Table Of Content

Electroweak and beyond the Standard Model results from HERA 9 0 0 Z. Zhanga (for the H1 and ZEUS Collaborations) 2 aLaboratoire de l’AccélérateurLinéaire, Université Paris-Sud 11 et IN2P3/CNRS, BP 34, 91898 Orsay n Cedex, France a J 0 The latest results from the e±p HERA collider both within the Standard (electroweak) Model and beyond 3 are reviewed. Most of the results are based on the full HERA data sample, which corresponds to an integrated luminosity of about 0.5fb−1 perexperiment (H1or ZEUS). ] x e - p e 1. INTRODUCTION 2. DOMINANT INCLUSIVE DIS PRO- h CESSES [ The electron-proton collider HERA ended its data taking on June 30, 2007. Over its lifetime At HERA, both the neutral current (NC) and 2 ofmorethan15yearsofoperation,ithasallowed the charged current (CC) interactions can be v 2 eachexperiment,H1andZEUS,tocollectaninte- studied. Thecrosssectionsoftheseprocessesmay 6 gratedluminosity of about100pb−1 and20pb−1 be written in the following simplified form: 6 in positron-proton and electron-proton collisions 4 α2 respectively in the first phase (HERA-1) from σ Φ (PDFs,v ,a ,P ), (1) 2. 1992to2000. Inthesecondphase(HERA-2)from NC∝Q4 NC q q e 081 2h0a0v3e tinoc2re0a0s7e,dthbeypaosfiatrcotonraonfd2elaenctdro1n0sraemsppelecs- σC±C∝G2F 11+±QP2e 2ΦCC(PDFs), (2) : tively. In addition, spin rotators installed at the (cid:16) MW2 (cid:17) v H1 and ZEUS interaction regions have provided where α and G are the fine structure constant i F X longitudinalelectronandpositronpolarizationat andFermiconstantforelectromagneticandweak HERA-2. r interactionsrespectively,v anda arevectorand a The results reviewed in the talk concern both q q axial-vector couplings of the Z boson to light theelectroweak(EW)measurementsintheStan- quarksq (u,d),P isthepolarizationvalueofthe e dard Model (SM) and searches beyond the SM. electronbeam,Q2 isthefour-momentumtransfer They are based either on the dominant inclusive squared, M the propagator mass of the W bo- W Deep Inelastic Scattering (DIS) processesof neu- son,andΦ arethestructurefunctionterms NC,CC tral and charged current interactions or on rare forNCandCCprocessesrespectively,whichpro- exclusive processes such as single W and lepton vide the primary constraint on the parton distri- pair productions. The advantage in the former bution functions (PDFs) of the proton. case is high statistics and in the latter case clean In NC interactions at high Q2, when Z ex- and well defined final states. change and γZ interference become increasingly While the emphasis is put on presenting the important, the NC cross section depends both latest results, some early results are also shown on v and a and on the beam polarization P . q q e in a few cases in order to illustrate the progress However, these dependencies cannot be factor- thathasbeenmadeovertheyearsandtheimpact ized, contrary to the P dependence of the CC e of the increased data samples. cross section. In addition, from the Q2 dependence and the normalizationof the CC cross section, one can determine the propagator mass of the W boson and the Fermi constant G respec- F 1 2 Z. Zhang tively. section in e−p interactions. With an increased e+p data sample of 2.1. The propagator mass of the W boson 47.7pb−1 taken in 1994-1997 by ZEUS, a simul- The first evidence of the massive W boson at taneous fit of M and G was performed re- W F HERA wasobtainedfromthe observeddeviation sultinginM =80.8+4.9+5.0+1.4GeV,wherethe W −4.5−4.3−1.3 of the CC cross section from a linear dependence threeerrorscorrespondtothe statistical,system- onthebeamenergybasedontheveryfirstdataof aticandPDFsuncertaintyrespectively[4]. When theH1collaborationtakenin1993corresponding fixing G to the world average value [5], ZEUS to an integrated luminosity of 0.35pb−1 [1]. The obtainedFM = 81.4+2.7 2.0+3.3GeV, where electron beam of 26.7GeV in collision with the W −2.6 ± −3.0 the last error from the PDFs dominates