John Leacock April 20, 2009 Qweak: A Precision Test of Standard Model and Determination of Weak Charge of the Proton Four fundamental interactions of the universe: gravitational, electromagnetic, weak, and strong Electromagnetic interaction e-e- γ p W-W- u e-e- d e Charged weak interaction Z0Z0 p e-e- Neutral weak interaction

John Leacock April 20, 2009 Parity Violation of Weak Interaction *Left-handed fermions are more likely to interact via the weak force than right-handed fermions* Right-handed fermion momentum Left-handed fermion spin momentum spin Parity Violation (parity operator: r  -r ) T.D. Lee, C.N. Yang; suggested based on various particle decays (1956) C.S. Wu – first experimental determination polarized 60 Co beta decay (1957)

John Leacock April 20, 2009 Exploit parity violation of weak interaction Elastic scattering of polarized electrons off of protons e - + p → e - + p Z p e 2 +  p e  p e 2  p e Z p e Z p e 2 ~ 3 x 10 -7

John Leacock April 20, 2009 The Weak Mixing Angle θ W ZμAμZμAμ = ( ) () cosθ W –sinθ W sinθ W cosθ W () W (3) μ B μ A μ is the photon and Z μ is the Z boson The photon and the Z boson are combinations of the same two massless states. This unifies the electromagnetic and weak interactions Electromagnetic and Weak interactions are manifestations of the same fundamental interaction, Electroweak. Coupling constants are same order of magnitude: e = g*sinθ W ~ g/2 M NC ~ g2g2 -Q 2 + M Z 2 M γ ~ e2e2 -Q 2 Weak Neutral CurrentElectromagnetic θ W is the weak mixing angle between the two neutral currents in the model Q 2 is 4 momentum transfer Q 2 = 4EE’sin 2 θ/2 Q 2 → 0 M NC ~ g2g2 MZ2MZ2

John Leacock April 20, 2009 How Asymmetry Relates to Weak Charge Q 2 for the Qweak experiment is 0.03 GeV 2 Because the momentum transfer is small the Qweak experiment is less sensitive to the internal structure of the proton.

John Leacock April 20, 2009 Standard Model predicts sin 2 θ W “runs” with Momentum Transfer Electroweak radiative corrections  sin 2  W varies with Q + + 

John Leacock April 20, 2009 Constraining New Physics Leptoquarks change a quark to a lepton R Parity Violating Super Symmetry Heavier Z boson R Parity Conserving Super Symmetric Particle Loops RPC If R parity is conserved (B-L=0) then the smallest SUSY particles may make up dark matter. If R parity is violated then long ago SUSY particles would have decayed into non-SUSY particles

John Leacock April 20, 2009 A 4% Q p Weak measurement probes with 95% confidence level for new physics at energy scales to: Indirect Probe of “New Physics” X + + The TeV discovery potential of weak charge measurements will be unmatched until LHC “warms up”. If LHC uncovers new physics, then precision low Q 2 measurements will be needed to determine charges, coupling constants, etc. ~ TeV

John Leacock April 20, 2009 Overview of the Q p Weak Experiment Incident beam energy: GeV Beam Current: 180 μA Beam Polarization: 85% LH 2 target power: 2.5 KW Central scattering angle: 8.4° ± 3° Phi Acceptance: 53% of 2 Average Q²: GeV 2 Acceptance averaged asymmetry:–0.29 ppm Integrated Rate (all sectors): 6.4 GHz Integrated Rate (per detector): 800 MHz Experiment Parameters (integration mode) Polarized Electron Beam 35cm Liquid Hydrogen Target Collimator with 8 openings θ= 8° ± 2° Region I GEM Detectors Region II Drift Chambers Toroidal Magnet Region III Drift Chambers Elastically Scattered Electron Eight Fused Silica (quartz) Čerenkov Detectors Luminosity Monitors small effect Need to be sensitive to elastic scattering only: Magnet focuses elastics to detector and bends inelastics away Azimuthally symmetric to limit false asymmetries.

John Leacock April 20, 2009 Target QTOR + Power Supply R-3 Rotation System R-2 HDCs Downstream Pb Shielding Beam Qweak Experimental Components GEMs R-3 VDC Main Detectors Lumis Collimators Lumis 6 feet

John Leacock April 20, 2009 Downstream Luminosity monitor  Symmetric array of 8 quartz Cerenkov detectors instrumented so rad hard PMTs operated in “vacuum photodiode mode” & integrating readout at small  (~ 0.8  ). Low Q 2, high rates ~29 GHz/octant. Expected signal components: 12 GHz e-e Moeller, 11 GHz e-p elastic, EM showers 6 GHz. Expected lumi monitor statistical error ~ (1/6) main detector statistical error. Expected lumi monitor asymmetry << main detector asymmetry. Sensitive check on helicity-correlated beam parameter corrections procedure. low Q 2 → low asymmetry Regress out target density fluctuations. Q p Weak Downstream Luminosity Monitors

John Leacock April 20, 2009 Downstream LUMI Design Quartz window PMT Light guide ~95% spectral reflective 4x3x1.3cm quartz e-e- photons Image from GEANT4 simulation of DS LUMI 35 cm Cerenkov radiation

