HERA e-p scattering events observed in the H1Detector
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Transcript of HERA e-p scattering events observed in the H1Detector
H1 Events Joachim Meyer DESY 2005 1
HERA e-p scattering events observed in the H1Detector
H1 Events Joachim Meyer DESY 2005 2
The idea The realisation
The eventsThe Physics
H1 Events Joachim Meyer DESY 2005 3
What we think what happens, when we scatter electrons on protons at HERA
Hadrons
Hadrons
or neutrino
ProtonW
H1 Events Joachim Meyer DESY 2005 4
e
pThe H1 detector at the e-p storage ring HERA
Tracking chambers
Calorimeters
Instrumented iron systemForward muondetector
H1 Events Joachim Meyer DESY 2005 5
Calorimeter
H1 Events Joachim Meyer DESY 2005 6
Principle of particle identification
H1 Events Joachim Meyer DESY 2005 7
Principle of particle identification
H1 Events Joachim Meyer DESY 2005 8
An event display : What do we see ?
Energy depositionsin calorimeter
Hits and reconstructedtracks in tracker
R-Z view :
e-p interactionpoint
e p
Hadronic calorimeter
Electromagnetic calorimetere
Hadrons
Scattered Electron
H1 Events Joachim Meyer DESY 2005 9
Same event in radial view :
Energydepositionsin calorimeter
Hits and reconstructedtracks in tracker
Hadronic calorimeter
Xeep '
e
X
H1 Events Joachim Meyer DESY 2005 10
The hits (fired wires) in the tracking chambers
Gas volumen withsense wires at HV
Hits = Signalsrecorded on sense wires
H1 Events Joachim Meyer DESY 2005 11
..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 chambers
H1 Events Joachim Meyer DESY 2005 12
.. and the same procedure in R-Z view :
Electron
Hadrons
Central tracking chambers
H1 Events Joachim Meyer DESY 2005 13
another event :
Here you see the CJC hits includingthe ‘mirror hits’(ambiguity notresolved)
Curlingtracks
track
Mirror tracks
H1 Events Joachim Meyer DESY 2005 14
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
H1 Events Joachim Meyer DESY 2005 15
Side view (R-z)
Transverse view (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
H1 Events Joachim Meyer DESY 2005 16
)( peep
Electron
Photon
Proton leavesunseen down thebeam pipe
A very simple event :
H1 Events Joachim Meyer DESY 2005 17
Here an electron and two photons are recorded
Electrons ‘easily’radiate photons
H1 Events Joachim Meyer DESY 2005 18
Photons tend to convert to e+ e- pairs in material
Photon
Chamber material
e+ e- Pair
eeXeep ......
e
PhotonX
e
Photon
H1 Events Joachim Meyer DESY 2005 19
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
ee
Conversion point
H1 Events Joachim Meyer DESY 2005 20
Another ‘simple’ event : A elastic dimuon production
)( peep
Muons penetrate thick materials !
MUON
MUON
IRON
H1 Events Joachim Meyer DESY 2005 21
An inelastic dimuon production without visible scattered electron
Xeep )(
X
X
H1 Events Joachim Meyer DESY 2005 22
Another inelastic dimuon production without visible scattered electron
Xeep )(
X
X
The muons are low energetic and don’t read the iron,they are ‘mips’ in calorimeter
H1 Events Joachim Meyer DESY 2005 23
Another inelastic dimuon production without visible scattered electron
Xeep )(
X
X
One muon identified in calorimeter, the other in the iron system
H1 Events Joachim Meyer DESY 2005 24
In the ‘forward direction’ muons are measured by the ‘Forward Toroid Muon Detector’
Forward ToroidMuon Detector
2
21
1
H1 Events Joachim Meyer DESY 2005 25
Here it is very visible how electron, muon and photon are distinguished
ee
H1 Events Joachim Meyer DESY 2005 26
No detector is perfect : Here the scattered electron enters a nonsensitive region (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
H1 Events Joachim Meyer DESY 2005 27
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 ee
H1 Events Joachim Meyer DESY 2005 28
Muons also come from the sky ……
This is BACKGROUND, which we do not like !
