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 We+/- + 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)

- Two layers of Pixel Hybrid Detectors with pad size 50 x 425 μm2

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) μm2, (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%X0 ( Si – 0.37, Cooling – 0.3, Bus – 0.17, Support – 0.1 )

Variant I – 4 Double Si strip/Pad1st – 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 cm2 (X/Z); 2nd – 4x4 cm2 (X/Pad); 3rd – 4x4 cm2 (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 ( 640x640 pads, 30x30 μm2 size, 4 read-out ports, 50 MHz read-out frequency 2. ms read-out time )

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. cm2

Strip/pad 0.0002125 0.02 0.04 cm2

N hits (8, 3) (7, 2) (18, 7) (20, 7) (17, 4) ( max, aver)

N “destroyed” hitsbecause 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 variantBlue: good one, 3Si2 variantBlack: all tracks PIXEL variant

Primary Vertex reconstructionTPC + 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 32SSD + PIXEL 2 + APS 28 33All 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)

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, We(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/Pt30 %dPt/Pt

η

The reconstruction “chain” has to work well; TPC track EEMC cluster electron E electron P (HELIX Radius) matching hits from IT constraintRefit 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