Electromagnetic form factor of the pion from twisted-mass lattice QCD at N{sub f}=2

Journal Article · Wed Apr 01 00:00:00 EDT 2009 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.79.074506· OSTI ID:21308187

Frezzotti, R ^[1]; Lubicz, V ^[2]; Simula, S ^[3]

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1. Dip. di Fisica, Universita di Roma Tor Vergata and INFN, Sez. di Roma Tor Vergata, Via della Ricerca Scientifica, I-00133 Roma (Italy)
2. Dipartimento di Fisica, Universita di Roma Tre and INFN, Sez. di Roma Tre, Via della Vasca Navale 84, I-00146 Roma (Italy)
3. Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tre, Via della Vasca Navale 84, I-00146 Roma (Italy)

We present a lattice calculation of the electromagnetic form factor of the pion obtained using the tree-level Symanzik improved gauge action with two flavors of dynamical twisted Wilson quarks. The simulated pion masses range approximately from 260 to 580 MeV, and the lattice box sizes are chosen in order to guarantee that M{sub {pi}}L > or approx. 4. Accurate results for the form factor are obtained using all-to-all quark propagators evaluated by a stochastic procedure. The momentum dependence of the pion form factor is investigated up to values of the squared four-momentum transfer Q{sup 2}{approx_equal}0.8 GeV{sup 2} and, thanks to the use of twisted boundary conditions, down to Q{sup 2}{approx_equal}0.05 GeV{sup 2}. Volume and discretization effects on the form factor appear to be within the statistical errors. Our results for the pion mass, decay constant and form factor are analyzed using (continuum) chiral perturbation theory at next-to-next-to-leading order. The extrapolated value of the pion charge radius is <r{sup 2}>{sup phys}=0.456{+-}0.030{sub stat}{+-}0.024{sub syst} in nice agreement with the experimental result. The extrapolated values of the pion form factor agree very well with the experimental data up to Q{sup 2}{approx_equal}0.8 GeV{sup 2} within uncertainties which become competitive with the experimental errors for Q{sup 2} > or approx. 0.3 GeV{sup 2}. The relevant low-energy constants appearing in the chiral expansion of the pion form factor are extracted from our lattice data, which come essentially from a single lattice spacing, adding the experimental value of the pion scalar radius in the fitting procedure. Our findings are in nice agreement with the available results of chiral perturbation theory analyses of {pi}-{pi} scattering data as well as with other analyses of our collaboration.

• OSTI ID: 21308187
• Journal Information: Physical Review. D, Particles Fields, Vol. 79, Issue 7; Other Information: DOI: 10.1103/PhysRevD.79.074506; (c) 2009 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
BOUNDARY CONDITIONS
CHIRALITY
ELECTROMAGNETIC FORM FACTORS
EXPANSION
FLAVOR MODEL
FOUR MOMENTUM TRANSFER
LATTICE FIELD THEORY
MASS
MEV RANGE 100-1000
PARTICLE DECAY
PERTURBATION THEORY
PIONS
PROPAGATOR
QUANTUM CHROMODYNAMICS
QUARKS
SCATTERING
SIMULATION
STOCHASTIC PROCESSES