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Does g-2 point to new physics?: Current Status and Future Plans. The g-2 Collaboration

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slide1

Does g-2 point to new physics?: Current Status and Future Plans

The g-2 Collaboration

Boston University, Brookhaven National Laboratory, University of Heidelberg (* KVI), University of Illinois, University of Minnesota, Budker Institute, Yale University, KEK, Tokyo Institute of Technology, Cornell University

slide2

The Magnetic Moment

(e+e-, m+m-,t+t-)

m

m

m

g

g

g

m =geh s 2mc 2

Wheregis thegyromagnetic ratiowhich relates the angular momentum to the intrinsic spin

g=2for charged, point-like, spin 1/2 particles.

Hadronsg(neutron) = -3.82 ≠ 0

Large deviations => quark substructureg(proton) = +5.58 ≠ 2

Leptons Small deviations => coupling to virtual fields

Deviations from g=2 are characterized by the Anomaly:

a =g-2 (a~ .001 for a lepton) 2

slide3

Coupling to X goes asmm2/mX2factor of 40,000 compared to e

Muon anomalous magnetic moment

am(SM) = am(QED) + am(weak) +am(had)

x 10-10

am(QED) = 11658471.935 (.143)

BNL E821 data

slide4

zo

m

µ

µ

W

W

µ

µ

B field

Coupling to X goes asmm2/mX2factor of 40,000 compared to e

Muon anomalous magnetic moment

am(SM) = am(QED) + am(weak) +am(had)

x 10-10

am(QED) = 11658471.935 (.143)

+ am(weak) = 15.4__ (.2)

+3.89

BNL E821 data

-1.94(Higgs < 0.01)

slide5

Coupling to X goes asmm2/mX2factor of 40,000 compared to e

Muon anomalous magnetic moment

am(SM) = am(QED) + am(weak) +am(had)

x 10-10

am(QED) = 11658471.935 (.143)

+ am(weak) = 15.4__ (.2)

+ am(had1sto) = 696.3__ (7.2)

+ am(had h.o.) = -10.0__ (.6)

BNL E821 data

Requires Data

slide6

Coupling to X goes asmm2/mX2factor of 40,000 compared to e

Muon anomalous magnetic moment

am(SM) = am(QED) + am(weak) +am(had)

x 10-10

am(QED) = 11658471.935 (.143)

+ am(weak) = 15.4__ (.2)

+ am(had1sto) = 696.3__ (7.2)

+ am(had h.o.) = -10.0__ (.6)

+ am(hadl-by-l) = + 13.6__ (2.5)

BNL E821 data

slide7

D am= any new physics

Coupling to X goes asmm2/mX2factor of 40,000 compared to e

Muon anomalous magnetic moment

am(SM) = am(QED) + am(weak) +am(had)

x 10-10

am(QED) = 11658471.935 (.143)

+ am(weak) = 15.4__ (.2)

+ am(had1sto) = 696.3__ (7.2)

+ am(had h.o.) = -10.0__ (.6)

+ am(hadl-by-l) = + 13.6__ (2.5)

BNL E821 data

slide8

How to Measure a Magnetic Moment

Brookhaven provides the pions from protons on nickel tgt

Forward-going daughter muons are polarized

0

m- p- nm

slide9

How to Measure a Magnetic Moment

wc (Tc = 149 ns) wa = ws- wc (precesses ~120 per cycle)

ws = 1+g (g-2) eB and wc = eB 2 mcg mcg

wa = ws - wc = (g-2) eB 2 mc

(am- ) b x E

e

mc

1

g2 -1

Quadrupole E field gives additional term in wa :

+

Which vanishes at the “magic momentum” of 3.094 GeV/c

slide10

WEAK-FOCUSSING MUON STORAGE RING

B = 1.45 T Pm= 3.094 GeV/c Rring = 7.112 m Rstor = 4.5 cm

Kicker

Quad

Quad

Inflector

24 SciFi Calorimetersrecord time and energy of decay e+ (or e-)

nmne m-e-

Quad

Calorimeters select high energy e’s

These e’s are preferentially emitted in the direction of the m spin

Quad

slide11

2001 data set: 4 billion e+ (E > 1.8 GeV, t > 32 ms after injection)

Cyclotron Frequency at early times

g-2 Precession Frequency after debunching

Fit for g,m radial distribution, bxE correction: (0.47 + 0.05) ppm

Million evts per 149.2 ns

Fit for wa: No e-t/gt (1 + A cos (wat +j)) is no longer good enough.

slide12

m

e

Energy Spectrum

late time(no pileup)

early + late

early + late(corrected)

