PrHEP hep2001 collisions are discussed. The − e + ) − µ + µ hadrons) → → − e International Europhysics Conference on HEP − + e + (e 0 (e σ σ = R ) 2 Z 5 GeV, but of relevance to electroweak are those of the ratio The current status of experimental tests of the electroweak sector of the ∗ M ( s< α √ [email protected] < PROCEEDINGS Abstract: Standard Model is reviewed. Many results presented here are preliminary: they are not labelled explicitly for lack At low energies, new hadronic cross-section results in e Speaker. ∗ Royal Society University Research Fellow School of Physics &The Astronomy BIRMINGHAM B15 2TT, UK E-mail: new measurement of the anomalouscompared magnetic with moment recent at Brookhaven Standard isdata Model reported sample and calculations. are ResultsSLD. reviewed, from The the together synthesis now of with complete manycomprehensive of LEP recent fit these is results results summarised. into from a Finally, the global prospects test for Tevatron, of the HERAof the next Standard space. and few Model References years via should are a considered. be consulted for details. 2. R and The BES-II detector atoperating the since BEPC 1997. electron-positronrange Many collider 2 measurements in have Beijing, been China, made has in been the centre-of-mass energy 1. Introduction The field of preciseencompasses a experimental wide tests rangereport, of of with the experiments. emphasis electroweak placed The sectortheme on current common new of status developments to of the in many these Standard theare measurements is comparable. year Model is reviewed preceding The that in summer theoretical theoretical this uncertainties, 2001.calculations, usually and can A coming experimental be from uncertainties the at lack least of as higher-order hard to estimate reliably as the experimental errors. David Charlton Experimental Tests of the PrHEP hep2001 generator, c resonance 4 GeV. Many . David Charlton 1 LUARLW (b) (a) s< √ (GeV) (GeV) cm cm < E E 36 range; (b) in the c . s ), is the lowest-order QED pre- √ s (3 / is of most concern. Good descriptions (0) s 2 √ πα –2– )=4 − µ + µ → 2345 were made, in collaboration with the Lund Monte Carlo − e s BESII (1998) BESII (1999) Gamma2 MarkI pluto + 3.8 4 4.2 4.4 4.6 √ (e 0 σ collider at Novosibirsk taken over 0 − e 5 4 3 2 6 5 4 3 2 1 + production.

− R Value R R Value R π + π Measurements of R from BES: (a) Over the full In order to achieve such an improvement, detailed studies of the detector acceptance At even lower energies, analysis continues of the large data sample from CMD-2 [2] A key application of the low energy R measurements is in the prediction of the value of exclusive final-states are studied,arising from with the main contribution to the overall cross-section diction. The BES measurements [1]in of quality R over are presented previous,events in often are Figure used 1, very where at early, the each85 measurements improvement energy, energy is and points. an clear. average Thefactor precision point-to-point Around of of correlated 1000 6.6% 2 error hadronic is to is obtained 3 estimated at improvement to each over be earlier of 3.3%, the measurements. forhadroniceventsatlow providing a of the hadronic event data were obtained from a tuned version of the and the hadronic model-dependent uncertainty is estimated toat be the as low VEPP-2M as e 2-3%. team. The experimental acceptance2 for to hadronic 4.8 events GeV varies respectively, in so the the range modelling 50 at low to 87% from Figure 1: where the denominator, International Europhysics Conference on HEP region[1]. PrHEP hep2001 ,of a decay ω τ is measured a term contains ω David Charlton , respectively) are (5) had . ) α 2 top Z . α M ) ( i top − α ) and ∆ 2 Z s ∆ ( M R − eµτ ) − α 00020 may be obtained [4]. 2 Z . s c ( 0 i µ M s ± ( B m h ds 00036, approximately a factor two more a . e (5) had 2 π (0) R ω 0 α ∞ m α R ± − 4 = ∆ Z λ 2 − < –3– ) = 2 2 − Z 2 Z 02761 π µ . g 3 a , by measuring the spin-precession frequency, M mass scale. This is modified from its zero-momentum αM ( µ ≡ a 0 − µ )=0 eµτ a 2 Z α )= ∆ M 2 Z ( − M (5) had 1 ( α (5) had )= α extracted from: 2 Z ∆ µ 03599976(50), by vacuum polarisation loop corrections: . M a ( α 137 / ,and p ω (0) = 1 α Prospects for further improvements in measurements of the hadronic cross-section polarised in a magnetic field: by observing the time variationoff of (2 production GeV), of as decayNMR shown electrons in probes: above Figure one a 2. fixed fixedand The set energy another mean mounted cut- set bending around placed field thechamber. on is ring a In measured and trolley practice, using used the which two forfrequency, magnetic can sets continuous field be of monitoring, is pulled re-expressed right in around terms the of evacuated the beam mean proton NMR low-energy hadronic loops, and must be calculated via a dispersion integral: sufficiently well calculated knowing only the particle masses. The ∆ The contributions from leptonic and loops (∆ The R data pointsticated must, methods at are least, employed bespectral by interpolated different function to authors, data evaluate and viasumptions this use has isospin integral. may obtained symmetry. also ∆ More be sophis- A made recent of calculation [3] using minimal as- The muons circulate inuniform a magnetic special-purpose field across storage its ring aperture. constructed The to spin-precession have frequency an extremely value, at low energiesincreased are luminosity; good: CLEO proposes anto to examine upgraded the run region at accelerator from lowerwith 3 in centre-of-mass to radiative 5 Beijing energies events; GeV; than should DAΦNE and maywith before finally give be the able the substantially present to concept access PEP-II the ofand LER low 2 a energy could GeV. very range give low access energy to ring the to poorly work covered together region between 1.4 precise than a previousextra theory-driven similar assumptions, estimate an which error did as low not as use the new BES-II data. With The Brookhaven E821muon experiment anomalous has magnetic moment, recently reported [5] a new measurement of the 3. The Muon Anomalous Magnetic Moment g-2 International Europhysics Conference on HEP the electromagnetic coupling at the Z PrHEP hep2001 , 10 are − .To − µ 10 a µ 9 × ] 10 s 29) µ . × s vertex, which [ 0 µ David Charlton s ± µ µµγ and 3 57 Time . + 32-82 µ 467-700 9 ) 10 s ( 10 × s ˆ 2GeV in E821[5]. The periodicity − 2 K µ s ) decays is [5]: s 10 ( + E> × ), optional additional theory-driven ) = (11 657 470 R µ 2 Z 9 6) ds M 2 π ( 10 ± ∞ QED m 233-467 α ( 4 × 14 µ Z a 95 ± . 2 (0) π s –4– 2 3 µ α . The hadronic corrections, although much smaller )= 10 − LO 32-233 32-233 10 ; = (11 659 202 × + had µ s ( 4) µ a . µ 0 a is the ratio of muon to proton magnetic moments. ± λ 2 . 650-700 = 2 at lowest order. The corrections may be subdivided into electro- and g p 0 50 100 150 200 5 4 3 2 7 6 /ω )=(15 a

