Charm and beauty proton structure functions F 2 cc and F 2 bb at HERA

1. - - Charm and beauty proton structure functions F2cc and F2bbat HERA Vladimir Chekelian (Shekelyan) MPI for Physics, Munich Measurements of F2cc and F2bb using the H1 vertex detector at high Q2: Q2 > 150 GeV2(scattered positron in Lar calorimeter) Eur. Phys. J. C40 (2005) 349 [hep-ex/0411046] at low Q2: 6.3 <Q2 < 120 GeV2(scattered positron in Spacal) DESY-05-110 (July 2005), submitted to Eur. Phys. J. C [hep-ex/0507081] ’ the e+p data 1999-2000, Lint= 57.4 pb-1 V. Chekelian, Charm and Beauty SF

2. Structure Functions, Heavy Quarks and QCD DIS cross section and SFs QPM Q2 >>M2HQ in QPM: Treatment of HQ in QCD mc2; 2.5 GeV2, mb2 ; 25 GeV2 Q2 >>M2HQmassless scheme Q2 ~ M2HQ massive approach (FFNS) full Q2 range: Variable FNS (VFNS: ACOT,MRST) Boson Gluon Fusion (BGF) Q2 ~M2HQ ,b • ’exp. checks of HQ calculations in pQCD • (calculation techniques, pdfs from QCD fits) • direct access to gluon via BGF - ,b V. Chekelian, Charm and Beauty SF

3. Main methods used so far to study HQ at HERA Open Charm: - exclusive D* and D meson production - small branching (-> limited statistics) - large extrapolation to get F2cc ’ see talk of S. Fourletov Open Beauty: b ’mX make use of large b mass and long lifetime: ptrel(m transverse to b-jet) d (impact parameter) ptrel d ’ see talk of B. Naroska V. Chekelian, Charm and Beauty SF

4. The H1 vertex detector FST CST BST Forward, Central and Backward Silicon Trackers ep 27.6 920 GeV • - 2 cylindical layers of double-sided • silicon strip detectors surrounding • the beam pipe • radii 5.7 cm and 9.7 cm • hit resolution: 12 μm in r-φ • 25 μm in z • impact parameter resolution (for central • tracks with CST hits in both layers): used in this analysis: CST (30o < q < 150o) V. Chekelian, Charm and Beauty SF

5. Inclusive lifetime tagging of HQ Goal:be as inclusive as possible - use impact parameter in r-φ plane for - all tracks with pt> 500 MeV and 2 hits in CST y • sign of impact parameter is defined • using φ of the HQ direction: secondary vertex (resolution + secondary vertices) (due to resolution only) d2 d1 r-φplane primary vertex x -> high acceptances for long lived c (b) hadrons: 82% (96%) at low Q2; 93% (96%) at high Q2 -> small extrapolation to the full phase space -> the method is cross checked at high Q2 by using explicit reconstruction of the secondary vertex V. Chekelian, Charm and Beauty SF

6. Reference axis (HQ direction) Reference axis in r-φ plane fref. axis = fjet of the highest transverse momentum jet with pt>2.5 GeV low Q2 : jet is found for 81% (95%) c(b) events fref. axis = 180o – fscattered elec. if no jet found Checks of the fresolution: fD* - fref. axis : azimuthal difference between reconstructed D* and reference axis jet no jet found Resolution in f is 5o for events with jets and 35o if jet is not found ’ data are well described by MC V. Chekelian, Charm and Beauty SF

7. Signed impact parameter and Significance Tracks matched to the reference axis |ftr-fref. axis|<p/2 SignificanceS = d/s(d) of the track (in r-φplane) - remove |d|>1mm (to suppress long lived strange particles, e.g. Ks0) Signed impact parameter Significance (r-φplane) distributions are well described by MC V. Chekelian, Charm and Beauty SF

8. Significance distributions at low Q2 S1 S2 S1– highestabsolute significance track S2– 2nd highestabsolute significance track with the same sign as S1 S3– 3d highestabsolute significance track with the same sign as S1 and S2 S3 V. Chekelian, Charm and Beauty SF

9. Subtracted significance distributions at low Q2 subtract the contents of negative bins from the contents of the corresponding positive bins -> substantially reduce uncertainty due to resolution of d and light quark normalisation S1 S2 -> dominated by c with increasing b fraction at high Si Simultaneous fit to the subtracted S1,S2,S3 distributions and total number of inclusive events before track selection using c, b and uds shapes from MC 3 parameters: - Pc scale factor for charm MC (b decays are excluded) - Pb scale factor for beautyMC - Pl scale factor for light quark MC S3 For complete low Q2 sample: ’ individual fit for each x-Q2 interval V. Chekelian, Charm and Beauty SF

10. Reduced cross sections and F2cc, F2bb Pc,Pb,Pldefined for each x-Q2 interval measured inclusive reduced cross section bin center correction to convert the bin average to x-Q2 point ’ F2cc,bb are obtained using FLcc,bb from the NLO QCD predictions V. Chekelian, Charm and Beauty SF

11. Charm structure function F2cc  lifetime results are consistent with H1 and ZEUS D* measurements  extention of H1 measurements to higher Q2 consistent with gluon from scaling violations V. Chekelian, Charm and Beauty SF

12. Beauty reducedcross section the first measurement of sbb (and F2bb)  consistent with pQCD prediction important for LHC experiments (e.g. bb->H) MRST04: VFNS CTEQ6HQ: VFNS CCFM: massive (BGF) V. Chekelian, Charm and Beauty SF

13. F2cc vs Q2 F2bb vs Q2 Scaling violations of F2cc, F2bb are increasing with decreasing of x (similarly to F2) Compared with NLO and NNLO QCD predictions: ’the data are more precise than the spread of QCD predictions V. Chekelian, Charm and Beauty SF

14. Cross section fractions fcc Charm fraction fcc - roughly constant with Q2 - slightly decreasing with x - around 24% on average Beauty fraction fbb - increases rapidly with Q2 from ~0.3% to ~3% (i.e. by a factor of 10) fbb Well described by MRST04 (VFNS) V. Chekelian, Charm and Beauty SF

15. Summary Charm and beauty structure functions F2cc and F2bb are measured in the Q2 range from 12 GeV2 to 650 GeV2 using lifetime tagging (impact parameter method)  Charm contribution to F2 is around 24% on average  Beauty contribution to F2 changes from 0.3% to 3%  F2bb is measured for the first time  Both F2cc and F2bb are well described by NLO/NNLO QCD Large potential for HERA II: H1: CST, FST, BST ZEUS: MVD (see talk of M. Corradi) V. Chekelian, Charm and Beauty SF