Leonid AFANASYEV JOINT INSTITUTE FOR NUCLEAR RESEARCH

1. Last results of DIRAC experiment at CERN Leonid AFANASYEV JOINT INSTITUTE FOR NUCLEAR RESEARCH on behalf of the DIRAC collaboration NEW TRENDS IN HIGH-ENERGY PHYSICS September 23 – 29, 2013 Alushta, Crimea, Ukraine

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 SINP of Moscow State UniversityMoscow, Russia INFN-Laboratori Nazionali di FrascatiFrascati,Italy IHEPProtvino, Russia University of MessinaMessina, Italy Santiago de Compostela UniversitySantiago de Compostela,Spain KEKTsukuba, Japan Bern University Bern,Switzerland Kyoto UniversityKyoto, Japan Zurich University Zurich,Switzerland Kyoto Sangyo UniversityKyoto, Japan

3. Contents 1.Hadronic atoms and low-energy QCD predictions. 2. Method of pp and Kp atom investigation. 3. DIRAC setup. 4. Status of p+p- atom investigation. 5.Status of K+p-, K-p+ atom investigation. 6.Status of K+p-, K-p+ atom investigation. 7. Future of DIRAC at SPS CERN

4. 1. Hadronic atoms and low energy QCD predictions

5. π+ π0 π0 π Pionium lifetime 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 a0 and a2 are the  S-wave scattering lengths for isospin I=0 and I=2. If

6. K+ π0 K0 π K+π- andK-π+ atoms lifetime 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

7. ππ scattering lengths In ChPT the effective Lagrangian, which describes the  interaction, is an expansion in (even) terms: (tree) (1-loop) (2-loop) Colangelo et al. in 2001, using ChPT (2-loop) & Roy equations: These results (precision) depend on the low-energy constants (LEC) l3 and l4: Lattice gauge calculations from 2006 provided values for these l3 and l4. Because l3 and l4 are sensitive to the quark condensate, precision measurements of a0, a2 are a way to study the structure of the QCD vacuum.

8. Lattice calculations of l3 , l4 • 2006: l3, l4 First lattice calculations • 2012: 10 collaborations: 3 USA, 5 Europe, 2 Japan • J. Gasser, H. Leutwyler: Model calculation (1985) l3=2.62.5, Dl3/l3 1 • Lattice calculations in near future will obtain Dl3/l3 0.1 or Dl3 0.2-0.3 • To check the predicted values of l3 the experimental relative errors of pp-scattering lengths and their combinations must be at the level (0.2-0.3)%

9. ππ scattering ChPT predicts s-wave scattering lengths: The expansion of Mp2 in powers of the quark masses starts with the linear term: where is the quark condensate, reflecting the property of QCD vacuum. The estimates indicate values in the range 0 < l3 < 5 Measurement of l3 improved the value of

10. πK scattering lengths I. ChPT predicts s-wave scattering lengths: V. Bernard, N. Kaiser, U. Meissner. – 1991 A. Roessl. – 1999 J. Bijnens, P. Dhonte, P. Talavera. – April 2004 II. Roy-Steiner equations: P.Büttiker et al. − 2004

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

12. 2. Method of π+π−and Kπ atom observation and investigation

13. Method of π+π−atom observation and investigation Target Ni 98 m π+ p A2π (nA) Atomic pairs 24 GeV/c (NA) π− Interaction point π+ Coulomb pairs (NC) p π− 24 GeV/c ,,,… π+ π+ p Non-Coulomb pairs π− 24 GeV/c η, η’,… π+ Interaction point π0 π+ Atomic pairs p Accidental pairs 24 GeV/c π− p

14. Method of Kπ atom observation and investigation

15. Coulomb pairs and atoms For the charged pairs from the short-lived sources and small relative momentum Q there is strong Coulomb interaction in the final state. This interaction increases the production yield of the free pairs with Q decreasing and creates atoms. p+p-, K+p-, K-p+, K+K-, p+m-, p-m+ (p+p-), (K+p-), (K-p+), (K+K-), (p+m-), (p-m+) Coulomb pairs Atoms There is precise ratio between the number of produced Coulomb pairs (NC) with small Q and the number of atoms (NA) produced simultaneously with these Coulomb pairs:

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

17. 3. DIRAC setup

18. Experimental setup 1 Target station with Ni foil; 2 First shielding; 3 Micro Drift Chambers; 4 Scintillating Fiber Detector; 5 Ionization Hodoscope; 6 Second Shielding; 7 Vacuum Tube; 8 Spectrometer Magnet;9 Vacuum Chamber;10 Drift Chambers;11 Vertical Hodoscope; 12 Horizontal Hodoscope; 13 Aerogel Čerenkov; 14 Heavy Gas Čerenkov; 15 Nitrogen Čerenkov; 16 Preshower;17 Muon Detector

19. Experimental conditions

20. Published results on π+π- atom lifetime and scattering length * theoretical uncertainty included in systematic error

21. 4. Status of π+π−atom investigation

22. π+π−atoms – run 2008-2010 Run 2008-2010, statistics with low and medium background (2/3 of all statistics). Point-like production of all particles, the K+K-, pp admixture has not been take into account |QL| distribution analysis on |QL| and QT forQT < 4 MeV/c |QL| distribution analysis on |QL| forQT < 4 MeV/c Pbr (2001-2003) = 0.4460.0093

23. π+π−atoms – run 2008-2010 QT distribution analysis on |QL|, QT for |QL| < 2 MeV/c QT distribution analysis on |QL|, QT for |QL| > 2 MeV/c

24. π+π−pair analysis

25. π+π−data Statistics for measurement of |a0-a2| scattering length difference and expected precision * There is 1/3 of the data with a higher background whose implication will be investigated.

