Post on 28-May-2020
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Miriam Fritsch PANDA Luminosity Measurements/Restgas – May 4, 2020 2
Why do we need luminosity ?
Absolute cross sections
→ Absolute time-integrated luminosity
Number of Events Time-
integrated Luminosity
Cross section
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Why do we need luminosity ?
ECM
measuredrate
beamprofile
resonance
Scan experiments
→ Relative time-integrated luminosity
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Method
Measurement of beam current and target density
Measurement of a certain reaction channel with simple kinematics and large cross section→ Elastic pp scattering
Our goal5% systematic uncertainty for absolute time-integrated luminosity
1% systematic uncertainty for relative time-integrated luminosity
Monitor the change of the relative luminosity during the run
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PANDA Detector
GEM FTS
FTOF
FRICHDisc DIRC
Target System
Solenoid Magnet
Muon System
Dipole Magnet
FRS LMD
BarrelDIRC & TOF
MVD STT Barrel EMC
FE EMC
FSC
BE EMC
HypernuclearSetup not shown
Beampipe
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Elastic pp cross section
At small |t| (and small θ)
• Coulomb scattering dominates
• Differential cross section can be calculated
At larger |t| (and larger θ)
• Hadronic part dominates
• Description by models using data
• Large uncertainties of the model
Angle of the forward scattered antiproton in lab frame
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Luminosity Detector
Optimization detector resolution• Low material budget• High spatial precision
Tracking detector~11 m behind IP4 planes with 10 modulesFull azimuthal range
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Sensors Modules and Half Detector
HV-MAPS glued on diamond
CVD diamond wafer clamped to the aluminum frame
Steelpipe melted in aluminum
Diamond wafer (200 μm)
HV-MAPS(50 μm)
2 cm
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Reconstruction Software
Extraction of the differential counting rate dN(θ)/dθ
POCA to IP
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Reconstructed angular distribution (1.5 GeV/c)
N(θ)/dθ: Number of events in dependence on scattering angle θ
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Luminosity Determination
Number of Events
Time-integrated Luminosity
Differential cross section
Reconstructionefficiency
Detector resolution
Scattering angle
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Reconstruction efficiency
1.5 GeV/c 15 GeV/c
Limitations due to magnetic fields of solenoid and dipole magnets
~ 100%
Reconstruction efficiency: 95-100%
~95%
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Detector Resolution
1.5 GeV/c 15 GeV/c
Resolution is different in x and y direction Resolution is better for large beam momenta
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Luminosity Determination (Ideal world)
Uncertainty of the extraction method: <1‰
1.5 GeV/c 15 GeV/c
Difference between data and fit
Simulated data after back tracking
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Complications
IP distribution
IP displacement
Beam tilt
Beam divergence
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Influence of the IP distribution (1.5 GeV/c)
Uncertainty of the extraction method:<5‰ <0.5 ‰
Fit w/o IP distribution w/ IP distribution
Difference between data and fit
Simulated data after back tracking
IP profile: σx = σy = 0.8 mmσz = 3.5 mm
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IP distribution
Simulation of target distribution -50 cm < z < 50 cm
No sensitivity for the z coordinate of the track
x and y profile: beam spread x and y variation
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IP displacement
Displacement simulated: -3.5 mm in x and y direction
Beam profile: σx = σy = 0.8 mm and σz = 3.5 mm
Reconstructed profiles much broaderPosition very accurate
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IP displacement (15 GeV/c)
Remaining offset in x-direction of ~40 μm
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Global Fit – “realistic scenarios”
Uncertainty of the extraction method: < 0.7%
Beam tilt and beam divergence estimated by the global fit:
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Vacuum situation around the IP
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Vacuum situation around the IP
Measured gas load of 10-2 mbar·l/s
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Vacuum situation
Target density:1-2·1015 atoms/cm2
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Vacuum situation
Restgas ~30-60%
Change of diameter upstreamincrease ~10%
Effects directly luminosity measurement → No sensitivity in z direction
Target density:1-2·1015 atoms/cm2
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Large IP
We thought of various designs
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Large IP and Cryo pump
Cryo pump:Reduction ~45-60%
Large IP:Reduction 1·1014 atoms/cm2
Both together:Reduction ~60%
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MVD
Old design
Silicon pixel sensors
Silicon microstrip sensors
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MVD – partly inside the beampipe ?
Old design New design ?
Silicon pixel sensors
Silicon microstrip sensors
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Vacuum with MVD partly inside
Only small effect on the vacuum
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Work is going on ..
Restgas issue has to be solved at least reduced as much as possible
Gas is evaporating from the target (clusters or pellets)→ Pumping required
Restgas affects• Beam quality• Beam lifetime• Reconstruction of neutral particles• Reconstruction of delayed vertices with no prompt track problematic• Luminosity determination
Implications on Luminosity determination• Profil is not a certain percentage of target beam (can vary with time)• Reconstruction efficiency not constant over z • Restgas profile has to be measured independently
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Group Meetings
SeminarLong talk 30-40 Minutes
Biweekly Short presentation of all group members→ Meant as an update
Preparation of 3 slides each (not too special !)• Overview of the topic• Recent work, Achievements, Problems• Next steps
Announcements
Discussion of topics of common interest