1. EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH CERN Geneva, Switzerland Czech Technical University Prague, Czech Republic Institute of Physics ASCR Prague, Czech Republic Ioannina University, Greece INFN - Laboratori Nazionali di Frascati Frascati, Italy Trieste University and INFN-Trieste Italy KEK Tsukuba, Japan Kyoto Sangyou University Japan UOEH-Kyushu Japan Tokyo Metropolitan University Japan National Institute for Physics and Nuclear Engineering IFIN-HH Bucharest, Romania JINR Dubna, Russia Skobeltsyn Institute for Nuclear Physics of Moscow State University Moscow, Russia IHEP Protvino, Russia Santiago de Compostela University Spain Basel University Switzerland Bern University Switzerland 75 Physicists from 17 Institutes CERN-SPSC-2004-009 SPSC-P-284 Add. 4 12 April, 2004 L. Nemenov 27 April 2004 LIFETIME MEASUREMENT OF AND ATOMS TO TEST LOW ENERGY QCD Addendum to the DIRAC Proposal

2.  The proposed experiment is the further development of the current DIRAC experiment at CERN PS. It aims to measure simultaneously the lifetime of  +  - atoms (A 2  ), to observe  K atoms (A  K ) and to measure their lifetime using 24 GeV proton beam PS CERN and the upgraded DIRAC setup.  The precision of A 2  lifetime measurement will be better than 6% and the difference |a 0 - a 2 | will be determined within 3% or better.  The accuracy of A  K lifetime measurement will be at the level of 20% and the difference |a 1/2 -a 3/2 | will be estimated at the level of 10%.  The pion-pion and pion-kaon scattering lengths have never been verified by experimental data with the sufficient accuracy. For this reason the proposed measurements will be a crucial check of the low energy QCD predictions and our understanding of the nature of the QCD vacuum.  The observation of the long-lived (metastable) A 2  states is also considered with the same setup. This will allow us to measure the energy difference between ns and np states and to determine the value of 2a 0 +a 2 in a model-independent way. L. Nemenov 27 April 2004

3. perturbative QCD: L QCD (q,g) interaction  „weak“ (asympt. freedom): expansion in coupling Check only L sym chiral sym. & break: L eff (GB: ,K,  ) interaction  „strong“ (confinement) - but: expansion in energy Check L sym as well as L break-sym q-condensate QFD QCD QED Standard Model Q>>Q<< LOW energy (large distance) HIGH energy (small distance) L. Nemenov 27 April 2004

4. ChPT predicts s-wave scattering lengths: Chiral expansion of the  mass: (1)  scattering L. Nemenov 27 April 2004

5. A2A2 * is a metastable atom small angle     + + External beam p For p A = 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  43 cm 4p  170 cm L. Nemenov 27 April 2004 Target Z Thickness Μm BrΣ (l ≥1) 2p 0 3p 0 4p 0 Σ (l =1, m = 0) 041004.45%5.86%1.05%0.46%0.15%1.90% 06505.00%6.92%1.46%0.51%0.16%2.52% 13205.28%7.84%1.75%0.57%0.18%2.63% 2859.42%9.69%2.40%0.58%0.18%3.29% 78218.8%10.5%2.70%0.54%0.16%3.53% Probabilities of the A 2π 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)

6. L. Nemenov 27 April 2004 Rosselet et al. CERN, 1977 Pislak et al. E865/BNL, 2001/03 1) using Roy eq. 2a) 2c) 2b) using Roy eq. & same method as in 2b: Colangelo, Gasser, Leutwyler, 2001 > 94% 

7. L. Nemenov 27 April 2004 I. ChPT predicts s-wave scattering lengths:  K scattering V. Bernard, N. Kaiser, U. Meissner. – 1991 J. Bijnens, P. Talaver. – April 2004 A. Rossel. – 1999 II. Roy-Steiner equations: III. A  K lifetime: J. Schweizer. – 2004

