  The expanding molecular ring (EMR) manifests itself as a parallelogram in the
position-velocity diagram of spectral line emission from the Central Molecular
Zone (CMZ) surrounding the Galacic centre (GC). Using multiwavelength data, we
investigate the gas kinematics, star formation activity, and the presence of
shocked gas in a 200 pc long high velocity gas stream (V~ +150 km/s) with a
double helix morphology named the helix stream, that is located 15-55 pc above
the CMZ and is kinematically associated with the EMR/parallelogram. We carried
out molecular line observations using the IRAM 30m, Yebes 40m, and APEX 12m
telescopes. The detection of four rotational transitions of the SiO molecule
indicate the presence of shocks. We derived the SiO column densities and
abundances in different regions of the helix stream. The presence of
protostellar clumps and a candidate HII region signify the ongoing star
formation activity within the helix stream. The cloud is massive (2.5x10^6
M_sun) and highly turbulent. We find evidence of cloud-cloud collisions towards
the eastern edge (l~1.3{\deg}), suggesting a dynamic interaction with the CMZ.
An expanding shell is detected within the cloud with radius of 6.7 pc and an
expansion velocity of 35 km/s. The shell might be powered by several supernovae
or a single hypernova. The SiO abundance within the helix stream implies
extensive shock processes occurring on large scales. The helical or cork-screw
velocity structure of the helix stream indicates twisting and turning motions
within the cloud. We propose that the helix stream is the continuation of the
near side bar lane, that is overshooting after brushing the CMZ. Our findings
carry profound implications for understanding star formation in extreme
conditions and elucidate the intricate properties of gas and dust associated
with nuclear inflows in barred spiral galaxies.
