A. Babaev

Using the ARGUS detector at the DORIS II storage ring we have searched in three different ways for B0-B0 mixing in ϒ (4S) decays. One explicitly mixed event, a decay ϒ (4S)→B0B0, has been completely reconstructed. Furthermore, we observe a 4.0 standard deviation signal of 24.8 events with like-sign lepton pairs and a 3.0 standard deviation signal of 4.1 events containing one reconstructed B0(B0) and an additional fast ℓ+(ℓ)−. This leads to the conclusion that B0-B0 mixing is substantial. For the mixing parameter we obtain r=0.21±0.08.

Using the ARGUS detector at the e+e− storage ring DORIS II at DESY, we searched for b→u transitions in exclusive hadronic B meson decays. A systematic analysis of B decays into pions has been performed for decay modes with 2–7 pions in the final state. In none of the decays a positive signal was observed. The upper limits obtained on various branching ratios are consistent with the current model predictions.

General aspects of the H1 detector at the electron-proton storage ring HERA as well as technical descriptions of the magnet, luminosity system, trigger, slow-control, data acquisition and off-line data handling are given. The three major components of the detector, the tracking, calorimeter and muon detectors, will be described in a forthcoming article. The present paper describes the detector that was used from 1992 to the end of 1994. After this a major upgrade of some components was undertaken. Some performance figures from luminosity runs at HERA during 1993 and 1994 are given.

A measurement of the proton structure function F2 (x, Q2) is presented with about 1000 neutral current deep inelastic scattering events for Bjorken x in the range x ⋍ 10−2 – 10−4 and Q2 > 5 GeV2. The measurement is based on an integrated luminosity of 22.5 nb−1 recorded by the H1 detector in the first year of HERA operation. The structure function F2 (x, Q2) shows a significant rise with decreasing x.

A detailed analysis is presented of the diffractive deep-inelastic scattering process ep→eXY, where Y is a proton or a low mass proton excitation carrying a fraction 1-xIP>0.95 of the incident proton longitudinal momentum and the squared four-momentum transfer at the proton vertex satisfies |t|<1 GeV2. Using data taken by the H1 experiment, the cross section is measured for photon virtualities in the range 3.5≤Q2≤1600 GeV2, triple differentially in xIP, Q2 and β=x/xIP, where x is the Bjorken scaling variable. At low xIP, the data are consistent with a factorisable xIP dependence, which can be described by the exchange of an effective pomeron trajectory with intercept αIP(0)=1.118±0.008(exp.)+0.029 -0.010(model). Diffractive parton distribution functions and their uncertainties are determined from a next-to-leading order DGLAP QCD analysis of the Q2 and β dependences of the cross section. The resulting gluon distribution carries an integrated fraction of around 70% of the exchanged momentum in the Q2 range studied. Total and differential cross sections are also measured for the diffractive charged current process e+p→ν̄eXY and are found to be well described by predictions based on the diffractive parton distributions. The ratio of the diffractive to the inclusive neutral current ep cross sections is studied. Over most of the kinematic range, this ratio shows no significant dependence on Q2 at fixed xIP and x or on x at fixed Q2 and β.

Technical aspects of the three major components of the H1 detector at the electron-proton storage ring HERA are described. This paper covers the detector status up to the end of 1994 when a major upgrading of some of its elements was undertaken. A description of the other elements of the detector and some performance figures from luminosity runs at HERA during 1993 and 1994 are given in a paper previously published in this journal.

A new measurement of the proton structure function F2 (x, Q2) is reported for momentum transfers squared Q2 between ].5 GeV2 and 5000 GeV2 and for Bjorken x between 3 · 10−5 and 0.32 using data collected by the HERA experiment H1 in 1994. The data represent an increase in statistics by a factor of ten with respect to the analysis of the 1993 data. Substantial extension of the kinematic range towards low Q2 and x has been achieved using dedicated data samples and events with initial state photon radiation. The structure function is found to increase significantly with decreasing x, even in the lowest accessible Q2 region. The data are well described by a Next to Leading Order QCD fit and the gluon density is extracted.

A measurement is presented, using data taken with the H1 detector at HERA, of the contribution of diffractive interactions to deep-inelastic electron-proton (ep) scattering in the kinematic range 8.5 < Q2 < 50GeV2, 2.4 × 10−4 < Bjorken-x < 0.0133, and 3.7 × 10−4 < χp < 0.043. The diffractive contribution to the proton structure function F2(x,Q2) is evaluated as a function of the appropriate deep-inelastic scattering variables χp, Q2, β (= χχp) using a class of deep-inelastic ep scattering events with no hadronic energy flow in an interval of pseudo-rapidity adjacent to the proton beam direction. the dependence of this contribution on χp is measured to be χp−n with n = 1.19 ± 0.06 (stat.) ± 0.07 (syst.) independent of β and Q2, which is consistent with both a diffractive interpretation and a factorisable ep diffractive cross section. A first measurement of the deep-inelastic structure of the pomeron in the form of the Q2 and β dependences of a factorised structure function is presented. For all measured β, this structure function is observed to be consistent with scale invariance.

The detector ARGUS has been designed as a universal tool to investigate final states from e+e− annihilation processes in the energy range of the ϒ resonances. ARGUS started operation in October 1982 and has since successfully taken data at the ϒ(1S), ϒ(2S) and ϒ(4S) energies, and in the nearby continuum. The detector combines excellent charged particle identification and good photon energy resolution over more than 90% of the full solid angle. A particle originating from the interaction vertex and leaving the beam tube traverses the following components: the vertex drift chamber, the main drift chamber which determines its momentum and specific ionization, the time-of-flight system through which its velocity is determined, and the electromagnetic calorimeter. Muons pass through the magnet coils and the flux return yoke and finally hit the muon chamber system which surrounds the detector. The momentum resolution of ARGUS is σ(pT)PT = (0.012 + (0.009pT[GeV/c])2)12, the photon energy resolution in the barrel shower counters is σ(E)E = (0.0722+0.0652E[GeV])12. Combining the information from all p devices, more than 80% of all charged hadrons can be recognized unambiguously. The electron-hadron and muon-hadron rejection rates are 1:200 and 1:50 respectively.

A measurement of the proton structure function F2(x, Q2) is reported for momentum transfers squared Q2 between 4.5 GeV2 and 1600 GeV2 and for Bjorken x between 1.8 × 10−14 and 0.13 using data collected by the HERA experiment H1 in 1993. It is observed that F2 increases significantly with decreasing x, confirming our previous measurement made with one tenth of the data available in this analysis. The Q2 dependence is approximately logarithmic over the full kinematic range covered. The subsample of deep inelastic events with a large pseudo-rapidity gap in the hadronic energy flow close to the proton remnant is used to measure the “diffractive” contribution to F2.

