ZEUS Highlights for ICHEP02... a personal selection

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1 Highlights for ICHEP... a personal selection Main Questions at HERA: Tancredi.Carli@desy.de What is the structure of the proton? Is DGLAP working at low-x? How are heavy quarks produced? Is the SM valid at high energies? Incl. DIS & PDF Fits strange, charm, beauty Tau High Et: electrons&jets How can we understand soft processes? More complex proton description : GPD? DVCS/J/Ψ & F D3 What drives colour singlet proton component?

2 em F -log (x) 5 x=6.3e-5 x=. x=.6 x=.53 x=.4 x=.5 x=.63 x=.8 NLO QCD fit tot. error 96/97 Final incl. DIS PDF-Fits x=.3 BCDMS 4 3 x=. x=.3 x=.5 x=.8 E665 NMC Proton structure function F : impressive precision over wide x, Q range x=.3 x=. x=.3 x=.5 x=.8 x=.3 x=.8 x=.5 x=.4 x= Q (GeV ) Final PDF-fits: Needs precise data and careful evaluation of exp. uncertainties much improved fit technique Not always Gaussian

3 Extraction of parton densities and exp. uncertainties xf NLO QCD fit α s (M Z ) =.8 tot. error CTEQ 6M MRST Q = GeV xu v.4 xg(.5) xd v.3 α impressive precision agreement with global fits simultaneous fit: PDF & α s : s ( ).. M Z =.66 ±.8 (uncorr) ± ±.36 (norm) ± xs(.5) (corr) (model) plus additional ±.4 from ren. scale x

4 Valence Quarks from One Experiment: US only, i.e. F HERA-I: high-q NC/CC + fixed target QGeV = GeV NLO QCD fit GeV ONLY fit (prel.) (94- data) - xq V x u better known than d, d can be fixed by high-q CC, no need to discuss deuterium binding corrections in fixed target data... hardly need fixed target data GeV GeV GeV x

5 Parity Violating Part of the Proton Structure Function xf 3 d dx dq L,R x F ~.4. σ NC e ± L,R πα x Q = ± ( x q(x) x q (x)) 3 Comparing e+p/e - p Q = 5 GeV Q = 3 GeV Q = 5 GeV e ± p S [ L,R L,R ] Y F m Y x F with Y = ± ( - y) sensitive to valence quark a) First measurement Need more luminosity with e - p -..4 Q = 8 GeV Q = GeV Q = 3 GeV

6 Gluon Density 6 Q = GeV.5 GeV Greatly improved precision! Gluon known within % for Q > GeV and -4 <x< - by only considerable uncertainty for x>. -> include jets! xf 4 - xs ONLY fit xg 7 GeV tot. error uncorr. error xs xg GeV Gluon valence-like or even negative for Q ->: end of applicability of DGLAP? Fitted F L also negative direct determination of F L would provide additional independent information -> lower HERA E p or use ISR 3 xs xg GeV xg xs xg GeV xg xs xs

7 Q (GeV ) New F Points at low Q : ISR Analysis ISR lowers electron energy difficult analysis: need precise knowledge of Bethe-Heitler overlays previously unexplored! (Prel.) BPT 997 SVX 995 ISR 996 (Prel.) NMC BCDMS CCFR E665 Kinematic limit y= y= So far only small data set analysed F x Q =.3 GeV Q =.65 GeV Q =.3 GeV Q =.5 GeV Q = 4.5 GeV Q = GeV Q = GeV x (prel.) ISR 96 BPC 96/97 SVX 95 96/97 Consistency in overlap region: prove of method -> direct F L in reach? NLO-QCD Fit ALLM97

8 Lab: Breit: Φ meson: Access to Strange Sea? s s Φ current quark hemisphere s Φ dσ / d x p (φ) (nb).6.4 entries/(.5 MeV) < x p < M (GeV) (prel.) Monte Carlo models (CTEQ5) LEPTO,ARIADNE (. < λ s <.3):. with γ * s s+x without γ * s s+x x p = p Q : Φ leading particle HERWIG with γ * s s+x HERWIG without γ * s s+x x p -> : need strange sea as expected from PDF-fits low x p : better understanding of Φ formation needed! x p (φ)

