Measurement of the muon anomaly to high and even higher precision David Hertzog* University of Illinois at Urbana-Champaign * Representing the E821 Collaboration: Boston, BNL, Budker Inst., Cornell, KFI, Heidelberg, Illinois, KEK, Minnesota, Tokyo Tech, Yale & new E969 groups: JMU, Kentucky, LBL/UC-Berkeley

Outline The muon is a little brother of the tau n The “old” BNL experiment  With the 2004 result on  - n The theoretical ingredients and overall motivation u Lots will follow today by the real experts n The “new” experiment – 0.2 ppm is the new goal u Some fresh new ideas and bold ambition u Approved this week at BNL with Highest “Must Do” Status

(1) Precession frequency (2) Muon distribution (3) Magnetic field map Muon g-2 is determined from 3 measurements B

And, 4 miracles make it happen n P olarized muons    

Muons are created from in-flight  decay and enter ring in a bunch

And, 4 miracles make it happen n P olarized muons P recession proportional to ( g -2)     µ

Momentum Spin e The muon spin precesses faster than the cyclotron frequency: a  is proportional to the difference frequency

And, 4 miracles make it happen n P olarized muons P recession proportional to ( g -2) P  The magic momentum E field doesn’t affect muon spin when  = 29.3     µ

BNL Storage Ring incoming muons Quads KICK ns 100 kV Only a few percent get stored!

Magnetic Field Continuously monitored using 150 fixed probes mounted above and below the storage region Measured in situ using an NMR trolley 1 ppm contours

And, 4 miracles make it happen n P olarized muons P recession proportional to ( g -2) P  The magic momentum E field doesn’t affect muon spin when  = 29.3 n P arity violation in the decay     µ

2.5 ns samples Measuring the difference frequency “  a ” e+e+ TIME Counts < 20 ps shifts < 0.1% gain change

Few billion events Getting a good  2 is a challenge Fit to Simple 5-Par Function N(t) = N 0 e -t/  [1+Acos(  a t +  )]

Fourier Spectrum of Residuals to 5-par Fit f g-2 ≈229 KHz f CBO ≈466 KHz In 2001, we adjusted the ring index to avoid overlap

Detector “Swims” Beam into storage volume Detector “Breathes” (smaller effect) Coherent Betatron Oscillations Radius Acceptance Inflector mapping to storage volume Acceptance vs average radius

Modulation of N 0, A,  with f cbo

Pileup Subtraction Phase shift possible Separate when you can... low rate deadtime corrected Energy of positrons Extrapolate to zero deadtime on average using out-of-time resolved events Build pileup-free histogram with deadtime

Muon Loss & Stored Protons Excess loss rate Constant loss rate Uncertainty, mostly due to protons muon decay hit  Account for “slow effects” by correction of muon flux in ring beyond exponential decay Do these muons have a different phase ?

Internal Consistency: Chi-Sq, Run # Normalized  2 vs. Start Time of Fit Precession Frequency vs. Run Number

Internal Consistency: Start Time, Detector, Energy Precession Frequency vs. Detector # Precession Frequency vs. Fit Start Time Precession Frequency vs. Energy Band

Five complementary analyses of  a Low n (black), high n (clear), combined (red) data sets. G2off production 9-parameter ratio G2Too production 3 - parameter ratio with cancellation G2off production Multi-parameter G2off production Multi-parameter quad corrections G2Too production Multi-parameter, E th =1.5 GeV asymmetry-weighted,

The new result is in excellent agreement with previous measurements on  + g-2 Collaboration: PRL (2004) a  = (8)(3)  (0.7 ppm) -

g ≠ 2 because of virtual loops, many of which can be calculated very precisely B    QED Z Weak  Had VP  Had LbL Many of the next 8! talks will discuss the standard model theory

Hadronic vacuum polarization is obtained from e + e - and/or tau data h µ h --  h e+e+ e-e-  is related toand also

The  - e + e - comparison Davier, et al hep-ex/ Jan 04 Difference is significant AND energy dependent

Pion Formfactor CMD-2 KLOE s  [GeV 2 ] From G. Venanzone And, from ICHEP, A. Hocker is stepping back from the Tau result until isospin issues are fully understood: Today, we’ll hear about the latest KLOE “confirmation” of CMD2

