1. Status of ZEUS Wolfram Zeuner DESY/Hamburg for the ZEUS Collaboration ZEUS Operation Shutdown Activities Physics Highlights Outlook & Summary PRC open session November 10, 2005

2. ZEUS Operation Congratulation to the HERA crew for the best running period ! HERA delivered 202pb -1 more than all HERA I HERA is able deliver to >1pb -1 /day for extended periods of time ZEUS is in very good shape, almost all gated data can be used for physics

3. ZEUS Operation ZEUS gated 150 pb -1 Efficiency: 74% ZEUS can record >1 pb -1 /day Recently typical efficiency ~80% Weekly efficiencies 2004 and 2004/05 DAQ very stable Main source of losses: HV trips caused by p-beam spikes

4. ZEUS Operation Recent example: good and bad fills Dead time due to HV trips and enormous trigger rates (Oct. 8 – Nov. 7): p-beam background e-beam background CTD current Efforts to improve the p-beam stability are appreciated good fill bad fill CTD Trips

5. Shutdown Activities Forward Straw Tube Tracker (STT) has insufficient cooling Interferes with solenoid operation STT is off since Oct. 2004 Adding cooling close to the solenoid should solve the problem. Problem – have to remove FDET without breaking the beam vacuum now With add. cooling 700 Kg CTD SC coil (~4.5K) p e

6. Shutdown Activities Pull detector over the GO magnet with a special jig Design has been reviewed by external engineers The jig is ready and tested The FCAL has to go off the bottom yoke onto extension rails ---------- The rest is standard repair and maintenance work Keeping in mind that the detector has to run for ~16 month without major shutdown Time schedule is ok

7. Physics Highlights HERA I data still being analyzed All publications so far on HERA I data First HERA II analysis close to publication Summer conferences were very successful ZEUS: 42 contributed papers to LP05/HEP05 5 HERA II analyses Report here: High Q 2 Cross Sections with Polarized e + /e - Beams Strong Coupling Constant from Inclusive Jets Charm Fragmentation Ratios and Fractions Factorization in Diffraction Isolated Leptons

8. High Q 2 Cross Sections with Polarized e + /e - Beams Q 2 > 200 GeV 2, y < 0.9 ZEUS DATA SAMPLE HERA II Right-handedLeft-handed e+e+ L=14.1 pb -1 P=31.8% L=16.4 pb -1 P=-40.2% e-e- L=6.5 pb -1 P=29.2% L=35.3 pb -1 P=-25.9% NC CC e-e- e-e-

9. High Q 2 Cross Sections with Polarized e + /e - Beams Charged current cross section with polarized leptons Direct observation of the chiral structure of the weak interaction Linear dependency on P clearly visible Agreement with SM prediction No indication of W R e+pe+p e-pe-p First CC measurement as function of polarization

10. Charged current cross sections with polarized leptons Effect of weak interaction visible in diff. distribution over full phase space Good agreement with SM prediction Can be used to further constrain PDFs in QCD fits e+pe+p e-pe-p

11. Neutral current cross sections with polarized leptons Again good agreement with SM Electroweak effect starts to become visible e+e+ e-e-

12. Strong Coupling Constant from Inclusive Jets Inclusive jets in Breit frame Previous measurement is published and used to extract α s Recently included in QCD-fit to reduce PDF uncertainties Now 2-fold statistics Prediction infrared insensitive High precision measurement Compare to NLO QCD (DISENT)

13. Strong Coupling Constant from Inclusive Jets (0.1182±0.0027) Best value for Q 2 > 500 GeV 2 Fit NLO QCD calc. Precision comparable to any other single measurement

14. Charm Fragmentation Ratios and Fractions Test universality of charm fragmentation Measure: (+ anti-particles) in photoproduction (Q 2 3.8 GeV) Calculate: R u/d : Ration of neutral to charged D-meson production rate γ s : Strangeness suppression factor P d v : Fraction of D-mesons produced in a vector state f(c  D,  c ): Fragmentation fraction of charm into D or  c

15. Charm Fragmentation Ratios and Fractions Charged and neutral D-mesons are produced with the same rate Ratio of strange to non-strange is 26% in charm fragmentation 57% of the charged D-mesons are produced in a vector state Smaller than spin counting prediction of 75%

16. Charm Fragmentation Ratios and Fractions General good agreement with e + e - Fragmentation fraction c  D * is lower and c  c is higher than in e + e - (correlated) First measurement of in γp Highest precision single measurement Universality of fragmentation is supported

17. Factorization in Diffraction Exchange of colorless object with quantum numbers of vacuum Cross section = Product of parton density function & hard scattering cross section J.C. Collins showed that factorization holds in ep DIS Phys. Rev. D57 3051(1998), J. Phys. G28 1069 (2002)

18. Dijets in Diffractive DIS NLO Calculations DISENT + diffr. Extension Data consistent with ZEUS and H1 QCD NLO fit GLP fit too low Shape of distr. not well described Sensitivity on diffractive PDF  main uncertainty No indication of factorization violation

19. Factorization in Diffraction Problem: CDF-Dijet rates factor 3-10 lower than expected, using HERA diffractive PDFs Idea: Cross section suppression by second. interactions Test at HERA with resolved photoproduction photon fluctuates into hadronic system, which takes part in hadronic scattering similar to hadron interactions prediction by Kaidalov et al res. γp cross section has to be rescaled by 0.34 Phys.Lett.B567 (2003),61 Dijets in photoproduction D * in photoproduction Hard scale: E T of jet or charm mass

20. Diffractive γp Production of Dijets Direct PhPResolved PhP NLO overestimates data by factor 1.6 Shape reasonably described Scaling the resolved component does not describe the resolved enriched sample No indication of factorization violation

21. Diffractive D * in Photoproduction NLO does not overestimate data opposite to dijets Shapes are reasonably described No indication of factorization violation Further studies needed: Diffractive PDFs PDF dependence of cross sections NLO description of inclusive and diffractive PDFs is consistent

22. Isolated Leptons SM process for isolated leptons with missing transverse momentum is single W production – cross section (LO) : 1.1pb SM background are DIS NC and CC an dileptons with some mis-measurement The favorite exotic process with the same signature is single top production Single top production ZEUS all HERA I data No excess to SM Neither e + nor e - Phys. Lett. B559,153 (2003) 1999-2000

23. New analysis Measure W cross section Cuts very close to those from H1 Analyse: HERA I e + data from 1999/2000 HERA II e + data from 2003/2004 Isolated e candidatesP T X > 25 GeV ZEUS (prel.) 99-00 e + p (66 pb -1 ) Obs:1; Exp: 0.92±0.09 (79% W) ZEUS (prel.) 03-04 e + p (40 pb -1 ) Obs:0; Exp: 0.58±0.09 (76% W) No excess to SM prediction Both samples are described by MC Signal: SM W-production Isolated Leptons

24. Outlook Reconstruction/Tracking very active field at ZEUS Well advanced: New pattern recognition combines CTD + MVD Kalman filter track fit and vertex reconstruction Under development: Integration of forward tracker and wheels of MVD Prelim. Impact parameter distribution of muons in γp MVD tagged D+ Pushing the tracking at HERA II towards the optimal performance More and more analyses will profit from high precision tracking

25. Summary HERA finishes its best running period ZEUS is performing very well and has taken lots of high quality data The STT will be operational again after the shutdown Many new and interesting physics results Majority of results still from HERA I data HERA II analyses well advanced Looking forward to a successful data taking in 2006/07