9 Charm: D * Cross Sections in γp Collisions dσ/dp T (nb/gev) dσ/dw (nb/gev) (prel.) 98- a) NLO QCD FONLL 5 5 p T (D * ) (GeV) c) dσ/dη (nb) dσ/dz (nb) b) - η(d * ) d) central NLO significantly below data largest disagreement: medium p T,D forward η low z=(e-p z ) D /(E-P z ) all major exp. progress: data errors smaller than theory errors! FONLL: massive NLO QCD plus resummation of NLO logs not better Need better theory W (GeV) z(d * )

10 dσ/dη (nb) (prel.) 98- a).9 < p T (D * ) < 3.5 GeV dσ/dη (nb) < p T (D * ) < 5 GeV b) Central NLO significantly below data largest disagreement: medium p T,D forward η low z=(e-p z ) D /(E-P z ) all 4.5 dσ/dη (nb).8 - η(d * ) 5 < p T (D * ) < 8 GeV c) dσ/dη (nb) η(d * ) 8 < p T (D * ) < GeV d) major exp. progress: data errors smaller than theory errors!.6.4. NLO QCD FONLL - FONLL: massive NLO QCD plus resummation of NLO logs not better η(d * ) η(d * )

11 Beauty in γp Collisions - semi-leptonic µ decay Full HERA-I data set -> data error ~ theory errors dσ/dη µ (pb) Visible beauty cross-section: ep -> e + jet + jet + µ+x dσ dη µ (ep bb e jj µ X) Q < GeV.<y<.8 p j,j >7,6 GeV η j T <.5 p µ T >.5 GeV (prel.) 96- NLO QCD x hadr. NLO QCD dσ/dp T µ (pb/gev) dσ dp T µ (ep bb e jj µ X) Q < GeV.<y<.8 p j,j >7,6 GeV η j T <.5 -.6<η µ <.3 (prel.) 96- NLO QCD x hadr. NLO QCD η µ p T µ (GeV) data/theory ~.4, but compatible within exp/theo uncertainty!

12 Beauty in γp Collisions - via µ and D * -decay Full HERA-I data set: µ jet D B K π π secondary vertex D* candidates (prel.) 96- beauty charm (prompt µ) charm (fake µ) µ K D B primary vertex Almost background free sample! 5 jet e 5 Gives access to low p T study b close to kin limit 5 σ ( ) * γ p bb X D µ X = 59 ± 4 (stat) ± 65(syst) pb R (µ-d * )

13 dσ/dq (pb/gev ) Beauty in DIS - semi-leptonic µ-decay First time differential distributions (L~ 6 pb - ) In Breit frame: Visible beauty cross-section: ep -> e + jet + µ+x σ(e + p e + bb - X e + µ ± Jet X) (prel.) 99- NLO QCD (HVQDIS) 4.5 < m b < 5. GeV /4(Q +4m b ) < µ < 4(Q +4m b ) dσ/dq (pb/gev ) σ(e + p e + bb - X e + µ ± Jet X) (prel.) 99- O(α s ) QCD CCFM (CASCADE) O(α s ) QCD DGLAP (RAPGAP) -.5 < y <.7 P µ > GeV, 3 o < θ µ < 6 o Breit > 6 GeV, - < η Lab <.5 E t,jet Jet -.5 < y <.7 P µ > GeV, 3 o < θ µ < 6 o E Breit > 6 GeV, - < η Lab <.5 t,jet Jet Q (GeV ) NLO agrees within uncertainties, LO+CCFM perfect 3 B-puzzle solved!? Q (GeV )

14 Tau-Identification: consider hadronic tau -decay based on internal jet structure: collimated (pencil-like) jets, mostly only track Multi-variate Discriminant (hep-ph/4) based on range searching optimised on CC-DIS and W->ντ sample: dn dd N + (prel.) 99- e p SM CC DIS - SM W ντ (hadr.) - -3 QCD jets Tau jets D Good separation tau efficiency ~5% bg rejection ~55

