Alignment study

19/May/2010(S. Haino)

Summary on Alignment review

• Inner layers are expected to be kept “almost” aligned when AMS arrives at ISS

• Small shifts (30~50 μm) in z-direction will be possible due to (1) Change of gravity (2) Shrink of foam support

• Momentum (or Energy) reference is needed for the absolute rigidity calibration

Alignment methods for AMS-PM

• Monitoring Layer 1N/9 movement8-layer acceptance (8 Layers+ Layer 1N or 9)103~104 protons (E > 10 GV)

• Incoherent alignment (ladder base alignment)Maximum acceptance (~ 0.5 m2sr)> 106 protons (E > 10 GV)

• Coherent alignment (momentum calibration)9-layer +Ecal acceptance (< 0.05 m2sr)~103 e+ and ~104 e- (E > ~100 GeV)

Alignment monitoring

Layer 1NLayer 9

dY dZ

dθxy

MC data generated withGbatch/PGTRACK Alignment accuracy estimated from Gaussian fitting error on the residual of layer 1N/9 hit Proton flux weight above 10 GV

Coherent alignment• Check of absolute alignment for

outer layersby comparing Rigidity measured by Tracker (RTracker)and Energy measured by Ecal (EEcal)on high energy e+ and e- sample

• Radiation energy loss makes PTracker=|RTracker| smaller w.r.t. EEcal

• Alignment shift makes RTracker shifted to the opposite direction for e+ and e-

Coherent alignment - simulation

• AMS-B Gbatch/PGTRACK simulation(For details please see presentation by P. Zuccon)

• 108 e- and e+ each are injected in uniform Log10E distribution (10 < E < 500 GeV)isotropically from a plane 2.4m × 2.4m at Z = 1.8m Only trajectories which pass all the Tracker 9 layersare simulated

• Physics switches : LOSS= 1, DRAY= 1, HADR= 0, MULS= 1,BREM= 1, PAIR= 1

Ecal energy correction• Absolute energy scale • Linearity due to the shower leak

Before

After

EEcal/PTracker VS Egen

In case Layer 1N is shifted by ΔY = ±20 μm

Coherent alignment - simulation

• Compare EEcal/PTracker distribution between RTracker > 0 and RTracker < 0for e+ and e- sample with EEcal > 80 GeV

• Flux weight applied assuminge- flux tuned by Fermi/LAT datae+ flux tuned and extrapolated by Pamela dataSimulated acceptance (full Ecal) :0.025 m2srLive data taking time :

100 days• Kolmogorov probability (P) is calculated

for the compatibility of two scaled histograms with RTracker > 0 and RTracker < 0

EEcal/PTracker comparison

P: Kolmogoro

v probability

In case Layer 1N is shifted by ΔY = ±20 μm : T = 100 days

P: Kolmogoro

v probability

-Log P VS ΔYIn case Layer 1N is shifted by ΔY : T = 100 days

Estimated error

~5 μm

Alignment methods for AMS-PM

• Monitoring Layer 1N/9 movement2~3 μm accuracy (dY) for 10 min. live time

• Incoherent alignment (ladder alignment)> 106 protons (E > 10 GV) for 1~2 daysStudy in progress

• Coherent alignment (momentum calibration)~5 μm accuracy for 100 days live time

Backup slides

Alignment difference

Between Pre-int. (2008) and Flight-int. (2009)

• Ext. planes seem rotating w.r.t. Int. planes by order of 100 μm/60 cm ~ 10-2 degrees

• A small (~50 μm) Z-shift found in Ext. planes

• No significant shift found for internal layers

Alignment differencebetween Pre-int.(2008) and Flight-int.(2009)

Ladder Rotaion (dY/dX)

Ladder Shift (dX)

Ladder Shift (dY)

Ladder Shift (dZ)

Alignment with test beam• B-off runs with 400 GeV/c proton

beam (4B70D0BF-4b710CBF, 58 points available) are reconstructed with straight tracks

• The following three parameters are tuned w.r.t. the CR alignment (2009)(1) Layer shift along z-axis : ~20 μm(2) Ladder shift along x-axis : 5~10 μm(3) Ladder shift along y-axis : 5~10 μm

Test beam alignmentLadder Shift (dX) RMS ~5 μm

Layer Shift (dZ) RMS ~15 μm

Ladder Shift (dY) RMS ~5 μm

Mean of (400GV)/Rigidity

before alignment

Mean of (400GV)/Rigidity

After alignment

Alignment study with B-off/on

• The 5 alignment applied to proton TB runs

1. Linear fitting on B-OFF runs

2. Curved fitting (1/R = 0 fixed) on B-OFF runs

3. Curved fitting (1/R free par.) on B-OFF runs

4. Curved fitting (R = 400 GV fixed) on B-ON runs

5. Curved fitting (1/R free par.) on B-ON runs

Alignment study with B-off/on

Alignment study with AMS-01

dZ = 31±44 μm

Alignment monitoring - simulation

• AMS-B Gbatch/PGTRACK simulation(For details please see presentation by P. Zuccon)

• 108 protons injected in uniform Log10R distribution (1 GV < R < 10 TV)isotropically from a plane 2.4m × 2.4m at Z = 1.8m

• Physics switches : LOSS= 1, DRAY= 1, HADR= 0, MULS= 1

• Alignment accuracy estimated from Gaussian fitting error on the residual of layer 1N/9 hit weighted by proton flux above 10 GV

GeometryLayer8 Layer 1N

Layer1

Layer 2,3

Layer 4,5

Layer 6,7

Layer 9

Ecal 65 × 65 cm2

Layer 9

External layes are kept as they are

Elena Vannuccini

In-flight alignment: STEP 1

Step 1 Correction for random displacements of the sensors (incoherent alignment)

– Done with relativistic protons – Input trajectory evaluated from (misaligned) spectrometer fit

measured step 1

Flight dataSimulation

X side Y side

protons 7-100 GV (6x6y, all plane included in the fit)

After incoherent alignment:• residuals are centered• width consistent with nominal resolution + alignment uncertainty (~1mm)

Elena Vannuccini

Elena Vannuccini

In-flight alignment: STEP 2

step 2step 1

After Step1: (possible) uncorrected global distortions might mimic a residual deflection

® spectrometer systematic effect

Step 2 Correction for global distortions of the system (coherent alignment)

– Done with electrons and positrons– Energy determined with the calorimeter

DE/E < 10% above 5GeV

Energy-rigidity match

HOWEVER, the energy measured by the calorimeter can not be used directly as input of the alignment procedure, for two reasons:

1. Calorimeter calibration systematic uncertainty

2. Electron/positron Bremstrahlung above the spectrometer

deflection offset

1

SpeSpeCalCal ΔηηPEP

CalSpe PP

calorimetercalibration uncertanty

ε1EP CalCal

Δη

Elena Vannuccini

Elena Vannuccini

Bremsstrahlung effect

From Bethe-Heitler modelThe probability distribution of z– depends on the amount of traversed material– does not depend on the initial momentum

it should be the same for electrons and positrons!!

With real data:

– Spectrometer systematic gives a charge-sign dependent effect

– Calorimeter systematic has the same effect for both electrons and positrons

0

Spe

P

Pz

*P0

PSpe

PCal~P0

t~0.1X0

g e±

e±

€

z ~ 1

PCal

ηSpe

⏐ → ⏐ 1

PCal

1+ε ⎛ ⎝ ⎜ ⎞

⎠ ⎟ η

Spe±Δη

⎛

⎝

⎜ ⎜

⎞

⎠

⎟ ⎟