# Presentation: 246699

## STAR TU, simulation status

- N. Smirnov
- Physics Department, Yale University,
- STAR Collaboration Meeting, MIT, July, 2006

## What does mean STAR TU ?

- Conserve / Improve TPC performance ( RHIC II Luminosity).
- High resolution Vertex Detector ( heavy quark Physics ).
- “special” tracking in EEMC “direction” ( pp  W  e+/- ).
- Tracking data for PMD ( |η| > 2.); pp, dA
- μ – detector (?)

## Conserve / Improve TPC performance ( RHIC II Luminosity).

- Additional tracking / calibration detectors inside and outside of TPC
-  Pad or XY strip GEM Detectors is a good choice :
- Required 3d- precision
-  low mass,
- fast.
- Solves TPC space charge distortions correction problem {“charge” value / number of hits as a F ( t, φ, z);  model (can/should be different for pp and AA); correction on “track level”}
-   and part of tracking (large surface to be covered, R~35 cm).
- Together with other “fast” detectors, help to solve the “Event pile-up” problem.
- TPC its own improvements; IFC shielding; “gap” between sectors; OFC gas leak  membrane HV, CF4 gas mixture  smaller diffusion, faster drift (new FEE, on-line cluster finding/reconstruction). Gas amplification calibration
- TPC MWPC data: number of tracks in drift volume, tracking for |η| > 1.

## High resolution Vertex Detector ( heavy quark Physics ).

- Today (HFT) proposal relays on:
-    -- perfect TPC space charge distortions correction (not in a simulation),
-    -- perfect SSD performance ( does not work still, and ...),
-    -- perfect alignment,
-    -- factor X improvement in APS read-out speed (X = 2 ?,  2 ms / frame),
-    -- primary vertex is a “key factor”,
-    -- D reconstruction efficiency and background – two different simulation steps,
-    -- APS simulation (N of hits / frame and their position) is not a “realistic” one
-    -- unknown beam-beam background conditions for small R.
-       R&D “step” to demonstrate “hit – track” matching was not done, but in a schedule.
- It is too optimistic (my opinion)
- Natural limitations: high multiplicity events to get a primary vertex with “needed” precision ( multi-loop approach can help ?)
- Conclusion: needs a high precision, fast “pointer” ( SVT was a “candidate”, but ...)
-       The best: 3 points in space to be “independent” from TPC data.

- A lot of simulation results have been presented during last STAR Upgrade meeting (December 1-2,2005)
- Some conclusions:
-     - fast, high precision, low mass tracking detectors in front and behind TPC ( GEM) can be crucial to help with TPC “space charge distortions correction”.
-     - HFT with 4 ms read-out time will work in a combination with TPC+SSD+(GEM) up to L=1x1027, but not a RHIC II Detector.
-     - IT has to provide a high quality “search corridor” for HFT to “help” with occupancy, primary vertex reconstruction, PP, dA, ....;
-     - three double layers Si strip detector (MIT proposal) is not the  best solution.
-     - tracking detector in front of EEMC is useless for We+/- + X study because  TPC end-cap material budget.
-     - IT has to solve this problem: high Pt particle reconstruction in EEMC acceptance.
-     Three possible variants for IT (personal opinion)
-        - 3 or 4 double layers of Si strip detectors; first and last – with 90 deg strip direction rotation, and to use pad detectors ( with 2x2 mm2 size) instead of stereo ones for 2 intermediate layers (Gerrit’s idea).
-       - microTPC with fast, low diffusion gas mixture and MicroPattern read-out (no gating grid)

## Variant with Si Pixel Det., SPD + Si strip + GEM (III)

- TPC “IN field-cage”

- “safety” Kapton foil

- GEM with X-Y read out

- SSD

- Si strip, 4x4 cm2
-  two layers, X and Z

- SPD (Hybrid Pixel)
- Two layers with 90 deg
-  rotation

- HFT

- SPD – Design Parameters (ALICE)

- Two barrel layers;  R1 = 6.4 cm,  R2 = 7.6 cm.     Pixel Cell: 50(rφ) x 425 (z) μm**2**, (90 deg rot. second layer)
- Pixel ASIC thickness: <=150 μm.    Si sensor ladder thickness: <=200 μm. “Bumps” technology.
- Cooling: water / C6F14/ [C3F8 (evaporative)]
- Material budget (each layer):  0.9%X**0** ( Si – 0.37, Cooling – 0.3, Bus – 0.17, Support – 0.1 )

## Variant I – 4 Double Si strip/Pad1st – 2x2 cm2 (X/Z);  2nd – 4x4 cm2 (X/Pad);  3rd – 4x4 cm2 (X/Pad); 4th – 4x4 cm2 (X/Z)

