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HERMES: status and selected recent results

HERMES: status and selected recent results. Workshop on Hadron Structure and Spectroscopy Paris, 1-3 March 2004 K. Rith.  The quark helicity distributions  Transversity  The Pentaquark  +  DVCS  The tensor asymmetry A T and structure function b 1 d.

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HERMES: status and selected recent results

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  1. HERMES: status and selected recent results Workshop on Hadron Structure and Spectroscopy Paris, 1-3 March 2004 K. Rith  The quarkhelicity distributions  Transversity  The Pentaquark +  DVCS  The tensor asymmetryATand structure functionb1d

  2. TheHERMESSpectrometer

  3. TheHERMESSpectrometer

  4. The HERMES internal polarised atomic gas-target

  5. TheHERMES dual-radiator RICH Silica aerogel: n = 1.03, thresh = 4.2 C4F10: n = 1,0005, thresh = 32 1 0.5 0 PK Pp P 0.8 0.5 0 PKK PK PpK 0.8 0.5 0 Pp PKp Ppp 5 10 15 5 10 15 5 10 15 P (GeV)

  6. Quark helicity distributions, semi-inclusive asymmetries =E - E‘ z = Eh/ Leading hadron originates with large probability from struck quark D(z):= Fragmentation function

  7. Semi-inclusive asymmetries-1 In leading order: P.L. B 464 (1999) 123 zq2q(x)Dqh(z) A1h(x,z) = zq2q(x)Dqh(z) zq2q(x)Dqh(z) q(x) = zq‘2q‘(x)Dq‘h(z)q(x) Quark-‘Purity‘ Phq Different targets and hadrons h: Solve linear system for Q with A = (A1,p, A1,d, A1,p, A1,d, A1,pK ) A = PQ

  8. Semi-inclusive asymmetries from the Deuteron ,K, p asymmetries identified with RICH PionsKaons P.R.L.92 (2004) 012005  Statistics sufficient for 5-parameter-fit Q(x) = (u(x)/u(x), d(x)/d(x), u(x)/u(x), d(x)/d(x), s(x)/s(x) )

  9. Purities (Probability that observed hadron originates from quark of type f) Kaons have about 10% sensitivity to the strange sea  Adequate degree of orthogonality: Shaded bands: systematic uncertainties

  10. Extracted quark helicitydistributions P.R.L.92 (2004) 012005 u > d ? The HERMES data are consistent with flavour symmetry of spin-dependent sea  d(x) - 0.4 u(x) (!?) What is the dynamics behind this?? Data with much higher statistical accuracy urgently needed s < 0 ? x

  11. Transverse quark polarisation ,‘Transversity‘ h1 Complete description of nucleon in leading order QCD: 3 distribution functions  f1 = Quark momenta,  q q   g1 = - longitudinal quark spin, , q   5q HERMES1995-2000  h1 = - transverse quark spin, , q 5 q HERMES2002.....  h1 is chiral odd, can only be measured in conjunction with other chiral odd distribution (pol. Drell-Yan) or fragmentation function (SIDIS) See reviews by P. Mulders and P. Ratcliffe tomorrow

  12. Single Spin Asymmetries(SSA) ep(d)e‘hX N+() -N-() AUL() = N+() +N-() U: unpol. e-beam L: long. pol. Target Fit sin() to asymmetries AULsin() transverse spin component: ST sin  (15% - 20%)

  13. SSA from longitudinally polarized target Deuteron Proton P.L. B 562 (2003) 182 + P.R. D 64 (2001) 097101. o o + - - K+ - + 0  - +  0 2.4 M DIS 8.9 M DIS

  14. AULsin() from longitudinally polarized target + Deuteron Proton o - K+

  15. AULsin() from longitudinally polarized target + AULsin  SL(M/Q) za2 x [hLa(x) H1a(z) - x h1La(x) Ha(z)/z + ..] - ST za2 x h1a(x) H1a(z) SL >> ST Collins fragmentation function o Theory predictions seem to explain the data well A.V. Efremov et al., Eur. Phys. J. C 24 (2002) 47 B. Ma et al., P.R. D66 (2002) 094001 but contain a lot of assumptions: magnitude of H1/D1 4 ...12% only part of Twist-3 contribution taken into account no Sivers contribution taken into account - K+

