Best guess is that Helix is a family of switch system on chip silicon, not a single product. What the parts seem to have in common is 1 Gb/s access ports and eight 10 Gb/s uplink ports. The uplink ports are commonly presented as SFP+ sockets. The silicon is capable of ganging pairs of 10 Gb/s together in a QSFP arrangement to provide uplink ports that would be used to build switch stacks.

An example p/n is BCM56309 that has 4 Mbyte of on-chip packet buffer. This part is called out in the Arctica 4804iq data sheet. The BCM56342 is called out for the HPE Altoline 6900. The switch silicon is integrated with a dual core ARM processor which is used for the switch control plane.

The release notes for Broadcom's SDK from 2009 shows lots of details of the StraXGS family tree at its writing. It includes the product code names:

BCM56300 Helix
BCM56310 Helix+
BCM56320 Helix3

So it appears that Helix4 was introduced later. Switches described in the release notes have 24 access ports. 48-port silicon came later.

Note added August 2019

BCM56340 Helix4 with 54 ports
BCM56342 Helix4 with 30 ports

Helix4 is used in the Edgecore AS4610-XXX switches. These switches had their design submitted to OCP in January 2016. Note that Helix4 is more than just a switch chip. It also includes the CPU integrated into the package.