Post on 05-Jul-2020
for the APEX Collaboration
The Aʹ′ Experiment (APEX) Searching for New Gauge Bosons in the Aʹ
Experiment at Jefferson Laboratory
Natalia Toro (Perimeter Institute)
1
S. Abrahamyan, Z. Ahmed, K. Allada, D. Anez, T. Averett, A. Barbieri, K. Bartlett, J. Beacham, J. Bono, J.R. Boyce, P. Brindza, A. Camsonne, K. Cranmer, M.M. Dalton,
C.W. de Jager, J. Donaghy, R. Essig (co-spokesperson), C. Field, E. Folts, A. Gasparian, N. Goeckner-Wald, J. Gomez, M. Graham, J.O. Hansen, D.W.
Higinbotham, T. Holmstrom, J. Huang, S. Iqbal, J. Jaros, E. Jensen, A. Kelleher, M. Khandaker, J.J. LeRose, R. Lindgren, N. Liyanage, E. Long, J. Mammei, P.
Markowitz, T. Maruyama, V. Maxwell, S. Mayilyan, J. McDonald, R. Michaels, K. Moffeit, V. Nelyubin, A. Odian, M. Oriunno, R. Partridge, M. Paolone, E. Piasetzky,
I. Pomerantz, Y. Qiang, S. Riordan, Y. Roblin, B. Sawatzky, P. Schuster (co-spokesperson), J. Segal, L. Selvy, A. Shahinyan, R. Subedi, V. Sulkosky, S.
Stepanyan, N. Toro (co-spokesperson), D. Walz, B. Wojtsekhowski (co-spokesperson), J. Zhang and The Hall A Collaboration
0.001 0.01 0.1 110-1110-1010-910-810-710-610-510-40.001 0.01 0.1 1
10-1110-1010-910-810-710-610-510-4
mA' HGeVL
a'êa
APEXêMAMITest Runs
U70
E141
E774
am, 5s
am,±2s favored
ae
BaBar
KLOE
Orsay
HPS APEXDarkLight
VEPP3
HPS
Outline
2
1) The APEX experiment: general setup and rationalea few important details
2) Test run (July 2010)results
3) Full APEXextended targetSciFi optics calibration for
better mass resolutionnew septum
In brief: APEX is a spectrometer-based search, at JLab Hall A, for 50-500 MeV hidden-sector photons decaying promptly to e+e–.
PRL 107:191804,2011, arxiv:1108.2750
JHEP 1102:009,2011, arxiv:1001.2557
APEX Concept and Dark Photon Production
��mA
E
⇥3/2
(wide)
(narrow)
e�
Energy = E
e�
��mA
E
⇥1/2 l+
l�
� mA
EA�
EAʹ′≃Ebeam-mAʹ′
Ee-≃mAʹ′
3
HRS−right
HRS−left
Electron, P = E0/2
Positron, P = E0/2
.
.
Septum
W target
Beam
Nucleus
A�
e+
e�
e�
The High Resolution Spectrometers
4
Lead Glass
Calorimeter S2m
Gas Cherenkov
VDC
S0
0.3<p<4.0 GeV/c -4.5%<Δp/p<4.5% δp/p ≤ 2 10-4 12.5º<θ0<150º 6msr δφ=0.5 mrad (H)
δθ=1 mrad (V) (4.5 msr at θ0=5º with septum)
Range Acceptance Resolution
Distinctive kinematics
Aʹ′ Production and Background Kinematics (mAʹ′≪Ebeam)
0.0 0.2 0.4 0.6 0.8 1.005101520253035
HE++E-LêEbeam
Evtsês
A' Ha'êa=3 10-6L
QED Backgroundê103
A′ Production
Nucleus
A�
e+
e�
e�
5
QED Backgrounds
Aʹ products carry (almost) full beam energy!
γ*
(rates before angular cuts)
σ ~ αʹ′/m2 = ε2α/m2 dσ~α2/m3 dm
Symmetric energy, angles in two arms optimize A′ acceptance
E+ ≈ E– ≈Ebeam/2also suppresses e– singles & other pair backgrounds
After rejecting accidental e–π+ (demonstrated in test run), event rate dominated by QED backgrounds above
APEX test run
• Test run performed in Hall A, July 2010
• Verified all key aspects of apparatus performance– VDC tracking performance at 4–6 MHz singles rates– Gas Cerenkov detector in coincidence trigger to reject π+’s– spectrometer optics & mass resolution– measurement of physics backgrounds
• Resonance search on 700K good trident events
6
Many thanks to JLab & Hall A staff for tremendous support!