  16. Azimuthal asymmetries:CollinsvsSiverseffect 2 different possible sources for azimuthal asymmetry:  product of chiral-odd transversity distribution h1(x) and chiral-odd fragmentation function H1(z)(Collins)  product of naive time-reversal odd distribution function f1T and familiar unpolarised fragmentation function D1(z) (Sivers) (requires orbital angular momentum of quarks) Longitudinally polarised target: Collins and Sivers effect indistinguishable Transversely polarised target: 2 azimuthal angles, Collins andSivers effect distinguishable AUTsin( + s ) AUTsin( - s )

  17. Data taking with transverse target polarisation Transverse target magnet installed end of 2000  Since then: rather unsatisfactory performance of HERA 2002: 600 k DIS-events with polarised H-target (present analysis) 2003: 450 k Dis events 2004: > 300 k DIS events (until now) (2000 > 9 M DIS events from pol. D-target)  We still are hoping for substantial improvements  Possibly continuation until summer 2005

  18. First measurement of transverse asymmetry - H target „Collins“ moments „Sivers“ moments

  19. ph/M-weighted azimuthal asymmetries „Collins“ moments „Sivers“ moments

  20. Interpretation of transverse asymmetries  Sivers function nonzero  orbital angular momentum Sivers flavor separation possible  Collins asymmetries show an unexpected pattern Expect A+  Ao  0 and A -  0 and smaller in magnitude HERMES data for AULCollins show A+  0 but Ao  A-  0 and larger in magnitude !  Interpretation: forthcoming paper  Extraction of transversity distributions underway

  21. HERMEScontribution to thePentaquark story u d s u d Theoretical motivation and experimental status: see reviews by M. Polyakov and M. Ostrick tomorrow

  22. Exotic Hadrons All until now observed Hadrons are (qq)- oder (qqq)-states But Model predictions do very often not agree with measured masses Many ‚missing‘ resonances QCD allows additional „exotic“ hadrons: Glueballs(gg) Hybrid states(qqg) Multiquark mesons(qqqq) Multiquark baryons, eg. Pentaquark(qqqqq) Di-baryons[(qqq)(qqq)] Again and again there were announcements of the discovery of such states. None did survive so far

  23. Theoretical prediction for 5-quark states [qqqqq + ‚sea‘] Bag models [R. Jaffe (1977), J.J De Swart (1980) et al.] Skyrme model [M. Praszalowicz (1987) et al.] Prediction: Lightest 5-q state has M = 1530 MeV Baryon-meson states [H.J. Lipkin (1987) et al.] Chiral Soliton Model[D. Diakonov, V. Petrov, M. Polyakov(1997) et al.] Excitement of chiral field in baryon: additional qq-pair Reproduces mass splittings in baryon-octet and decuplet within <1% Prediction: New anti-decuplet with + (uudds), M = 1530 MeV, positive parity, width < 15 MeV Diquark-pair model [R.L. Jaffe, F. Wilzcek (2003)] Strongly correlated diquark-pairs plus antiquark: ([qiqj]2q)

  24. 5-Quark states in the SM D. Diakonov,V. Petrov and M. Polyakov, Z. Phys. A 359 (1997) 305 S uud ds Prediction +(1530) 1 I3 sdu.. duu(dd+ss) N(1710) -1 1 *0 180 MeV sdd.. sdu.. suu(dd+ss) (1890) -1 *- *0 3/2(2070) ssu.. ssd (uu+dd) ssd du ssu ud

  25. Experimental evidence for Q+ (1530) Last year: after 30 years of futile search, sudden explosion of experimental evidence Experiments Resultats Mass Width Significance (MeV) (Mev) (s) LEPS DIANA CLAS SAPHIR ITEP (n’s) 1540105 G  25 4.61 15392”few”G 8 4.4 154225FWHM 21 5.30.5 154042G  25 4.8 15335 G  29 6.7 World average 15392.5 Prediction 1530 G < 15I=0 S=+1 JP=½+

