Andrey Korytov

1. QCD Physics at Tevatron Andrey Korytov

2. Tevatron Delivered 3.46 fb-1 Recorded 2.96 fb-1 2003 2004 2005 2006 2007 CDF p-pbar collisions sqrt(s) = 1.96 TeV peak L = 31032 cm-2s-1 D0

3. PDFs Need for higher order pQCD Jet definitions Precision expectations Enchanted forest of low pT physics models pQCD Typical Q2 QCD Physics at Tevatron High PT QCD Light quark and gluon scattering (jets) Heavy flavor production (t, b, c) W/Z/g + jets • High PT physics • various production cross sections • language: pQCD • precision expectations soar, but: • - uncertainties in PDFs… • - need for higher order pQCD… • - jet-vs-parton uncertainties… as as as • Low PT physics • broad range of phenomena • Language: • - npQCD, • - resummed pQCD approx., • - QCD-inspired models, • - ad hoc models… • precision varies, models tunable... Low PT QCD Jet fragmentation Underlying event structure Diffractive processes Hadron spectroscopy as as

4. QCD Physics at Tevatron High PT QCD Jet production Heavy flavor production (t, b, c) W/Z/g+jets cross sections Low PT QCD Jet fragmentation Underlying event Diffractive physics Hadron spectroscopy

5. Hadronic showers EM showers From a primary scattering onward… • Pick two partons and their momenta • phenomenological parton density functions, PDF • Hard Scattering: 2  X • pQCD exact matrix element at LO, NLO, some NNLO • Soft final state radiation • pQCD approximate resummation in all orders: LLA (leading log approximation), NLLA • Underlying event • phenomenological models • Hadronization • phenomenological models • Calorimeter response • electromagnetic shower for photons • hadronic shower for “stable” hadrons

6. Hadronic showers EM showers So what are jets? • Calorimeter level: • calorimeter towers lumped together according to an experimentalist’s favored algorithm • Particle level: • sprays of long lived observable particles lumped together… • Parton level (resummed pQCD): • outgoing partons accompanied by a few soft bremsstrahlung gluons lumped together… • Parton level (NLO pQCD at Tevatron): • outgoing 1 parton or 2 partons lumped together mimicking a particular experimental jet finding algorithm NOTE: the border between THEORY and EXPERIMENT is variably put in any of three gaps above, depending on one’s personal convictions… underlying event “pollution”

7. Jets at Tevatron: jet finding algorithms • JetClu Cone Algorithm: • cluster together calorimeter towers by their “angular” proximity in (h, f) space • merging/splitting of overlapping cones is not infrared stable (at NNLO) • ad hoc Rsep=1.3 to match theory and exp. • Tevatron Run I legacy • MidPoint Cone Algorithm: • cone algorithm with modifications improving infrared stability • replaces JetClu Cone • kT Algorithm: • cluster together calorimeter towers by their kT proximity • infrared stable (no splitting/merging) • no clusters left out  underlying event contribution unclear • favored choice at e+e- colliders

8. Jets at Tevatron: jet finding algorithms

9. Inclusive jet production • ET spectra • for different h-bins…

10. Inclusive jets (MidPoint algorithm) 8 orders 60% of 1 TeV Very good agreement (no sign of quark compositeness) Experimental errors ~ PDF uncertainties UE pollution is negligible >100 GeV

11. Inclusive jets (kT-algorithm) Very good agreement (no sign of quark compositeness) Experimental errors ~ PDF uncertainties UE pollution is small >200 GeV

12. MidPoint vs kT: both match theory well MidPoint kT

13. CDF vs D0 CDF D0 There are some differences in analyses  cannot compare them directly However, both CDF and D0 agree with the theory within their systematic errors

14. High-x gluon PDF? Jet Jet high x gluon (few) low x (lots) Uncertainty on gluon PDF (from CTEQ6) Huge uncertainties on gluon pdf at large x (HERA probes quark pdf’s) Forward jets allow to probe high-x gluon pdf at Tevatron

15. Forward Jets Midpoint kT Both MidPoint and kT algorithm produce results with experimental errors < current pdf uncertainties One can use these data to tune high-x gluon pdf