Evidence is presented using data taken with the H1 detector at HERA for a class of deep inelastic electron-proton scattering (DIS) events (5 < Q2 < 120 GeV2) at low Bjorken-x (10−4 < x < 10−2) which have almost no hadronic energy flow in a large interval of pseudo-rapidity around the proton remnant direction and which cannot be attributed to our present understanding of DIS and fluctuations in final state hadronic fragmentation. From an integrated luminosity of 273 nb−1, 734 events, that is about 5% of the total DIS sample, have no energy deposition greater than 400 MeV forward of laboratory pseudo-rapidity ηmax = 1.8 up to the largest measurable pseudo-rapidity of about 3.65. Evidence that about 10% of observed rapidity gap events are exclusive vector meson electroproduction is presented. Good descriptions of the data are obtained using models based either on a vector meson dominance like picture, which includes a large fraction of inelastic virtual photon dissociation, or on deep inelastic electron-pomeron scattering in which the partonic sub-structure of the latter is resolved.

The cross-section for deeply virtual Compton scattering in the reaction ep→eγp has been measured with the ZEUS detector at HERA using integrated luminosities of 95.0 pb−1 of e+p and 16.7 pb−1 of e−p collisions. Differential cross-sections are presented as a function of the exchanged-photon virtuality, Q2, and the centre-of-mass energy, W, of the γ∗p system in the region 5<Q2<100 GeV2 and 40<W<140 GeV. The measured cross-sections rise steeply with increasing W. The measurements are compared to QCD-based calculations.

A measurement is presented of elastic deeply virtual Compton scattering e++p→e++γ+p at HERA using data taken with the H1 detector. The cross section is measured as a function of the photon virtuality, Q2, and the invariant mass, W, of the γp system, in the kinematic range 2<Q2<20GeV2, 30<W<120GeV and |t|<1GeV2, where t is the squared momentum transfer to the proton. The measurement is compared to QCD based calculations.

A narrow resonance in D∗−p and D∗+p̄ invariant mass combinations is observed in inelastic electron–proton collisions at centre-of-mass energies of 300 GeV and 320 GeV at HERA. The resonance has a mass of 3099±3(stat.)±5(syst.) MeV and a measured Gaussian width of 12±3(stat.) MeV, compatible with the experimental resolution. The resonance is interpreted as an anti-charmed baryon with a minimal constituent quark composition of uuddc̄, together with the charge conjugate.

A detailed study of the lepton momentum spectrum in υ(4S) decays has been made using the ARGUS detector at the DORIS II e+e− storage ring at DESY. In the region from 2.3 to 2.6 GeV/c, which is above the endpoint for contributions from B decays via b→c transitions, we observe 41±10 events in excess of known backgrounds. These events are interpreted as a signal for b→u transitions. A model dependent value of 0.10±0.01 is obtained for the ratio of Cabibbo-Kobayashi-Maskawa matrix elements |Vub|/|Vcv|, using the Altarelli et al. model.

The cross section for the diffractive deep-inelastic scattering process $ep \to e X p$ is measured, with the leading final state proton detected in the H1 Forward Proton Spectrometer. The data analysed cover the range \xpom <0.1 in fractional proton longitudinal momentum loss, 0.08 < |t| < 0.5 GeV^{-2} in squared four-momentum transfer at the proton vertex, 2 < Q^2 < 50 GeV^2 in photon virtuality and 0.004 < \beta = x / \xpom < 1, where x is the Bjorken scaling variable. For $\xpom \lapprox 10^{-2}$, the differential cross section has a dependence of approximately ${\rm d} \sigma / {\rm d} t \propto e^{6 t}$, independently of \xpom, \beta and Q^2 within uncertainties. The cross section is also measured triple differentially in \xpom, \beta and Q^2. The \xpom dependence is interpreted in terms of an effective pomeron trajectory with intercept $\alpha_{\pom}(0)=1.114 \pm 0.018 ({\rm stat.}) \pm 0.012 ({\rm syst.}) ^{+0.040}_{-0.020} ({\rm model})$ and a sub-leading exchange. The data are in good agreement with an H1 measurement for which the event selection is based on a large gap in the rapidity distribution of the final state hadrons, after accounting for proton dissociation contributions in the latter. Within uncertainties, the dependence of the cross section on x and Q^2 can thus be factorised from the dependences on all studied variables which characterise the proton vertex, for both the pomeron and the sub-leading exchange.

Measurements are presented of inclusive charm and beauty cross sections in e^+p collisions at HERA for values of photon virtuality 12 \le Q^2 \le 60 GeV^2 and of the Bjorken scaling variable 0.0002 \le x \le 0.005. The fractions of events containing charm and beauty quarks are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 vertex detector. Values for the structure functions F_2^{c\bar{c}} and F_2^{b\bar{b}} are obtained. This is the first measurement of F_2^{b\bar{b}} in this kinematic range. The results are found to be compatible with the predictions of perturbative quantum chromodynamics and withprevious measurements of F_2^{c\bar{c}}.

At the Large Hadron Collider (LHC), absolute luminosity calibrations obtained by the van der Meer (vdM) method are affected by the mutual electromagnetic interaction of the two beams. The colliding bunches experience relative orbit shifts, as well as optical distortions akin to the dynamic-$\beta$ effect, that both depend on the transverse beam separation and must therefore be corrected for when deriving the absolute luminosity scale. In the vdM regime, the beam-beam parameter is small enough that the orbit shift can be calculated analytically. The dynamic-$\beta$ corrections to the luminometer calibrations, however, had until the end of Run 2 been estimated in the linear approximation only. In this report, the influence of beam-beam effects on the vdM-based luminosity scale is quantified, together with the associated systematic uncertainties, by means of simulations that fully take into account the non-linearity of the beam-beam force, as well as the resulting non-Gaussian distortions of the transverse beam distributions. Two independent multiparticle simulations, one limited to the weak-strong approximation and one that models strong-strong effects in a self-consistent manner, are found in excellent agreement; both predict a percent-level shift of the absolute pp-luminosity values with respect to those assumed until recently in the physics publications of the LHC experiments. These results also provide guidance regarding further studies aimed at reducing the beam-beam-related systematic uncertainty on beam-beam corrections to absolute luminosity calibrations by the van der Meer method.

A measurement of the derivative (d ln F_2 / d lnx)_(Q^2)= -lambda(x,Q^2) of the proton structure function F_2 is presented in the low x domain of deeply inelastic positron-proton scattering. For 5*10^(-5)<=x<=0.01 and Q^2>=1.5 GeV^2, lambda(x,Q^2) is found to be independent of x and to increase linearly with ln(Q^2).

The inclusive production of D∗±(2010) mesons in deep-inelastic scattering is studied with the H1 detector at HERA. In the kinematic region 1<Q2<100 GeV2 and 0.05<y<0.7 an e+p cross section for inclusive D∗± meson production of 8.50±0.42(stat.)+1.21−1.00(syst.) nb is measured in the visible range ptD∗>1.5 GeV and |ηD∗|<1.5. Single and double differential inclusive D∗± meson cross sections are compared to perturbative QCD calculations in two different evolution schemes. The charm contribution to the proton structure, F2c(x,Q2), is determined by extrapolating the visible charm cross section to the full phase space. This contribution is found to rise from about 10% at Q2=1.5 GeV2 to more than 25% at Q2=60 GeV2 corresponding to x values ranging from 5×10−5 to 3×10−3.