Comparison of final results and theory a  (world avg  = (6)  (0.5 ppm)  ee  =25±9 Includes new HLbL shift and KLOE result ee-  marriage ± Opps Divorce! Opps2 KLOE

Discrepancy with e + e - based theory n What might this mean? n New physics or a fluctuation

Non-zero  a  appeals to a catalog of SM Extensions New physics … SUSY Leptoquarks Muon substructure Anomalous W couplings µ µ W µ W B Sensitive for supergravity grand unification, especially for large tan  Chargino-Sneutrino Neutralino-Smuon tan  = a  SUSY [ ] smuon mass (GeV) ee -expt tau -expt

Courtesy K.Olive based on Ellis, Olive, Santoso, Spanos In CMSSM, a  can be combined with b→s , cosmological relic density  h 2, and LEP Higgs searches to constrain  mass Allowed  band a  (exp) – a  (e+e- thy) Excluded for neutral dark matter Preferred tan  =10 Excluded by direct searches

Same Discrepancy Standard Model  a   25(5) x (5   a   0 (5) x Two “futures” when new experiment and improved theory are complete

E969 is a new g-2 experiment at BNL Strategy is basic: Get more muons – E821 was statistics limited (  stat = 0.46 ppm,  syst = 0.3 ppm) u AGS 20% more protons u Backward-decay beam u Higher-transmission beamline u New, open-end inflector u Upgrade detectors, electronics, DAQ Reduce  B, systematic uncertainty on magnetic field, B u Improve calibration, field monitoring and measurement Reduce   a systematic uncertainty on precession, ω a u Improve the electronics and detectors u New parallel “integration” method of analysis n Keep the main ideas and ring Expect 5 x more rate

E821 used forward decay beam, which permitted a large  component to enter ring GeV/c Decay GeV/c Pedestal vs. Time Near sideFar side This baseline limits how early we can fit data

New experiment uses a backward decay beam with large mismatch in  momentum at final slits Expect for both sides 5.32 GeV/c Decay GeV/c No hadron-induced prompt flash Approximately the same muon flux is realized x 1 more muons

Decay region will include more quads to capture muons Lattice doubled E821 lattice x 2 more muons

Improved transmission into the ring Inflector Inflector aperture Storage ring aperture E821 Closed EndP969 Proposed Open End Outscatters muons x 2 more muons

Systematic Error Evolution by Factor of 2 n Field improvements will involve better trolley calibrations, better tracking of the field with time, temperature stability of room, improvements in the hardware n Precession improvements will involve new scraping scheme, lower thresholds, more complete digitization periods, better energy calibration Systematic uncertainty (ppm) E969 Goal Magnetic field –  p Anomalous precession –  a

E969: Precession Measurement n Expect 5 x more rate u Segment calorimeters u 500 MHz waveform digitization u Greatly increased data volume for DAQ n Introduce parallel “Q” method of data collection and analysis u Integrate energy flow vs. time T Method Q Method

Starting ideas for new, fast, dense and segmented W-SciFi calorimeters n 20-fold segmentation n 0.7 cm X 0 n 14%/Sqrt(E) n Greatly constrained space

Conclusions n E821 was very successful, reaching 0.5 ppm final uncertainty n Theory has gone from  5 ppm →  0.6 ppm during same time period Today’s status: tantalizing 2.7  discrepancy n Next phase includes new, approved experiment and continued work on hadronic issues related to theory u KLOE, BaBar, Belle, radiative corrections, lattice, … u Together, expect reduction in expt-thy comparison by x 2

Extra Slides Follow

Field Uncertainties - History * higher multipoles, trolley voltage and temperature response, kicker eddy currents, and time-varying stray fields. Source of Uncertainty Absolute Calibration0.05 Calibration of Trolley Trolley Measurements of B Interpolation with the fixed probes Inflector fringe field uncertainty from muon distribution Other* Total

Systematic errors on ω a (ppm) σ systematic E969 Pile-up AGS Background0.10 * Lost Muons Timing Shifts E-Field, Pitch *0.05 Fitting/Binning * CBO Beam Debunching0.04 * Gain Change Total Σ* = 0.11

The  - decay input to H-VP n Data precise n Related by CVC with corrections  Isospin asymmetry (      vs        W-W-  Issues with      mass and width raised last year u Long-distance radiative corrections Bottom line, can the  data contribute in the long run at sub % level? 