1. Diffractive W/Z Bosons Andrew Brandt UTA Run I Diffractive W/Z Boson Production Recap Run II Preliminary Search for Diffractive Z Bosons (Courtesy of Tamsin Edwards, Manchester)

2. 2 Why study Diffractive W/Z Boson Production?

3. 3 Diffractive processes at the Tevatron Diffractive processes are mediated by color singlet exchange: one or both protons remains intact color singlet: referred to as Pomeron, now usually thought of as a gluon pair or gluon ladder.. e.g. single diffraction: in hard diffraction, this can be high p T jets, W, Z... Signature of diffractive events: Rapidity gap - absence of particles or energy above threshold in some region of rapidity Proton track - detection of intact p/p in Forward Proton Detector

4. 4 Tracking North South Finding rapidity gaps Luminosity Monitors Forward Calorimeter Two arrays of scintillators close to beam pipe 2.7 < |η| < 4.4 Detect proton break-up Currently in Run II the output is ‘on/off’ for each side (in Run I multiplicity available) off for diffractive Use the electromagnetic and fine hadronic layers in region behind LM e.g. sum energy or count number of cells above threshold

5. 5 Run I Data Samples Z boson sample: Start with Run1b Z ee candidate sample Central and forward electron W boson sample: Start with Run1b W e candidate sample hep-ex/0308032;Accepted by Phys. Lett B

6. 6 Observation of Diffractive W/Z Observed clear Diffractively produced W and Z boson signals Background from fake W/Z gives negligible change in gap fractions Sample Diffractive Probability Background All Fluctuates to Data Central W(1.08 + 0.19 - 0.17)% 7.7  Forward W(0.64 + 0.18 - 0.16)% 5.3  All W(0.89 + 0.19 – 0.17)% 7.5  All Z (1.44 + 0.61 - 0.52)% 4.4  n cal n L0 Diffractive W and Z Boson Signals Central electron WForward electron W All Z n cal n L0 n cal n L0 DØ Preliminary

7. 7 Run I DØ/CDF Comparison CDF {PRL 78 2698 (1997)} measured R W = (1.15 ± 0.55)% for |  |<1.1 where R W = Ratio of diffractive/non-diffractive W (a significance of 3.8  ) This number is corrected for gap acceptance using MC giving 0.81 correction, so uncorrected value is (0.93 ± 0.44)%, consistent with our uncorrected data value: We measured (1.08 +0.19 –0.17)% for |  |<1.1 Uncorrected measurements agree, but corrections derived from MC do not… Our measured(*) gap acceptance is (21 ± 4)%, so our corrected value is 5.1% ! (*) : derived from POMPYT Monte Carlo Comparison of other gap acceptances for central objects from CDF and DØ using 2-D methods adopted by both collaborations: DØ central jets 18% (q) 40%(g) CDF central B 22%(q) 37% overall CDF J/  29% It will be interesting to see Run II diffractive W boson results!

8. 8 Run II Rapidity Gap System Use signals from Luminosity Monitor and Veto Counters (designed at UTA) to trigger on rapidity gaps with calorimeter towers for gap signal Work in progress (Mike Strang UTA, Tamsin Edwards U. Manchester); LM: 2.5 <  < 4.4 VC: 5.2 <  < 5.9

9. 9 Z bosons in the muon channel at DØ Z 0 → μ + μ - analysis Emily Nurse & Paul Telford DØ Note 4231 14 th Aug 2003 Dataset: February - June 2003 Before this run period the muon triggers required fastz, which vetoes diffraction Excluded data: Runs declared bad by SMT, CFT and muon groups Bad luminosity blocks

10. 10 3627 Z candidates Two central tracks matched to two ‘loose muons’ ‘loose’ - refers to quality of tracks in muon chambers Both muons have p T > 15 GeV Muons have opposite charge Di-muon invariant mass M μμ > 30 GeV At least one muon is isolated in calorimeter and tracking detectors Timing difference of hits in muon chambers |Δt| < 13ns Distance of closest approach < 0.16cm for both muon tracks Event fired one of the di-muon triggers Both muons are within |η| < 1.8 and not in muon chamber gap Z bosons in the muon channel at DØ Event selection and cuts: to exclude bb events to exclude cosmic rays

11. 11 Luminosity Monitor categories Fastz on (N+S both on) Gap N N off and S on and fastz off Gap S S on and N off and fastz off Gap SN S off and N off and fastz off Single diffractive candidates: Double Pomeron Exchange candidates: Non-diffractive candidates: N and S on and fastz off (this can happen due to halo or fastz inefficiency)

12. 12 Invariant mass: LM gaps All Z fastz on Gap S Gap SN N+S on fastz off 3627 3420 40 111 48 8 Gap N

13. 13 North EM Energy Sum All Z fastz on Gap S Gap SN N+S on fastz off Gap N E (GeV) If Gap is on south expect energy on North only Little energy on side of LM gap

14. 14 Run II Forward energy: noise sample E (GeV) High energy tail: hot towers/cells real energy deposits (e.g. if LM inefficient) 95% of noise sample has an energy sum of less than 3 GeV on at least one side Empty crossing data sample: No LM hits, No vertex

15. 15 Invariant mass: LM + calorimeter gaps All Z fastz on Gap S Gap SN N+S on fastz off 3627 3420 18 111 21 3 Gap N

16. 16 Comparing Z candidates However, the issue is not really whether these are Z’s but whether these are diffractive Z’s. Gap definition is still being defined

17. 17 Diffractive Z candidate event Strong candidate for diffractive Z event: LM N gap calorimeter N gap track in FPD on N side Red: EM energy Blue: Hadronic energy Yellow: missing E T (not including muons) RZ view XY view muon hits in 3 layers (overwrapped in φ here)

18. 18 Diffractive Z candidate event N side = outgoing anti-proton FPD system includes a dipole spectrometer on this side: Two scintillating fiber tracker detectors inserted into beam pipe Situated after the dipole magnet outside DØ If proton loses longitudinal momentum in a diffractive exchange, it is bent inwards by the dipole magnet Track position in detector 1 vs detector 2: Vertical plane Horizontal plane unbent vertically bent horizontally

19. 19 Current status and plans Gap definition: Highest priority: we need strong distinction between noise and real energy: Trying new variables (multiplicity of cells, clusters, towers above threshold) Fixing/killing bad calorimeter data such as hot cells Once standardized: make available to DØ to apply to any (all?!) analyses (anything you can do we can do diffractively) Diffractive Z analysis: Cannot progress without gap definition Manchester will continue with Z → μμ analysis update diffractive search alongside this aim to present at Moriond conference early 2004