over the proton beam of 820GeV resulted in a center of statistical and other systematic errors. mass energy √s of 296GeV.1 This is equivalent In all above results, the correlation between toanelectronbeamwithenergyofalmost50TeV the EW parameters with the PDFs was not fully hitting a fixed target. taken into account. A first analysis which con- The first quantitative determination of the sidered such a correlation was performed by H1, propagator mass of the W boson, MW = 76 using the complete high Q2 NC and CC cross ± 16stat 13systGeV, was derived from the Q2 de- section data and all available low Q2 data from ± pendence oftheCCcrosssectiondσ /dQ2 with CC HERA-1 [6]. The result on the propagator mass an e−p data sample of 0.54pb−1 [2]. Together wasM =82.87 1.82+0.30GeV, wherethefirst with the NC cross section dσ /dQ2, it was W ± −0.16 NC error is experimental and the second the model shownthattheQ2 dependenceoftheNCandCC uncertainty [6]. Within the SM, a much more cross sections are very different. At low Q2 the precise W mass determination, M = 80.786 W electromagneticinteractionismuchstrongerthan 0.205+0.063GeV,wasobtainedusingthe SMcon±- −0.098 the weak interaction. The difference diminishes, straintbetween M , G and other EW parame- however, as Q2 increases, and the cross sections W F ters become comparablewhenQ2 values reachthe W and Z boson mass squared, demonstrating the πα M2 1 G = Z , (3) EW unification in DIS. F √2(M2 M2 )M2 1 ∆r Z − W W − The propagator mass determination in the whereM isthemassoftheZ boson,and∆rrep- space-like regime at HERA is complementary to Z resentsradiativecorrectionswhichcontainamong othermeasurementsusingtime-likeproductionof othersaquadratictopquarkmasstermandalog- W bosons at the Tevatron and at LEP and con- arithmic Higgs mass term [6]. stitutes an important experimental consistency The ten-fold increase of the e−p data from check of the SM. Based on an e−p (e+p) sample of 0.29pb−1 HERA-2 should substantially improve the final (2.7pb−1), H1 has performed a similar deter- precision of the W mass determination from mination of the W propagator mass: Me−p = HERA. W 78+11+4GeV(Me+p =97+18+5 GeV),wherethe 2.2. Thelightquark couplingsto theZ bo- −9−3 W −15−10 first error is statistical and the second system- son atic[3]. Itisinterestingtonotethattheprecision Using the same HERA-1 data sample, H1 has is better with the e−p data, albeit with a smaller also performeda combinedEW-PDFfit inwhich integrated luminosity. This is because the W− the four light quark couplings vu, au, vd and ad (W+) exchangeprobes mostly the u (d) quark in to Z have been determined taking into account the proton resulting in a much larger CC cross theircorrelationwiththePDFs[6]. Theresulting precisioniscomparablewiththosefromCDFand 1From1994on,theelectronbeamenergywasincreasedto the combinedLEP/SLDEWfit. Inaddition, the 27.5GeV andfrom1998 on,the protonbeam energywas alsoincreasedto920GeV resultingin√s=300GeV and HERA data can resolve the sign ambiguity seen √s=318GeV. in some of the other determinations. Electroweakand beyond the Standard Model results from HERA 3 The polarizedelectron beam at HERA-2 is ex- The preliminary results combining the H1 and pectedto giveadditionalsensitivityto these cou- ZEUSHERA-2dataareshowninFig.2[10]. This plings in particular the vector couplings. In- is the first observation of parity violation in NC deed, including new preliminary NC cross sec- DIS at HERA. tionmeasurementsbasedonpartofthe analyzed HERA-2 data, a new fit has substantially im- proved the precision [7]. The comparison for the uquarkcouplingswiththeresultsofCDF[8]and HERA LEP/SLD [9] is shown in Fig. 1. A 1 0.8 H1+ZEUS Combined (prel.) 0.6 ZEUS u 0.4 v 11 ZtoEtaUlS u-pnocel-rvtu.-vd-au-ad-PDF (prel.) 0.2 uncorr. uncert. 