Physics at HERA. Contents HERA and ZEUS Electroweak results Structure of the proton. Katsuo Tokushuku (KEK, ZEUS)

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1 Physics at HERA e p Contents HERA and ZEUS Electroweak results Structure of the proton Katsuo Tokushuku (KEK, ZEUS) 3/March/5 KEKPH5

2 / HERA: 7.5GeV 9GeV the world largest electron microscope H ZEUS 3/March/5 KEKPH5

3 A view of the HERA ring tunnel Proton ring Electron ring 3/March/5 KEKPH5 3

4 The corner stone In 984 3/March/5 KEKPH5 4

5 H 3/March/5 KEKPH5 5 Experiments started in 99

6 esolution Wavelength h Q Q ( ) q i q f Resolved dimension [fm]. Rutherford Hofstadter SLAC ep nuclei proton partons [m] -6 Progress in accelerator enables us to investigate the smaller structure. HERA: 7.5GeV electron vs 9GeV proton. CERN µ,ν N Q max=s=4e e E p ~GeV.. No sub-parton structure down to.85x -8 m (HERA-I result) HERA 9 95 THERA Year -9 cf. in the rest frame E e M p In order to obtain the same CMS energy as HERA in a fixed target experiment, it requires 54TeV electron beam. 3/March/5 KEKPH5 6

7 ERA probes the quarks in the proton neutrino Photon, W quark 9x GeV Proton 9GeV Electron 7.5GeV new interactions and new particles search for quark structure Scattered quark Jet Parton distribution in the proton HERA High Energy High Resolution Polarized experiment Neutral Current Good sensitivity to the interaction type 3/March/5 KEKPH5 7

8 Introduction: Deep Inelastic Scattering Described by kinematic variables p x = Q /p.q F = e xq f ( x, Q ) f q f ( x, Q ) : quark distribution functio 3/March/5 KEKPH5 8

9 inematical region for HERA structure function measurements s=q xy Q (GeV ) 4 ZEUS ZEUS (Preliminary) ZEUS BPT 997 ZEUS SVX 995 order higher region in Q, order lower region in x Wide (O( 6 )) span in : Precise measurements or Q evolution 3 NMC BCDMS CCFR E665 Kinematic limit y= - y= /March/5 KEKPH5 9 x

10 Statistics 5 ZEUS e p ZEUS y = Q (GeV ) 4 3 ZEUS ZEUS (Preliminary) ZEUS BPT 997 ZEUS SVX 995 NMC BCDMS CCFR 4 θ =.64 rad e E665 Kinematic limit y= - y= x 3 θ e =.5 rad High Q measurements: still limited by statistitics HERA II E e = GeV 3/March/5 KEKPH5 y =. y =. y( x) =.4

11 Neutral Current (NC) Charged Current (CC) Scattered positron Positron Proton Jet Scattered positron Jet Anti-neutrino positron 7GeV Z quark u,d,s,c..) Proton 9GeV positron 7GeV 3/March/5 Scattered quark KEKPH5 -quark jet jet W Proton 9GeV

12 Measurements of NC/CC Cross sections ZEUS HERA-I Final Results ZEUS e + p NC 99- ZEUS e p NC SM e + p NC (CTEQ6D) SM e p NC (CTEQ6D) At high Q (Q ~M WZ ), dσ dq NC CC α ( ) Q + M Exchange NC ~ CC Electroweak unification ZEUS e + p CC 99- ZEUS e p CC SM e + p CC (CTEQ6D) SM e p CC (CTEQ6D) Good agreement with the SM Mw = 8.3 ±.(stat)±.(syst)±.(pdf) GeV (from ZEUS e pdata) NC(e + p) < NC(e - p) Z interference 3 4 CC(e + p)<cc(e - p) u,d-quark distribution in the proton 3/March/5 K.Tokushuku(KEK) Q (GeV@ ) KEKPH5

13 N/N CTEQ5D ZEUS ZEUS 94- e ± p R q = (.85-6 cm) R q = -(.6-6 cm) Quark Radius Limits softer scattering If the quark is not point-like 3 4 Q (GeV ) λ SCALAR LEPTOQUARKS WITH F= ( S, L ) - - EXCLUDED H CI L3 indir. limit Preliminary ZEUS limit H direct limit (e - p) D limit 3/March/5 Excess in K.Tokushuku(KEK) data (e + KEKPH q q p p LQ g LQ e q e p λ LQ e e Good agreement with the SM Quark Radius

