Deep inelastic scattering (DIS) events, selected from 1993 data taken by the H1 experiment at HERA, are studied in the Breit frame of reference. The fragmentation function of the quark is compared with those of e + e ? data. It is shown that certain aspects of the quarks emerging from within the proton in e ? p interactions are essentially the same as those of quarks pair-created from the vacuum in e + e ? annihilation. The measured area, peak position and width of the fragmentation function show that the kinematic evolution variable, equivalent to the e + e ? squared centre of mass energy, is in the Breit frame the invariant square of the four-momentum transfer. We comment on the extent to which we have evidence for coherence eeects in parton showers.

At the HERA electron-proton collider an event has been observed in the H1 detector which shows an isolated muon recoiling against a hadronic system, both of high transverse momentum. The event was registered in a total integrated luminosity of 4 pb ?1 .

A measurement of the inclusive cross section for the deep-inelastic scattering of positrons oo protons at HERA is presented at momentum transfers 8:5 Q 2 35 GeV 2 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 t to the structure function F 2 at lower y values, the contribution of F 2 to the measured cross section at high y is calculated and, by subtraction, the longitudinal structure function F L is determined for the rst time with an average value of

Events with no hadronic energy ow in a large interval of pseudo-rapidity in the proton direction are observed in photon-proton interactions at an average centre of mass energy < p s p > of 200 GeV. These events are interpreted as photon diirac-tive dissociation. Evidence for hard scattering in photon diiractive 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.

A measurement is presented, using data taken with the H1 detector at HERA, of the contribution of diiractive interactions to deep{inelastic electron{proton (ep) scattering in the kinematic range 8:5 < Q 2 < 50 GeV 2 , 2:410 ?4 < Bjorken{x < 0:0133, and 3:7 10 ?4 < x IP < 0:043. The diiractive contribution to the proton structure function F 2 (x; Q 2) is evaluated as a function of the appropriate deep{inelastic scattering variables x IP , Q 2 , and (= x=x IP) using a class of deep{inelastic ep scattering events with no hadronic energy ow in an interval of pseudo{rapidity adjacent to the proton beam direction. The dependence of this contribution on x IP is measured to be x ?n IP with n = 1:19 0:06(stat:) 0:07(syst:) independent of and Q 2 , which is consistent with both a diiractive interpretation and a factorisable ep diiractive cross section. A rst measurement of the deep{inelastic structure of the pomeron in the form of the Q 2 and dependences of a factorised structure function is presented. For all measured , this structure function is observed to be consistent with scale invariance.

An investigation of the hadronic nal state in diiractive and non{diiractive deep{inelastic electron{proton scattering at HERA is presented, where diiractive data are selected experimentally by demanding a large gap in pseudo{rapidity around the proton remnant direction. The transverse energy ow in the hadronic nal state is evaluated using a set of estimators which quantify topological properties. Using available Monte Carlo QCD calculations, it is demonstrated that the nal state in diiractive DIS exhibits the features expected if the interaction is interpreted as the scattering of an electron oo a current quark with associated eeects of perturbative QCD. A model in which deep{inelastic diiraction is taken to be the exchange of a pomeron with partonic structure is found to reproduce the measurements well. Models for deep{inelastic ep scattering, in which a sizeable diiractive contribution is present because of non{perturbative eeects in the production of the hadronic nal state, reproduce the general tendencies of the data but in all give a worse description.

An analysis is presented of scaling violations of the proton structure function F 2 (x; Q 2) measured with the H1 detector at HERA in the range of Bjorken x values between x = 310 ?4 and 10 ?2 for four-momentum transfers Q 2 larger than 8.7 GeV 2. The structure function F 2 (x; Q 2) is observed to rise linearly with lnQ 2. Under the assumption that the observed scaling violations at small x 0:01 are described correctly by perturbative QCD, an estimate is obtained of the gluon distribution function G(x; Q 2 o) at Q 2 o = 20 GeV 2 .

Evidence is presented using data taken with the H1 detector at HERA for a class of deep inelastic electron{proton scattering (DIS) events (5 < Q 2 < 120 GeV 2) at low Bjorken-x (10 ?4 < x < 10 ?2) which have almost no hadronic energy ow in a large interval of pseudo-rapidity around the proton remnant direction and which cannot be attributed to our present understanding of DIS and uctuations in-nal 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 400MeV forward of laboratory pseudo-rapidity max = 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.

ISSN 0418-9833 August 1994 A Search for Heavy Leptons at HERA H1 Collaboration Abstract: A search for direct production of new leptons in the mass range from 10 GeV up to 225 GeV is presented by the H1 experiment at HERA. The data were obtained during 1993 and correspond to an integrated luminosity of 528 nb 1. The search includes heavy lepton decays to nal states e ( ) and e ( )W , e ( )Z with the subsequent decay of the W and Z bosons into jets or lepton pairs. No evidence was found for the production of new massive electrons or neutrinos in any of the decay channels. Rejection limits for excited electrons and neutrinos are derived.

