HERA Physics. Hans-Christian Schultz-Coulon Universität Dortmund

Transcription

1 HERA Physics Hans-Christian Schultz-Coulon Universität Dortmund 5 th Annual Graduate School of Particle Physics Joint Belgian-Dutch-German Summer School Tagungsstätte Walberberg, September, 3

2 Selected Topics Proton Structure Introduction HERA experiments F QCD Fits Parton Ladders and Photon Structure DGLAP vs. BFKL Forward Jets Photon Structure Diffraction Introduction F D Pomeron Structure Physics at High Q NC & CC Scattering PDFs at High x Searches HERA II: Goals & Status

3 Masses of Bound States Ratio of the mass of the parts to the mass of the whole: Positronium [e + e - ]: x 5 kev/ kev = Bottonium [bb]: x 4. GeV/9.5 GeV =.9 Pion [ud]: (3 + 6) MeV/35 MeV =.7 - Proton [uud]: ( x 3 + 6) MeV/938 MeV =. Proton mass = Σ E B Understanding mass needs understanding of IA inside proton

4 Quantum-Chromo-Dynamics Q α s α s IA of coloured quarks IA via gluon exchange gluons carry colour non-abelian theory coupling constant: α s Confinement Asymptotic freedom [pertrubative methods applicable] Proton radius: ~ fm non-perturbative effects become relevant

5 Electron HERA: maximum resolution: -8 - h/q ~ m Proton Ideal QCD laboratory

6 DIS Kinematics Electron (e ± ) k Q : four-momentum transfer Q [spatial resolution ~ /Q] : x: fractional momentum x: of the struck quark γ k Electron (e ± ) Q = -q = -(k-k ) P q y = Pq/Pk: inelasticity fractional energy transfer in proton rest frame P q = xp X Proton P Q = sxy [ s: cms-energy] [ x ; y ]

7 e Electron-Quark scattering (spinless case) q Structure Function F γ e q dσ( eq) dq = 4πα e q 4 q Rutherford scattering on pointlike target dσ( ep) dq xq(x) /3 4πα = [ e u + e d ] = q 4 Naive QPM x p = uud > x = /3 4πα q 4 With quark-quark interactions xq(x) dσ( ep) dxdq = 4πα [ e q 4 u u( x) + e d d( x) + ] = 4πα F ( x) q 4 x QPM: Structure Function F independent of Q /3 x

8 Electron (e ± ) Electron (e ± ) Cross Section: dσ ~ dσ eq F γ q q Proton SF F = e q xq(x) describes structure of proton probability to find quark with momentum fraction x QPM: independent of Q. Correct? Proton Remnant

9 Scaling [SLAC 97] F Q [GeV ]

10 Scaling Violations [99++] SLAC 97

11 DGLAP Evolution Intuitive picture

12 QCD Improved Parton Model F ( x) = x e q dξq( ξ)δ x ξ = x e q q( x) q q ξp QPM QCD z = x/ξ F x ( ) x e q = ---- dξ q( ξ) δ x -- α s x P ξ ξ qq -- π ξ Q + log µ x ξp x k, k T σ γ q qg σ γ q qg µ : cutoff parameter α s P π qq ( z) µ Q dk T k T α s P π qq ( z) log Q µ q( x, Q ) = q( x) q( x, µ ) = q( x) + + α s Q log π µ x α s µ log π µ x dz P z qq z dz P z qq z ( ) q( x z) ( ) q( x z) (A) (B) Splitting function: Probability to find quark with momentum fraction z of a parent quark having emitted a gluon with momentum (-z) q( x, Q ) = q( x, µ ) + α s Q log π µ x dz P z qq z ( ) q( x z) (A)-(B)

13 DGLAP Equations DGLAP: Dokshitzer, Gribov, Lipatov, Altarelli, Parisi DGLAP evolution equations arise from requirement that q(x,q ) should not depend on the choice of scale µ: & α s Q dz log P π µ z qq ( z) q( x z ) x dq( x, µ ) α = s d logµ dz P π z qq ( z) q( x z) =! x q( x, Q ) = q( x, µ ) dq( x, Q ) d logµ dq( x, µ ) d logµ = α s π x From iteration dz P z qq ( z) q( x z, µ ) z z --- [ z + ( z )] PDFs ( z) z 6 z z z z( z) z

14 ep Cross Section [low Q approximation] Rutherford Proton Structure q F ( x, Q ) = x e q q x, Q [ ( ) + q( x, Q )] Evolution according to DGLAP d σ = 4πα F dxdq xq 4 x, Q ( ) [ + ( y) ] y F L ~ influence small related to gluon density [contribution high y] [LO: F L =] Considering spin e Before spin e Before q q q q After d e After d e M y J d λ, λ' pq E p E e ( cosθ * ) = = = pk E p E e d, = + cosθ d *, = ( cosθ * ) M + ( y) y-dependence describes helicity structure of interaction

15 F at Low Bjorken-x [Pre-HERA Knowledge] DGLAP: No prediction for the x-dependence of F [except asymptotic behaviour] A. De Rujula et.al. 974 Fixed Target Measure!!

