The g2p Experiment The g2p Experiment

K. Slifer, UNHSept. 30, 2010

E08-027/007 Collaboration meeting

Inclusive ScatteringInclusive Scattering

SFs parameterize everything

we don’t know about hadron vertex

Construct the most generalTensor W consistent with

Lorentz and gauge invariance

Inclusive Polarized Cross Section

q

p

P

p’

W

E08-027 : Proton g2 Structure Function Fundamental spin observable has never been measured at low or moderate Q2

BC Sum Rule : violation suggested for proton at large Q2, but found satisfied for the neutron & 3He.

Spin Polarizability : Major failure (>8 of PT for neutron LT. Need g2 isospin separation to solve.

Hydrogen HyperFine Splitting : Lack of knowledge of g2 at low Q2 is one of the leading uncertainties.

Proton Charge Radius : also one of the leading uncertainties in extraction of <Rp> from H Lamb shift.

A- rating by PAC33 Camsonne, Crabb, Chen, Slifer*

E08-027 : Proton g2 Structure Function Fundamental spin observable has never been measured at low or moderate Q2

BC Sum Rule : violation suggested for proton at large Q2, but found satisfied for the neutron & 3He.

Spin Polarizability : Major failure (>8 of PT for neutron LT. Need g2 isospin separation to solve.

Hydrogen HyperFine Splitting : Lack of knowledge of g2 at low Q2 is one of the leading uncertainties.

Proton Charge Radius : also one of the leading uncertainties in extraction of <Rp> from H Lamb shift.

A- rating by PAC33

BC

Su

m R

ule

Camsonne, Crabb, Chen, Slifer*

E08-027 : Proton g2 Structure Function Fundamental spin observable has never been measured at low or moderate Q2

BC Sum Rule : violation suggested for proton at large Q2, but found satisfied for the neutron & 3He.

Spin Polarizability : Major failure (>8 of PT for neutron LT. Need g2 isospin separation to solve.

Hydrogen HyperFine Splitting : Lack of knowledge of g2 at low Q2 is one of the leading uncertainties.

Proton Charge Radius : also one of the leading uncertainties in extraction of <Rp> from H Lamb shift.

A- rating by PAC33

BC

Su

m R

ule

Camsonne, Crabb, Chen, Slifer*

Sp

in P

ola

riza

bili

ty

LT

E08-027 : Proton g2 Structure Function Fundamental spin observable has never been measured at low or moderate Q2

BC Sum Rule : violation suggested for proton at large Q2, but found satisfied for the neutron & 3He.

Spin Polarizability : Major failure (>8 of PT for neutron LT. Need g2 isospin separation to solve.

Hydrogen HyperFine Splitting : Lack of knowledge of g2 at low Q2 is one of the leading uncertainties.

Proton Charge Radius : also one of the leading uncertainties in extraction of <Rp> from H Lamb shift.

A- rating by PAC33 Camsonne, Crabb, Chen, Slifer*

nucleus ≈ 10-15

Atom ≈ 10-10

The finite size of the nucleon (QCD) plays a small but significant role in calculating atomic energy levels in QED.

Proton Charge Radius from P lamb shift disagrees with eP scattering result by about 6%

<Rp> = 0.84184 ± 0.00067 fm Lamb shift in muonic hydrogen

<Rp> = 0.897 ± 0.018 fm World analysis of eP scattering

<Rp> = 0.8768 ± 0.0069 fm CODATA world average

R. Pohl et.al Nature, July 2010

I. Sick PLB, 2003

Proton Charge Radius from P lamb shift disagrees with eP scattering result by about 6%

<Rp> = 0.84184 ± 0.00067 fm Lamb shift in muonic hydrogen

<Rp> = 0.897 ± 0.018 fm World analysis of eP scattering

<Rp> = 0.8768 ± 0.0069 fm CODATA world average

R. Pohl et.al Nature, July 2010

I. Sick PLB, 2003

Possible Implications : Some experimental mistake ? Fairly straightforward spectroscopy.

Rydberg constant off by 5? Really unlikely.

We don’t know how to calculate in QED ? Missing some terms?

Something about muons we don’t understand ?

Underestimating finite size effect uncertainties?

