Spin Physics with the PHENIX Silicon Vertex

Tracker

Junji TojoRIKEN

for the PHENIX Collaboration

Advanced Studies Institutes - Symmetries and SpinJuly 27 - August 3, 2005, Prague

Silicon Vertex Tracker (VTX) Upgrade for PHENIX

• The PHENIX baseline detector was completed since RHIC-Run3 (2003).

• The detector upgrade program has been developed to enhance the physics capabilities.→ M. Grosse Perdekamp’s talk

• The VTX upgrade in the PHENIX Central Arm Spectrometers has been proposed for :– Precise measurement of heavy-quark (charm & bottom) production w/

displaced decay vertices,– Large acceptance tracking especially for jet production.

• The VTX has to be operated is in high luminosity and high multiplicity environment for polarized pp, p(d)A, and AA collisions in the future RHIC running.

Spin Physics with the VTX Detector• Gluon polarization

meas. w/ longitudinal double-spin asymmetry ALL for – heavy-quark

production– photon-jet production

• Precise determination by extending x-rangein different channels beyond the baseline

( ) ( )

( ) ( )LLA

Gluon Polarizationwith Heavy-Quark Production

• Dominated by gluon-gluon fusion :Clean process with wide xg-range

• Limitation in the baseline detector– Indirect meas. w/ inclusive electrons– Huge background from π0 Dalitz decay and photon conversion

• Precise vertexing w/ VTX allows direct meas. by detecting displaced decay vertices thr. distance of closest approach (DCA).

1 2

1 2

( ) ( )ˆ ( )

( ) ( )LL LL

g x g xA a gg QQ

g x g x

Parton level asymmetryfrom pQCD calculation

gg

Q

Q

m (GeV) cμmD0 1865 125D± 1869 317B0 5279 464B± 5279 496

D, B

e

Primary event vertex

Displaced vertex

DCA

Gluon Polarizationwith Photon-Jet Production

• Dominated by gluon Compton process :Golden channel for precise measurement

• Limitation in the baseline detector– Recoil jet reconstruction is desirable for better parton kinematics constr

aint, but difficult due to limited acceptance.

• Large acceptance tracking w/ VTX makes it possible to determine recoil jet axis and thus improve xg determination.

1

( )ˆ( ) ( )

( )g p

LL q LLg

g xA A x a gq q

g x

Parton level asymmetryfrom pQCD calculation

g

γq

qMeasured inpol DIS

• Specifications– 4 layers with large acceptance ( & < 1.2)– Displaced vertex measurement : < 40 m– Charged particle tracking : p/p ~ 5% p at high pT

– Working detector for both of heavy ion and pp collisions• Technology Choice

– Hybrid pixel detectors in 2 inner layers– Stripixel sensors w/ SVX4 readout chip in 2 outer layers

The VTX Detector

Pixel layersr=5.0 cm, Δz~±10 cmr=2.5 cm, Δz~±10 cm

Strip layersr=10.0 cm, Δz~±16 cmr=14.0 cm, Δz~±19 cm

Beam pipe

The VTX Detector in PHENIX

VTXVTX

|η| < 1.2

Hybrid Silicon Pixel Detector

Solder bump ~ 15 μm

• Hybrid pixel detector– Technology developed by CERN/ALICE– Bump-bonding btw R/O chip

and sensor• R/O chip : ALICE1/LHCB chip

– 0.25μm process, rad hard ~ 30Mrad– Matrix of 32 x 256=8,192 cells– Pixel size 50 x 425 m2

– Active area 12.8 x 13.6 mm2

– 150μm thickness– Operation at 10 MHz– Power consumption ~ 1 W/chip

• Pixel sensor– p+/n/n+ structure– Same pixel size as R/O chip– Bump-bonded to 4 R/O chip– 200μm thickness

SensorR/O Chip

Pixel sensor

Hybrid Silicon Pixel Detector• Half-module

– 2 bump-bonded ladder– High density Al/Kapton bus

• 70μm pitch & 5 layers• R&D on-going

– 1 pilot module : R/O & control• 2 half-modules makes 1 ladder

Bus

2 bump-bonded ladder2 bump-bonded ladder

Bus

Support+cooling

• Production of bump-bonded ladder and ladder test w/ 90Sr are on-going

Silicon Strip Detector• Strip sensor

– BNL’s new “stripixel” concept : single-sided sensor w/ 2-D position sensitivity