16 Selected List of Fixed Target Experiments [Mostly Pre-HERA] Experiment Year Reaction Beam Energy SLAC - MIT 968 ep, ed 4.5- GeV CDHS, CHARM <984 ν µ Fe <6 GeV FMMF <988 ν µ <5 GeV CCFR ν µ Fe <6 GeV BCDMS µp, µd -8 GeV EMC <983 µp, µd <35 GeV NMC µp, µd 9-8 GeV E µp, µd 9-47 GeV NuTeV ν µ Fe <6 GeV Electron energy limited by synchrotron radiation Muon beam experiments Different processes Universality of parton density functions

17 Q 4 3 Accessing Lower Bjorken-x HERA Experiments Fixed Target Experiments Q =sxy access to highest Q y = [HERA: s ~ 5 GeV ] y = [Fixed Target: s < 3 GeV ] Fixed Target: accessing lower x at fixed Q needs higher s s = M p E e s = 5 GeV E e = 5 TeV ep-collider: - access to lowest x at very low Q x s = 4E p E e E e = 3 GeV E p = 9 GeV s = 5 GeV

18 The HERA Accelerator Complex [7.6 GeV] e Halle Nord H e p 36m R=797m [9 GeV] p Halle Ost HERMES NW e p HERA- Halle West N NO Halle West HERA-B HERA Trabrennbahn 36m s Stadion Stellingen = 3 GeV W Kältehalle PETRA Magnet- Testhalle H -Linac DESY II/III e PIA + e -Linac e --linac p O Proton ring: Energy*: 9 GeV Mag. Field: 4.68 T Current: ~ ma * before 998: 8 GeV ZEUS Halle Süd Electron ring: SW Energy: 7.5 GeV Mag. Field:.64 T Current: ~ 4 ma General: Proton bypass SO Energy in cms: 38 GeV Circumference: 6.3 km BX rate:.4 MHz Lumi:.5. 3 cm - s -

19 HERA Detectors ZEUS Uranium Calorimeter σ(e)/e = 8% E for electrons σ(e)/e = 35%/ E for hadrons Central Tracker Resolution σ(p t )/p t =.58 p t /GeV.65 H LAr Calorimeter σ(e)/e = %/ E for electrons σ(e)/e = 5%/ E for hadrons Central Tracker Resolution σ(p t )/p t =.6 p t /GeV. Central Muon System Forw. Tracking Central Tracking Silicon Detectors [ZEUS Collaboration] e FPS FNC ToF ToF Lumi p Forw. Muon System Toroid Solenoid SpaCal [H: Schematic View] LAr-Calorimeter

20 TEST Typical DIS-Event [as seen by the H detector] Calorimeter Scattered Quark Backward Electrons Forward ϑ Scattered Electron Q Protons Trackers Q = 4E e E e cos (ϑ/)

21 Kinematic Reconstruction E e Electron θ' e δy e y δe ' e y e E' e θ j Proton Electron method: E j Q e = E e E' e ( + cosθ' e ) E' y e e ( cosθ' e ) = E e x e Q e ( s y e ) = Hadron method: E y j ( cos θj) h = E e E Q j ( sin θj) h = ( y h ) δy e y [ ] δ E j ( cos θ j ) E j ( cos ) θ j x h = Q h ( sy h )

22 Q (GeV ) Structure Function F [Principle of Measurement] ZEUS > 5 Events > 65 Events > Events < Events Basic (simplified) Procedure: σ 4πα F xq 4 κ and σ F = = In reality much more difficult as acceptances, backgrounds, higher order corrections etc. have to be taken into account. N L N κl N: Number of events L : Luminosity y= y= - y= - Kinematic limit Q =5 GeV x

23 MRS D,D - : Fit to fixed target data only Different assumptions on xg(x,q ) H '9 MRS D - F.6 Q =5 GeV.4..8 HERA MRS D.6.4. CTEQ5D MRST99 ZEUS 96/97 H 96/97 NMC, BCDMS, E Fixed Target x -3% Precision

24 F [ i ] x =.5, i = x =.8, i = x =.3, i = 9 x =., i = 8 x =.3, i = 7 x =.5, i = 6 x =.8, i = 5 x =.3, i = 4 x =., i = 3 x =.3, i = x =.5, i = x =.8, i = x =.3, i = 9 x =., i = 8 x =.3, i = 7 H e + p x =.5, i = 6 ZEUS e + p BCDMS NMC x =.8, i = 5 x =.3, i = 4 x =.8, i = 3 x=5. -3 x=.3 x=.8 Scaling Violations [HERA & fixed target data] Precision: -3% [bulk region] For x < - : df dlogq ~ g(x,q ).α s (Q ) NLO QCD Fits: - x =.5, i = x =.4, i = Quark densities Gluon density Strong coupling α s - -3 H PDF Extrapolation x =.65, i = x=.65 Q [GeV ]

