Searches for New Physics by the H1 Experiment at HERAPresented at the PIC 2007 conference, on behalf of the H1 Collaboration

Searches for New Physics by the H1 Experiment at HERAthanks: Presented at the PIC 2007 conference, on behalf of the H1 Collaboration

trinh thi nguyet
Centre de Physique des Particules de Marseille, Marseille, 13288 cedex 09, France

The high energy program of the HERA ep collider ended in March 2007, where data equivalent to an integrated luminosity of  fb has been collected by the H1 experiment. In this context, some of the most recent results from H1 about searches for new phenomena are presented.

The direct observation of excited states of fermions () as a natural consequence of the compositeness models [1, 2] via their decay into a fermion and a gauge boson would be an evidence for a new level of substructure. New H1 results about the search for excited leptons () make use of a total luminosity of up to  pb. In the absence of a signal,  CL upper limits on the coupling are derived as a function of the excited lepton mass as presented in figure 1. The new limits extend at high masses previous bounds reached at LEP and Tevatron colliders.

Figure 1: Limits at 95% CL on the coupling constants for excited neutrino (left) and electron (right).

Events containing an isolated electron or muon, large missing transverse momentum and an high transverse momentum () hadronic system have been investigated by the H1 Collaboration [3]. The full HERA data corresponding to a luminosity of  pb are used. The main SM contribution to such a signature comes from the production of a real boson with subsequent leptonic decay. Figure 2 shows the observed distributions separately for the and data together with the corresponding SM expectations. For   GeV, data events are observed compared to a SM prediction of . In this region, an excess of data events is observed, equivalent to a fluctuation of order . The observation in the data is consistent with the SM expectation.

Figure 2: Distributions of the transverse momentum of the hadronic system for the electron and muon channels combined in the  (left) and  (right) data.

A model independent general search for deviations from the SM has been performed by H1 using all HERA II data. Following [4], all final states containing at least two objects () with  GeV in the central region of the detector are investigated. Figure 3 shows the event yield subdivided into event classes for the data and SM expectation for and , respectively. A general good agreement is observed between the data and the SM prediction. A statistical algorithm is used to quantify the significance of possible deviations from the SM. The largest deviation is observed in data in the -- channel, which corresponds to the topology of isolated lepton events.

Figure 3: The data and the SM expectation for all event classes with observed data events or a SM expectation greater than 1 event.


  • [1] H. Harari, Phys. Rept. 104 (1984) 159.
  • [2] F. Boudjema, A. Djouadi and J. L. Kneur, Z. Phys. C 57 (1993) 425
  • [3] H1 Collaboration, contributed paper to The International Europhysics Conference on High Energy Physics, EPS07, Manchester 2007, Abstract 228.
  • [4] H1 Collaboration, A. Aktas et al., Phys. Lett. B 602 (2004) 14.
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