14 NC Cross section including Z dσ/dx (pb) 3 5 d σ ± dxdq e p F ( x, Q xf ( x, Q 3 πα = 4 xq ) = ) = Q > GeV q q [{ + ( y) } F m { ( y) } xf ] { e f { e e f ZEUS a f f a v e f v P Z e P Z + 4v + ( v ZEUS e p s=38 GeV ZEUS-S γ + Z ZEUS-S γ f a f f + a v e a f e )( v P Z 3 e + ae ) PZ }[ xq( x, Q ) + xq( x, Q )] [ xq( x, Q ) xq( x, Q )] } σ 3 ZEUS e p s=38 GeV ZEUS e + p s=3 GeV ZEUS P sin θ w Q Q + M = z Z e p ZEUS-S s=38 GeV e + p ZEUS-S s=3 GeV 5 ZEUS e + p s=3 GeV ZEUS-S γ + Z ZEUS-S γ γz interference effect x Q (GeV ) 3/March/5 KEKPH5 4

15 HERA I II Longitudinal polarization of lepton beam : Direct EW sensitivity Sokolov-Ternov effect Lepton beam has transverse polarization + Spin rotator before/after the H/ZEUS/HERMES detectors. Polarization build-up at HERA Luminosity Upgrade : High-Q requires large luminosity Final focusing magnets in the detector 3/March/5 KEKPH5 5

16 CC Expectations σ CC TOT (Q > GeV ) (pb) Cross section ZEUS CC Cross Expectation Sections e + p Data (48 pb - ) e + p SM s=3 GeV e + p SM (MC) s=3 GeV (5 pb - ) e - p Data (Prelim. 6 pb - ) e - p SM s=3 GeV e - p SM (MC) s=3 GeV (5 pb - ) Left handed electron electron neutrino (left handed) s-quark left handed -quark (Jet Right handed electron neutrino Proton 8GeV Proton 8GeV Left handed P Right handed With ~ pb - for each polarized beam, Right handed electron s-quark (right handed -quark Jet M WL 8MeV M WR >4GeV 3/March/5 KEKPH5 6

17 HERA is back again with polarized positron beam Integrated Luminosity (pb - ) HERA delivered Even better performance with e - p days of running Polarisation [%] Polarisation [%] Polarisation [%] Average HERA polarisation Oct 3 Nov 3 Dec 3 Jan Feb 4 Mar 4 Jun 4 Jul Day in month Apr 4 May Aug Day in month Day in month Highest Luminosity : 3.8 x 3 cm - s - Average longitudinal Polarization P=+3% P=-4% (~5% in Feb 5) 3/March/5 KEKPH5 7

18 Polarized Charged Current Cross section σ CC (Q > GeV ) (pb) ZEUS ZEUS CC (prel.) 3-4 e + p (3.5 pb - ) ZEUS CC 99- e + p (P=) SM (ZEUS-S) Left handed R = (pb) W R 6GeV M. Kataoka (NaraWU) D-thesis to be submitted on /Jan Polarization 3/March/5 KEKPH5 8 P Right handed Q > GeV P = ±.9% ( L = 4. pb ) σ = 46.7 ±.4( stat.) ±.( syst. ±.3( lumi) pb 3.4 above the unpol. predictio P = 4. ±.% ( L = 6.4 pb ) σ =.5 ±.6( stat.) ±.5( syst ±.( lumi) pb 6. below the unpol. predictio The first measurement of Left/Right asymmetry in CC in this energy region.

19 CC Single Differential Cross-Sections [ZEUS] dσ/dq (pb/gev ) dσ/dy (pb) Q (GeV ) y ZEUS dσ/dx (pb) ZEUS CC (prel.) 3-4 e + p (4.pb - ) ZEUS CC (prel.) 4 e + p (6.4pb - ) SM (ZEUS-S) P = +3% SM (ZEUS-S) P = -4% 3/March/5 KEKPH5 9 x d / dq d / dx d / dy Polarization effects observed in overall, i.e. no phase space bias. Agrees with the SM prediction of : overall normalization change by (+P) factor.

20 CC Cross-Sections [H/ZEUS] H (prel.) H ZEUS (prel.) ZEUS SM (MRST) HERA II e + p ν _ X H preliminary result on R σcc ( P= ) = 3.7 ±.4( stat.) ±.7( syst.) pb H cross sections are slightly lower but the two results are consistent. CC (RH)= 3 Q > 4 GeV y<.9 Q > 4 GeV y < /March/5 KEKPH5 P

21 (d σ/dxdq ) / (d σ em /dxdq ) olarized Neutral Current Cross section Very subtle effect from γ-z interference Larger effect in e-p (The experiment has started in Nov 4) Pol=7% a) =.69 (w/ Pol.) =.9 (w/o Pol.) at Q > GeV e - L e - R e + R e + L /March/5 KEKPH5.5 Q (GeV ) dσ/dq ratio P=+3% / P= P=-4% / P= P=+3% / P=-4% ZEUS 3-4 P=+3% (prel.) / 99- P= P=-4% (prel.) / 99- P= SM (ZEUS-S) P=+3% (prel.) / 4 P=-4% (prel.) 3 4 Q (GeV ) Q (GeV )

