October 28, 2003V.Kekelidze 1 Experiment NA48/2 A Precision Measurement of Charged Kaon Decay Parameters (CERN/SPSC ) Status Report (SPSC ) CERN, Chicago, Dubna, Ferrara, Firenze, Mainz, Northwestern, Perugia, Pisa, Saclay, Torino, Vienna Cambridge, Edinburgh, Siegen Collaboration:
October 28, 2003V.Kekelidze 2 NA48 Collaboration (Pisa, September, 2003)
October 28, 2003V.Kekelidze 3 Report content Goals New beam line Set-Up upgrade Beam detector KABES Trigger Data taking in 2003 Asymmetry express analysis: - observable definition - major systematics estimation Ke4 & Rare decay examples Semileptonics Conclusions & beam request
October 28, 2003V.Kekelidze 4 Direct CP violation in K ± ± + -, K ± ± 0 0 (A g ) 10 – 4 (limited by statistics) Goals g + - g - A g = ———— g + + g - Requirements to experiment: high statistics (> 2 10 9 decays) stability in time set –up symmetry
October 28, 2003V.Kekelidze 5 K e4 to measure - scattering length ( ) < 1 10 2 required statistics > 10 6 (430k ) Rare decays to test PT & search for A CP K , K 0 DE K e + e , K + , K e2 K l l + l K 0 , K 0 l + l , … etc. Semileptonic decay Br’s: K e3, K 3 to improve precision of |V us | & check CKM unitarity Goals Goals (continuation)
October 28, 2003V.Kekelidze 6 Simultaneous K + and K - beam line (schematic vertical section) not to scale axes are steered to coincide within 1 mm
October 28, 2003V.Kekelidze 7 - =4.0, mm + =4.1, mm 0 =1.23 0.01, mm = 0.01, mm K-K- K-K- K+K+ Beam spots on the DCH x, mm +50 y, mm x, mm -50 achromat: K + Down (H D ) K+K+ K+K+ K+K+ K-K x, mm x, mm achromat: K + Up (H U )
October 28, 2003V.Kekelidze 8 New K12 beam line built for NA48/2 first achromat second achromat
October 28, 2003V.Kekelidze 9 Set-up Upgrade Beam detector KABES (TPC micromegas) 3 double stations + read-out: put in operation DCH3: fully instrumented DCH1- 4 read-out electronics: re-mapped to be Right –Left ( Saleve – Jura ) symmetric L2 trigger: new processors & interface to neutral part Decay vacuum tank: extended (+24 m) magnetic field remeasured Beam profile monitor: new pixel detector
October 28, 2003V.Kekelidze 10 Upgraded NA48 Set-Up (schematic top view) not to scale
October 28, 2003V.Kekelidze 11 KABES-1/2 entrance window K + time resolution 67 ps K - time resolution 63 ps T/2 ns, Station2 – Station3 Beam rate ~20 MHz P 0 /P(K) - P 0 /P(S) Momentum resolution 1.1% P(S), GeV/c P(K), GeV/c Beam rate ~20 MHz K +, K - X,Y space resolution ~100 m T/2 ns, Station2 – Station3 moved out by ~20 cm
October 28, 2003V.Kekelidze 12 Three stage logic for (satisfies K e4 ): pre-trigger: 2 tracks in Hod & no surrounding anti L2 processor (mass-box) 2 vertices (~ 94%) or 1 vertex (~ 98%) or “fake track” (excluding ± 0 mode ) (~99.5%) L3 software flags (to simplify splits) Trigger logic Logic for K ± ± 0 0 : pre-trigger: clusters in LKr Cal (Nx > 2 or Ny > 2) L2 “fake track” L3 flags + various triggers for: rare decays, semileptonics, efficiency study, random events,...