8. L. Nemenov 27 April 2004 In the 60’s and 70’s set of experiments were performed to measure πK scattering amplitudes. Most of them were done studying the scattering of kaons on protons or neutrons, and later also on deuterons. The kaon beams used in these experiments had energies ranging from 2 to 13 GeV. The main idea of those experiments was to determine the contribution of the One Pion Exchange (OPE) mechanism. This allows to obtain the πK scattering amplitude. Analysis of experiments gave the phases of πK-scattering in the region of 0.7 ≤ m(πK) ≤ 2.5 GeV. The most reliable data on the phases belong to the region 1 ≤ m(πK) ≤ 2.5 GeV.  K scattering, experimental results The measurement of s-wave πK scattering length would test our understanding of chiral SU(3) L  SU(3) R symmetry breaking of QCD ( u, d and s ), while the measurement of ππ scattering length checks only SU(2) L  SU(2) R symmetry breaking ( u, d ). This is the main difference between ππ and πK scattering! What new will be known if  K scattering length will be measured?

9. Schematic top view of the DIRAC spectrometer. Upstream of the magnet: microstrip gas chambers (MSGC), scintillating fiber detectors (SFD), ionization hodoscopes (IH) and shielding of iron. Downstream of the magnet, in each spectrometer arm: drift chambers (DC), vertical and horizontal scintillation hodoscopes (VH, HH), gas Cherenkov counter (Ch), preshower detector (PSh) and, behind the iron absorber, muon detector (Mu). L. Nemenov 27 April 2004

10. Schematic top view of the updated DIRAC spectrometer. Upstream of the spectrometer magnet: microdrift chambers (MDC), scintillating fiber detectors (SFD), ionization hodoscopes (IH). Downstream of the magnet, in each spectrometer arm: drift chambers (DC), vertical and horizontal scintillation hodoscopes (VH, HH), gas Cherenkov counters (Ch), preshower detector (PSh) and, behind the iron absorber, muon detector (Mu). In the left arm: Aerogel Cherenkov counters. L. Nemenov 27 April 2004

11. present shielding new shielding L. Nemenov 27 April 2004

12.  Size of sensitive area: 50  50 mm2  SciFi used: KURARAY SCSF-78, 0.28 mm ø.  Number of SciFi layers/bundle: 7  Thickness of the bundles: 3 mm ( 1% X 0 )  Fiber pitch: 0.205 mm  Number of channels: 240(X) + 240(Y)  Number of PSPM(H6568): 15(X) + 15(Y) L. Nemenov 27 April 2004

13. Yield of  +, K + and p at the proton energy of 24 GeV/c, in arbitrary units (T.Eichten and D.Haidt Nucl. Phys. B44 (1972) 333) Targetθ, mrdGeV/c  + + K + p  /K + p/K + Cu87452.96.2524.88.54.0 Cu87618.62.8220.26.67.2 Cu127427.84.0217.96.94.5 Cu12766.381.209.305.37.7 L. Nemenov 27 April 2004

14. AtomsYields 11.0·10 -10 0.52·10 -10 0.29·10 -10 0.81·10 -10 Table 1: Yields of detected A  and A  K ( N A per one p-Ni interaction). Yield of A  K for the reaction p + Ni→A  K + X (left figure for  - K + and right for  + K - ) at the proton energy E p =24 GeV as a function of the atom momentum. Yellow histogram shows A  K emitted into the angular aperture of the secondary channel. Green histogram refers to the atoms detected by the DIRAC setup. Yield of A 2  in the upgraded setup for the reaction p + Ni→ A 2  + X at the proton energy E p =24 GeV as a function of the atom momentum. Yellow histogram shows A 2  emitted into the angular aperture of the secondary channel. Green histogram refers to atoms detected by the DIRAC setup. L. Nemenov 27 April 2004

15. Trajectories of  - and K + from the A  K break up The numbers to the right of the tracks lines are the  - and K + momenta in GeV/c. The A  K,  - and K + momenta are shown in the table in the upper left corner. L. Nemenov 27 April 2004