15 Search for Isolated Tau-Leptons and Missing Pt Event selection: - p miss T (D - not - not > - isolated track with p track,track GeV electron or muon acoplanar >.5, D track,jet 5 GeV 4 events found! 3 are compatible with tau hypothesis, i.e. Discriminant D >.95 D data : P X T > > data :.95 : 3 5 GeV : SM : T > > SM :.3 ±..8) ± events (prel.) 94- SM W only Single Top MC X (GeV) P T

16 Tau- Candidate P 37 GeV P 48 GeV M CAL X T = T = T = 3 GeV

17 Tau- Candidate P 39 GeV P 37 GeV M CAL X T = T = T = 68 GeV

18 Status: Isolated Lepton Events at HERA I H (e and µ events) (τ events)

19 e p e p Grape: e e γ/ζ + γ/ζ l l - l γ l γ N p γ (a) Bethe-Heitler type diagrams γ - l + l e N (b) QED-Compton type diagrams e p + electroweak diagrams Two electrons : Data Data SM.8 ± SM M Three electrons :,. E.4 ±. γ.4 ± Multi-Electron Events γ > 3 GeV GRAPE. e l - + l N > GeV : T, GRAPE.5 ±. e l - + l N events - - (prel.) 94- GRAPE+NC+QEDC NC+QEDC QEDC M (GeV) Overall good agreement no excess at high mass in µ channel no event M> GeV

20 E = 56 GeV E 53 GeV M T T = = 34 GeV

21 E E E T T T3 = 5 GeV = 47 GeV = 36 GeV θ θ θ 3 =. rad =.76 rad =.58 rad M = 94 GeV

22 dσ/de T jet (pb/gev) Inclusive Jet-Cross Sections in γp (prel.) 98- (8. pb NLO QCD LO QCD - ) - - (Data-NLO QCD)/NLO QCD jet energy scale uncertainty NLO uncertainty E jet T (GeV) High precision data Excellent agreement over 4 orders of magnitude no excess at high E T

23 d 3 σ/d(p jet ) 3 (E T jet ) 4 E jet (Data-NLO QCD)/NLO QCD -4 (prel.) 98- (8. pb - ) NLO QCD LO QCD - < η jet γp < and W γp = 55 GeV Invariant Inclusive Jet-Cross Sections jet energy scale uncertainty NLO uncertainty jet x T = E T /W γp Ratio of scaled cross sections.4..8 (prel.) 98- (8. pb - ) NLO QCD scaling W γp = 8 GeV/W γp = 55 GeV - < η jet γp < jet energy scale uncertainty NLO uncertainty..3.4 x T = E T jet /W γp Evidence for scaling violations in γp collisions

24 Impressive description of NLO QCD of these precise data: dσ/de T,jet B (pb/gev) Inclusive Jet Production in DIS Jet energy scale uncertainty NLO QCD: (corrected to hadron level) α s (M Z )=.75 DISENT MRST99 (µ R =ET,jet B ) DISENT MRST99 (µ R =Q) 5 < Q < 5 GeV ( 5 ) 5 < Q < 5 GeV ( 4 ) 5 < Q < GeV ( 3 ) < Q < GeV ( ) < Q < 5 GeV ( ) Q > 5 GeV ( ) E B T,jet (GeV) α s (E T,jet B ) for α s (M Q Z ) Theoretical uncertainty from α s (M Z )= > 5 GeV : =. ± (syst).3 (stat).8.7 E B T,jet (GeV) Very precise measurement! (theo)

