HERA and the LHC Report on a workshop on HERA LHC

1. HERA and the LHCReport on a workshop on HERALHC A. De Roeck/CERN Saclay seminar 4/7/05 • Introduction andGoals of the workshop • Overview & Highlights • The end of phase I and the continuation of the Workshop

2. …Origin of the Workshop http://mlm.home.cern.ch/mlm/mcwshop03/mcwshop.html Turned out to be a good experience After this workshop: discussion started to try to do more

3. x1p x2p ep and pp colliders ep collisions (HERA) *Ideal tool to study the structure of hadrons via deep inelastic scattering (structure functions/parton densities) * Can use the photon as a pointlike or hadronic particle through its virtuality * Main contributions are in the area of QCD: Small-x, diffraction, saturation, high densities, jets… * Tests of new approaches/QCD pp collisions (LHC) * Highest energies reachable * Can reach highest masses for new particles production * Precision often limited by knowledge of quark/gluon structure of proton * QCD effects need to be controlled to the best of our knowledge fa fb x = momentum fraction of quark in proton

4. The HERA Collider 27.5 GeV e X 920 GeV p Björn Wiik (1937-1999) ep collisions √ s = 318 GeV Δr ≥ 0.001 fm HERA:  Structure of the proton (and photon)  Detailed study of QCD  Heavy flavour studies  Diffraction  …EW, BSM  HERA collected 100 pb-1 in phase HERA-I (1992-2000)  Luminosity upgrade started 2002  HERA will terminate summer 2007

5. HERA-II running 300 200 100 0 HERA-II increasing luminosity Peak luminosity so far 4.5 1031 cm-2 sec-2 Expect to accumulate ~ 500-700 pb-1 Pb-1 A deep inelastic scattering event

6. ~1200 Super conducting dipoles needed >600 dipoles delivered The LHC In LEP tunnel (circonf. 26.7 km) • 25 ns bunch spacing  2835 bunches with 1011 p/bunch • First years lumi • ~2.1033cm-2s-1 20 fb-1/year • Design Luminosity: • 1034cm-2s-1100 fb-1/year 23 events per bunch crossing

7. LHC Machine Progress Superconducting cables Superconducting dipoles Production Just in time line Crucial part: 1200 superconducting dipoles (10m long each) Can follow progress on the CERN web page (dashboard) http://lhc-new-homepage.web.cern.ch/lhc-new-homepage/

8. LHC FAQs (Frequently Asked Questions) Picture becoming more clear now after the cryogenic line problem (and solution): according to the current plan (*) • LHC will be closed and set up for beam on 1 July 2007 • First beam in machine: August 2007 • LHC commissioning will take time! • First collisions expected in November 2007 • Followed by a short pilot run • First physics run in 2008 (starting April/May; a few fb-1? ) • First big discovery ?? • When will they close the LHC/inject beams (Detector experimentalists) • When will be first collisions in the LHC? (Analysis experimentalists) • When will we have first physics from the LHC? (Theorists) • When will we have the new big discoveries at the LHC? (politicians thinking on whether to finance an International Linear Collider ) (*) M. Lamont at the TeV4LHC Workshop @CERN 30/4

9. j1 W j2 t b-jet Physics at the LHC: pp @ 14 TeV Extra Dimensions? Higgs! CP triangle! Supersymmetry? QGP? Black Holes??? Precision measurements e.g top! But also QCD, diffraction, b & c physics,… especially in the early phase These need to be understood for precision measurements, bkg understanding etc Important role for HERA data & HERA expertise  This workshop

10. Workshop Aims  Five Working Groups  Parton density functions  Multi-jet final states  Heavy quarks (charm and beauty)  Diffraction  MC-tools Workshop Chairs H. Jung, ADR

11. Examples: HERA LHC Underlying event: tunable elementarity of one beam particle p *p collisions LHC: event complexity B-production: B quark PDFs of the proton LHC: Higgs production Structure functions and parton distributions LHC: cross sections/precision Diffraction LHC: diffractive scalar production

12. Meetings First meeting: 26-27 March CERN (~ 250-300 participants) Intermediate meeting: 1-4 June/ DESY Second meeting: 11-13 October CERN Intermediate meeting: 15-19 November/ DESY Intermediate meeting 17-21 January 2005/ CERN Final meeting: 21-24 March 2005/ DESY (~150 particpants) http://www.desy.de/~heralhc Joint DESY/CERN Report in fall 2005 So, how well did we do?