  26. Momentum range: p (1-15 GeV), p (4-9 GeV) Cuts: data quality, distance between p+ - p-,Ks - p, Q+-beam Ks: decay length > 7 cm, 485MeV< M(Ks) < 509 MeV L(1116) excluded: reject event if M(p-p) within 1s of nominal L mass Experimental Evidence from HERMES e D -> pK0sX -> p+ - X Ee = 27.6 GeV, Target: pol/ unpol D Reaction:

  27. KS -> + - optimizedyield of Kspeak in M(p+p-) while minimizing background NO constraints optimized to increase significance of signal in final M(pp+p-)

  28. Detector Calibration with KS, , , -, * Particle observed mass PDG mass [MeV] [MeV] KS +- 496.8  0.2 497.67  p- 1115.7  0.1 1115.68 - p-+ 1321.5  0.3 1321.31  0.3 * pK- 1522.7  1.9 1519.5  1.0 Excellent Proton identification by RICH: K+ and p+contamination negligible for 4GeV< P p< 9 GeV , , -, *...well identified

  29. Monte Carlo Simulation ofpKSpp+p- Input: Resonance at 1540MeV with width = 2 MeV, decay into pKs Full detector simulation Results: MassM = 1540  0.3 MeV Width = 6.2  1 MeV, FWHM = 14.6  2.4 MeV Masses are well reconstructed, apparative resolution determines width of the signal

  30. M(p+p-p) Spectrum - fit with polynomial background hep-ex/0312044 Fit: 4th-order polynomial Resonance is observed at M(p+p-p)= 1528  2.6  2.1 MeV Width:FWHM = 19.5  5  2 MeV somewhatlargerthanexp.res. Naive significance:56/144  4.7  True significance:59/16  3.7  Unbinned fit is used; result does not depend on size of bin and starting point

  31. M(p+p-p) Spectrum - efforts to reproduce background hep-ex/0312044 Mixed event background PYTHIA6 simulation (no resonances (Q+or S*+) in mass range 1.4 – 1.7 GeV) Remaining strength due to ‘known’ broad resonances ((1480), (1560), (1580), (1620), (1660), (1670)) plus new structure M(p+p-p)= 1527  2.3  2.1 MeV Width:FWHM = 22  5  2 MeV Naive significance:74/145  6.1  True significance:78/18  4.3 

  32. Naïve estimator: • neglects uncertainty in background -> overestimates sign. of peak • statistics books: stress 2nd factor • Second estimator: • gives somewhat lower value • ?? • “Realistic” estimator: • Ns are of peak from fitting function, dNs its fully correlated uncertainty • measures how far peak is away from zero in units of its own stand. dev. • all correlated uncertainties, incl. of bkg parameters, are accounted for Significance

  33. Massand width of the signal  mass FWHM NsNb naive Total signif, [MeV][MeV]in 2 in 2 sign. Ns Ns a) 1527.0  2.3  2.1 22  5  2 74 145 6.1  78  18 4.3  a‘) 1527.0  2.5  2.1 24  5  2 79 158 6.3  83  20 4.2  b) 1528.0  2.6  2.1 19  5  2 56 144 4.7  59  16 3.7  b‘) 1527.8  3.0  2.1 20  5  2 52 155 4.2  54  16 3.4  a) Fit with 4th-order polynomial b) PYTHIA6 + fit to resonances `) with invariant mass of pKs-system, M(Ks) constrained to PDG-value Experimentalwidth larger than detector resolution of 14.6  2.4 MeV

  34. World average: M(Q+)= 1536.2  2.6 MeV (taken syst. uncertainty for DIANA and ITEP: 3 MeV) HERMESresult for mass 2.1 s below world average Comparison with other Experiments

  35. Isosinglet vs isotensor Clear *(1520) signal inpK-mass spectrum cross section estimate 62  11 (stat) nb No peak structure inpK+mass spectrum, Gaussian + pol. fitgive 0 counts with 91%CL No indication ofQ++, rule out isotensor, observed state is very likely isosinglet

  36. Pentaquark summary A narrow exotic resonance has been observed by the HERMES experiment in quasireal photoproduction via eD KspX Mass:M = 1528  2.6  2.1 MeV, this is by 2.1 s below world average Width:FWHM = 19  5  2 MeV, this is somewhat larger than the experimental resolution of the spectrometer Preferably this is an isosingletstate as no peak structure is seen in the pK+ mass spectrum A production cross section of (100 - 220 nb)  25% is estimated

