Muon g-2 … Why? How? Where? David Hertzog (UIUC)

1. Muon g-2 … Why? How? Where?David Hertzog (UIUC) • Muon magnetic dipole moment experiments are more than 50 years old • … like other “precision” measurements, the method and precision have certainly evolved ! • Emphasis on difference of g from 2, a 1/800 effect. • In each generation, significant advances were made • QED through many orders ~5th order • Hadronic VP to better than 1% • Weak loops required, through 2nd order • g-2 measured now to 0.54 ppm • From BNL, a 3.4 s difference exists from SM • Dam(expt – thy)≈ 300 ± 88 x 10-11 • Statistics limited • The next-generation effort is about precision input to pin down the parameters of the New Standard Model • Where should it be located ? hertzog@uiuc.edu

2. Excerpts from P5  inconclusive, but not promising support • A next-generation (g-2) experiment could be mounted at Brookhaven or Fermilab or offshore at JPARC. • There is an excellent physics case … • … estimated cost to the US particle physics programis substantial andwould compromise the timely development of higher-priority precision physics experimentssuch as muon-to-electron conversion. [ estimate was provided at about $55M ] • US participation in an experiment at JPARC would cost less and the US in-kind contribution of the existing precision storage ring, which is central to the experiment, would be substantial. • A modest level of R&D support should be made available for the (g-2) collaboration to determine the optimal path toward a next generation experiment.

3. Dam improvement requires both experimental and theoretical progress Recent: new KLOE Had VP agrees with other e+e- inputs to SM units: x 10-11 Combined Error This would get to ~9s Experimental Error Actual path ? Theory Error

4. Muon g-2 is very sensitive to SUSY through loops, which are amplified by tanb R-parity conserving Supersymmetry (vertices have pairs) See full Topical Review: D. Stöckinger hep-ph/0609168v1, J.Phys. G34 (2007) R45-R92

5. Typical CMSSM 2D space showing g-2 effect(note: NOT an exclusion plot) Present: Dam = 297 ± 88 x 10-11 Future Dam = 297 ± 39 x 10-11 Here, neutralino accounts for the WMAP implied dark matter density scalar mass 2s 1s Excluded for neutral dark matter gaugino mass With new experimental and theoretical precision and same Dam This CMSSM calculation: Ellis, Olive, Santoso, Spanos. Plot update: K. Olive

6. Expt The Snowmass Points and Slopes give reasonable benchmarks to test observables with model predictionsMuon g-2 is a powerful discriminatorno matter where the final value lands!! Future? Model Version SPS Definitions

7. Just yesterday ... And, many more plots in this paper and other papers

8. And, even at this User’s Meeting … Antonio Masiero LFV vs. MUON (g – 2) Isidori, Mescia, Paradisi, Temes

9. e Momentum Spin Final report: Bennett et al, PRD 73, 072003 (2006) Considerations to aim at ~15 x 10-11 experimental precision

10. The BNL storage ring will remain the central element

11. wa 1 ppm contours Muon g-2 is determined by a ratio of two precision measurements:waand B(and some knowledge of the muon orbit) Improving here requires greater statistics … x 25 And, reducing background and controlling fit parameters from beam motions B Improving here requires more uniform field – shimming, and in the delicate procedure to calibrate and measure the field – using pNMR

12. Then, to accept the higher rate, changes in the experiment are required; e.g., 4 Segmented detectors More muons are available, even in the existing experimental setup. Open inflector 2 1 Quad doubling 3 Improve kicker

13. Extend the beamline to catch more muons and remove pions FNAL min Removed pions BNL Even more Ideal…

14. Ideal conditions at FNAL using 8 GeV p • Long beamline possible; more m, less flash • High repetition rate of muon fills in ring • 84 fills / 1.4 sec  60 Hz 14.5 x BNL • > 20 times statistics in one year Target where pbar target sits g-2

15. This experiment could also nicely move to J-PARC … and a lot of thinking has started in this direction …

16. The interest in a JPARC version has been mounting since January, 2008 … from N. Saito et al • Proton bunch harmonics 9  18 (longitudinal); 18  90 (transverse)  26 Hz • Site layout could exist with Fast extraction in Slow extraction hall (see cartoon below) • “Backward” decay beam ideal here to remove flash (30 GeV proton flux is very high for rate)