Measurements are presented of inclusive charm and beauty cross sections in e + p collisions at HERA for values of photon virtuality Q 2 > 150 GeV 2 and of inelasticity 0.1 < y < 0.7.The charm and beauty fractions are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 vertex detector.The data are divided into four regions in Q 2 and Bjorken x, and values for the structure functions F cc 2 and F

First results on inclusive $$\mathop {D^0 }\limits^{( - )} $$ andD*± production in neutral current deep inelasticep scattering are reported using data collected by the H1 experiment at HERA in 1994. Differential cross sections are presented for both channels and are found to agree well with QCD predictions based on the boson gluon fusion process. A charm production cross section for 10 GeV2≤Q2≤100 GeV2 and 0.01≤y≤0.7 of $$\sigma (ep \to ec\bar cX) = (17.4 \pm 1.6 \pm 1.7 \pm 1.4) nb$$ is derived. A first measurement of the charm contribution $$F_2^{c\bar c} (x,Q^2 )$$ to the proton structure function for Bjorkenx between 8·10−4 and 8·10−3 is presented. In this kinematic range a ratio $$F_2^{c\bar c} /F_2 = 0.237 \pm 0.021 \pm 0.041$$ is observed.

The results of a measurement of the proton structure function F2(x,Q2) and the virtual photon-proton cross section are reported for momentum transfers squared Q2 between 0.35 GeV2 and 3.5 GeV2 and for Bjorken-x values down to 6 × 10−6 using data collected by the HERA experiment H1 in 1995. The data represent an increase in kinematic reach to lower x and Q2 values of about a factor of 5 compared to previous H1 measurements. Including measurements from fixed target experiments the rise of F2 with decreasing x is found to be less steep for the lowest Q2 values measured. Phenomenological models at low Q2 are compared with the data.

We present first results on the total photoproduction cross section measurement with the H1 detector at HERA. The data were extracted from low Q2 collisions of 26.7 GeV electrons with 820 GeV protons. The γp total cross section has been measured by two independent methods in the γp center of mass energy range from 90 to 290 GeV. For an average center of mass energy of 195 GeV a value of σtot (γp) = 159 ± 7 (stat.) ± 20 (syst.) μb was obtained.

Using the ARGUS detector at the e+e− storage ring DORIS II, we have observed the decay τ−→π−π−π−π+π+ντ in tau-pair events produced at center-or-mass energies between 9.4 and 10.6 GeV. From the 5π invariant mass distribution we derive an upper limit of m(ντ)<35 MeV/c2 at the 95% confidence level. The branching ratio for this decay channel is found to be (0.064±0.023±0.01)%.

B mesons have been reconstructed in five decay channels of the type B→D∗±nπ(n=1,2,3) using data accumulated by the ARGUS experiment at the e+e− storage ring DORIS II at DESY. In total, we find 40 neutral B mesons above a background of 15±6 events with a mass of (5278.2±1.0±3.0) MeV/c2 and 32 charged B mesons above a background of 17±6 events with a mass of (5275.8±1.3±3.0) MeV/c2. The decays B0D∗+π−π0, B0D∗+π−π−π+, and B−→D∗+π−π−π0 have been observed for the first time. We find substantially smaller branching ratios for the decay modes B0→D∗+π− and B−→D∗+π−π− than previously published by the CLEO collaboration.

Using the ARGUS detector at the e+e− storage ring DORIS II at DESY, a search for decays B→K∗γ has been performed where K∗ represents seven different K mesons. No evidence for such decays has been found, and upper limits are quoted. These provide valuable constraints on the top quark mass, the Higgs sector of the standard model, and a variety of extensions thereto.

Measurements are presented of differential dijet cross sections in diffractive photoproduction (Q^2<0.01 GeV^2) and deep-inelastic scattering processes (DIS, 4<Q^2<80 GeV^2). The event topology is given by ep-> e X Y, in which the system X, containing at least two jets, is separated from a leading low-mass proton remnant system Y by a large rapidity gap. The dijet cross sections are compared with NLO QCD predictions based on diffractive parton densities previously obtained from a QCD analysis of inclusive diffractive DIS cross sections by H1. In DIS, the dijet data are well described, supporting the validity of QCD factorisation. The diffractive DIS dijet data are more sensitive to the diffractive gluon density at high fractional parton momentum than the measurements of inclusive diffractive DIS. In photoproduction, the predicted dijet cross section has to be multiplied by a factor of approximately 0.5 for both direct and resolved photon interactions to describe the measurements. The ratio of measured dijet cross section to NLO prediction in photoproduction is a factor 0.5+-0.1 smaller than the same ratio in DIS. This suppression is the first clear observation of QCD hard scattering factorisation breaking at HERA. The measurements are also compared to the two soft colour neutralisation models SCI and GAL. The SCI model describes diffractive dijet production in DIS but not in photoproduction. The GAL model fails in both kinematic regions.

The first observation of open b production in ep collisions is reported. An event sample containing muons and jets has been selected which is enriched in semileptonic b quark decays. The visible cross section σ(ep→bb̄X→μX′)for Q2<1GeV2, 0.1<y<0.8 is measured to be 0.176±0.016(stat.)+0.026−0.017(syst.)nb for the muons to be detected in the range 35°<θμ<130° and p⊥μ>2.0GeV in the laboratory frame. The expected visible cross section based on a NLO QCD calculation is 0.104±0.017nb. The cross sections for electroproduction with Q2<1GeV2 and photoproduction are derived from the data and found to be σ(ep→ebb̄X)=7.1±0.6(stat.)+1.5−1.3(syst.)nb and σ(γp→bb̄X)=111±10(stat.)+23−20(syst.)nb at an average 〈Wγp〉∼180GeV, respectively.

With the H1 detector at the ep collider HERA, D∗ meson production cross sections have been measured in deep inelastic scattering with four-momentum transfers Q2 > 3 GeV2 and in photoproduction at energies around Wγp ≈ 88 GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe the differential cross sections within theoretical and experimental uncertainties. Using these calculations, the NLO gluon momentum distribution in the proton, xgg(xg), has been extracted in the momentum fraction range 7.5 × 10−4 < xg < 4 × 10−2 at average scales μ2 = 25 to 50 GeV2. The gluon momentum fraction xg has been obtained from the measured kinematics of the scattered electron and the D∗ meson in the final state. The results compare well with the gluon distribution obtained from the analysis of scaling violations of the proton structure function F2.

A measurement of the inclusive cross section for the deep-inelastic scattering of positrons off protons at HERA is presented at momentum transfers 8.5 ≤ Q2 ≤ 35 GeV2 and large inelasticity <y> = 0.7, i.e. for the Bjorken-x range 0.00013 ≤ x ≤ 0.00055. Using a next-to-leading order QCD fit to the structure function F2 at lower y values, the contribution of F2 to the measured cross section at high y is calculated and, by subtraction, the longitudinal structure function FL is determined for the first time with an average value of FL = 0.52 ± 0.03 (statt)−0.22+0.25 (syst) at Q2 = 15.4 GeV2 and x = 0.000243.

Transverse momentum spectra of charged particles produced in deep inelastic scattering are measured as a function of the kinematic variables x_B and Q2 using the H1 detector at the ep collider HERA. The data are compared to different parton emission models, either with or without ordering of the emissions in transverse momentum. The data provide evidence for a relatively large amount of parton radiation between the current and the remnant systems.

