HERA e-p scattering events observed in the H1Detectorjmeyer/H1-event.tutorial.pdf · CJC 1 CJC 2...
Transcript of HERA e-p scattering events observed in the H1Detectorjmeyer/H1-event.tutorial.pdf · CJC 1 CJC 2...
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HERA e-p scattering events observed in the H1Detector
H1 Events Joachim Meyer DESY 2005 1
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H1 Events Joachim Meyer DESY 2005 2
The idea The realisation
The eventsThe Physics
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What we think what happens, when we scatter electrons on protons at HERA
Hadrons
Hadrons
or neutrino
ProtonW
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pThe H1 detector at the e-p storage ring HERA
Tracking chambers
Calorimeters
Instrumented iron systemForward muondetector
e
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Calorimeter
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Principle of particle identification
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Principle of particle identification
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An event display : What do we see ?
Energy depositionsin calorimeter
Hits and reconstructedtracks in tracker
R-Z view :
e-p interactionpoint
Hadronic calorimeter
Electromagnetic calorimetere
Hadrons
Scattered Electron
e p
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H1 Events Joachim Meyer DESY 2005 9
Same event in radial view :
Energydepositionsin calorimeter
Hits and reconstructedtracks in tracker
Hadronic calorimeter
Xeep '→
e
X
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The hits (fired wires) in the tracking chambers
Gas volumen withsense wires at HV
Hits = Signalsrecorded on sense wires
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..and the result of the pattern recognition program trying to combinethe hits to tracks (red lines) :
Tracks bend inmagnetic field :momentum determination
Electron
Hadrons
Central tracking chambersH1 Events Joachim Meyer DESY 2005 11
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H1 Events Joachim Meyer DESY 2005 12
.. and the same procedure in R-Z view :
Electron
Hadrons
Central tracking chambers
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another event :
Here you see the CJC hits includingthe ‘mirror hits’(ambiguity notresolved)
Curlingtracks
H1 Events Joachim Meyer DESY 2005 13track
Mirror tracks
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and here the tracks found by the pattern regognition programsuccessfully fitted to the event vertex
Note :The curling tracks seenon the last picture arenot vertex-fitted
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Side view(R-z)
Transverseview(R-Phi)
Calorimeterenergies
Xeep '→
Event : Combined view (R-z, R-Phi , calorimeter energies)
Electron and hadronic system X balanced in transverse momentum
e
e
X
X
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A very simple event :
)( peep γ→
Electron
Photon
Proton leavesunseen down thebeam pipe
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Here an electron and two photons are recorded
Electrons ‘easily’radiate photons
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H1 Events Joachim Meyer DESY 2005 18
Photons tend to convert to e+ e- pairs in material
Photon
Chamber material
e+ e- Pair
−+→→ eeXeep γγ ......
e
PhotonX
e
Photon
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This looks like a di-electron, but is not. A photon converted to a small angle e+ e- pair within the beam pipe
e
e
pairee −−+pairee −−+
)( peep γ→
−+→ eeγ
Conversion point
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H1 Events Joachim Meyer DESY 2005 20
Another ‘simple’ event : A elastic dimuon production
)( peep −+→ µµ
Muons penetratethick materials !
MUON
MUON
IRON
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An inelastic dimuon production without visible scattered electron
Xeep −+→ µµ)(
X
X
+µ+µ
−µ−µ
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Another inelastic dimuon production without visible scattered electron
The muons are low energetic and don’t read the iron,they are ‘mips’ in calorimeter
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Xeep −+→ µµ)(
XX
+µ+µ−µ
−µ
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Another inelastic dimuon production without visible scattered electron
Xeep −+→ µµ)(
XX
+µ+µ
−µ−µ
One muon identified in calorimeter, the other in the iron system
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In the ‘forward direction’ muons are measured by the ‘Forward Toroid Muon Detector’
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Forward ToroidMuon Detector
2µ
2µ1µ
1µ
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Here it is very visible how electron, muon and photon are distinguished
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ee
γγ µ
µ
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No detector is perfect : Here the scattered electron enters a nonsensitiveregion (Phi-crack) of the electromagnetic calorimeter
Electron penetrates intohadronic part of calorimeter
e
e
Such an effect has to be recognized in thephysics analysis !