25 Gluons from Scaling Violations z z --- [ z + ( z )] ( z) z 6 z z z z( z) z At small x: gluon dominates as P gq, P gg ~ /z. Simple approximation: neglect quarks (Method of Prytz) dq( x, Q ) dlogq = α s π x dz P z qg ( z) g( x z, Q )

26 Gluons from Scaling Violations dq( x, Q ) dlogq x dq( x, Q ) dlogq df ( x, Q ) dlogq = = = α s π x dz P z qg ( z) g( x z, Q ) α s dz P π qg ( z) G( x ( z), Q ) ---- α s 9 π ( x ) ( x ) dz ( z + ( z) ) G( x ( z), Q ) Taylor expansion of G(x/(-z) ): G( x ( z) ) = G( z = / ) + ( z ) dg dz z = / set xg(x,q ) = G(x,Q ) substitute z z F = xσ e q q(x,q ) sum over quark charges [N F =4] insert: P qg = z + (-z) neglect ( z ) d G d z z = / dg dz z = / dz ( z + ( z) ) ( z ) = [vanishes at integration step] df ( x, Q ) dlogq = α s G x, Q 9 π ( x ) ( ) dz ( z + ( z) ) df ( x, Q ) dlogq = α s G( x, Q ) 9 π 3 -- ~ α s. g(x,q )

27 QCD Fits: Principle Fit Procedure Parametrize parton distribution functions (PDFs) at starting scale Q = Q as function of x. Perform QCD evolution using DGLAP equations. [usually NLO, special treatment of heavy quark PDFs] Calculate predictions for experimental observables. [cross sections, structure functions,...] Determine PDF parameters from χ -fit to experimental data. For p = u v, d v, Σ ( q + q), g or p = u + d, u d, s: xp( x, Q ) A p x ap ( x) b p = P( x; c p,...) characterizes PDFs at x =. [sea: a p <, valence: a p >] characterizes PDFs at x =. [b p > for all PDFs] weakly x-dependent function. [ fine tuning ]

28 QCD Fits: Inputs Fixed target data l p l p: BCDMS, NMC, E Fixed target data l p νp: CCFR, CDHS, BEBC... H, ZEUS data structure function and cross H, ZEUS data section measurements Sum rules: u v ( x ) d x =, d v ( x) dx =, dx x g( x) + Σ [ q( x) + q( x) ] =, I d G x ( ) = = dx ( u d). 3 3 F lp F ln Other experimental data: pp W + X qq W u, d, u/d νn µ + µ + X νs µc s pp, pn l + l + X qq l + l d /u hh γ + X qg qγ g pp jets ± X gg gg, qg... g Valence quarks Momentum sum rule Gottfried sum rule [Experiment (NMC): I G =.35 ±.6 u < d ]

29 Comparison H vs. ZEUS H α s fit: H PDF fit: ZEUS PDF fit: Dedicated to α s and g(x). H ep NC data (low Q ) & BCDMS µp data. Parametrization of valence, sea quark and gluon. Starting scale: Q = 4 GeV. α s = ±.5 Dedicated to PDF-determination. Fit A: H data only (NC, CC, low & high Q ). Fit B: H data & BCDMS µp data. Parametrization of U, U, D, D and gluon. Starting scale: Q = 4 GeV. scale uncertainty exp. & model uncertainty Dedicated to PDF-determination (main goal). Simultaneous fit to strong coupling constant. Data: ZEUS NC data, BCDMS, NMC, E665, CCFR. Starting scale: Q = 7 GeV. α s = ±.4 exp. & model uncertainty scale uncertainty

30 Parton Densities HERA Results xf i (x) xf(x,q )..8.6 H PDF ZEUS-S PDF Q = GeV H Fit A H Fit B xu V xf(x,q ) ZEUS NLO QCD fit α s (M Z ) =.8 CTEQ 6M tot. error MRST uncorr. error Q = GeV xu v xg(.5).4 xg(.5) xd v.4 xd V.3. xs(.5).. xs(.5) x x x x

31 xg ZEUS NLO QCD fit Q = GeV.5 GeV tot. error (α s free) tot. error (α s fixed) uncorr. error (α s fixed) Example: ZEUS Fit GeV GeV Low-x gluon PDF determined by HERA precision data Fixed Target data constrain valence quark distributions.5 Uncertainty of gluon PDF: ~ % [for Q > GeV, -4 < x < - ] Simultaneous extraction of PDFs and as uncertainties larger. GeV GeV Important input for LHC x

32 Possible Impact of d -u Asymmetries H + BCDMS H + BCDMS [a u, a d, b u, b d constrained] [a u, a d, b u, b d unconstrained] xp(x).8 xp(x) xu xu.6.4 xu xu. xu v. xu v xd xd.6 xd xd.4.4. xd v. xd v 6 4 xg PDFs at Q = 4 GeV experimental errors model uncertainties x 6 4 xg PDFs at Q = 4 GeV experimental errors model uncertainties x x parton distribution x parton distribution Enforce: x(d - u x ) a u, a d, b u, b d : free parameters