Using the ARGUS detector at the e+ e− storage ring DORIS II at DESY we have updated our result on charmless semileptonic B decays and searched for direct evidence for b→u transitions through reconstruction of complete events. This approach has successfully identified two ϒ (4S) events which contain B meson decays to a non-charm final state. In one case, a B0 meson is found in the channel π+μ−ν, while in the other a decay B+→ωμ+ν is seen. These events show that the previously observed signal of charmless semileptonic B decays is due to b→u transitions from which we obtain |VubVcb| = 0.11±0.012 using the model of Altarelli et al.

Using the ARGUS detector at the e+e− storage ring DORIS II at DESY we have investigated the decays B0→D∗−e+v and B0→D∗−μ+ν. The B0 mesons were produced in 39600 ϒ(4S)→B0B0 decays. Assuming electron-muon universality we obtain a branching ratio BR(B0→D∗−e+v)=BR(B0→D∗−γm+ν)=(7.0±1.2±1.9)%.

Results on diffractive photoproduction of ψ(2S) mesons are presented using data collected between 1996 and 2000 with the H1 detector at the HERA ep collider. The data correspond to an integrated luminosity of 77 pb−1. The energy dependence of the diffractive ψ(2S) cross section is found to be similar to or possibly somewhat steeper than that for J/ψ mesons. The dependences of the elastic and proton dissociative ψ(2S) photoproduction cross sections on the squared momentum transfer t at the proton vertex are measured. The t-dependence of the elastic channel, parametrised as ebt, yields belψ(2S)=(4.31±0.57±0.46) GeV−2, compatible with that of the J/ψ. For the proton dissociative channel the result bpdψ(2S)=(0.59±0.13±0.12) GeV−2 is 2.3 standard deviations smaller than that measured for the J/ψ. With proper account of the individual wavefunctions theoretical predictions based on perturbative QCD are found to describe the measurements well.

Using the ARGUS detector at the e+e− storage ring DORIS II, we have observed charmless decays of B mesons into the final states pp̄π± and pp̄π+π−. The significance of the signal corresponds to more than five standard deviations. The branching ratios are (5.2±1.4±1.9)×10−4 for the three-body and (6.0±2.0±2.2)×10−4 for the four-body final state. These decays cannot proceed via the dominant b→c transitions, and we show that they are not the result of penguin-type processes. Thus, the observed decays must represent b→u quark transitions. Consequently, the Kobayashi-Maskawa matrix element Vub is non-zero.

A direct search for new particles in the H1 experiment at HERA is presented for masses ranging from 35 GeV up to ∼ 250 GeV. The data sample of 24 nb−1 accumulated during the first year of operation was analysed for signatures of scalar and vector leptoquarks, leptogluons, excited electrons and excited neutrinos with flavours of the first generation. No evidence for the production of such particles was found in various possible decay channels. Rejection limits are derived.

Using the ARGUS detector at the DORIS II ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ storage ring at DESY, we have obtained evidence for a new charmed resonance which decays into ${D}^{\mathrm{*}\ifmmode\pm\else\textpm\fi{}}$(2010)${\ensuremath{\pi}}^{\ensuremath{\mp}}$. The observed mass and width are 2420\ifmmode\pm\else\textpm\fi{}6 MeV/${c}^{2}$ and 70\ifmmode\pm\else\textpm\fi{}21 MeV/${c}^{2}$, respectively. The fragmentation function is found to be hard, as expected for a state containing a leading charm quark produced by nonresonant ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ annihilation.

Using the ARGUS detector at DORIS II, we have analyzed tau decays into π−π−π+π0ντ. The branching ratio was determined to be (4.2±0.5±0.9)%. From a study of the three pion sub-system, we find evidence for the decay τ−→ωπ−ντ with a branching ratio of (1.5±0.3±0.3)%. The ωπ− system is found to be predominantly in a JP=1− state. There is no evidence for second-class axial-vector currents. The spectral function for the ωπ− final state is in agreement with a prediction based on CVC and σe+e−→ωπ0.

The elastic electroproduction of φ mesons is studied at HERA with the H1 detector for photon virtualities 1<Q2<15GeV2 and hadronic centre of mass energies 40<W<130 GeV. The Q2 and t dependences of the cross section are extracted (t being the square of the four-momentum transfer to the target proton). When plotted as function of (Q2 + MV2) and scaled by the appropriate SU(5) quark charge factor, the φ meson cross section agrees within errors with the cross sections of the vector mesons V = ρ, ω and J/ψ. A detailed analysis is performed of the φ meson polarisation state and the ratio of the production cross sections for longitudinally and transversely polarised φ mesons is determined. A small but significant violation of s-channel helicity conservation (SCHC) is observed.

The production of transverse energy in deep inelastic scattering is measured as a function of the kinematic variables $x$ and $Q^2$ using the H1 detector at the ep collider HERA. The results are compared to the different predictions based upon two alternative QCD evolution equations, namely the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) and the Balitsky-Fadin-Kuraev-Lipatov (BFKL) equations. In a pseudorapidity interval which is central in the hadronic centre of mass system between the current and the proton remnant fragmentation region the produced transverse energy increases with decreasing $x$ for constant $Q^2$. Such a behaviour can be explained with a QCD calculation based upon the BFKL ansatz. The rate of forward jets, proposed as a signature for BFKL dynamics, has been measured.

The cross section for the elastic photoproduction of ϱ0 mesons (γp → ϱ0p) has been measured with the H1 detector at HERA for two average photon-proton centre-of-mass energies of 55 and 187 GeV. The lower energy point was measured by observing directly the ϱ0 decay giving a cross section of 9.1 ± 0.9 (stat.) ± 2.5 (syst.) μb. The logarithmic slope parameter of the differential cross section, dσ/dt, is found to be 10.9 ± 2.4 (stat.) ± 1.1 (syst.) GeV−2. The ϱ0 decay polar angular distribution is found to be consistent with s-channel helicity conservation. The higher energy cross section was determined from analysis of the lower part of the hadronic invariant mass spectrum of diffractive photoproduction and found to be 13.6 ± 0.8 (stat.) ± 2.4 (syst.) μb.

Using the ARGUS detector at the e +e− storage ring DORIS II, we have studied the colour-suppressed decays B→Jψ X and B→ψ′ X. We find the inclusive branching ratios for these two channels to be (1.07±0.16±0.19) % and (0.46±0.17±0.11) %, respectively. From a sample of reconstructed exclusive events the masses of the B0 and B+ mesons are determined to be (5279.5±1.6±3.0) MeVc2 and (5278.5±1.8±3.0) MeVc2, respectively. Branching ratios are determined from five events of the type B0→Jψ K∗0 and three of B+→J/ψ K+. In the same data sample a search for B0→e+e−, μ+μ− and μ±e∓ leads to upper limits for such decays.

Inclusive production cross sections are measured in deep inelastic scattering at HERA for meson states composed of a charm quark and a light antiquark or the charge conjugate.The measurements cover the kinematic region of photon virtuality 2 < Q 2 < 100 GeV 2 , inelasticity 0.05 < y < 0.7, D meson transverse momenta p t (D) ≥ 2.5 GeV and pseudorapidity |η(D)| ≤ 1.5.The identification of the D-meson decays and the reduction of the combinatorial background profit from the reconstruction of displaced secondary vertices by means of the H1 silicon vertex detector.The production of charmed mesons containing the light quarks u, d and s is found to be compatible with a description in which the hard scattering is followed by a factorisable and universal hadronisation process.