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mass [MeV]-e+e180 190 200 210 220 230 240 250
Resid
ual
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ts / 0
.5 M
eV
0
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6000
8000
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BaBar
MAMIKLOE+a
TestAPEX
[MeV]A'm100 200 300 400 500
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_
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Accidental
QED (no efficiency
correction)
Data
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e+e-HA'LMass HGeVL
a'êaH2s
sensitivityL
Sensitivity of Proposed Run Plan
C AD
B0.1 0.2 0.3 0.4 0.5
-710
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BaBar
MAMIKLOE+a
TestAPEX
[MeV]A'm100 200 300 400 500
100 300 500_'/
_
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400200
Full APEX run plan and sensitivity
7
1 Month Beam Time– 6 days at 1,2,3 GeV– 12 days at 4.5 GeV)
>100x test-run statistics
Approved by JLab PAC 37 with recommendation to run as soon as possibleExplores parameter space with unparalleled efficiency (particularly above ~300 MeV)
0.1 0.2 0.3 0.4 0.5-710
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BaBar
MAMIKLOE+a
TestAPEX
[MeV]A'm100 200 300 400 500
100 300 500_'/
_
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400200
A1 Experiment
Achim Denig Dark Photon Search @ MAMI
Mixi
ng P
aram
eter
ε2
mγ’ [MeV]
This work:MAMI 2012MESA, 10°MESA, 20°
10-8
10-7
10-6
10-5
10-4
10 100
(g-2)µ
|(g-2)µ|< 2σ
E141
E774
KLOE
MAMI
APEX
(g-2)e vs. α
Figure 12. Compilation of existing exclusion limits and our predictions: For a better visualization we restrict ourselves to theregion currently accessible at fixed-target experiments. Only existing limits as published in Refs. [16, 21, 36, 37, 39, 40] areshown, represented by the shaded regions. We do not show the predictions for other experiments [25, 28–30] in this figurewhich are scheduled to probe the same region of parameter space. The limits of MAMI and APEX are those as given in theirpublications [26, 27]. The prediction of this work for the exclusion limit expected for the MAMI 2012 experiment discussedin section IIIB is depicted by the dashed curves. The prediction for MESA obtained in section IV is indicated by the dotted(dashed-dotted) curve for the setups with a central scattering angle of 10! (20!).
signal cross section given in Ref. [21].For comparison we show in Fig. 10 the acceptance integrated cross section depending on me+e! for a proton targetwith a beam energy of E0 = 80MeV. In the left panel the same curves as in Fig. 9 are plotted. In the right panel ofFig. 10 it is demonstrated, that the VCS contribution corresponding with the Feynman diagrams in Fig. 2 are smallerby more than 6 orders of magnitude in the chosen kinematic setting, and can thus be neglected. As indicated by theshape of the curves for !!SL+TL
!",D+X and !!TL!",D in Figs. 9 and 10, the ratio of these two quantities is equal and thus
the kind of target does not a!ect the exclusion limit concerning the QED background.Fig. 11 shows the calculated ratio !!!/!!TL
! which reaches a value around 8 ! 10 for the proposed settings. Theexpected exclusion limit on "2 as obtained from Eq. (14), to the invariant mass spectra of Fig. 9, is presented onFig. 12, where a mass resolution of 0.125MeV was assumed. The dotted (dashed-dotted) curve on Fig. 12 representsthe settings with central angle of 10! (20!). At very low masses below 10MeV Eq. (14) does not serve as a goodapproximation for the exclusion limit anymore, since Eq. (19) of Ref. [21] overestimates the #" signal cross section byup to 50%.