H1 Events Joachim Meyer DESY 2005 29
Interaction of cosmic primaries create showers in the atmosphere,and multimuons reach us here
H1 Events Joachim Meyer DESY 2005 30
Cosmic dimuon seen in calorimeter and central track detector
H1 Events Joachim Meyer DESY 2005 31
Another cosmic dimuon …
wires in iron system
pads in iron system
Muon radiates
H1 Events Joachim Meyer DESY 2005 32
…and it can be even more fierce ….
H1 Events Joachim Meyer DESY 2005 33
Muons interact rarely, but they do
Hit pattern in the central track detector(transverse view)
H1 Events Joachim Meyer DESY 2005 34
Here a cosmic muon radiates a photon which gets absorbed in the calorimeter. The muon then exits the detector.
The radiated energydeposition
H1 Events Joachim Meyer DESY 2005 35
A HERA ep event overlayed with a cosmic muon
Cosmic muon
ep event
Such an effect has to be recognizedin the physics analysis !
H1 Events Joachim Meyer DESY 2005 36
There is not only background from cosmics but also from the Proton beam interacting with the restgas
Event vertex is here
e-p event vertex should be here
P - beam
H1 Events Joachim Meyer DESY 2005 37
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 38
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
H1 Events Joachim Meyer DESY 2005 39
Here a NC event is overlayed by a beam halo muon
Such an effect has to be recognizedin the physics analysis !
H1 Events Joachim Meyer DESY 2005 40
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
/))(( Jpeep
/J
H1 Events Joachim Meyer DESY 2005 41
Another event where the J/Psi particle decays into two muons (this time ‘backward’)
Iron
Muon
Muon
/J
/))(( Jpeep
H1 Events Joachim Meyer DESY 2005 42
e
e
Backward calorimeter
Central Tracker
particle has a sister the /JThe
)( peep
'
H1 Events Joachim Meyer DESY 2005 43
Most events are much more complicated :
Very high track multiplicity
Small visibleenergy incalorimeter
H1 Events Joachim Meyer DESY 2005 44
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
H1 Events Joachim Meyer DESY 2005 45
Another event with detailed track measurementin the CST
CST : R-z view CST : R-Phi view
H1 Events Joachim Meyer DESY 2005 46
Tracks seen in the Forward Silicon Track Detector (FST)
FST
CJC 1
CJC 2
CST
Forward
Direction
The FST allows to cover very small forward angles
H1 Events Joachim Meyer DESY 2005 47
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
H1 Events Joachim Meyer DESY 2005 48
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
H1 Events Joachim Meyer DESY 2005 49
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
H1 Events Joachim Meyer DESY 2005 50
.and here its even more virulent.
The squared momentum transfer is 22 50000GeVQ , this corresponds to a space resolution of
mx 1810
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 '
H1 Events Joachim Meyer DESY 2005 51
A NC-DIS event with two jets 21' JetJeteep
e
e
Jet1
Jet1
Jet2
Jet2
e
J1 J2
H1 Events Joachim Meyer DESY 2005 52
Here the ‘forward scattered’ electron radiates a very energetic photon
electron
electron
electron
photon
photon
photon
Xeep '
H1 Events Joachim Meyer DESY 2005 53
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-track
converted photontracks
combined electromagneticshower in calorimeter
H1 Events Joachim Meyer DESY 2005 54
Xeep '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
H1 Events Joachim Meyer DESY 2005 55
There is also a chance that two photons are radiated : 21' Xeep
11 22e e
H1 Events Joachim Meyer DESY 2005 56
In this NC event a muon is produced within the hadronic final state XXeep '
e
e
X
X
H1 Events Joachim Meyer DESY 2005 57
Hadrons X
A new event class : In this event the hadrons X are NOT balanced by an electron !
Xep The Neutrino does not leave a trace in the detector
This is a different typeof DIS eventIt is pure weak interaction.