Using the ARGUS detector at the DORIS II storage ring at DESY, we have observed a charmed meson of mass (2455±3±5) MeV/c2, decaying to D+π−. The natural width of this state is determined to be (15+13+5−10−10) MeVc2. The fragmentation function is hard, as expected for a leading charmed particle from nonresonant e+e− annihilation. Analysis of the decay angular distribution supports the hypothesis that the observed state is an L=1 excited charmed meson with spin-parity 2+.

Using the ARGUS detector at DORIS II, we have observed a signal of 36.7±8.0 events in the decay channel D0→Ks0φ. In the same data sample, we have observed the well established decay D0→Ks0π+π−, and find the ratio, Br(D)0→Ks0φ)Br(D)0→Ks0π+π−), to be 0.186±0.052. The substantial value of (0.99±0.32±0.17)% then derived for the branching ratio for D0→K0φ gives direct evidence that W exchange contributes D0 decay.

Using data collected with the ARGUS detector, we have performed a decay angular analysis of the enhancement, previously known as the D∗ (2420), seen in the final state D∗(2010)+π−. We thereby exhibit that the observed broad structure is actually due to two relatively narrow resonances, one of which is identified as the D∗(2459)0, while the massof the other is measured to be (2414±2±5) MeV/c2. The results of the analysis are in good agreement with the interpretation of the two states as L=1 D mesons of spin-parities 2+ and 1+ respectively.

The total cross sections for the elastic electroproduction of P and Jψ mesons for Q2 > 8 GeV2 and 〈W〉 ⋍ 90 GeV/c2 are measured at HERA with the H1 detector. The measurements are for an integrated electron-proton luminosity of ⋍3 pb−1. The dependences of the total virtual photon-proton (γ∗p) cross sections on Q2, W and the momentum transfer squared to the proton (t), and, for the ϱ, the dependence on the polar decay angle (cos θ∗ are presented. The Jψ : ∂ cross section ratio is determined. The results are discussed in the light of theoretical models and of the interplay of hard and soft physics processes.

At the electron-proton collider HERA the inclusive D∗± meson photoproduction cross section has been measured with the H1 detector in two different, but partly overlapping, kinematical regions. For the first, where 〈Wγp〉 ≈ 200 GeV and Q2 < 0.01 GeV2, the result is σ(γp → ccX) = (13.2 ± 2.2−1.7 −4.8+2.1 +9.9) μb. The second measurement for Q2 < 4 GeV2 yields σ(γp → ccX) = (9.3 ± 2.1−1.8 −3.2+1.9 +6.9) μb at 〈Wγp〉 ≈ 142 GeV and σ(γp → ccX) = (20.6 ± 5.5−3.9 −7.2+4.3 +15.4 μb at 〈Wγp〉 ≈ 230 GeV, respectively. The third error accounts for an additional uncertainty due to the proton and photon parton density parametrizations. Differential cross sections are presented as a function of the D∗± transverse momentum and rapidity. The results compare reasonably well with next-to-leading order QCD calculations. Evidence for diffractive photoproduction of charm quarks is presented.

Using the ARGUS detector at the e+e− storage ring DORIS-II, we have measured the inclusive semileptonic decays of B-mesons into electrons and muons. The data originate from 220.5 events/pb on the ϒ(4S) resonance. We find BR (B→e+veX = (10.3 ± 0.6 ± 0.2)% and BR (B→μ+vμX) = (10.0 ± 0.6 ± 0.2)% using the model of Altarelli et al. for extrapolating over all lepton momenta, and BR (B→e+veX) = (9.9±0.6)%, BR(B→μ+vμX) = (9.7±0.6)% using the model of Grinstein et al. For semileptonic decays into baryons, we obtain an upper limit of BR (B→pe+vX)<0.16%(90%CL).

We present a QCD analysis of the proton structure function F2 measured by the H1 experiment at HERA, combined with data from previous fixed target experiments. The gluon density is extracted from the scaling violations of F2 in the range 2 · 10−4 < x < 3 · 10−2 and compared with an approximate solution of the QCD evolution equations. The gluon density is found to rise steeply with decreasing x.

A measurement of the beauty production cross section in ep collisions at a centre-of-mass energy of 319 GeV is presented. The data were collected with the H1 detector at the HERA collider in the years 1999-2000. Events are selected by requiring the presence of jets and muons in the final state. Both the long lifetime and the large mass of b-flavoured hadrons are exploited to identify events containing beauty quarks. Differential cross sections are measured in photoproduction, with photon virtualities Q^2 < 1 GeV^2, and in deep inelastic scattering, where 2 < Q^2 < 100 GeV^2. The results are compared with perturbative QCD calculations to leading and next-to-leading order. The predictions are found to be somewhat lower than the data.

Using the ARGUS detector at the e+e− storage ring DORIS II, we have measured the average polarization of D∗+ mesons originating from exclusive decays B̄0 → D∗+ℓ−ν. By comparing the D∗+ decay angular distribution to a functional form 1 + α cos2≡, we determine α to be α=0.7±0.9. This value of α leads to a ratio of longitudinal to transverse decay with Γl/ΓT=0.85±0.45, which allows the determination, |Vcb|=0.052±0.011. The importance of the transverse helicity component is manifested in the q2 and lepton spectra,which are also presented.

Using the ARGUS detector at DORIS II, we have studied the production of the charmed baryon Λc in e+e− annihilation at centre-of-mass energies near 10 GeV. The Λc+ was seen in the three decay modes pK−π+, Λπ+π−π+ and K̄0p, with products of normalized cross section times branching ratio [R·Br] of (10.8±1.4±1.2)×10−3, 6.6±1.5±0.9)×10−3 and (6.7±1.4±0.8)×10−3 respectively. The measured mass for the Λc was (2283.1±1.7±2.0) MeV/c2. A limit on the decay rates to Λπ+ is reported. The fragmentation function of the Λc was measured.

The diffractive photoproduction of J/psi mesons is measured with the H1 detector at the ep collider HERA using an integrated luminosity of 78 pb^-1. The differential cross section d sigma(gamma p -> J/psi Y) / d t is studied in the range 2 < |t| < 30 GeV^2, where t is the square of the four-momentum transferred at the proton vertex. The cross section is also presented as a function of the photon-proton centre-of-mass energy W in three t intervals, spanning the range 50 < W < 200 GeV. A fast rise of the cross section with W is observed for each t range and the slope for the effective linear Pomeron trajectory is measured to be alpha^\prime= -0.0135 \pm 0.0074 (stat.) \pm 0.0051 (syst.) GeV^-2. The measurements are compared with perturbative QCD models based on BFKL and DGLAP evolution. The data are found to be compatible with s-channel helicity conservation.

Using the ARGUS detector at the DORIS II e+e− storage ring we measured for the first time the τ neutrino helicity from a parity violating asymmetry in the τ decay into three charged pions. From the measured asymmetry we derived the normalized product of the axial and vector coupling constant 2gAgv/ (gA2 + gV2) = 1.14±0.34−0.170.34, which is in good agreement with the standard model prediction.

