Л. Афанасьев ОИЯИ от коллаборации ДИРАК

1. Точноеизмерениевременижизни+−атома в эксперименте ДИРАК Л.Афанасьев ОИЯИ от коллаборации ДИРАК Workshop on Precision Physics and Fundamental Physical Constants Всероссийское совещание по прецизионной физике и фундаментальным физическим константам Дубна, 1-4 декабря

2. DIRAC collaboration CERN Geneva, Switzerland Tokyo Metropolitan University Tokyo,Japan Czech Technical University Prague, Czech Republic IFIN-HHBucharest, Romania Institute of Physics ASCR Prague, Czech Republic JINRDubna, Russia Nuclear Physics Institute ASCR Rez, Czech Republic IHEP Protvino, Russia INFN – Laboratori Nazionali di Frascati Frascati,Italy SINP of Moscow State University Moscow, Russia Trieste University and INFN-TriesteTrieste,Italy Santiago de Compostela UniversitySantiago de Compostela,Spain Bern University Bern,Switzerland University of MessinaMessina, Italy KEKTsukuba, Japan Zurich University Zurich,Switzerland Kyoto Sangyou UniversityKyoto, Japan

3. Pionium lifetime π+ π0 π0 π Pionium (A2) is a hydrogen-like atom consisting of + and -mesons: EB=-1.86 keV, rB=387 fm, pB≈0.5 MeV The lifetime of +− atoms is dominated by the annihilation process into 0 0: * *Gasser et al (2001) Uretsky 1961; Bilenkiy 1969 a0 and a2 are the  S-wave scattering lengths for isospin I=0 and I=2.

4. Theoretical Status In ChPT the effective Lagrangian which describes the pp interaction is an expansion in (even) terms: 1966Weinberg (tree): 1984Gasser-Leutwyler (1-loop): 1995Knecht et al. (2-loop): 1996Bijnens et al. (2-loop): 2001Colangelo et al. (& Roy): And the theoretical results for the scattering lengths up to 2-loops are: These results (precision) depend on the low-energy constants (LEC) l3 and l4. Because l3 and l4 are sensitive to the quark condensate, precise measurements of a0, a2 are a way to study the structure of the QCD vacuum. Lattice gauge calculations from 2006 provided values for these l3 and l4.

5. Coulomb pairs.They are produced in one proton nucleus collision from fragmentation or short lived resonances and exhibit Coulomb interaction in the final state Non-Coulomb pairs.They are produced in one proton nucleus collision. At least one pion originates from a long lived resonance. No Coulomb interaction in the final state Accidental pairs.They are produced in two independent proton nucleus collision. They do not exhibit Coulomb interaction in the final state Production of pionium Atoms are Coulomb bound state of two pions produced in one proton-nucleus collision Nemenov 1985 Background processes:

6. Method of A2π observationand lifetime measurement (A2π) is too small to be measured directly. E. m. interaction of A2π in the target: A2π → π+π− Q < 3MeV/c, Θlab< 3 mrad Target Ni 98 m π+ p A2π “atomic pairs” (nA) (NA) 24 GeV/c π− π+ Coulombfrom short-lived sources (NC) p π− NA = K(Q0) NC(Q<Q0) with known K(Q0) ,… 24 GeV/c Breakup probability: Pbr=nA/NA π+ π+ p non-Coulombfrom long-lived sources π− 24 GeV/c η, η’,… π+ π0

7. Lifetime and breakup probability The Pbr value depends on the lifetime value, t. To obtain the precise Pbr(t) curve a large differential equation system must be solved: where s is the position in the target, pnlm is the population of a definite hydrogen-like state of pionium. The anlmn´l´m´ coefficients are given by: if nlmn´l´m´, snlmn´l´m´beingthe pionium-target atom cross section, N0 the Avogadro Number, r the material density and A its atomic weight. The detailed knowledge of the cross sections (Afanasyev&Tarasov; Trautmann et al) (Born and Glauber approach) together with the accurate solution of the differential equation system permits us to know the curves within 1%.

8. Break-up probability Cross section calculation precision 0.6% Solution of the transport equations provides one-to-one dependenceof the measured break-up probability (Pbr) on pionium lifetime τ dt=10% dPbr =4% All targets have the same thickness in radiation lengths 6.7*10-3 X0 There is an optimal target material for a given lifetime

9. ISO-VIEW SIDE-VIEW

10. DIRAC experimental setup 2007 10

11. DIRAC Spectrometer Setup features: angle to proton beam =5.7 channel aperture =1.2·10–3 sr magnet 2.3 T·m momentum range 1.2p7 GeV/c Thin targets: ~ 7 ×10–3 X0, Nuclear efficiency: 3 ×10−4 resolution on relative momentum QX≈ QY≤0.3 MeV/c,  QL≈0.5 MeV/c Proton beam ~ 1011 proton/spill

12. Analysis based on MC Atoms are generated in nS states using measured momentum distribution for short-lived sources. The atomic pairs are generated according to the evolution of the atom while propagating through the target Background processes: Coulomb pairs are generated according to AC(Q)Q2 using measured momentum distribution for short-lived sources. Non-Coulomb pairs are generated according to Q2 using measured momentum distribution for long-lived sources.

