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Hadronic Final States and QCD at HERA

Hadronic Final States and QCD at HERA. Claire Gwenlan (Oxford, STFC Fellow) a celebration of HERA and the UK role IOP meeting: 25 June 2008. = This means significant UK effort!. With many thanks to: Claudia Glasman, Thomas Kluge, Steve Maxfield, Mark Sutton, Dan Traynor.

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Hadronic Final States and QCD at HERA

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  1. Hadronic Final States and QCD at HERA Claire Gwenlan (Oxford, STFC Fellow) a celebration of HERA and the UK role IOP meeting: 25 June 2008 = This means significant UK effort! With many thanks to: Claudia Glasman, Thomas Kluge, Steve Maxfield, Mark Sutton, Dan Traynor

  2. Hadronic Final States UK has played a leading role in all of the above What? Final states containing hadrons(particles, jets) Why? Study of Hadronic Final States at HERA allows: • tests of our understanding of pQCD • extraction of QCD parameters (s,…) • in regions where experimental and theoretical uncertainties are small • constraints on proton and photon structure • highlight areas that require further theoretical input • low-x region, non-perturbative hadronisation process, underlying event, … Hadronic Final States and QCD at HERA  Claire Gwenlan 1/26

  3. … and How? We Measure: e Particle Production Jets e Cross Sections Substructure Forward Jets Hadrons Photons Event Shapes * fragmentation to obtain results on: • tests of pQCD predictions • measurements of s • proton, (photon) structure • explore low x region: breakdown of DGLAP? • non-perturbative effects (hadronisation, underlying event, …) Hard Scatter (pQCD,s) p proton structure proton remnant/ underlying event Hadronic Final States and QCD at HERA  Claire Gwenlan 2/26

  4. … and How? We Measure: e Particle Production Jets e Cross Sections Substructure Forward Jets Hadrons Photons Event Shapes * fragmentation (Rough) outline of talk: • tests of pQCD predictions • measurements of s • proton, (photon) structure • explore low x region: breakdown of DGLAP? • non-perturbative effects (hadronisation, underlying event, …) (+ a few extras if I have time…) Hard Scatter (pQCD,s) p proton structure proton remnant/ underlying event Hadronic Final States and QCD at HERA  Claire Gwenlan 2/26

  5. Jet Production at HERA HERA: ideal environment for precision studies of QCD  tests of hadron-induced reactions (unlike e+e-) but cleaner than pp in case of “resolved” p, need photon PDF as well Observable =ΣflavoursPDFmatrix-element Observable =ΣflavoursPDFPDFmatrix-element Observable =ΣflavoursPDFmatrix-element parton density: describes structure of proton sub-process cross section (calculable in pQCD) Hadronic Final States and QCD at HERA  Claire Gwenlan 3/26

  6. Blast from the Past… from FIRST H1 physics paper Some FIRST measurements of jet production at HERA (in DIS and p) in p in DIS 1992 data (27nb-1) June-July 1992 (51 events) Hadronic Final States and QCD at HERA  Claire Gwenlan 4/26

  7. Situation Today… EXAMPLE: inclusive jets in DIS NOW: many many very high precision measurements in DIS and p: • extending to high Q2,ET • single,double,triple differential • inclusive,dijet,multijet (+ using infra-red/collinear safe jet definition) typical experimental precision ~5% C.F. ~50-60% at the Tevatron Small hadronic energy scale uncertainty by energy balance with scattered e Hadronic Final States and QCD at HERA  Claire Gwenlan 5/26

  8. Jets at HERA also sensitive to strong coupling s: fundamental parameter of QCD (but has to be extracted from experiment) s input from Liverpool theory uncertainty often larger than experimental !! DIS Some more examples (in DIS and p): excellent description by NLO QCD over many orders of magnitude in the cross section (pQCD working well!!!) Glasgow FIRSTs from p DIS p Hadronic Final States and QCD at HERA  Claire Gwenlan 6/26