A search for single top quark production is performed in e^\pm p collisions at HERA. The search exploits data corresponding to an integrated luminosity of 118.3 pb^-1. A model for the anomalous production of top quarks in a flavour changing neutral current process involving a t-u-gamma coupling is investigated. Decays of top quarks into a b quark and a W boson are considered in the leptonic and the hadronic decay channels of the W. Both a cut-based analysis and a multivariate likelihood analysis are performed to discriminate anomalous top quark production from Standard Model background processes. In the leptonic channel, 5 events are found while 1.31 \pm 0.22 events are expected from the Standard Model background. In the hadronic channel, no excess above the expectation for Standard Model processes is found. These observations lead to a cross section \sigma (ep -> e t X) = 0.29 +0.15 -0.14 pb at \sqrt{s} = 319 GeV. Alternatively, assuming that the observed events are due to a statistical fluctuation, upper limits of 0.55 pb on the anomalous top production cross section and of 0.27 on the t-u-gamma coupling \kappa_{t-u-gamma} are established at the 95% confidence level.

Using the ARGUS detector at the e+e− storage ring DORIS II, we have measured the vτ energy spectrum in the decay π+π−π±vτ of τ leptons produced near s=10 GeV. From this energy spectrum, we derive an upper limit of m(vτ)<70MeVc2 at the 95% confidence level.

Measurements are presented of diffractive open charm production at HERA. The event topology is given by ep→eXY where the system X contains at least one charmed hadron and is well separated by a large rapidity gap from a leading low-mass proton remnant system Y. Two analysis techniques are used for the cross section measurements. In the first, the charm quark is tagged by the reconstruction of a D*±(2010) meson. This technique is used in deep-inelastic scattering (DIS) and photoproduction (γp). In the second, a method based on the displacement of tracks from the primary vertex is used to measure the open charm contribution to the inclusive diffractive cross section in DIS. The measurements are compared with next-to-leading order QCD predictions based on diffractive parton density functions previously obtained from a QCD analysis of the inclusive diffractive cross section at H1. A good agreement is observed in the full kinematic regime, which supports the validity of QCD factorization for open charm production in diffractive DIS and γp.

Photoproduction of 2-jet events is studied with the H1 detector at HERA. Parton cross sections are extracted from the data by an unfolding method using leading order parton-jet correlations of a QCD generator. The gluon distribution in the photon is derived in the fractional momentum range 0.04 ⩽ xγ ⩽ 1 at the average factorization scale 75 GeV2.

The inclusive jet cross section in photoproduction has been measured as a function of transverse energy and pseudorapidity using the H 1 detector at the HERA electron-proton collider. The results are compared with leading order QCD calculations.

The cross section of the charged current process e−p → ve + hadrons is measured at HERA for transverse momenta of the hadron system larger than 25 GeV. The size of the cross section exhibits the W propagator.

We present a study of Jψ meson production in collisions of 26.7 GeV electrons with 820 GeV protons, performed with the H1-detector at the HERA collider at DESY. The Jψ mesons are detected via their leptonic decays both to electrons and muons. Requiring exactly two particles in the detector, a cross section of σ(ep → JψX) = (8.8±2.0±2.2) nb is determined for 30 GeV ≤ Wγp ≤ 180 GeV and Q2 ≲ 4 GeV2. Using the flux of quasi-real photons with Q2 ≲ 4 GeV2, a total production cross section of σ(γp → J/ψX) = (56±13±14) nb is derived at an average Wγp=90 GeV. The distribution of the squared momentum transfer t from the proton to the Jψ can be fitted using an exponential exp(−b∥t∥) below a ∥t∥ of 0.75 GeV2 yielding a slope parameter of b = (4.7±1.9) GeV−2.

Using the ARGUS detector at the e+e− storage ring DORIS II at DESY, a search for penguin decays of B mesons involving b→s gluon has been performed. No evidence for the penguin mechanism was found and a number of upper limits are quoted.

A search for leptoquarks at HERA was performed in H1 using 1994 e+ p data corresponding to an integrated luminosity of about 3 pb−1. Single leptoquarks were searched for in direct positron-quark fusion processes taking into account possible decays into lepton-quark pairs of either the first, the second, or the third generation. No significant deviation from the Standard Model predictions is found in the various final states studied and mass dependent exclusion limits are derived on the Yukawa couplings of the leptoquarks. Compared with earlier results from an analysis of e− p data, exclusion limits are considerably improved for leptoquarks which could be produced via e+ -valence quark fusion. For leptoquarks with lepton flavour conserving couplings, masses up to 275 GeV (depending on the leptoquark type) are excluded for coupling values larger than 4πλem. For leptoquarks with lepton flavour violating couplings, masses up to 225 GeV are excluded for couplings with leptons of the second or third generation larger than 4πλem. Fourteen possible combinations of couplings are studied and stringent exclusion limits comparable or better than any existing direct or indirect limits are obtained for each leptoquark type.

A model-independent search for deviations from the Standard Model prediction is performed in e+p and e−p collisions at HERA using H1 data corresponding to an integrated luminosity of 117pb−1. For the first time all event topologies involving isolated electrons, photons, muons, neutrinos and jets with high transverse momenta are investigated in a single analysis. Events are assigned to exclusive classes according to their final state. A statistical algorithm is developed to search for deviations from the Standard Model in the distributions of the scalar sum of transverse momenta or invariant mass of final state particles and to quantify their significance. A good agreement with the Standard Model prediction is observed in most of the event classes. The most significant deviation is found for a topology containing an isolated muon, missing transverse momentum and a jet, consistent with a previously reported observation.

A search for events with a high-energy isolated electron or muon and missing transverse momentum has been performed at the electron–proton collider HERA using an integrated luminosity of 13.6 pb−1 in e−p scattering and 104.7 pb−1 in e+p scattering. Within the Standard Model such events are expected to be mainly due to W boson production with subsequent leptonic decay. In e−p interactions one event is observed in the electron channel and none in the muon channel, consistent with the expectation of the Standard Model. In the e+p data a total of 18 events are seen in the electron and muon channels compared to an expectation of 12.4±1.7 dominated by W production (9.4±1.6). Whilst the overall observed number of events is broadly in agreement with the number predicted by the Standard Model, there is an excess of events with transverse momentum of the hadronic system greater than 25 GeV with 10 events found compared to 2.9±0.5 expected. The results are used to determine the cross-section for events with an isolated electron or muon and missing transverse momentum.

The reaction e+p→e+X is studied with the H1 detector at Hera. The data cover momentum transfers Q2 between 200GeV2 and 30000GeV2 and correspond to an integrated luminosity of 35.6pb−1. The differential cross section dσ/dQ2 is compared to the Standard Model expectation for neutral current scattering and analysed to search for (ēe)(q̄q) contact interactions. No evidence for new phenomena is observed. The results are used to set limits on scales within models of electron–quark compositeness, quark form factors and the exchange of virtual heavy leptoquarks. A search for gravitational effects mediated through the exchange of virtual gravitons which propagate into large extra dimensions is presented.

