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Results from DIRAC

Results from DIRAC. LIFETIME MEASUREMENT OF PIONIUM. Collaboration DIRAC (DImeson Relativistic Atom Complex)  cern.ch/DIRAC. Pionium lifetime of O (femtosecond) Pionium detection / lifetime measurement Magnetic double arm spectrometer at PS Data taking and results Summary.

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Results from DIRAC

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  1. Results from DIRAC LIFETIME MEASUREMENT OF PIONIUM Collaboration DIRAC (DImeson Relativistic Atom Complex)  cern.ch/DIRAC • Pionium lifetime of O(femtosecond) • Pionium detection / lifetime measurement • Magnetic double arm spectrometer at PS • Data taking and results • Summary Important items: CD2003 10/09/03 JS

  2. Pionium lifetime

  3. Motivation for DIRAC Experimental aspects Theoretical aspects • atomic physics @ high energy • measure lifetime @ order of 10-15 s • study of QCD @ low energy • π π scattering: theory ahead of experiment

  4. Theoretical motivation Physics behind DIRAC: p-p atom (pionium) QCD & EM interplay Some keywords: Non-perturbative QCD  chirality spontaneous breakdown  Goldstone Boson pp scattering ChPT/EFT:

  5. Pionium lifetime ...in the framework „QCD including photons“: • Workshops „HadAtom01“, hep-ph/0112293 and „HadAtom02“, hep-ph/0301266 • J.Gasser, V.Lyubovitskij, A.Rusetsky, A.Gall, „Decays of the π+π- atom“, PR D64 (2001) 016008: DIRAC

  6. S-wave scattering lengths: (a0 , a2) plane • Roy equations only admit sol-  utions in the „universal band“. • The dot () indicates Weinberg‘s   leading order result. • The black ellipse represents the final result in SChPT. • The narrow band (LET) shows   the region allowed in GChPT. “universal band“ final 1-loop 2-loop • • l.o. Low Energy Theorem Reference:G.Colangelo, J.Gasser and H.Leutwyler, Nucl.Phys. B603 (2001) 125

  7. S-wave scattering lengths: (a0 , a2) plane E865 BNL: a0=0.216±6% • Roy equations only admit sol-  utions in the „universal band“. • The dot () indicates Weinberg‘s   leading order result. • The black ellipse represents the final result in SChPT. • The narrow band (LET) shows   the region allowed in GChPT. “universal band“ final 1-loop 2-loop • • l.o. Low Energy Theorem Reference:G.Colangelo, J.Gasser and H.Leutwyler, Nucl.Phys. B603 (2001) 125

  8. S-wave scattering lengths: (a0 , a2) plane ∆=0.260±5% E865 BNL: a0=0.216±6% • Roy equations only admit sol-  utions in the „universal band“. • The dot () indicates Weinberg‘s   leading order result. • The black ellipse represents the final result in SChPT. • The narrow band (LET) shows   the region allowed in GChPT. “universal band“ final 1-loop 2-loop • • l.o. Low Energy Theorem Reference:G.Colangelo, J.Gasser and H.Leutwyler, Nucl.Phys. B603 (2001) 125

  9. S-wave scattering lengths: condensate? SChPT: standard size condensate (chiral limit)  0 : (a0,a2) H.Sazdjian, PL B490 (2000) 203 SChPT GChPT: non-fixed condensate < 0 : (a0,a2)condensate size The band, delineated by the dotted lines, takes into account the estimated uncertainties (around 2.5%). Abbreviations: SChPT ... Standard Chiral Perturbation Theory GChPT ... Generalized ChPT

  10. 2 GeV/c < pA < 14 GeV/c A2π Target X Ni p (24 GeV/c) 11 p/spill CERN - PS: Ip ~ 10 Production of pionium A2p originates from short-lived sources (r,K*... ): [ L. Nemenov, SJNP 41 (1985) 629 ]

  11. 1) Annihilation decay length dec  20m  int (1S):Pann  0.38 3) Breakup (ionization)  „atomic pairs“ (nA): Pbr  0.47 • Q(CM) < 3 MeV/c • E+ = E- (3‰) & +- (mrad)  6/  0.35 Detection of pionium Fate of produced relativistic A2p Use thin & dense target  100m Ni: 2) Excitation . . . . . discrete (dsc) states