Main Disturbances

  • Pileup of real pulses <5 ns apart1% at earliest times: model and subtract
  • Muon Lossesbump beam and scrape (first 11 ms) scintillator paddles measure triples
  • Rate dependent calorimeter responsechanges the effective Ethrin situ laser calibration system
  • Bunched beamrandomize time spectrum in bins of Tcyclotron
  • Coherent Betatron Oscillations image of the inflector exit moves around the ring as a beat frequency of wc and wb fiber harp and traceback chamber measure stored muon profile vs time
slide13

Consistency between analyzers checked

G2off productionMulti-parameter quad corrections

G2Too productionMulti-parameter, Eth=1.5 GeV asymmetry-weighted,

G2off productionMulti-parameter

G2off production9-parameter ratio

G2Too production3 - parameter ratio with cancellation

Low n (black), high n (clear), combined (red) data sets.

slide14

Measuring the Magnetic Field

0.5 ppm contours are 750 nT over an average field of 1.45 Tesla.

muon sees the field averaged over azimuth

vertical distance (cm)

-4 -3 -2 -1 0 1 2 3 4

-4 -3 -2 -1 0 1 2 3 4

17 calibrated NMR probes inside the trolley measure the field every cm

horizontal distance (cm)

slide15

Blind Analysis

Decay positrons NMR

wa = am e B mp B = h wp mc

am = Rl + R

where R = wa / wp is measured by E821

and l = mm / mpfrom muonium hyperfine structure

  • Offline Team (5 analyses) Magnet Team (2 analyses)
  • wa wp
  • Both w’s and all analyses have computer-generated secret offsets.
  • Study stability of R under all conditions
  • Finish all studies and assign all uncertainties BEFORE revealing offset.
slide16

Results from the 2000/2001 datasets & World Average

In order to use the t-decay data, you need

CVC – its not perfect.

Isospin violation - include r mass differences?

Experimental problems - normalization?

am x 10 -10 - 11659000

World average am = 11659208(6) x 10-10

Recall am = R/(l-R) where we measure R = wa/wpand where l = mm/mp = 3.18334539(10)

Quote CPT results in terms of DR = (3.5 + 3.6) x 10-6

slide17

Taking Dam = am(exp)-am(thry): the details are still changing…

QED 11658472.07 (.12) 5-loop: Laporta & Remiddi + Kinoshita & Nio update up from 11658470.57 (.29)

EW LO 19.5 1st order e.g. Fujikawa, Lee, Sanda ’72EW HO -4.07(2) 2-loop, NL+LL Czarnecki, Krause, Marciano ‘96 updated: Czarnecki, Marciano, Vainshtein ’03 15.4 (.2)agrees with 15.3 (.2) Knecht, Peris, Perrottet, DeRafael

Had LO (e+e-) 696.3 (6.2)(3.6) Davier,Eidelman, Hoecker, Zhang hep-ph/0308213v2692.4 (5.9)(2.4) Hagiwara, Martin, Nomura, Teubner hep-ph/0312250 add KLOE 694.4 (5.6)(3.6)Davier, Hoecker, Eidelman, Zhang ICHEP04add QCD 693.4 (5.3)(3.5)

Had NL -9.8 (.1) Hagiwara, Martin, Nomura, Teubneragrees with -10.1 (.6) Krause ’97

Had l-by-l 13.6 (2.5) Melnikov & Vainstein hep-ph/0312226up from 8.0 (4.0) Nyffler ’02

World Avg (moving target) D am = 25.2 (9.2) x 10-102.7 susing the latest – See Hoecker’s talk this morning…

slide18

Improvement in Theory will continue over the next decade

Precision in the dispersion integral

CMD-2 (e+e- at 0.3-1.4) has 5 times more e+e- data still unanalyzed

VEPP-2000 upgrade (2.0 GeV, 10 x L, CMD-3, SND)

More data from Beijing (e+e- from 2-5 GeV) after intensity upgrade

Radiative return measurements at BaBar, KLOE, (Belle?)

 Estimate am(had VP from e+e-)  0.3 ppm

Other Avenues

Further understanding t vs e+e- discrepancy (Belle, Cleo2)

Improvements in hadronic light-by-light term

Lattice gauge calculations

0.6%

0.1% (2010)

slide19

New KLOE data using “radiative return” method

Initial State Radiationlowers the CM energy and also tags the event

BaBar is also doing this. They can measure e+e-  m+m- directly since photon is hard

slide20

Evolution of the Experimental Uncertainties

Data Set: 1997 1998 1999 2000 2001

p-injection kicker installed 1st long run new inflector reverse polarity field stabilized