25 e p Q γ * Deeply Virtual Compton Scattering GPD-based Model (FFS) High-x (HERMES) e x x γ p e Low-x () x x p Q γ x e x dx A ~ C( ξ/x,q ) H(x, ξ,q ) x H: Off-diagonal PDF γ p σ(γ * p γp) (nb) - (prel.) 96-97,99- e + p FFS DD 4 < W < 4 GeV W = 89 GeV Colour Dipole Model (DD) γ * z R z b γ A ~ * γ Ψini R,z σ dipole - Ψ γ out σ Q - n, n.47 DVCS = ± Data getting precise Q spectrum seems harder than predicted by FFS HERA-II: e + /e - and polarisation! Q (GeV )

26 e(k') e e e(k) Q γ * γ γ V σ(γ * p γp) (nb) 4 8 p(p) p(p') (prel.) 96-97,99- e + p FFS DD 5 < Q < GeV Q = 9.6 GeV δ σdvcs W, δ =.78 ±. σ γp J/ψp (nb) p J/ψ µ + µ J/ψ e + e - H E4 E56 p W δ fit to data δ =.69 ±. (stat.) ±.3 (syst.) W (GeV) W-dependence points to hard process as e.g. in J/Ψ production W (GeV)

27 x β P = New: F D3 Data e p γ* M x gap M N Analysis using FPC (L=4 pb - ): coverage 4. < η < 5. increased M X range +extension reduced bias from nucleon dissociation to lower Q D3 if F ~ x P if diffraction from = x ( + x x p data : diffraction W M λ X is has /Q ) expect soft ( λ hard x P F D3 ) ~ const, component! M X < (prel.) 98/ <β>=.63 <β>=.3 <β>=.7 <β>=.9 <β>= GeV <β>=.8 <β>=.7 <β>=.3 <β>=. <β>=.9 <β>=.94 <β>=.43 <β>=.77 <β>=.4 <β>=.5 <β>=.43 <β>=.4 <β>=.66 <β>=.8 <β>=.48 <β>=. <β>=.6 <β>=. <β>=.9 <β>=.87 <β>=.59 <β>=.9 <β>=.97 <β>=.33 <β>=.5 <β>=.93 <β>=.73 <β>=.43 <β>=.7 <β>=.64 <β>=.3 <β>=.8 <β>=.84 <β>=.58 <β>=.9 <β>=. <β>=.58 Q =. - 3 GeV Q = 3-5 Q = 5-7 Q = 4-8 Q = - 4 Q = - Q = 7 -

28 What happens here? Much improved precision! Same energy dependence in inclusive and diffractive scattering! M X = - GeV M X = - 4 GeV (prel.) 98/99 M X = 8-5 GeV M X = 5-5 GeV Naive expectation: σ tot ~ g(x,q ) ~ x -λ Hard : Soft : σ σ diff diff ~ ~ x g(x,q -ε ) ~ x - λ, ε =.8 << λ M X = 4-8 GeV M X = 5-35 GeV Diffraction contains soft and hard pieces even at large Q Recently models (like CDM) tried to explain this -> new challenge by more precise data!

29 Conclusions New level of extraction of parton density and α s and their experimental uncertainties reached...hardly need fixed target data HERA-II: e + / e - program ahead of us! (also for xf 3!) Direct F L measurement seems in reach via ISR analysis HERA-II: dedicated run with lower beam energy? Analysis of hadronic final state enters new stage: many interesting results from jets -> combine with incl. DIS particle ID: strange, charm, bottom,...tau HERA holds the key for production mechanism of heavy quarks Isolated Lepton story continues: wait for answer at HERA-II Can the SM hold the strength? DVCS: towards determination of off-diagonal PDF HERA-II: e + / e - and polarisation new precise F D3 new challenge for models

30 < n sbj > Internal Jet structure y cut = - Q > GeV (prel.) e + p CC - DIS MEPJET (NLO) CDM (LO) E jet T > 4 GeV - < η jet < E jet T [ GeV ] Internal jet structure well described by NLO and MC

31 Isolated high-pt lepton selection: events (prel.) 94- SM W only Single Top MC p miss T (D > isolated track with p track,track GeV >.5, D track,jet 5 GeV.8) not electron or muon, not acoplanar 4 events found 3 are compatible with tau hypothesis T > > D> log(-d)