22 inematical region for HERA structure function measurements s=q xy Q (GeV ) 4 ZEUS ZEUS (Preliminary) ZEUS BPT 997 ZEUS SVX 995 order higher region in Q, order lower region in x Wide (O( 6 )) span in : Precise measurements or Q evolution 3 NMC BCDMS CCFR E665 Kinematic limit y= - y= /March/5 KEKPH5 x

23 Predictions of F Gluck, Reya and Vogt pqcd : parton evolution HERA Kinematic Limit Early ZEUS data showed rapid increase of F at low x. Donnachie & Landshoff 3/March/5 KEKPH5 3 Hadronic : Regge theory Fixed targe data

24 Scaling violation DGLAP evolution Dokshitzer, Gribov, Lipatov, Altarelli, Parisi df α s ( Q ) dy = eq qq qg, d ln Q π y q Q larger high-x q and g are split into low x q and g. xq x [ ( ) ( ) + ( ) ( )] P x y q y, Q P x y g y Q splitting function (known from pqcd) P qq ( x y) y x (y-x) P qg ( x y) x x y (y-x) 3/March/5 KEKPH5 4

25 Results of F Structure Function HERA F Strong rise of F as x decreases Soft sea of quarks in the proton Slope of rise gets steeper as Q softer parton resol. smaller em F Q =.7 GeV 3.5 GeV 4.5 GeV 6.5 GeV 8.5 GeV GeV GeV 5 GeV 8 GeV GeV 7 GeV 35 GeV dynamics of quarks and gluons 45 GeV 6 GeV 7 GeV 9 GeV Good agreement with fixedtarget experiments at middle - high x Sea + valence quarks 3/March/5 KEKPH5 ZEUS 96/97 5 GeV -3 5 GeV ZEUS NLO QCD fit tot. error H 96/97 BCDMS E665 NMC

26 F for fixed x, as a function of Q At low x, strong scaling violation is seen. Large gluon density + g qq splitting F increases At x ~., approximate scaling. At higher x, F decreases as Q. Quark radiates off gluon: q qg Line = result of QCD fit All data points well described. em F -log (x) HERA F x=6.3e-5 x=. x=.6 x=.53 x=.4 x=.5 x=.63 x=.8 x=.3 x=. x=.3 x=.5 ZEUS NLO QCD fit x=.8 x=.3 tot. error x=. H 94- prelim. H 96/97 ZEUS 96/97 BCDMS E665 NMC x=.3 x=.5 x=.8 x=.3 x=.8 x=.5 x=.4 x= Q (GeV ) 3/March/5 KEKPH5 6

27 F p +c i (x) 6 4 x=. (i=4) x=.3 x=.5 x=.8 x=.3 x=. x=.3 NMC BCDMS SLAC H (i=) x=.5 H 96 Preliminary (ISR) H 97 Preliminary (low Q ) H Preliminary (high Q ) x=.8 x=.3 x=. x=.3 NLO QCD Fit H Preliminary c i (x)=.6 (i(x)-.4) 8 x=.5 x=.8 x=.3 (i=) 6 x=. x=.3 4 x=.5 x=.8 x=.3 x=.8 x=.5 3/March/5 KEKPH5 7 x=.4 x= (i=) Q /GeV

28 PDF parameterization xf(x) = p x p (-x) p3 (+p 5 x) at Q =7GeV p: normalization p(p3): x (x ) bahavior p5: high-x shape Some assumptions For xu v and xd v, fix p= (not sensitive to low-x valence) For xg, fix p5= (not sensitive to high-x gluon shape) xsea=(xubar+xdbar+xstrange+xcharm), xstrange=.*xsea (CCFR) Use MRST form for x(ubar-dbar) shape (only fit p) Sum-rule constraints (number and momentum) u v (x)dx=, d v (x)dx=, x f(x)dx= Total: free parameters, 63 data points 3/March/5 KEKPH5 8

29 PDFs obtained from the fits xf ZEUS ZEUS NLO QCD fit α s (M Z ) =.8 tot. error CTEQ 6M Q = GeV xu v xf HERA: PDF determination H PDF Fit (prel.) α s (M Z ) =.85 fixed data set: H (94/) + BCDMS Q = GeV As seen ZEUS in NLO the QCD F fit rise at low-x, α many s (M sea Z ) =.8 fixed quarks. data set: ZEUS (96/97) + BCDMS, NMC, E665, CCFR MRST xg(.5) xd v Gluons are dominant at low-x xs(.5) Similar conclusion from ZEUS and the PDF fitters (Durham, CTEQ) xd v xu v. xs(.5). How about H results?.. experimental errors only Note the scale factor. Gluon dominant at low-x x x H/ZEUS comparison: The main difference comes from Initial Parameter Selection of low energy experiments 3/March/5 KEKPH5 9