Using the H1 detector at HERA, charged particle multiplicity distributions in deep inelastice + p scattering have been measured over a large kinematical region. The evolution withW andQ 2 of the multiplicity distribution and of the multiplicity moments in pseudorapidity domains of varying size is studied in the current fragmentation region of the hadronic centre-of-mass frame. The results are compared with data from fixed target lepton-nucleon interactions,e + e − annihilations and hadron-hadron collisions as well as with expectations from QCD based parton models. Fits to the Negative Binomial and Lognormal distributions are presented.

Properties of the hadronic final state in photoproduction events with large transverse energy are studied at the electron-proton collider HERA. Distributions of the transverse energy, jets and underlying event energy are compared to % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWexLMBb50ujb% qeguuDJXwAKbacfiGaf8hCaaNbaebacqWFWbaCaaa!3DB7! $$\bar pp$$ data and QCD calculations. The comparisons show that theγp events can be consistently described by QCD models including — in addition to the primary hard scattering process — interactions between the two beam remnants. The differential jet cross sectionsdσ/dE T jet anddσ/dη jet are measured.

Using the ARGUS detector at the e+e− storage ring DORIS II at DESY, we have studied semileptonic charmed meson decays through ф- and K∗0-electron correlations in continuum production. Evidence for the decay D−s→фe−v has been observed, with a branching ratio relative to the channel D−s→фπ− determined to be 0.57±0.15±0.15. The decay D−→K∗0e−v was also seen, with a value of 0.55±0.08±0.10 extracted for the branching ratio relative to the channel D−→K+π−π−. The ratio of the two measurements, after application of SU(3) corrections, implies a branching ratio for D−s→фπ− of (2.4±1.0)%.

A search for scalar and vector leptoquarks coupling to first generation fermions is performed using the e+p and e−p scattering data collected by the H1 experiment between 1994 and 2000. The data correspond to a total integrated luminosity of 117pb−1. No evidence for the direct or indirect production of such particles is found in data samples with a large transverse momentum final state electron or with large missing transverse momentum. Constraints on leptoquark models are established. For leptoquark couplings of electromagnetic strength, leptoquarks with masses up to 275–325GeV are ruled out at 95% confidence level. These limits improve and supercede earlier H1 limits based on subsamples of the data used here.

Using the ARGUS detector at the e+e− storage ring DORIS II, we have investigated the decay B0→D−ℓ+ν, where ℓ+ is e+ or μ+. The B0 mesons were produced in 150 000 ϒ(4S) decays. Assuming electron-muon universality we obtain a branching ratio BR(B0→D−e+ν)=BR(B0→D−μ+ν)=(1.8±0.6±0.5)%.

Dijet production in deep inelastic ep scattering is investigated in the region of low values of the Bjorken-variable x (10 -4 < x < 10 -2 ) and low photon virtualities Q 2 (5 < Q 2 < 100 GeV 2 ).The measured dijet cross sections are compared with perturbative QCD calculations in next-to-leading order.For most dijet variables studied, these calculations can provide a reasonable description of the data over the full phase space region covered, including the region of very low x.However, large discrepancies are observed for events with small separation in azimuth between the two highest transverse momentum jets.This region of phase space is described better by predictions based on the CCFM evolution equation, which incorporates k t factorized unintegrated parton distributions.A reasonable description is also obtained using the Color Dipole Model or models incorporating virtual photon structure.

Using the ARGUS detector at the DORIS II e+e− storage ring we have studied the electron and muon energy spectra in τ−→e−νν and τ−→μ−νν decays. The measured value of the Michel parameter, ρ=0.742±0.035±0.020, is in good agreement with a standard V-A coupling at the τ-ντ-W vertex. Pure V, A and V + A couplings are completely excluded by this measurement. Upper limits have been obtained for two-body tau decays, including final states with a Goldstone boson.

Using the ARGUS detector at the DORIS II e+e− storage ring we have measured direct photons from the decay ???(1S)→γgg. The ratio Rγ=Γ(???(1S)→γgg)/Γ(???(1S)→ggg)=(3.00±0.13±0.18)% has been determined, from which we deduce values of the strong coupling constant αs=0.225±0.011±0.019 and the QCD scale parameter ΛMS=115±17±28 MeV defined in the modified minimal-subtraction scheme. The shape of the measured spectrum clearly rules out the predictions of the lowest order QCD calculations.

Using the ARGUS detector at the e+e− storage ring DORIS II, we have observed the colour suppressed decay B → Jψ X, with a branching ratio of (1.37+0.6−0.5)% for the mixture of charged and neutral B's produced on the ϒ(4S). From the momentum distribution of the Jψ we conclude that Br(B → Jψ X) < 0.7% (90% CL), for recoil masses, mx, less than 1 GeV/c2.

The reaction γγ→ϱ+ϱ−→π+π−π0π0 has been studied with the ARGUS detector at the e+e− storage ring DORIS II at DESY. Near threshold, the cross section for this reaction is about four times smaller than for the reaction γγ→ϱ0ϱ0.

Inclusive D*± production is measured in deep-inelastic ep scattering at HERA with the H1 detector. In addition, the production of dijets in events with a D*± meson is investigated. The analysis covers values of photon virtuality 2 ≤ Q2 ≤ 100 GeV2 and of inelasticity 0.05≤y≤0.7. Differential cross sections are measured as a function of Q2 and x and of various D*± meson and jet observables. Within the experimental and theoretical uncertainties all measured cross sections are found to be adequately described by next-to-leading order (NLO) QCD calculations, based on the photon–gluon fusion process and DGLAP evolution, without the need for an additional resolved component of the photon beyond what is included at NLO. A reasonable description of the data is also achieved by a prediction based on the CCFM evolution of partons involving the kT-unintegrated gluon distribution of the proton.

The response of a sampling total absorption counter (STAC) to protons, neutrons, pions, and electrons with incident energies up to 60 GeV is described. A good linearity was observed, and for protons a resolution of ±6% at 60 GeV/c could be achieved. The absolute fwhm rises slowly with energy from 4.5 GeV/c at 10 GeV/c to 7.2 GeV/c at 60 GeV/c. The fraction of the energy deposited in the scintillator by incident π+ and e+ is on the average 9% and 50% higher than that deposited by protons.

Single particles and jets in deeply inelastic scattering at low x are measured with the H1 detector in the region away from the current jet and towards the proton remnant, known as the forward region. Hadronic final state measurements in this region are expected to be particularly sensitive to QCD evolution effects. Jet cross-sections are presented as a function of Bjorken-x for forward jets produced with a polar angle to the proton direction, theta, in the range 7 < theta < 20 degrees. Azimuthal correlations are studied between the forward jet and the scattered lepton. Charged and neutral single particle production in the forward region are measured as a function of Bjorken-x, in the range 5 < theta < 25 degrees, for particle transverse momenta larger than 1 GeV. QCD based Monte Carlo predictions and analytical calculations based on BFKL, CCFM and DGLAP evolution are compared to the data. Predictions based on the DGLAP approach fail to describe the data, except for those which allow for a resolved photon contribution.

Events with no hadronic energy flow in a large interval of pseudo-rapidity in the proton direction are observed in photon-proton interactions at an average centre of mass energy 〈√sγp〉 of 200 GeV These events are interpreted as photon diffractive dissociation. Evidence for hard scattering in photon diffractive dissociation is demonstrated using inclusive single particle spectra, thrust as a function of transverse energy, and the observation of jet production. The data can be described by a Monte Carlo calculation including hard photon-pomeron scattering.