  9. s from HERA extraction of s: • Generate cross section predictions for different s • Parameterise: • (s) = As+Bs2 • Compare to measured cross section • Read off s and it’s uncertainty cross section NLO QCD measured value 0.110 … 0.116 … 0.122 s(MZ) Before looking at set of HERA s values, take a look at one more measurement … Hadronic Final States and QCD at HERA  Claire Gwenlan 7/26

  10. Jet Substructure Bristol and Glasgow including FIRSTmeasurement in p p: • Quark and gluon jets different (gluon broader) • Direct processes, mostly quarks through g qq (– like DIS) • Resolved processes give rise to quark and gluon jets through: qgqg, gg gg, … Why? • more stringent tests of pQCD predictions • study differences between quark- and gluon-initiated jets • determinations of s resolved photon region • also method to obtain quark- or gluon-enriched samples Results:consistent with expectations Hadronic Final States and QCD at HERA  Claire Gwenlan 8/26

  11. Jet Substructure Bristol and Glasgow including FIRSTmeasurement in p p: • Quark and gluon jets different (gluon broader) • Direct processes, mostly quarks through g qq (– like DIS) • Resolved processes give rise to quark and gluon jets through: qgqg, gg gg, … Why? • more stringent tests of pQCD predictions • study differences between quark- and gluon-initiated jets • determinations of s DIS: shape well described by NLO QCD, sensitivity to s  Hadronic Final States and QCD at HERA  Claire Gwenlan 8/26

  12. HERA s UK led Bristol, Glasgow, Oxford, UCL more than 1/3 of these analyses led by UK groups… HERA s summary • Wealth of precision extractions from HERA from variety of observables * * * • Consistent with each other and with world average • Dominating uncert.: theory (need NNLO) * * = mentioned in this talk Hadronic Final States and QCD at HERA  Claire Gwenlan 9/26

  13. HERA Combined s input from Liverpool, QMUL • Wealth of precision extractions from HERA from variety of observables averageof HERA determinations  [C. Glasman et al. ] (now included in Bethke world average) RECENT IDEA (HERA combined s): • combined H1+ZEUS fit of one observable: inclusive jets in DIS • program towards the HERA s (+ another example of recent collaborative effort) HERA combined s (2007):s(MZ) = 0.11980.0019(exp.)0.0026(th.) [c.f. world average in 1989: s(MZ)=0.110.01 (only at 10%) - now PDG and Bethke world averages constantly updated] Hadronic Final States and QCD at HERA  Claire Gwenlan 9/26

  14. HERA s HERA jet data s(Q) • Wealth of precision extractions from HERA from variety of observables clear running of s experimental precision as good as LEP Hadronic Final States and QCD at HERA  Claire Gwenlan 9/26

  15. Final States and the Gluon LO QCD: ~s.g(x) Jet Jet • Gluon in proton mainly  constrained by HERA S.F. data • only indirectly sensitive to gluon • constrains low x region • Global fits for proton structure: • high x gluon poorly known • impact on high energy pp collisions • low x: gluon large…DGLAP sufficient? Several final states directly sensitive to the gluon in the proton jets, prompt photon, heavy flavours, … Hadronic Final States and QCD at HERA  Claire Gwenlan 10/26

  16. Gluon PDF led by Oxford and UCL PIONEERING method allowing FIRSTrigorous use of jet data in an NLO QCD fit HERA Jets: sensitive to gluon (and quark) content of proton p: also to photon structure TopCite 50+ • included in fit for proton PDFs • DIS andp data used (along with NC/CC inclusive data) Hadronic Final States and QCD at HERA  Claire Gwenlan 11/26

