Recent results from the HERA-B experiment

Transcription

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 june 2004, St. Petersburg (1)

2 Outline Main physics studies at 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 (2)

3 Main physics studies at HERA-B D o(+,*+) o(+,*+),, J/ψ, ψ(2s), χ cc p T,, x F and decay angle A-dependence K oo s, s, Λ, Λ, φ, φ, K **,, hyperons ~ dilepton triggered events ~300 k J/ψ ~ minimum bias events ~ hard photon triggered events Charm production Strangeness production Hard photons γ, γ, π 0, η Beauty production Pentaquark production bb, ϒ(1-3S) search Θ + +, Ξ + c.c. c.c. (3)

4 Physics motivation Test of QCD predictions: NRQCD confirmed at high energy (CDF s =1.8 TeV) and large p T, no conclusive results at lower energy Investigation of nuclear effects for correct interpretation of results from ultra relativistic heavy ion collisions (QGP) charm production beauty production no (or very few) results in the negative x F range few results on the J/ψ, ψ(2s) polarization contradictory results on R(χ c /J/ψ) σ(bb): only two other measurements (E771, E789) with large uncertainties and poor compatibility σ(ϒ): testing ground for the theoretical models (4)

5 Charmonium Production in 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 (<p T > dependence on A) Final state: Nuclear absorption (dependence on x F ), Comover 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 (5)

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 ( mrad in bending plane) High resolution spectrometer very good particle ID for (e, µ, π, K, p) (6)

7 Target system 8 wire targets (C, Al, Ti, W, Pd) in proton halo Station 1 Station 2 Pd Al Ti C Proton Beam Ti W W C Target materials as injan 2003 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 (7)

8 Silicon Vertex Detector The vertex detector 7 superlayers of silicon microstrips High primary vertex resolution (σ x ~ σ y ~ 50 µm, σ z ~ 450 µm) Vertex-wire distance v z (cm) v x (cm) (8)

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

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

11 Particle Identification (Ecal) E p = cluster energy on Ecal momentum from tracker Bremsstrahlung tag ECAL µ = 0.99 σ = 0.06 pn magnet e γ X ~ 1/E e 100 X 50 Z E/p Entries/(0.033 GeV/c 2 ) x Entries/(0.033 GeV/c 2 ) E/p & opt cut 4000 Entries/(0.033 GeV/c 2 ) k J/ψ k J/ k J/ψ ee Invariant mass GeV/c BR ee Invariant mass GeV/c ee Invariant mass GeV/c 2 (11)

12 Particle Identification (Muon) drift tubes + iron absorber 4 superlayers MB events Entries/(0.010 GeV/c 2 ) Without likelihood request µµ Invariant mass GeV/c 2. With likelihood request J/ψ peak is visible (12)

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

14 Dilepton data analysis - charmonium production - J/ψ, χ c, ψ - A-dependence - D _ o µ + µ (FCNC process) - bb production - ϒ - Low mass studies (φ, ρ/ω) - Exotics production (14)

15 Dielectron spectra Entries/(0.033 GeV/c 2 ) J/ψ Total e + e - statistics: ~108,000J/ψ σ =64 MeV/c 2 ~ 1600 ψ(2s) ee Invariant mass GeV/c 2 ρ/ω φ ψ(2s) Entries/(0.033 GeV/c 2 ) ρ,ω ee Invariant mass GeV/c 2. φ Low mass range Signals clearly visible: various e-id cuts applied to reduce high bkg level (15)

16 Dimuon spectra ~ 177,000 J/ψ σ =44MeV/c 2 ~3000ψ(2S) Entries per 11.1 MeV/c ρ,ω φ Low mass range µ + µ [GeV/ c2 M ( ) ] Signal clearly visible, low bkg situation 2 independent analyses high statistics & quality in both samples High mass range ϒ(1S) ϒ(2/3S) (16)