12 M e+ 84 M e+ 1 B e+ 4 B e+ 4 B e-Statistics

(Ne above Ethr)12.5 ppm 4.9 ppm 1.25 ppm 0.6 ppm 0.7 ppm

Systematics2.9 ppm 1 ppm 0.5 ppm 0.4 ppm 0.3 ppm

dwa 2.6 ppm 0.7 ppm 0.3 ppm 0.3 ppm 0.21 ppm

Dominated byWFD threshold pileup pileup coherent betatron gain stability pion flash AGS mistune AGS mistune m loss, pileup m loss

dwp1.3 ppm 0.5 ppm 0.4 ppm 0.24 ppm 0.17 ppm

Dominated bythermal fluctuations trolley position trolley position trolley position trolley position no active feedback inflector inflector

Still statistics dominated!

slide21

Proposal P969 for another Run at BNL

Improve am by a factor of 2.5 to match expected theory improvement500 hrs setup (pulse-on-demand) + 1500 hrs dedicated5 x faster than before by higher intensity and the following changes

Provide More Muons

Double number of beamline quads + use backward-going muons Flux x 2.1 and no accompanying pions to create “flash”

Store More Muons

Open-end inflector design + 4th muon kicker

m’s x 2 and reduced systematics from Coherent Betatron Oscillation

Handle Higher rates

Increased Calorimeter Segmentation Continuous WFD, Commercial MTDC’s, IIncrease DAQ throughput

Improve B-field Measurement

In situ measurements of field changes with kicker eddy current Trolley position calibration and mapped NMR positions

slide22

Evolution of the Experimental Uncertainties

Data Set: 1999 2000 2001 2006-7

1st long run new inflector reverse polarity improved BNL

(20 week run)

1 B e+ 4 B e+ 4 B e- 70 B e+Statistics

(Ne above Ethr) 1.25 ppm 0.6 ppm 0.7 ppm 0.14 ppm

Systematics 0.5 ppm 0.4 ppm 0.3 ppm 0.15 ppm

dwa 0.3 ppm 0.3 ppm 0.21 ppm 0.11 ppm

Dominated by pileup coherent betatron gain stability AGS mistune m loss, pileup m loss, pileup

dwp 0.4 ppm 0.24 ppm 0.17 ppm 0.11 ppm

Dominated by trolley position trolley position trolley position trolley position inflector

slide23

In CMSSM, am can be combined with b sg, cosmological relic density Wh2, and LEP Higgs searches to constrain c mass

Da = 24 x 10-10 favors higher tan b andavoids coannihilation region

From Keith Oliveusing the g-2 PRL (2003) Dam and the method described in Ellis, Olive, Santoso, Spanos

Excluded by direct searches

Allowed 2s band am(exp)– am(e+e- thy)

cosmologically preferred region Wh2= 0.09 - 0.12

Excluded for neutral dark matter

slide24

The CMSSM plot with error on Dam of 4.6 x 10-10(assuming better theory and a new BNL g-2 experiment)

Dam=24(4.6) x 10-10 (discrepancy at 6 s) Dam = 0 (4.6) x 10-10

Current Discrepancy Standard Model

slide26

Access to the vertical oscillation comes from auxiliary detectors listed in order of segmentation:

  • FSD: 5 scintillator bars in front of detector (9 stations) gives average y-position and rms width.
  • PSD: 32 x 20 tile/fiber strips. (2 – 5 stations) gives x-y position and profile shape
  • Traceback: Strawtube tracking chamber (1 station) gives vertical angle

For example, a fit to the average y-position in the FSD vs time yields the amplitude of the “out-of-phase” component.

slide27

Data analysis on the 2000 & 2001 runs continues

Look for an edm paper in the next couple months

Reduced the limit on edm by ~ x4 Reduced potential effect on wa by ~ x16

Also work is proceeding on

Edm of m- (2001 data with PSD – improve another x2)

Combine with g to get best m- lifetime (20 ppm)Comparison of m+ vs m- lifetime Limit on sidereal variation

dm+ < 2.8 x 10-10 e-cm (95% C.L.) using 2000 data & FSDs (McNabb et al, hep-ex/0407008)

Precise lifetime G

slide28

Conclusions

  • Things are getting exciting
  • One can reasonably hope to reduce the error on Dam by a factor of 3 over the next decade provided we have another run.
  • If the g-2 hint is real & due to SUSY  then the new particles will be seen in the LHC
  • If WIMP’s are neutralino’s consistent with g-2  then CDMS will see them in the next few years.
  • If LHC sees new particles, but CDMS doesn’t find WIMP’s  the particles are not supersymmetric and/or dark matter is not supersymmetric
  • If g-2 shows a discrepancy, but nothing is seen in LHC or CDMS II  then we need to examine extra dimensions, edm’s
  • Many possibilities beyond simple confluence…