33 9 LHC parton kinematics 8 x, = (M/4 TeV) exp( ±y) Q = M M = TeV 7 6 M = TeV LHC Q (GeV ) 5 4 M = GeV 3 LHC needs: y = M = GeV 6 knowledge on parton densities HERA fixed target extrapolation over orders of magnitude x

34 The Gluon Density, LHC and the Higgs ~ GeV ~ TeV M = x x s =: τs H Gluon-Gluon Luminosity τdl = g( x, Q )g( τ x, Q ) dx dτ τ x with Q = τs [gg CMS-Energy]

35 PDFs Are they universal? x g(x) NLO QCD fit µ f = GeV H jet data for α s (M z ) =.84 ±.3 gluon from jets CTEQ5M MRST99 Botje99 xg(x,q ).5 gluon from charm Q = GeV µ =5 GeV incl. k algorithm - - x H prel. exp thy D* (DIS) D* (γp) x

36 Parton Ladders and Photon Structure

37 Why DGLAP Sums Leading Logs? [Tentative motivation, not a proof] F x = ( ) x e q d ---- ξ ξ q( ξ) δ x -- α s x P ξ qq -- π ξ Q d k + T dq( x, µ ) d logµ dq( x, µ ) d logµ Iteration effectively includes higher orders = = α s z π P qq ( z) q( x z ) d z α s dz π P z qq ( z) q( x z, µ ) µ log k T Q µ + + q(x) Δq(x,Q ) Δ(Δq(x,Q )) + higher orders F x x ( ) e = q d ---- ξ ξ q( ξ) δ x -- α s x P ξ qq -- π ξ Q d k T d d µ If: Q»» k T k T k T α s 4π µ Q k T k T dk T µ k T... k T [ log Q µ ] [Proof via Mellin Moments: A.Martin, Lectures at XXI Int. Meeting on Fundamental Physics, Miraflores, DTP/93/66]

38 Electron Electron log(/x) BFKL CCFM DLLA x DGLAP Q logq x small breaking of k T -ordering additional log /x terms Proton Proton Remnant

39 Forward Particle Production Backward dσ π / dx / nb 5 5 Forward π production H data p* T,π >.5 GeV LEPTO 6.5 RAPGAP.6 mod. LO BFKL [ ] Forward Jet Production ZEUS Q / GeV [ ] dσ/dx [nb] 4 high p t Forward [ ] 8.5 < E T/Q < ZEUS Data RAPGAP, dir+res RAPGAP, dir LEPTO x DGLAP log /x Evol. γ-structure a) -4-3 x

40 Electron Electron Proton

41 σ γ*p (Q ) / nb 4 4 < E t * < 5 GeV 3 H data LEPTO ARIADNE < E t * > Q / GeV

42 γ Direct x γ = P t = Q Photon Structure Nomenclature Proton γ Resolved Events Proton Remnant x γ P t Proton Proton Remnant x γ

43 Can HERA measure γ F = x γ e q q γ (x,p T )? γp Dijet Cross Section Sensitivity to xg γ

44 γp Dijet Cross Section e e ~ f p Proton ~ f γ γ Photon Remnant JET JET Proton Remnant dσ / dlog(x γ,jets ) [nb] E T,Jet > 6 GeV H data PHOJET (GRV) PYTHIA (GRV).. gluons quarks direct γ Photon Flux Effective Parton Density of Proton Measure! Matrix Element - x γ,jets

45 Extraction of the effective parton density of the photon ~ α - x γ f γ, eff F γ (Q,udsc) / α OPAL (. < x <.6) AMY (.3 < x <.8) JADE (. < x <.) DELPHI prel. (.3 < x <.8) TPC (.3 < x <.6) GRV LO (. < x <.6) TOPAZ (.3 < x <.8) ALEPH prel. (.3 < x <.8) L3 prel. (.3 < x <.8) p T [GeV ] 3 γ H f eff (.4 < x <.7) /α x γ f eff γ H Data GRV 9 quark/antiquark contribution Gluons GRV LO (. < x <.9) GRV LO (.3 < x <.8) SaSD (. < x <.6) HO (. < x <.6) ASYM (. < x <.6) 3 γ ~ x=.5 F = <e q > f γ Q [GeV ] as gluon contribution small at large x Quarks - x γ

46 Gluon Density of the Photon P T = 74 GeV ~ f γ = q(x γ,p ) + 9 / T 4 g(x γ,p T ) α - x γ g(x γ ) H jet data, 996 H single particles, 994 GRV 9 GRS 99 SaSD LAC Known [e.g. from LEP] HERA 3 Observation of low x - x γ

47 Diffraction

48 Hadron-Hadron Scattering Total x-sec σ tot Regge-Theory: σ tot ~ (W ).8 pp Optical Theorem: pp [forward] γp HERA: Q ~ [quasi-real γ s] γγ W

