HOWTO: Search for specific package

pacman -Ss <package_name>

HOWTO: Clean pacman package cache on ArchLinux

a) Install paccache utility

    pacman -S pacman-contrib

b) Delete all cached versions of each package, except most recent 3

    paccache -r

c) Remove all cached versions of uninstalled packages

    paccache -ruk0

d) Perform clean-up tasks via pacman, if a)–c) do not help

    pacman -Scc

e) Query to which package a file belongs

    sudo pacman -Qo time

f) Remove unused (orphan) packages and their configuration files

    sudo pacman -Rns $(pacman -Qtdq)

https://wiki.archlinux.org/index.php/Pacman/Tips_and_tricks