1. 1 Lessons of  physics at LEP Anatoly Sokolov, IHEP Protvino February 28, 2006 e+e- collisions from  to , Novosibirsk

2. 2 OUTLINE  Kinematics of two-photon interactions  Extraction of  collision events at LEP and B-factories experiments  Two-photon event statistic for the low invariant mass range (W<4.5 GeV)  Study of some special two-photon reactions at LEP  Summary

3. 3 Two-photon collisions Q 2 = -q 1 2 = 2  E 1  E 1  ( 1 - cos  1 ) P 2 = -q 2 2 = 2  E 2  E 2  ( 1 - cos  2 ) W 2 = (  i E i ) 2 - (  i P i ) 2  The final state can be: 1. Lepton pairs 2. A single resonant state 3. A non-resonant hadronic state 

4. 4 The two-photon events can be classified as: 1. Non-tagged events (Q 2 ~ P 2 ~ 0)  Both scattered e  are lost in the beam pipe  Both photons are quasi-real.  We can study:   tot of  collisions  Inclusive Charm and Beauty Production  Single particle and Dijet production  Resonances 2. Single-tagged events (Q 2 >> P 2 ~ 0)  Only one scattered electron is detected.  One photon is highly virtual and the other is quasi-real  Q 2 is well measured  We can study:  Photon structure functions  The photon-meson transition form factor

5. 5 The two-photon events can be classified as: 3. Double-tagged events (Q 2, P 2 >> 0)  Both scattered electrons are detected.  Q 2 and P 2 are well measured.  W 2  can be measured directly  No unfolding  We can study:  Cross section of  collisions  BFKL Pomeron  Virtual photon structure function

6. The LEP Experiments The LEP Accelerator e + e - collisions at  s  91 GeV (LEP I),  s = 167-207 GeV (LEP II) Integrated luminosity ~150 pb -1 /experiment (LEP I), ~700 pb -1 /experiment (LEP II) The dominant interactions at LEP II are two-photon processes LEP II is the best place to study two-photon physics (high energy, high cross section, low background)

7. The KEKB/Belle Experiment The KEKB Accelerator e + e  collisions at  s  10.6 GeV The world-highest luminosity 1.58  10 34 cm -2 s -1 and integrated luminosity ~500 fb -1 The Belle Detector Excellent energy/momentum resolutions and particle-separation capabilities The cross sections observable there e + e   (4S)  BB --- 1.1 nb e + e   qq (uds) --- 2.1 nb e + e   cc --- 1.2 nb e + e      --- 0.9 nb   hadrons (W  >0.8GeV) --- ~1 nb (within the acceptance) visible

8. 8 Experiment  s ee GeV  Ldt pb -1  nb N ev CLEO II 11 3000 1 3  10 6 TPC/2  29 69 4 3  10 5 PLUTO 35 45 5 2  10 5 LEP I 91 150 * 4 10 9  10 5 LEP II 198 700 * 4 15 1  10 7 Belle 10.6500 000 1 5  10 8 LEP II advantages  ( e + e   e + e  h) rises with  s e+e   bkg ~ 1/s   hadrons events and background events are more separated Disadvantages detector acceptance and trigger efficiency is reduced  ( e + e   e + e  hadrons) for different experiments Belle advantages high event statistic big detector acceptance Disadvantages   hadrons events and background events are less separated Acceptance dependent

9. 9 Two-photon interaction kinematic (1) Photon flux LEP II  s =200 GeV =8.6 GeV LEP I  s =91 GeV =5.4 GeV Belle, Babar  s =10.6 GeV = = 1.8 GeV u(d)u(d ) cc bb ss - - - cc  c0 bb W  < 40 GeV W  < 90 GeV W  < 4.5 GeV Belle, BaBar – resonances, low multiplicity states (W  <4.5 GeV ~ ) LEP – high virtual photon study (W  < 90 GeV ~ ) --

10. 10 Two-photon interaction kinematic (2) Detection efficiency of  events Background from e + e – annihilation events LEP II  s =200 GeV LEP I  s =91 GeV Belle  s =10.6 GeV Belle  s =10.6 GeV Belle  s =10.6 GeV LEP II  s =200 GeV LEP I  s =91 GeV LEP I, LEP II Low W  (<4.5 GeV)  (Belle)   (LEP) trigger eff.