October 28, 2003V.Kekelidze 13 Stability of trigger efficiencies day-sample u 1% level trigger inefficiency 00 for K + + + - ( ) & K - - - + ( )
October 28, 2003V.Kekelidze 14 MNP33 current alternation each day (B U / B D ) swapping of achromat magnetic fields (H U / H D ) during each MD on Wednesday (due to long tuning procedure) data taking cycle two weeks - a supersample Running conditions to compensate variation in time of beam and set-up: more frequent alternation desirable (even on the expense of statistics) as learned from 2003:
October 28, 2003V.Kekelidze 15 Beam availability & supersamples SS-1 August 6- 20
October 28, 2003V.Kekelidze 16 Statistics for asymmetry Statistics of supersamples in raw K ± ± + - without acceptance cuts (not to scale to the Proposal) H D B U H D B D H U B U H U B D total total ~ 450 mln K ± ± + - events of SS-1 reprocessed for the express analysis in 10 6 ~ 50 millions of K ± ± 0 0
October 28, 2003V.Kekelidze 17 Reconstructed K ± ± + - P K, GeV/c K-K- 0 P GeV/c K+K+ 0 M(3 ) + GeV/c 2 K+K+ K-K- M(3 ) - GeV/c 2 ~120 mln ~220 mln SS-1 : day-samples samples H D H U
October 28, 2003V.Kekelidze 18 Dalitz for accepted u = (2M K /m 2 ) (M K /3 - E * ) M(u,v) 2 1 + g u + h u 2 + k v 2 v = (2M K /m 2 ) E * 2 Square of matrix element u v run 15323
October 28, 2003V.Kekelidze 19 N + (u) a + (u) (1 + g + u) N - (u) a - (u) (1 + g - u) A g = ————— if a + (u) = a - (u) - acceptance cancel R(u) = N + (u) / N - (u) ~ 1 + g u g = (g + - g - ) 2g A g R(0) = 1 - normalization g – < u < Definitions for asymmetry u = (2M K /m 2 ) (M K /3 - ) u = (m 2 2 -M 2 K /3) / m g + - g - g + + g - slope
October 28, 2003V.Kekelidze 20 u- spectra & their Ratios N+(u)N+(u)N - (u) R(u)R(u) (not normalized) statistics of SS-1 (each plot - one momentum bin) beam pipe cut
October 28, 2003V.Kekelidze 21 Observable: A S & A J - slopes of R(u) BU N+(u)BU N+(u) if a S (u) & a J (u) are stable in time t ~ 1 day A S = A J g A = 0.5 (A S + A J ) g if R a (u) = a S (u) / a J (u) is stable in time BU N-(u)BU N-(u) BD N+(u)BD N+(u) BD N-(u)BD N-(u) aS(u)aS(u) -acceptance aS(u)aS(u) ASAS aJ(u)aJ(u) aJ(u)aJ(u) A J
October 28, 2003V.Kekelidze 22 BU N+(u)BU N+(u) BU N-(u)BU N-(u) BD N+(u)BD N+(u) BD N-(u)BD N-(u) Systematic checks A+A+ t = 1 day A-A- AUAU ADAD R a (u) = a S (u) / a J (u): S a - slope A U g + S a ; A D g - S a if S a is stable in time A + + S a ; A - - S a ; (A + + A - )/ 2 0 -S a +S a -S a (A U + A D )/ 2 g
October 28, 2003V.Kekelidze 23 Selection criteria radial cuts around the beam centres (in DCH1,4) to symmetrize acceptances day-by-day definition of the beam COG’s in each momentum bin to reduce acceptance variations in time Conservative cuts: R (DCH1) > 11.5 cm R (DCH4) > 13.5 cm leave 60% of raw statistics ( beam stability dependent )
October 28, 2003V.Kekelidze 24 Spectrometer alignment M K – M PDG, KeV/c 2 ~ 35 KeV/c 2 ~4 m / day x DCH4 day-sample B U K + & B D K - ( to Jura ) B D K + & B U K - ( to Saleve) surprising effect time variation term was compensated (after fine tuning of B)
October 28, 2003V.Kekelidze 25 Acceptance cancellation check = (A + + A - )/ 2 = (1.2 2.3) 10 -4
October 28, 2003V.Kekelidze 26 Beam geometry effects A ± for different achromat polarities HDHD HUHU > 0 < 0
October 28, 2003V.Kekelidze 27 Time stability of acceptances in momentum bins
October 28, 2003V.Kekelidze 28 A stability with momentum
October 28, 2003V.Kekelidze 29 Time stability of acceptances HDHD HDHD HUHU HUHU different achromats
October 28, 2003V.Kekelidze 30 Time stability of A HDHD HUHU
October 28, 2003V.Kekelidze 31 Systematics summary Major systematics related to - acceptance asymmetry - time variation effects are under control Other possible systematics: - residual (+ Earth) magnetic fields - trigger efficiencies - DCH’s efficiencies - accidentals - ….. are found to be less significant
October 28, 2003V.Kekelidze 32 First look on K ± + - e ± events in SS-1 BR = (3.87 ± 0.20) ( PDG: (4.08 ± 0.09) ) 7 10 5 expected K ± + - e ± in 2003 Background ~1% of K e4 from K ± + - ± ~1% of K e4 from K ± ± 0 D M(3 ) GeV/c 2 P K, GeV/c K mass
October 28, 2003V.Kekelidze 33 Rare decay K Rare decay K e + e events in 1 month of data taking ~ 3500 events expected in 2003 run M e + e - GeV/c 2 Events / 2 MeV/c 2
October 28, 2003V.Kekelidze 34 Semileptonics study In addition, all major modes: leptonic & semi.. K e2, K e3, K 2, K 3 hadronic K 2 , K 3 are accumulated with min. bias trigger strong constraint for Br’s 0 (missing mass) 2, (GeV/c 2 ) example of K e selected from ~1700 burts
October 28, 2003V.Kekelidze 35 Conclusion NA48/2 experiment has been prepared: beam line, detector and trigger are put in operation & tuned the major systematics are under control & do not exceed statistical precision to reach the proposal goals quoted statistics are needed can profit from more Beam Request for 2004 as much proton time as possible (400 GeV protons ~1·10 12 ppp on T10) as few beam interruptions as necessary