The cross section for the elastic photoproduction of ρ mesons (γp → ρp) has been measured with the H1 detector at HERA for two average photon-proton centreof-mass energies of 55 and 187 GeV. The lower energy point was measured by observing directly the ρ 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. The ρ 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. S. Aid, V. Andreev, B. Andrieu, R.-D. Appuhn, M. Arpagaus, A. Babaev, J. Bähr, J. Bán, Y. Ban, P. Baranov, E. Barrelet, R. Barschke, W. Bartel, M. Barth, U. Bassler, H.P. Beck, H.-J. Behrend, A. Belousov, Ch. Berger, G. Bernardi, R. Bernet, G. Bertrand-Coremans, M. Besançon, R. Beyer, P. Biddulph, P. Bispham, J.C. Bizot, V. Blobel, K. Borras, F. Botterweck, V. Boudry, A. Braemer, W. Braunschweig, V. Brisson, D. Bruncko, C. Brune, R. Buchholz, L. Büngener, J. Bürger, F.W. Büsser, A. Buniatian, S. Burke, M.J. Burton, G. Buschhorn, A.J. Campbell, T. Carli, F. Charles, M. Charlet, D. Clarke, A.B. Clegg, B. Clerbaux, S. Cocks, J.G. Contreras, C. Cormack, J.A. Coughlan, A. Courau, M.-C. Cousinou, Ch. Coutures, G. Cozzika, L. Criegee, D.G. Cussans, J. Cvach, S. Dagoret, J.B. Dainton, W.D. Dau, K. Daum, M. David, C.L. Davis, B. Delcourt, A. De Roeck, E.A. De Wolf, M. Dirkmann, P. Dixon, P. Di Nezza, W. Dlugosz, C. Dollfus, J.D. Dowell, H.B. Dreis, A. Droutskoi, D. Düllmann, O. Dünger, H. Duhm, J. Ebert, T.R. Ebert, G. Eckerlin, V. Efremenko, S. Egli, R. Eichler, F. Eisele, E. Eisenhandler, R.J. Ellison, E. Elsen, M. Erdmann, W. Erdmann, E. Evrard, A.B. Fahr, L. Favart, A. Fedotov, D. Feeken, R. Felst, J. Feltesse, J. Ferencei, F. Ferrarotto, K. Flamm, M. Fleischer, M. Flieser, G. Flügge, A. Fomenko, B. Fominykh, M. Forbush, J. Formánek, J.M. Foster, G. Franke, E. Fretwurst, E. Gabathuler, K. Gabathuler, F. Gaede, J. Garvey, J. Gayler, M. Gebauer, A. Gellrich, H. Genzel, R. Gerhards, A. Glazov, U. Goerlach, L. Goerlich, N. Gogitidze, M. Goldberg, D. Goldner, K. Golec-Biernat, B. Gonzalez-Pineiro, I. Gorelov, C. Grab, H. Grässler, R. Grässler, T. Greenshaw, R. Griffiths, G. Grindhammer, A. Gruber, C. Gruber, J. Haack, D. Haidt, L. Hajduk, M. Hampel, M. Hapke, W.J. Haynes, G. Heinzelmann, R.C.W. Henderson, H. Henschel, I. Herynek, M.F. Hess, W. Hildesheim, K.H. Hiller, C.D. Hilton, J. Hladký, K.C. Hoeger, M. Höppner, D. Hoffmann, T. Holtom, R. Horisberger, V.L. Hudgson, M. Hütte, H. Hufnagel, M. Ibbotson, H. Itterbeck, M.-A. Jabiol, A. Jacholkowska, C. Jacobsson, M. Jaffre, J. Janoth, T. Jansen, L. Jönsson, K. Johannsen, D.P. Johnson, L. Johnson, H. Jung, P.I.P. Kalmus, M. Kander, D. Kant, R. Kaschowitz, U. Kathage, J. Katzy, H.H. Kaufmann, S. Kazarian, I.R. Kenyon, S. Kermiche, C. Keuker, C. Kiesling, M. Klein, C. Kleinwort, G. Knies, W. Ko, T. Köhler, J.H. Köhne, H. Kolanoski, F. Kole, S.D. Kolya, V. Korbel, M. Korn, P. Kostka, S.K. Kotelnikov, T. Krämerkämper, M.W. Krasny, H. Krehbiel, D. Krücker, U. Krüger, U. Krüner-Marquis, H. Küster, M. Kuhlen, T. Kurča, J. Kurzhöfer, D. Lacour, B. Laforge, F. Lamarche, R. Lander, M.P.J. Landon, W. Lange, U. Langenegger, P. Lanius, J.-F. Laporte, A. Lebedev, F. Lehner, C. Leverenz, S. Levonian, Ch. Ley, G. Lindström, M. Lindstroem, J. Link, F. Linsel, J. Lipinski, B. List, G. Lobo, P. Loch, H. Lohmander, J.W. Lomas, G.C. Lopez, V. Lubimov, D. Lüke, N. Magnussen, E. Malinovski, S. Mani, R. Maraček, P. Marage, J. Marks, R. Marshall, J. Martens, G. Martin, R. Martin, H.-U. Martyn, J. Martyniak, S. Masson, T. Mavroidis, S.J. Maxfield, S.J. McMahon, A. Mehta, K. Meier, T. Merz, A. Meyer, A. Meyer, H. Meyer, J. Meyer, P.-O. Meyer, A. Migliori, S. Mikocki, D. Milstead, J. Moeck, F. Moreau, J.V. Morris,

Results obtained by the H1 Collaboration in deep-inelastic e+p scattering up to 4-momentum transfers Q2 up to 35000 GeV2 are presented. At Q2 > 15000 GeV2 12 events are observed in neutral current (NC) interactions, where only 4.71±0.76 events are expected. In charged current (CC) interactions in the same range of Q2 4 events are observed, while the standard expectation is 1.77±0.87 events.

