Measuring Charm and Bottom using the PHENIX Silicon Vertex Detectors

1
Measuring Charm and Bottom using the PHENIX
Silicon Vertex Detectors

• Hubert van Hecke,
• Los Alamos National Laboratory
• for the PHENIX collaboration

Outline

• Motivation
• Detector requirements
• Description of the detectors
• Some MC results
• Construction Timeline

2
Physics Goals for the Silicon Vertex Detectors
e-

• Study production and flow mechanisms of heavy
  quarks
• Study of production and suppression of quarkonia
• Measure reaction plane
• Improve p resolution
• Improve high-pT tracking
• q, g contribution to proton spin

m

• Signal channels
• b-gtB-gt??e
• c-gtD-gt ??e
• J/?, ?-gt ?? ???,ee-
• hadrons

e
m-
3
Separate Signal from Backgrounds

• The problem backgrounds (? -gtm?e and K-gt m?e)
  overwhelm the signal

Solution Mean ?,K -gtm?e decay distance is
large D, B mesons travel some distance before
semileptonic decay to muons or electrons Prompt
m?e have 0 DCA By measuring the DCA to the
primary vertex, we can separate D, B decays from
prompt leptons and from long-lived decays from ?,
K
4
Detector Specifications

• Need sufficient DCA resolution (50?m central,
  100?m forward)
• Need occupancy low enough to find tracks in
  central AuAu events (ltfew )
• Need enough hits to reconstruct a track (gt3
  hits)
• Need to match tracks with Central Arm detectors
  ?-0.35, or with the Muon System ? 1.2 - 2.4
• Large solid angle coverage

5
Detectors
80 cm
40 cm
38 cm

• .

Forward vertex detectors (FVTX)
Barrel vertex detector (VTX)
6
Barrel Inner 2 Pixel Layers

• Inner 2 layers
• pixels 50 x 425 ?m
• 150 ?m - thick Siilicon
• R 2.5, 5.0 cm
• Length 22 cm
• 1.3, 2.6M channels
• Readout with ALICE1LHCb chip
• Bump-bonded to detector
• RL 1.44 total

7
Barrel Inner 2 Pixel Layers (contd)
Test of half-ladder, extension cable, spiro
board successfully completed
Carbon support cooling tube prototype
8
Barrel Outer 2 Layers

• Outer 2 layers stripixels
• elements 80 x 1000 ?m
• 650 ?m - thick Silicon
• R10,14 cm
• Length32, 38 cm
• 140K, 280K channels
• Readout with SVX4 chip
• RL 2.7 total

Single_sided, 2D readout
9
Barrel - strip layers (contd)
Strip pixel sensor wafer made by HPK
ROC-3 prototype currently under study
CFC
10
Forward Detectors
Basic unit wedge

• 4 disks / side
• 48 wedges/disk
• 75 um strips,
• 2.8-11.2 mm long
• 1664 strips/column
• 1.1M channels total
• readout with FPHX chip,
• derived from BTeV chip.

11
Forward detectors (contd)
Mechanical design 80 done
Wedges front and back
Electronics chain fully prototyped
Honeycomb support panel
Thermally conducting silicone
12
Barrel Expected DCA resolution
Hadron background
s 40 mm

• Results of simulation of AuAu collision.
• After a chi2 cut, DCA distributions of light
  hadrons and D0 decay are clearly separated

DCA distribution for single simulated pions in
3ltpTlt4 GeV/c. Simulation is done with 200 micron
pixel layers and 650 micron strip layer. The
passive material is 1.0 per pixel layer and
2.75 per strip layer.
13
Endcaps Open charm, bottom signal

• In the forward detectors
• Using DCA cuts, plus ?? and isolation cuts, we
  can now improve the signal/background for D,B-gt?

D- -gt??
B- -gt??
S/N
14
Improved resolution background reduction
?

• Simulated RHIC-II pp run
• - better background . rejection
• - better mass resolution
• - separate ????

Without FVTX
??
?
With FVTX
?
15
Status and outlook
- Barrel construction well underway
pixel layers completion in 2009 stripixels
completion 2010 - Forward detector
construction started in FY08, installation in
2011

• Collaborating institutions
• KEK, RIKEN, Rikkyo, Ecole Polytechnique, Columbia
  U. SUNY Stony Brook, Los Alamos, Brookhaven, Oak
  Ridge U. New Mexico, New Mexico State U. Iowa
  State U. Bhabha Atomic Research Centre, India
  Saclay, France Charles University, Prague Czech
  Technical University, Prague Institute of
  Physics, Academy of Sciences, Prague Kyoto
  University University of Jyvaskyla, Finland
  Yonsei University, Korea

16
.

• backups

17
Endcaps DCA resolutions
100 ?m

• Since the barrel pixels are // to the beampipe
  (orthogonal to the FVTX mini-strips), using them
  greatly improves phi resolution

18
External mount
19
Acceptance

• Since the event vertex spans
• -10 cm in z, we can use the barrel hits for
  some events.

20
Can we match muon arm tracks with a FVTX track?

• Use the chi2 of the Kalman track fitter

3 GeV muon 75 correct match
9 GeV muons 93 correct match