ω

10 10 10 10 10 10 10 ) is a known bounded function. As for Number of Positrons/150ns of Number Time spectrum of positrons observed with energy s = ( weak ˆ ( R K µ ), the dominant corrections may be subdivided into the lowest and higher-order vac- a Interpretation of this result in terms of the Standard Model and possible new physics The latest E821 result, obtained using 0 3 α ( and magnetic (QED), weak andweak hadronic terms parts are according respectively to the calculated type to of be loops. The QED and in hand, and should result in a factor tworequires improvement in detailed the near calculations future. gives of the loop original corrections to the simple QED O assumptions may be made. Recent estimates of the lowest-order vacuum polarisation term than the QED correction, provide the main source of uncertainty on the predicted uum polarisation terms and higher-orderpolarisation) “light-on-light” term terms. is The numerically lowest-orderrelation: much (vacuum the largest. It can be calculated using a dispersion where The overall precision obtainedand is 0.5 relatively ppm 1.3 from parts systematic per errors. million: Data 1.2 from ppm a from further statistics 4 Figure 2: from spin precession is observed over more than ten muon lifetimes. where International Europhysics Conference on HEP PrHEP hep2001 led to µ a 10 − . µ 15 a ± David Charlton about the treat- 9 6 9 8 8 6 16 15 11 10 ± ± ± ± ± ± − ± ± ± 10 700 692 701 695 702 695 × 703 695 699 5 ∼ (LO; hadronic) / 10 µ a 10 x 10 µ a –5– data data data data data, QCD sum rules data τ τ τ τ τ τ & & data data & & & & − − − − − − − − e e e e e e e e + + + + + + + + e QCD+renormalons & data e e e e e Based on e e Recent calculations of the lowest-order hadronic correction to + + + µ µ µ 11659000 11659200 11659400 + − ocker (“DH(98/2)”), which is numerically the lowest of the calculations. Measurements of the muon anomalous magnetic moment and recent predictions. µ µ Table 1: N(01) [10] DH(98/1) [8] DH(98/2) [9] J(01) [11] CLS(01) [13] ADH(98) [7] ADH(98) [7] dTY(01) [12] Authors BW(96) [6] The summed corrections are shown in figure 3 and compared with the new and previous Recent calculations World averageNarison, Jegerlehner, de Troconiz+Yndurain, Davier+Hocker Cvetic+Lee+Schmidt 11659203 CERN E821 (97) E821 (98) E821 (99) CERN Figure 3: a difference between datacalculations and reduce theory that of difference,also around in suggesting some 2.6 cases that standard to the deviations the error [5]. one on standard the More deviation prediction recent level, may thus have been too optimistic. At present ment of further photon radiationhere in some or of as these a calculations,data as higher-order includes it final-states correction, may with be dependingthe included extra also either overall photons. on errors, The whether which estimatesIt is the agree is not input with notable surprising that each experimental the otherDavier since best and within the value H¨ data available at employed the is time mostly of in the common. E821 publication was that of measurements [14]. The major experimentalis improvement striking. from the new At E821 the measurement time of publication, the most precise available calculation of International Europhysics Conference on HEP are shown in Table 1. There is some ambiguity at the level of PrHEP hep2001 ) b FB A David Charlton 0.0012 0.00036 ± 0.00026 0.00053 0.00031 0.00079 0.00041 0.00017 ± ± ± ± ± ± ± 0.0021 GeV ± Preliminary 5.1 GeV ± . 0.2324 = 0.02761 /d.o.f.: 12.8 / 5 0.23099 0.23226 0.23272 2 = 91.1875 (5) had 0017 = 174.3 Z t χ . ∆α∆α m m 0 lept eff ± θ 2 –6– sin 0990 . as giving evidence of physics beyond the Standard . In doing this, it is effectively assumed that the b µ a =0 lept eff b θ , Pole 0 FB 2 0 A 3 2 0.23 0.232 0.234