30 Simultaneous extraction of α s and PDF Scaling violation: F / lnq ~ α s xg(x,q ) Data at low x allow disentangling correlation of α s and xg α s -free fit gives: H: α s =.5 ± (additionally ±.5 from renormalization scale) ZEUS: α s =.66 ± (additionally ±.4 from renormalization scale).7(exp) (model) Difference in exp. error mainly from the treatment of systematic error and normalization of data points in the fitting procedure and error propagation. th. uncert. x=6.3e-5 Jet shapes in NC DIS x=. exp. uncert. ZEUS (DESY hep-ex/4565) x=.6 ZEUS NLO QCD fit x=.53 Multi-jets in NC DIS ZEUS prel. (contributed paper tot. error x=.4 to ICHEP4) Inclusive x=.5 jet cross sections in γp 5 ZEUS x=.63 (Phys Lett B 56 (3) H 7) 94- prelim. x=.8 Subjet multiplicity in CC DISH 96/97 ZEUS (Eur Phys Jour C 3 (3) 49) x=.3 Subjet multiplicity in NC DISZEUS 96/97 ZEUS (Phys Lett B 558 (3) BCDMS 4) NLO QCD x=. fit ZEUS prel. (contributed paper E665 4 to ICHEP4) NLO QCD fitx=.3 NMC ZEUS (Phys Rev D 67 (3) 7) Inclusive jet cross x=.5 sections in NC DIS ZEUS (Phys Lett B 547 () 64) Dijet cross sections in NC DIS ZEUS (Phys Lett B x=.8 57 () 7) 3 World average (S. Bethke, hep-ex/47) x= α s (M Z ) HERA F 3 4 3/March/5 KEKPH5 3 em F -log (x).49(exp) ±.8(model) x=. x=.3 x=.5 x=.8 x=.3 x=.8 x=.5 x=.4 x=.65

31 What if there were no HERA data? ZEUS Q =.7 GeV 3.5 GeV 4.5 GeV 6.5 GeV 8.5 GeV GeV GeV 5 GeV 8 GeV GeV 7 GeV 35 GeV HERA data determine the low-x gluon and sea-quark PDF. HERA revealed: F is very steep. HERA ZEUS F Q =.7 GeV 3.5 GeV 4.5 GeV 6.5 GeV Q = GeV.5 GeV ZEUS NLO QCD fit WITHOUT-ZEUS fit tot. error tot. error 8.5 GeV GeV GeV 5 GeV 7 GeV GeV 8 GeV GeV 7 GeV 35 GeV em F xg 45 GeV 6 GeV 7 GeV 9 GeV 45 GeV 6 GeV 7 GeV 9 GeV GeV GeV GeV -3 5 GeV -3-3 ZEUS NLO-QCD fit tot. error -3 WITHOUT-ZEUS fit tot. error ZEUS 96/97 BCDMS E665 NMC 3/March/5 x KEKPH x 3 GeV -3 5 GeV ZEUS NLO QCD fit tot. error H 96/97 ZEUS 96/97 BCDMS E665 NMC

32 Low-Q sea and gluon distributions 6 Q = GeV ZEUS NLO QCD fit 4 xs ZEUS.5 GeV xg At Q ~ GeV, gluon becomes valence-like (and even tends to be negative) Sea quark is still rising ZEUS xs xg (a) xf - xs xg 7 GeV tot. error (α s free) Q xg xs GeV tot. error (α s fixed) uncorr. error (α s fixed) xg 5 x=. x=. ZEUS NLO QCD fit tot. error (α s -free) tot. error (α s -fixed) GeV GeV 3 5 x=. xg xg x=. xs xs 3/March/5 KEKPH

33 S.F.measurements with fb - Expected precision in F and gluon determination 3/March/5 KEKPH5 33

34 Flavor-specific measurements Complete mapping of the proton d/uat high x: charged current Strange: charm in CC and/or leading φ particle Charm and bottom: improved tagging with micro-vertex Charm 5 pb - Bottom/charm 5 pb - 3/March/5 KEKPH5 34

35 Summary HERA and ZEUS/H experiments Collider = x extended region in Q and x. High- Q NC and CC: electroweak effects NC: effect of Z exchange (different coupling of quark-antiquark) CC: flavor-specific (sees positive and negative quarks differently) HERA-II with longitudinal polarization just started. W should couple with only right-handed e + (and left-handed e ). F measurement and PDF determination Very steep rise of sea and gluon at low x. 3/March/5 KEKPH5 35