  17. Gluon PDF led by Oxford and UCL PIONEERING method allowing FIRSTrigorous use of jet data in an NLO QCD fit HERA Jets: sensitive to gluon (and quark) content of proton p: also to photon structure • Gluon uncerts. substantially reduced !!! (medium to high x) • precisionextraction of s also obtained (treat as additional free parameter in fit – see backups) Proof of Principle:wealth of other HERA-I and -II data also now available!!! Hadronic Final States and QCD at HERA  Claire Gwenlan 11/26

  18. Prompt Photons Prompt Photons: • further constraints on proton and photon structure • sensitive/clean probe of QCD • less sensitive to hadronisation • also background to H   resolved  ep: Q2 >> 1 GeV2 p: Q2 ~ 0 GeV2 led by Glasgow Group FIRSTobservations in p and DIS at HERA p DIS Latest Status(more recent H1+ZEUS measurements): SURPRISE:NLO QCD too low at small ET Hadronic Final States and QCD at HERA  Claire Gwenlan 12/26

  19. Prompt Photons Prompt Photons: • further constraints on proton and photon structure • sensitive/clean probe of QCD • less sensitive to hadronisation • also background to H   e p resolved  ep: Q2 >> 1 GeV2 p: Q2 ~ 0 GeV2 data from Glasgow Group extra contribution  plot from James Stirling prediction only currently available for inclusive prompt  in DIS Interesting Aside: proton PDF containing photons (MRSTQED04) able to describe data? Hadronic Final States and QCD at HERA  Claire Gwenlan 12/26

  20. Multijets Multijets(and the Underlying Event) expected to contribute at small x s s s multiparton interactions: secondary interaction(s) between beam remnants EXAMPLE: 4-jets at LO: O(s3) Rich testing ground: • multijet production directly sensitive to higher order QCD • tests of parton showers in Monte Carlo models Rich testing ground: • multijet production directly sensitive to higher order QCD • tests of parton showers in Monte Carlo models Also: sensitive to multiparton interactions /underlying event  test/tune models Hadronic Final States and QCD at HERA  Claire Gwenlan 13/26

  21. Multijets(and the Underlying Event) NB: HERWIG MPI model (Jimmy) also UK contribution; created for HERA p Since these data published, pO(s3) calculation has become available Glasgow; Bristol and UCL • Need contribution from multi-parton interactions at low x(and low invariant mass) • Can tune models to data (HERWIG+MPI is in this case!) • input for LHC models !!! FIRST measurement of 3jets in p; FIRST (and still only) measurement of 4jets in p • precise hadronic data (testing ground for higher order pQCD predictions, as well as hadronisation and MPImodels) Hadronic Final States and QCD at HERA  Claire Gwenlan 14/26

  22. Gaps Between Jets LOOK at high-pT jets, with large : [means that s >> -t~|pT2| >> ΛQCD2] (diffractive limit, yet perturbatively calculable) 2 proton remnant Jet 2 proton remnant Jet      Gap Jet photon remnant Jet 0   photon remnant 0   IDEA:search for strongly interactinghard colour singlet exchange:“QCD pomeron” (complementary to other diffractive studies) • standard QCD:- exchange of coloured quark or gluon  hadronic activity between jets • colour-singlet exchange:- little or no activity in region between jets  a “Gap” excess of “Gap” events  evidence for strongly interacting hard CSE Hadronic Final States and QCD at HERA  Claire Gwenlan 15/26

  23. Gaps Between Jets Manchester; UCL and Oxford IDEA:search for strongly interactinghard colour singlet exchange:“QCD pomeron” (complementary to other diffractive studies) Fraction of events with a gap (f): • measured excess over predictions of standard QCD!!! • can be described by models with colour singlet exchange excess of “Gap” events  evidence for strongly interacting hard CSE Hadronic Final States and QCD at HERA  Claire Gwenlan 15/26