0 H1 prel. (HERA I+II 94-05) 00..55 -0.2 -0.4 00 A+ -0.6 A- H1 2000 PDF --00..55 -0.8 ZEUS-JETS PDF SM CDF -1 68% CL LEP/SLD 103 104 --11 Q2 (GeV2) --11 --00..55 00 00..55 11 a Figure2. MeasurementsofA± byH1andZEUS. u Theerrorbarsdenotethetotaluncertaintywhich Figure 1. HERA results at 68% confidence level is dominated by the uncorrelated error contribu- (CL) on u quark couplings to Z in comparison tions. The curvesdescribe the theoreticalpredic- with those from CDF and LEP/SLD. tions in NLO QCD as obtained in PDF fits to the H1 inclusive data and to the inclusive and jet ZEUS data, respectively. Both fits have been 2.3. Parity violation in NC DIS at high Q2 performed using the unpolarized HERA-1 data. In the early HERA-1 data with unpolarized electronbeam,differentNCcrosssectionsathigh Q2 between e−p and e+p interactions were observed, exhibiting the γZ interference and Z ex- 2.4. Limits on finite quark radius and con- change contribution at high Q2. With the polar- tact interactions ized electron beam at HERA-2, additional dif- NC interactions at high Q2 at HERA provide ferences in the cross sections between the left- an important test of the SM at the high energy handed polarization (P ) and the right-handed L frontier. Indeed, the SM Q2 spectrum is ex- polarization(P )areexpectedfortheweakinter- R pected to be modified if the interacting electron action of Z exchange. A polarization asymmetry and quark have a finite size: A± for e± beams can thus be introduced 2 σ±(P ) σ±(P ) dσ dσSM A± = R − L . (4) NC = NCf2(Q2)f2(Q2), (5) P P σ±(P )+σ±(P ) dQ2 dQ2 e q R L R L − 4 Z. Zhang where f(Q2) = 1 hr2iQ2 is the electron or ZEUS quark form factor, −r2 6being the mean squared 94-06 (prel.) e±p 330 pb-1 h i -1/L 2 best fit value +1/L 2 best fit value radius of the EW charge distribution. Assum- allowed ±1/L 2 range ing a point-like electron, i.e. setting fe 1 as L - (TeV) L + (TeV) ≡ it has been well constrained elsewhere [11], and VV 8.0 6.3 using the full HERA (preliminary HERA-2 and AA 6.7 6.1 published HERA-1) data, an upper limit on the VA 3.2 3.5 X1 4.9 4.7 radiusofthe lightuanddquarks,Rq =qhrq2i< X2 5.5 4.7 0.75 10−18m, at 95% CL has been derived by X3 6.6 5.3 · X4 5.4 4.9 H1[12]. ThelimitR <0.62 10−18mfromZEUS q X5 5.5 4.5 · is similar [13]. X6 3.8 4.6 New interactions between e and q involving U1 5.8 5.4 mass scales Λ above the center of mass energy U2 6.5 5.3 U3 7.9 6.2 can also modify the SM NC cross section at high U4 6.0 5.1 Q2 via virtual effects. Such interactions can be U5 6.6 5.0 modeled as four-fermion contact interactions as U6 4.1 5.1 aneffectivetheorybyadditionalterms inthe SM LL 4.7 4.2 LR 2.0 3.7 Lagrangian RL 2.2 3.6 RR 4.5 3.7 = ηeq(e¯γµe )(q¯γ q ), (6) L X ij i i j µ j -0.2 0 0.2 ±1/L 2 (TeV-2) where the sum runs over electron and quark he- licities and quark flavors. In Eq.(6), only vector Figure 3. Confidence intervals of 1/Λ2 at 95% currents are considered as strong limits have al- ± CL for the studied contact interaction scenarios. ready been placed on scalar and tensor contact interactions. The coupling ηeq may be written as Thenumbersattherightandleftmarginsarethe ij corresponding lower limits on the mass scale Λ+ ηeq = ǫeq4π, where the coefficient ǫeq may take ij ij Λ2 ij (η >0) and Λ− (η <0) respectively. the values 1 or zero. In the HERA contact in- ± teraction analyses, 19 different chiral structures have been considered. The preliminary results from ZEUS are shown in Fig. 3 [13]. The typical ticipates in the weak interaction, and the corre- excluded scale is Λ> 5TeV at 95% CL. Compa- sponding cross sections thus vanish for P = 1 e − rable limits were achieved by H1 [14]. (e+p)andP =1(e−p). Theproductionofright- e handed CC would result in a deviationfrom zero 2.5. TotalCCcrosssectionsandconstraint at these polarization values. The contribution of on right-handed currents aright-handedCCcanbe derivedfromlinearfits According to Eq.