Recent results from HERA. Robert Ciesielski

Transcription

1 Recent results from HERA Robert Ciesielski Seminarium Zakladowe, Warszawa, 13 Listopad 009

2 Outline Introduction to HERA and DIS Inclusive measurements and proton structure Exotic searches including results from first H1 and ZEUS combined analyses! Will not cover: Jets and Hadronic Final States, Heavy Flavours Production, Diffraction (selected material in backup slides)

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4 HERA operation World's only ep collider, located at DESY Hamburg. Ended in June 007, after 15 years of successful running. Two colliding experiments: H1 and ZEUS. p (80/90 GeV) e (7.5 GeV) s = 318 GeV HERA I ( ) L=~10 pb 1 collected per experiment. Mostly e+p. HERA II (00 007) L=~360 pb 1 collected per experiment. Similar amount of e+p and e p. Longitudinal polarisation of lepton beam (P= ). L ~0.5 fb 1 per experiment 4

5 H1 and ZEUS detectors 5

6 Deep Inelastic Scattering at HERA (1) Two processes: Neutral Current (NC) exchange and Z0 (e± p e± X) Charged Current (CC) exchange of W± (e± p X) Q = q = k k ' Q x= p q p q y= p k QPM Q =s x y the probing power virtuality of exchanged boson the Bjorken scaling variable the inelasticity s= p q Kinematic range: 0 (photoproduction) < Q < GeV, x >

7 Deep Inelastic Scattering at HERA () CC DIS NC DIS Event selection based on: scattered electron missing pt 7

8 Deep Inelastic Scattering at HERA (3) NC ± d e p = [Y F x,q Y xf x, Q y F x, Q ] 3 L 4 dxdq xq Y ± =1± 1 y F x q q dominant contribution xf 3 x q q only sensitive at high Q ( Z interference) F L s xg x, Q important at high y Similarly for CC: W±, xw±3, W±L (CC purely week, xw±3 contributes over full phase space) F measured with HERA I data xf3, FL with HERA II data 8

9 HERA I Data 9

10 Low and Medium-Q NC cross sections, F low Q = 0.5 Q 1 GeV medium Q : 1 Q 150 GeV Recently H1 measured the NC cross sections using HERA I data taken at Ep =90 GeV and combined them with HERA I published results at E p = 80 GeV. H1 final low and medium Q results. 10

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12 H1+ZEUS combined HERA I cross sections Significantly reduced experimental uncertainties compared to the separate analyses of the ZEUS and H1 experiments. (experiments cross calibrate each other). Complete set of published inclusive NC/CC HERA I DIS data ( , L=40 pb 1 ) 1400 data points, spanning 6 order of magnitude in x and Q. 110 syst. error sources Data show good consistency: /ndf = 637/656 small shifts of global normalisation. pull distributions are OK. 1

13 H1+ZEUS combined HERA I cross sections 1 % precision in the medium Q region. New standard HERA data input for future DGLAP analyses! 13

14 NLO QCD fit to combined HERA I data HERAPDF1.0 Parametrisation in x at Q0=1.9 GeV and DGLAP evolution in Q. Detailed study of the PDFs uncertainties. Much increased precision for sea quarks and gluons. They are < % at the scale relevant for Z/W production at the LHC. 14

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18 HERA II Data 18

19 High-Q NC and CC cross sections NC ± d e p = [Y F x,q Y xf 3 x, Q ] 4 dxdq xq Y ± =1± 1 y QCD+EW e e+ 4 CC MW d e p G F = [ u c 1 y d s ] Q M W dxdq 4 CC MW d e p G F = [ u c 1 y d s ] Q M W dxdq EW effects enhanced with polarised lepton beam. 19

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21 Z F, F = x e q, e q v q q q R. Ciesielski, ZRecent Results from HERA xf 3 =x e q aq q q 1

22 Unpolarised NC Cross Sections, xf3 e e+ xf Z 3 x,q = x F 3 Q M Z ae Q Sensitivity to valence quark distributions in a region where there were no previous DIS measurements with pure proton target.

