  In the present paper we introduce the notion of strongly orthogonal
martingales. Moreover, we show that for any UMD Banach space $X$ and for any
$X$-valued strongly orthogonal martingales $M$ and $N$ such that $N$ is weakly
differentially subordinate to $M$ one has that for any $1<p<\infty$ \[ \mathbb
E \|N_t\|^p \leq \chi_{p, X}^p \mathbb E \|M_t\|^p,\;\;\; t\geq 0, \] with the
sharp constant $\chi_{p, X}$ being the norm of a decoupling-type martingale
transform and being within the range \[ \max\Bigl\{\sqrt{\beta_{p, X}},
\sqrt{\hbar_{p,X}}\Bigr\} \leq \max\{\beta_{p, X}^{\gamma,+}, \beta_{p,
X}^{\gamma, -}\} \leq \chi_{p, X} \leq \min\{\beta_{p, X}, \hbar_{p,X}\}, \]
where $\beta_{p, X}$ is the UMD$_p$ constant of $X$, $\hbar_{p, X}$ is the norm
of the Hilbert transform on $L^p(\mathbb R; X)$, and $\beta_{p, X}^{\gamma,+}$
and $ \beta_{p, X}^{\gamma, -}$ are the Gaussian decoupling constants.