16. Dijet production • What one might want to look at: • MJJ • qcm • Df12 • …

17. Di-jets: largest dijet mass event Mjj = 1.4 TeV Mjj/Ecm = 70%

18. Di-jets Many new physics models lead to resonance di-jet states Look for bumps—none is seen. Oh well…

19. QCD and hadron Physics at CDF High PT QCD Jet production Heavy flavor production (t, b, c) W/Z/g+jets cross sections Low PT QCD Jet fragmentation Underlying event Diffractive physics Hadron spectroscopy

20. b 85% t W t W  l + n  q + q W  l + n  q + q W b 15% t-quark productio • di-lepton (BR=11%): • lepton + jets (BR=44%): • all jets (BR=45%):

21. t-quark production • Run II data agree with Run I and pQCD production mechanism

22. b-quark production Leading Order Matrix Elements Flavor Excitation Flavor Creation Next to Leading Order Matrix Elements Gluon Splitting Flavor Excitation Flavor Creation

23. b-jet tagging b-tagging efficiency b-tagging purity Collision point

24. Inclusive b-jet production Rule of thumb: about 3-5% of all jets are b-jets

25. bb-dijet production gluon splitting flavor creation To get angular distribution right, it takes - NLO calculations plus - Underlying Event

26. K D B p Heavy flavor production: c-quark • Measured cross sections • D0, D+, D*+, Ds • Theory • FONLL (Cacciari, Nason) • m=1.5 GeV • CTEQ6M • Data/Theory~1.5 (similar for all…) • Direct Charm quark production • Measure D-meson production • Remove fraction of BD D meson from B decay has larger impact parameter

27. QCD and hadron Physics at CDF High PT QCD Jet production Heavy flavor production (t, b, c) W/Z/g+jets cross sections Low PT QCD Jet fragmentation Underlying event Diffractive physics Hadrons (exotic states)

28. Z+jets production Z production LO NLO + (LO for Z+1jet) NNLO + + … (LO for Z+2jets) Excellent agreement

29. G g, q Jet g, q Z+jets spin-off: Extra Dimension searches • Large Extra Dimensions (ADD) • Arkani-Hamed, Dimopoulos, Dvali, Phys Lett B429 (98) • Main background:

30. QCD and hadron Physics at CDF High PT QCD Jet production Heavy flavor production (t, b, c) W/Z/g+jets cross sections Low PT QCD Jet fragmentation Underlying event Diffractive physics Hadrons (exotic states)

31.  k, gluon momentum kT=ksin gluon transverse momentum Jet Fragmentation: intrinsically soft QCD kT distribution of particles in jets Differential probabilities of gluon emission: 2 GeV 1 GeV From data we know that most particles have kT<1 GeV as comes with a large factor ~ ln2(E/kTcutoff) in all orders as is not small forkT<1 GeV any hope?

32. R~1/MJJ R~1/Qcutoff R~1/~1/m~1 fm Jet Fragmentation: doing it analytically • Jet fragmentation: • parton shower development: resummation in ALL order of pQCD in Next-to-Leading-Log approximations  e.g., MLLA, Modified Leading Log Approximation with single parameter Qeff=Qcutoff=LQCD • hadronization: no coherent theory  LPHD, hypothesis of Local Parton Hadron Duality with one parameter KLPHD=Nhadrons/Npartons • MLLA+LPHD: • cannot describe all details… • but all analytical… • and works surprisingly well… Which of the two?

33. Charged particle momenta • Charged particles in jets • Two parameter fit: • Qeff = 23040 MeV ☞ kT-cutoff can be set as low as LQCD • KLPHD( ) = 0.56  0.10 ☞ number of hadrons  number of partons

34. Multiplicities in gluon and quark jets • calculations (for partons), various extensions of NLLA r=1.5-1.7 • e+e- data: • 15+ papers (r = 1 to 1.5) • theory: • back-to-back jets • valid in small opening angle around jet axis • e+e- data: • three-jet events • often very large (full 4p) angle • CDF: • back-to-back jets • opening angle 0.5 rad • r=1.60.2

