The Forward Proton Spectrometer of the H1 Experiment



Pot-View

Where the FPS is:

Since 1995 the H1 experiment at HERA is operating a Forward Proton Spectrometer (FPS). Scattered protons are detected in stations at 81 and 90 m behind the interaction point. The FPS has been extended with stations at 80 and 63 m starting to operate in 1997. In all stations the protons are detected with scintillating fiber hodoscopes.
Each station consists of a moveable vacuum section, a so called Roman Pot, in which the detector elements are mounted. Thus the detector can be brought a few milimeters close to the proton beam. During injection and acceleration the Roman Pots are retracted.Otherwise they would cut into the machine aperture.


What the FPS detects:

At the HERA collider facility a class of events is observed in deep inelastic electron proton scattering and photoproduction, which is characterized by the absence of secondary particles in a region of phase space between the outgoing proton debris and the target jet. Deep inelastic high energy e-p interactions (DIS) predominantly proceed by the exchange of a virtual vector boson ( , W or Z°) between the incident electron and a constituent quark or gluon in the proton. The rest of the proton is essentially unaffected by the interaction and continues along the flight path of the incoming proton.
In about one quarter of the neutral and charged current deep inelastic interactions the protons remnants fragment into final states containing an energetic forward going proton at forward angles. In general these leading protons escape through the beam pipe and are not detected in the central HERA detectors (take a look at the intersection of the H1 detector with the beampipe on the H1 homepage). With the FPS forward scattered protons at angles in the order of mrad are detectable. These protons are recorded and their energy is measured. Further kinematical constraints can thus be applied and additional information on deep inelastic scattering final states is gained.


Roman Pots: These moveable vacuum sections were first used at the Intersecting Storage Rings (ISR) at CERN by a collaboration, in which a group from the Institutio Superiore di Sanità in Rome played an important role.



Move back to FPS homepage or H1 Home Page or DESY Home Page