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24 Clear evidence of parity violation at high Q Z Z a e F F ~ a e v q 4

25 Polarised High-Q CC cross sections Total cross sections as a function of lepton beam polarisation. Demonstration of chiral structure of the Standard Model. e Cross sections depend linearly on P, vanish for right handed particles (left handed antiparticles). e+ Weak interactions left handed. P e= N R N L N R N L 5

26 Polarised High-Q CC cross sections e+p Cross sections as a function of Q, x and P= and P= Scale with polarisation independently of kinematic variables. CC CC P = 1±P 0 e p e p ± ± 6

27 Unpolarised CC cross sections e p Sensitive to uv quark. Flavour decomposition e+p e p X =[ u c 1 y d s ] e p X =[ u c 1 y d s ] Sensitive to dv quark. 7

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29 FL and gluons FL is proportional to the longitudinally polarised photon proton cross section. In the QPM FL=0 (Callan Gross relation FL(x)=F xf1=0) In QCD, a gluon radiation contribute to the non zero FL. How to measure FL? Sensitivity to gluons. For fixed x and Q need different y. Q=sxy need data at different s. 9

30 Measurement of FL NC e+p data from dedicated running periods: HER: Ep=90 GeV s = 318 GeV L=44.5 pb 1 MER: Ep=575 GeV s = 51 GeV L= 7.1 pb 1 LER: Ep=460 GeV s = 5 GeV L=13.9 pb 1 Reduced cross sections measured for 0<Q<130 GeV and < x <

31 Measurement of FL Rosenbluth plots in bins of Q and x. Straight line fit to r vs y/y+. F intercept, FL slope. 31

32 Measurement of FL (and F) Non zero FL. Most precise ZEUS measurement of F in this kinematic region. Predictions for F and FL (ZEUS JETS) are consistent with data. 3

33 Measurement of FL low Q medium and high Q Kinematic region of H1 measurements:.5<q<800 GeV and < x <

34 FL vs Q Comparison to theory predictions. Predictions agree well with data for Q >10 GeV And slightly underestimate the measurements at lower Q. (better agreement with CTEQ6.6) FL data are expected to further constrain the low x theory. 34

35 ZEUS Inclusive HERA II Measurements Where are we? NC e+p HER, MER, LER (FL meas.), published NC e p, published CC e p, published CC e+p, preliminary, publication imminent NC e+p, preliminary, in progress Impact of new data ZEUS09 NLO QCD fit 35

36 ZEUS09 NLO QCD fit With the approach described in the ZEUS JETS publication study the impact of new HERA II NC e p, CC e p on PDFs xuv improved by NC and CC e p data 36

37 ZEUS09 NLO QCD fit With the approach described in the ZEUS JETS publication study the impact of new HERA II NC e p, CC e p and CC e+p on PDFs xuv improved by NC and CC e p data xdv improved by CC e+p data 37

38 ZEUS09 NLO QCD fit With the approach described in the ZEUS JETS publication study the impact of new HERA II CC e±p, NC e p and NC e+p HER/MER/LER data on PDFs Consistent with ZEUS JETS. Slightely steeper gluons at low x. xuv improved by NC and CC e p data xdv improved by CC e+p data xg improved by NC e+p data (FL meas.) 38 Further improvement of the HERA PDFs for LHC promising

39 Exotic Searches Quark radius Contact Interactions LED, Heavy Leptoquarks General Searches Multi leptons Isolated leptons and missing p T FCNC single top production Excited Fermions Squark production in RPV SUSY Presented results are based on full datasets, ~0.5 fb 1 per experiment 39

40 High-Q NC and CC Cross Sections Main processes studied at HERA: Neutral Current (NC) DIS, ep ex, mediated by or Z0. Charged Current (CC) DIS, ep X, mediated by W±. Excellent agreement between data and SM predictions over many orders of magnitude. Q (resolving power) up to GeV. Spatial resolution ~ 1/Q m = 10 3 fm. 1/1000 of proton radius. Search for Beyond SM physics by studying processes at highest Q and/or processes with high pt objects in the final state. 40