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 = 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.

Measurements of ep scattering with squared 4{momentum transfer Q 2 up to 35000 GeV 2 are compared with the expectation of the standard deep-inelastic model of lepton{nucleon scattering (DIS). For Q 2 > 15000 GeV 2 , N obs = 12 neutral current candidate events are observed where the expectation is N DIS = 4:71 0:76 events. In the same Q 2 range, N obs = 4 charged current candidates are observed where the expectation is N DIS = 1:77 0:87 events. The probability P(N N obs) that the DIS model signal N uctuates to N N obs in a random set of experiments is 6 10 ?3 for neutral current and 0:14 for charged current. The diierence in the observed and expected number of Neutral Current events is mostly due to events at large masses M = p x s in which the positron is backscattered at large y = Q 2 =M 2 .

We present a search for excited electrons, neutrinos and quarks using the H1 detector at the ep collider HERA, based on data taken in 1994 with an integrated luminosity of 2.75 pb(-1). Radiative decays of excited quarks and neutrinos have been investigated as well as decays of excited electrons into all possible electroweak gauge bosons. No evidence for new particle production is found and exclusion limits are derived.

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 study is presented of the process γp → XY, where there is a large rapidity gap between the systems X and Y. Measurements are made of the differential cross section as a function of the invariant mass M X of the system produced at the photon vertex. Results are presented at centre of mass energies of 〈W〉 = 187 GeV and 〈W〉 =231 GeV, both where the proton dominantly remains intact and, for the first time, where it dissociates. Both the centre of mass energy and the \(M_X^2\) dependence of HERA data and those from a fixed target experiment may simultaneously be described in a triple-Regge model. The low mass photon dissociation process is found to be dominated by diffraction, though a sizable subleading contribution is present at larger masses. The pomeron intercept is extracted and found to be αP(0) = 1.068 ± 0.016 (stat.) ± 0.022 (syst.) ± 0.041 (model), in good agreement with values obtained from total and elastic hadronic and photoproduction cross sections. The diffractive contribution to the process γp → Xp with \(M_X^2/{W^2} < 0.05\) is measured to be 22.2 ± 0.6 (stat.) ± 2.6 (syst.) ± 1.7 (model)% of the total γp cross section at 〈W〉 = 187 GeV.

Transverse momentum spectra of charged particles produced in deep inelastic scattering are measured as a function of the kinematic variables x and Q(2) 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.

A study is presented of the process p ! XY , where there is a large rapidity gap between the systems X and Y. Measurements are made of the diierential cross section as a function of the invariant mass M X of the system produced at the photon vertex. Results are presented at centre of mass energies of hWi = 187 GeV and hWi = 231 GeV, both where the proton dominantly remains intact and, for the rst time, where it dissociates. Both the centre of mass energy and the M 2 X dependence of HERA data and those from a xed target experiment may simultaneously be described in a triple-Regge model. The low mass photon dissociation process is found to be dominated by diiraction, though a sizable subleading contribution is present at larger masses. The pomeron intercept is extracted and found to be IP (0) = 1:068 0:016 (stat:) 0:022 (syst:) 0:041 (model), in good agreement with values obtained from total and elastic hadronic and photoproduction cross sections. The diiractive contribution to the process p ! Xp with M 2 X =W 2 < 0:05 is measured to be 22:2 0:6 (stat:) 2:6 (syst:) 1:7 (model) % of the total p cross section at hWi = 187 GeV.

The scale dependence of the evolution of photoproduction cross sections with the photon-proton centre of mass energy W is studied using low Q^2 < 0.01 GeV^2 e^+p interactions collected by the H1 experiment at HERA. The value of the largest transverse momentum of a charged particle in the photon fragmentation region is used to define the hard scale. The slope of the W dependence of the cross section is observed to increase steeply with increasing transverse momentum. The result is compared to measurements of the Q^2 evolution of the W dependence of the virtual photon-proton cross section. Interpretations in terms of QCD and in terms of Regge phenomenology are discussed.

The Q2 dependence and the total cross sections for charged and neutral current processes are measured in e±p reactions for transverse momenta of the outgoing lepton larger than 25 GeV. Comparable size of cross sections for the neutral current process and for the weak charged current process are observed above Q2 ∥ 5000 GeV2. Using the shape and magnitude of the charged current cross section we determine a propagator mass of mW = 84−7+10 GeV.