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HERA E-P Scattering Events Observed in the H1detector

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HERA E-P Scattering Events Observed in the H1detector HERA e-p scattering events observed in the H1Detector H1 Events Joachim Meyer DESY 2005 1 The idea The realisation The Physics The events H1 Events Joachim Meyer DESY 2005 2 What we think what happens, when we scatter electrons on protons at HERA Hadrons W Proton Hadrons or neutrino H1 Events Joachim Meyer DESY 2005 3 The H1 detector at the e-p storage ring HERA p Tracking chambers Calorimeters Forward muon Instrumented iron system detector e H1 Events Joachim Meyer DESY 2005 4 Calorimeter H1 Events Joachim Meyer DESY 2005 5 Principle of particle identification H1 Events Joachim Meyer DESY 2005 6 Principle of particle identification H1 Events Joachim Meyer DESY 2005 7 An event display : What do we see ? R-Z view : Hadrons Hadronic calorimeter Hits and reconstructed tracks in tracker e p e-p interaction Electromagnetic calorimeter e point Energy depositions Scattered Electron in calorimeter H1 Events Joachim Meyer DESY 2005 8 ' Same event in radial view : ep → e X Hadronic calorimeter X Hits and reconstructed tracks in tracker e Energydepositions in calorimeter H1 Events Joachim Meyer DESY 2005 9 The hits (fired wires) in the tracking chambers Hits = Signals recorded on sense wires Gas volumen with sense wires at HV H1 Events Joachim Meyer DESY 2005 10 ..and the result of the pattern recognition program trying to combine the hits to tracks (red lines) : Hadrons Tracks bend in magnetic field : momentum determination Electron Central tracking chambers H1 Events Joachim Meyer DESY 2005 11 .. and the same procedure in R-Z view : Hadrons Electron Central tracking chambers H1 Events Joachim Meyer DESY 2005 12 another event : Here you see the CJC hits including the ‘mirror hits’ (ambiguity not Curling tracks resolved) Mirror tracks track H1 Events Joachim Meyer DESY 2005 13 and here the tracks found by the pattern regognition program successfully fitted to the event vertex Note : The curling tracks seen on the last picture are not vertex-fitted H1 Events Joachim Meyer DESY 2005 14 Event : Combined view (R-z, R-Phi , calorimeter energies) Transverse ' view ep → e X (R-Phi) e e X Calorimeter energies X Side view (R-z) Electron and hadronic system X balanced in transverse momentum H1 Events Joachim Meyer DESY 2005 15 A very simple event : ep → eγ ( p) Photon Proton leaves unseen down the beam pipe Electron H1 Events Joachim Meyer DESY 2005 16 Here an electron and two photons are recorded Electrons ‘easily’ radiate photons H1 Events Joachim Meyer DESY 2005 17 Photons tend to convert to e+ e- pairs in material ep → eγX......γ → e+e− Photon Photon e X e+ e- Pair e Chamber material Photon H1 Events Joachim Meyer DESY 2005 18 This looks like a di-electron, but is not. A photon converted to a small angle e+ e- pair within the beam pipe ep → eγ ( p) γ → e+e− e e Conversion point e+e− − pair e+e− − pair H1 Events Joachim Meyer DESY 2005 19 Another ‘simple’ event : A elastic dimuon production ep → eµ + µ − ( p) MUON IRON Muons penetrate thick materials ! MUON H1 Events Joachim Meyer DESY 2005 20 An inelastic dimuon production without visible scattered electron ep → (e)µ + µ − X + µ µ + X µ − X µ − H1 Events Joachim Meyer DESY 2005 21 Another inelastic dimuon production without visible scattered electron The muons are low energetic and don’t read the iron,they are ‘mips’ in calorimeter − + µ − µ µ µ + X X ep → (e)µ + µ − X H1 Events Joachim Meyer DESY 2005 22 Another inelastic dimuon production without visible scattered electron One muon identified in calorimeter, the other in the iron system ep → (e)µ + µ − X µ + µ + X X µ − µ − H1 Events Joachim Meyer DESY 2005 23 In the ‘forward direction’ muons are measured by the ‘Forward Toroid Muon Detector’ µ2 µ1 µ1 µ2 Forward Toroid Muon Detector H1 Events Joachim Meyer DESY 2005 24 Here it is very visible how electron, muon and photon are distinguished µ γ µ γ e e H1 Events Joachim Meyer DESY 2005 25 No detector is perfect : Here the scattered electron enters a nonsensitive region (Phi-crack) of the electromagnetic calorimeter Such an effect has to be recognized in the physics analysis ! e e Electron penetrates into hadronic part of calorimeter Phi-crack in em. calorimeter H1 Events Joachim Meyer DESY 2005 26 Here a photon converts and the e+ e- pair enters an insensitive ep → eγX region of the em. calorimeter (z- and Phi-cracks) γ → e+e− Phi-crack e e z-crack Converted photon H1 Events Joachim Meyer DESY 2005 27 Muons also come from the sky …… This is BACKGROUND, which we do not like ! H1 Events Joachim Meyer DESY 2005 28 Interaction of cosmic primaries create showers in the atmosphere, and multimuons reach us here H1 Events Joachim Meyer DESY 2005 29 Cosmic dimuon seen in calorimeter and central track detector H1 Events Joachim Meyer DESY 2005 30 Another cosmic