13. WG1: PDFs Simple spread of existing PDFs gives up to 10% uncertainty on Higgs cross section  we have to do better than that!

14. ADD extra dimensions: di-jet final state Graviton exchange contributions reduce the cross section (interference) S. Ferrag Reduction of the sensitivity due to PDF uncertainty (CTEQ6)

15. Heavy flavour production M. Cacciari PDF uncertainties are getting as large as the ones from scales The scale uncertainties will improve with HO calculations Hence also the PDF determination will need to be improved

16. WG1: Structure Functions • Potential experimental and theoretical accuracy for various LHC processes (DY,W,Z,WW,+jet…) Precision measurements at LHC/luminosity determination? • Cross sections and distributions • Benchmark with LHC detector simulation • Impact of PDF’s on LHC measurements • Making the most of HERA data • Need for FL or eD scattering? • Can we judge which PDF is “preferred”? Most precise PDFs + errors • Impact of small x and large x resumations and saturation corrections on pdfs. QCD evolution validation (DGLAP,…) • Impact for LHC? • Verify with HERA data. L. Magnea ~15%

17. WG1 Precision physics at the LHC!!  List of interesting LHC reactions and assessment of their theoretical and experimental accuracy, including ratios. Document in progress example Contact M. Dittmar • Includes Drell-Yan, Z,W production • -final states, di-boson event, top quarks, multi-jet events… Use LHC data for PDF determination?

18. HERA-II precision But foreseen to end in 2007 The promise… HERA-II run  500-1000 pb-1 High precision at large Q2, precise determination of the gluon distribution, flavour separation (via CC), u(x)/d(x) for x1,…

19. PDF Fits • PDFs became available with error bands : GOOD! But.. Parton distributions do not fully agree (even within the error bands) • Different choices of data and (J. Stirling) • tolerance to define  fi(CTEQ: Δχ2=100, Alekhin: Δχ2=1) • factorisation/renormalisation scheme/scale • Q02 • parametric form Axa(1-x)b[..] etc • αS • treatment of heavy flavours • theoretical assumptions about x→0,1 behaviour • theoretical assumptions about sea flavour symmetry • evolution and cross section codes (removable differences) H1 + ZEUS combine data followed by a common fit Issues on fits are being addressed in depth during the workshop

20. Combined Data Sets from HERA? I think the World wants it (like we want one top mass etc…)  HERA PDFs will be THE standard for a long time to come An effort is starting  Averaged data set… (A. Glazov et al.) M. Cooper et al. • Compare PDF fit to • H1+ZEUS data sets, • and to the ‘average • data set. • Improved error? • Caution! • Averaging procedure still very preliminary •  Some disagreements • between the data • set at low Q2 Being continued in a working group

21. Making the most of HERA data… • Global fits do have the problem • of consistent treatment (errors) • and sometimes ‘tensions’ • Fits of inclusive cross + jets (+..) within one “experiment” Improvement on g(x) C. Gwenlan et al. Improvement on s

22. DGLAP evolution Q. is NLO (or NNLO) DGLAP sufficient at small x? Are higher-orders ~ αSn logm x important? CCFM? BFKL? Non-linear effects? Saturation? QCD Evolution of PDFs At the LHC: momentum fractions x1 and x2determined by mass and rapidity of X HERA measurements do not cover the LHC region, eg. for central Higgs production  PDFs evolved via DGLAP equations from (x,Q20) to (x,Q2)

23. Near Future: from NLONNLO

24. NNLO splitting functions have arrived… S. Moch et al.  NNLO fits to come

25. Low-x Resummation Global fits: effects of including low x resummation (R.Thorne) Differences can be larger than 20% at x ~ 10-3, low Q2 Need for other methods to extract the gluon or verify the QCD evolution/corrections

26. Need for FL? Deuterons? R. Thorne H. Stenzel FL could referee the gluon distribution! FL is like F2: little theoretical ambiguity (compared to e.g. F2C) Deuterons: good for flavour separation, non-singlet SF extraction HERA is unique: looks to me that you would want to do that!!  MUST make a strong quantitative argument!