) 0.23159

>

τ

10 H 10 fb

GeV cross-section, width, and asymmetries have been available for many m ] (P (SLD) 0.23098 [ 0,c fb 0,l fb l l 0,b fb Q 0 A < Average 0.23152 A A A A in terms of sin b FB A Comparison of asymmetry measurements interpreted simply as measurements of . lept eff This result may be compared with other asymmetry measurements from LEP and SLD θ 2 from ALEPH and DELPHI, usingquark inclusive lifetime-based charge b-tagging indicators. techniques and Substantialmeasurements, various improvements so are that obtained this oversion type earlier to of lifetime-tag that asymmetry using measurement aand now traditional together has lepton give a tag. a comparable LEP The preci- average lepton Z and pole lifetime results asymmetry are of compatible, Model. The accuracy ofby an the experimental theoretical measurement predictionsfuture. with will a Theoretical be factor progress even two more isprecise smaller severely essential measurement. error, to challenged as obtain expected a in maximum the physics near return from such a years from LEP and SLDnew data, results and [17] most have become results available have on now the been b finalised quark forward-backward [15, asymmetry 16]. ( Recently by interpreting Figure 4: sin 4. Recent News from the Z Measurements of the Z International Europhysics Conference on HEP there is therefore no reason to consider PrHEP hep2001 differ )[20]. 0 fb bosons in Q 0 1.89 0.800 0.678 0.463 0.436 , as indicated 0 Limit (TeV) David Charlton , differ at the level 95% CL lower limits b FB η A χ ψ LR ) [18]; from the left-right Model τ P Sequential and Table 2: on the mass of new Z various models [21]. LR A ,from per exper- lept eff θ 1 2 − –7– bosons which do not mix with the Z 0 from the entire LEP 1 polarisation measurements ( − τ values derived from the leptonic forward-backward asymmetry from lept eff θ 2 ) [15]; that from the l , 0 fb A With the completion of LEP-2 data-taking at the end from the Standard Modelpresent, and expectations, direct but measurementsasymmetry such via an at the interpretation SLD left-rightasymmetry is are polarised measurements not not forward-backward compelling using precise b theissue, at quark but enough existing scope LEP to for data help. such improvement samples is may Future limited. help improvements elucidate in this b quark The two most precise determinations of sin in Table 2. of 3.2 standard deviations. This might suggest that the b quark couplings to the Z polarisation asymmetry at SLDand from [16]; inclusive from hadronic the event charm forward-backward asymmetry forward-backward measurements asymmetry ( [19]; iment, in total giving each 1 fb programme. Following onLEP-1 from the Z measurements lineshape ofstudies of and the fermion-pair production forward-backward have continued asymmetries, at2. LEP- At thesesubdivided higher into energies, those fermion-pair where“radiatively events returned” the may to pair be the invariantradiative Z mass region events has or with below, closeergy. and to non- The the cross-sections fullthe centre-of-mass and full range en- forward-backward of asymmetries LEP-2pair energies for final are states, non-radiative shown averaged between in events allhave Figures at four been 5 LEP and made experiments 6 [21]. for forscribe electrons, Analogous hadronic, measurements the b muon and and data tau c well.example, quarks limits [21]. may Limits be The can placed Standard on be new Model placed Z expectations on de- new physics from these data [21]. As an LEP ( 6. Z’s and W’s at CollidersElectroweak with fermion-pair Hadrons production hasYan also process. been Updated studiedence at results the [22, on Tevatron, high 23]: in massModel the both electron Drell- expectations, pairs cross-sections and were andFigure extend presented 7). asymmetries beyond at As the are this indicated LEP-2 confer-improvements well in on mass the described that figure, of reach by LEP there to the should is around come some Standard with 500 sensitivity the GeV to Run new (see 2 physics data. models, and of 2000, theof integrated 161 luminosity GeV collected and above at has energies reached 700 pb 5. LEP-2 and Fermion-Pair Production International Europhysics Conference on HEP quark couplings are given bycomparing their Standard to Model sin values. The result is shown in figure 4, PrHEP hep2001 2 Q 0.370 0.180 0.089 0.270 0.084 0.060 ± ± ± ± ± ± LEP preliminary Mass (GeV) David Charlton 80.360 80.410 80.470 80.350 80.498 80.454 ν e (GeV) ) s )  γ γ → ( √ ( − − µ τ + + µ τ 0.85 > → →