41 Quark Radius If a quark has a finite size, the SM cross section is expected to decrease at higher Q. Quark form factor (electron assumed to be point like): SM d d dq dq = [ 1 R q 6 Q ] Rq is a root mean square radius of the EW charge distribution in the quark. The same dependence expected for e p and e+p. Excellent agreement with SM expectations up to highest Q. ZEUS: Rq < 0.63 x 10-3 fm H1: Rq < 0.74 x % C.L. 41

42 Contact Interactions (CI) Reminder: before W and Z0 were discovered, weak interactions ( MW) were described as 4 fermion CI with Fermi constant GF=g/MW. LEP HERA New interactions at higher scale ( s ) can be effectively described at lower energies as 4 fermion eeqq Contact Interactions (CI). Tevatron L CI =, eq e q q e, electron, quark helicities (L,R). CI modify the tree level eq eq scattering amplitudes + M eq Q = e eq Q ge gq e eq sin W cos W Q M Z Search for deviations from SM cross sections at highest Q. 4

43 CI, General Models Also referred to as Compositeness Models. Couplings eq are related to the effective mass scale of new interactions: eq = gci gci is a coupling strength (gci = 4 ), = ±1. Different models assume different helicity structure of new interactions (given by set of 4 couplings eq ) Parity conserving models fulfill the relation: eq eq eq eq LL LR RL RR =0 Family universality assumed. 43

44 CI, General Models ZEUS CI analysis based on full NC sample of L=0.44 fb 1. Models with 19 different helicity structure tested. eq = gci ZEUS: > C.L. 44

45 CI, Large Extra Dimensions Arkani Hamed Dimopolous Dvali Model If gravity propagates in 4+ dimensions, effective Plank scale MS can be as low as 1 TeV. Contribution of graviton exchange (Kaluza Klein tower) to e±p NC DIS: =±1 coupling strengh. G = 4 MS ZEUS: MS+ > 0.94 TeV, MS- > % C.L. CI, heavy Leptoquarks eq M LQ Buchmueller Rueckl Wyler Model 7 scalar, 7 vector Leptoquarks at HERA. Yukawa LQ e q couplling. MLQ / > C.L. 45

46 General Searches Analysis based on complete set of H1 e p data, L=0.46 fb 1. Model independent, generic search for final states with high pt objects high pt objects:, e,,, jet pt > 0 GeV 10 < < 140 D(, ) > 1 Events counted in distinct channels, separately for e+p and e p data. 3 high pt objects 4 high pt objects Good agreement of event yields with SM expectations (NC, CC, photoproduction, lepton pair production, W production, QEDC). Good understanding of detector and physics processes at HERA. No indication for BSM physics. All deviations compatible with statistical fluctuations (largest for e e channel in e+p data). 46

47 Multileptons The main multi lepton process at HERA is process. Precise SM QED predictions, modelled with GRAPE. Cross section steeply falling with p, low at high masses T any deviation is an indication of new phenomena, eg. exotic resonances (H ). Combined H1 and ZEUS analysis in the common phase space, L= ~ 1 fb 1. Events selected by requiring at least isolated, high pt e or. Two leptons must satisfy: 0 < < 150, pt > 15, 10 GeV Events classified into independent exclusive samples: ee,, e, eee, e,... eee event in H1 detector: Inv. mass of highest pt leptons for eee, e channel (examples): 47

48 Multileptons Overall good agreement with the SM. For pt> 100 GeV: 7 events observed in e+p data, while expected (.6 significance). Differential cross section for the ℓℓ process measured as a function of pt of leading lepton and lepton pair mass. Measured total visible cross section: 0.66 ± 0.03 (stat.) ± 0.03 (sys.) pb in agreement with the SM prediction of pb (GRAPE). 48

49 Isolated Leptons & missing pt The main corresponding SM process is single W production. Modelled with EPVEC ( NLO corr., ~15% unc.). Rare process, ~ 1.3 pb. Search for new phenomena (eg. anomalous single top production, bosonic stop decay). Combined H1 and ZEUS analysis in the common phase space, L= ~ 1 fb 1. isolated high pt e or ( pt > 10 GeV, 15 < < 10 ) missing pt (ptmiss > 1 GeV) hadronic system ptx. High purity (75 %) of W production, clear jacobian peak 49