A compilation of the existing exclusion limits is presented in Fig. 12, which shows the region 5MeV " m!# "600MeV and 10#8 " "2 " 10#4 accessible at fixed-target experiments. Furthermore, existing limits as published inRefs. [16, 21, 36, 37, 39, 40] are also shown, and are represented by the shaded regions. Let us mention that otherplanned experiments [25, 28–30] are scheduled to probe the same region of parameter space. The limits of MAMI andAPEX are those as given in their publications [26, 27]. Our prediction for the exclusion limit expected in the MAMI2012 experiment discussed in section III B is depicted by the dashed curves. The prediction for MESA obtained insection IV is indicated by the dotted (dashed-dotted) curves for the setups with a central scattering angle of 10! (20!).Our calculation shows, that the 2012 experiment is well suited to exclude a large region of the parameter space and
14
Mainz MAMI/A1 experiment– superficially similar
(spectrometer e+e– coincidence)– similar test-run sensitivity
but...– hitting detector rate limits
at least 6mo run needed to match APEX below 200 MeV
– Search above ~200 MeV also hitting beam current and radiation limits
APEX in Context
PRL 106 2518021303.2540
Bottom line: APEX has unique advantage due to high-rate capability and septum magnet (small angle ⇒ higher signal acceptance) 8
0.01 0.110-8
10-7
10-6
10-5
10-40.01 0.1
10-8
10-7
10-6
10-5
10-4
mA' HGeVL
a'êa
APEXfull
A1 Experiment
Achim Denig Dark Photon Search @ MAMI
Mixi
ng P
aram
eter
ε2
mγ’ [MeV]
This work:MAMI 2012MESA, 10°MESA, 20°
10-8
10-7
10-6
10-5
10-4
10 100
(g-2)µ
|(g-2)µ|< 2σ
E141
E774
KLOE
MAMI
APEX
(g-2)e vs. α
Figure 12. Compilation of existing exclusion limits and our predictions: For a better visualization we restrict ourselves to theregion currently accessible at fixed-target experiments. Only existing limits as published in Refs. [16, 21, 36, 37, 39, 40] areshown, represented by the shaded regions. We do not show the predictions for other experiments [25, 28–30] in this figurewhich are scheduled to probe the same region of parameter space. The limits of MAMI and APEX are those as given in theirpublications [26, 27]. The prediction of this work for the exclusion limit expected for the MAMI 2012 experiment discussedin section IIIB is depicted by the dashed curves. The prediction for MESA obtained in section IV is indicated by the dotted(dashed-dotted) curve for the setups with a central scattering angle of 10! (20!).
signal cross section given in Ref. [21].For comparison we show in Fig. 10 the acceptance integrated cross section depending on me+e! for a proton targetwith a beam energy of E0 = 80MeV. In the left panel the same curves as in Fig. 9 are plotted. In the right panel ofFig. 10 it is demonstrated, that the VCS contribution corresponding with the Feynman diagrams in Fig. 2 are smallerby more than 6 orders of magnitude in the chosen kinematic setting, and can thus be neglected. As indicated by theshape of the curves for !!SL+TL
!",D+X and !!TL!",D in Figs. 9 and 10, the ratio of these two quantities is equal and thus
the kind of target does not a!ect the exclusion limit concerning the QED background.Fig. 11 shows the calculated ratio !!!/!!TL
! which reaches a value around 8 ! 10 for the proposed settings. Theexpected exclusion limit on "2 as obtained from Eq. (14), to the invariant mass spectra of Fig. 9, is presented onFig. 12, where a mass resolution of 0.125MeV was assumed. The dotted (dashed-dotted) curve on Fig. 12 representsthe settings with central angle of 10! (20!). At very low masses below 10MeV Eq. (14) does not serve as a goodapproximation for the exclusion limit anymore, since Eq. (19) of Ref. [21] overestimates the #" signal cross section byup to 50%.