49 Incoming Electron Diffractive Signature Colour Field Standard DIS Diffr. Event Incoming Proton Events 5 4 ZEUS 994 data Pompyt DIFF MC Ariadne DIS MC Diffr. Events Incoming Electron Rapidity Gap 3 No Colour Flow P Incoming Proton η max = ln tan(ϑ min /)

50 Diffractive Cross Section d σ dxdq = πα [ + ( y) ] F xq 4 ( x, Q ) Structure of the proton d 3 σ D dx P dβdq = πα ( y) D 3 [ + ] F βq 4 ( ) ( β, Q, ) x P Structure of the Pomeron [+ Pomeron flux]

51 D F ( 3 ) = Deviation due to meson exchange ( R-Exchange) [at large x P ] f P x P p + R x P p... f ( ) F P β, Q ( ) +... ( )F R β, Q F P ( β, Q D 3 ) x P F ( ) F D(3) Q ( ) = [for small x] 3 Q =4.5 GeV β=.4 Q =7.5 GeV β=.4 Q =9 GeV β=.4 Q = GeV β=.4 Q =8 GeV β=.4 Q =8 GeV β=.4 Q =45 GeV IP+ IR IP only β= Q =4.5 GeV β=. Q =7.5 GeV β=. Q =9 GeV β=. Q = GeV β=. Q =8 GeV β=. Q =8 GeV β=. Q =45 GeV β=. Q =75 GeV β= H 994 Data Q =4.5 GeV β=. Q =7.5 GeV β=. Q =9 GeV β=. Q = GeV β=. Q =8 GeV β=. Q =8 GeV β=. Q =45 GeV β=. Q =75 GeV β= Q =4.5 GeV β=.4 Q =7.5 GeV β=.4 Q =9 GeV β=.4 Q = GeV β=.4 Q =8 GeV β=.4 Q =8 GeV β=.4 Q =45 GeV β=.4 Q =75 GeV β= Q =4.5 GeV β=.65 Q =7.5 GeV β=.65 Q =9 GeV β=.65 Q = GeV β=.65 Q =8 GeV β=.65 Q =8 GeV β=.65 Q =45 GeV β=.65 Q =75 GeV β= Q =4.5 GeV β=.9 Q =7.5 GeV β=.9 Q =9 GeV β=.9 Q = GeV β=.9 Q =8 GeV β=.9 Q =8 GeV β=.9 Q =45 GeV β=.9 Q =75 GeV β= x I P Characteristic / x P -Dep. [Regge-Theo.] [exp. proven ] β

52 F P.5 H 994 H Preliminary 995 x IP =.5 β =. The Pomeron Structure in comparison to the proton.5 β =.4 F P.3 NMC BCDMS SLAC.5.5 β =. β =.. H Preliminary NLO QCD Fit x=.4.5 β = β =.65 β =.9 Q (GeV ) Q / GeV Different behaviour compared to proton Rises also for large parton momenta

53 Parton Content of the Pomeron z f(z).5.5 (a) Q =4.5 GeV Gluon Light Quarks H H 994 Result Uncertainty? DGLAP Gluon: Q =4.5 GeV Q =4.5 GeV (b) Q = GeV (c) Q =75 GeV z z β

54 New NLO Fit [to new (997) diffractive data] H σ r D NLO QCD Fit z Σ(z,Q ).. Singlet z g(z,q ) Gluon Q [GeV ] 6.5 (exp. error) (exp.+theor. error) H σ r D LO QCD Fit z z 5 9 dz z g(z,q ) / dz z [Σ+g](z,Q ) Gluon Momentum Fraction for.<z< H σ r D NLO QCD Fit (exp. error) (exp.+theor. error) Q [GeV ]

55 Study of Hadronic Final States in diffractive events Gluon dominated P* T large (GeV - ) /N dn/dp T * - Gluon dominated. < X F <.4 H 994 DATA M X = GeV EMC W = 4 GeV RG-F D (fit 3) RG-F D (fit ) LEPTO 6.5 γ * P Quark dominated - Quark dominated γp Proton p T * (GeV )

56 Is the Pomeron Universal? Electron Electron Proton Remnant Q Hard Process P Remnant Jet Jet Remnant Proton γp jj +X HERA F jj D pp jj +X TEVATRON Anti- Proton Jet Jet Anti- Proton Proton dσ/dz [pb] Hard Process P Remnant z HERA: ok TEVATRON: fails? z

57 Physics at High Q and the HERA Upgrade Project

58 DIS Cross High Q e ± e ± (ν,ν - ) Influence high y γ, Z (W ± ) q q d σ e ± ( ) ξf ζxf 3 ηy F L dxdq + Proton SF Remnant different contribution from xf 3 for different lepton charge Neutral Current: F x [ q i + q i ] i xf 3 x q i q i i [ ] Use e + p/e p data to extract xf 3 Sensitivity to valence quark density Charged Current: d σ e + d σ e ( ) x [ d + u] ( ) x [ u + d] Use e + p/e p data to disentangle up-/down-quark content at high x

