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 on at HERA

Hadrons

W

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 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 (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 is a well collimated bundle of particles. This is called JET Jets are the ‘footprints’ of the and 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 origin It is likely that here the photon is of hadronic (prompt photon) e event, but here the scatted electron and photon are far apart

γ γ X ' e → X ep H1 Events Joachim Meyer DESY 2005 54 Another ' 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.

It is a Charged Current (CC) ν event

ν

H1 Events Joachim Meyer DESY 2005 57 2 The CC event with the highest recorded transverse momentum Q

ep →νX

The quark on which the electron scattered had nearly all of the proton momentum

H1 Events Joachim Meyer DESY 2005 58 This is a CC event with a pronounced two-jet structure ep →νj1 j2

ν

j1 j1 j2

j2

H1 Events Joachim Meyer DESY 2005 59 CC event with three jets

J2

J3 J1

J1

J2 J3

H1 Events Joachim Meyer DESY 2005 60 Also CC events exhibit multijet structures

ν

H1 Events Joachim Meyer DESY 2005 61 In this CC event the ‘Jet’ is very broad

H1 Events Joachim Meyer DESY 2005 62 A CC event with a photon radiated from the incident electron ep →νγX

γ

γ

H1 Events Joachim Meyer DESY 2005 63 This CC event shows a muon separated from the jet

µ

µ

This could be a muon produced in the semileptonic decay of a

H1 Events Joachim Meyer DESY 2005 64 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

e Needles of energy

Jet 2

H1 Events Joachim Meyer DESY 2005 65 A dijet event with very high dijet-mass

H1 Events Joachim Meyer DESY 2005 66 Here a THREE-JET-EVENT

J1

J1 J2 J3 J2

J3

H1 Events Joachim Meyer DESY 2005 67 A very high three-jet mass

H1 Events Joachim Meyer DESY 2005 68 Here 5 jets are visible, there is no limit in the number.

J5

J1 J3 J4 Quarks radiate gluons, which in turn may radiate gluons or produce quark- antiquark pairs. All turn (if energetic enough) J2 to visible jet structures

H1 Events Joachim Meyer DESY 2005 69 The jets can be so energetic that they are not absorbed in the main calorimeter but leak out into the instrumented iron yoke.

Leakage Energy

H1 Events Joachim Meyer DESY 2005 70 It happens that a jet is associated to only a single charged particle

Explanation : -statistical fluctuation ? -physics reason Tau – ? τ → πν

H1 Events Joachim Meyer DESY 2005 71 We also record events with an unbalanced jet associated to a single particle.

Are these events with isolated tau-mesons and missing transverse momentum ?

H1 Events Joachim Meyer DESY 2005 72 Sometimes strange features show up :

Muonic Electromagnetic behavior

Neutral

Explanation ?? H1 Events Joachim Meyer DESY 2005 73 The most exciting issue : Are there new phenomema, we don’t expect ?

' We have seen ep → e X DIS - events But this looks like ep → µX (As such forbidden in HEP )

Muon Muon

Fluctuating background or sign of new physics ?

X X

H1 Events Joachim Meyer DESY 2005 74 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 75 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.

e µ µ e ν

ν

ep → eXW...... W → µν H1 sees more events than expected from this reaction. New physics ?

H1 Events Joachim Meyer DESY 2005 76 Here only an unbalanced electron is visible. This topology is predominantly expected for ep → (e)(X )W...... W → eν

e

e

H1 Events Joachim Meyer DESY 2005 77 The W decays Jet2 also into quark-antiquark producing two Jet1 jets. Jet1 The jet-jet-mass is 80 GeV, just the known W-mass.

Jet2

H1 Events Joachim Meyer DESY 2005 78 The W particle has a sister, the Z , of 90 GeV mass, decaying into lepton pairs

+ − Z0 → e e

H1 Events Joachim Meyer DESY 2005 79 In this event an even more massive e+ e- pair ….. : What physics is that ?

H1 Events Joachim Meyer DESY 2005 80 A collinear electron pair

Such events we were used to see at the electron- collider PETRA

H1 Events Joachim Meyer DESY 2005 81 Here a positron and 2 electrons are recorded. Presumably the scattered electron and a pair created in the interaction

Note : All ‘electrons’ are well confined in the electromagnetic part (green) of the calorimeter

H1 Events Joachim Meyer DESY 2005 82 There are also dilepton events with different lepton types : Electron and muon

e

muon e

muon

H1 Events Joachim Meyer DESY 2005 83 Here it is evident that a pair of muons is produced

µ1 µ1

µ2

Muon2 identified e as minimum ionizing particle in calorimeter µ2

e

H1 Events Joachim Meyer DESY 2005 84 A pair of tau-mesons with the scattered electron ep → e( p)τ +τ −

τ + → µ +ν + + µ µ τ − → π −π +π −ν

e 3π

3π

H1 Events Joachim Meyer DESY 2005 85 Summary

H1 Events Joachim Meyer DESY 2005 86 The Method: e p scattering

Nobel prize 2004 Cartoon

The Data

H1 Events Joachim Meyer DESY 2005 87 Physics Results examples :

Protonstructure : Quarks and Gluons Electroweak Unification

..and many more …..

H1 Events Joachim Meyer DESY 2005 88 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 89 …and thanks to HERA….

H1

−18 .. the worlds most powerful microscope ∆x ≈10 m H1 Events Joachim Meyer DESY 2005 90