− − LEP combined fermion pair pdata s e e  + +  ´/ e e s  W mass measurements from hadron √ All p D0 Run 1A D0 Run 1B 120 140 160 180 200 220 UA2 W 1 0 0 CDFCDF Run 1A Run 1B

0.8 0.6 0.4 0.2 0.2

FB FB -0.2

Forward-Backward Asymmetry Forward-Backward

-A A Experiment Sample

M S meas Figure 6: forward-backward asymmetries in the LEP-2 energy region[21]. Table 3: colliders. –8– 17 GeV, at this conference [23]. LEP . 0 preliminary ± ) γ (GeV) =2.23 p collisions provided, ) s )  γ γ ( √ ( − W − µ τ + + hadrons( µ τ 0.85 > → → →

− − − 13 GeV) [25] some time ago. D0 presented a new measurement using all s e e e .  + + +  0 ´/ e e e LEP combined fermion pair cross- s  ± √ 2 120 140 160 180 200 220 1

1

1.2 1.1 0.9 0.8

10 10

Cross section (pb) section Cross =2.05

SM meas

/ The presence of the is primarily probed at HERA via t-channel W production in p The high tail of the distribution of the transverse mass of the lepton-missing momen- σ σ Figure 5: sections in the LEP-2 energy region[21]. W exchange. The charged and neutral current differential cross-sections as a function of the Run 1 data, of Γ tum system provides information(Γ about the W width. CDF finalised their Run 1 result before LEP-2, the onlyof direct the measurements W mass,and using muon reconstructed momenta and electron inferred missingmentum mo- information. The main resultsCDF from and D0available from for Run some 1cently time data updated [24]. have their been new Run D0 analysis 1 have making results re- to use with calorimeter of cell a electrons edgesportance [23]. close of the The extra main data is im- calorimeter to calibration allow a from better Z events.summarised Measurements in of Table 3. the W mass from the Tevatron are International Europhysics Conference on HEP PrHEP hep2001 2 ∨ neutral /GeV 2 2 Q 4 p 94-97 Q p prel. + - 10 p 94-00 prel. p − + David Charlton H1 e H1 e ZEUS e ZEUS e 3 10 Neutral Current 0.9 < Standard Model (H1 97 PDF Fit) y Neutral-current differential cross- -1 -2 -3 -4 -5 -6 -7 1

10

10 10 10 10 10 10 10

NC

/ pb GeV pb / /dQ d

σ

-2 2 Figure 9: sections measured at HERA[27]. exchange can be seen in the high- 0 2 –9– /GeV 2 Q 4 p 94-00 prel. p 10 + − H1 e H1 e Measurements of Drell-Yan lepton-pair production by CDF. p 94-97 p prel. + - 3 Charged Current 10 Charged-current differential ZEUS e ZEUS e 0.9 s=320 GeV < Standard Model (H1 97 PDF Fit) √ y Figure 7: -7 -8 -4 -5 -6 -1 -2 -3 1

10 10 10 10 10 10 10 10

CC

pb GeV pb /dQ d

σ

-2 2 cross-sections measured at HERA[26]. Figure 8: are shown in Figures 8exchange, and 9 and respectively. is sensitive The to chargedthe current the overall process W normalisation). proceeds mass only via The by the W effect propagator term of (and Z also, indirectly, via International Europhysics Conference on HEP PrHEP hep2001 decays being τ David Charlton p cross-sections. + pande − Preliminary ] ) corrections to the doubly-resonant W- YFSWW 1.14 RacoonWW α GeV ( [