59 NC and CC Cross Sections dσ/dq [pb/gev ] - ~Q -4 H e p NC CC H e + p NC 94- CC 94- H PDF NC Standard Model describes cross sections over large range of Q Electroweak unification at large Q ~ M Z -3 e + p/e p cross sections differ due to different quark contributions -5 y <.9 CC helicity structure of EW interactions -7 s = 39 GeV 3 4 Q [GeV ]

60 rφ view NC DIS Event [as seen in a typical HERA detector] Q = 695 GeV Protons Electrons rz view

61 Neutral Current Interactions σ e e e e γ q e q q + ξ e ξ q Z q q q q Q Q + M Z = Q 4 Q Q + M Z Q + M Z with: ξ e = v e +λa e ξ q = v q +λa q λ = ± (Helicity) = κ Σ e Q 4 q q( x) κ Σ e Q Q q ξ e ξ q q( x) + + M Z κ Σ ξ Q ( + M Z ) e ξ q q( x)

62 [Polarized] Cross Section Expression ± d σ NC ( e L, R ) dxdq = πα Y xq 4 + F L, R L, R + Y xf 3 Different sign for positrons and electrons ~ y L, R F L { Y ± = ( ± ( y) )} Helicity Structure L, R F L, R x F 3 = = i x q i ( x, Q ) q i ( x, Q L, R [ + )] A q i x q i ( x, Q ) q i ( x, Q L, R [ )] B q L, R A q L, R B q = = e q e q ( v e ± a e )v q χ Z ( v e ± a e ) + ( v q + a q )( χ Z ) Q q ( v e ± a e )a q χ Z + ( v e ± a e ) v q a q ( χ Z ) Propagator: Q χ Z Q + M Z Pure Photon exchange γz-interference Pure Z exchange

63 NC Reduced Cross Section σ 3 ZEUS e p ZEUS e + p s=38 GeV s=3 GeV e p ZEUS-S e + p ZEUS-S s=38 GeV s=3 GeV ± --- Y + σ NC xq d σ NC e ± ( ) πα dxdq [/(xq 4 )-dependence removed] xf 3 Extraction: σ NC ( e ) = ξf + ζxf 3 σ NC ( e + ) = ξf ζxf ZEUS 3 4 Q (GeV ) xf 3 = xf 3 - ζ [ σ NC ( e ) σ NC ( e + )] Σ [ q ( x, Q ) q( x, Q )] At high Q : sensitivity to valence quark densities down to x ~ -

64 σ NC Q = 5 GeV Q = 5 GeV Q = GeV s = 39 GeV H PDF : e + p e p e + p H 94- e p H ~ xf 3.5 xf 3.. H H PDF Agreement of data with QCD fit at fixed Bjorken-x xf ~ 3 rises with Q due to: χ = Z s W cw Q + M Z Q Z-Propagator x = Q xf 3 e a e Q q a q x[ q i q i ] χz + v e a e v q a q x[ q i q i ] γz xf 3 Q e a e { xf 3 } χ Z x contribution to xf ~ 3 < 3% ( χ Z )

65 γ Z xf Data H PDF Q = 5 GeV 5 GeV GeV xf 3 γz xf γ Z transformed to Q = 5 GeV H H PDF.65 γz F [H measurement].65 γz F 3. = = ± ±.6. [H PDF ] x γz F 3 = Q q a q q i q i 5 [ ] = Q u a u N u + Q d a d N d = -- ( α s /π) [sum rule a la Gross Llewellyn-Smith] 3

66 rz view Protons Electrons rφ view Neutrino [not detected] CC DIS Event

67 Charged Current Cross Section e - (e + ) _ ν(ν) e - e - e + e + + u d + ν + d u + ν + d u + ν + u d + ν Proton W -(+) u-type (d-type) d-type (u-type) SF d σ CC ( e ) dxdq = πα s W x[ u + c ( y) ( d + s) ] Q ( + M W ) Probes u-quark density d σ CC ( e + ) dxdq = πα s W x[ u + c ( y) ( d + s) ] Q ( + M W ) Probes d-quark density

68 dσ/dq (pb/gev ) ~ G F [constant] ~ (-y) d(x) HERA Charged Current Cross Section ~ u(x) H e + p 94- prelim. H e - p ZEUS e + p 99- prelim. ZEUS e - p prelim. SM e + p (CTEQ5D) SM e - p (CTEQ5D) ~ Q ( + M W ) -7 y< Q (GeV )