  12. A in matter 2π DIRAC o π o π + + π π - π Detection of pionium  our GOAL! + π A2p ann. - π A2p break-up π-

  13. is compared with : Pionium lifetime measurement ? There exists a precise relation between NA and the total number NC of Coulomb pairs with small Q :

  14. Pionium lifetime measurement Probability: A2pbreakup in targets dt=10% dPbr =4%

  15. DIRAC Spectrometer Downstream detectors: DC, VH, HH, C, PS, MU. Upstream detectors: MSGC, SFD, IH.

  16. DIRAC Spectrometer Setup features angle to p beam: =5.7 channel aperture: =1.2 msr magnet: 2.2 T·m momentum range: 1.2p7 GeV/c resolution on relative momentum: QX= QY=0.4 MeV/c & QL=0.6 MeV/c

  17. π+π- pairs detected with DIRAC N1,N4 N3 N2nC N2C from fit for Q > 4MeV/c ( without atomic pairs )  and N2[atomic pairs]

  18. N N 1231349 Entries Entries 40000 568804 30000 6000 20000 4000 10000 2000 0 0 0 2.5 5 7.5 10 12.5 15 17.5 20 -20 -15 -10 -5 0 5 10 15 20 Q Q Accidental Accidental L N N 642993 30000 Entries Entries 10000 306068 20000 7500 10000 5000 2500 0 0 0 2.5 5 7.5 10 12.5 15 17.5 20 -20 -15 -10 -5 0 5 10 15 20 Q Q Real Real L N N 1500 1000 2000 500 1000 0 0 0 2.5 5 7.5 10 12.5 15 17.5 20 -20 -15 -10 -5 0 5 10 15 20 Q Q Atomic pairs L Atomic pairs Ni 2001 data QT < 3MeV/c dashed curves…only free pairsobtained from the shape with Q>4MeV/c (QL>2MeV/c) red histograms…Monte Carlo data SIGNAL

  19. N N < N (|Q | 1.5) = 5542. ± 504. < N (|Q | 1.5) = 2376. ± 476. A L 4000 A L 2000 3500 Ni 2001 Ni 2002 24GeV 3000 1500 2500 1000 2000 1500 500 1000 500 0 0 0 2.5 5 7.5 10 12.5 15 17.5 20 0 2.5 5 7.5 10 12.5 15 17.5 20 |Q | |Q | L L N < N (|Q | 1.5) = 12280 ± 680 A L 8000 Ni 2000-2003 6000 4000 2000 0 0 2.5 5 7.5 10 12.5 15 17.5 20 |Q | L Nickel 2000-2003 • Strong selection criteria: • clean sample of more than 12‘000 „atomic“ π+π- pairs 

  20. br P Ni2001 0.5 Preliminary 0.4 0.3 1 2 3 4 5 6 7 8  Breakup probability vs. pionium lifetime 0.6 94µm Ni ChPT  = (2.9±0.1) fs

  21. N = N - N s m N 1000 800 600 † 400 200 0 -200 0 2.5 5 7.5 10 12.5 15 17.5 20 | (MeV/c) |Q L Ni2002+03: Difference Single - Multi layer minus Single & Multi layer target data Multi layer target (98m Ni): Segmented target consisting of 12 foils with 1 mm gap between each. The combined thickness of all foils is about equal to that of the single layer target. The single & multi layer target event distributions are the same in all respects but one: The multi layer target yields a lower number of dissociated (atomic) pairs due to annihilation in the interlayer gaps. The signal is extracted in one step from the difference between the single and multilayer distributions.

  22. The DIRAC 2-arm spectrometer provides a pair relative momentum (Q) resolution of 1MeV/c for Q < 30MeV/c. • The extracted signal sample consists of >12000 dissociated π+π-(atomic pairs) from π+π- atoms A2π. • The analysis of Ni 2001 data leads to a preliminary A2π lifetime: • Our final goal: • to improve on statistics  analyse full π+π- sample • to improve on systematics: • different analysis procedures • detailed study of multiple scattering • alternative experimental method by combining data from single - multi layer target arrangements Results from DIRAC - summary -

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