O cm E –10– 18 17 16 RacoonWW / YFSWW 1.14 160 170 180 190 200 210 LEP

5 0

20 15 10

pb

] [ σ LEP averaged W-pair production cross-section measurements[29]. WW Figure 10: 0.3, which is 90% composed of W production and decay [28]. These events have been Real W production may also have been observed at HERA, by looking for events Each LEP experiment now has a sample of around 12000 W-pair events from the full ± interpreted as possible evidenceModel of new their physics, natural but interpretation within is the as framework W of production. the Standard with high transverse momentuma electrons recoiling or hadronic muons,above missing system. 40 transverse momentum, GeV, For and H12.0 transverse and momenta ZEUS of together the observe recoiling 6 hadronic events system compared to an expectation of pair production diagrams,predictions. and give The a agreement cross-sectioncross-sections can approximately as be 2% a tested lower functionnormalisation by than comparing of of earlier the centre-of-mass the experimental energy.standard data and deviations well, The predicted of the new the old calculations experimental error ones describe [29]. over-estimate the it by between two and three LEP-2 data sample.optimisations Event for selections the highest areand energy well purities data. established, in Typical the and selectionthe 80-90% have performances range most needed give for challenging. only efficiencies almostand minor all compared The channels to – measured the channelsprograms. predictions W-pair with of These cross-section the programs [29] RacoonWW incorporate is [30] full and shown YFSWW in [31] Figure Monte Carlo 10, 7. W Physics at LEP-2 International Europhysics Conference on HEP current region where it gives rise to a difference between the e PrHEP hep2001 ± 43 . 0.032 0.049 0.038 0.051 0.028 0.054 results ”), are qqqq”), ± ± ± ± ± ± `ν 0.21 0.039 `ν → ± ± )=10 qq qq 0.038 0.045 0.053 0.048 0.033 0.030 `ν ± ± ± ± ± ± → → David Charlton 80.40 → 80.450 W Mass (GeV) 091 GeV is found. 80.477 80.399 80.491 80.389 80.448 80.457 . 0 ± 150 . W mass measurements from =2 (161 GeV) `ν W qqqq qq WW σ → → Table 5: LEP [33, 34].reconstruction technique Results unless are indicated. from the direct DELPHI (1997-2000) L3 (1997-2000) OPAL (1997-1999) WW Sample ALEPH (1997-2000) WW From LEP combined –11– 0.27 0.09 0.17 0.16 0.22 ± ± ± ± ± events, which has been included in the WW 67.92 10.69 10.54 10.54 11.09 `ν`ν Branching ratio (%) → ν e `ν τν µν W decay branching ratio measure- hadrons → → → → → W W W W Decay mode W After the kinematic fit, the W mass statistical sensitivity is very similar for the two The W mass and width are measured above the W-pair threshold at LEP-2 by direct The selected W-pair events are also used to measure the W decay branching ratios. Table 4: ments from LEP[29]. 25% [32]. . reconstruction of themomenta W and decay energies. products [33], Events with using two measuredused hadronically by lepton all decaying momenta experiments. W’sconstraining and the (“WW total jet A energy and kinematic momentumreconstructing fit to the be is that unobserved of made neutrino thesignificantly to colliding in improves beam the mixed the particles, thus resolution reconstructed hadronic-leptonic on decaycan event the events. quantities, be W mass. This fitted fit Thecomplicated, to reconstructed techniques obtain mass to distributions extract the theused W most by W mass, some mass or information experiments.contained from the ALEPH the in W fitted and WW events mass OPAL are alsoquoted. and use width the together. small amount of Other, information more event types. The systematicthe error main sources correlated are systematicshadronisation largely come modelling. different from between the the Thements, knowledge two W and channels: of averaged mass by the measurements channel, LEPall are obtained beam shown the by in energy, measurements, table the and 5.60 and four There MeV LEP the is from experi- overall good hadron consistencyessentially precision colliders. unchanged, between [34] and If a now the LEP W improves combined width significantly value of is on Γ also the fitted, the W mass measurement is or where one W decays hadronically and the other leptonically (“WW The combined LEP resultswith [29] lepton are universality, shown and inratio, so Table corrected are 4. combined to The to1% massless leptonic measure relative charged results the error, are leptons. average and consistent is leptonic is This significantly branching consistent measurement more with nowsection precise the data, has than assuming Standard a Standard a Model better Model value expectation production than extracted of of W’s, from 10.83%. which the is Br(W It Tevatron W and Z cross- 0 International Europhysics Conference on HEP PrHEP hep2001 )(seetext) q decays may Q q ( David Charlton D → qqqq channel (see 0 data 98-2000 (++,--) inter+intra BEC intra BEC → Distribution of Figure 12: for DELPHI data,Monte Carlo compared models[37]: tocorrelations within “intra” different one refers Wthose to decay, between “inter” W to decays. –12– ) resc φ L3 data 189-207 GeV N R rescaled angle ( % Particle flow ratio for parti- No CR SKI SKI 100 Particle flow (all clusters) 0 0.2 0.4 0.6 0.8 1 1

0.8 0.6 0.4 1.4 1.2 A substantial effort has been spent in understanding the possible effects of FSI models. The 39 MeV error on the combined LEP result includes 26 MeV statistical and 30 MeV The basic physical problem which gives rise to the uncertainty over final-state interac-