69 Reduced CC Cross Section σ CC ± 4s W Q ( + M W ) = πα σ CC + σ CC σ CC = = d σ CC ( e ± ) dxdq x[ u + c + ( y) ( d + s) ] x[ u + c + ( y) ( d + s) ].5 Q = 53 GeV H e p ZEUS e p H e + p 94- ZEUS e + p 99- SM e p (CTEQ6D) SM e + p (CTEQ6D) H e p H e + p 94- SM e p (CTEQ6D) ZEUS e p ZEUS e + p 99- SM e + p (CTEQ6D) σ Q = 8 GeV Q = 53 GeV Q = 95 GeV - - x.5.5 Q = 7 GeV Q = 3 GeV Q = 53 GeV Q = 95 GeV Q = 7 GeV Q = 3 GeV x u (-y) x d Sensitivity to u(d)-quark density More statistics! [HERA II Data] x

70 Knowledge of d/u Ratio M.Botje Fit to HERA ep data [H 994, ZEUS 994] Fixed Target proton and deuteron data [E665, NMC, BCDMS, SLAC] Neutrino data [CCFR] Drell-Yan data [E866] Constrained by W-Asymmetry DIS data Constrained by DIS data only Large uncertainty at high x [dependence on parametrization] [e.g. due to nuclear corrections] Can be further constrained with NC and CC HERA data.

71 c xu - - Valence Quark Distribution x =.8 [c=56] x =.3 [c=64] x =.8 [c=6] x =.5 [c=4] x =.4 [c=] x =.65 [c=] c xd MRST CTEQ6 H PDF Uses: H high-q data, [NC/CC e + p and e - p data] H low-q data x =.3 [c=6] x =.5 [c=4] x =.4 high x 3 Q / GeV Q / GeV H data points determined via local extraction method for data points where the xq v contribution is >7%. xq xq v = σ v meas σ fit more statistics from HERA II H Collaboration To constrain d, u at high x further is needed.

72 ZEUS Microvertex Detector HERA Upgrade ZEUS: H: Lumi System Triggering Microvertex Forw. Tracking Lumi System Triggering Fwd/Bwd Silicon Forw. Tracking

73 HERA I HERA II HERA I Luminosity Integrated Luminosity (/pb) 5 e E P = 9 GeV E P = 8 GeV e H Time in Days HERA I e + p Scattering: L ~ pb - e - p Scattering: L ~ 5 pb - HERA II Int. Luminosity: pb - e ± -Polarisation ~5% e + p, P=+ ~5 pb - e + p, P=- ~5 pb - e - p, P=+ ~5 pb - e - p, P=- ~5 pb - In addition: ~ 5 pb - at reduced cms-energy

74 Polarization for H and ZEUS Spin Rotator (exists) HERMES utilises Compton scattering measures energy weighted asymmetry Laser LPOL Polarimeter Spin Rotator (new) H Spin Rotator (new) Laser Goal: <% accuracy per bunch per minute ZEUS TPOL Polarimeter utilises Compton scattering measures spatial asymmetry HERA B electrons

75 (d σ/dxdq ) / (d σ em /dxdq ) NC e - L e - R e + R e + L Q (GeV ) Polarisation Utilising Exploit sensitivity to EW couplings at high Q σ obs (P) / pb ± σ CC = ( ± P)σ CC, P= ( ) +: Probe d v quark distribution (P= +) -: Probe u v quark distribution (P= -) ± e - p νx [Q > GeV ] ± σ NC ± σ NC = = ± σ NC, + ± Pσ NC, P f( q, q, EW couplings) Four independent equations one each for Q e = ± and P= ±. CC Possibility to Polarisation Disentangle individual quark densities Measure EW couplings v u, v d, a u, a d

76 EW Couplings v u,a u. LEP Preliminary 4 x 5 pb - [Q e =±, P=±]. HERA II P=.5 v c (v u ).8 σ SM HERA: Complementary measurement [HERA: u,d quark couplings] [LEP: c,b quark couplings] Precision compatible with LEP results %CL a c (a u )

77 Searches? at HERA Many limits Excess seen in two areas

78 Searches Examples [ Open windows for discoveries? ] Leptoquarks: e ± q e ± q [Signature: high Q ] Anomalous top prod.: e + u top [Signature: Isolated leptons & missing p t ] u tuγ t Doubly charged Higgs: e + γ e - H ++ [Signature: 3-Lepton events]

79 Leptoquark Search Mass Spectrum Events 3 H data SM with uncertainty Events H data SM with uncertainty H PRELIMINARY e + p e + X 5 5 Mass (GeV) H PRELIMINARY e + p ν X 5 5 Mass (GeV) M LQ = (k+xp) = xs [since s = 4E e E p ] xp k

80 Leptoquark Search Branching Ratio LQ eq β e Present Status D Run I H Preliminary e + p β e Future Sensitivity TEVATRON : L.5 fb - HERA 4 pb - HERA 8 pb λ=.3 λ=.5 λ=. λ= M LQ (GeV).3.. HERA : λ =.5 (eu - LQ) M LQ (GeV) HERA will provide best limits for low branching ratios

81 High P t Leptons with missing Transverse Momentum P t,miss = 43.5 GeV M T(µν) =.6 GeV P t,µ = 7.7 GeV Clear Signature!