(2), the CC cross section of to the measuredcrosssectionsandfromextrapo- purely weak interactions is expected to have a lating the results of the fits to P = 1. The up- e linear dependence on the beam polarization P . ± e per limit on the right-handed CC cross sections The (preliminary) measurements of the total CC can be further translated into lower mass limits cross section for Q2 > 400GeV2 and inelasticity on a right-handed W [15]. y < 0.9 with polarized HERA-2 data are shown in Fig. 4 together with the corresponding cross 2.6. Other searches in inclusive DIS pro- sections of the published HERA-1 data with un- cesses polarized beams [15]. The measurements are in Many searches for new particles such as lepto- good agreement with the expected linear depen- quarks(LQs),squarks(the supersymmetricpart- dence. ners of quarks) and excited states of fermions In the SM, only the left-handed W boson par- have been carried out at HERA, since the very Electroweakand beyond the Standard Model results from HERA 5 most exciting moments happened in 1997 when Charged Current e–p Scattering bothH1andZEUSreportedanexcessofhighQ2 pb)pb)112200 e-p fi n X events basedon their 1994-1996data of less than ( (CC H1 2005 (prel.) 20pb−1 [19]. The excess generatedin a shortpe- CC 110000 H1 98-99 ss riod of time a huge number of speculations on ZEUS 04-05 (prel.) ZEUS 98-99 possible new physics including resonant produc- 8800 e+p fi n X tion of LQs or squarks. However, the later high H1 99-04 ZEUS 06-07 (prel.) statistics data samples collected by both experi- ZEUS 99-00 mentsdidnotconfirmtheexcess,andconstraints 6600 on LQ production were derived. CTEQ6D An example for the existing constraints using MRST 2004 4400 the full HERA data sample from H1 on a scalar LQ,whichdecaysexclusivelyintoanelectronand 2200 Q2 > 400 GeV2 a quark,is presentedin Fig.5 [20]. The new preliminary limitsignificantly improvesthe previous y < 0.9 limit from HERA-1 [21]. For moderate Yukawa 00 --11 --00..55 00 00..55 11 coupling values λ of about 0.03 0.6, it also ex- PPee tends wellbeyondthe directlimi−t fromthe Teva- tron [22] and the indirect limit from LEP [23]. Figure 4. The dependence of the measured total CC cross sections on the e± beam polarization in comparison with the expectations from CTEQ6D [16] and MRST 2004 [17]. Leptoquark Search, HERA I+II (449 pb-1) l 11 beginning of data taking. Both H1 and ZEUS haveperformedtheirfirstsearchusingthedataof 1ep99c2ololifdleerssisthananid3e0anlbm−a1ch[1in8e].tIonldoeoekd,fotrhreeHsoEnRanAt 1100--11 E xclu d e d S~1/2,L (e+d) H1 prelim. single LQ productionofnewparticles(LQs,squarks),which H1 (94-00) single LQ couple via Yukawa couplings directly to a lepton and a parton, up to the center of mass energy. 2 D0 pair prod. Thisisincontrasttothepair-productionine+e− 1100--22 OPAL indir. limit at the LEP or in pp¯ at the Tevatron collider, in 220000 225500 330000 335500 440000 which case the mass reach for a direct search is M / GeV LQ up to half of the center of mass energy. The searchfor the first generationLQs consid- Figure 5. Example of mass-dependent upper ers its decay into an electron and a quark or into bounds on the Yukawa coupling λ of a first gen- a neutrino and a quark. These LQ decays lead eration leptoquark coupling to ed (S˜ (ed)). 1/2,L to final states identical to DIS events. One cannot distinguish them on an event by event basis, buthas to relyondifferentangulardistributions, e.g.flatforscalarLQsandsteeplyfalling forDIS Searches for LQs coupling to first and sec- events. ond generation fermions have also been per- InthehistoryoftheHERArunning,oneofthe formed [24]. In this case, the final state lepton is different from the incident electron(lepton fla- 2Beyond the kinematic limit,the search sensitivityarises fromu-channelvirtualexchangeofnewparticlescoupling vorviolatingprocesses),andthesearchesarethus tolepton-quarkpairs. essentially background free. The corresponding 6 Z. Zhang constraints are also more stringentthan those on 3.1. Multi-lepton events at high PT the first generation LQs. Using the full