star tu, simulation status n. smirnov physics department, yale university, star collaboration...

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