Hard exclusive electroproduction of π+π− pairs off hydrogen and deuterium targets has been studied by the HERMES experiment at DESY. Legendre moments P1 and P3 of the angular distributions of π+ mesons in the center-of-mass frame of the pair have been measured for the first time. Their dependence on the π+π− invariant mass can be understood as being due to the interference between relative P-wave (isovector) and S-, D-wave (isoscalar) states of the two pions. The increase in magnitude of P1 as Bjorken x increases is interpreted in the framework of generalized parton distributions as an enhancement of flavour non-singlet exchange for larger values of x, which leads to a sizable admixture of isoscalar and isovector pion pairs. In addition, the interference between P-wave and D-wave states separately for transverse and longitudinal pion pairs has been studied. The data indicate that in the f2(1270) region at Q2=3 GeV2 higher-twist effects can be as large as the leading-twist longitudinal component.
Hard exclusive electroproduction of π+π− pairs
CIULLO, Giuseppe;CONTALBRIGO, Marco;FERRETTI, Paola;FABBRI, Riccardo;LENISA, Paolo;MASOLI, Francesco Antonio;REGGIANI, DAVIDE;STANCARI, Michelle Dawn;STATERA, Marco;
2004
Abstract
Hard exclusive electroproduction of π+π− pairs off hydrogen and deuterium targets has been studied by the HERMES experiment at DESY. Legendre moments P1 and P3 of the angular distributions of π+ mesons in the center-of-mass frame of the pair have been measured for the first time. Their dependence on the π+π− invariant mass can be understood as being due to the interference between relative P-wave (isovector) and S-, D-wave (isoscalar) states of the two pions. The increase in magnitude of P1 as Bjorken x increases is interpreted in the framework of generalized parton distributions as an enhancement of flavour non-singlet exchange for larger values of x, which leads to a sizable admixture of isoscalar and isovector pion pairs. In addition, the interference between P-wave and D-wave states separately for transverse and longitudinal pion pairs has been studied. The data indicate that in the f2(1270) region at Q2=3 GeV2 higher-twist effects can be as large as the leading-twist longitudinal component.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