John Leacock April 20, 2009 JLAB Beam Test (June 2008) Tested Prototype of Qweak DS lumi and G0 lumis in JLAB beam Goals of Test: 1.Test downstream Qweak LUMI monitor prototype near experimental conditions 2.Use known working G0 lumis to compare Qweak prototype lumi 3.Determine dependence of boiling asymmetry widths to data taking frequency

John Leacock April 20, 2009 Lumi Asymmetry Distribution In general the width of the asymmetry depends on these sources of random noise; the number of events, the electronic noise, the beam parameter correlation, and the density fluctuations of the target Not interested in the mean value of the asymmetry in this test Only interested in width of the asymmetry measurement i.e. how well we can measure the asymmetry

John Leacock April 20, 2009 Normalized yields 30Hz Expect normalized LUMI signal to be independent of beam current for a linear LUMI monitor approx. the same (~1%) Yield drops by ~20% at 80 uA → evidence of boiling

John Leacock April 20, 2009 Fitting model to data for Carbon Above is an example of a typical fit Counting statistics A = > 230 ppm at 80uA Electronic noise B = > 98 ppm at 80uA Beam position correlation C = ppm --> constant A C I B I A                statistical error elec. noise beam position

John Leacock April 20, 2009 Asymmetry width vs. beam current All six LUMI asymmetry widths increase for LH2 Dominated by boiling All six LUMI asymmetry widths decrease for Carbon Dominated by counting statistics

John Leacock April 20, 2009 LH2 boiling width Boiling increases with current at 250 Hz density term nonzero Boiling increases with current for 30Hz Fit LH2 asymmetry vs. current to then extracted the density term

John Leacock April 20, 2009 Boiling width vs. data taking frequency The boiling asymmetry widths decrease as a function of data taking frequency What does it all mean? Possibly less stringent boiling requirements for the liquid hydrogen target for Qweak

John Leacock April 20, 2009 Upstream LUMI Picture from GEANT4 simulation Upstream lumis will be less sensitive to distance from beam line and beam current. Good test of target boiling. US lumi position

John Leacock April 20, 2009 Upstream LUMI Recent result from upstream lumi monitor setup with quartz 133 GHz expected rate with unity gain PMT base yields ~1 pe/event-PMT → 133x10 9 e - /second → 21 nA x 50 MΩ → ~1 Volt photons/event

John Leacock April 20, 2009 Future Work 1.Design housings for upstream and downstream lumis and test them at VT 2.Complete R375 PMT linearity test 3.Move to Jefferson Lab this Fall 4.On-site VT drift chamber expert at JLAB 5.National Nuclear Physics Summer School at Michigan State June 28-July 10 6.PAVI conference (PArity VIolation in the electroweak interaction) June Qweak installation begins December Qweak data taking May 2010

John Leacock April 20, 2009 Extra Slides

John Leacock April 20, 2009 Precision Measurements far Below the Z-pole are Sensitive to New Physics Precision measurements well below the Z-pole have more sensitivity (for a given experimental precision) to new types of tree level physics, such as additional heavier Z’ bosons.

John Leacock April 20, 2009 The setup Pictures: (clockwise from top left) 1. LUMI monitors position (directly in front of beam dump) 2. Beam cups inside the beam pipe 3. LUMI1 Left G0, LUMI2 Top QWEAK proto, LUMI3 Right G0, LUMI4 Bottom G0 Note: LUMI5, LUMI6 attached to outside of beam pipe near LUMI1 (already removed)

John Leacock April 20, 2009 Beam Parameter Correlation Lumi asymmetry width due to beam position fluctuations in x: ( mm -1 ) ( mm) ~ 411 ppm Slope ~ mm -1  (  x) ~ mm

John Leacock April 20, 2009 Our statistical width is given by: We can reduce the relative contribution of the target boiling term by going to higher data-taking frequencies (increased  counting ) assuming  target either stays constant or decreases with frequency. The data here indicate that the boiling term drops with frequency as What do we gain from higher data-taking rates?

John Leacock April 20, 2009 LH2 asymmetry model N H /N C correction factor needed because normalized yield varies with beam current At 80uA normalized yields are the same

John Leacock April 20, 2009 Compare to data values The fitted values of the electronic noise and beam position parameter contributions can be independently determined directly from the data

John Leacock April 20, 2009 Results for Qweak Prototype Lumi Qweak downstream prototype lumi Crude rate simulation (5.7 GeV, 20 cm LH 2 target, 80  A) gives ~ 1 GHz expected rate (mostly Mollers)  With 10 pe’s event, this gives an expected unity gain photocathode current of ~ 1.6 nA  TRIUMF I/V on 50 M  setting  0.08 V  For Qweak expect ~ 100 GHz  8.0 V output from preamp expected, so this setting (or the 25 M  setting) should be fine Also moved one lumi radially by ~ 8 cm = 0.2 degrees (from 0.6 to 0.8 degree scattering angle)  Observed rate drop by factor of 9 (expected 3) more simulation needed

John Leacock April 20, 2009 Electronic Noise Contribution (60 cycle noise) 250,1000Hz runs have 60 cycle dependence (linephase monitor implemented by Paul King and Bill Vulcan) Worst Case Best Case Fit results to a 9 th order polynomial to remove linephase dependence