27. WG2: Multi-jet Final States & Eflows • Underlying event/minimum bias events • New models appeared during the workshop • Tunes to pp data validated • Study similar observables in ep as in pp Task force in action • Gap survival • Still not sufficiently understood/ Consequences for the LHC! • New measurements like effects in leading neutron spectra in ep? • Cascade, based on CCFM (contrary to DGLAP) • Shows effects at the LHC at low x • Unintegrated pdfs and their importance e.g for pt of the Higgs • ME-PS matching • Resummations for event shape variables • Future parton shower developments • Unintegrated parton correlation functions and QEDxQCD exponentiation

28. Underlying events/minimum bias R. Field  Studies and tunes made on Tevatron/lower energy data  These tunes should be validated on HERA data  work in progress Similar studies should be made as for the Tevatron data  New models on the market that should be tested (new Pythia, Jimmy, Sherpa)

29. Effect of underlying event on central jet veto in VBF Higgs Uncertainty of the central jet veto efficiency due to UE model; ATLAS. H->WW*->2l in qqH prod. Rapidity of the central jet in Higgs events; CMS; full simulation, L=2x1033cm-2s-1 Pythia 6.214 ATLFAST 602 S. Nikitenko “bkg. like” behaviour for soft jets; fake jets: pile up+UE+detector

30. Matrix elements and parton showers •  Will be very important at the LHC/ get the high pT tails right •  Need to understand jet topologies of up to 8 jets (and more) • Matching algorithms now also being implemented for ep scattering •  Can be benchmarked to HERA multi-jet data.

31. Initial kT at HERA and LHC Jung Cascade calculation Initial kT in the hard scattering Higgs <kT> large  unintegrated parton PDFs will be needed Test predictions at HERA Measure unintegrated PDFs f(x,Q2,kT2) at HERA via final states

32. WG3: Heavy Flavours List of measurements of measurements to be made at HERA (need > 400 pb-1) • F2cc/bb • Charm exclusive final states (p and DIS) • Cross sections • Fragmentation universality • Contribution from higher charm resonances • Charm exclusive final states with jets (p and DIS) • Beauty exclusive final states (p and DIS) • Double quark tag • Charm and beauty in charged current events • Quarkonia • Diffraction Several of these have direct impact on the LHC

33. F2b at large Q2 Need to measure the F2b at the same scale as ~MH/2 Possibly reduce error by a factor of 4 at HERA-II

34. Charm production

35. WG4: Diffraction • Diffractive Higgs production • Backgrounds to diffractive Higgs • Diffractive factorization breaking • Dijet production • Charm production • Leading neutrons • Rapidity gap survival (with WG2) • New measurements e.g FLD • Exclusive diffractive dijets • Saturation effects and relation to MI/gap survival • Large part of the activities was transfer of experience of the knowledge, and of design and operation of detectors for forward physics from HERA to the LHC

36. Diffractive Higgs Production Exclusive diffractive Higgs production pp p +H+ p : 2-10 fb Inclusive diffractive Higgs production pp  p+H+X+p : O(100) fb -jet E.g. V. Khoze et al M. Boonekamp et al. B. Cox et al. … gap gap H h p p Advantages Exclusive:  Jz=0 suppression of ggbb background  Mass measurement via missing mass -jet beam dipole dipole M = O(1.0 - 2.0) GeV p’ P. Landshoff not convinced that the cross sec. is small p’ roman pots roman pots

37. Exclusive Higgs Production:Models… Different models give different predictions for The cross sections Gap Survival Probabilities/Sudakov supression The mass/energy dependence of the cross sections Almost all calculations now converge to a cross section of 2-10 fb for a light Higgs J. Forshaw BL Bialas Landshof (soft Pomeron) KMR: Khoze Martin Ryskin HERA and Tevatron can test these models

38. Exclusive Higgs production A lot of useful and necessary discussion during this workshop on  Different model comparisons  Realism of such measurement at the LHC M. Tasevsky •  Differences understood (Sudakov factors, parton distributions…) • Khoze-Martin-Ryskin pQCD calculations checked by independent group  ok • But pQCD + soft contributions to cross ection (R. Peschanski et al.)?

