DSA MENU Qweak final
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First Result from Q weak David S. Armstrong College of William & Mary MENU 2013 Rome, Italy Oct 2 2013
Transcript of DSA MENU Qweak final
First Result from Qweak
David S. Armstrong College of William & Mary
MENU 2013 Rome, Italy Oct 2 2013
Search for physics Beyond the Standard Model
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• Neutrino mass and their role in the early universe 0νββ decay, θ13 , β decay,… • Ma3er-‐an5ma3er asymmetry in the present universe EDM, DM, LFV, 0νββ, θ13 • Unseen Forces of the Early Universe Weak decays, PVES, gμ-‐2,…
LHC new physics signals likely will need addi3onal indirect evidence to pin down their nature
• Neutrons: LifeJme, P-‐ & T-‐ViolaJng Asymmetries (LANSCE, NIST, SNS...) • Muons: LifeJme, Michel parameters, g-‐2, Mu2e (PSI, TRIUMF, FNAL, J-‐PARC...) • PVES: Low-‐energy weak neutral current couplings, precision weak mixing angle
(SLAC, Jefferson Lab, Mainz) Atoms: atomic parity violaJon
Ideal: select observables that are zero, or significantly suppressed, in Standard Model
-‐ Received Wisdom: Standard Model is incomplete, and is low-‐energy effecQve theory of more fundamental physics
-‐ Low energy (Q2 <<M2) precision tests: complementary to high energy measurements
Qweak: Proton’s weak charge
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EM Charge Weak Charge
u 2/3
d -‐1/3
P (uud) +1
N (udd) 0 -‐1
“Accidental suppression”
sensiQvity to new physics
-‐ Neutral current analog of electric charge
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Parity-‐violaQng electron sca[ering
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APV ∝
G FQ2
4πα 2gA
e gVT + βgV
e gAT( ) ~ 10−4Q2 GeV2⎡⎣ ⎤⎦
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Electroweak interference
Qweak: Proton’s weak charge
Use four-‐fermion contact interacQon to parameterize the effecQve PV electron-‐quark couplings (mass scale and coupling)
Large θ Small θ
Erler, Kurylov, and Ramsey-‐Musolf, PRD 68, 016006 2003
A 4% measurement of the proton’s weak charge would probe TeV scale new physics
New physics:
new Z', leptoquarks, SUSY ...
For electron-‐quark sca[ering:
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SM
Qweak kinemaQcs Hadronic term extracted from fit
ExtracQng the weak charge
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Hadron structure enters here: electromagneQc and electroweak form factors…
Previous experiments (strange form factor program: SAMPLE, HAPPEX, G0, PVA4 experiments at MIT/Bates, JLab and MAMI) explored hadron structure more directly; allow us to subtract our hadronic contribuQon
Reduced asymmetry more convenient:
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PVES challenges: • StaQsQcs
– High rates required
• High polarizaQon, current
• High powered targets with large acceptance
• Low noise – Electronics, target density fluctuaQons
– Detector resoluQon
• SystemaQcs – Helicity-‐correlated beam parameters
– Backgrounds (target windows)
– Polarimetry
– Parity-‐conserving processes
PVES Challenges
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Qweak’s goal: most precise (relaQve and absolute) PVES result to date.
Parity violaQng asymmetry
Uncertainty
Difficulty
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MeeQng PVES Challenges
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-‐ Rapid helicity reversal (960 Hz) -‐ 180 μA beam current (JLab record) -‐ Small sca[ering angle: toroidal magnet, large acceptance -‐ GHz detected rates: data taking in integraQng mode -‐ High power cryogenic target -‐ Exquisite control of helicity-‐correlated beam parameters -‐ Two independent high-‐precision polarimeters -‐ RadiaQon hard detectors -‐ Low noise 18-‐bit ADCs -‐ High resoluQon Beam Current monitors
The Qweak Apparatus
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Main detectors 8-‐fold symmetry
Ver3cal driA chambers (VDC)
(rotate)
Trigger scin3llator
Shield wall
Lintels
QTOR
Lead collar
Cleanup collimators
Target
Tungsten plug Horizontal driA
chambers (HDC) (rotate)
e- beam e- beam
Acceptance defining collimator
QTOR
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35 cm, 2.5 kW liquid hydrogen target
World’s highest powered cryotarget
• Temperature ~20 K • Pressure: 30-‐35 psia
• Beam at 150 – 180uA
Qweak Target
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Target boiling might have been problemaQc!
