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The XVIIIth International Workshop High Energy Physics and Quantum Field Theory

Recent results from the HERA-B experiment. Roberto Spighi, INFN Bologna Italy For the HERA-B Collaboration. The XVIIIth International Workshop High Energy Physics and Quantum Field Theory 17-23 june 2004, St. Petersburg. Outline. Main physics studies at HERA-B. Detector.

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The XVIIIth International Workshop High Energy Physics and Quantum Field Theory

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  1. Recent results from the HERA-B experiment Roberto Spighi, INFN Bologna Italy For the HERA-B Collaboration The XVIIIth International Workshop High Energy Physics and Quantum Field Theory 17-23 june 2004, St. Petersburg

  2. Outline Main physics studies at HERA-B Detector Physics topics addressed: • Production of: • Open and hidden Charm • Open and hidden Beauty • FCNC process • Hard photons • Strangeness production • Pentaquark search Summary Disclaimer: All results are preliminary

  3. production bb, (1-3S) ˉ Main physics studies at HERA-B Do(+,*+),J/ψ,ψ(2S), c pT , xF and decay angle A-dependence Charm production Beauty production Strangeness production Pentaquark Hard photons Kos ,Λ, f, K*, hyperons search Θ+ , Ξ  + c.c. , π0, η • ~ 150 · 106 dilepton triggered events ~300 k J/ • ~ 210 · 106 minimum bias events • ~ 35 · 106 hard photon triggered events

  4. Physics motivation • Test of QCD predictions: NRQCD confirmed at high energy (CDF √s =1.8 TeV) and large pT, no conclusive results at lower energy • Investigation of nuclear effects for correct interpretation of results from ultra relativistic heavy ion collisions (QGP) beauty production charm production • no (or very few) results in the negativexF range • few results on the J/, (2S)polarization • contradictory results on R(c/J/) • (bb): only two other measurements (E771, E789) with large uncertainties and poor compatibility • (): testing ground for the theoretical models

  5. Charmonium Production in media Investigation of nuclear effects • Further physics for production in media • Nuclear effect in initial and final state • Initial state: • Shadowing, parton energy loss, transverse momentum broadening (<pT> dependence on A) • Final state: • Nuclear absorption (dependence on xF), Co-mover suppression Necessary to study the charmonium differential distributions Important baseline measurements for QGP study HERA-B is in the ideal condition to study these effects

  6. The Hera-B Detector Electron beam • Fixed target detector at HERA (DESY) — IR 5 – 10 MHz • 920 GeV/c proton beam (√s = 41.6 GeV) • High angular coverage (15-220 mrad in bending plane) • High resolution spectrometer — very good particle ID for (e, , , K, p)

  7. Target system 8 wire targets (C, Al, Ti, W, Pd)in proton halo Different targets (range A[12:184]) can be used simultaneously A-dependence measurements  control of systematic errors Events from different wires can be easily separated

  8. The vertex detector Vertex-wire distance Silicon Vertex Detector • 7 superlayers of silicon microstrips • High primary vertex resolution • (x ~ y ~ 50 m, z ~ 450 m)

  9. Main tracking system The world largest honeycomb tracker Track efficiency ~ 90-95% Momentum resolution ~ 1.5%

  10. Particle Identification (RICH) Example:  reconstruction Pion/kaon sep : 10< p <60 GeV Kaon/proton sep: 20< p <90 GeV

  11. Particle Identification (Ecal) ECAL Bremsstrahlung tag e magnet μ = 0.99 σ = 0.06 pN X ~ 1/Ee  X Z 51k J/ 25k J/ E/p & opt cut + 1-2 BR

  12. Particle Identification (Muon) MB events • drift tubes + iron absorber • 4 superlayers Without likelihood request With likelihood request  J/ peak is visible

  13. Dilepton trigger system on average ½ interaction per proton bunch Dilepton trigger: 5 MHz • at least 2 pretrigger seeds • coincidence with at least 1 FLT track • coincidence with at least 2 SLT tracks Pretriggers: ECAL cluster or MUON hit coincidence FLT: track-based hardware trigger (track finding behind magnet) 20 kHz SLT (PC farm): track finding, SVD, vertexing 100 Hz total suppression factor 1:50000 4LT (PC farm): online reconstruction 1000-1500 J/ψ h-1

  14. charmonium production • J/, c, ’ • A-dependence • Do(FCNC process) • bb production •  • Low mass studies (, /) • Exotics production _ Dilepton data analysis

  15. Dielectron spectra Total e+e- statistics: ~ 108,000 J/ σ= 64 MeV/c2 ~ 1600 (2S) J/ /  (2S) ,  • Signals clearly visible: • various e-ID cuts applied to reduce high bkg level Low mass range

  16. Dimuon spectra  ~ 177,000 J/σ= 44 MeV/c2 , Low mass range ~ 3000 (2S) (1S) Signal clearly visible, low bkg situation (2/3S) • 2 independent analyses • high statistics & quality in both samples High mass range

  17. pT differential distribution of J/ pT J/ transverse momentum Arbitrary scale normalization 15% of e+e- sample HERA-B range pT < 4.5 GeV/c Preliminary results for ‹pT> (GeV/c) Good agreement between e+e-/μ+μ- analyses wide pT range A dependence?

