v)| 2 ~ 1 + g ± u + hu 2 + kv 2 CP Violation: A g = (g + -g - )/(g + +g - )≠0 Charged mode is statistically favored (~4:1) but neutral mode has a larger absolute value of g: g c = ± (K ±  ±  +  - ) g n = ± (K ±  ±     ) If acceptances are equal for K + and K -, A g can be extracted by a linear fit N(u,K +,B up ) = R(u) = N(1+g + u)/(1+g - u) ~ N(1+2gA g u) N(u,K -,B down ) If acceptances are equal for K + and K -, A g can be extracted by a linear fit N(u,K +,B up ) = R(u) = N(1+g + u)/(1+g - u) ~ N(1+2gA g u) N(u,K -,B down ) Direct CP NA48/23

Asymmertry: Theory Vs. Experiment Theoretical predictions for A g : (2~4) · Belkov( ) (2.3 ± 0.6) · Maiani (1995) ~ Scimemi (2003) A g c =A g n · [1+O(  )]  = A ½ /A 3/2 ~ 1/20 Experimental Results: BNL(1970): A g c = (-7.0±5.3) · FNAL, HyperCP (2000): A g c = (2.2±1.5±3.7) · (Choong, PhD Thesis) Protvino, ISTRA+: A g n = (-0.3±2.5) · (Denisov, Frontier Science 2002) NA48/2 goal  A g < 2·10 -4 Direct CP NA48/24

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 1.3·10 11 p/s Direct CP NA48/25

NA48/2 Detectors Main detector components: Kabes (MicroMega TPC) 1mm strips Max 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 Direct CP NA48/26

NA48 Strategy for A g 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 ● B up ≠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 NA48/27

Track Momentum Correction ●  and  corrections applied: P=p(1+  )(1+qb  p) 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  +M  3  )/2 to PDG value of K mass ●  : corrects the misalignment (DCHs relative movement) by putting the difference between M + 3  and M  3  to zero Day-sample b(M  3  -M + 3  ), keV 70  m DCH shift K±±+-K±±+- Direct CP NA48/28

Kaon spectra and Statistics K±±+-K±±+- Events K+K+ K-K- M 3 π, GeV/c 2 Mass Resolution: 1.7 MeV ALLK-K ALL 19070SS SS SS1 Events per supersample (in 10 6 ) Direct CP NA48/29

Acceptance Cancellations K±±+-K±±+- Physical asymmetries: ● A S → slope of ratio N(K +,B up )/N(K -,B down ) ● A J → 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 direction) Saleve Jura X axis Top view of the setup A SJ = (A S +A J )/2 physics asymmetry A ± = (A + +A - )/2 = (A S -A J )/2 asymmetry induced by experimental setup [ many of the effects observed in A ± cancel in A SJ ] Direct CP NA48/210

Asymmetry Stability Vs. K momentum K±±+-K±±+- Statistical error of A : 2, Statistical error of A g : 2,  2 /ndf 6/11 A SJ + offset = 0 ± 0,  2 /ndf 6,7/11 A  = (0,131 ± 0,117) P K, GeV/c A S +offset A J +offset A+A+ A-A- (A S +A J )/2 + offset (A + +A - )/2 Direct CP NA48/211

Asymmetry Stability Vs. Time K±±+-K±±+-  2 /ndf 5,6/12  2 /ndf 13,5/12 A S +offset A J +offset A+A+ A-A- (A S +A J )/2 + offset (A + +A - )/2 Day-sample pair Direct CP NA48/212

Conclusions ● More than10 9 K ±  ±  +  - decays in 1 month of 2003 data taking ● The statistical error of A g at this level of analysis is 2.7 · ● Major sources of systematics identified, up to now the error dominated by statistics. ● About 4 · 10 7 K ±  ±  0  0 decays have been collected. Very early stage of analysis of the CP-violation in this mode ● The statistical error of A g is about 5 · ● RUN 2004, 60 days of data taking are on progress. ● NA48/2 is NOT only direct CP violation, many other interesting analysis on progress K e2, K e3, K e4,        K±±+-K±±+- K±±K±± Direct CP NA48/213