MD LH2 Asymmetry
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35 cm, 2.5 kW liquid hydrogen target
World’s highest powered cryotarget
• Temperature ~20 K • Pressure: 30-‐35 psia
• Beam at 150 – 180uA
Qweak Target
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LH2 staQsQcal width (per quartet): • CounQng staQsQcs: 200 ppm
• Main detector width: 92 ppm
• BCM width: 50 ppm
• Target noise/boiling: 37 ppm
228 ppm
Target boiling might have been problemaQc!
MD LH2 Asymmetry
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• Main detectors
Toroidal magnet focuses elasQcally sca[ered electrons onto each bar – 8 Quartz Cerenkov bars – Azimuthal symmetry maximizes rates and reduces systemaQc uncertainQes
– 2 cm lead pre-‐radiators reduce background
Main Detectors
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SimulaQon of sca[ering rate MD face
Close up of one detector in situ
Measured
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•
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Correct for radiaQve effects in target with Geant 4 simulaQons, benchmarked with gas-‐target & solid target studies
SimulaQon blue
Data red
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KinemaQcs (Q2) determinaQon
Beam Polarimetry
PolarizaQon is our largest systemaQc uncertainty (goal: 1%) This is a challenging goal; so we built a second, independent measurement device.
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Møller polarimeter – Precise, but invasive – Thin, pure iron target – Brute force polarizaQon – Limited to low current
Compton polarimeter – Installed for Q-‐weak – Runs conQnuously at high currents – StaQsQcal precision: 1% per hour
We detect both recoil electron and photon.
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Beam Polarimetry
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Note the good agreement between both polarimeters
Preliminary Run 2 PolarizaQon – For IllustraQve Purposes Only
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A of Auxiliary Measurements
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Qweak has data (under analysis) on a variety of observables of potenQal interest for Hadron physics:
• Beam normal single-‐spin asymmetry* for elasQc sca[ering on proton • Beam normal single-‐spin asymmetry for elasQc sca[ering on 27Al • PV asymmetry in the region. • Beam normal single-‐spin asymmetry in the region. • Beam normal single-‐spin asymmetry near W= 2.5 GeV • Beam normal single-‐spin asymmetry in pion photoproducQon • PV asymmetry in inelasQc region near W=2.5 GeV (related to box diagrams) • PV asymmetry for elasQc/quasielasQc from 27Al • PV asymmetry in pion photoproducQon
*: aka vector analyzing power aka transverse asymmetry; generated by imaginary part of two-‐photon exchange amplitude (pace Wim van Oers)
N → Δ
N → Δ
γZ
Q-‐weak ran from Fall 2010 – May 2012 : four disQnct running periods • Hardware checkout (Fall 2010-‐January 2011) • Run 0 (Jan-‐Feb 2011) • Run 1 (Feb – May 2011)
• Run 2 (Nov 2011 – May 2012)
First result
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We have completed and unblinded the analysis of “Run 0” (about 1/25th of our total dataset).
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arXiv:1307:5275 accepted in PRL, to appear online Oct. 13
Reduced Asymmetry
Hadronic part extracted through global fit of PVES data.
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in the forward-‐angle limit (θ=0)
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Reduced Asymmetry
Hadronic part extracted through global fit of PVES data.