(A+B)/dn/d dn/d (C+D) φ φ Figure 11: cles between jets comingrelative from to the those sameent between W W’s[35]. jets Datawith from are no compared differ- colour to reconnection,model[36]. and models to the SKI not properly describe them.subdividing them Phenomenological into “colour models reconnection” are inmodels, the used and parton-shower to phase possible of study the Bose-Einsteinhadronisation possible Monte process. correlations Carlo effects, between identical particles formed in the Recent work, in adetermining collaborative the common effort sensitivity between to all different models four between LEP different experiments, experiments, and has focused on systematic contributions. Systematic errors are larger in the WW Table 5), having the effectno of systematic deweighting that errors channel, this to22 deweighting just MeV. would 27%, The in not main the occur,beam systematic average. and energy errors With measurement the on contributes statistical the asation error highly combined modelling correlated would result 17 uncertainties be are MeV contribute as tobetween another follows all 17 the channels; [34]: MeV; hadronic hadroni- The “final-state decay LEP interactions”certainties products (FSI) – of different two for W’s theon contribute different photonic 13 experiments corrections MeV; – detector-related contribute contributefore 8 10 un- the MeV. MeV; and The results uncertainties main areprogramme improvements finalised is that in lie are progress in expected to the be- reduce areas the error, of and thetions the LEP is final-state that interactions. beam when energy,is two where W’s smaller a in than concerted the typicaltherefore same not hadronisation event both be scales. decay independent, hadronically, and The the so hadronisation decay hadronisation distance of models tuned the to two Z systems may International Europhysics Conference on HEP PrHEP hep2001 p Q → decays, and `ν David Charlton qq → 033 GeV is obtained. . 0 ± 069 GeV. ) . 0 Q ( 451 ρ ± . . ) 134 Q . ( )+∆ ). This may be expressed as [39]: Q ) ) may be examined: =2 ( WW mix Q Q ρ ( ( W WW production. The cross-section measured ρ WW mix D 0 ρ )+ Z WW 0 ρ Q ( )+ –13– W Q qqqq events [36]. This is illustrated in Figure 11. , given in Table 5 is combined with that from p ( ρ , for single hadronically decaying W’s in WW 2 and Z ρ W W → ρ γ m ≡ 0 ) qqqq events ( Q )=2 ( → Q D ( WW ρ ) distribution is shown in Figure 12: a deviation from unity at low Q ), and for WW ( W D ρ is evaluated from mixing hadronic W decays from WW qqqq events. Alternatively the ratio → WW mix ρ events ( When the LEP measurement of W-pair production at LEP-2 involves the triple gauge coupling vertex in two of the Other measurements of triple gauge boson couplings are made at LEP-2 [45] in the Sensitivity to the effect of colour reconnection models has been obtained by studying Bose-Einstein correlations are also being studied in data [38], in this case by comparing is any extra part arising from correlations between particles from different W decays `ν ρ An observed would most clearly signaldifferent W’s. the As effect illustrated of incolour Bose-Einstein this reconnection, figure, correlations work no is between evidenceconstrain in particles is progress the observed from to possible of derive such effect combined an on effect. LEP the results As W in for mass order measurement. better to where for the latterpredictions. process Measurements is of quartic shownwere gauge discussed in couplings in have Figure detail also 13 in been other made and contributions at is to LEP-2, this and well-described conference by [46]. Standard Model ∆ in WW The gauge group ofboth the in Standard form Model anda dictates strength. fundamental the The test self-couplings direct of ofhave measurement the been the of Standard these measured vector Model couplings bosons, directly gaugeLEP therefore structure. at are provides both more Electroweak LEP stringent. gauge and couplings the Tevatron: atthree present lowest-order constraints doubly-resonant diagrams. from Sensitivityis to found possible in anomalous the couplings W-pairMeasurements cross-section, have and been theresults W reported production have at and been decay previous angleneglected, released conferences distributions. are recently thought [40], because to but be [30, comparable no 41] to combined higher-order theneutral current LEP corrections, experimental vector previously precision boson [42]. processes of Z 8. Tests of the Gauge Couplings of Vector Bosons International Europhysics Conference on HEP on developing ways to measure visible effects predictedthe by particle the models. flow between jetsThe data in show WW some sensitivity toand the effects work as predicted continues in thesensitivity. to colour reconnection combine models, results from the fourthe LEP two-particle experiments correlation to functions, qq improve the colliders as given in Table 3, a world average W mass of 80 A similar combination of W width results gives Γ PrHEP hep2001 , p top m 1 GeV . 5 ± .TheLEP 3 . H m David Charlton = 174 top [50] and, new this year, m 1 in the Standard Model for top m Preliminary and N”) scattering W ] ν m GeV [

033 GeV obtained by combining LEP and p . cm 0 E –14– ± result obtained differs from the expected value by three W uncertainty θ 451 . 2 % 2.0 ± YFSZZ ZZTO =80 W LEP m N and APV results to predict the masses of the top quark, ν 170 180 190 200 0 1