HERA data, H1 has com- In supersymmetric (SUSY) models where the pleted [30] a study on the multi-lepton events of so-called R-parity (R ) is not conserved, squarks which an excess was reported earlier based on p couldberesonantlyproducedatHERAsimilarto HERA-1 data [31]. Seven final state topologies LQs. In addition to the LQ-like decays, squarks ee, µµ, eµ, eee, eµµ, eeµ and eeee have been an- alsoundergodecaysintogauginos(thesupersym- alyzed. Inalltopologies,the predictedeventrate metric partners of gauge bosons). A dedicated agrees with the number of observed events [30]. searchrequiresalargenumberoffinalstatestobe However, when a comparison is made requiring analyzed. This has been pioneeredby H1 in [25], for the invariant mass of the two highest P lep- T wherethefullHERA-1datahavebeenusedtoset tons M > 100GeV, an excess is observed in 12 constraints on SUSY models. A similar analysis most of the topologies (Table 1), although the looking for the SUSY partner of the top quark number of observed events remains statistically has been performed by ZEUS [26]. limited. Demanding P >100GeVforthelep- T The observedreplicationof three fermion fam- tons, 5 (0) events arPe observed in the e+p (e−p) ilies suggests the possibility that these fermions sample with 0.96 0.12 (0.64 0.09) expected. ± ± may be composite particles, consisting of combi- Also shown in Table 1 are preliminary results nations ofmore fundamental entities. The obser- from ZEUS on di-electron and tri-electron sam- vationofexcitedstatesofleptonsorquarkswould ples [32]. In both samples no excess has been be a clear signal that these particles are compos- observed. ite rather than elementary. At HERA, excited electrons, quarks and neutrinos (e∗,q∗,ν∗) with masses up to the kinematic limit of the center of mass energy could be produced directly via t- channel exchange of a gauge boson. The full HERA e±p data sample collected by 3.2. Search for doubly-charged Higgs H1 has been used to search for excited elec- bosons trons via the decays e eγ, e∗ eZ and Motivated by the observedexcess of the multi- ∗ → → e∗ νW [27]. A similar preliminary search has lepton events discussed above, a search for → alsobeenperformedforexcitedquarksviathede- doubly-charged Higgs bosons (H±±) has been cays q∗ qγ and q∗ qW [28]. The search for performed by H1 using the HERA-1 data [33]. → → excitedneutrinosdecayingviaν∗ νγ,ν∗ νZ Thesearchlooksforeventswithasinglyproduced → → and ν∗ eW has been made using only e−p col- H±± decaying into a high mass pair of same → lisions as the corresponding cross section in e+p chargeleptons,oneofthembeinganelectron. No is much smaller [29]. No evidence for excited evidence for H±± production is observed; out of fermions has been found, and limits on the char- theobservedmulti-leptoneventsfromtheHERA- acteristic couplings have been derived [27–29]. 1 data, only one di-electron event is compatible with the H±± signature. Mass dependent upper limits are derived on the Yukawa coupling 3. RARE EXCLUSIVE PROCESSES h ofthe Higgs bosonto anelectron-leptonpair. el The large data sample of HERA has made it Assuming that the doubly-charged Higgs decays possible to use rare exclusive processes with well onlyintoanelectronandamuonviaacouplingof measured and isolated final states for perform- electromagnetic strength h =√4πα =0.3, a eµ em ing EW measurements and for searching for de- lower limit of 141GeV on the H±± mass is ob- viations from the SM. Two examples are multi- tained at 95% CL. For a doubly-charged Higgs leptoneventswithhightransversemomenta(P ) decaying only into an electron and a tau and a T and isolated lepton events with large missing coupling h = 0.3, masses below 112GeV are eτ transverse momentum (P ). ruled out. T 6 Electroweakand beyond the Standard Model results from HERA 7 Table 1 The number of observed events and SM expectations in different multi-lepton topologies for M > 12 100GeV. The