Phi-crack in em. calorimeter
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Converted photon
e
e
z-crack
Phi-crack
Here a photon converts and the e+ e- pair enters an insensitiveregion of the em. calorimeter (z- and Phi-cracks)
Xeep γ→−+→ eeγ
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Muons also come from the sky ……
H1 Events Joachim Meyer DESY 2005 28This is BACKGROUND, which we do not like !
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Interaction of cosmic primaries create showers in the atmosphere,and multimuons reach us here
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Cosmic dimuon seen in calorimeter and central track detector
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Another cosmic dimuon …
wires in iron system
pads in iron system
µ µ
Muon radiates
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…and it can be even more fierce ….
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Muons interact rarely, but they do
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Hit pattern in the central track detector(transverse view)
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Here a cosmic muon radiates a photon which gets absorbed in the calorimeter. The muon then exits the detector.
The radiated energydeposition
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A HERA ep event overlayed with a cosmic muon
Cosmic muon
ep event
Such an effect has to be recognizedin the physics analysis !
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There is not only background from cosmics but also from the Proton beam interacting with the restgas
Event vertex is heree-p event vertex
should be here
P - beam
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Scattering of the HERA-proton on a nucleus of the restgas.The nucleus dissociates into lots of protons (positive tracks) and neutrons
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Another kind of beam-related background : Protons lost in the ring create showers and muons from decaying pionsaccompany the beam and may be visible in the detector
Beamhalo muons
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Here a NC event is overlayed by a beam halo muon Such an effect has to be recognizedin the physics analysis !
µµ
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Back to HERA -e-p scattering events : A very forward Dimuon event
Muons bent in the magneticfield of the forward toroidmagnet
These muons are decay products of the famous J/Psi particle
Ψ→ /))(( Jpeep
−+→Ψ µµ/J
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Another event where the J/Psi particle decays into two muons(this time ‘backward’)
Iron
Muon
Muon
−+→Ψ µµ/J
Ψ→ /))(( Jpeep
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Ψ′particle has a sister the Ψ/JThe
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+µ
+µ
−µ
−µ
+π
+π−π
−π
e
e
Backward calorimeter
Central Tracker
Ψ′→ )( peep
−+Ψ→Ψ ππ'
−+→Ψ µµ
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Most events are much more complicated :
Very high track multiplicity
Small visibleenergy incalorimeter
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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
CSTCST Reconstruction
SecondaryVertex
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Another event with detailed track measurementin the CST
CST : R-z view CST : R-Phi view
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Tracks seen in the Forward Silicon Track Detector (FST)
FST
CJC 1
CJC 2
CSTForward
Direction
The FST allows to cover very small forward angles
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Often there is activity in forward direction around the beam pipe :that are the ‘left overs’ of the ‘broken’ proton
Electron scattered undersmall angle intobackward calorimeter
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But in 10% of all cases there is no forward activity :the proton stays intact, and disappears down the beam pipe
p e
e-tagger
e-tagger
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Back to the Deep-Inelastic-Electron-Proton-Scattering (DIS) Xeep '→
Incident e
Scattered e
The electron is scattered backby 160 degree and got an energyof 300 GeV.Very virulent scattering !
e
eX
X
27 GeV
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.and here its even more virulent.
22 50000GeVQ ≈ , this corresponds to a space resolution of
mx 1810−≈∆The squared momentum transfer is
Notice :The hadronic system Xis a well collimated bundle of particles.This is called JET
Jet
Jete
e
Jets are the ‘footprints’of the quarks and gluons
Xeep '→
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21' JetJeteep →A NC-DIS event with two jets
e
e
Jet1
Jet1
Jet2
Jet2
e
J1 J2
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Here the ‘forward scattered’ electron radiates a very energetic photon
electron
electron
electron
photon
photon
photon
γXeep '→
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In general the photon is ‘near’ to the electron. Here both created a singleelectromagnetic shower in the calorimeter, but can be resolved in the tracker
electron-trackconverted photontracks
combined electromagneticshower in calorimeter
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γXeep '→Another event, but here the scatted electron and photon are far apart
It is likely that herethe photon is of hadronic origin(prompt photon)
e
X
γ
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21' γγXeep →There is also a chance that two photons are radiated :
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1γ1γ 2γ2γe e
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In this NC event a muon is produced within the hadronic final state XµXeep '→
µµ
ee
X
X
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A new event class : In this event the hadrons X are NOT balanced by an electron !