17. A long task list with exciting challenges • At either location • New decay beamline designs • New Inflector • New / improved storage ring kicker • New calorimeters, hodoscopes, waveform digitizers, DAQ, … • Improved shimming, measuring, monitoring system • Improved scraping and other beam controls • Simulations ! Offline analysis • Specific location issues • Proton beam gymnastics • Physical layout • Moving and re-installing a delicate instrument • Forming full and new collaborations • Costs under tight budget constraints

18. Conclusions • A next-generation experiment is likely to happen. • Nuclear Physics LRP strong endorsement • P5: supportive • Motivation sharp with respect to LHC era physics search • A few theory clarifications will go a long way • Resolution of tau vs ee problem in HVP (perhaps understood) • Confirmation of VEPP-2M ee result from KLOE (done) and BaBar (pending) • Progress (or at least a believable path) toward improved HLbL hertzog@uiuc.edu

19. SPS points and slopes • SPS 1a: ``Typical '' mSUGRA point with intermediate value of tan_beta. • SPS 1b: ``Typical '' mSUGRA point with relatively high tan_beta; tau-rich neutralino and chargino decays. • SPS 2: ``Focus point '' scenario in mSUGRA; relatively heavy squarks and sleptons, charginos and neutralinos are fairly light; the gluino is lighter than the squarks • SPS 3: mSUGRA scenario with model line into ``co-annihilation region''; very small slepton-neutralino mass difference • SPS 4: mSUGRA scenario with large tan_beta; the couplings of A, H to b quarks and taus as well as the coupling of the charged Higgs to top and bottom are significantly enhanced in this scenario, resulting in particular in large associated production cross sections for the heavy Higgs bosons • SPS 5: mSUGRA scenario with relatively light scalar top quark; relatively low tan_beta • SPS 6: mSUGRA-like scenario with non-unified gaugino masses • SPS 7: GMSB scenario with stau NLSP • SPS 8: GMSB scenario with neutralino NLSP • SPS 9: AMSB scenario SPS PLOT www.ippp.dur.ac.uk/~georg/sps/sps.html

20. TIME Compare K. Hagiwara, A.D. Martin, Daisuke Nomura, T. Teubner Arguably, strongest experimental evidence of Physics Beyond Standard Model The Standard Model theory has improved. Hopefully at this Workshop we will learn even more • Key points: • Theory: 0.48 ppm • Experimental 0.54 ppm (0.46 ppm stat; 0.31 ppm syst.) • Dam(expt-thy) = (297±88) x 10-11 (3.4 s) deRafael, Glasgow MDM

21. Suppose the MSSM reference point SPS1a* is realized and parameters determined by global fit (from LHC results) • sgn(m) can’t be obtained from the collider • tanbcan’t be pinned down by collider With these SUSY parameters, LHC gets tan b of 10.22 ± 9.1. Tan b “blue band” plot based on present aμ. Possible future “blue band” plot, where tan β is determined from aμ to < 20% or better D. Stockinger sexp = 25 x 10-11 * SPS1a is a ``Typical '' mSUGRA point with intermediate tanb = 10 *Snowmass Points and Slopes: http://www.ippp.dur.ac.uk/~georg/sps/sps.html

22. UED Here is an example, related to g-2 SUSY SUSY Extra Dimensions The future am measurement will separate the two models by more than 7 standard deviations and thus allow for a clear decision in favor of one of them The quest for new physics understanding requires different tools • LHC: direct search for new particles • But, what new physics will they reveal? • Precision measurements: • Lepton flavor violation (m, t) • EDMs of e, n, atoms, etc. • Rare decays • 0nbb • Unitarity tests • Muon g-2 Consider a post-LHC world with many new mass states found

23. 3.15 GeV/c pions 5.4 GeV/c pions 3.094 GeV/c muons For JPARC, high-intensity, 30 GeV p beam, and tight space suggests backward decay beam