  18. xF differential distribution of J/ xF —> J/ Feynman-x Arbitrary scale normalization HERA-B range -0.35 < xF < 0.15 15% of e+e- sample Preliminary results for c[5:6.5] ± 0.2 Not clear panorama. Now negative xF range accessible with HERA-B.

  19. <pT> and c dependence on √s phenomenologic <pT> = A + B √s Fermilab-pub-91/62-E(1991) (E672/706 Coll) A=0.813 ± 0.014 GeV/c B=0.0105 ± 0.0004c-1 <pT> (GeV/c) √s (GeV) phenomenologic c = D/(1 + E /√s) Fermilab-pub-91/62-E(1991) (E672/706 Coll) D=8.80 ± 0.41 E=23.9 ± 2.7 GeV √s (GeV) HERA-B precision competitive with previous results

  20. cos differential distribution of J/  is the Gottfried-Jackson decay angle J/ polarization described by  parameter  = (0,1,-1) (no, trans., long.) polarization 15% of e+e- sample Important tests for models HERA-B variation range [-0.5,0.1] ±0.1

  21. A dependence of J/ production Parameterization of cross section: Determine  from two different targets: • C (A=12.0) and W (A=183.8) • 25% of full e+e- sample • Ratio of luminosities under investigation  norm. to E866 stat. errors only E866 with Be, Fe and W

  22. A dependence of J/ NRQCD pred.: R. Vogt Nucl. Phys. A700 (2002) 539 χc all J/ Expected stat. error for full data muon sample: direct J/ ’ BCKT pred.: K.G. Boreskov, A.B. Kaidalov JETP. Lett. 77 (2003) 599 HERA-B range all J/

  23. (1.6 ± 0.2stat)% C (1.8 ± 0.4stat)% W ψ’ / J/ψ production ratio Measurement of • ε efficiency • Br branch. ratio √s from electron analysis (compatible results from muons) Experimental situation A (E288, E331, ISR, E444, E705, E537, E789, E771, NA51, NA38, NA50) Competitive measurement from HERA-B

  24. ψ’ differential distributions ‹pT> ~ 1.4 stat err 0.1 GeV/c c’ = [4:5.5] ± 0.7 dσ/dpT2 dσ/dxF • HERA-B compatible with previous results • Comparable precision • First measurement in the negative xF range ! E789: 800 GeV/c p-Au E771: 800 Gev/c p-Si

  25. c J/  +-  and e+e-  In 15% of  sample ≈1300c expected ~15 k for full sample c to J/ production ratio No distinction between c1 and c2 (M = 46 MeV/c2) c0 neglected due to small Br ≈ 1 ≈ 0.4 Rc = 0.21 ±0.05 Systematic studies ongoing M (GeV/c2)

  26. Rc experimental situation and expectations No clear experimental panorama Theoretical expectations Rc = 0.21 ±0.05 R(c) = 0.320.060.04 Results of 2000 (Phys.Lett. B561(2003) 61) N(c) = 37074 (both +-, e+e-) √s (GeV) HERA-B results agree with NRQCD expectations Final precision more stringent tests

  27. 18 evt 3 evt 6 evt Do Search of FCNC in the decay BR(Do): expected BR for Standard Model ~ 10-19 supersimmetric model enhances to ~ 10-7 Upper limit on the branching ratio: BR(Do) < 2.0 x 10-6 (90% cl) hep-ex/0405059 Submitted to Phys Lett B Previous limit: CDF: BR(Do)< 2.5 x10-6 Phys.Rev. D 68 (2003) 091101 Currently best upper limit

  28. pA bb+ X, bJ/+Y Open beauty production Select detached vertex to separate B (decay length ~7 mm) from J/ (e+) (e-) Dilepton vertex resolution 0.5 mm Results of 2000: Eur. Phys.J. C26(2003) 345: e+e- = ; +-= †