Deep inelastic e p scattering data, taken with the H1 detector at HERA, are used to study the event shape variables thrust, jet broadening and jet mass in the current hemisphere of the Breit frame over a large range of momentum transfers Q between 7 GeV and 100 GeV. The data are compared with results from e+e− experiments. Using second order QCD calculations and an approach to relate hadronisation effects to power corrections an analysis of the Q dependences of the means of the event shape parameters is presented, from which both the power corrections and the strong coupling constant are determined without any assumption on fragmentation models. The power corrections of all event shape variables investigated follow a 1/Q behaviour and can be described by a common parameter α0.

A measurement of inclusive jet cross-sections in deep-inelastic ep scattering at HERA is presented based on data with an integrated luminosity of 21.1 pb−1. The measurement is performed for photon virtualities Q2 between 5 and 100 GeV2, differentially in Q2, in the jet transverse energy ET, in ET2/Q2 and in the pseudorapidity ηlab. With the renormalization scale μR=ET, perturbative QCD calculations in next-to-leading order (NLO) give a good description of the data in most of the phase space. Significant discrepancies are observed only for jets in the proton beam direction with ET below 20 GeV and Q2 below 20 GeV2. This corresponds to the region in which NLO corrections are largest and further improvement of the calculations is thus of particular interest.

We report a measurement of the production of antideuterons d in e+e− annihilation at centre-of-mass energies around 10 GeV using the ARGUS detector at the DORIS II storage ring. We observe an enhancement of d production in direct hadronic ϒ(1S) and ϒ(2S) resonance decays. From 21 events width a d candidate the inclusive cross section 1σdirhad · dσdp and the production rate of antideuterons are determined. A production rate of (6.0±2.0±0.6) × 10-5d per direct hadronic ϒ decay and a 90% CL upper limit of 1.7 × 10−5d per e+e−→qq continuum event are obtained. These results are related to antiproton production through a simple model.

Direct observations of the semileptonic decay of Λc+ in the decay channels Λc+→Λe+X and Λc+→Λμ+X have been made using the ARGUS detector at the DORIS II e+e− storage ring. The cross section times branching ratio were found to be σ(e+e−→Λc+X)·BR(Λc+→Λe+X)=4.20±1.28±0.71 pb and σ(e+e−→Λc+X)·BR(Λc+→Λμ+X)=3.91±2.02±0.90 pb.

Using the ARGUS detector at the DORIS II e+e− storage ring at DESY, we have obtained evidence for a new charmed-strange meson which decays into D*+K0. Its mass is observed to be 2535.9±0.6±2.0 MeV/c2 and its width to be less than 4.6 MeV/c2 at the 90% confidence level. No structure is observed at this mass in the D+K0 invariant mass spectrum, which suggests that an unnatural spin-parity is preferred.

Results on hyperon production are reported for data accumulated at 10 GeV centre-of-mass energy with the ARGUS detector. Signals for both the octet states Λ, Σ0 and Ξ− and the decuplet states Σ± (1385), Ξ0 (1530) and Ω− are observed 1 (references to a specific state are to be interpreted as also implying the charge conjugate state), some for the first time in e+e− annihilation. Baryon rates from γdir (1S) decays are enhanced by a factor of about 3 over the continuum.

We report the first direct observation of B meson decays into Λc+ baryons using the decay channel Λc+ → pK−π+. The product of branching ratios Br(B→Λc+X)·Br(Λc+→pK−π+ = (0.30±0.12±0.06)% is derived from an observed signal of 208±89 events. Using previous measurements of inclusive baryon rates we find a branching ratio for Λc+ → pK−π+ of (4.1±2.4)%. The measured Λc+ momentum spectrum indicates that the multi-particle final states dominate the decay B→Λc+X.

Using the deep inelastic e^+p and e^-p charged and neutral current scattering cross sections previously published, a combined electroweak and QCD analysis is performed to determine electroweak parameters accounting for their correlation with parton distributions. The data used have been collected by the H1 experiment in 1994-2000 and correspond to an integrated luminosity of 117.2 pb^{-1}. A measurement is obtained of the W propagator mass in charged current ep scattering. The weak mixing angle sin^2 theta_W is determined in the on-mass-shell renormalisation scheme. A first measurement at HERA is made of the light quark weak couplings to the Z^0 boson and a possible contribution of right-handed isospin components to the weak couplings is investigated.

A search for the single production of doubly-charged Higgs bosons H^{\pm \pm} in ep collisions is presented. The signal is searched for via the Higgs decays into a high mass pair of same charge leptons, one of them being an electron. The analysis uses up to 118 pb^{-1} of ep data collected by the H1 experiment at HERA. No evidence for doubly-charged Higgs production is observed and mass dependent upper limits are derived on the Yukawa couplings h_{el} of the Higgs boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only decays into an electron and a muon via a coupling of electromagnetic strength h_{e \mu} = \sqrt{4 \pi \alpha_{em}} = 0.3, a lower limit of 141 GeV on the H^{\pm\pm} mass is obtained at the 95% confidence level. For a doubly-charged Higgs decaying only into an electron and a tau and a coupling h_{e\tau} = 0.3, masses below 112 GeV are ruled out.

A measurement of charm and beauty photoproduction at the electron proton collider HERA is presented based on the simultaneous detection of a D*± meson and a muon. The correlation between the D* meson and the muon serves to separate the charm and beauty contributions and the analysis provides comparable sensitivity to both. The total and differential experimental cross sections are compared to LO and NLO QCD calculations. The measured charm cross section is in good agreement with QCD predictions including higher order effects while the beauty cross section is higher.

Data taken with positrons of different longitudinal polarisation states in collision with unpolarised protons at HERA are used to measure the total cross sections of the charged current process, e^+ p \to \bar{\nu}X, for negative four-momentum transfer squared Q^2 > 400 GeV^2 and inelasticity y<0.9. Together with the corresponding cross section obtained from the previously published unpolarised data, the polarisation dependence of the charged current cross section is measured for the first time at high Q^2 and found to be in agreement with the Standard Model prediction.

A measurement of charm and beauty dijet photoproduction cross sections at the ep collider HERA is presented. Events are selected with two or more jets of transverse momentum $p_t^{jet}_{1(2)}>11(8)$ GeV in the central range of pseudo-rapidity $-0.9<\eta^{jet}_{1(2)}<1.3$. The fractions of events containing charm and beauty quarks are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 central vertex detector. Differential dijet cross sections for charm and beauty, and their relative contributions to the flavour inclusive dijet photoproduction cross section, are measured as a function of the transverse momentum of the leading jet, the average pseudo-rapidity of the two jets and the observable $x_{\gamma}^{obs}$. Taking into account the theoretical uncertainties, the charm cross sections are consistent with a QCD calculation in next-to-leading order, while the predicted cross sections for beauty production are somewhat lower than the measurement.

The differential cross sections for neutron-proton elastic charge-exchange scattering have been measured with a two-arm technique for incident neutron momenta between 22 and 65 GeV/c and for values of the momentum transfer squared between 0.002 and 0.8 (GeV/c)2. The sharp forward peak observed previously at lower energies is also present at momenta up to 65 GeV/c; however the s dependence of the cross section is slowing down.