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in the forward-‐angle limit (θ=0)
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The C1q & the neutron’s weak charge
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0.22
0.24
-0.70 -0.65 -0.60 -0.55 -0.50 -0.45 -0.40
0.18 0.17
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0.14 0.13
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C1u < C1d
C1u
+ C
1d
sin e |2
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0.26
133Cs APV PVES
Inner Ellipses - 68% CLOuter Ellipses - 95% CL
ZW
The C1q & the neutron’s weak charge
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0.22
0.24
-0.70 -0.65 -0.60 -0.55 -0.50 -0.45 -0.40
0.18 0.17
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0.14 0.13
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C1u < C1d
C1u
+ C
1d
sin e |2
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-
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-
-
-
-
-
0.20
0.26
133Cs APV PVES
Inner Ellipses - 68% CLOuter Ellipses - 95% CL
ZW
Combining this result with the most precise atomic parity violaQon experiment we can also extract, for the first Qme, the neutron’s weak charge:
Weak mixing angle result
* Uses electroweak radiaQve correcQons from Erler, Kurylov, Ramsey-‐Musolf, PRD 68, 016006 (2003)
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Recall: in Standard Model, at tree-‐level, = = (1 -‐ 4sin2θW)
0.0001 0.001 0.01 0.1 1 10 100 1000 10000
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sin2 θ
w (Q
)
Q (GeV)
Erler MSbar
This Result
Published
Ongoing
NuTeV
LEP
SLD
Tevatron
QW(Cs) APV
QW(e) E158
QW(p) JLab (estimated final uncertainty)
QW(p) JLab (4% of Qweak data
+ PVES)
“Teaser”
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“Teaser”
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An5cipated precision of full data set
Summary
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First result (4% of data set):
Lots of work to push down systemaQc errors, but no show-‐stoppers found….
Expect final result in 12-‐18 months Qme.
Grazie to MENU-‐2013 organizers for the chance to give this talk!
Thanks to my Qweak collaborators, from whom many slides borrowed…
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Qweak CollaboraQon
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D.S. Armstrong, A. Asaturyan, T. Averett, J. Balewski, J. Beaufait, R.S. Beminiwattha, J. Benesch, F. Benmokhtar, J. Birchall, R.D. Carlini1, J.C. Cornejo, S. Covrig, M.M. Dalton, C.A. Davis, W. Deconinck, J. Diefenbach, K. Dow, J.F. Dowd, J.A. Dunne, D. Dutta, W.S. Duvall, M. Elaasar, W.R. Falk, J.M. Finn1, T. Forest, D. Gaskell, M.T.W. Gericke, J. Grames, V.M. Gray, K. Grimm, F. Guo, J.R. Hoskins, K. Johnston, D. Jones, M. Jones, R. Jones, M. Kargiantoulakis, P.M. King, E. Korkmaz, S. Kowalski1, J. Leacock, J. Leckey, A.R. Lee, J.H. Lee, L. Lee, S. MacEwan, D. Mack, J.A. Magee, R. Mahurin, J. Mammei, J. Martin, M.J. McHugh, D. Meekins, J. Mei, R. Michaels, A. Micherdzinska, K.E. Myers, A. Mkrtchyan, H. Mkrtchyan, A. Narayan, L.Z. Ndukum, V. Nelyubin, Nuruzzaman, W.T.H van Oers, A.K. Opper, S.A. Page1, J. Pan, K. Paschke, S.K. Phillips, M.L. Pitt, M. Poelker, J.F. Rajotte, W.D. Ramsay, J. Roche, B. Sawatzky,T. Seva, M.H. Shabestari, R. Silwal, N. Simicevic, G.R. Smith2, P. Solvignon, D.T. Spayde, A. Subedi, R. Subedi, R. Suleiman, V. Tadevosyan, W.A. Tobias, V. Tvaskis, B. Waidyawansa, P. Wang, S.P. Wells, S.A. Wood, S. Yang, R.D. Young, S. Zhamkochyan
1Spokespersons 2Project Manager Grad Students
