latest on muon g-2 from experiment

Latest on muon g-2 from experiment

Meson production at Intermediate and High Energies - Messina 10/11/11

G.Venanzoni LNF/INFN

• Long established discrepancy (>3) between SM prediction and BNL E821 exp.

• A twofold improvement on a TH-EXP from 2001

(thanks to BNL and new e+e- measurements)!

• Theoretical error aSM (56x10-10) dominated by

HLO VP (45x10-10) and HLbL (2.54x10-10).

• Experimental error aEXP =6.3 x10-10 (0.54 ppm),

E821. Plan to reduce it to 1.6 10-10 (0.14 ppm) by the new g-2 experiments at FNAL (E989) and J-PARC.HLO VP H LbL

T.Teubner, PHIPSI08

aHLO = (692.34.2)10-10

[A.Hoecker, LP11]a

HLbL =(10.52.6)10-10 [P. dR&V. 08](11 4)10-10 (J.N.)

aHLO ~0.6%

Muon anomaly as precision test of the SM

In 2001 aEXP-a

TH=(2316)•10-10

aHLbL ~25-40%

Hagiwara et al. arxiv:1105.3149

aHLO:

L.O. Hadronic contribution to a can be estimated by means of a dispersion integral:

- K(s) = analytic kernel-function- above sufficiently high energy value, typically 2…5 GeV, use pQCD

Input: a) hadronic electron-positron cross section data b) hadronic t- decays, which can be used with the help of the CVC-theorem and an isospin rotation (plus isospin breaking corrections)

H

1 / s2 makes lowenergy contributionsespecially important:

in the range < 1 GeVcontributes to 70% !

(A., D., H. ’97)

(G.dR 69, E.J.95, A.D.H.’97,….)

Cross section data:Two approaches:

Energy scan (CMD2, SND, BES,CLEO):

Radiative return (KLOE, BABAR, BELLE, BESIII?):

• energy of colliding beams is changed to the desired value • “direct” measurement of cross sections• needs dedicated accelerator/physics program• needs to measure luminosity and beam energy for every data point

• runs at fixed-energy machines (meson factories) • use initial state radiation process to access lower energies or

resonances• data come as by-product of standard physics program• requires precise theoretical calculation of the radiator function• luminosity and beam energy enter only once for all energy points• needs larger integrated luminosity

ISR: Initial State Radiation5

Particle factories (DAFNE, PEP-II, KEK-B) can measure hadronic cross sections as a function of the hadronic c.m. energy using initial state radiation (radiative return to energies below the collider energy √s).

hadrons

hard photon radiated in initial state

incoming e+ and e-

with M2ee= s

virtual photon g* with M2

g*< s

The emission of a hard g in the bremsstrahlung process in the initial state reduces the energy available to produce the hadronic system in the e+e- collision.

e+e- data: current and future/activities

DAFNE-2(?)

~1% ~3-5%HAD~7-15% ~6%

SuperB(?)

Measured cross section for e+e- →p+ p-

(2010) ( data: different experiments

B. Lee Roberts for the New Muon (g-2) Collaboration – DPF 10 August 2011

- p. 7/57

Measured Cross section for e+e- →p+ p-

08

Most data points dominated by systematic uncertainties that are correlated between data points

Davier et al., EPJ C 71, 1515 (2011)

Situation of Two-pion channel

A. Hoecker LP11

An alternative way to obtain |Fp|2 is the bin-by-bin ratio of pionover muon yields (as done by BaBar).

meas. quantities

Many radiative corrections drop out:• radiator function• int. luminosity from Bhabhas• Vacuum polarization

preliminary

See Mandaglio’s talk Good agreement with previous measurement!

New KLOE result on e+e- →p+ p- by ppg/g ratio (ISR)

BABAR measured (almost) all the exclusive e+e– ® hadrons modesMany inconsistencies resolvedHuge impact on hadronic vacuum polarisation calculation

Davier et al., EPJ C 71, 1515 (2011)

Multihadron channels between 1 and 2.5 GeV

A.Hoecker LP 11

s (GeV)

1) Most recent inclusive

measurements: MEA and B antiB,

with total integrated luminosity of

200 nb-1 (one hour of data taking at

1032 cm-2 sec-1).10% stat.+ 15%

syst. Errors

2) New BaBar data is improving a lot

this region. However still the

question on the completeness of

exclusive data vs systematics of old

inclusive measurements

s (GeV)

T. Teubner 08

E. Solodov, unpublished

Exclusive vs inclusive measurements?

First data from VEPP-2000 @Novosibirsk (L ~ 1031 cm-2 sec-1)

CMD3

Additional results also from BaBar, Belle (BES) with ISR, and possibly with DAFNE upgraded in energy (DAFNE-2, see arXiv:1007.521)

SND

New data at the horizon:

L~30 pb-1

e+e- →3p+3 p-

e+e- →2p+2p0

Missing isospin corrections and/or problems with data? Additional data are needed. Meanwhile…

Two-pion e+e- vs t spectral functions

Jegerlehner and Szafron claim that the e+e- vs t is solved if an additional correction (r-g mix.) is included

F. Jegerlehner and R. Szafron, Eur. Phys. J. C71 (2011) 1632

JS 11

DHMZ 11

• A new 2-3% lattice result for the lowest-order hadronic (u,d quarks only) contribution:

Feng, Jansen, Petschlies, Renner, arXiv:1103.4818v1 [hep-lat]

Very promising results!