A compilation of the existing exclusion limits is presented in Fig. 12, which shows the region 5MeV " m!# "600MeV and 10#8 " "2 " 10#4 accessible at fixed-target experiments. Furthermore, existing limits as published inRefs. [16, 21, 36, 37, 39, 40] are also shown, and are represented by the shaded regions. Let us mention that otherplanned experiments [25, 28–30] are scheduled to probe the same region of parameter space. The limits of MAMI andAPEX are those as given in their publications [26, 27]. Our prediction for the exclusion limit expected in the MAMI2012 experiment discussed in section III B is depicted by the dashed curves. The prediction for MESA obtained insection IV is indicated by the dotted (dashed-dotted) curves for the setups with a central scattering angle of 10! (20!).Our calculation shows, that the 2012 experiment is well suited to exclude a large region of the parameter space and
14
Mainz MAMI/A1 experiment– superficially similar
(spectrometer e+e– coincidence)– similar test-run sensitivity
but...– hitting detector rate limits
at least 6mo run needed to match APEX below 200 MeV
– Search above ~200 MeV also hitting beam current and radiation limits
APEX in Context
PRL 106 2518021303.2540
Bottom line: APEX has unique advantage due to high-rate capability and septum magnet (small angle ⇒ higher signal acceptance) 8
0.01 0.110-8
10-7
10-6
10-5
10-40.01 0.1
10-8
10-7
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mA' HGeVL
a'êa
Dashed green is updated sensitivity estimate for ~14 total beam-days (9 settings) [1303.2540 Beranek, Merkel, Vanderhaeghen]
Detector, beam, and radiation limitations ⇒ Mainz probably can only access high-coupling & low-mass portion of APEX sensitivity (without major upgrades)
APEX vs. Mainz
Mixi
ng P
aram
eter
ε2
mγ’ [MeV]
This work:MAMI 2012MESA, 10°MESA, 20°
10-8
10-7
10-6
10-5
10-4
10 100
(g-2)µ
|(g-2)µ|< 2σ
E141
E774
KLOE
MAMI
APEX
(g-2)e vs. α
Figure 12. Compilation of existing exclusion limits and our predictions: For a better visualization we restrict ourselves to theregion currently accessible at fixed-target experiments. Only existing limits as published in Refs. [16, 21, 36, 37, 39, 40] areshown, represented by the shaded regions. We do not show the predictions for other experiments [25, 28–30] in this figurewhich are scheduled to probe the same region of parameter space. The limits of MAMI and APEX are those as given in theirpublications [26, 27]. The prediction of this work for the exclusion limit expected for the MAMI 2012 experiment discussedin section IIIB is depicted by the dashed curves. The prediction for MESA obtained in section IV is indicated by the dotted(dashed-dotted) curve for the setups with a central scattering angle of 10! (20!).
signal cross section given in Ref. [21].For comparison we show in Fig. 10 the acceptance integrated cross section depending on me+e! for a proton targetwith a beam energy of E0 = 80MeV. In the left panel the same curves as in Fig. 9 are plotted. In the right panel ofFig. 10 it is demonstrated, that the VCS contribution corresponding with the Feynman diagrams in Fig. 2 are smallerby more than 6 orders of magnitude in the chosen kinematic setting, and can thus be neglected. As indicated by theshape of the curves for !!SL+TL
!",D+X and !!TL!",D in Figs. 9 and 10, the ratio of these two quantities is equal and thus
the kind of target does not a!ect the exclusion limit concerning the QED background.Fig. 11 shows the calculated ratio !!!/!!TL
! which reaches a value around 8 ! 10 for the proposed settings. Theexpected exclusion limit on "2 as obtained from Eq. (14), to the invariant mass spectra of Fig. 9, is presented onFig. 12, where a mass resolution of 0.125MeV was assumed. The dotted (dashed-dotted) curve on Fig. 12 representsthe settings with central angle of 10! (20!). At very low masses below 10MeV Eq. (14) does not serve as a goodapproximation for the exclusion limit anymore, since Eq. (19) of Ref. [21] overestimates the #" signal cross section byup to 50%.
A compilation of the existing exclusion limits is presented in Fig. 12, which shows the region 5MeV " m!# "600MeV and 10#8 " "2 " 10#4 accessible at fixed-target experiments. Furthermore, existing limits as published inRefs. [16, 21, 36, 37, 39, 40] are also shown, and are represented by the shaded regions. Let us mention that otherplanned experiments [25, 28–30] are scheduled to probe the same region of parameter space. The limits of MAMI andAPEX are those as given in their publications [26, 27]. Our prediction for the exclusion limit expected in the MAMI2012 experiment discussed in section III B is depicted by the dashed curves. The prediction for MESA obtained insection IV is indicated by the dotted (dashed-dotted) curves for the setups with a central scattering angle of 10! (20!).Our calculation shows, that the 2012 experiment is well suited to exclude a large region of the parameter space and
14
–no publishable result expected from 2012 run
–present dark-force plans focus on lower Aʹ′ mass, including MESA APEX
full
1303.2540
9
Readiness for Full Run
• APEX extended target– target built for test run is at JLab
• SciFi detector for optics calibration– design and production complete; first arm
assembled and tested
• Septum– design nearly finalized & vendor quotes obtained
• HRS detector maintenance is proceeding
10
Target Design: Minimizing Multiple Scattering
schematic overhead view
beam5º
15µm W
Goals: • σ(θ)mult scat≤0.5 mrad
⇒ typical e+e– pair must only go through 0.3% X0 (2-pass) • Target thickness 0.7–8% X0 (depending on Ebeam)
• High-Z target (reduce π yield for given QED rates)• Stable under currents up to ~100 μA
long target ⇒ wider single-run mass coverage 11
Target designed and built by SLAC APEX group for the test run (but not installed), currently at JLab.
