The STAR HBT transient microDST - draft

M.A. Lisa and D.H.Hardtke

The transient microDST is all the information passed from the StHbtEventReader to the rest of the infrastructure. (See the StHbt code documentation for details on this.) Thus, while we would like to keep memory and storage considerations in mind, it is important that all information neccessary to do HBT studies in STAR is contained in these structures.

To keep things "finite," we will try to have only three main classes in the microDST. The first is StHbtEvent; besides event-wise information like multiplicity and reaction plane orientation (we hope), it has pointers to two collections of the other main classes. These are StHbtTrack and StHbtV0, whose names are hopefully self-explanatory.

StHbtEvent

This is the "head" object. The structure and contents were defined by Dave Hardtke, with input from the rest of the HBT PWG. The data stored in it is (see header for methods):

StHbtEvent contents

Information DataType
Event Number unsigned short
CTB Multiplicity unsigned short
East and West ZDC ADC values unsigned shorts
Number of TPC hits int
Number of TPC tracks unsigned short
Number of "good" TPC tracks unsigned short
Reaction plane angle and uncertainty floats
Primary vertex position StHbtThreeVector

StHbtEvent contents

`Information`	`DataType`
`Event Number`	`unsigned short`
`CTB Multiplicity`	`unsigned short`
`East and West ZDC ADC values`	`unsigned shorts`
`Number of TPC hits`	`int`
`Number of TPC tracks`	`unsigned short`
`Number of "good" TPC tracks`	`unsigned short`
`Reaction plane angle and uncertainty`	`floats`
`Primary vertex position`	`StHbtThreeVector`

In addition, as mentioned above, the StHbtEvent object has pointers to collections of StHbtTrack and StHbtV0 objects.

StHbtTrack

An event probably has tracks in it. These are represented in our microDST by the StHbtTrack object.

Note: there is no PID assigned!! PID information (like dEdx) is here, but the PID itself is assigned after the StHbtTrack passes a StHbtParticleCut and becomes a StHbtParticle.

StHbtTrack contents

Information DataType
Charge Sign char
Number hits on track int
Number possible hits on track unsigned short
Nsigma from pion,kaon,proton dEdx^* floats
dEdx in TPC float
DCA from primary vertex (z) float
DCA from primary vertex (x-y) float
Chi2 (x-y) float
Chi2 (z) float
Momentum StHbtThreeVector
Pt float
Helix StPhysicalHelixD

StHbtTrack contents

`Information`	`DataType`
`Charge Sign`	`char`
`Number hits on track`	`int`
`Number possible hits on track`	`unsigned short`
`Nsigma from pion,kaon,proton dEdx^*`	`floats`
`dEdx in TPC`	`float`
`DCA from primary vertex (z)`	`float`
`DCA from primary vertex (x-y)`	`float`
`Chi2 (x-y)`	`float`
`Chi2 (z)`	`float`
`Momentum`	`StHbtThreeVector`
`Pt`	`float`
`Helix`	`StPhysicalHelixD`

StHbtV0

An event may have v0-decays in it. These are represented in our microDST by the StHbtV0 object.

We are building on the expertise of the STAR Strangeness PWG on this. They have a strangeness microDST maker, and we will just copy into our structures the information they build. This is a work in progress, and Helen Caines and Tom Humanic are the main ones working on this.

Note: as with the StHbtTracks, there is no PID assigned!! Information with various hypotheses is present, but PID itself is assigned after the StHbtV0 passes a StHbtParticleCut and becomes a StHbtParticle.

Contents of the Strangeness V0 microDST object

Information DataType
Decay Length float
Decay Position float[3]
DCA of V0 to daughters float
DCA of positive daughter to prim vtx float
DCA of negative daughter to prim vtx float
Momentum of positive daughter float[3]
Momentum of negative daughter float[3]
Momentum of V0 float[3]
Total momentum of positive daughter float
Total momentum of negative daughter float
V0 pT float
Momentum component along V0 (+) daughter float
Momentum component along V0 (-) daughter float
Number of TPC hits (+) daughter int
Number of TPC hits (-) daughter int


`Information`	`DataType`
`Decay Length`	`float`
`Decay Position`	`float[3]`
`DCA of V0 to daughters`	`float`
`DCA of positive daughter to prim vtx`	`float`
`DCA of negative daughter to prim vtx`	`float`
`Momentum of positive daughter`	`float[3]`
`Momentum of negative daughter`	`float[3]`
`Momentum of V0`	`float[3]`
`Total momentum of positive daughter`	`float`
`Total momentum of negative daughter`	`float`
`V0 pT`	`float`
`Momentum component along V0 (+) daughter`	`float`
`Momentum component along V0 (-) daughter`	`float`
`Number of TPC hits (+) daughter`	`int`
`Number of TPC hits (-) daughter`	`int`