17 p T differential distribution of J/ψ dn/dp T % of e + e - sample p T J/ψ transverse momentum Arbitrary scale normalization dσ 35π p dpt 256 pt 2 2 T 2 6 HERA-B range p T < 4.5 GeV/c p T GeV/c Preliminary results for p T > (GeV/c) Good agreement between e + e - /µ + µ - analyses Target electron C 1.24 W 1.29 wide p T range muon stat. err A dependence? Exp. Interaction & p-momentum Range (GeV/c) p T > (GeV/c) E GeV < ± 0.01 E GeV < ± 0.01 (17)

18 x F differential distribution of J/ψ dn/dx F 10 4 x F > J/ψ Feynman-x Arbitrary scale normalization dσ dx F (1- x F ) c % of e + e - sample HERA-B range < x F < x F. Preliminary results for c [5:6.5] ± 0.2 Exp. Interaction & p-momentum Range c E672/E GeV 0.0< x F < ± 0.16 E GeV 0.30< x F < ± 0.05 E GeV < x F < ± 0.23 E GeV 0.30 < x F < ± 0.04 E GeV < x F < ± 0.18 Not clear panorama. Now negative x F range accessible with HERA-B. (18)

19 <p T > and c dependence on s <p T > p (GeV/c) T (GeV/c) Be, AG H 2, NA3 Pt, NA3 (C,Cu,W), E444 Be, E705 Be, E672/706 Si, E771 Au, E789 p, ISR p, ISR p, ISR C, HERA-B W, HERA-B PRELIMINARY phenomenologic <p T > = A + B s Fermilab-pub-91/62-E(1991) (E672/706 Coll) A=0.813 ± GeV/c B= ± c s (GeV) s (GeV) x F exponent c Be, SIGMA Be, AG C, E331 Sn, E331 (C,Cu,W), E444 Be, E705 Fe, E379 Be, E672/706 Si, E771 Au, E789 Be, E789 HERA-B PRELIMINARY s (GeV) 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 HERA-B precision competitive with previous results (19)

20 dn/dcosθ cosθ differential distribution of J/ψ 15% of e + e - sample cosθ. HERA-B variation range [-0.5,0.1] ±0.1 Exp. E379 E672/E706 E672/E706 E771 Interaction & p-momentum 400 GeV 530 GeV 800 GeV 800 GeV dγ θ is the Gottfried-Jackson decay angle dcosθ = γ (1 + λcos2 θ) J/ψ polarization described by λ parameter λ = (0,1,-1) (no, trans., long.) polarization λ 0.16 ± ± ± ± 0.12 λ Important tests for models p T GeV/c (20)

21 A dependence of J/ψ production Parameterization of cross section: σ = σ A α ; σ = N/( ε L) pa pn Determine α from two different targets: 1 NW LC ε C α = ln ln( AW / AC) N C LW εw stat. errors only C (A=12.0) and W (A=183.8) 25% of full e + e - sample Ratio of luminosities under investigation norm. to E866 E866 with Be, Fe and W (21)

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

23 Measurement of + Br(ψ ) σ(ψ ) Nψ ε = + Br(J / ψ ) σ(j / ψ) N ε Br σ(ψ ) Br σ(j/ψ) = ψ ψ / J/ψ production ratio J/ψ J/ψ ψ (1.6 ± 0.2 stat )% C (1.8 ± 0.4 stat )% W from electron analysis (compatible results from muons) Experimental situation (E288, E331, ISR, E444, E705, E537, E789, E771, NA51, NA38, NA50) Competitive measurement from HERA-B ε Bσ(ψ ) / Bσ(J/ψ) (%) efficiency Br branch. ratio Bσ(ψ ) / Bσ(J/ψ) (%) HERA-B (not fitted) A HERA-B (not fitted) s sqrt(s) (GeV) target atomic weight (A) (23)