11. 11 Resonance production in  interactions   resonance  hadrons Measure the product of resonance two-photon width and branching fractions  (R   )  B(R  hadronic final state) Internal (electromagnetic) structure of the resonance Tests of qq–meson models, perturbative/non-perturbative QCD Search for new resonance (C=+) states Collision of two quasi-real photons (Q 2 <0.001GeV 2 ) with W  =0.8 -4.5 GeV Exclusive processes

12. 12 Low multuplicity hadronic states production in  interactions Tests of qq–meson models, perturbative/non-perturbative QCD Collision of two quasi-real photons (Q 2 <0.001GeV 2 ) with W  =0.8 - 4.5 GeV Exclusive processes Event Selection Two-photon  Exclusive event p t -balance -- p t < 0.1 GeV/c in the e + e - CM frame Exclusive requirement bkg. Charmonium signal at Belle

13. 13 Event statistic of exclusive two-photon interactions      / K + K - Belle  Ldt = 87.7 fb -1 N(  +  - ) = 20 000 N(K + K - ) = 9 700 N(  +  - )/fb = 230 N(K + K - )/fb = 110 DELPHI  Ldt = 480 pb -1 N(  +  - ) = 3 100 N(K + K - ) = 220 N(  +  - )/fb = 6460 N(K + K - )/fb = 460 Test of models (S.J.Brodsky and G.P.Lepage; M.Diel, P.Kroll and C.Vogt)

14. 14 Event statistic of exclusive two-photon interactions  pp Belle  Ldt = 89 fb -1 N(pp) = 19 200 N(pp)/fb = 216 L3  Ldt = 667 pb -1 N(pp) = 990 N(pp)/fb = 1480 ---- - Test of models (three quarks; quark-diquark; handbag) Also study of  ,   0  0,… reactions --

15. 15 Event statistic of two-photon resonance production   c  K + K -  +  - Belle  Ldt = 280 fb -1 N(  c  2K2  ) = 1287  185 N(  c )/fb = 4.5 L3  Ldt = 610 pb -1 N(  c  2K2  ) = 30  10 N(  c )/fb = 50  

16. 16 Resonances studied at LEP M.N. Kienzle-Focacci, L3 ~20-25% ~25-40% ~10-25%

17. 17  4 , 2K2 , 4K. Results of G     Br Process Present G(eV) previous (PDG2004) direct indirect Upper limits – 95%CL obtained by the  2 fits Indirect: G indir (R  X) = G(R  A)  Br(R  X)/Br(R  A) R  A - normalization process G/Br(  c  KsK  ), G/Br(  c0  ), G/Br(  c2  J  )   - measured only in limited channels S.Uehara Belle (preliminary) ~15% ~12% ~11%

18. 18 Exclusive reactions   0  0,   +  - (LEP) L3 non-tagged events (0 < Q 2 < 0.02 GeV 2 ) + single-tagged events (0.2 GeV 2 < Q 2 < 30 GeV 2 )  Ldt=850 pb -1 N untag (  +  -  +  - ) ~ 75000 N tag (  +  -  +  - ) ~ 1900 N untag (  +  -  0  0 ) ~ 7500 N tag (  +  -  0  0 ) ~ 760 1.1 GeV < W  < 3 GeV  0  0 n = 2.9  0.14  +  - n = 2.3  0.15 GVDM

19. 19   cross section  The relative magnitude of  +  - and  0  0 production changes in the vicinity of Q 2  1GeV 2  different  -pair productions mechanisms at low and high Q 2.  The Q 2 dependence of the process   0  0 is well reproduced by parametrisation based on GVDM model over the region Q 2 > 0.2GeV 2.  +  - data cannot be satisfactory described by such a parametrisation in the whole Q 2 range. preliminary  The discrepancy between the   0  0 cross section in the low Q 2 range measured by PLUTO and L3.

20. 20 J/  Inclusive J/  production in two-photon collisions (LEP II, DELPHI) J/  e + e -   e + e -     e + e -  J/  X a sensitive tool for the gluon distribution in the photon Main contribution VDM “Resolved”

21. 21 J/  Inclusive J/  production in two-photon collisions (LEP II, DELPHI) N ch  4 3 GeV < W vis < 35 GeV E T (char) > 3 GeV  Ldt=617 pb -1 DELPHI N ev = 274 000 + 2 muons (2 GeV/c < p  < 20 GeV/c) N(  +  - )  100

22. 22 J/  Inclusive J/  production in two-photon collisions (LEP II, DELPHI) Results of the fit: M = 3.119  0.008 GeV  = 0.035  0.007 GeV N obs = 36  7 Fit by the form Result: f = (74.0  22.0)% J/   (e + e -   e + e -  J/  X) = (25.2  10.2) pb J/  (74  22)% of the observed J/  are due to “resolved” photons

23. 23 Open charm and beauty production in two-photon collisions - D* tagging used for extracting the open charm cross section Muon and electron spectra global fit gives the open c and b cross section A naive increase of beauty QCD cross section gives an excess of charm  (e + e -   e + e - cc)  1000 pb (  10%)  (e + e -   e + e - bb)  13 pb (  30%) -

24. 24 Summary  The possibility to extract  -collisions at e + e - collider experiments increases logarithmically with. At LEP this possibility is only a few time higher than at B(c-,  -)-factories.  The study of two-photon interactions at high energy e + e - collisions (LEP) has advantages because of the enlarged kinematical range of these reactions.  For the low invariant mass range (W<4.5(2) GeV) B(c-,  -)-factories have advantages because of much higher luminosities than LEP.  Two-photon interactions at B(c-,  -)-factories give a possibility for detail study of dynamic of hadron production at invariant mass range W<4.5(2) GeV. These interactions are a powerful tool for precision measurement of resonance parameters, search for new low-lying resonance states.