– Charge sharing by 2 spirals in one pixel (80 μm ×1000 μm)& projective x/u-strip readout

– Pre-production sensor (Hamamatsu)

• p+/n/n+ structure• 3.5×6.4 cm2

• 625/500 μm thickness• Spiral : 5/3μm line/gap• Pixels : 384×30×2=23,040• Strips : 384×2×2=1,536

– Probing tests are on-going for evaluation

Z. Li, NIMA518, 738 (2004)

x3’ u1’ u2’

x2’ x1’ u1’u2 u3 x3

u1 x1 x2

0.00E+00

1.00E-12

2.00E-12

3.00E-12

4.00E-12

5.00E-12

6.00E-12

7.00E-12

8.00E-12

9.00E-12

1.00E-11

0 50 100 150 200 250 300 350 400

V_bias [V]

C [

F]

0.00E+00

5.00E-10

1.00E-09

1.50E-09

2.00E-09

2.50E-09

3.00E-09

3.50E-09

0 50 100 150 200 250 300 350 400

V_bias [V]

I [A

]CVIV

• Readout chip– FNAL/LBNL’s SVX4 chip

• 0.25μTSMC process, radiation hard > 20 Mrad

• 128ch pipelined mixed signal chip• 128ch parallel 8-bit ADC• “Dead timeless operation”• Multi-event buffering (4 events)• Selectable on-chip 0-suppression• Power consumption ~ 0.4W/chip

– 12 SVX4s and control chip(RCC) per sensor

• R&D is on-going– SVX4 3-chip hybrids– Readout control board for 4 hybrids– Sensor+hybrid test will start soon.

Silicon Strip DetectorReadout Control Board

Hybrid

Hybrid

Hybrid Hybrid

Hybrid

Sensor

Detector Integrationin the VTX Region

±40 cm

±34 cm

42 cm

Magnet

Calorim

eter

Magnet

Calorim

eter

VTX Endcapextension

VTX Endcapextension

Expected Performance :Occupancy

• Layer-by-layer occupancy calculation– Maximum occupancy estimated from simulated central

Au-Au collisions at 200 GeV– Au-Au collisions generated with HIJING event generato

r– The VTX Detector implemented in a GEANT-based PHE

NIX detector simulation (PISA)

The VTX Detector will work for both heavy ionand polarized pp collisions.

Expected Performance :Heavy-Quark Detection w/ Displaced Vertices

• Displaced vertex meas. using the distance of closest approach (DCA)

• DCA resolution of 36μm simulated w/ two inner-most pixel layers & 2 GeV/c pions : consistent w/ rφ pitch (50 μm) and detector geometry

DCA (m)

200μmDCA cut

• Electron DCA distribution from- π0 Dalitz decay- Charm semi-leptonic decay- Bottom semi-leptonic decay

Charm S/N improvementw/ VTX

Bottom S/N improvementw/ VTX

Significant S/N improvement

Expected Performance :Jet axis Determination w/ Large Acc. Tracking

• Reconstruction of recoil jet axis (η jet, φjet ) in direct photon event• Simple cone algorism : pT-weighted ave. of charged tracks’ (ηi ,

φi) w/ > 1 GeV/c within VTX & corn radius < 0.5

Photon pT = 6.0-7.0 GeV/c•η-distribution of - Recoil quark- Recoil quark within VTX -η(recons. jet)-η(quark)

Strong constraint of jet axis

No jet info. w/ jet axis reconst.

Improved parton kinematics determination

Summary

• Silicon vertex tracker (VTX) upgrade was proposed to enhance the physics capability of the PHENIX detector.

• Intensive R&Ds and production are on going.• Expected performance showed significant improv

ement especially for spin physics capabilities w/ heavy-quark & photon+jet production.

• Installation and operation of the VTX is planned in RHIC-Run8 (2007/2008).