Beauty jet production at HERA with ZEUS

Transcription

1 DESY and University of Hamburg wo recent measurements of beauty production in deep inelastic ep scattering with the detector are presented. In the first analysis, beauty production was identified using muons associated to a. In the second measurement, beauty content was extracted using the decay length significance and invariant mass of secondary vertices. Measured differential cross sections were compared to theoretical predictions. he beauty contribution to the proton structure function F was extracted. PoS(EPS-HEP000 XXIst International Europhysics Conference on High Energy Physics -7 July 0 Grenoble, Rhône-Alpes France Speaker. on behalf of the Collaboration c Copyright owned by the author(s under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.

2 . Introduction Beauty production in deep inelastic scattering (DIS regime is important for several reasons. Production of beauty quarks is dominated by the boson gluon fusion process, hence this process provides a direct probe of the gluon component of the proton. In addition, the mass of b quarks provides a large scale for perturbative QCD (pqcd calculations, but on the other hand, presence of multiple hard scales (photon virtuality, quark mass and momentum can spoil the series convergence due to large logarithmic terms. herefore, a precise measurement of beauty production allows to distinguish between different theoretical approaches to treat mass effects in pqcd predictions.. Measurement of beauty production using events with a and a muon he production of b quarks was measured in events with a and a muon with the detector at HERA using 4pb of data []. he reaction ep eb bx e µ X was measured in the kinematic region of Q > GeV, 0.05 < y < 0.7, E > 5GeV and.0 < η <.5 including a muon of p µ >.5GeV and.6 < η µ <.5 inside a cone of R < 0.7 to the axis, where R = ( φ +( η. Jets were reconstructed using the k cluster algorithm in the massive mode with the E recombination scheme. he beauty signal was extracted from the distribution of the transverse momentum of the muon with respect to the momentum of the associated, p rel. he fraction of beauty events in the data was obtained from a two component fit to the shape of the measured p rel distribution (see Fig.. Figure shows the measured differential cross section as a function of the photon virtuality compared to the next to leading order (NLO QCD calculations as well as the MC predictions scaled to the data. Both predictions describe the shape of the measured cross sections reasonably well. Events 4 4 pb MC bb MC cc+lf MC bb+cc+lf (pb/gev dσ/dq 4 pb MC RAPGAP. NLO (HVQDIS PoS(EPS-HEP p rel (GeV Q (GeV Figure : Measured p rel distribution and the fit using templates obtained from the Monte Carlo simulations for beauty, charm and light flavour (LF events. Figure : Differential beauty cross sections as a function of Q compared to the Monte Carlo and the NLO QCD predictions.

3 Entries 5 4 (prel. 54 pb Monte Carlo LF Charm Beauty L XY / σ(l Figure : Decay length significance for the data and the Monte Carlo samples for different flavour production in the region < M V X < 6GeV.. Measurement of beauty production using inclusive secondary vertices A measurement of beauty quark production in DIS was also done using the decay length significance and invariant mass of secondary vertices, M V X, using an integrated luminosity of 54pb collected between 004 and 007 []. he kinematic region is defined by: 5 < Q < 00GeV, > 5GeV and.6 < η <.. he same clustering algorithm as described in Section was used to reconstruct s. A secondary vertex was fitted for any selected if at least two tracks with p > 500MeV were associated to the using R < criteria. he beauty fraction in the sample was determined using the decay length significance, S = L XY /σ(l XY, where L XY is the decay length projected on the axis in the plane perpendicular to the beam (the XY plane and σ(l XY is its uncertainty. he significance distribution observed in the data as well as beauty, charm and LF distributions predicted by the MC simulations are shown in Fig.. he left side of the S distribution was mirrored on and subtracted from the positive side to suppress the symmetric LF component. o extract the beauty contribution in the data a binned χ fit of the mirrored significance distributions simultaneously in three bins of M V X was performed. Figure 4 shows the measured differential cross sections for beauty production as a function 0.0 < y < 0.7, E and η. NLO QCD predictions as well as Monte Carlo simulations scaled to the data are also shown. he shapes of the measured cross sections are described by both predictions. he data tend to lie 0 0% above the NLO QCD calculations. of E XY PoS(EPS-HEP Extraction of the beauty contribution to the proton structure function F, F b b In both analyses presented in Section and Section the double differential cross sections in Q and x were also measured. he double differential cross section for inclusive beauty production in DIS can be expressed as: dσ b b dq dx = πα ( xq 4 [+( y ]F b b (Q, x y FL b b (Q, x,

4 (pb / GeV / de dσ data / HVQDIS (pb / dη dσ data / HVQDIS (prel. 54 pb HVQDIS+-S hadr rad HVQDIS+ABKM hadr rad Rapgap x.6 ep e bbx e X E E (GeV (GeV (prel. 54 pb HVQDIS+-S hadr rad HVQDIS+ABKM hadr rad Rapgap x.6 ep e bbx e X η η Jet Figure 4: Measured differential cross sections as a function of E, η i bb F HERA 0. (prel. vtx 54 pb x=0.000 i=7 x=0.000 i=6 x= i=5 x=0.00 i=4 x=0.00 i= x=0.005 i= x=0.0 i= x=0.0 i=0 e 6 pb µ 4 pb µ+vtx 6 pb H vtx 46 pb -S+HVQDIS ABKM NNLO MSW08 NLO MSW08 NNLO CEQ6.6 NLO JR09 Q (GeV Figure 5: F b b as a function of Q at the fixed values of x. Results from the + µ (open triangles and secondary vertex (red triangles analyses are compared to the previous measurements by and H (various symbols and different predictions (lines and bands. PoS(EPS-HEP000 o extract F b b from the measured visible cross sections in bins of Q and x, an extrapolation to the full phase space was performed using NLO QCD calculations. he results of the extrapolation are shown in Fig. 5. he new measurements agree with other and H measurements [] as well as with various theoretical predictions. he measurement with the secondary vertices is the most precise F b b measurement from. 5. Conclusions Cross sections of beauty production in DIS were measured in events with muons and displaced secondary vertices. he measurements are well described by theoretical calculations. he beauty 4

5 contribution to the structure function F was found to be in agreement with previous H and measurements as well as with various predictions. References [] Coll., H. Abramowicz et al., Eur. Phys. J. C 69 (0 47 [hep-ex/05.96]. [] Coll., -prel [] Coll., H. Abramowicz et al., Eur. Phys. J. C 7 (0 57; Coll., S. Chekanov et al., Eur. Phys. J. C 65 (0 65; H Coll., F. Aaron et al., Eur. Phys. J. C 65 (0 89. PoS(EPS-HEP000 5