dimuon … µ µ wires in iron system pads in iron system Muon radiates H1 Events Joachim Meyer DESY 2005 31 …and it can be even more fierce …. H1 Events Joachim Meyer DESY 2005 32 Muons interact rarely, but they do Hit pattern in the central track detector (transverse view) H1 Events Joachim Meyer DESY 2005 33 Here a cosmic muon radiates a photon which gets absorbed in the calorimeter. The muon then exits the detector. The radiated energy deposition H1 Events Joachim Meyer DESY 2005 34 A HERA ep event overlayed with a cosmic muon Such an effect has to be recognized in the physics analysis ! ep event Cosmic muon H1 Events Joachim Meyer DESY 2005 35 There is not only background from cosmics but also from the Proton beam interacting with the restgas P - beam Event vertex is e-p event vertex here should be here H1 Events Joachim Meyer DESY 2005 36 Scattering of the HERA-proton on a nucleus of the restgas. The nucleus dissociates into lots of protons (positive tracks) and neutrons H1 Events Joachim Meyer DESY 2005 37 Another kind of beam-related background : Protons lost in the ring create showers and muons from decaying pions accompany the beam and may be visible in the detector Beamhalo muons H1 Events Joachim Meyer DESY 2005 38 Here a NC event is overlayed by a beam halo muon Such an effect has to be recognized in the physics analysis ! µ µ H1 Events Joachim Meyer DESY 2005 39 Back to HERA -e-p scattering events : A very forward Dimuon event These muons are decay products of the famous J/Psi particle ep → (e)( p)J / Ψ Muons bent in the magnetic field of the J / Ψ → µ + µ − forward toroid magnet H1 Events Joachim Meyer DESY 2005 40 Another event where the J/Psi particle decays into two muons (this time ‘backward’) Muon Iron ep → (e)( p)J / Ψ J / Ψ → µ + µ − Muon H1 Events Joachim Meyer DESY 2005 41 The J / Ψ particle has a sister the Ψ′ Central Tracker µ + − µ + π π + − π − µ ep → e( p)Ψ′ e Ψ' → Ψπ +π − π + µ − Backward calorimeter Ψ → µ + µ − e H1 Events Joachim Meyer DESY 2005 42 Most events are much more complicated : Very high track multiplicity Small visible energy in calorimeter H1 Events Joachim Meyer DESY 2005 43 The Central Silicon Detector (CST) measures hits very precisely (10 micrometer). search for secondary vertices of heavy quark (charm,bottom) decays : Zoom in …. H1 Central Tracker Secondary Vertex CST CST Reconstruction H1 Events Joachim Meyer DESY 2005 44 Another event with detailed track measurement in the CST CST : R-z view CST : R-Phi view H1 Events Joachim Meyer DESY 2005 45 Tracks seen in the Forward Silicon Track Detector (FST) FST Forward Direction CST CJC 1 CJC 2 The FST allows to cover very small forward angles H1 Events Joachim Meyer DESY 2005 46 Often there is activity in forward direction around the beam pipe : that are the ‘left overs’ of the ‘broken’ proton Electron scattered under small angle into backward calorimeter H1 Events Joachim Meyer DESY 2005 47 But in 10% of all cases there is no forward activity : the proton stays intact, and disappears down the beam pipe e-tagger p e e-tagger H1 Events Joachim Meyer DESY 2005 48 ' Back to the Deep-Inelastic-Electron-Proton-Scattering (DIS) ep → e X X X e Incident e 27 GeV e Scattered e The electron is scattered back by 160 degree and got an energy of 300 GeV. Very virulent scattering ! H1 Events Joachim Meyer DESY 2005 49 ' .and here its even more virulent. ep → e X 2 2 The squared momentum transfer is Q ≈ 50000GeV , this corresponds to a space resolution of ∆x ≈10−18 m e Notice : The hadronic system X e Jet is a well collimated bundle of particles. This is called JET Jets are the ‘footprints’ of the quarks and gluons Jet H1 Events Joachim Meyer DESY 2005 50 ' A NC-DIS event with two jets ep → e Jet1Jet2 Jet2 e Jet2 e Jet1 e J2 Jet1 J1 H1 Events Joachim Meyer DESY 2005 51 Here the ‘forward scattered’ electron radiates a very energetic photon ep → e' Xγ electron photon electron photon electron photon H1 Events Joachim Meyer DESY 2005 52 In general the photon is ‘near’ to the electron. Here both created a single electromagnetic shower in the calorimeter, but can be resolved in the tracker combined electromagnetic shower in calorimeter converted photon tracks electron-track H1 Events Joachim Meyer DESY 2005 53 ' Another ep → e Xγ event, but here the scatted electron and photon are far apart It is likely that here the photon is of hadronic origin (prompt photon) X e γ H1 Events Joachim Meyer DESY 2005 54 ' There is also a chance that two photons are radiated : ep → e Xγ 1γ 2 γ e e 2 γ 2 γ 1 γ 1 H1 Events Joachim Meyer DESY 2005 55 In this NC event a muon is produced within the hadronic final state X ep → e' Xµ µ µ X X e e H1 Events Joachim Meyer DESY 2005 56 A new event class : In this event the hadrons X are NOT balanced by an electron ! ep →νX The Neutrino does not leave a trace in the detector X Hadrons X This is a different type X of DIS event It is pure weak interaction.
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