Proton Charge Radius from P lamb shift disagrees with eP scattering result by about 6%

I. Sick (Basel) : “What gives? I don’t know”. “Serious discrepency” [ELBA XI, Nature.com]

C. Carlson (W&M) : “Something is missing, this is very clear.” [Nature.com]

P. Mohr (NIST) : “would be quite revolutionary.” [L.A. Times.]

B. Odom (N.Western) : “...very surprised to find strong disagreement.” [N.P.R.]

J. Flowers (N.P.L.) “...could mean a complete rethink of QED”. [National Geographic]

“...opens door for a theorist to come up with next [NY Times] theoretical leap, and claim their Nobel prize”.

<Rp> = 0.84184 ± 0.00067 fm Lamb shift in muonic hydrogen

<Rp> = 0.897 ± 0.018 fm World analysis of eP scattering

<Rp> = 0.8768 ± 0.0069 fm CODATA world average

R. Pohl et.al Nature, July 2010

I. Sick PLB, 2003

Polarizability : Integrals of g1 and g2 weighted by 1/Q4

Zemach radius : Integral of GEGM weighted by 1/Q2

Dominated by Kinematic region of E08-027 and E08-007

E08-027 : Status Update

→Polarized Solid Ammonia Target.

→Magnetic Chicane/Beamline modifications.

→Room temp Septa Magnets.

→Low current BCM/BPMs.

Expensive. End of Year funding from DOE + user financial contributions will

make possible, but we’ll be on a very tight budget.

Tight Schedule : Start installation in May 2011.

E08-027 : Status Update

→Polarized Solid Ammonia Target.

→Magnetic Chicane/Beamline modifications.

→Room temp Septa Magnets.

→Low current BCM/BPMs.

Expensive. End of Year funding from DOE + user financial contributions will

make possible, but we’ll be on a very tight budget.

Tight Schedule : Start installation in May 2011.

Nevertheless, These are good problems to have!

Thanks to all who worked tirelessly to make sure these two experiments stayed on the schedule

Backups

Measure fundamental (but relatively unknown) spin observable g2 for 0.015<Q2<0.35 GeV2.

Provide benchmark test of PT, via the forward spin polarizability LT

which will help resolve a major failure (8) of existing state-of-the-art LT calculations.

Provide data needed for test of the BC sum rule.

Reduce major uncertainty in Hydrogen Hyper Fine splitting. HHF experimentally known to 13 sigfigs, but only calculable to 6 sigfigs (a few ppm). The largest error comes from finite proton size corrections. Breakdown:

-41.0±0.5 ppm from elastic (Zemach) contribution.

1.45±0.2 ppm from inelastic F2 and g1.

0.13+-0.13 ppm from g2, assuming Hall B model but no data at low Q2 and none of the available g2 models are favored by the existing data. g2 contribution to the HHF could be as large as 0.5±0.5ppm if we assume the Maid model which reproduces the existing data pretty well. -

E08-027: Measurment of g2p and the LT spin polarizability

Argonne : 10K parts or machining. + 2 tech staff that can help with design work.

Rutgers : 25-30K machining in Rutgers shop (CNC available).

Tel Aviv : 10-20K machining of beamline components.

Temple : 10K in beamline parts or machining.

UVa : 60K in target magnet repairs at Oxford. 5K to repair target refrigerator.

UVa(2) : 10K in machining and parts (+tungsten beam dump).

UNH : 10K in parts or machining. 2K in target stick repair.

William&Mary : 5K in parts or machining + manpower.

147-162 K in confirmed user contributions

Additional anticipated contributions

UNH : 20K supplemental request for parts/machining.

Spokesman Guy Ron will move from post-doc to faculty position with associated startup funding within the next few months.

(as of June 24)

Applications to Atomic PhysicsApplications to Atomic Physics

nucleus ≈ 10-15

Atom ≈ 10-10

The finite size of the nucleus plays a small but significant role in atomic energy levels.

Hydrogen HF Splitting

≈1ppm ≈5ppm <1ppm ≈40ppm

Friar & Sick PLB 579 285(2003)

Elastic Scattering Inelastic

Structure dependence of Hydrogen HF Splitting

Nazaryan,Carlson,Griffieon PRL 96 163001 (2006)

Z=-41.0±0.5ppm pol≈ 1.3±0.3 ppm

0.2265 ppm

Elastic piece larger but with similar uncertainty

1 well determined from F2,g1 data

2 Not well determined at all, assumedsmall.

If assume Maid Model instead of Eg1 model, the uncertainty on g2 would be 2X uncertainty from g1