Today's Progress 27. Apr. 2010

Normalized proton spectra with E549+E570 100% statistics

Here, we try to construct the normalized inclusive proton spectrum with E549+E570 100% statistics, taking into account the improvement of proton selection procedure achieved at 2007 July 11th report. Furthermore, we also take inefficiency by energy loss correction procedure, which has not been considered ever. The proton spectrum presented here will be the final version of inclusive proton spectrum of E549/E570.

Revised Acceptance Curve and Normalized Inclusive Spectrum

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 proton momentum range	200-800 (MeV/c)
generated proton momentum distribution	uniform
generated proton 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.

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. Now, we see a discrepancy between E549 and E570 to be systematic and significant with very small statistical errors. The tendency of the discrepancy is similar to that seen for deuteron spectrum, and it should originate from common sources.

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

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

At last of this section, normalized proton 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 as well as the deuteron case.

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

Missing mass (³S⁰ mass) spectrum with E549+E570 100% statistics, with the updated acceptance curve.

We finally adopt the results with the new acceptance curve.

Resolution of proton momentum

Here, the evaluated proton momentum resolution is plotted. The resolution was given once in the previous report, but the TOF resolution of PB was revised to 90 psec from 80 psec here. The evaluated resolution is 5 MeV/c (standard deviation) at 509 MeV/c, where we expect monochromatic peak by the ⁴_&LambdaHe -> t + p process.