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Status of A g measurement in NA48/2

Status of Direct CP violation measurement in K ±  3 p @ NA48/2. Status of A g measurement in NA48/2. Status of A g measurement in NA48/2. DA F NE 2004 L uca Fiorini Scuola Normale Superiore and INFN Pisa on behalf of NA48/2 collaboration:

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Status of A g measurement in NA48/2

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  1. Status of Direct CP violationmeasurement in K±3p@NA48/2 Status of Ag measurement in NA48/2 Status of Ag measurement in NA48/2 DAFNE 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

  2. Direct CP violation @ NA48/2 2 Main Goal and Data samples • 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

  3. Lorentz-invariants si = (PK-Pi)2, i=1,2,3 s0 = (s1+s2+s3)/3 u = (s3-s0)/m2 v = (s2-s1)/m2 -1.2 < u < 1.2 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) Measurement Principles Kinematics Dynamics p1 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± ±00) Mk p3 p2 Direct CP violation @ NA48/2 3

  4. Asymmertry: Theory Vs. Experiment • Theoretical predictions for Ag: • (2~4) ·10-4Belkov(1989-1995) • (2.3± 0.6) · 10-6Maiani (1995) • ~ 10-5Scimemi (2003) • Agc=Agn · [1+O( w)] w= A½/A3/2 ~ 1/20 • Experimental Results: • BNL(1970): Agc= (-7.0±5.3) · 10-3 • FNAL, HyperCP (2000):Agc= (2.2±1.5±3.7) · 10-3 (Choong, PhD Thesis) • Protvino, ISTRA+: Agn= (-0.3±2.5) · 10-3(Denisov, Frontier Science 2002) • NA48/2 goal • dAg < 2·10-4 Direct CP violation @ NA48/2 4

  5. NA48/2 Beam Line Simultaneous K+ and K- focused beams with momentum 60±3 GeV/c Beams steered to coincide within <1mm at DCH1 1.3·1011p/s 114m decay volume y z Direct CP violation @ NA48/2 5

  6. NA48/2 Detectors Main detector components: • Kabes (MicroMega TPC) 1mm strips Max rate:2MHz/strip D X = 50 mm(drift) D Y = 80 mm(strips) D t = 0.7 ns • Magnetic spectrometer (4 DCHs): Dp/p(KBS) Dp/p(DCH) ~ 1% (60 GeV K) • Liquid Krypton EM calorimeter (LKr) DE/E = 3.2%/E  9%/E  0.42% • Hadron calorimeter, photon vetos, muon veto counters Direct CP violation @ NA48/2 6

  7. NA48 Strategy for Ag Spectrometer magnet current inversion: every 24h (every ~3h in 2004) Achromat magnet current inversoin: every 7days 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 ≠Bdown 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 pkick), 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

  8. K±±+- 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 betweenM+3andM3to zero b(M3-M+3), keV 70 m DCH shift Day-sample Direct CP violation @ NA48/2 8

  9. K±±+- K+ Events Mass Resolution:1.7 MeV M3π, GeV/c2 K+ K- ALL SS1 310 170 480 Events K- SS2 290 160 450 SS3 120 70 190 ALL 720 400 1120 Kaon spectra and Statistics Events per supersample (in 106) Direct CP violation @ NA48/2 9

  10. K±±+- ASJ = (AS+AJ)/2physics asymmetry A± = (A++A-)/2 = (AS-AJ)/2asymmetry induced by experimental setup [ many of the effects observed in A± cancel in ASJ ] Acceptance Cancellations Physical asymmetries: • AS → slope of ratio N(K+,Bup)/N(K-,Bdown) • AJ → slope of ratio N(K+,Bdown)/N(K-,Bup) Apparatus-induced asymmetries: • A+ → slope of ratio N(K+,Bup)/N(K+,Bdown) • A-→ slope of ratio N(K-,Bup)/N(K-,Bdown) Top view of the setup Saleve Jura Z axis (beam direction) X axis Direct CP violation @ NA48/2 10

  11. K±±+- 2/ndf 6/11 ASJ + offset = 0 ± 0,117.10-3 AS+offset AJ+offset Statistical error of Ag: 2,7.10-4 Statistical error of A : 2,7.10-4 2/ndf 6,7/11 A = (0,131 ± 0,117).10-3 A+ A- Asymmetry Stability Vs. K momentum (AS+AJ)/2 + offset PK, GeV/c PK, GeV/c (A++A-)/2 Direct CP violation @ NA48/2 11

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

  13. K±±+- K±±00 Conclusions • More than109K±±+-decays in 1 month of 2003 data taking • The statistical error of Ag at this level of analysis is2.7·10-4 • Major sources of systematics identified, up to now the error dominated by statistics. • About 4·107K±±00decays have been collected. Very early stage of analysis of the CP-violation in this mode • The statistical error of Ag is about5·10-4 • 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 , p+gg , p+0g , ..... Direct CP violation @ NA48/2 13

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