50 Isolated Leptons & missing pt Overall good agreement with the SM. For ptx > 5 GeV: 3 events observed in e+p data, while expected (1.9 significance). Differential cross section for W production extracted as a function of hadronic transverse momentum ptx. Branching ratio of W leptonic decays (~10 %) used to measure full W production cross section. Measured total single W production cross section: 1.07 ±0.16 (stat.) ± 0.08 (sys.) pb in agreement with the SM prediction of pb (EPVEC). 50

51 Anomalous single-top production The SM single top production negligible at HERA ( <1 fb). FCNC single top production predicted by several BSM theories. At HERA sensitivity to anomalous t u and t u Z couplings. Search for t bw, with W ℓ : topology as for isolated lepton and missing pt but higher ptx (b jet) W qq : 3 jets H1 analysis based on full dataset (L=0.47 fb 1 ) No significant excess in the signal region. Set limits on anomalous tu coupling (Vtu Z=0). HERA limits on tu most stringent. 51 tu <0.13, ZEUS prel. (L=~0.4 fb 1 )

52 Excited Fermions Excited fermions would be a signature for compositeness. Explanation of 3 lepton families and mass hierarchy. Effective lagrangian (Hagiwara et. al.): Parameters: compositeness scale f, f', fs relative strengh to Z/W,, g SU() U(1) SU(3) Decay to standard fermions and gauge bosons: f* f +,Z,W with Z ee,, qq and W e,, qq'. Variety of experimental signatures: isolated leptons, missing pt,, jets. H1 analysis based on full dataset (L=0.47 fb 1 ). 80% 90% of decay channels looked at. 5

53 Excited Fermions No deviation from SM observed. Limits set on f/ ratio (95% C.L.). Best sensitivity achieved for masses beyond LEP reach. f/ limits can be can be translated into mass limits assuming f/ =1/Mf* Me* > 7 GeV M * > 13 GeV Mq* > 5 GeV (for fs=0, HERA unique) 53

54 Squark Production in RPV SUSY R parity: 3B+L+S RP=( 1) ( +1 for SM, 1 for SUSY particles ) Production: RPV RP conserved pair production of SUSY particles, RP violated single production If RPV single resonant squark production possible at HERA. Decays: RPV Gauge coupling (neutralinos or charginos) Many final states: DIS like or multi jets with isolated lepton(s), missing pt 54

55 Squark Production in RPV SUSY No deviations from SM observed. Limits set (SUSYGEN3). Photino like neutralino Parameter scan For = 4 =0.3: Md squark < 90 GeV Mu squark < 75 GeV 55

56 Summary HERA still provides a wealth of data. Inclusive/High Q/EW/Exotics measurements are getting to their final shape. Precision on PDF fits is still improving H1+ZEUS start to combine analyses (~1 fb 1 ) in order to further improve statistical precison. Thank you for your attention 56

57 Contact Interactions + 4 fermion CI at HERA: e e q e q g e g eq M eq Q = Q sin W cos W Q M Z, electron, quark helicities (L,R). NC e p scattering: d e p sx = q x P M L L P M R R 1 y P M L R P M R L dxdy 16 { q x { P + NC e p scattering: M L R P M R L 1 y P M R R P M L L } } d e p sx = q x P M L R P M R L 1 y P M L L P M R R dxdy 16 { q x { P M L L P M R R 1 y P M L R P M R L At high Q and high x quark distribution dominate (valence quarks). Some contributions are suppresed by helicity factor (1 y). NC e p sensitive to LL and RR, NC e+p sensitive to LR and RL configurations. } } P± =1± P SM MEs modyfied by quark form factor: M eq Q = M eq Q SM 1 R q Q / 6 57

58 Leptoquarks Production The Buchmueller Rueckl Wyler Model Leptoquarks (LQ) hypothetical bosons connecting lepton and quark sectors. Carry SU(3) colour, fractional charge, lepton (L),barion (B) and fermion number F=3B+L=0,. Chiral objects ie. either left or right handed coupling to lepton, but not both. At HERA: 7 scalar and 7 vector LQs coupling to eq. 4 LQs couple also to q. e p e+p LQs can be resonantly produced in s channel (MLQ < s) or exchanged in u channel. s channel u channel is the Yukawa LQ e q couplling. Limit setting on MLQ /. 58

