Ⅱ-4. Hadron Physics

RIKEN Accel. Prog. Rep. 52 (2019)

Tracking performance simulation for INTT at sPHENIX

Fig. 1. (Left) In-time vertex tagging and (Right) out-of-timevertex tagging eﬃciency versus event multiplicity.
∗1
∗2
∗3
∗4
∗5

RIKEN Nishina Center
Department of Physics, Rikkyo University
Brookhaven National Laboratory
Nara Women’s University
Tokyo Metropolitan Industrial Technology Research Institute- 89 -sPHENIX Simulation

107

10 MHz p+p, 2 INTT layers
|Z106

RECO

|<10cm, |η|<1.0In time, GenRECO

105

In time, Reco (N≥20)
TPCPile-up, Gen

104

Pile-up, Reco (N≥20 && NINTT ≥1)

47RECOTPCRECO

1031021010123568910p (GeV/c)
TFig. 2. Number of tracks from in-time and pile-up events asa function of pT with diﬀerent tracking requirements.
MVTX cluster association efficiency

The sPHENIX tracking system comprises, from theinside to outside, i) the Monolithic-Active-Pixel-Sensorbased Vertex Detector (MVTX),1) ii) the Intermediate
Silicon Strip Tracker (INTT),2) and iii) the Time Projection Chamber (TPC).2) MVTX measures the distance ofclosest approach for heavy-ﬂavour physics. TPC aims at
a momentum resolution of 1.2% for diﬀerent Υ state separations. INTT has a narrow timing window of 100 ns,
which is orders smaller than those of MVTX (4000 ns)
and TPC (26400 ns), which provides rejection powers on
pile-up events and tracks.
The INTT tracking performance and its optimal layer
conﬁguration are evaluated via 1) pile-up event rejections, 2) pile-up track rejections, and 3) MVTX cluster association eﬃciency to TPC track seeds. For
these studies,√ Geant4 simulations with PYTHIA8 p+p
events at s = 200 GeV, embedded at realistic collision rates at sPHENIX, are employed. Tracks are reconstructed only with MVTX hit triplets and a cluster
in one of the INTT layers for the (1), while tracks areseeded in TPC and interpolated to INTT and MVTX
hits with the Hough transformation for the (2) and (3).
Figure 1 Left (Right) shows the event vertex tagging(rejection) eﬃciency in (out of) the INTT time window
as a function of PYTHIA event multiplicity at the collision rate of 12 MHz. The integrated in-time vertex
tagging eﬃciency is 98.4 ± 0.3%, and the integrated outof-time, i.e. pile-up, vertex rejection eﬃciency is 99%.
This indicates 1 INTT cluster provides a good rejectionof pile-up tracks.
Figure 2 shows the numbers of tracks per pT bin widthfrom in-time and pile-up events as a function of pT at
the collision rate of 10 MHz. The blue and red lines
are the generated tracks in in-time and pile-up events.

NRECO TRK / 0.5 GeV/cT. Todoroki,∗1 Y. Akiba,∗1 H. Aso,∗1,∗2 D. Cacace,∗3 E. Desmond,∗3 T. Hachiya,∗1,∗4 T. Ichino,∗1 M. Isshiki,∗4T. Kondo,∗5 H. Kureha,∗4 E. Mannel,∗3 G. Mitsuka,∗1 I. Nakagawa,∗1 R. Nouicer,∗3 R. Pisani,∗3 K. Sugino,∗4A. Suzuki,∗4 M. Tsuruta,∗1 and Y. Yamaguchi∗110.8
0.6+/- 5 µs MVTX timing window
RECO

NMVTX CLUS≥20.4

No pileup

10 MHz p+p

345p (GeV/c)

2INTT Layers
1INTT Layer

0.20INTT Layer

0012T

Fig. 3. MVTX cluster association eﬃciency to TPC trackseeds as a function of pT with diﬀerent number of INTTlayers.

The red circles show that the pile-up contribution in thereconstructed tracks becomes two orders smaller thanthat from the in-time events (blue squares) by requiring
1 INTT cluster in addition to 20 TPC clusters in tracking. This also indicates 1 INTT cluster provides a good
rejection of pile-up tracks.
Figure 3 shows MVTX cluster association eﬃciency
to TPC track seeds as a function of pT at no pile-up(0 Hz) and 10 MHz collision rates. The worst eﬃciency
is obtained without INTT (0INTT Layer) because ofthe large distance between MVTX and TPC. INTT hits
in the association reduce the uncertainty in searching
MVTX hits, resulting in better eﬃciency. The eﬃciency
is the best with 2 INTT layers. These studies show thata two-layer INTT detector is optimal for obtaining thebest tracking performance at sPHENIX.
References

1) MVTX proposal submitted to the DOE Oﬃce of Science2) sPHENIX proposal, arXiv:1501.06197