Today's Progress 21. Apr. 2010

The final form of normalized deuteron spectra and deuteron momentum resolution

Since deuteron selection rule was reconsidered after the gain tune of PA ( 2007 Dec 7th report) and reconstruction of deuteron selection ( 2007 Dec 19th report) after the PRC publication ( 2007 July 13th report), we try to construct the final normalized deuteron spectrum. Here, we also take inefficiency by energy loss correction procedure, which was not considered at 2007 Dec 19th report yet.

Revised Acceptance Curve and Normalized Inclusive Spectrum

Here, we compare the previous and the updated acceptance curves. The conditions are tabulatted below. Due to the inefficiency of the energy loss correction, acceptance becomes smaller than that calculated neglecting it. Therefore, the resulting bin-by-bin value of the normalized spectrum will increase.

Adopted conditions for the acceptance calculation.
software	GEANT3.21 (tuned tracking parameters for slow perticles)
generated deuteron momentum range	300-900 (MeV/c)
generated deuteron momentum distribution	uniform
generated deuteron angler distribution	uniform on unit sphare i.e. cos&theta and &phi are uniform with no correlation
generated event number	4*10⁸
target center	(-0.3,0.,1.3):E549 (-0.5,0.5,1.2):E570 by cm unit
x/y generation point distribution	4.0 cm sigma Gaussian centered at (x,y)=(-0.3,0.)
z generation point distribution	uniform
multiple scattering	on(Moliere)
energy loss straggling	on(Gauss/Landau/Vavilov are internally selected adequately)
nuclear reaction of deuteron	on(GHEISHA)
coincidense time gate for PA-PB	45 nsec
Birk's coefficient for plastic scintillator	0.013/(MeV/cm)
Time resolution of PA/PB	60/90 psec (~108.2 psec in total), fixed at MIP-measured value.
Inefficiency of energy loss correction	Newly considered. As the reaction vertex, exact position is adopted. The direction vector at the PDC position is adopted as the direction vector to simulate properly the experimental effect.

First of all, we compare calculated acceptance curves cycle-by-cycle below. At the low-momentum region, acceptance decreases significantly, mainly due to a larger multiple scattering effect. As is already known in the old version of acceptance curves, a thicker radiation shield for E570 cycle (Al:0.2mm -> 0.6mm) causes significantly smaller acceptance compared to that for E549 at low-momentum region.

A comparison of old (black) and revised (red) curves for E549.

A comparison of old (black) and revised (red) curves for E570.

A comparison of acceptance curves for E549(black) and E570(red).

The cycle-by-cycle comparison of the spectrum, before and after the revison of acceptance, is as below. Below 500 MeV/c, discrepancy between E549 and E570 is significant, and the normalized spectrum is not reliable. The discrepancy originates from uncertainty of the thickness of Al inside the modified cryostat dedicated to the K⁴He Xray measurement.

A comparison of deuteron momentum spectra from E549(black), E570-1(red) and E570-2(green) with old acceptance curve

A comparison of deuteron momentum spectra from E549(black), E570-1(red) and E570-2(green) with new acceptance curve

At last of this section, normalized deuteron spectra are presented and compared to the last results. Due to the reduced detection efficiency by the inclusion of energy-loss correction efficiency, resulting bin-by-bin values are increased at low-momentum region.

A comparison of momentum spectrum with E549+E570 100% statistics, with the last (black) and the present (red) acceptance curve.

A comparison of missing mass (²X⁰ mass) spectrum with E549+E570 100% statistics, with the last (black) and the present (red) acceptance curve.

We finally adopt the results with the new acceptance curve.

Resolution of deuteron momentum

Here, the evaluated deuteron momentum resolution is plotted. The resolution is defined as the standard deviation (&sigma) of fitted Gaussian the to the simulated distribution of momentum residual,

Res(p) = p_gen - p_sim.

at the interested moemntum. Here, p_gen is the generated momentum and p_sim is simulated measured momentum including various experimental effect as tabulatted above. It is very clearly seen that the value increase very slowly up to ~300 MeV/c, then start to be more steeply. The former part is dominated by the energy loss straggling, while the latter part is dominated by the TOF resolution of PA-PB.