V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA XI International Workshop on Deep Inelastic Scattering St. Petersburg, April 2003 Vincenzo Chiochia Deutsches Elektronen Synchrotron on behalf of the ZEUS Collaboration

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA2 Outline Event topologyEvent topology Event selectionEvent selection Signal extraction and cross section calculationSignal extraction and cross section calculation QCD predictions and related uncertaintiesQCD predictions and related uncertainties Results: total and differential cross sectionsResults: total and differential cross sections Comparison with other measurementsComparison with other measurements Summary and outlookSummary and outlook

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA3 Process topology in the ZEUS experiment laboratory frame Inner muon chambers Outer muon chambers Barrel and rear calorimeter electron proton Central tracking detector (forward)(rear)

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA4 Summary of the event selection Data sample ZEUS e + p (60 pb -1 ) DIS cuts Q 2 >2 GeV <y<0.7 40<E-p z <65 GeV box cut 12x24 cm Muon cuts P( 2 )>1% p  >2 GeV 30º<  <160º Jet cuts At least one jet in the Breit frame: E T Breit >6 GeV -2< Lab <2.5 Jet associated to the muon: E T Breit >4 GeV QED radiation cuts Increase acceptance on signal Increase background rejection Kinematic region Background rejection and good electron reconstruction Probability cut: remove fake muons Momentum cut: from inner and outer muon chamber requirement Polar angle: good associated track

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA5 Extraction of the s.l. b-decays (1) After the selection cuts the data sample is a mixture of several processes: –Fake muons: Punch-through, Sail-through, pions and kaons in-flight decays (cross checked with real data) –Semi-leptonic decays of charmed hadrons –Semi-leptonic decays of beauty hadrons Introduce an observable to distinguish, on statistical basis, between the different processes: p T rel jet axis p T rel muon pe+e+ Jet and and muon are associated using the jet algorithm

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA6 836 events after all cuts836 events after all cuts Charm and light-quark ptrel distributions are added together according to the respective cross sections The b-fraction is extracted with the Binned maximum likelihood method f b = (25.3±4.8)% The algorithm takes in account the statistical errors of the data and MC samples in each binThe algorithm takes in account the statistical errors of the data and MC samples in each bin Extraction of the s.l. b-decays (2) ~210 beauty events

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA7 Comparison with the simulation ~25% of events from b-decays Good description of the event kinematics with the extracted fractions muonvariables jetvariables

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA8 QCD predictions: NLO calculations The calculation of the NLO QCD predictions proceeds in three steps: 1)HVQDIS (B.Harris, J.Smith, hep-ph/ ) : *gbb, *gbbg, *qbbq, etc. 2)Fragmentation of the b-quark into a B-meson 3)Semileptonic decay of the B-meson b quark pQCD O(  s ) corrections Charmed hadron Neutrino Experiment Lepton Fragmentation Peterson function with  =0.002 Muon momentum spectrum extracted from MC

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA9 Results and QCD predictions ep  e b b X  e  Jet X Kinematic region: Q 2 > 2 GeV 2, GeV 2, 0.05<y<0.7 At least one jet in the Breit frame with: E T Breit > 6 GeV, -2 6 GeV, -2< Lab <2.5 At least one muon with: p  >2 GeV, 30 2 GeV, 30<  <160 Measured cross section:  vis = 38.7±7.7(stat.)+6.1(syst.)-5.0(syst.) pb NLO QCD (HVQDIS):  NLO = pb  R,F 2 = Q 2 +4m b 2 m b =4.75 GeV Peterson frag. function Proton parton distribution: CTEQ5F4 ModelProgramCross Section (pb) LOHVQDIS14.4 ME+DGLAPRAPGAP17.1 CDMRAPGAP16.3 ME*+CCFMCASCADE36.8  R,F 2 = p T 2 +4m b 2 Data/NLO ~ 1.4 but in agreement within exp. and theoretical uncertainties

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA10 d/dQ 2 measured at HERA for the first time! NLO MC

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA11 d/dlog(x bj ) NLO MC

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA12 NLO QCD uncertainties more sources: Hadronization (jet): ~ 10% Fragmentation (muon): 5-10% Factorization and renormalization scales  b-quark mass: 10-15% Gluon uncertainty from the ZEUS NLO QCD fit:~5% CTEQ5F4/ZEUS NLO FIT

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA13 A tricky business... H1 DIS: jets extrapolated to the full phase space H1 Photoproduction: jets extrapolated to the full phase space red: ICHEP02 results ZEUS D*-muon: extrapolated to the parton level ZEUS Photoproduction muon extrapolated to the full phase space The visible cross section agrees with the NLO! This analysis visible cross section jets in the Breit frame

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA14 Summary and conclusions The description of the b-quark production is still an open question. Cannot draw a unique conclusion from the existing results. We have measured a visible cross-section of b-quark production in DIS and single differential cross-sections (Q 2, x bj ) for the first time at HERA The cross section is measured with events containing the scattered positron, a hard jet in the Breit frame and a muon traversing the inner and outer muon chambers. Detailed analysis of the theoretical uncertaities has been performed The measured cross-section is a factor ~1.4 above the NLO QCD predictions but in agreement within the experimental and theoretical uncertainties Similar result in the ZEUS measurement in photoproduction

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA15 SPARE SLIDES

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA16 Acceptance, efficiency, purity ME+PS CDM ME+PS (e - p) ME*+CCFM

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA17 b-quark fragmentation [hep-ph/ ]

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA18 Event simulation: Monte Carlo Parton shower with DGLAP Evolution Matrix Element with incoming on-shell gluon K T ordering in the gluon ladder RAPGAP: –Lund string model –Color dipole model and ME+PS Parton shower with CCFM-like evolution CASCADE Matrix Element with incoming off-shell gluon Angular ordering in the gluon ladder Direct (pointlike) component only Gluon density unintegrated in k T and extracted from a fit to the HERA structure function F 2 Lund string model Increasing virtuality Increasing emission angle Light quarks: ~120·10 6 events (200 pb -1 ) Charm quarks:~7.5·10 6 events (94 pb -1 ) Beauty quarks:~430·10 3 events (540 pb -1 )...more samples generated to understand the model dependance

V. Chiochia DIS 2003 Workshop Production of beauty quarks in deep inelastic scattering at HERA19 Visible vs extrapolated measurements Visible cross sectionVisible cross section: the kinematic region is close to the detector acceptance Example: ep  bbx   Jet Jet X Model assumptions are not absorbed in the experimental result but in the corresponding QCD predictions → published measurements are then safe Extrapolated cross sections Extrapolated cross sections: 1)Extrapolation to an unmeasured kinematic region: 1)Extrapolation to an unmeasured kinematic region: the unmeasured phase space is taken from a Monte Carlo simulation (for example: extrapolation to the jet or muon full phase space) It is nice to quote more general and inclusive measurements, but... Is the  and E T spectrum of the extrapolated region the same in the NLO as in the Monte Carlo? How large are the extrapolation factors? Are they reported in the published results? Is the extrapolation considered in the estimation of the systematic uncertainties? 2)Extrapolation from detector to parton/hadron level: 2)Extrapolation from detector to parton/hadron level: the corresponding correction factors are extracted from a Monte Carlo simulation