- TPC in field cage

- GEM Detectors

- SSD

- Si Strip

- HRVD

## Simulation / Reconstruction approach

- Stand – along routines (FORTRAN) on the basis of personal experience and knowledge from previous experiments and R&D activities
- Special for fast (but reliable) test / checking different detector SetUps including PiD (dE/dX, Ch.Det., RICH, TRD) and secondary Vertexes  finding/reconstruction.
- GEANT-3 (GSTAR)
- Detector response simulation – 4 variants:
-           -- GEANT hits, but not GSTAR variants (sometimes)
-           -- Gaussian smearing
-           -- “intermediate” scale simulation ( to save a compute time)
-           -- “full” scale simulation ( check Hans Bichsel web page)
- Two variants of a “helix fit”
- Keep all needed “pointers” for evaluation / control

## One particle (π+) /event. Hits in a fit - only IT detectors (primary vertex – OFF); 100% efficiency, perfect alignment.

- dZ, cm

- dX, cm

- dX, cm

- Pt, GeV/c

- Matching performance: IT track crossing position – 2nd HFT layer hit (Local CS).

- Variant III

- Here it will be presented the simplest, “first step” simulation results:
-  “one  π/event”, GEANT hits with Gaussian smearing

## Matching performance: track crossing point – HFT L2 hit position (LCS)

-  SSD,  Vertex in FIT;  All hits
- Lines – Sp.Ch. effect

- Set Up Variant:  TPC +

- GEM + SSD + 1 double SiStrip + 2 Si Pixel;  ITH

-  SSD + 2 Si Pixel;  All hits

-  SSD + 1 Si Pixel;  All hits

-  GEM + SSD + 2 Si Pixel;  ITH

-  GEM + SSD + 1 Si Pixel;  ITH

- GEM + SSD + 3 double Si strip/pad
-  ( MIT proposal),  ITH

- GEM + SSD + 2 double Si strip/pad
-    + 2 Si strip XZ
-  ( MIT proposal)mod,  ITH

- “ITH” – only IT hits are in Fit,
- “All hits” -- + TPC hits.

- dZ

- dX

- σ of Gauss fit, cm

- Vertex OFF

## Matching performance: track crossing point – HFT L2 hit position (LCS)

-  SSD,  Vertex in FIT;  All hits
- Lines – Sp.Ch. effect

- Set Up Variant:  TPC +

- GEM + SSD + 1 double SiStrip + 2 Si Pixel;  ITH

-  SSD + 2 Si Pixel;  All hits

-  SSD + 1 Si Pixel;  All hits

-  GEM + SSD + 2 Si Pixel;  ITH

-  GEM + SSD + 1 Si Pixel;  ITH

- GEM + SSD + 3 double Si strip/pad
-  ( MIT proposal),  ITH

- GEM + SSD + 2 double Si strip/pad
-    + 2 Si strip XZ
-  ( MIT proposal)mod,  ITH

- “ITH” – only IT hits are in Fit,
- “All hits” -- + TPC hits.

- dZ

- dX

- σ of Gauss fit, cm

- Vertex OFF

- Variant “3Si2” – 3 Double Si strip/Pad1st – 2x2 cm**2** (X/Z);  2nd – 4x4 cm**2**** **(X/Pad);  3rd – 4x4 cm**2**** **(X/Pad)

- Variant “Pixel” - 1 or 2 (with 90 deg rotation)
-  layers of SPD (ALICE, LHCB, PHENIX)

-      “Special Variant” for detector response simulation;
-   TPC, GEM, SSD – gaussian smearing
-   SPD, Si-strip / pad – “intermediate”, q with noise, but no FEE , no cross-talk,...
-    APS – Yes/No but realistic read-out and background hits simulation / reconstruction

## Si detectors, number hits (Central HJ)

-  PIXEL                              3Si2

- R pos    6.4    7.6            6.4    11.    16.    cm
- Det. Size  1.74                 4.        16.        cm**2**
- Strip/pad   0.0002125     0.02     0.04      cm**2**
- N hits   (8, 3) (7, 2)        (18, 7)   (20, 7)  (17, 4)
-   ( max, aver)
- N “destroyed” hits
- because occupancy
-             ~0.3%                               ~ 15%

- Number of tracks that “contributed” in
-  reconstructed hit

- 3Si2

- PIXEL

## Tracks finding / reconstruction (Vertex OFF)( TPC   SSD  Si...)

-    PIXEL  1         2                     3Si2

-    Eff:      0.8       0.7                   0.7
-  Ghost:   0.064   0.046               0.4

- Track DCA parameters

- DCA, XY, cm

- DCA, Rz, cm

- Red:  all tracks  3Si2 variant
- Blue:  good one, 3Si2 variant
- Black: all tracks PIXEL variant