24 ψ ψ differential distributions p T > ~ 1.4 stat err 0.1 GeV/c c = [4:5.5] ± dσ/dp 2 T dσ/dx F dσ(ψ )/dp T 2 [nb GeV -2 c 2 /nucleon] E789 E771 HERA-B (arbitrarily normalized) p T [GeV/c] dσ(ψ )/dx F [nb/nucleon] E789 E771 HERA-B (arbitrarily normalized) x F HERA-B compatible with previous results Comparable precision First measurement in the negative x F range! E789: 800 GeV/c p-au E771: 800 Gev/c p-si (24)

25 R χ c 2 χ c to J/ψ production ratio No distinction between χ c1 and χ c2 ( M = 46 MeV/c 2 ) χ c0 neglected due to small Br χ c J/ψ γ µ + µ - γ and e + e - γ σ( χ ) Br( χ J / ψγ) N ( χ ) ε J / ψ σ ( J / ψ ) N( J / ψ ) ε ε ci ci i= 1 c = = χ J / ψ γ / 45 P P E-02 P E E-02 P E E / 45 P P E-02 P E E-02 P E E-04 Rχ c = 0.21 ± M (GeV/c 2 ) Systematic studies ongoing In 15% of µµ sample 1300 χ c expected ~15 k for full sample (25)

26 R χc χc experimental situation and expectations Exp. Interaction & s R(χc) E GeV 0.47 ± 0.23 E GeV 0.30 ± 0.04 E GeV 0.74 ± 0.17 R(χ c )= 0.32±0.06±0.04 Rχ c = 0.21 ±0.05 R χc No clear experimental panorama Theoretical expectations πa pa pa (HERA-B) CSM πn pn Results of 2000 (Phys.Lett. B561(2003) 61) N(χ c ) = 370±74 (both µ+µ-, e+e-) average NRQCD πn pn HERA-B results agree with NRQCD expectations s s (GeV) Final precision more stringent tests (26)

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

28 pa bb+ X, b J/ψ+Y Open beauty production Select detached vertex to separate B (decay length ~7 mm) from J/ψ (e + ) (e - ) Dilepton vertex resolution 0.5 mm σ bb Results of 2000: Eur. Phys.J. C26(2003) 345: e + e = 8.6 ; µ + µ = ( ) 14 6 bb = 12 7 σ + + n 1 = σ J / Ψ n ε ε Br( bb J / ψ ) B z J / Ψ R B 32 nb / N (28)

29 Analysis of 2002/03 data: 35% of e + e - and µ+µ- statistics Expect N B ~ 100 for full sample Carbon + Tungsten targets J/ψ acceptance: -0.35<x F <0.15 (90% of bb cross section) Open beauty production Preliminary results of both channels compatible 1.5 σ lower than 2000 result σ ( ) bb = nb / N (29)

30 Hidden beauty production σ n Br( J / Ψ l l ) + J / ψ Υ Υ = σ J / ψ + Υ nj / ψ Br( Υ l l ) ε ε pn ϒ + X, ϒ µ + µ -,e + e - Drell-Yan Drell-Yan Comb. BG Comb. BG Drell-Yan contribution compatible with E866 M(µ + µ - ) (GeV/c 2 ) M(e + e - ) (GeV/c 2 ) Relative production of ϒ(1S)/ϒ(2S)/ϒ(3S) fixed on E605 data (30)

31 Hidden beauty production µ + µ - e + e - both Events 33±7 31±10 Br dσ/dy y=0 3.9±1.1 pb/n 2.9±1.2 pb/n 3.4±0.8 pb/n All C and W data used (150 M evts) Not used in fit Modified Craigie applied to allow for nuclear suppression: α=0.99±0.05 dσ Υ mo Br ( s) = σ o exp A dy s y = 0 α 1 s (GeV) (31)