  24. Problematic Regions:p to DIS REMINDER: • p:direct and resolvedphoton • resolved is suppressed as Q2 increases  so not usually considered in DIS calculations BUT: separation between p and DIS is unclear !!! Results (for low Q2 DIS): • NLO QCD fails at low ET, Q2 • MC with resolved photon OK Need resolvedvirtual photon? input from Liverpool [Glasgow: similar analysis on ZEUS] Hadronic Final States and QCD at HERA  Claire Gwenlan 16/26

  25. Low x: breakdown of DGLAP? No evidence for breakdown of DGLAP in S.F. data  turn to HFS • Probing Parton Dynamics: forward jetsused to hunt for signs of breakdown of standard DGLAPevolution and onset of BFKL dynamics expected at low x DGLAP: kT increases DGLAP:assumptions mean that large transverse energy jets/particles in forward direction (near proton) are suppressed (i.e. kT1 << kTn) BFKL (expected at small x):no such suppression in forward direction HERA: DIS probes down to xBj~10-5 Hadronic Final States and QCD at HERA  Claire Gwenlan Hadronic Final States and QCD at HERA  Claire Gwenlan 17/26

  26. Forward Jets input from Liverpool RG: DGLAP Monte Carlo CDM: unordered kT DGLAP NLO QCD • Direct DGLAP fails • - Resolved photon MC better (‘mimics’ higher orders) • - ‘BFKL-like’ (CDM) also better – BUT (still) no full BFKL calculation NB. same data in both Hintsof breakdown of DGLAP but status still unclear !!! Hadronic Final States and QCD at HERA  Claire Gwenlan 18/26

  27. Hadronisation Process Hadronic Final State can be characterised by Event Shape observables • Event Shape Variables:describe energy and momentum flow (i.e. the ‘shape’) of the final state • inspired by e+e- measurements • typical example: thrust (measures collimation of hadronic system) thrust: pencil-like 1-T  0 spherical 1-T > 0  also broadening, C-parameter, jet mass, … Sensitive to non-perturbative hadronisation process Hadronic Final States and QCD at HERA  Claire Gwenlan 19/26

  28. Event Shapes in DIS ZEUS effort led by Glasgow Depends on new parameter 0 Hadronisation described by: • (usually) phenomenological models as implemented in MCs OR: • ‘Power Correction Model’ [Dokshitzer and Webber] - understand hadronisation from first principles? ZEUS data vs pQCD+PC predictions Good agreement • Compare event shape data to combination of NLO QCD and power correction model (F = event shape) F = Fperturbative + Fpower-correction ZEUS pQCD bit hadronisation bit (~1/Q) Hadronic Final States and QCD at HERA  Claire Gwenlan 20/26

  29. Event Shapes in DIS ZEUS effort led by Glasgow • can get good description of event shapes using power corrections (added to pQCD) • universal non-perturbative parameter: 0 = 0.5 10% • can also extract s (consistent with world average) • Compare event shape data to combination of NLO QCD and power correction model (F = event shape) F = Fperturbative + Fpower-correction pQCD bit Depends on new parameter 0 hadronisation bit (~1/Q) Hadronic Final States and QCD at HERA  Claire Gwenlan 20/26

  30. “There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.” Lord Kelvin vs. Dave Milstead Hadronic Final States and QCD at HERA  Claire Gwenlan 21/26

  31. Chasing the Magnetic Monopole magnetic charge: when n=1, g = gD(Dirac magnetic charge) Q = electric charge (eg. e for electron) e HERA em e g m m In some theories, monopoles can have low masses - even O(10 GeV)  produced at HERA? g p (a bit of novelty value!!!) monopoles? • natural explanation for electric charge quantisation (Dirac) • predicted or permitted in unification theories previous experimental searches:  no conclusive evidence Hadronic Final States and QCD at HERA  Claire Gwenlan 22/26

