sPHENIX tracking discussion

[Haiwang Yu <yuhw.pku AT gmail.com>]

Hi Christof,

This solves the mystery. I also observed similar thing in the full tracking.

After the fixing the bug in the track propagation on Tuesday, the track propagation performance has been improved a lot.

In both efficiency and speed. (Attached slides)

One remaining issue is the relatively low tracking efficiency (88% for cylindrical, 79% for ladder) in high multiplicity environments (1000 low momentum pions) that caused by this strict seeding requirements.

I tried to loosen the seeding requirement to 6/8, but I got many ghost even in 100 pion environment. (~200(seeds)/100(input)).

I am working on two things to make the seeding ghost in control:

• seeds cleanup - merge seeds
• eliminate track propagation if incremental chi2 consecutively large in several layers

BTW, central Hijing events could be run, just consumes a lot of memory. (ana. 49, more than 18GB) I think reading in the DST nodes actually takes the bulk part. But GenFit is also heavy. Will seek help from Chris and Jin for that.

Cheers,

Haiwang

On Fri, Apr 28, 2017 at 11:04 AM David Morrison <dave.patrick.morrison AT gmail.com> wrote:

Hi Christof,

That looks very encouraging – and makes sense too.

Dave

On 4/28/17 9:50 AM, Christof Roland wrote:
> Hi Everybody,
>
> I had a look at the seeding/tracking efficiency.
>
> As suspected in the last meeting it turns out that the seeding layers are not really hermetic.
> Especially the INTT layers are not 100% efficient, which is probably to be expected.
> This in turn means the the current seeding requirement of 8 out of 8 layers hit is
> responsible for a large part of the inefficiency we saw in the kalman tracking.
>
> Releasing the number of hit requirement in the seeding step from 8 out of 8 to
> 6 out of 8 hits increases the single track reconstruction efficiency from ~86% to ~98%
>
> Please see the attached plots below.
>
> In the region below 1 GeV the 6 out of 8 seeding scheme results in some segmentation
> violations. We'll have to take a look at that.
>
> Cheers
>
>    Christof
>
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Attachment: KalmanPatRec_2017-04-28.pdf
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