Measurement of the polarization of the $Υ(1S)$ and $Υ(2S)$ states in $p\bar{p}$ collisions at $\sqrt{s}=$1.96 TeV

TL;DR

A study of the polarization of the Upsilon (1S) and Upsilon(2S) states using a 1.3 fb;-1 data sample collected by the D0 experiment in 2002-2006 during run II of the Fermilab Tevatron Collider is presented.

Abstract

We present a study of the polarization of the $Υ(1S)$ and $Υ(2S)$ states using a $1.3 $ fb$^{-1}$ data sample collected by the D0 experiment in 2002--2006 during Run II of the Fermilab Tevatron Collider. We measure the polarization parameter $α=(σ_{T}-2σ_{L})/(σ_{T}+2σ_{L})$, where $σ_{T}$ and $σ_{L}$ are the transversely and longitudinally polarized components of the production cross section, as a function of the transverse momentum ($p_{T}^Υ$) for the $Υ(1S)$ and $Υ(2S)$. Significant $p_{T}^Υ$-dependent longitudinal polarization is observed for the $Υ(1S)$. A comparison with theoretical models is presented.

Figures (5)

• Figure 1: [Color online] Signal extraction from the dimuon invariant mass distribution for events in the $0.4 < |\cos\theta^{\ast}| < 0.5$ region. a,c) $2<p_{T}^{\Upsilon}<4$ GeV/$c$; b,d) $10<p_{T}^{\Upsilon}<15$ GeV/$c$. Dashed curves are the combinatoric background.
• Figure 2: [Color online] Monte Carlo $|\cos\theta^{\ast}|$ distributions after all selection requirements for different $\alpha$ values: $-1$ (dashed histogram), $0$ (solid histogram) and $+1$ (dotted histogram). a) $0<p_{T}^{\Upsilon}<1$ GeV/$c$, b) $p_{T}^{\Upsilon}>$15 GeV/$c.$
• Figure 3: Comparison of data (points) and Monte Carlo (solid histogram) for $\Upsilon(1S)$ with $2<p_{T}^{\Upsilon}<4$ GeV/$c$: a) momentum of $\Upsilon(1S)$, b) polar angle of $\Upsilon(1S)$, c) angle between muons, d) $|\cos\theta^{\ast}|$.
• Figure 4: [Color online] Dependence of $\alpha$ on $p_{T}^{\Upsilon}$ for inclusive $\Upsilon(1S)$ candidates. Black circles are data. The band is the NRQCD prediction cn6. Curves are two limiting cases (see text) of the $k_t$-factorization model kt.
• Figure 5: [Color online] Dependence of $\alpha$ on $p_{T}^{\Upsilon}$ for inclusive $\Upsilon(2S)$ production. Circles are our data. The band is the NRQCD prediction cn6.