It is a Charged Current (CC)event
X
X
H1 Events Joachim Meyer DESY 2005 58
The CC event with the highest recorded transverse momentum 2Q
The quark on whichthe electron scatteredhad nearly all of theproton momentum
Xep
H1 Events Joachim Meyer DESY 2005 59
This is a CC event with a pronounced two-jet structure
21 jjep
j1
j2
j2
j1
H1 Events Joachim Meyer DESY 2005 60
CC event with three jets
J1
J1
J2
J2
J3
J3
H1 Events Joachim Meyer DESY 2005 61
Also CC events exhibit multijet structures
H1 Events Joachim Meyer DESY 2005 62
In this CC event the ‘Jet’ is very broad
H1 Events Joachim Meyer DESY 2005 63
A CC event with a photon radiated from the incident electron
Xep
H1 Events Joachim Meyer DESY 2005 64
This CC event shows a muon separated from the jet
This could be a muonproduced in the semileptonic decayof a charm quark
H1 Events Joachim Meyer DESY 2005 65
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
H1 Events Joachim Meyer DESY 2005 66
A dijet event with very high dijet-mass
H1 Events Joachim Meyer DESY 2005 67
Here a THREE-JET-EVENT
J1
J2 J3J1
J2
J3
H1 Events Joachim Meyer DESY 2005 68
A very high three-jet mass
H1 Events Joachim Meyer DESY 2005 69
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
H1 Events Joachim Meyer DESY 2005 70
The jets can be so energetic that they are not absorbed in the main calorimeterbut leak out into the instrumented iron yoke.
Leakage Energy
H1 Events Joachim Meyer DESY 2005 71
It happens that a jet is associated to only a single charged particle
Explanation :-statistical fluctuation ?-physics reason Tau –Lepton ?
H1 Events Joachim Meyer DESY 2005 72
We also record events with an unbalanced jet associated to a single particle.
Are these events withisolated tau-mesonsand missing transverse momentum ?
H1 Events Joachim Meyer DESY 2005 73
Sometimes strange features show up :
Muonic
Electromagnetic
Neutral
behavior
Explanation ??
H1 Events Joachim Meyer DESY 2005 74
The most exciting issue : Are there new phenomema, we don’t expect ?
Xeep 'We have seen DIS - events
But this looks like Xep
Fluctuating backgroundorsign of new physics ?
XX
MuonMuon
(As such forbidden in HEP Standard Model)
H1 Events Joachim Meyer DESY 2005 75
A similar event, but here muon and hadronic jet are not back-to-back :clear evidence for unobserved particle (neutrino ?)
?
H1 Events Joachim Meyer DESY 2005 76
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.
WeXWep ......H1 sees more events than expected from this reaction. New physics ?
e
e
H1 Events Joachim Meyer DESY 2005 77
Here only an unbalanced electron is visible. This topology is predominantlyexpected for
e
e
eWWXeep ......))((
H1 Events Joachim Meyer DESY 2005 78
The W decaysalso into quark-antiquarkproducing two jets.The jet-jet-massis 80 GeV, just the known W-mass.
Jet1
Jet2
Jet1
Jet2
H1 Events Joachim Meyer DESY 2005 79
The W particle has a sister, the Z , of 90 GeV mass, decaying into lepton pairs
eeZ0
H1 Events Joachim Meyer DESY 2005 80
In this event an even more massive e+ e- pair ….. : What physics is that ?
H1 Events Joachim Meyer DESY 2005 81
A collinear electron pair
Such events we wereused to see at the electron-positron collider PETRA
H1 Events Joachim Meyer DESY 2005 82
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
H1 Events Joachim Meyer DESY 2005 83
There are also dilepton events with different lepton types : Electron and muon
e
e
muon
muon
H1 Events Joachim Meyer DESY 2005 84
Here it is evident that a pair of muons is produced
e
e
11
2
2
Muon2 identifiedas minimum ionizingparticle in calorimeter
H1 Events Joachim Meyer DESY 2005 85
A pair of tau-mesons with the scattered electron )( peep
e
3
3
H1 Events Joachim Meyer DESY 2005 86
Summary
H1 Events Joachim Meyer DESY 2005 87
The Method:
Nobel prize 2004 Cartoon
The Data
e p scattering
H1 Events Joachim Meyer DESY 2005 88
Physics Results
Protonstructure : Quarks and Gluons Electroweak Unification
examples :
..and many more …..
H1 Events Joachim Meyer DESY 2005 89
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
H1 Events Joachim Meyer DESY 2005 90
…and thanks to HERA….
.. the worlds most powerful microscope mx 1810
H1