Strength of intermediate-range forces coupling to isospin

Abstract

An experimental search for new forces coupling to nuclear isospin with a range of >3 m was conducted using a torsion balance driven in resonance by a set of masses configured to generate a nearly pure isospin source field. The strength of any such coupling § in units of gravity per atomic mass unit is found to be bounded by -2.3x 10~4< §< 4-2.7x 10 ~5, where the positive sign represents an attractive force between like isospin charges.PACS numbers: 04.90.+e, 14.80.Pb Experimental searches 1 for new intermediate-range forces weaker than gravity during the last three years have yielded much valuable information, even though, as yet, they have failed to provide any generally accepted positive evidence for the existence of such a force at the level first suggested by the reanalysis of the Eotvos experiment and by the mine-gravity data. 2 The hypothetical force is usually represented by a Yukawa potential which, when added to the standard Newtonian gravitational potential, reads as K(r)--Gmim 2 r" 1 [14-aexp(-rA)] , where a is the new coupling in units of gravity and X is its range. The composition dependence can be made explicit by writing a ^qiq^ with qi-cosO(N + Z)i/tii + sin9(N-Z)i/iii , where the new effective charge has been written as a linear combination of the baryon number and nuclear isospin per atomic mass unit, in standard notation. In the present paper we assume a pure isospin coupling, i.e., 0 = K/2 and q t -(TV -Z)//^,. We have modified our } earlier configuration of source masses so as to increase the expected signal for an isospin coupling and to suppress, further, the effects of gravity and its gradients on the pendulum. This has enabled us to extend the search for isopin-dependent forces to considerably higher levels of sensitivity than those reported earlier, the present measurement being characterized by the ability to measure differential accelerations of -5xlO" 13 cms~2.A brief description of the apparatus can be found in Refs. l(j) and 3. The torsion pendulum consists of two semicircular rings of copper and lead each of mean radius about 8.5 cm and mass about 700 g joined along their diameters; two pairs of grooves in the lead make its mass distribution match closely that of the copper half, l(j)3 to reduce the coupling of the ring to gradients in the gravity field. This dual ring is suspended with its plane horizontal ix-y plane) by means of a tungsten fiber 250 cm long and 105 /xm in diameter inside a vacuum chamber with pressure below 10 ~8 Torr. But for imperfections of fabrication and small tilts of the ring, the quadrupole moment tensor Q of the ring is diagonal and also has the property Q xx ^Qyy. An optical-quality mirror, in an assembly weighing about 35 g, is attached to the ring at a height of 40 cm and within about 0.1 cm of the fiber axis. An autocollimating optical lever views this mirror and yields the angular orientation of the ring with an accuracy of 5xl0~9 rad/Hz 1/2 . The natural period of torsional oscillation of the pendulum was measured to be 795.6 s; this corresponds to...

Proposal for an experiment to search for Randall-Sundrum-type corrections to Newton’s law of gravitation

“…These experiments set limit on the strength α for distance scale λ, implying the absence of additional force whose strength relative to Newtonian gravity, at distance scale λ, is equal to or larger than α. Even before the provocations from string inspired models, in the years when a hypothetical 'fifth force' was searched for, experimentalists had put stringent constraints in the α − λ plane at length scale down to a few mm [7,8,9]. University of California at Irvine group used "null-geometry" for torsion balance experiment and set limit in the range : α = 10 −2 at λ = 3mm to α = 10 −4 at λ = 3cm [7].…”

… and Fall

“…72 Boynton disagreed with the conclusion expressed in Heckel et al (1989). (From Jekeli et al 1990) on isospin coupling of < 4:6 10 4 (Stubbs et al 1989b), < 2:3 10 4 (Cowsik et al 1990), and < 1:8 10 4 (Nelson et al 1990, preprint). He still had no explanation of the Index I result, however.…”

“…They did, in addition, present an analysis of their data using Fischbach's suggested exponential force, and found limits similar to those they had found previously for the Yukawa model. During 1990 two other groups Cowsik et al (1990) and Kuroda and Mio (1990) presented more stringent limits resulting from improved experimental apparatuses. They continued to conclude that there was no evidence for a composition dependent force.…”

Performance Characteristics of a Rotational Seismometer for Near-Field and Engineering Applications

“…In the beginning of the twentieth century, Eötvos made a highly innovative use of the balance to measure gradients in Earth's gravity and to study Einstein's equivalence principle. During the recent decades scientists led by Dicke (Roll et al, 1964), Braginsky (Braginsky and Panov, 1972), Cowsik (Cowsik, 1981;Cowsik et al, 1988Cowsik et al, , 1989, Ritter (Ritter et al, 1990), Adelberger (Cowsik et al, 1988(Cowsik et al, , 1990Adelberger et al, 2003), Boyn-1 The instrumentation effort described here emerged from an ongoing program to study short-range gravity and Einstein's equivalence principle at Washington University in St. Louis, Missouri. ton (Boynton et al, 1987), and Newman (Newman et al, 1990) have adapted the torsion balance for their investigations of the equivalence principle and to search for new extremely feeble forces that couple to baryon or lepton number, to nuclear isospin or spin, etc.…”