0.5 1.5

NC02

pb ] [ σ ZZ ), the . The result obtained is shown in Figure 14 by the solid (red) contour. 2 Z W M ( m as measured in neutrino-nucleon (“ α W LEP averaged Z-pair production cross-section measurements[43] compared to Standard N scattering result was reported by the NuTeV Collaboration [51] during the final stage of θ ν 2 Before making the full fit, the precise electroweak data from LEP and SLD can be used Anew 1 standard deviations. and of the W, electroweak working group has,combined for fit a to number a ofThese large years, number results carried of are out measurements reporteduse such sensitive here global to the for Standard tests electroweak the Model libraries via dataprovide parameters. a ZFITTER available the at version Standard this 6.36 Model conference. [47] predictions.detailed and These studies Theoretical global TOPAZ0 uncertainties of version fits are missing 4.4QCD included corrections [48] following higher [49]. to order The electroweakas precise corrections are LEP, sin SLD and and their Tevatron electroweak interplay data with are included, from the Tevatron [53] and atomic parity violation (“APV”) measurements in caesium [52]. together with Also shown are the direct measurements (dotted/green contour) of 9. Global Electroweak Tests Many of theprovide individual a results global reportedmodel test in is of preceding observed, consistency sections itModel, with is may the the justifiable be unknown Standard to used remaining go Model. together parameter, on the to to If mass deduce, consistency of in the with the Higgs framework the boson, of the Standard Figure 13: Model predictions[44]. International Europhysics Conference on HEP results; and the expected relationship between preparation of this contribution. The sin PrHEP hep2001 but W m measurements. David Charlton W , the best-fit value m 2 χ , which is a reflection of and as a function of the mass b FB 2 top A χ m Preliminary ] ). This latter effect is controversial, 2 Z [54]. This has little effect via ∆α W /m GeV m 2 W [ N, APV Data

m t ν 1000 − m –15– Data (1 − ] W 300 κ CL = % GeV [

68 LEP1, SLD, LEP2, pp 114 lept eff H θ m 2 130 150 170 190 210 , is shown in Figure 16. The darker shaded/blue band enclosing H

80.6 80.5 80.4 80.3 80.2 m

W

GeV m ] [ Comparison of direct and indirect constraints on the top and W masses. of the fit is 22.9 for 15 degrees of freedom, corresponding to an 8.6% GeV, where the error is asymmetric because the leading corrections depend 2 consistent with those observed – in both cases within two standard deviations (shaded/yellow). It can be seen that the precise input data predict values of χ 35 W H +53 − measurements favour a light rather than a heavy one. . The variation above the minimum value of the m m H top curve provides an estimate of the theoretical uncertainty on the shape of the curve. m =88 Figure 14: 2 and m Going further, the full fit is made including also the H / χ m W top does have an impact via sin The overall of each input datumas is the compared difference with between theresults observation are and actual shown best-fit measurement, in divided and Figure by the 15. the pull The measurement calculated poorest error. description The is of the same disagreement discussedis earlier in Section 4. The best fit value of the Higgs mass of the Higgs boson, and may well overestimate the true theoretical uncertainty, but it is currently included the probability. To provide an impression of the contributions to this on log – demonstrating that theparticles. electroweak For corrections the can W, correctlyto the predict that precision of the of the mass the predictionas direct of the via measurement. heavy prediction. the For It Standard the is Modelm observed top fit in mass, is addition the that similar both measurement the is precise twice input data as and precise the direct m This band is ahigher-order little (fermionic broader two-loop) than calculation previously of estimated because of the inclusion of a new International Europhysics Conference on HEP different PrHEP hep2001 )[4] 2 Z M ( (5) had α David Charlton moves to 222 GeV with this H m in the next couple of years, which 1 − -3 -2 -1 0 1 2 3 -3 -2 -1 0 1 2 3 –16– prediction is sizable compared to the theoretical 0.0012 .86 0.0021 1.22 0.70 .56 0.0021 1.47 0.0033 -.54 0.0021 .03 0.020 0.026 -.64 .06 0.039 1.32 0.060 .93 0.037 0.025 1.60 1.11 0.0031 -.12 0.0017 -2.90 0.0034 -1.71 0.00095 .69 0.00065 1.12 0.00036 -.35 0.0023 -.48 5.1 -.30 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± H Summer 2001 Summer m 0.922 0.670 174.3 Pulls from the global electroweak fit. Measurement Pull Pull 80.450 80.454 41.540 20.767 0.1719 0.0990 0.0685 2.4952 91.1875 0.01714 0.21646 0.02761 ] ] ) 0.2324 fb ) ]] N)N) 0.2255 ]] ]] Z ] (Q GeV GeV νν 196 GeV at 95% C.L. Also shown in the Figure is the effect of [ [ ((