numbers shown in parentheses correspond to the contribution from the dominant pair production in γγ interactions. Topology H1 ZEUS Data SM (pair) Data SM (pair) ee 3 1.34 0.20 (0.83) 2 1.7 0.2 (0.9) ± ± eµ 1 0.59 0.06 (0.59) ± eee 3 0.66 0.09 (0.66) 2 1.0 0.1 (1.0) ± ± µµ 1 0.17 0.07 (0.17) ± eµµ 2 0.16 0.05 (0.16) ± Table 2 The number of observed events and SM expectations for three types of leptons in e±p data samples for PX >25GeV. The SM signal (dominated by W production) is shown in percentage in parentheses. T Dataset Lepton H1 [36] ZEUS [37] Data Exp (signal) Data Exp (signal) e 9 4.32 0.71 (82%) 3 4.0 0.6 (77%) ± ± e+p µ 8 3.70 0.63 (92%) 3 3.4 0.5 (81%) ± ± τ 0 0.82 0.12 (46%) ± e 1 3.18 0.58 (70%) 3 3.2 0.5 (69%) ± ± e−p µ 0 2.40 0.41 (92%) 2 2.3 0.4 (85%) ± ± τ 1 0.68 0.11 (31%) ± 3.3. Isolatedleptonevents at large missing responding signal contribution (purity) for the e PT and µ channels is also shown in Table 2. Sincethe observationofthefirstisolatedmuon event with large P by H1 in 1994 [34], searches 6 T 3.4. Single W production cross section havebeenpursuedandextendedbyH1andZEUS From the previous section, we noticed that the toallthreetypesofleptonsandwithincreasingly isolated lepton events with large P are domi- larger data samples [35]. The results [36,37] 3 6 T nated by the SM W production. It is possible, with the full HERA data are summarized in Ta- usingthesamesample,tofurtherenhancetheW ble 2. H1 has observed an excess in both the signal with additional selection cuts and to mea- e and the µ channel. The excess is, however, sure the W production cross section. not confirmed by ZEUS. ZEUS has, on the other The extracted production cross section from hand, observed 2 isolated τ lepton events with a ZEUS [37] is σ(ep lWX) = 0.89+0.25(stat) hadronic final state (X) at large transverse mo- → −0.22 ± 0.10(syst)pb at √s = 316GeV corresponding to mentum(PX >25GeV)for0.20 0.05expected, T ± the luminosity weighted mean of center of mass basedonthe HERA-1 data, of which49%is con- energiesofthe differentdatasamples. The corre- tributed by the SM signal events from single W sponding theoretical expectation is 1.2pb which productionwitha genuineisolatedτ andmissing has anerrorof15%due to the uncertaintyof the transversemomentuminthefinalstate. Thecor- next to leading order corrections. The corresponding measurement from H1 3The preliminary results of H1 shown at the workshop σ(ep lWX)=1.14 0.25(stat) 0.14(syst)pb have been replaced by the published one. The same is → ± ± truefortheresultsshowninsections3.4and4. is quoted for √s = 317GeV and is in agreement 8 Z. Zhang with the prediction of 1.27 0.19pb [36]. ment with the SM and compatible with anoma- ± BothmeasurementsfromZEUSandH1havea lous single top production via flavor changing significance of about five standard deviations. neutral current (FCNC, sec. 3.6). 3.5. W polarization fractions at HERA 3.6. Single top production To test the compatibility of the observed W The production of single top quarks is kine- decays with the SM, a measurement of the W matically possible at HERA. The signature of a boson polarization is performed by H1 [36]. The top decay to b and W with subsequent decay of measurement is based on the cosθ∗ distribution theW intheleptonicelectronandmuonchannels in the decay W e/µ+ν, where θ∗ is defined wouldbealeptonandmissingtransversemomen- → as the angle between the W boson momentum tum. This signature coincides with that of the in the lab frame and that of the charged decay observed isolated lepton events discussed above. lepton in the W boson rest frame. The angu- Thesearchisperformedforanomaloustopquark lar distribution is expected to have three distinct productioninanFCNCprocessinvolvingthecou- terms, 3/4F ( 1 cos2θ∗), 3/8F (1 cosθ∗)2 pling κ . The dominant process for SM single 0 − tuγ − − − and 3/8F (1+cosθ∗)2 with F , F and F cor- top production at HERA has a cross section of + 0 − + responding to the longitudinal, left-handed and less than 1fb and is treated as background. right-handedfractionsrespectively,ofwhichonly The limits from HERA [38,39] are compared two are independent as F +F +F 1. with other experiments [40,41] in Fig. 7. The H1 0 − + ≡ The results on the polarization fractions F limitisbasedonthefullHERAdata,whereasthe 0 and F are obtained from a simultaneous fit to ZEUSlimits areobtainedfromthe HERA-1data − the measured angular distribution and shown in taking into account not only κ but also v tuγ tuZ Fig. 6. The measurement is found in good agree- both in top production and decay. ZEUS also studied the dependence of the limits on the top mass. It is found that the limits are more stringent for a smaller top mass value, as expected. W Polarisation at HERA 1 F− H1 H1 Data EPVEC 4. GENERIC SEARCH AT HIGH PT ANOTOP Different from specific searches presented so far, a generic and model-independent search for deviations from the SM prediction for all high 68% CL 0.5 transversemomentumfinalstateconfigurationin- N ot volvingelectrons(e),muons(µ),jets(j),photons all (γ)orneutrinos(ν)wasperformedbyH1firstus- o 95% CL we ing the HERA-1 data [42] and now including the d HERA-2 data [43]. Events areclassifiedindiffer- entclasses. Eacheventclasscontainsatleasttwo 0 finalstateobjects(e,µ,j,γ,ν)withP >20GeV 0 0.5 11 T F in the polar angle range 10◦ < θ < 140◦. All 0 0.5 F eventclasses with observeddata events orwith a 0 SMexpectationgreaterthan0.01eventareshown Figure 6. Preliminary W boson polarization for all H1 e+p data in Fig. 8. In a further step, (point) at 1 and 2σ CL (contours). Also shown a statistical algorithm is used to search for devi- are the values for the SM prediction (triangle) ations from the SM in the distributions of the and anomalous single top production via FCNC scalar sum of transverse momenta or invariant (square). mass of final state particles. Electroweakand beyond the Standard Model results from HERA 9 H1 General Search at HERA (e+p, 285 pb-1) jjj---jjj | | H1 Preliminary (HERA I+II) mmmeee------jjjjjj uZuZ nnn---jjj vvtt eee---nnn || Excluded eee---eee 11 eee---mmm mmm ---mmm ggg---jjj ggg---eee ggg---mmm Excl. by ZEUS ggg---nnn ggg---ggg jjj---jjj---jjj Excl. by CDF mmmeee------jjjjjj------jjjjjj nnn---jjj---jjj eee---eee---jjj eee---eee---nnn eee---eee---eee mmm ---mmm ---jjj Excl. by L3 eee---mmm ---mmm 1100--11 mmmeee---mmm---mmm---nnn---jjj k tcg = vtcZ = 0 mmmeee------nnnnnn------jjjjjj mt = 175 GeV eee---mmm ---nnn ggg---jjj---jjj 1100--11 11 ||kk ttuugg || gggggg------eeennn------jjjjjj eee---jjj---jjj---jjj nnn---jjj---jjj---jjj ggg---nnn---jjj---jjj eee---nnn---jjj---jjj H1 Figure 7. Exclusion limits at 95% CL on the ggg---eee---jjj---jjj eee---eee---nnn---jjj anomalous κtuγ and vtuZ couplings obtained by eee---mmmjjj---jjj------nnnjjj------jjjjjj H1 Data the H1, ZEUS, CDF and L3 experiments. The eee---jjj---jjj---jjj---jjj SM nnn---jjj---jjj---jjj---jjj charm quark couplings κtcγ and vtcZ are ne- jjj---jjj---jjj---jjj---jjj glected, and the limits are shown assuming a top 10-210-1 1 10 102 103 104 105 mass m =175GeV. Events t Figure 8. The data and the SM expectation for all event classes with observed data events or a 5. SUMMARY SM expectation greater than 0.01 event. The er- rorbandsonthepredictionsincludemodeluncer- The HERA ep collider is first of all a precision taintiesandexperimentalsystematicerrorsadded QCDmachineprovidingdominantconstraintsfor in quadrature. partondistributionfunctionsatlowx. Itisalsoa highenergycollidercomplementarytoLEPe+e− and the Tevatron pp¯ colliders allowing rich electroweak measurements as well as many searches observedbyH1ontheisolatedelectronandmuon for new particles to be performed. eventswithlargemissingtransverseenergy,which There is a good prospect to achieve much im- has around 2.4 standard deviations. 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