16. Side view of the target station and the new shielding 1. The target station, the shielding and the rectangle vacuum tubes (initial part of the secondary particle channel and part of the proton tube) are cut along the proton beam. The secondary beam and a collimator for the secondary beam are shown. The small permanent magnet is visible in vacuum between the target station and shielding. L. Nemenov 27 April 2004

17. 1.Single–multilayer targets decrease the systematic errors. 2.Identification of e ±,  ±, K ± and p 3.Increasing of statistics and efficiency of the setup  Shielding K ≈ 1.9  Formation of time structure of the spill with the trigger of setup  Microdrift chambers  New electronics for SFD  Increase in the aperture on VH hodoscope and PSH  Total K ≈ 4 L. Nemenov 27 April 2004

18. Cost estimation for A 2  and A  K experiment Setup upgrading Vacuum channel and shielding: 20 kCHF Micro Drift Chambers: 18 kCHF Electronics for SFD (960 channels): 210 kCHF Drift Chambers: 30 kCHF Electronics for VH (72 channels): 20 kCHF Scintillation counters (8 counters): 20 kCHF Aerogel detectors(2 detectors): 48 kCHF Upgrade of the existing Cherenkov counters: 20 kCHF Gas Cherenkov counters with heavy gas (2 counters): 52 kCHF Preshower detector: 30 kCHF Trigger and Readout system: 100 kCHF _______________________________________________ Overall cost of the setup upgrading: 568 kCHF It is 16% from the cost of the existing DIRAC setup Cost of the existing DIRAC setup Setup: 3.5 MCHF Electronics rented from CERN pool: 0.4 MCHF 3.9 MCHF L. Nemenov 27 April 2004

19.  Microdrift Chambers with readout electronics JINR Dubna, Bazel;  Scintillating Fiber Detector Japanese group, INFN–Trieste, IHEP Protvino;  Ionization Hodoscope IHEP Protvino;  Drift Chambers with readout electronics JINR Dubna;  Vertical Hodoscope Santiago de Compostela University;  Horizontal Hodoscope IHEP Protvino;  Preshower Detector IFIN–HH Bucharest;  Cherenkov Counters INFN Frascati  Muon Counters IHEP Protvino;  Trigger and DAQ JINR Dubna with the support of the collaboration. L. Nemenov 27 April 2004

20. Manufacture of all new detectors and electronics: 18 months Installation of new detectors: 3 months 2006 Upgraded setup test and calibration: 4 months Observation A 2  in the long-lived states. 2007 and 2008 Measurement of A 2  lifetime: 10 months In this time 66000  atomic pairs will be collected to estimate A 2  lifetime with precision of: In the same time we also plan to observe A  K and to detect 5000  K atomic pairs to estimate A  K lifetime with precision of: This estimation of the beam time is based on the A 2  statistics collected in 2001-2003 and on the assumption of having 2.5 spills per supercycle during 20 hours per day. Time scale for the A 2  and A  K experiment L. Nemenov 27 April 2004

21. (2001) G. Colangelo, J. Gasser and H. Leutwyler   E2 ≈  0.56 eV L. Nemenov 27 April 2004  Energy Splitting between np – ns states in (  + -   ) atom For n = 2 a 0 = 0.220 ± 0.005 a 2 =  0.0444 ± 0.0010 21  Annihilation  Annihilation: A 2  →  0 +  0 1/ 1/τ=W ann ~ (a 0 – a 2 ) 2  Measurement of τ and  E allows one to obtain a 0 and a 2 separately

22. L. Nemenov 27 April 2004 1.Goals of the experiment 2.Theoretical motivation 3.  scattering 4.  K scattering 5.Metastable atoms 6.Present setup and the upgrades 7.Efficiency gain 8.Cost estimate of the setup upgrade and sharing responsibilities 9.Time scale for the experiment