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E. Sauvan
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We present a search for excited neutrinos and electrons using all data collected by the H1 experiment at HERA at a center-of-mass energy of 320 GeV with an integrated luminosity of up to 435 pb$^{-1}$. No evidence for excited neutrino or electron production is found. Mass dependent exclusion limits are determined for the ratio of the coupling to the compositeness scale, $f/{Lambda}$. These limits greatly extend the excluded region to higher masses than has been possible in previous searches.
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Recent results on searches for new particles at the electron-proton collider HERA are reported. Based on roughly 100pb-1 of e^+p data and 16pb-1 of e^-p data per experiment, taken in the years 1994-2000, the H1 and ZEUS collaborations have derived new exclusion limits for the direct production of excited fermion states and leptoquarks. The latter are searched for in different decay channels, including lepton-flavor violating decays. The production of R_P-violating squarks followed by leptoquark-like decays to lepton and quark is studied, as are cascade decays yielding multi-jet plus lepton signatures. New limits from indirect searches are also reported. Several of the searches obtain sensitivities of the same order or exceeding those of other experiments, indicating the substantial discovery potential of future HERA running.
Recent results on searches for new particles at the electron-proton collider HERA are reported. Based on roughly 40pb-1 of e^+p data taken in the years 1994-1997, the H1 and ZEUS collaborations have derived new exclusion limits for the direct production of excited fermion states and of leptoquarks in different decay channels, including lepton-flavor violating decays. The results of searches for contact interactions further constrain the parameter space for such particles and their couplings in the high-mass regime, where direct production is kinematically prohibited. Also preliminary analyses of the e^-p data taken in 1998 and 1999 do not find signals of new physics.
The forward proton spectrometer is part of the H1 detector at the HERA collider. Protons with energies above 500 GeV and polar angles below 1 mrad can be detected by this spectrometer. The main detector components are scintillating fiber detectors read out by position-sensitive photo-multipliers. These detectors are housed in so-called Roman Pots which allow them to be moved close to the circulating proton beam. Four Roman Pot stations are located at distances between 60 m and 90 m from the interaction point.
Measures taken to extend the acceptance of the H1 detector at HERA for photoproduction events are described. These will enable the measurement of electrons scattered in events in the high y range 0.85 < y < 0.95 in the 1998 and 1999 HERA run period. The improvement is achieved by the installation of an electromagnetic calorimeter, the ET8, in the HERA tunnel close to the electron beam line 8 m downstream of the H1 interaction point in the electron direction. The ET8 will allow the study of tagged gamma p interactions at centre-of-mass energies significantly higher than those previously attainable. The calorimeter design and expected performance are discussed, as are results obtained using a prototype placed as close as possible to the position of the ET8 during the 1996 and 1997 HERA running.
New measurements of the reduced cross section $sigma_r^{D(3)}$ for the diffractive process $ep to eXY$ in the kinematic domain $12 leq Q^2 leq 90$ GeV$^2$, $0.01 leq beta leq 0.65$ and $xpom<0.1$ are presented. Data events recorded by the H1 detector during the years 1999--2000 and 2004 have been used, corresponding to a total integrated luminosity of 68 pb$^{-1}$. The measurements are derived in the same range as previous H1 data, namely $M_Y < 1.6$ GeV and $|t| < 1.0$ GeV$^2$. Two different analysis methods, rapidity gap and $M_X$, are used and similar results are obtained in the kinematic domain of overlap. Finally, together with previous data, the diffractive structure function measurements are analysed with a model based on the dipole formulation of diffractive scattering. It is found to give a very good description of the data over the whole kinematic range.
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