Hadrons X
Xep ν→ The Neutrino does not leave a trace in the detector
ν
ν
This is a different typeof DIS eventIt is pure weak interaction.
It is a Charged Current (CC)event
X
X
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2QThe CC event with the highest recorded transverse momentum
Xep ν→
The quark on whichthe electron scatteredhad nearly all of theproton momentum
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21 jjep ν→This is a CC event with a pronounced two-jet structure
ν
j1
j2
j2
j1
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CC event with three jets
J1
J1
J2
J2J3
J3
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Also CC events exhibit multijet structures
ν
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In this CC event the ‘Jet’ is very broad
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A CC event with a photon radiated from the incident electron
Xep νγ→
γ
γ
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This CC event shows a muon separated from the jet
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µ
µ
This could be a muonproduced in the semileptonic decayof a charm quark
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Another event class : ‘Photoproduction’Here two jets are visible, but the scattered electron is not recorded,it leaves the detector under very small scattering angle
Jet 1
Jet 2
Needles of energy
e
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A dijet event with very high dijet-mass
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Here a THREE-JET-EVENT
J1
J2 J3J1
J2
J3
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A very high three-jet mass
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Here 5 jets are visible, there is no limit in the number.
J1
J2
J3J4
J5
Quarks radiate gluons,which in turn may radiate gluons or produce quark-antiquark pairs.All turn (if energetic enough)to visible jet structures
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The jets can be so energetic that they are not absorbed in the main calorimeterbut leak out into the instrumented iron yoke.
Leakage Energy
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It happens that a jet is associated to only a single charged particle
Explanation :-statisticalfluctuation ?-physics reasonTau –Lepton ?
πντ →
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We also record events with an unbalanced jet associated to a single particle.
Are these events withisolated tau-mesonsand missing transverse momentum ?
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Sometimes strange features show up :
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MuonicElectromagnetic
Neutral
behavior
Explanation ??
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The most exciting issue : Are there new phenomema, we don’t expect ?
Xeep '→XepDIS - eventsWe have seen
But this looks like µ→
Fluctuating backgroundorsign of new physics ?
X X
MuonMuon
(As such forbidden in HEP Standard Model)
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A similar event, but here muon and hadronic jet are not back-to-back :clear evidence for unobserved particle (neutrino ?)
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?
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Similar event, but here also the scattered electron is visible.This allows to reconstruct the invariant mass of the muon-neutrino-system.It turns out to be 82 GeV. That’s close to the W mass.
µν→→ WeXWep ......H1 sees more events than expected from this reaction. New physics ?
ν
ν
e
e µ
µ
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Here only an unbalanced electron is visible. This topology is predominantlyexpected for
e
e
νeWWXeep →→ ......))((
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The W decaysalso into quark-antiquarkproducing two jets.The jet-jet-massis 80 GeV, just the known W-mass.
Jet1
Jet2
Jet1
Jet2
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The W particle has a sister, the Z , of 90 GeV mass, decaying into lepton pairs
−+→ eeZ0
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In this event an even more massive e+ e- pair ….. : What physics is that ?
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A collinear electron pair
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Such events we wereused to see at the electron-positron collider PETRA
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Here a positron and 2 electrons are recorded.Presumably the scattered electron and a pair createdin the interaction
Note :All ‘electrons’ are well confined in theelectromagnetic part (green) of the calorimeter
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There are also dilepton events with different lepton types : Electron and muon
e
e
muon
muon
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Here it is evident that a pair of muons is produced
e
e
1µ1µ
2µ
2µ
Muon2 identifiedas minimum ionizingparticle in calorimeter
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A pair of tau-mesons with the scattered electron −+→ ττ)( peep
νµτ ++ →
νπππτ −+−− →
e
+µ+µ
π3
π3
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Summary
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The Method:
e p scattering
Nobel prize 2004 Cartoon
The Data
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Physics Results
examples :
Protonstructure : Quarks and Gluons Electroweak Unification
..and many more …..
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All this became possible thanks to the work of the H1 members……
Some members of the H1 Collaboration
Work at the innermost parts of the H1 detector
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…and thanks to HERA….
H1
mx 1810−≈∆.. the worlds most powerful microscope H1 Events Joachim Meyer DESY 2005 90