  37. Orbital angular momentum contributions Lq,g to nucleonspin ? ½ = ½  + Lzq + G + Lzg 0,10 > 0,6 ? ‘No one knows how to measure it‘ (R. Jaffe) one hope: Exclusive processes, Generalised parton distributions (GPDs) X.Ji:Jq= ½  + Lzq = lim ½ dx x [H(x,,t) + E(x,,t)] t  0 * *  , K,  ,,      p p p p DVCS

  38. DVCS Example: DVCS (Interference of DVCS and Bethe-Heitler) Azimuthal asymmetries: LU beam polarisation, Cbeam charge, ULtarget polarisation Beam Polar. Beam Charge P.R.L. 87 (2001) 182001

  39. DVCS - deuteron target Target Polar. Deuteron is Spin-1 9 GPDs Beam Polar.

  40. DVCS - nuclear targets Neon is Spin-0 1 GPD

  41. DVCS Expected accuracies for 2 years of data taking HERMES Recoil-Detector Ready for installation this summer 2 years of data taking

  42. AT, b1and b2- deuteron  Deuteron is spin-1 target V = Pz= p+ - p- , Pz1 T = Pzz= p+ + p- -2p0 , -2 Pz z +1  More structure functions meas = u [1 + PbVA + ½TAT] A  g1/F1 [ 1 + ½ TAT] AT  2/3 b1/F1 Proton Deuteron F1½ zq2 [q+ + q-] 1/3  zq2 [q+ + q-+ q0] F2 2xF1 2xF1 g1½ zq2 [q+ - q-] ½ zq2 [q+ - q-] b1½ zq2 [2q0 - (q+ + q-)] b2 2xb1

  43. AT, b1and b2- deuteron First measurement, only possible with atomic gas target Model: K. Bora, R.L. Jaffe, PRD 57 (1998) 6906

  44. AT, b1and b2- deuteron  Deuteron is spin-1 target AT  10-2 little impact on det. of g1 b1dis sizeable ! and interesting by itself related to - nuclear binding - D-stateadmixture - diffractive nuclear shadowing - nuclear excess pions inD - VMD+ double scattering - - - See e.g.: - P. Hoodboy et al., N.P. B312 (89) 571 - R.L. Jaffe & A. Manohar N.P. B321 (89) 343 - X. Artru & M. Mekhfi, Z. Phys. C45 (90) 669 - N.N. Nikolaec & W. Schäfer, P.L. B398 (97) 245 - J. Edelmann et al., Z. Phys. A357 (97) 129, P.R. C57 (98) 3392 - K. Bora & R.L. Jaffe, P.R. D57 (98) 6906 - -

  45. Further results - Outlook Many more results: hadronisation in nuclei(P.L. B 577 (2003) 37- 46)  DIS on nuclear targets (P.L. B567 (2003) 339-346)  quark hadron duality in A1p(P.R.L. 90 (2003) 092002)  Q2 dependence of GDH-integral (Eur. Phys. J. C26 (2003) 527-538) DSAfor exclusive VM production (Eur. Phys. J. C29 (2003) 171-179) Nuclear attenuation of coherent and incoherent ‘s (coherence length, colour transparency) (P.R.L. 90 (2003) 052501) pion multiplicities and fragmentation functions longitudinal and transverse  polarisation vector meson production hyperon production  

  46. Hadronisation in nuclei  Hadronmultiplicity ratios for different nuclei contain information about the space-time development of the hadronisation process hadron formation time q h nuclear medium dependent fragmentation functions D(z,A)  induced energy loss by multiple scattering and gluon radiation 

  47. Hadronisation in nuclei Data for N and Kr from 12 GeV and 27.5 GeV  Strong reduction of hadron multiplicities for low   Attenuation goes away with increasing (when hadrons are formed outside of the nucleus)  Attenuation stronger for h-than for h+  Attenuation much stronger for Krypton than for Nitrogen: ratio  A2/3 See also: Eur. Phys. J. C 20 (2001) 479

  48. Hadronisation in nuclei P.L. B 577 (2003) 37

  49. Hadronisation in nuclei P.L. B 577 (2003) 37

  50. Hadronisation in nuclei P.L. B 577 (2003) 37 Cronin effect

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