13. Atomic pairs MC

14. Atomic pairs (2001)

15. Lifetime of Pionium Result from DIRAC: ChPT prediction: Phys. Lett. B 619 (2005) 50-60; hep-ex/0504044

16. Experimental results 2001-2003

17. Experimental results 2001-2003

18. DIRAC preliminary results with GEM/MSGC QL distribution ←All events ←After background subtraction

19. DIRAC preliminary results with GEM/MSGC QT distribution ←After background subtraction for QL<2MeV/c QL<2 MeV/c QL>2 MeV/c

20. DIRAC Experimental results A2πlifetime 2005 DIRAC(PL B619, 50) ...based on 2001 data (6530 observed atoms) 2008 DIRAC(SPSC 22/04/08) ...major part 2001-03 data (13300observed atoms) Including GEM/MicroStripGasChambers => number of reconstructed events is 18000 => the statistical error in |a0-a2| is 3%, and the expected full error is <5%.

21. Comparison with other experimental results K3: 2006 NA48/2(PL B633, 173) ...with ChPT constraint between a0 and a2: 2009NA48/2(seminar at CERN) ...without constraint (a2 free): ...with ChPT constraint between a0 and a2:

22. Comparison with other experimental results Ke4: 2008NA48/2(EPJ C54, 411) ...without constraint (a2 free): 2009NA48/2(seminar at CERN) ...without constraint (a2 free): ...with ChPT constraint between a0 and a2:

23. a0-a2 DIRAC 2008 G.Colangelo 2009

24. K+π− and K−π+ atoms lifetime K+ π0 K0 π K-atom (AK) is a hydrogen-like atom consisting of K+ and −mesons: EB= -2.9 keV rB = 248 fm pB ≈ 0.8 MeV The K-atom lifetime (ground state 1S), =1/is dominated by the annihilation process into K00: * * J. Schweizer (2004) From Roy-Steiner equations: If

25. K scattering lengths I. ChPT predicts s-wave scattering lengths: V. Bernard, N. Kaiser, U. Meissner. –1991 A. Rossel. – 1999 J. Bijnens, P. Talaver. – April 2004 II. Roy-Steiner equations: P.Büttiker et al. − 2004

26. K scattering What new will be known if K scattering length will be measured? The measurement of the s-waveπKscattering lengths would test our understanding of the chiralSU(3)L SU(3)Rsymmetry breaking of QCD(u, dandsquarks),while the measurement of ππ scattering lengths checks onlythe SU(2)L SU(2)Rsymmetry breaking(u, dquarks). This is the principal difference betweenππandπKscattering! Experimental data on the πK low-energy phases are absent

27. Trajectories of π− and K+ from the AKπ break-up The numbers to the right of the tracks lines are the πand K+momentain GeV/c The AKπ, π−and K+momentaare shownin the following table:

28. Upgraded DIRAC experimental setup Modifided parts

29. π−K+and π+K−atom signal In total: 173±54 K-atomic pairs are observed with a significance of 3.2. B. Adeva et al.,“Evidence for πK-atoms with DIRAC”, Physics Letters B 674 (2009) 11 Y. Allkofer, PhD Thesis, Universität Zürich, 2008.

30. QL-distribution for K+π− pairs from 2007 data QT -distribution for K+π− background pairs from 2007 data

31. QL-distribution for π+π− pairs from 2008 data QL-distribution for π+K− pairs from 2008 data QL-distribution for K+π− pairs from 2008 data

32. Results of 2009 The comparison of the events collected in years 2008 and 2009 in the DIRAC experiment. The time correlated events were selected by the cuts in the transverse and longitudinal components Qx, Qy and QL :

33. Metastable Atoms For pA = 5.6 GeV/c and  = 20 1s = 2.9 × 10 15 s , 1s = 1.7 × 10 3 cm 2s = 2.3 × 10 14 s , 2s = 1.4 × 10 2 cm 2p = 1.17 × 10 11 s , 2p = 7 cm 3p  23 cm 4p  54 cm 2μ 100μ Illustration for observation of the A2πlong-lived states with breaking foil.

34. Energy splitting between np - ns states in + atom  E2 ≈  0.56 eV For n = 2 (1979) A. Karimkhodzhaev and R. Faustov (2000) D. Eiras and J. Soto (1983) G. Austen and J. de Swart (2004) J. Schweizer, EPJ C36 483 (1986) G. Efimov et al.A. Rusetsky, priv. comm. (1999) A. Gashi et al.

35. Metastable Atoms Probabilities of the A2π breakup (Br) and yields of the long-lived states for different targets provided the maximum yield of summed population of the long-lived states:Σ(l ≥ 1)

36. Prospects of DIRAC Creation of an intense source of ππ, πKand other exotic atoms at SPS proton beam and using them for accurate measurements of all S-wave ππandπKscattering length to check the precise low energy QCD predictions

37. Yields of atoms at PS and SPS DIRAC prospects at SPS CERN 37

38. DIRAC prospects at SPS CERN Present low-energy QCD predictions forππand πKscattering lengths …will be improved by Lattice calculations K …will be significantly improved by ChPT Planned results of DIRAC ADDENDUM at PS CERN after 2008-2009 2010-2011 Observation of metastable π+π− atoms and study of a possibility to measure its Lamb shift. Study of the possibility to observe K+K− and atoms using 2008-2009 data. DIRAC at SPS CERN beyond 2011

39. Thank you for your attention