35. Quark and gluon jets: how do we know? di-jet events g-jet events ~60% of gluon jets at Mjj~100 GeV ~40% of quark jets ~20% of gluon jets at Mjj~100 GeV ~80% of quark jets

36. kT of particles in jets • We compare shapes only: data and theory normalized to 1 at kT=1 GeV • Theory has very weak dependence on Qeff, i.e. almost “parameter-free” • Excellent agreement between data and nMLLA kT=ksin transverse momentum  k, momentum

37. kT of particles in jets • Pythia and Herwig MC generators described data very well • But note the level of tuning going into MC: • parton distribution follows LLA approximation and is way off • phenomenological hadronization is tuned to compensate

38. Two-particle momentum correlations • consider all particle pairs in cone q=0.5 around jet axis • theory: Expansion around the peak: Dx=x-x0 normalized to unity Dx=x-x0

39. Momentum correlations (cont’d) • hadron correlations follow the pattern expected for partons

40. Momentum correlations (cont’d) • hadron correlations follow the pattern expected for partons

41. Momentum correlations (cont’d) • fit to c1 and c2 coefficients for Qeff cutoff Qeff ~ 130 ± 80 MeV Qeff ~ 150 ± 80 MeV Q = Ejet qcone (GeV) Q = Ejet qcone (GeV)

42. Jet fragmentation = QCD + Hadronization • Momentum of charged particles in jets ~ partons • Multiplicity of charged particles in jets ~ partons • Quark/Gluon jet differences ~ partons • Transverse momenta of particles in jets ~ partons • Momentum correlations of particles in jets ~ partons • The role of hadronization is small (once pQCD is resummed) HADRONIZATION

43. QCD and hadron Physics at CDF High PT QCD Jet production Heavy flavor production (t, b, c) W/Z/g+jets cross sections Low PT QCD Jet fragmentation Underlying event Diffractive physics Hadrons (spectroscopy and exotics)

44. Hadrons: X(3872) • Aug 2003: Belle announced discovery of X(3872)  J/y p+p- • M=3872.00.6 0.5 MeV • G < 2.3 MeV • pp masses are always high (>500 MeV) • Sep 2003: confirmed by CDF • Also confirmed by D0, BaBar • Interpretation still remains unclear: • 3D2 charmonium? • too heavy for it (expected M~3810-3840) • also, not seen to decay to c1g • M(X)~M(D0)+M(D*0) = 1864.6 + 2006.7 = 3871 MeV • DD* molecule? • M(J/y)+M(r) = 3097+770 = 3867 MeV • ???

45. Hadrons: pentaquarks • 5 quark state predictedby • Diakonov, Petrov, Polyakov(1997): • Q+ : uudds • Mass ~ 1530 MeV • Width ~ 15 MeV • Decays equally to nK+ and pK0 10 experiments report evidence 3 experiments report no observation: HERA-B, PHENIX, BES In addition, NA49 at SPS/CERN (pp collider at Ecm = 17.2 GeV): ssddu(1862) H1 at HERA ep collider: D*- p state: Qc=uuddc(3099) STATISTICAL SIGNIFICANCE VARIES FROM ~4 to ~8 sigmas

46. X−− as seen at NA49 M=1.862± 0.002 GeV X−− X0 X(1530)

47. X–hyperon track sample at CDF • CDF developed tracking of long lived hyperons (X and W) in the SVX detector Two Track Trigger Jet 20 Trigger • Two Track Trigger: NTTT ~ 18 times larger than NA49 data • Jet20 Trigger: NJet20 ~ 2 times larger than NA49 data

48. X-- (1860) is not found at CDF TTT Jet20

49. Minbias data Jet20 data f K+K- L(1520) pK- K*+ K0Sp+ Q+ pK0S limit on+ @90%CL 19,721273 3,276327 15,695775 1856 <89 26,658385 4,915702 35,7691,390 -56103 <76 q+ (1530) is not found at CDF Resonance statistics higher than any of the Q+→pK0S reports High statistics reference signals , K+*, (1520) No evidence of narrow resonanceQ+→ pK0S

50. Hadrons: Pentaquark Searches • CDF Collaboration have searched for c⁰,⁺,3/2states • No evidences of these states have been found