Prospects for HLBL?

What about the lattice?

Experimental value:

Excellent agreement

• Constrain the on-shell amplitudes and remove a significant portion of the theoretical uncertainty on the HLBL

• A reasonable improvement on ap0

•

- p. 16/57

KLOE-2 to measure gg* → p0,h to constrain aHLBL

See Moricciani and Mascolo talks

M. Davier, et al., Eur. Phys. J. C (2011) 71: 1515

well known significant work ongoing

The SM Value for a from e+e- → hadrons

• New experiment at FNAL (E989) at magic momentum, consolidated method. 20 x w.r.t. E821. Relocate the BNL storage ring (12 T) to FNAL. Has got a Stage-1 Approval!

• Alternative proposal at J-PARC w/out magic momentum and no E field, requiring ultra-slow muons generated from laser-ionised muonium atoms

We need a new (possibly more) (g-2) experiment(s)!

Current discrepancy limited by experimental uncertainty. Two proposals to improve it x4:

Precision target ~ 16 10-11 . If the central value remains the same ~7 from SM!

• New experiment at FNAL (E989) at magic momentum, consolidated method. 20 x w.r.t. E821. Relocate the BNL storage ring (12 T) to FNAL. Has got a Stage-1 Approval!

• Alternative proposal at J-PARC w/out magic momentum and no E field, requiring ultra-slow muons generated from laser-ionised muonium atoms

We need a new (possibly more) (g-2) experiment(s)!

Current discrepancy limited by experimental uncertainty. Two proposals to improve it x4:

Precision target ~ 16 10-11 . If the central value remains the same ~7 from SM!

Fermilab (g-2) Experiment:• E821 at Brookhaven

• E989 at Fermilab– move the storage ring to Fermilab, improved shimming, new

detectors, electronics, DAQ– new beam structure that takes advantage of the multiple rings

available at Fermilab, more muons per hour, less per fill of the ring

B. Lee Roberts, University of Sussex – 8 July 2011

- p. 21/33

B. L. Roberts, Fermilab , 3 September 2008 - p. 21/68

Inflector

Kicker Modules

Storagering

Central orbitInjection orbit

Pions

-π

p=3.1GeV/c

Experimental Technique

B

• Muon polarization

R=711.2cm

d=9cm

(1.45T)

Electric Quadrupoles

xc ≈ 77 mmb ≈ 10 mradB·dl ≈ 0.1 Tm

xc

R

R b

• injection & kicking• Muon storage ring

• focus with Electric Quadrupoles• 24 electron calorimeters

Target

25ns bunch of ≥ 1 X 1012 protons

- p. 22/33

Waveform digitizer gives t, E

Picture of a Lead-Scifi Calorimeter from E821In E989 we plan to us W-SciFi Calorimeters

s

gt = 64.4 s; (g-2): ta = 4.37 s; Cyclotron: tC = 149 ns

gt

Ee ≥ 1.8 GeV

Systematic uncertainty on wa expected to be reduced by 1/3 at E989 (compared to E821) thanks to reduced pion contamination, segmented detectors, and an improved storage ring kick of the muons onto orbit.

The arrival time spectrum of high-energy e-

• wp= Larmor frequency of the free p• We measure wa and wp independently• Use l = /p as the “fundamental constant”

Blind analysis

wp

Systematic uncertainty on wp expected to be reduced by a factor ~2 thanks to better shimming (uniformity of B), relocations of critical NMR probes, and other incremental changes

The magnetic field is measured and controlled using pulsed NMR and the free-induction decay.

• The existence of many storage rings that are interlinked permits us to make the “ideal” beam structure.– proton bunch structure:

• BNL 4 X 1012 p/fill: repetition rate 4.4 Hz• FNAL 1012 p/fill: repetition rate 15 Hz

– using antiproton rings as an 900m pion decay line• 20 times less pion flash at injection than BNL

– 0o muons • ~5-10x increase /p over BNL

– Can run parasitic to main injector experiments (e.g. to NOVA) or take all the booster cycles

Why Fermilab?

• Uses 6/20 batches* – parasitic to n program

• Proton plan up to AP0 target is almost the same as for Mu2e

• Modified AP2 line (+ quads)• New beam stub into ring

*Can use all 20 if MI program is off

beam rebunched in Recycler4 x (1 x 1012) p

Fermilab beam complex for (g-2)Polarized muons delivered and stored in the ring at the magic

momentum, 3.094 GeV/c

B. Lee Roberts for the New Muon (g-2) Collaboration – DPF 10

- p. 27/30

The 900-m long decay beam reduces the pion “flash” by x20 and leads to 6 – 12 times more stored muons per proton (compared to BNL)

Stored Muons / POT

Flash compared to BNLparameter FNAL/BNL

p / fill 0.25

p / p 0.4

p survive to ring 0.01

p at magic P 50

Net 0.05

• New segmented detectors to reduce pileup– W-scifi prototype under study X0 = 0.7 cm– NIM A602 :396-402 (2009).