  32. Chasing the Magnetic Monopole (a bit of novelty value!!!) Liverpool and Lancaster First (and only!!!) search at HERA • magnetic monopoles produced in ep collisions may stop in the beam pipe if stable, they remain permanently trapped H1 beam pipe:- home to monopoles? IDEA: Chop H1 beampipe into strips Pass through superconducting coil  expect persistent current from monopoles (but not from dipoles) Performed at Southamption Oceanography Centre, UK Hadronic Final States and QCD at HERA  Claire Gwenlan 23/26

  33. Chasing the Magnetic Monopole (a bit of novelty value!!!) Liverpool and Lancaster First (and only!!!) search at HERA Result • look for non-zero persistent currents • some significant one-off measurements • not reproducible  no monopoles harmed (or found!) in this experiment Hadronic Final States and QCD at HERA  Claire Gwenlan 23/26

  34. Pentaquarks at HERA? (minimum quark content uudds) ZEUS strangeness state * 1522 MeV TopCite 100+ *: H1 and ZEUS not incompatible  remains to be resolved Hadronic Final States and QCD at HERA  Claire Gwenlan 24/26

  35. Pentaquarks at HERA? charmed state c mass: 309935 MeV width: 123 MeV H1 observed D*p resonance in DIS and p with HERA-I data(minimum quark content uuddc)  pentaquark candidate not seen by ZEUS TopCite 100+ Hadronic Final States and QCD at HERA  Claire Gwenlan 25/26

  36. Pentaquarks at HERA? charmed state c mass: 309935 MeV width: 123 MeV H1 observed D*p resonance in DIS and p with HERA-I data(minimum quark content uuddc)  pentaquark candidate not seen by ZEUS TopCite 100+ H1: peak not confirmed at HERA-II (also, no evidence for Ξ5q--(0) at HERA) Hadronic Final States and QCD at HERA  Claire Gwenlan 25/26

  37. Summary • HFS studies at HERA are a vital tool for understanding the underlying QCD process both at HERA … and elsewhere!!! • Many many precision measurements now exist, and improved calculations have become availablethroughout HERA running • With current understanding, QCD works(!), describing HERA data • excellent agreement with pQCD over wide range of scales • many consistent extractions of s; running in accordance with QCD • Some regions not so well understood – cannot yet conclusively confirm observation of BFKL dynamics • Magnetic monopoles  ; Pentaquarks??? UK has made a massiveandoften unique contribution to the study of the Hadronic Final State at HERA + mustn’t forget the HFS coordinators, from:Bristol,Glasgow,Oxford,Liverpool,QMUL,UCL Hadronic Final States and QCD at HERA  Claire Gwenlan 26/26

  38. and Finally, Apologies… .. For those areas in which the UK has made a huge contribution but which unfortunately I have not had time to even touch on today… • Fragmentation studies (Glasgow, Lancaster, QMUL) • charged particle multiplicities • scaled momenta • Strange particle production (+ QCD instantons) (Oxford) • (Anti-)deuteron production (Lancaster) • Azimuthal asymmetries/charged multiplicities (Glasgow) • Jets in CC DIS (Glasgow) • + other photoproduction studies(at least partially covered by Matthew) • … (I may have missed others?!!!) (For at least some of these I have put a bit of extra information in the backups…) Hadronic Final States and QCD at HERA  Claire Gwenlan

  39. Backups Hadronic Final States and QCD at HERA  Claire Gwenlan

  40. Scaling Violations in p Glasgow Group • Compare cross sections for same reaction epe+jet+X at different p centre-of-mass energies (Wp) • scaling: ratio of scaled cross section as a function of xT=2ETjet/Wpshould be unity FIRST observation of scaling violation in p Results show non-scaling behaviour in accordance with QCD Hadronic Final States and QCD at HERA  Claire Gwenlan

  41. Jet Substructure Bristol and Glasgow Hadronic Final States and QCD at HERA  Claire Gwenlan

  42. s extraction Oxford and UCL Groups NLO QCD fit with HERA jets: • jet data sensitive to quark and gluon densities in proton • breaks correlation between gluon and s • precision determination of s possible: Hadronic Final States and QCD at HERA  Claire Gwenlan