## Primary Vertex reconstructionTPC + SSD + PIXEL (1 or 2)

- PIXEL 1

- PIXEL 2

-  DCA, xy, cm

-  DCA, Rz, cm

- N of event

- N of event

## APS, number hits

- L = 2.x10**26, L1, 2 ms read-out time;  Nmax hits / det event = 79
-                                                                Naver                         = 42
- L = 2.x10**27,    L1 (2.8 cm R) - ( 815, 314),  L2 (4.6 cm) – (284, 135)
-                                                        (max, aver)                        (max, aver)

- N hits (L1)

- N detector

- Central HJ

-  plus background

- One detector, reco hits

- X, cm

- Y, cm

## Tracks finding / reconstruction (Vertex OFF)( TPC   SSD  PIXEL (1 or 2)  APS)

- Luminosity                        PIXEL   1              2
- 2.x10**26                        Eff   0.625            0.6
-                                     Ghost  0.016         0.013
- 2.x10**27                        Eff    0.65             0.6
-                                     Ghost   0.05             0.11

- Very preliminary

- DCA track parameters to Primary vertex

- Detector combination                   DCA, xy, μm              DCA, Rz,  μm   (sigma)
- APS only                                          ----------                       28.
- SSD + APS                                          39.                          39.
- PIXEL 1 + APS                                    71                           32
- SSD + PIXEL 2 + APS                         28                           33
- All hits                                                  53                           91

## What is the reason for GEM D ?
       -- not to use TPC hits (can be strong distortions) for the “final” step – to match track with APS hits,  and vertexes (both primary and secondary ) finding and reconstruction  
       -- the best “tool” to struggle with TPC hits space charge distortions, as a scaller and high precision tracker.
       -- help with events pile-up problem
       -- may be the first step – use one CTB slat for fast, precision tracking detector behind TPC.

Data from TPC before (in time) a trigger signal
       -- scaller data
       -- coordinate inform for particles in EEMC acceptance

SSD  <----> two layers of Si strip ( if it will be any problem or timing will be a “stopper” point) in a combination with GEM D.

Tracking in EEMC direction to study pp  W  e-/+ (next slide)

-        -- not to use TPC hits (can be strong distortions) for the “final” step – to match track with APS hits,  and vertexes (both primary and secondary ) finding and reconstruction
-        -- the best “tool” to struggle with TPC hits space charge distortions, as a scaller and high precision tracker.
-        -- help with events pile-up problem
-        -- may be the first step – use one CTB slat for fast, precision tracking detector behind TPC.
- Data from TPC before (in time) a trigger signal
-        -- scaller data
-        -- coordinate inform for particles in EEMC acceptance
- SSD  <----> two layers of Si strip ( if it will be any problem or timing will be a “stopper” point) in a combination with GEM D.
- Tracking in EEMC direction to study pp  W  e-/+ (next slide)

## IT set up -- asymmetric (in Z); Two more layers of Si strip detectors ( one side, 4x8 cm2) to cover “EEMC direction”, for pp program.   

- Sample of events, We(μ) + X

-  pp, √s=500, PYTHIA

- η

- Pt, GeV/c

- 30.

- 60.

- 1.

**“****barrel” position; NOT “disk”**

## Track reconstruction performance.One π+ / event; HFT + IT + minimum 6 TPC hits; perfect alignment

- dPt/Pt

- 30 %

- dPt/Pt

- η

- The reconstruction “chain” has to work well;  TPC track  EEMC cluster 
-  electron E  electron P (HELIX Radius)  matching hits from IT  constraint
- Refit  electron charge (+/-)

## Points to be discussed

- SSD status / performance / future
- GEMD; fast, reliable gas detector, COMPAS experience, 10x10 cm2 active size, XY data with q-selection power and “scaler” data to solve TPC sp.ch. distortions corrections on a “track” level (?); man-power support (MIT, Yale); needs “some R&D” ( low mass construction approach, FEE); good progress with foil mass-production.
- Si one sided strip detector: does not need R&D, reliable and good tested technology, SSD substitution and EEMC direction (pp); man-power support (MIT)
- Si pixel detector: the best way (my opinion) to get in STAR very powerful and reliable Vertex Detector; mass-production is in a progress and a lot of such detectors will be installed in nearest future (ALICE, LHCB, PHENIX). It is crucial to be “in a line” and keep a control and get an experience (can LBL takes a care?)
-          One layer will help a lot (special for 2. ms read-out variant); it means ~490 sensors (<2. M$),
-        but man-power, experience, DAQ,... are very difficult points.
- Very crucial – to prepare and control a “global” mechanical structure for IT and HFT (together!!) as a one construction part. Alignment problem can be very difficult to get a high precision tracking data, and it should be flexible for different variants of IT setup(s).
- STAR tracking is a “not easy” problem, and needs (may be) nonstandard decisions. It should be a “one person supervision” approach, with high “KEAL” factor, like HHW did a job for TPC