25. 25 Summary  c,  c0,  c2 in all the decay channels of        , K + K      and K + K  K + K  are observed.   c (2S) is not seen in any of these channels.  f 2 f 2, K*K*,  are observed in these decays (some of these are new).  Preliminary results for  Br were obtained.  (  c )  B(  c  …) are systematically smaller by about factor 3 in comparisons to previous experiments (although they are still not inconsistent).  for  c0,  c2 was measured  in the  c0,  c2     , K + K  decay modes.  Preliminary result for Br(  c  ) was obtained (first measurement ).  Helicity angle analysis of J/  → pp decay was performed.  Upper limit for the Br(B +  h c K + )  BR(h c   c ) was obtained.  Evidence of a signal from the  (4S)   (1S)     decay was observed. Preliminary result for the corresponding branching ratio  was obtained.

26. 26 Background

27. 27 Hadronic F 2 : e + e   e + e  hadrons  F 2 = F 2 + F 2  PLhadr QPM VDM, non-perturbative QCD Resolved , perturbative QCD F 2 : peaks at large x, include cc, bb PL F 2 : main part at small x hadr

28. 28 Hadronic F 2 : Components  At high x  Quark constituents are dominant At low x  Gluon constituents are dominant The low x region is sensitive to the gluon density

29. 29 F 2 : Kinematic region  The Q 2 ranges from 1 GeV 2 to 3000 GeV 2 The x ranges down to 0.001 at low Q 2

30. 30 F 2,QCD : W vis  Extract F 2,QCD from differential cross section.  Due to detector acceptance and efficiency W vis < W   Unfolding  Improve W vis  Use kinematics of e tag  Use unfolding for x rec  x

31. 31 The Present Study (  s=10.5-10.6GeV,  Ldt=280fb -1 )   c          ”4  ”  c0 K + K       ”2K2  ”  c2 K + K  K + K   ”4K”   c (2S) Event Selection Two-photon  Exclusive 4-prong event p t -balance -- p t < 0.1 GeV/c in the e + e - CM frame (Exclusive requirement)   /K separation - combined information from (CDC+ACC+TOF)

32. 32 Distributions of four-meson invariant masses We observe  c (2980)  c0 (3415), and  c2 (3555) in all the decay channels,  c (2S)  (3650)is not significantly seen in any of these channels.  c   c0  c2 44 2K2  4K misidentified  (2S)

33. 33  c   c0  c2 Fits of the invariant-mass distributions 44 2K2  4K Fit: background – 2 nd -order polynomial charmonium –  c,  c0 --- finite  and fixed  M  to MC  c2 --- assume  is negligibly small (  ~2MeV  comparing  to  M Preliminary

34. 34 Study of two-meson resonances in their decays Searches for resonance components decaying into , K , KK resonances The intervals  c – 50MeV,  c0 – 50 MeV,  c2 – 30MeV  0     f 2 (1270)     K* 0 (892)  K +     K + K  f 2 ’(1525)  K + K  etc. Sideband-subtraction technique Watch distributions in “signal  sideband”

35. 35 Resonance signals Uppers: crosses: signal region, histo  : sideband regions Lowers: signal – sideband=charmonium contribution K* 0  K  in  c2  2K2  KK in  c0  4K M(K  ) (GeV)  0 f 2 (1270)  in  c  4  M(  ) (GeV)

36. 36 Results of G   Br (each decay mode) Preliminary Process Present G(eV) previous (PDG2004) direct indirect Upper limits – 95%CL obtained by the  2 fits Indirect: G indir (R  X) = G(R  A)  Br(R  X)/Br(R  A) R  A - normalization process G/Br(  c  KsK  ), G/Br(  c0  ), G/Br(  c2  J  )   - measured only in limited channels

37. 37 Charmonium  c0,  c2 seen (The first observations in these reactions)   (  c0 ) = 2.62  0.23(stat.)  0.31(syst.)  0.24(Br) keV   (  c2 ) = 0.44  0.07(stat.)  0.05(syst.)  0.05(Br) keV   (  cJ ) = N  M 2 (  cJ )/ [4  (2J+1)   2  L  (M cJ )    Br(  cJ  M + M - )   ℒ dt] Charmonium production in      / K + K - Belle PLB 615, 39 (2005) Based on Belle’s 87.7fb –1 data