59 st 1 Generation Leptoquarks H1 analysis based on full NC and CC samples of L=0.45 fb 1 LQ eq Large SM background from NC and CC processes. Good description of data by SM prediction. No LQ signal observed. Limits set for all 14 LQs. H1: For = 4 =0.3 MLQ < GeV are excluded at 95%C.L. ZEUS CI (94 07 data): M LQ eq Example (F=0) MLQ / > C.L. LEP (OPAL, L3): indirect constraints from ee qq. Tevatron (D0): LQ+LQ pair production from qq anihilation or gg fusion ( independent). 59

60 nd Generation Leptoquarks /. 0.6 e p LQ X with e p data. Search for Lepton Flavour Violation mediated by LQ. Experimentaly clear process. Background dominated by lepton pair production. No evidence for signal. Limits set for 7 LQs (F=), under assumption: q= eq, q=0. For = 4 =0.3 MLQ < GeV are excluded at 95%C.L. 60

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63 Diffractive NLO QCD fit and dpdfs NLO QCD fits to inclusive DDIS data and diffractive di jets in DIS. Data with Q>5 GeV fitted within the combined framework of DGLAP evolution and proton vertex factorisation. TR VFNS treatement of heavy quarks. Inclusive data constrain the quark PDFs, Diffractive di jet data (BGF) constrain the gluon PDFs od the diffractive exchange 63

64 Diffractive NLO QCD fit and dpdfs Quark Gluon spdfs Predictions based on extracted dpdfs satisfactory describe: diffractive charm production diffractive di jet photoproduction cross sections 64

65 Jet production in NC DIS HERA II e p data (L=188 pb 1 ) Breit frame Measurement of αs (Mz) Input to PDFs 65

66 New measurements of s(mz) HERA II NC DIS inclusive jets: α s M Z =0. 119± stat exp th. 3.5% (total) First measurement from ZEUS HERAII data Re analysis of HERA I inclusive jets PhP (reduced theoretical unc., the same data): α s M Z =0. 13 ± stat. 0. exp th. 3.1% (total) Two most precise single ZEUS measurements of s(mz). NNLO calculations needed. 66

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69 DESY Subjets in NC DIS Subjets: pattern of parton radiation colour coherence Two resolved subjets (y_cut=0.05) L= 8 pb 1 Predictions: soft gluon radiation to be emitted towards proton direction subjet with lower ET emitted predominantly towards proton direction Three resolved subjets (y_cut=0.03) L= 344 pb 1 gives a handle on underlying colour dynamics angular corelations are sensitive to different colour configurations. NLO QCD descibes the data adequately. Angle between the two lowest ET subjets in plane 69

70 Isolated and Prompt Photons in DIS LL QQ + photons from quark hadronisation MRST p e e LL enhaunced NLO calculations needed 70

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72 Beauty in photoproduction HERA II data, 006/07 e+p (L=18 pb 1 ) First ZEUS inclusive di jet measurement with secondary vertexing. Fraction of b extracted from decay length significance, after reconstructing the decay vertices of B hadrons Invariant mass at the reconstructed vertices (mvtx ) used to distinguish beauty enriched regions Greatly improved precision compared to HERAI result In agreement with NLO QCD (FMNR) 7

73 Beauty in photoproduction Newest ZEUS results in red. Good overall agreement of ZEUS and H1 data with NLO QCD (FMNR). More precise theory would be useful. 73

74 Semileptonic charm and beauty in DIS DESY HERA II data, 005 e p (L=16 pb 1 ) Di jets with muons Q>0 GeV, 0.01<y<0.7 pt > 1.5 GeV, 1.6< <.3 The c and b fractions extracted simultaniously using ptrel, impact parameter and ptmiss (pt balance from neutrinos) Charm: good agreement with HVQDIS and RAPGAP. Beauty: good agreement in shape, HVQDIS predictions scaled by a factor of. 74

75 Fcc and Fbb DESY Good agreement between ZEUS and H1 measurements. Results well described by theory. 75

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