(m nb lept eff WW )) 0.1465 [ GeVGeV ττ

< θθ θθ GeVGeV GeVGeV [[ (Cs)(Cs) -72.50 [[ [[ 22 22

(5) had

(LEP) W tt (TEV) W ZZ (P(P (SLD)(SLD) 0.1513 WW ll bb cc 0,l fb ll 0,b fb 0,c fb bb cc ll ZZ 0 had H Q A A m sinsin m m m sin Q Γ σ RR AA A RR RR AA AA AA AA A ∆α m Γ ∆α σ m sin m m Figure 15: m curve may be used to derive a constraint on the Standard Model Higgs 2 χ estimate. At the Tevatron, Run 2 data-taking has recently begun. Although luminosities are so (5) had α (dashed curve). The effect on the ∆ uncertainty, for example. The 95% C.L. upper limit on using an alternative theory-driven estimate of the hadronic corrections to ∆ boson mass, namely far low, the expectation remains of accumulating 2 fb 10. A Forward Look, and Conclusions The eleven years ofhave data-taking established by that the Standard LEPmeasurements. Model experiments, radiative plus Data corrections the analysis describe contributions1995. of precision is SLD, Work electroweak close continues to tonext finish complete couple LEP-2 on of analyses, years. the and Improvements LEP-1better can final still data, understanding results be of can taken expected final-state be in frommeasurements interaction the expected 1989- W where effects over mass the in the measurement, full particular, from data and sample in is gauge-coupling not yet included. as equivalent two-loop calculationsavailable. The for Z widths and the effective mixing angle are not International Europhysics Conference on HEP PrHEP hep2001 W as a m 2 χ for the global H David Charlton m employed for the future H m Preliminary ] curve as a function of 2 χ 0.00036 0.00020 ± ± GeV 100 = [

(5) had H ∆α∆α 0.02761 0.02738 –17– m theory uncertainty 3 GeV. Combining the former result with the final ± Excluded

20 400

6 4 2 0

∆χ 2 , are shown in Figure 17 (the central value of H from the b forward-backward asymmetry at LEP, show two or three standard m Constraining the Standard Model Higgs: ∆ lept eff θ 2 Further substantial improvements in precision will have to wait for the LHC and a In summary, precise tests of the electroweak sector of the Standard Model have been function of is, of course, arbitrarily selected). future linear collider.further factor The two. LHC TheHiggs main should boson, improvement and improve would, a of the direct course, indication W come of from and whether a it top discoverymade is of mass by the the a simplest precisions wide Standard byand Model range the particle. of a Tevatron. experiments, Many from ofthe the these radiative g-2 correction tests structure measurement have is a inlations now high muon are rather sensitivity decays well-established. essential to to in Two radiative making LEP andprogress corrections, sufficiently three-loop and is precise calcu- still predictions for needed.of some sin A processes, small and more number of measurements, for example the measurement deviation differences from expectationdard Model which description, might but pointquality none to of are possible tests compelling will cracks at arriveof present. in slowly the the Further over improvements electroweak Stan- the in next symmetry-breaking the few mechanism years: will in likely particular further have elucidation to await an improved should allow a Wand mass a measurement top withresults mass 30 from measured MeV LEP-2 to precision should20 from provide MeV. each a The experiment world effect [55], average such improvements W could mass have, measurement for error example close on the to global fit ∆ Figure 16: International Europhysics Conference on HEP electroweak fit. The shadedshaded band area shows shows an the estimate region of excluded the by theoretical direct uncertainty, searches. and the lighter PrHEP hep2001 et (2000) Preliminary ] A 675 2 David Charlton 10 curve obtained with GeV [

2 H χ Summer 2001 Future (Run 2a) m Nucl. Phys. (2001) 2227; I. Logashenko, (1999) 1632; H.N. Brown (2000) 69. measurements of 20 MeV and 86 82 Typical ∆ top (1998) 123. m Excluded B 492 6 4 2 0

.

C2 and

; J.C. Chen, these proceedings.

∆χ 2 . (1996) 3237. W Figure 17: m 3 GeV precision,compared to respectively the current fit (dashed) result(solid). central and value (2000) 091101. Phys. Lett. (1998) 419. (1998) 427. Phys. Rev. Lett. Phys. Rev. Lett. D54 –18– D62 , CMD-2 Collaboration, Eur. Phys. J. B 419 B 435 hep-ph/0106025 onig, A. (1979) 1; et al. hep-ex/0102003 hep-ph/0107069 Phys. Rev. . ocker, (2001) 53. Phys. Rev. B 150 Phys. Lett. Phys. Lett. B 513 ocker, ocker, , Muon g-2 Collaboration, , Muon g-2 Collaboration, Nucl. Phys. hep-ph/0104304 ., , BES Collaboration, et al. et al. Phys. Lett. et al. et al. , Muon g-2 Collaboration, al. R.M. Carey 424c. these proceedings. unewald for his unstinting help, and Chris [2] See, for example, R.R. Akhmetshin [1] J.Z. Bai [3] H. Burkhardt and B. Pietrzyk, preprint[4] LAPP-EXP 2001-03, A.D. Martin, to J. appear Outhwaite in and Physics M.G. Ryskin, Letters. [5] H.N. Brown [8] M. Davier and A. H¨ [6] D.H. Brown and W.A. Worstell, [7] R. Alemany, M. Davier and A. H¨ [9] M. 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