  43. Scaled Momentum QMUL and Lancaster Groups Charged Multiplicities: • Clear observation of scaling violation in fragmentation • HERA agrees with other experiments over wide range in energy scale • supports concept of quark fragmentation universality • MC models cannot describe data over all Q2 and xp • NLO+FF based on e+e- data fail to describe xp distribution xp =2p(Breit)/Q2 Hadronic Final States and QCD at HERA  Claire Gwenlan

  44. Strange Particle Production Oxford Group • Measurements of: • Ks0 and Λcross sections • Λ/Λ asymmetry • Λ/Ks0 production ratio • Λpolarisation  typical set of results • ARIADNE mostly OK • Ratio of N(Ks0)/Nch (not shown) suggest value of s/u0.22 more appropriate? • N(Λ)=N(Λ) • Also, no evidence for Λ polarisation Hadronic Final States and QCD at HERA  Claire Gwenlan

  45. Charged Particle Asymmetries Glasgow Group • angle of particle, , in the hadronic centre- of-mass frame as a function of lower momentum threshold pc • Azimuthal dependence has form: predicted by QCD • Non-perturbative effects small for cos2 term At high pc, see FIRST clear observation of cos2 contribution • unambiguous evidence of perturbative QCD contribution Hadronic Final States and QCD at HERA  Claire Gwenlan

  46. HFS analyses with UK input ZEUS • High-ET dijet photoproduction (Phys. Rev. D76 (2007) 072011) • Photoproduction of events with rapidity gaps between jets at HERA (Eur. Phys. J. C50 (2007) 283) • Measuerment of K0s, Lambda, Antilambda production at HERA (Eur. Phys. J. C51 (2007) 1) • Event shapes in DIS (Nucl. Phys. B 767 (2007) 1) • The dependence of dijet photoproduction on photon virtuality in ep collisions at HERA (Eur. Phys. J. C35 (2004) 487) • Observation of isolated high-ET photons in DIS (Phys. Lett. B 595 (2004) 86) • Substructure dependence of jet cross sections at HERA and determination of s (Nucl. Phys. B 700 (2004) 3) • Three- and Four-Jet Final States in photoproduction at HERA (Nucl. Phys. B 792 (2008) 1) • Jet production in charged current e+p DIS at HERA (Eur. Phys. J. C31 (2003) 149) • Scaling violations and determination of as from jet production in p interactions at HERA (Phys. Lett. B 560 (2003) 7) • Measurement of event shapes in DIS at HERA (Eur. Phys. J. C27 (2003) 531) • Dijet photoproduction at HERA and the structure of the photon (Eur. Phys. J. C23 (2002) 4) • High mass dijet cross sections in photoproduction at HERA (Phys. Letts. B531 (2002) 9) Hadronic Final States and QCD at HERA  Claire Gwenlan

  47. HFS analyses with UK input ZEUS (cont.) • Study of the effective transverse momentum of partons in the proton using prompt photons in photoproduction at HERA (Phys. Letts. B 511 (2001) 19) • Measurement of azimuthal asymmetries in DIS (Phys. Letts. B 481 (2000) 2 • Measurement of inclusive prompt photon photoproduction at HERA (Phys. Letts. B 472 (2000) 1 • Angular and current-target correlations in DIS at HERA (Eur. Phys. J. C12 (2000) 1) • Measurement of dijet photoproduction at high transverse energies at HERA (Eur. Phys. J. C11 (1999) 1) • Measurement of three-jet distributions in photoproduction at HERA (Phys. Letts. B 443 (1998) 394) • Dijet cross sections in photoproduction at HERA (Eur. Phys. J. C1 (1998) 1/2, 109) • Observation of isolated high ET photons in photoproduction at HERA (Phys. Letts. B 413 (1997) 201) • Dijet angular distributions in resolved and direct photoproduction at HERA (Phys. Letts. B 384 (1996) 401) • Rapidity gaps between jets in photoproduction (Phys. Letts. B 369 (1996) 55) • Dijet cross sections in photoproduction at HERA (Phys. Letts. B 348 (1995) 665) • Observation of direct processes in photoproduction at HERA (Phys. Letts. B 322 (1994) 287) Hadronic Final States and QCD at HERA  Claire Gwenlan