82 Events P X t Distributions of high P t Lepton H: Excess in e/µ channel ZEUS: Excess in τ channel Electrons & Muons N data = 8 N SM =.4±.7 H Electron Dominant SM contribution W-Production Quark Taus Quark ` γ,z W Electron Neutrino X Lepton ZEUS P X T / GeV

83 High P t Leptons at High P t X Data/Expectation comparison H 94- e + p (4.7 pb - ) Electrons obs/exp. (W) Muons obs/exp. (W) Taus obs/exp. (W) 5 < P TX < 4 GeV /.94 ±.4 (.8) 3 /.89 ±.4 (.77) P TX > 4 GeV 3 /.54 ±. (.45) 3 /.55 ±. (.5) ZEUS 94- e ± p (3. pb - ) Electrons obs/exp. (W) Muons obs/exp. (W) Taus obs/exp. (W) P TX > 5 GeV / (45%) 5 / (5%) /. +.. (83%) P TX > 4 GeV / (6%) / (6%) / (83%)

84 Anomalous Top Production in FCNC HERA e + p etx [very sensitive to κ tuγ ] vtuz ZEUS κ tuγ v tuz exclusion region M TOP = 7 GeV M TOP = 75 GeV M TOP = 8 GeV (hep-ex/3) Excluded by H (prel.) (Contributed paper to ICHEP) Excluded by CDF (Phys Rev Lett 8 (998) 55) κ tcγ = v tcz = LEP e + e tu TEVATRON top decay γq,zq. Excluded by L3 (Phys Lett B 549 () 9) κ tuγ

85 Multi-Electron Production M = 3 GeV Multi-Electron Event P t =63GeV P t =6GeV Selection: electrons with () P t > GeV (5 GeV) [with o < θ < 5 o ] 3rd electron (if any) with E 3 > 5 GeV ( GeV) [with 5 o < θ < 75 o ] Observation of 6 events with M > GeV

86 Multi-Electron Analysis Events 6 4 H Data 5 pb Pair e Production (GRAPE) DIS +Compton Events e Events e - 5 E P z (GeV) - miss P T (GeV) - 4 P T hadrons (GeV) Events 3e Events 3e Events 3e - 5 E P z (GeV) - P T miss (GeV) - 4 P T hadrons (GeV) Good overall description of data by MC prediction

87 Multi-Electron Analysis Events Events H Data 5 pb - Pair Production (GRAPE) DIS +Compton e 5 5 M (GeV) 3e e e P + P (GeV) T T e e P + P (GeV) T T L MC(GRAPE) L MC(GRAPE) =5x L DATA 5 5 M (GeV) =5x L DATA e 3e M > GeV Data H Prel. SM e 3.5±.5 3e 3.3±.4 high M ee > GeV M > GeV Data ZEUS Prel. SM e.77±.8 3e.37± M (GeV) M (GeV) Needs confirmation with HERA II data

88 Doubly charged Higgs e + γ e - H ++

89 Searches etc. & Polarization++ Topic Preferred Beam Lumi [pb - ] Structure Functions σ NC, F, xg, α s e - [L,R] 5 - xf 3 e ± [L,R] 5 - G e - [L,R] 5/beam cc bb F, F e - [L] ss from CC e + [R] d/u from CC e + [R] F L and high-x partons e ± [3 < E p < 9] [L ~ /E 3... /E ] Electroweak CC vs. polarisation e ± [L,R] 5/beam NC vs. polarisation e ± [L,R] 5/beam G F vs. m t (and M W, M H ) e - [L] M W e - [L,R] R Searches High p t leptons e + Request for data samples of equal size highest poss. lumi highest poss. pol. R p -violating SUSY, stop e + [R] LQ, contact interactions e ± [L,R] Large extra dimensions Single top prod. Excited electrons Excited neutrinos e - [L] QCD Jets, α s...

90 HERA II Current Status Fast Startup: Summer Detector closed; start of machine operation October First ep collisions recorded at HERA II January Close to design specific luminosity... but until March 3: Problems with e- and p-induced backgrounds. L s [cm - s - ma - ] x x x x x L s =.5 cm - s - ma - [Design:.8 cm - s - ma - ] Task force formation Background review meetings x x [mm] Results: - Improvement of vacuum in interaction region. - Collimator/Absorber modifications to reduce background from synchrotron radiation and beam gas interactions. - extra 4 months shutdown. Luminosity operation resumes in October 3.

91 Polarisation at HERA II March 3: HERA II achieves up to 5% polarisation 3 pairs of spin rotators H & ZEUS solenoids on.

92 Concluding Remarks Proton HERA I F precision measurements DGLAP works (Q > GeV ) Parton densities Strong coupling constant α s Parton Ladders and Photon Structure DGLAP breakdown (small x) BFKL (& CCFM) Photon structure Photon parton content g γ (x,q ) Diffraction F D -measurement Pomeron structure Universality? Phyics at High Q Parton densities at high x, Q Electroweak couplings Searches: Excess for high p t and multi-leptons HERA II!