  29. Open beauty production Analysis of 2002/03 data: • 35% of e+e- and +- statistics • Expect NB ~ 100 for full sample • Carbon + Tungsten targets • J/ acceptance: -0.35<xF<0.15 (90% of bb cross section) • Preliminary results of both channels compatible • 1.5  lower than 2000 result

  30. Drell-Yan Drell-Yan Comb. BG Comb. BG M(e+e-) (GeV/c2) M(+-) (GeV/c2) Hidden beauty production pN  + X, +-,e+e- Drell-Yan contribution compatible with E866 Relative production of (1S)/(2S)/(3S) fixed on E605 data

  31. Not used in fit Hidden beauty production • All C and W data used (150 M evts) • Modified Craigie applied to allow for nuclear suppression: =0.990.05 √s (GeV)

  32. Hard photon analysis Direct production: dominant process gq q  Unique sensitivity to gluon density function pCπ°X Main bkg sources, also important to test QCD • HERA-B: • Widest rapidity range • Large pT range • Highest energy for pA • Ongoing analysis on heavier materials pCX pCX (normalization still arbitrary)

  33. MB data analysis • Open charm production • V0 production • Hyperon production • Strangeness production • Pentaquark search

  34. D0 K-p+ + c.c. D+ K-p+p+ + c.c. D*+ D0p+ K-p+p+ Open charm production Signals selected in Minimum Bias data + c.c. N = 189 ± 20 s= 25 ± 3 MeV M = 1863 ± 3 MeV N = 98 ± 12 s= 15 ± 2 MeV M = 1866 ± 2 MeV N = 43 ± 8 s= 0.89 ± 0.15 MeV q = 145.9 ± 0.2 MeV

  35. Open charm production mb/Nucl Important test for QCD

  36. π- V0 p-beam p A V0 production KS→π+π- →pπ- Armenteros-Podolanski plot Statistics: Ks ~ 3.40 x 106 evts σ~ 4.9 MeV Λ ~ 0.94 x 106 “ σ ~ 1.8 MeV Λ ~ 0.45 x 106 “ σ ~ 1.8 MeV • Measurement of the production cross section and ratio vs A • 2000 data analysis published in: Eur.Phys.J. C 29,181 (2003)

  37. x103 6 4 2 0 1.2 1.3 1.4 1.5 Mass GeV/c2 Hyperon production Ξ± (1321)  (1116) π± (1520)  p K- + c.c. (Carbon target) (all targets) : ~ 2000, σ ~ 8 MeV : ~ 1000, σ ~ 8 MeV - Strong signals Ξ-: ~ 11300, σ~ 2.6 MeV Ξ+: ~ 7700, σ~ 2.6 MeV • Good proton/kaon identification • Very large Ξ± statistics

  38. wire K-(us) or (uds) + (uudds) p K0 p Pentaquark search Possible pentaquark states Θ+(1530, uudds) → pK0(or nK+) Ξ (ddssu) → Ξπ(or ΣK) → Λππ and charge c. • Use the full MB data sample (~210M evts, 3 nuclear targets C, Ti, W) to: • search for the reported pentaquark signals • provide upper limits on particle yield ratios (vs Λ(1520) and Ξ0(1530)) • possibly determine physical quantities (width, spin, parity, charge) of pentaquarks for different final states (p-K0, -)

  39. Pentaquark search: Θ+→ pK0 sensitivity in BR•(d/dxf) ~ 5b/nucleon • No evidence of signals where expected (~ 1530 MeV/c2) • Upper limit on particle yield ratio: • Θ+/Λ1520 < 0.02 at 95% C.L. • (Hermes: ~ 1.6 ÷ 3.5) • Upper limit on nuclear cross section under evaluation assuming BR(Θ+ → pKS) = 0.25

  40. Pentaquark search: Ξ (Ξ++)→ Ξ π-(Ξ+ π+) Ξ π++ Ξ+ π Ξ0(1530) Good Ξ0(1530) reconstruction • No evidence of Ξ , Ξ++ around 1862 MeV/c2 • Upper limits (95% cl): • Ξ--(1862) / Ξ0(1530) < 0.077 • Ξ++(1862) / Ξ0(1530) < 0.058 • Nuclear cross section upper limit in progress Ξ , Ξ++ Ξ π- + Ξ+ π+

  41. Many physics topics addressed Detector Large acceptance (negative xF) good particle identification Large statistics collected Dilepton sample (+- &e+e-) J/(300k), (2S), c,  and bb MB sample Open charm, V0, hyperons, pentaquark High quality of data Preliminary results available on several topics Competitive with previous experimental panorama Summary Many thanks to the organizers for the invitation and the logistic support

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