Luminosity Me asurement and the Restgas Issue at PANDA · Miriam Fritsch PANDA Luminosity...

Luminosity Me asurement and the Restgas Issue at PANDA

Miriam FritschSeminar

May 4, 2020

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


Why do we need luminosity ?

ECM

measuredrate

beamprofile

resonance

Scan experiments

→ Relative time-integrated luminosity


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


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


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


Luminosity Detector

Optimization detector resolution• Low material budget• High spatial precision

Tracking detector~11 m behind IP4 planes with 10 modulesFull azimuthal range


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


Reconstruction Software

Extraction of the differential counting rate dN(θ)/dθ

POCA to IP


Reconstructed angular distribution (1.5 GeV/c)

N(θ)/dθ: Number of events in dependence on scattering angle θ


Luminosity Determination

Number of Events

Time-integrated Luminosity

Differential cross section

Reconstructionefficiency

Detector resolution

Scattering angle


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%


Detector Resolution

1.5 GeV/c 15 GeV/c

Resolution is different in x and y direction Resolution is better for large beam momenta


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


Complications


Complications

IP distribution

IP displacement

Beam tilt

Beam divergence


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


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


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


IP displacement (15 GeV/c)

Remaining offset in x-direction of ~40 μm


Global Fit – “realistic scenarios”

Uncertainty of the extraction method: < 0.7%

Beam tilt and beam divergence estimated by the global fit:


PANDA beampipe


Vacuum situation around the IP


Vacuum situation around the IP

Measured gas load of 10-2 mbar·l/s


Vacuum situation

Target density:1-2·1015 atoms/cm2


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


Large IP

We thought of various designs


Additional Cryopump


Large IP and Cryo pump


Large IP and Cryo pump

Cryo pump:Reduction ~45-60%

Large IP:Reduction 1·1014 atoms/cm2

Both together:Reduction ~60%


MVD

Old design

Silicon pixel sensors

Silicon microstrip sensors


MVD – partly inside the beampipe ?

Old design New design ?

Silicon pixel sensors

Silicon microstrip sensors


Vacuum with MVD partly inside

Only small effect on the vacuum


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


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

Luminosity Me asurement and the Restgas Issue at PANDA · Miriam Fritsch PANDA Luminosity...

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