38. 38 Primary event selection  There is exist a (ch+ch-)-pair with a M(ch+ch-)>9 GeV/c 2  Standard Belle hadronic event selection criteria N(tot) = 206700 N(     )  = 124500 (~60%) Search for  (4S)  (1S)  +  - decay Motivation: search for new bottomonium states, transitions. Data sample: 357 fb -1, Υ (4s) 386  10 6 BB – on-resonance 40 fb -1 – off-resonance  (1S)     

39. 39 Event selection            X  M(      >9 GeV/c 2 (e + e -      X )-events with M(e + e -  >9 GeV/c 2 are put down by the Belle trigger  10.5 GeV < Evis < 12.5 GeV  cos  < 0.95 reduce the bkg. e + e -  e + e -    (1S) ,   e + e -, e  are identified as   N(         X  = 957           X M(     , GeV M(fit)=9448.2  3.7 MeV  = 62.4  3.4 MeV  2 /NDF=0.59 M(  (1S)(PDG)=9460.30  0.26 MeV

40. 40 Resonance decays in the  (1S)      state on-resonance 9.4 GeV < M  <9.52 GeV Distribution of  M=[M          - M     )  off-resonance  M, GeV  M 21 =M(  (2S)) –M(  (1S))  M 31 =M(  (3S)) –M(  (1S))  M 41 =M(  (4S)) –M(  (1S))  M 21 =M(  (2S)) –M(  (1S))  M 31 =M(  (3S)) –M(  (1S))

41. 41 Peak parameters  M, GeV 1 st peak  (2S)  (1S)  +  - 2 nd peak  (3S)  (1S)  +  - 3 d peak  (4S)  (1S)  +  -  M=562.0  0.1 MeV  = 2.1  0.2 MeV  2 /NDF = 1.4  M(PDG) = 562.96  0.41 MeV  M=893.5  0.2 MeV  = 2.8  0.2 MeV  2 /NDF = 1.8  M=1119.0  1.4 MeV  = 5.9  1.5 MeV  2 /NDF = 0.5  M(PDG) = 894.9  0.56 MeV  M(PDG) = 1120.  3.5 MeV

42. 42 Invariant mass of the     system M(     , GeV 1 st peak  (2S)  (1S)  +  - 2 nd peak  (3S)  (1S)  +  - 3 d peak  (4S)  (1S)  +  - Bkg. Moxhay model PR D39 (1989)3497 Yan model PR D22 (1980) 1652 Yan model

43. 43 Branching fraction of the  (4S)   (1S)     decay Br(  (4S)   (1S)     ) = N obs /[N tot    Br(  (1S)      )]  N tot = 386  10 6 Br(  (4S)   (1S)  +  - ) = = (1.1  0.2(stat.)  0.4(syst.))  10 -4   = 0.035 Systematic - matrix element ~ 8% Belle hadronic event cut ~ 35%  Br(  (1S)      ) = 0.0248  (  (4S)   (1S)     ) = (2.26  0.41  0.80) keV  (  (2S)) = 8.1 keV  (  (3S)) = 1.2 keV Preliminary N peak = 48 N bkg. = 10 N  (4S) = 38  6.9 (after bkg. subtraction) 3 d peak  (4S)  (1S)  +  -  M, GeV  M=1119.0  1.4 MeV  = 5.9  1.5 MeV  2 /NDF = 0.5  M(PDG) = 1120.  3.5 MeV evidence of a signal (  5.5  )

44. 44 Open charm and beauty production in two-photon collisions - D* tagging used for extracting the open charm cross section Muon and electron spectra global fit gives the open c and b cross section A naive increase of beauty QCD cross section gives an excess of charm  (e + e -   e + e - cc)  1000 pb (  10%)  (e + e -   e + e - bb)  13 pb (  30%) -

45. 45 Open charm and beauty production in two-photon collisions p T of the  candidate with respect to the closest jet 2 distinct kinematical regions  Ldt=463 pb -1 N ev = 651 DELPHI N bb = 118  26  (e + e -   e + e - bb) = 14.9  3.3(stat.)  3.4(syst.) pb -

46. 46 J/  Inclusive J/  production in two-photon collisions (LEP II, DELPHI)  (Diffr.) = (1.79  0.07) %  (Res.) = (6.79  0.16) % The overall efficiency  = (3.93 )% +2.18 -1.03 J/   (e + e -   e + e -  J/  X) = (25.2  10.2) pb J/  (74  22)% of the observed J/  are due to “resolved” photons