[Brahms-l] Fw: New PHENIX paper on pi-0 cross section and A_LL in Run-5 p+p

FYI

Sent: Friday, April 20, 2007 2:55 PM
Subject: New PHENIX paper on pi-0 cross section and A_LL in Run-5 p+p


> Dear Tim, Wit, Flemming, and Peter;
> 
> In one week's time the PHENIX Collaboration will submit a paper to
> Phys. Rev. D Rapid Communications on pi-0 cross section and
> A_LL in Run-5 p+p collisions. Please find the title and abstract
> below.
> 
> Best regards,
> 
> Barbara
> 
> ----------------------------------------------------------------------------
> 
> TITLE:  Inclusive cross section and double helicity asymmetry for
> $\pi^{0}$ production in $p+p$ collisions at $\sqrt{s} = 200$ GeV:
> implication for the polarized gluon distribution in the proton
> 
> ABSTRACT:
> The PHENIX experiment presents results from the RHIC 2005 run with
> polarized proton collisions at $\sqrt{s}=200$ GeV, for inclusive $\pi^{0}$
> production at mid-rapidity.  Unpolarized cross section results are given
> for transverse momenta $p_T=0.5$ to $20$ GeV/$c$, extending the range
> of published data to both lower and higher $p_T$. The cross section is
> described well for $p_T<1$ GeV/$c$ by an exponential in $p_T$, and,
> for $p_T>2$ GeV/$c$, by perturbative QCD. Double helicity asymmetries
> $A_{LL}$ are presented based on a factor of 5 improvement in uncertainties
> as compared to previously published results, due to both an improved
> beam polarization of 50\%, and to higher integrated luminosity. These
> measurements are sensitive to the gluon polarization in the proton, and
> exclude maximal values for the gluon polarization.
>
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