32 Direct γ production: dominant process gq γq Unique sensitivity to gluon density function Hard photon analysis, arbitrary units E(d 3 σ/dp 3 )γ pc γx, S=41.6 GeV, HERA-B preliminary MinBias data, run HP trigger, run MB Monte Carlo Main bkg sources, also important to test QCD pc π X pc γx E T, GeV (normalization still arbitrary) HERA-B: Widest rapidity range Large p T range Highest energy for pa Ongoing analysis on heavier materials pc ηx (32)

33 MB data analysis - Open charm production - V 0 production - Hyperon production - Strangeness production - Pentaquark search (33)

34 Open charm production Signals selected in Minimum Bias data D 0 K - π + + c.c. D + K - π + π + + c.c. D *+ D 0 π + K - π + π + + c.c. N = 189 ± 20 σ = 25 ± 3 MeV M = 1863 ± 3 MeV N = 98 ± 12 σ = 15 ± 2 MeV M = 1866 ± 2 MeV N = 43 ± 8 σ = 0.89 ± 0.15 MeV q = ± 0.2 MeV (34)

35 Open charm production preliminary σ(d 0 )µb/nucl σ(d + )µb/nucl R(D + /D 0 ) -0.1 < x F < ±3.2± ±1.7±2.2 full x F 56.3±8.5± ±4.5± ±0.11±0.14 µb/nucl Important test for QCD (35)

36 V 0 production V 0 π - K S π + π - p-beam A p Λ pπ - Armenteros-Podolanski plot Statistics: K s ~ 3.40 x 10 6 evts σ ~ 4.9 MeV Λ ~ 0.94 x 10 6 σ ~ 1.8 MeV Λ ~ 0.45 x 10 6 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) (36)

37 Λ(1520) p K - + c.c. Hyperon production (Carbon target) Ξ ± (1321) Λ(1116) π ± x (all targets) 4 2 Strong signals Λ: ~ 2000, σ ~ 8 MeV - Λ: ~ 1000, σ ~ 8 MeV Ξ - : ~ 11300, σ ~ 2.6 MeV Ξ + : ~ 7700, σ ~ 2.6 MeV Mass GeV/c Good proton/kaon identification Very large Ξ ± statistics (37)

38 Pentaquark search Possible pentaquark states wire K - (us) or Λ(uds) Θ + (1530, uudds) pk 0 (or nk + ) Ξ (ddssu) Ξ π (or Σ K ) Λπ π and charge c. p Θ + (uudds) K 0 p 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 Ξ 0 (1530)) possibly determine physical quantities (width, spin, parity, charge) of pentaquarks for different final states (p-k 0, Ξ-π) (38)

39 Pentaquark search: Θ + pk 0 sensitivity in BR (dσ/dx f ) ~ 5µb/nucleon No evidence of signals where expected (~ 1530 MeV/c 2 ) Upper limit on particle yield ratio: Θ + /Λ 1520 < 0.02 at 95% C.L. assuming BR(Θ + pk S ) = 0.25 (Hermes: ~ ) Upper limit on nuclear cross section under evaluation (39)

40 Pentaquark search: Ξ (Ξ ) Ξ π - (Ξ + π + ) Ξ π + + Ξ + π Ξ 0 (1530) Good Ξ 0 (1530) reconstruction Ξ π - + Ξ + π + Ξ, Ξ ++ No evidence of Ξ, Ξ ++ around 1862 MeV/c 2 Upper limits (95% cl): Ξ -- (1862) / Ξ 0 (1530) < Ξ ++ (1862) / Ξ 0 (1530) < Nuclear cross section upper limit in progress (40)

41 Summary Many physics topics addressed Detector Large acceptance (negative x F ) good particle identification Large statistics collected Dilepton sample (µ + µ - &e + e - ) J/ψ (300k), ψ(2s), χ c, ϒ and bb MB sample Open charm, V 0, hyperons, pentaquark High quality of data Preliminary results available on several topics Competitive with previous experimental panorama Many thanks to the organizers for the invitation and the logistic support (41)