• New electronics– 500 MHz 12-bit WFDs, with deep memories

• Improvements in the magnetic field calibration, measurement and monitoring.

Upgrades at Fermilab

- p. 29/29

Sikorsky S64F 12.5 T hook weight (Outer coil 8T)

Muon (g-2) storage ring to be relocated to FNAL

Goal is to be ready for data in 2016

• Total project cost ~$4XM– CD0 expected this year– Conceptual Design Report being prepared

• FY2011 Funding began this June• FY12 and beyond is being discussed between DOE

and Fermilab

Timeschedule

Conclusion

• The muon (g-2) has served in the last 10 years as one of the strongest test of the SM

• Impressive accuracy of BNL experiment: aEXP = 0.54 ppm

• Theoretical prediction has steadily improved thanks to precise

e+e- data (uncertainty of ~1%, worldwide effort) aTH = 0.43

ppm

• Still a discrepancy of more than 3 “standard deviations” between SM and Experiment; error dominated by experiment

• New (g-2) experiments are foreseen at Fermilab and J-Parc a

EXP = 0.14 ppm

• Theoretical uncertainty will improve thanks to current and planned experimental activities (as well as theoretical ones)Stay Tuned!

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Latest on g-2 from experiment

G. Venanzoni LNF/INFN

LC11: understanding QCD at Linear Colliders in searching for old and new physics - Trento 12 - 16 September 2011

34

e+e-®3p

e+e-®4p

e+e-®2p2DAFNE-2

DAFNE-2 is statistically equivalent to 510 ab-1 (Super)B-factory

• Published BaBar results:89 fb-

1(ISR)▲ “BaBar” 10 (890 fb-1)o KLOE-2 energy scan: 20 pb-1/point @ L= 1032 cm-2 s-1, 25 MeV bin 1 year data-taking

Impact of DAFNE-2 on exclusive channels in the range [1-2.5] GeV with a scan (Statistics only)

arXiv:1007.521

aexp - a

theo,SM = (27.7 8.4)10-10 (3.3)8.4 = ~5HLO~3HLbL6BNL

1.6NEW G-22.6DAFNE-2 4 2.5

This means:HAD ~ 0.4% s<1GeV (instead of 0.7% as now) HAD ~ 2% 1<s<2GeV (instead of 6% as now)

7-8 (if 27.7 will remain the same)

[Eidelman, TAU08]

DAFNE-2

Possible at DAFNE-2!

With ISR at 1 GeVWith Energy Scan 1-2 GeV

Precise measurement of HAD at low energies very important also for em(MZ) (necessary for ILC) !!!

aHLO=5.3=3.3(s<1GeV) 3.9(1< s<2GeV) 1.2(s>2GeV)

aHLO ®2.6=1.9 (s<1GeV) 1.3 (s<1GeV) 1.2(s>2GeV)

Impact of DAFNE-2 on (g-2) arXiv:1007.521

However the project is not yet approved…

B. Lee Roberts, University of Sussex – 8 July 2011

- p. 36/57

The error budget for a new experiment represents a continuation of improvements already made during E821

Systematic uncertainty (ppm) 1998 1999 2000 2001 E821 final

P989Goal

Magnetic field – wp 0.5 0.4 0.24 0.17 0.07

Anomalous precession – wa 0.8 0.3 0.31 0.21 0.07

Statistical uncertainty (ppm) 4.9 1.3 0.62 0.66 0.46 0.1

Systematic uncertainty (ppm) 0.9 0.5 0.39 0.28 0.28 0.1

Total Uncertainty (ppm) 5.0 1.3 0.73 0.72 0.54 0.14

• Place polarized muons in a B field– spin precession frequency (q = ± e)

– cyclotron frequency

- p. 37/57

The a Experiments:

Since g > 2, the spin gets ahead of the momentum

- p. 38/29

Spin Motion: Use Electric Field for Vertical Focusing

0

Electrostatic quadrupoles cover 43% of ringSmall (< 1ppm) correction for muons not at the magic g.

G. Venanzoni for the New Muon (g-2) Collaboration – PHIPSI11, September 2011

- p. 39/57

G. Venanzoni for the New Muon (g-2) Collaboration – PHIPSI11, September 2011

Dispersion Integral:Contribution of different energy regions to the dispersion

integral and the error to aHLO

aexp® 1.5 10-10 = 0.2% on a

HLO

~40%

~75%(mostly 2p)

~55%

contributions error2

Very important also the region 1-2 GeV

New g-2 exp.

K(s)~1/s