EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

1. LIFETIME MEASUREMENT OF AND ATOMS TO TEST LOW ENERGY QCD Addendum to the DIRAC Proposal L. Nemenov 27 April 2004 CERN-SPSC-2004-009 SPSC-P-284 Add. 4 12 April, 2004 EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH CERNGeneva, Switzerland Czech Technical UniversityPrague, Czech Republic Institute of Physics ASCRPrague, 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

2. Goals of the experiment L. Nemenov 27 April 2004 • The proposed experiment is the further development of the current DIRAC experiment at CERN PS. It aims to measure simultaneously the lifetime of +  - atoms (A2), 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 A2 lifetime measurement will be better than 6% and the difference |a0 - a2| will be determined within 3% or better. • The accuracy of A K lifetime measurement will be at the level of 20% and the difference |a1/2-a3/2| 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) A2 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 2a0+a2 in a model-independent way.

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

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

5. Metastable atoms 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 is a metastable atom small angle  * A2 +   External beam p L. Nemenov 27 April 2004 For pA = 5.6 GeV/c and  = 20 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)

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

7. L. Nemenov 27 April 2004 K scattering 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: III. AK lifetime: J. Schweizer. – 2004

8. L. Nemenov 27 April 2004 K scattering, experimental results 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 theseexperiments had energies ranging from2 to 13 GeV. The main idea of those experiments was to determine the contribution of the One PionExchange (OPE) mechanism. This allows to obtain the πK scattering amplitude. Analysis of experiments gave the phases of πK-scatteringin the region of 0.7≤m(πK) ≤ 2.5 GeV. The most reliable data on thephases belong to the region 1 ≤m(πK) ≤ 2.5 GeV. What new will be known ifK scattering length will be measured? The measurement of s-waveπKscattering length would test our understanding of chiral SU(3)L SU(3)Rsymmetry breaking of QCD (u, dand s), while the measurement of ππ scattering length checks only SU(2)L SU(2)Rsymmetry breaking(u, d). This is the main difference betweenππ and πK scattering!

9. Present DIRAC setup L. Nemenov 27 April 2004 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).

10. Upgraded DIRAC setup L. Nemenov 27 April 2004 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.

11. Counting rates without and with the new shielding L. Nemenov 27 April 2004 present shielding new shielding

12. Prototype of high resolution SFD L. Nemenov 27 April 2004 • 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% X0) • Fiber pitch: 0.205 mm • Number of channels: 240(X) + 240(Y) • Number of PSPM(H6568): 15(X) + 15(Y)

13. Aerogel and gas Cherenkov counters L. Nemenov 27 April 2004 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)

14. Atom yields in to upgraded DIRAC setup L. Nemenov 27 April 2004 Table 1: Yields of detected A and A K(NA per one p-Ni interaction). Yield of A2 in the upgraded setup for the reaction p + Ni→ A2 + X at the proton energy Ep=24 GeV as a function of the atom momentum. Yellow histogram shows A2 emitted into the angular aperture of the secondary channel. Green histogram refers to atoms detected by the DIRAC setup. Yield of A K for the reaction p + Ni→A K+ X (left figure for  -K+ and right for  +K-) at the proton energy Ep=24 GeV as a function of the atom momentum. Yellow histogramshows A K emitted into the angular aperture of the secondary channel. Green histogram refers to the atoms detected by the DIRAC setup.

15. L. Nemenov 27 April 2004 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.

16. Side view of the target station and the new shielding L. Nemenov 27 April 2004 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.

17. Efficiency gain L. Nemenov 27 April 2004 • Single–multilayer targets decrease the systematic errors. • Identification of e±,  ±, K ± and p • Increasing of statistics and efficiency of the setup • Shielding K ≈ 1.9 • Formation of time structure of the spillwith the trigger of setup • Microdriftchambers • New electronics for SFD • Increase in the aperture on VH hodoscopeand PSH • Total K ≈ 4

18. L. Nemenov 27 April 2004 Cost estimation for A2 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

19. Responsibilities L. Nemenov 27 April 2004 • 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.

20. L. Nemenov 27 April 2004 Time scale for the A2 and AK experiment Manufacture of all new detectors and electronics:18 months Installation of new detectors:3 months 2006 Upgraded setup test and calibration:4 months Observation A2 in the long-lived states. 2007 and 2008 Measurement of A2lifetime:10 months In this time 66000  atomic pairs will be collected to estimate A2lifetime with precision of: In thesame time we also plan to observeA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 A2 statistics collected in 2001-2003 and on the assumption of having 2.5 spills per supercycle during 20 hours per day.

21. Why to observe the long-lived states (2001)G. Colangelo, J. Gasser and H. Leutwyler  E2 ≈  0.56 eV L. Nemenov 27 April 2004 • Annihilation: A2→ 0 + 0 1/τ=Wann~ (a0 – a2)2 • Energy Splitting between np – ns states in ( + -  ) atom For n = 2 a0 = 0.220 ± 0.005 a2 =  0.0444 ± 0.0010 • Measurement of τ and E allows one to obtain a0 and a2separately 21

22. L. Nemenov 27 April 2004 Outline • Goals of the experiment • Theoretical motivation • scattering • Kscattering • Metastable atoms • Present setup and the upgrades • Efficiency gain • Cost estimate ofthe setup upgrade and sharing responsibilities • Time scale for the experiment