Target Design: Minimizing Multiple Scattering
11
Target designed and built by SLAC APEX group for the test run (but not installed), currently at JLab.
Magnetic Spectrometer Optics
12Top view
Measuring Contributions to the Mass Resolution(dominant: angular resolution + mult. scatter)
Test Run Optics Calibration
13
Removable sieve plate is inserted upstream of septum.
Use surveyed locations of sieve holes to calibrate magnetic optics.
Use reconstructed hole sizes to measure resolution.
...this method only works for negative polarity, and requires running at different beam energy.
Mass resolution≈1 MeV~0.5%
Test Run Optics Calibration
13
Removable sieve plate is inserted upstream of septum.
Use surveyed locations of sieve holes to calibrate magnetic optics.
Use reconstructed hole sizes to measure resolution.
...this method only works for negative polarity, and requires running at different beam energy.
Mass resolution≈1 MeV~0.5%
After Calibration
Sieve H. Pos [m]
Siev
e V.
Pos
[m]
HRS optics“Active sieve slit”: tagging by a Sci Fiber detector1 mm fibers with 1/16” pitchProjected rate: 1-3 MHz per fiberOff-line time window < 5 nsNearing completion
Allows optics calibration at production beam energy & for both polarities
14
New HRS Septum Magnet
Designed for parallel field capability(minimize fringe field near beamline)
Optimized for full angular acceptance
High density coils used to enable high-energy use15
New HRS Septum Magnet
16
Design to be completed in next few weeks quotes obtained from vendors partially funded by NSERC DAS
New extension box (as for PREX) and vacuum connection to spectrometers needed
Requires 2kA for high-energy settings (same as SBS magnet)
Summary
17
APEX can explore important range of mass and coupling most efficiently and before other experiments
Opportunity for immediate science impact – even with commissioning-quality beam.
APEX has demonstrated feasibility and power of spectrometer searches for hidden-sector photonsStrong physics impact already from test run (most cited Hall A result in last 5 years)
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sensitivityL
Sensitivity of Proposed Run Plan
C AD
B0.1 0.2 0.3 0.4 0.5
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BaBar
MAMIKLOE+a
TestAPEX
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Thanks!
19
BACKUP SLIDES
Sieve Slit Method
20
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
HRS optics for APEX
21
Angular Resolutions
22
LHRS (mrad)LHRS (mrad) RHRS (mrad)RHRS (mrad)Δφ 0.10 Δφ 0.10
Δθ 0.24 Δθ 0.20
σφ_width 0.26 σφ_width 0.43
σθ_width 1.81 σθ_width 1.75
σφ 0.29 σφ 0.44
σθ 1.86 σθ 1.77
Optics calibration precisionTracking precision
φ/θ – hor / vert angles
Averages weighted according to statistics
Final resolutions
Mass Resolution
23
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
Coincidence trigger and particle ID performance
24)/psh + Eps
(E0 0.5 1 1.5 2 2.5
Even
ts
0
100
200
300
400
500
600Electron detection eff.Pion rejection eff.Pion leakage
0.9670.9690.044
Electron detection effPion rejection effPion leakage
0.9560.9810.027
= 765 kHzscinf
sample from GCπe sample from GC
Calorimeter
Amplitude0 200 400 600 800 1000 1200 1400 1600 1800 2000
Even
ts
1
10
210
310
Positron detection eff.Pion rejection eff.
0.9640.979
sample from LGπ sample from LG+e
Gas Cherenkov
raw TDC channels (0.5 ns)470 480 490 500 510 520 530 540 550 560 570
Eve
nts
0
500
1000
1500
2000
2500
containing coincident events10 ns timing gate
A on Tantalum target+ with 56 - e+Trigger level timing of e
coincidence peak for two-arm X–e+ trigger (requires coincident GC signal in positive-polarity arm)