39. Detailed Simulation Studies Signals and background for different Higgs masses Detailed studies ongoing Fast detector simulation Boonekamp/ATLAS Royon/CMS Include exclusive and inclusive bb background Include missing mass resolution from the tagged protons Experimental issue: L1 trigger 400m signals are too late for the L1 triggerL1 from central detector 100 fb-1 First look/needs to be optimized

40. Information from HERA Diffractive structure functions Study the process of p VM+ X+ p Planned: F2D H1 and ZEUS data combination B. Cox et al. Double pomeron exchange @ HERA Measurable cross section at HERAII + Future FLD measurements to constrain the gluon further

41. Understanding the Gap Survival A complementary way to study re-scattering effects in collisions  suggest to look at events with a leading neutron  Can be an ideal laboratory to study the dynamics of gap survival probability  Effects can be calculated, x-pt correlations etc. (A. Kadialov et al. to appear)  More measurements like the one shown here will be very usefull

42. Generalized Parton Distributions Generalized parton distributions F(x,x’,Q2) affect the predictions for diffractive Higgs production Can be measured at HERA eg. in exclusive J/ production J. Forshaw Upsilon production measurement would be even better!

43. Leading proton spectra in generators M. Ruspa PYTHIA used for pile-up background studies at LHC! How good is it when compared to data, e.g. from HERA?? b-slope Leading proton spectra

44. TOTEM/CMS Forward Detectors Totem: RPs 150, 180 and 220m ATLAS: RPs 240m FP420: RPs at 420m ? T2 Diffraction/Low-x is part of the LHC physics program (EOI) CMS/TOTEM work on common LOI for diffraction+lowx ATLAS starting…  Castor calorimeter 5.25< <6.5  T2 GEM tracker 5.3< <6.7  T1 CSC tracker 3.1<  <4.7  ZDC calorimeter  Region 7< <9 needs study Opportunities for new groups to join or contribute to the LOI !!

45. WG5: Tools • Parton distribution library: • LHAPDF now official carrier of the PDFs • Used by LHC experiments in generators • HERA pdfs have been added • Allows error uncertainty estimates • Pion and photon added, particularly for HERA. F2D next? • NLOLIB framework for NLO QCD programs • Uniform user interface/interface to HZTOOL • e+e-/ep included, pp can be added (but not done yet?) • HZTOOL/JetWeb/RunMC/Cedar(?) for tunning • All HERA results to be included, some e+e-. Include more pp? • RAPGAP, Cascade Monte Carlos for inclusive and diffractive pp • Plenty of exchange on other MC tools, leading to new MC tools and comparisons with ep where possible • Continuation of the MC@LHC workshop, concerning validation

46. Screen shot of RUNMC session S. Chekanov

47. Nutshell: Results for the LHC • Parton Distribution Functions • Dialogue/discussion between PDF fitters and community that delivers the data. • Combined data (H1/Zeus Datasets for F2, F2D), other data (e.g. TeV. jets)? • Discrepancies between PDFs will be ironed out, eg due to new measurements. Fits with 1- bands will be available. • Quantitative techniques for low-x/large-x resummation available • Timescale for the full program 1-2 years, i.e. just in time for the LHC  Will lead to more precise PDFs: maybe factor 2-3? (personal guess) • Diffraction • Improved understanding on the DPE/Higgs production and cross section • Final states • Lots of work/progress on underlying events (tuning), gap survival • Heavy quarks • Saturation effects measurable at low pt • Heavy quark parton distributions eg. for Higgs cross section calculations. • Tools • Tool developments ongoing strongly…

48. The Verdict      Many studies still ongoing  Quantitative results for Proceedings and Beyond I think we are not doing so bad!

49. Wait… did he say “beyond”? • Phase I of this workshop is over and will be concluded with the proceedings • However an important link between communities has been established. • We should not just let it fade away, but strongly exploit it, to the benefit of both communities.  Therefore this is not THE END • Keep momentum with one plenary HERA/LHC meeting per year • Keep also good contacts with TeV4LHC workshop activities (started Sept.2004) Continued… March 2006 CERN March 2007 DESY March 2008 CERN… (first physics @ LHC!?!)

50. HERA and the LHC This will be the beginning of a beautiful friendship !