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

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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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e

pThe H1 detector at the e-p storage ring HERA

Tracking chambers

Calorimeters

Instrumented iron systemForward muondetector

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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

e p

Hadronic calorimeter

Electromagnetic calorimetere

Hadrons

Scattered Electron

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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 chambers

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.. 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

track

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)

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

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)( peep

Electron

Photon

Proton leavesunseen down thebeam pipe

A very simple event :

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Here an electron and two photons are recorded

Electrons ‘easily’radiate photons

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Photons tend to convert to e+ e- pairs in material

Photon

Chamber material

e+ e- Pair

eeXeep ......

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

ee

Conversion point

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Another ‘simple’ event : A elastic dimuon production

)( peep

Muons penetrate thick materials !

MUON

MUON

IRON

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An inelastic dimuon production without visible scattered electron

Xeep )(

X

X

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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

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Another inelastic dimuon production without visible scattered electron

Xeep )(

X

X

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’

Forward ToroidMuon Detector

2

21

1

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Here it is very visible how electron, muon and photon are distinguished

ee

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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

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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 ee

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Muons also come from the sky ……

This 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

Muon radiates

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…and it can be even more fierce ….

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Muons interact rarely, but they do

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 !

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

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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 !

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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

/))(( Jpeep

/J

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Another event where the J/Psi particle decays into two muons (this time ‘backward’)

Iron

Muon

Muon

/J

/))(( Jpeep

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e

e

Backward calorimeter

Central Tracker

particle has a sister the /JThe

)( peep

'

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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

CST

Forward

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

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 '

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A NC-DIS event with two jets 21' JetJeteep

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

Xeep '

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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-track

converted photontracks

combined electromagneticshower in calorimeter

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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

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There is also a chance that two photons are radiated : 21' Xeep

11 22e e

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In this NC event a muon is produced within the hadronic final state XXeep '

e

e

X

X

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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

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The CC event with the highest recorded transverse momentum 2Q

The quark on whichthe electron scatteredhad nearly all of theproton momentum

Xep

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This is a CC event with a pronounced two-jet structure

21 jjep

j1

j2

j2

j1

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CC event with three jets

J1

J1

J2

J2

J3

J3

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Also CC events exhibit multijet structures

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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

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This CC event shows a muon separated from the jet

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 :-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)

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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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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

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Here only an unbalanced electron is visible. This topology is predominantlyexpected for

e

e

eWWXeep ......))((

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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

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

11

2

2

Muon2 identifiedas minimum ionizingparticle in calorimeter

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A pair of tau-mesons with the scattered electron )( peep

e

3

3

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Summary

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The Method:

Nobel prize 2004 Cartoon

The Data

e p scattering

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Physics Results

Protonstructure : Quarks and Gluons Electroweak Unification

examples :

..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….

.. the worlds most powerful microscope mx 1810

H1