Achim Geiser, DESY Hamburg. Inclusive Deep Inelastic Scattering Jets and Heavy Flavours in DIS Exclusive dipion electroproduction

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1 Deep Inelastic Scattering and dipion electroproduction at HERA Achim Geiser, DESY Hamburg EDS Blois workshop Qui Nhon, Vietnam, 2011 Inclusive Deep Inelastic Scattering Jets and Heavy Flavours in DIS Exclusive dipion electroproduction selection of recent results inclusive diffraction + diffractive dijets + total cross section -> talk A. Valkarova comparison of diffraction at HERA and Tevatron -> talks C. Royon & K. Giulianos exclusive vector meson production -> talk L. Favart HERA data and pomeron -> talk U. Maor A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 1

2 The HERA ep collider and experiments e + low energy e - e (27.6 GeV) HERA I: ~ 130 pb -1 (physics) HERA II: ~ 380 pb -1 (physics) combined: ~ 2 x 0.5 fb A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 2

3 Deep Inelastic ep Scattering at HERA A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 3

4 Inclusive DIS H1-ZEUS combinations & PDF fits: full expert treatment of exp. syst. uncertainties and correlations HERA data essential input to any PDF fit A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 4

5 A. Geiser, HERAscale to Terascale, Gomel 09 5

6 Combination of HERA data and PDF fit e.g. high Q 2 neutral current: JHEP ZEUS-prel , , H1-prelim , further new results (not yet included in average): ZEUS-prel , NLO and NNLO versions of HERAPDF 1.5 available on LHAPDF A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 6

7 Parton density functions (PDF) Q 2 Higgs W,Z, top, jets, QCD evolution LHC HERA Tevatron x * parton density gluon / 20 valence sea / 20 parton densities and flavour composition measured at HERA determine cross sections at LHC A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 7 x x

8 Example: W production in CMS HERAPDF prediction probably more examples in LHC talks this afternoon A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 8

9 Longitudinal structure function F L also H1-ZEUS combination: ZEUS-prel H1-prelim ZEUS update: ZEUS-prel F L data are valuable input to QCD fits A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 9

10 Jets and α s A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 10

11 Jets in ep interactions (HERA) QPM: single (or no) jets in DIS: measure quark densities no QCD, α s dijets in DIS or photoproduction: measure both (dijets) or integrate over 2 nd jet (inclusive jets) require high E T w.r.t. photon axis α s - check QCD - study performance of jet algorithms -measure α s and its running - measure gluon density A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 11

12 Inclusive jets in DIS H1-prelim double differential in Q 2 and p T well described by NLO QCD + HERAPDF A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 12

13 Multijet production + α s H1-prelim most precise (~α s2 ) A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 13

14 H1 summary of α s measurements optimised for minimization of experimental uncertainties good agreement with previous measurements and world average uncertainties dominated by NLO theory A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 14

15 Summary of ZEUS α s measurements ZEUS-prel α s running analyses optimized for minimization of theoretical uncertainties A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 15

16 PDF fit including Jets + free α s ZEUS-prel H1-prelim decorrelates α s and gluon agrees well with world average uncertainty dominated by NLO theory, need NNLO! A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 16

17 Heavy Flavours, c, c A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 17

18 Why are heavy flavours important? charm contribution to HERA data up to 30%! (beauty ~1-3%) kinematic effect of mass competing scales for perturbative expansion e.g. m, Q 2, p T -> terms log Q 2 /m 2 log p T2 /m 2 etc. => massless treatment (ZM-VFNS) allows resummation, but fails near mass threshold -> avoid! => massive treatment gets kinematics right, but does not allow resummation (fixed flavour number schemes, FFNS) or induces ambiguities in QCD corrections near flavour threshold (variable flavour number schemes, GM-VFNS) check different schemes against HERA data A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 18

19 charm contribution to F 2 combined HERA (H1 and ZEUS) charm data: sensitive to m c and to differences in Heavy Flavour schemes here: massive VFNS schemes fit to these data -> u/c flavour separation -> reduced uncertainties on W/Z cross sections at LHC H1-prelim ZEUS-prel also updated/new results (not yet included) ZEUS-prel , H1, DESY A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 19

20 PDF fit to all HERA data combined inclusive data, F L, jets, charm: all data consistent (good fit) -> QCD works ongoing work, future public release will further reduce model uncertainties (e.g. m c, gluon/α s correlations) A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 20

21 beauty contribution to F 2 new new ZEUS-prel DESY , arxiv: NLO and partial NNLO QCD in agreement with data, NNLO slightly better HERA LHC, e.g. H,Z Q 2 >> m b A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 21

22 DESY November > ππ Exclusive p p dipion electroproduction (other results on exclusive vector meson production see talk L. Favart) A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 22

23 ππ mass distribution, fit of F π ρ ρ ρ ρ background ρ ρ sensitive to m c and to differences in interference Heavy Flavour schemes here: massive VFNS schemes Santamaria parametrization: with Breit-Wigner A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 23

24 ππ mass distribution, fit of F π ρ ρ ρ ρ ρ masses and widths consistent with expectations (but ρ mass lower than PDG) Interference important! relative amplitudes measured, found to be real sensitive to m c and to differences in interference Heavy Flavour schemes here: massive VFNS schemes Santamaria parametrization: with Breit-Wigner A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 24

25 ππ mass distribution, F π fit vs Q 2 similar results, but some Q 2 dependence A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 25

26 comparison to e + e - here: massive VFNS schemes form factor in ep DIS very similar to e+edespite different production mechanism (ggγ* vs γ*) A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 26

27 Q 2 dependence of ratios ρ /ρ, ρ /ρ ρ /ρ ratio rises with increasing Q 2 - qualitatively expected due to node in ρ wave function (suppression at low Q 2 ) ρ /ρ ratio inconclusive A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 27

28 Summary and conclusions DIS measurements at HERA successfully test QCD and provide unique input to determination of parton densities HERAPDF 1.5 NLO/NNLO available on LHAPDF HERA jet and heavy flavour measurements successfully test and constrain QCD parameters, improve PDFs -> potential to yield competitive measurements of α s (need NNLO calculations! partially in progress). -> further improve cross section predictions for LHC combination of H1/ZEUS results ongoing -> towards full 1 fb -1 results (H1+ZEUS, HERA1+2). -> expect significant further improvements over next few years exclusive dipion electroproduction allows measurement of ρ, ρ and ρ production and their interference -> relative production amplitudes are real and similar to e+e- -> ρ /ρ ratio rising with Q 2 as expected A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 28

29 Backup A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 29

30 Dijets in DIS DESY , Eur. Phys. J. C70 (2010) 965 jet E T,B > 8 GeV M jj > 20 GeV A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 30

31 Heavy flavour contributions to F 2 detect ~ flavour tagging c or c QCD,, c c -> F 2 bb, F 2 cc A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 31

32 ππ control distributions A. Geiser, DIS and dipions at HERA, EDS 11 Qui Nhon 32