  48. HFS analyses with UK input H1 • Three- and Four-jet production at low x at HERA (Eur. Phys. J. C54 (2008) 389) • Measurement of inclusive jet production in DIS t high Q2 and determination of the strong coupling (Phys. Letts. B653 (2007) 134) • Dijet cross sections and parton densities in diffractive DIS at HERA (JHEP 0710:042 (2007)) • Charged particle production in high Q2 DIS at HERA (Phys. Letts. B654 (2007) 148) • Search for baryonic resonances decaying to Xi pi in DIS at HERA (Eur. Phys. J. C52 (2007) 507) • Tests of QCD factorisation in the diffractive production of dijets in DIS and photoproduction at HERA (Eur. Phys. J. C51 (2007) 549) • Photoproduction of dijets with high transverse momenta at HERA (Phys. Letts. B 639 (2006) 21) • Forward jet production in DIS at HERA (Eur. Phys. J. C46 (2006) 27) • A direct search for stable magnetic monopoles produced in positron-proton collisions at HERA (Eur. Phys. J. C41 (2005) 133) • Forward pi^0 production and associated transverse energy flow in DIS at HERA (Eur. Phys. J. C36 (2004) 441) • Measurement of dijet production at low Q2 at HERA (Eur. Phys. J. C37 (2004) 141) • Measurement of anti-deuteron photoproduction and a search for heavy stable charged particles at HERA (Eur. Phys. J. C36 (2004) 413) Hadronic Final States and QCD at HERA  Claire Gwenlan

  49. HFS analyses with UK input H1 (cont.) • Measurement of inclusive jet cross sections in photoproduction at HERA (Eur. Phys. J. C29 (2003) 497) • Measurement of inclusive jet cross sections in DIS ep-scattering at HERA (Phys. Letts. B542 (2003) 193) • Measurement of dijet cross sections in photoproduction at HERA (Eur. Phys. J. C25 (2002) 1) • Energy flow and rapidity gaps between jets in photoproduction at HERA (Eur. Phys. J. C24 (2002) 4, 517) • Measurement of dijet cross sections in photoproduction and photon structure (Phys. Letts. B 483 (2000) 36) • Forward Pi0-meson production at HERA (Phys. Letts. B462 (1999) 440) • Measurements of transverse energy flow in DIS at HERA (Eur. Phys. J. C12 (2000) 595) • Multiplicity structure of hadronic final states in diffractive deep-inelastic scattering at HERA (Eur. Phys. J. C5 (1998) 3, 439) • Evolution of ep fragmentation and multiplicity distributions in the Breit frame (Nucl. Phys. B 504 (1997) 3) • A study of the fragmentation of quarks in ep collisions at HERA (Nucl. Phys. B445 (1995) 3) • Energy flow and charged particle spectra in DIS at HERA (Z. Phys.C62 (1994) 377) • Measurement of hadronic final state in DIS at HERA (Phys. Letts. B298 (1992) 469) Hadronic Final States and QCD at HERA  Claire Gwenlan

  50. UK convenors of HFS (I think!) (alphabetically, not chronologically) • H1 • Tim Greenshaw • Steve Maxfield • Dave Milstead • Dan Traynor • ZEUS • Claudia Glasman • Nick Brook • Peter Bussey • Jon Butterworth • Mark Sutton • Matthew Wing Hadronic Final States and QCD at HERA  Claire Gwenlan

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