26. 5.a. Status of K−π+atom investigation

27. K−π+atoms – run 2008-2010 Run 2008-2010, statistics with low and medium background (2/3 of all statistics). Point-like production for all particles. |QL| distribution analysis on |QL| for QT < 4 MeV/c |QL| distribution analysis on |QL| and QT forQT < 4 MeV/c

28. K−π+ pair analysis

29. 5.b. Status of K+π−atom investigation

30. K+π- atoms – run 2008-2010 Run 2008-2010, statistics with low and medium background (2/3 of all statistics). Point-like production for all particles. |QL| distribution analysis on |QL| for QT < 4 MeV/c |QL| distribution analysis on |QL| and QT forQT < 4 MeV/c

31. K+π−pair analysis

32. K−π+ and K+π−pairs analysis

33. The first measurements of Кπ atom lifetime and Кπ scattering lengths Basing on 17849detected atomic pairs and 65342produced atoms we get the first preliminary results. The first measurements of Кπ atom lifetime! The first measurements of Кπ scattering lengths! Preliminary

34. 6. Searchfor long-lived states of π+π− atoms

35. Searchfor long-lived states of π+π− atoms During 2011-2012 the data were collected for observation of the long-lived states of π+π− atom. This observation opens the future possibility to measure the energy difference between ns and np states ΔE(ns-np) and the value of ππ scattering length combination |2a0+a2|. Magnetic field Foil of 2 µm Platinum Qt≈12 MeV/c for atomic pairs produced in the target Target of 100 µm Berylium Qt≤1,5 MeV/c for atomic pairs from long-lived atoms proton A2πbreakup point proton long-live A2π 100mm

36. Searchfor long-lived states of π+π− atoms Distribution of π +π− pairs over longitudinal component of relative momentum QL with polynomial-fitted background. The peak at zero at the level of 5σ is expected to be originate form breakup of the long-lived π +π− atoms inside the Platinum foil of 2 µm placed at 100mm behind the primary target. preliminary

37. 7. Future of DIRAC at SPS CERN.

38. Experiment DIRAC at SPS CERN In first half of 2013 DIRAC setup has been dismantledfromthe experimental hall of PS CERN. All detectorsarestoredforusing in thefutureexperiment. DIRAC collaboration is planning to continue investigation of π–K+, π+K–and π+π– atoms at SPS accelerator at CERN. The correspondent gains in production rates of these atoms at SPS relative to PS (450 GeV vs. 24 GeV) are 18, 24 and 12. This allows to increase significantly the collected data and to check the precise prediction of Low-Energy QCD at a higher accuracy. Now the collaboration is planning to submit the Letter of Intend for study πKand π+π– atoms at SPSto SPSC CERN in the beginning of 2014.

39. Yield of AKπ per one p-Ni interaction Yield of AKp dependence as a function of the atoms angle production and momentum in L. S. Bin = 9.6 MeV/c.

40. Yield of AπK per one p-Ni interaction Yield of ApK dependence as a function of the atoms angle production and momentum in L. S. Bin = 9.6 MeV/c.

41. Yield of A2π per one p-Ni interaction Yield of A2p dependence as a function of the atoms angle production and momentum in L. S. Bin = 15 MeV/c.

42. DIRAC prospects at SPS CERN

43. Thank you for your attention!

44. Supplementary slides

45. Experimental conditions (run 2008-2010)

46. Experimental conditions

47. Analysis of multiple scattering in Ni (100 μm) Run 2011. Analysis of multiple scattering in Ni (100 µm). Only events with one track in each projection were analyzed. δθ/θ ~ 0.7 %. After including in the analysis of all available events the statistics will be doubled and the expected value will be less than 0.5 %.

48. A2p and ApK production

49. Break-up dependencies Pbr of atom lifetime for K+π- atom (Akπ) and K-π+ atom (AπK) Probability of break-up as a function of lifetime in the ground state for ApK (solid line) and AKp atoms (dashed line) in Ni target of thickness 108 mm. Average momentum of AKp and ApK are 6.4 GeV/c and 6.5 GeV/c accordingly.

50. Break-up dependencies Pbr from the target thickness for K+p- atom (AKp) and K-p+ atom (ApK) Probability of break-up as a function of Ni target thickness for ApK (solid line) and AKp atoms (dashed line), t1S = 3.7•10-15 s. Average momentum of AKp and ApK are 6.4 GeV/c and 6.5 GeV/c accordingly.