# Presentation: 170346

## Measuring Charm and Bottom using the PHENIX Silicon Vertex Detectors

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

-  Physics goals
-  Detector requirements
-  Description of the detectors
-  Some MC results
-  Construction Timeline

- Outline:

## Physics Goals for the Silicon Vertex Detectors

- Signal channels:
-  b->B->e
-  c->D-> e
- J/, ’-> ,e+e-
- hadrons

- -

- e-

- 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

## Separate Signal from Backgrounds

- The problem: backgrounds (->e and K-> e) overwhelm the signal

- Solution:
- Mean ,K ->e decay distance is large
- D, B mesons travel some distance before semileptonic decay to muons or electrons
- Prompt 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

## Detector Specifications

- We require:
-  DCA resolution < 50 um for the central barrel
-                             < 100 um for the forward detectors
-  Occupancy < 10%
-  Large solid angle coverage
-   || < 1.2  - barrel, standalone
-   || < 0.35 - barrel, matches central arms
-   1.2 < || <2.4 -  forward detectors, covers most of
-                              the muon arms
-  Capability to match tracks with Central arm and
-   Muon arm tracking systems
-  Enough hits (>=3) to reconstruct a track
-  Minimal mass

## Detectors

- .

- Barrel vertex detector (VTX)

- Forward vertex
- detectors (FVTX)

- 80 cm

- 40 cm

- 38 cm

## Barrel: Inner 2 Pixel Layers

-  Inner 2 layers:
-  pixels: 50 x 425 m
-  200 m - thick Silicon
-  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
- AuAu occupancy: 0.5, 0.2%

## Barrel: Inner 2 Pixel Layers (cont’d)

- Test of half-ladder, extension cable,
- spiro board successfully completed

- Carbon support + cooling tube
- prototype

##  Barrel: Outer 2 Layers

- Single_sided, 2D readout

-  Outer 2 layers: stripixels
-  elements: 80 x 1000 m
-  650 m - thick Silicon
-  R=10,14 cm
-  Length=32, 38 cm
-  140K, 280K channels
-  Readout with SVX4 chip
-  RL 2.7% total
- AuAu occupancy: 4.6, 2.6%

## Barrel - strip layers (contd)

- ROC-3 prototype currently under study

- CFC

- Strip pixel sensor wafer
- made by HPK

## Forward  Detectors

- Basic unit: ‘wedge’

- 3.750

- 12.5 cm
- 1664 strips
- 13 chips

- 2.8mm strip

- 2.8 - 11.2mm strips,
- 75 um wide

- 75-um strips

-  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.
-  RL 2.4%

## Forward detectors (cont’d)

- Mechanical design ~80% done

- Electronics chain fully prototyped

- Some simulation results

## Barrel: Expected DCA resolution

- Results of simulation of Au+Au collision.
- After a chi**2 cut, DCA distributions of light hadrons and D0 decay are clearly separated

- ~ 40 m

- Hadron background

- DCA distribution for single pions in 3<pT<4 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.

## 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->

- D- ->

- B- ->

- S/N

## Improved resolution + background reduction

- Simulated RHIC-II p+p run
-  - improved background   	  .  rejection
-  - improved mass resolution
-  - separate ’

- Without FVTX

- With FVTX

- ’

- ’

- 

- 

## Status and outlook

-   - Barrel construction well underway
-        pixel layers completed in 2009, installed and ready for PHENIX run 10
-        stripixels completion 2010, insalled and ready for run 11
-   -  Forward detector construction started in FY08, installation in 2011, ready
-      for run 12

- 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

## .

- backups

## Endcaps: DCA resolutions

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

- 100 m

## External mount

## Acceptance

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

## 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