Post on 22-Feb-2016
description
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Bogdan Wojtsekhowski, Jefferson Lab
Experimental search for A’
for APEX collaboration
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Approach: Aʹ Production and Background Kinematics
Production diagrams analogous to photon bremsstrahlung
Nucleus
QED Backgrounds
Aʹ products carry full beam energy!
γ*
– Distinctive kinematics– Assists in background suppression
(rates before angular cuts)
N~ αʹ x branching N~α
Best kinematics to select events for Aʹ search
O(1)
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Hall A at Jefferson Lab
Two HRS Spectrometers● 0.3 < p < 4.0 GeV/c
● -4.5% < Δp/p < 4.5%● 6 msr at 12.5° <θ<150°
● 4.5 msr at θ=6° with septum● -5cm<Δy<5cm
Optics: (FWHM) ● dp/p 2∙10-4 (achieved)
● d=0.5 mrad, d=1 mrad● δy=1mm
● Luminosity ~ 1038 cm-2s-1
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• Signal dominated at E+ = E– = Ebeam/2
• Use septa to achieve 5° central angles
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(enhance e+e– rate relative to π rate)
Test Run: June 2010
Ebeam= 2.262 GeV, Ta target of 15 mg/cm2
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Test Run: June 2010
momentum sum of
coincident e+e
e+ momentumversus
e- momentum
Magnetic Spectrometer Optics
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Top view
Optics for APEX
Use tracking information from VDC 2D hit position / 2D angle
Reconstruct target side Small acceptance, large size Fine res. Momentum σ~0.5 × 10-3
Angle σ~0.5 mrad (H) , 1 mrad (V) + Multiple scattering in target (~0.4 mrad on angles)
Uncertainty contribution Tracking precision Optics calibration precision
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Sieve Slit Method
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After Calibration
Sieve H. Pos [m]
Siev
e V.
Pos
[m]
Before Calibration
Siev
e V.
Pos
[m]
Left HRS calibration used 35 holes, Right HRS calibration used 38 holes
Final Geometry Selection
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3D momentum acceptance cuts for both HRSs Represents region for which
optics was calibrated Approximately represents
acceptance PREX collimators
Reduced solid angle acceptance from 4.3 msr to 2.8 msr
Full running larger acceptance
Sieve
Angular Resolutions
Use sieve data to determine angular resolution 1D x and y projections near each sieve hole Fitted with Gaussian on linear background
Peak positions and RMS values compared with surveyed positions and geometrical widths of holes
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x (mm)910111213141516
0
20
40
60
80
100
120
peak: 12 .169 +/- 0.012s igma : 0.424 +/- 0 .008
x (3,5)
y (mm)681012141618202224
0
20
40
60
80
100
peak: 14 .669 +/- 0.042s igma: 1.444 +/- 0.032
L e ft S ie ve R un 1898-1899
y (3,5)
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HRS optics for APEX
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HRS optics for APEX
Big hole: diameter 0.105” ; observed sigma ~ 0.66 mm approx. due to the hole size
Small hole: diameter 0.055” ; observed sigma ~ 0.40 mm -> angular resolution Angular resolution (horizontal, at the hole) < 0.3 mrad
BIG HOLE
Angular Resolutions
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LHRS (mrad)
RHRS (mrad)
Δφ 0.10 Δφ 0.10Δθ 0.24 Δθ 0.20
σφ_width 0.26 σφ_width 0.43σθ_width 1.81 σθ_width 1.75
σφ 0.29 σφ 0.44σθ 1.86 σθ 1.77
Optics calibration precisionTracking precision
φ/θ – hor / vert angles
Averages weighted according to statistics
Final resolutions
Target Multi-Scattering
When traveling through the target, e-and e+ experience many small angle deflections due to Coulumb scattering from nuclei
Resulting angular distribution:
σM.S. = (13.6 MeV/p) sqrt(x/X0) [1+0.038ln(x/X0)] p = particle momentum x = avg. dist. traveled through target X0 = radiation length of target
For Tantalum target used in test run, σM.S. = 0.352 mrad
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Mass Resolution
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Mass (MeV) 180 195 210 225 240 AverageUsing different angular resolutions for each event 0.833 0.965 1.026 1.061 1.037 1.005Using angular resolutions listed in above table for all events 0.822 0.962 1.023 1.054 1.043 -Using angular resolutions from "Total" column in above table for all events 0.869 0.965 0.995 0.994 0.966 0.977
Mass (MeV) 180 195 210 225 240 AverageLeft theta (mrad) 1.95 1.87 1.89 1.93 1.88 1.86Left phi (mrad) 0.26 0.3 0.32 0.33 0.33 0.29Right theta (mrad) 1.69 1.74 1.81 1.85 1.85 1.77Right phi (mrad) 0.38 0.43 0.46 0.5 0.53 0.44
Mass resolutions (MeV) determined for different masses using 3 different methods
Angular resolution averages (mrad) determined for different masses
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Test Run Results
APEX test run found no evidence for A’in the mass range 175-250 MeV with the coupling above ~10-6
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PRL paper
Re: LH13073
Search for a new gauge boson in electron-nucleus fixed target scattering by the APEX experiment by S. Abrahamyan, Z. Ahmed, K. Allada, et al.
Dear Dr. Wojtsekhowski,
We are pleased to inform you that your manuscript has been accepted for publication as a Letter in Physical Review Letters.
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Sieve slit image for 5 and 10 mm thick plates
MC of HRS sieve slit
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MC of HRS sieve slit
20 mm W plate
10 mm W plate
Positive polarity Negative polarity
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HRS opticsActive “sieve slit”: tagging by
a Sci Fiber detector1 mm fibers with 1/16” pitch
connected to a maPMTReadout to via 1877s TDC 1-3 MHz rate per fiberOff-line time window of < 5 nsAll components are available
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Multi foil target
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APEX full Run