# Presentation: 592887

## Physics Motivation and Performance

- Brief Outline:
- Physics measurements at forward rapidity in PHENIX
- Limitations of measurements with current detector systems
- Critical Improvements FVTX provides
- Simulations that defined detector design and verified performance
- Many contributors:  Hubert, Dave L., Pat, Xiaorong, Anuj, Joel

## Physics Measurements from Forward PHENIX

**Physics Measurements from Forward PHENIX**

- Single/dimuon muon spectra give access to:
- Open heavy flavor via single , /K from decay muons and punch-throughs
- W from single muons at high pT, 500 GeV
- Vector mesons (J/, ’, )
- Drell-Yan
- Open heavy flavor from dimuons

## Open Heavy Flavor at Forward Rapidity

- _Open Heavy Flavor Physics Interests:_
- What is the total cross section for charm/beauty in all collision systems?
- Does asymmetry measurement in polarized pp collisions indicate contribution of gluons to proton spin?
- Is there  modification of charm production in cold nuclear matter:  gluon saturation,...
- Is there modification of charm production in heavy-ion collisions:  energy loss in medium
- Do heavy quarks flow?

## Current Limitations on Heavy Quark Measurements

- Single muon measurements limited at low pT by decays and at high pT by punch-throughs
- Single electrons limited at low pT by large contribution from 0, at high pT by PID capabilities
- Both suffer from not being able to separate charm and beauty

- pT (GeV/c)

## Charm Cross Section Uncertainty

- Total cross section is rather uncertain and forward heavy flavor measurements are limited in precision:
- Difficult to measure full pT range because of large backgrounds
- Rapidity distribution rather uncertain because central and forward rapidity both suffer large (uncorrelated) systematic errors
- No separation of charm and beauty components

## Heavy Flavor Suppression and Flow in AuAu

- Indications of heavy quark suppression and flow in AuAu collisions at central rapidity from PHENIX/STAR, but
- Systematic errors remain somewhat large because of large backgrounds
- Reaction plane resolution improvement would help
- Separation of charm/beauty would make interpretation of results less ambiguous
- Rapidity and pT dependence should help separate effects of hot/dense medium, cold-nuclear matter effects

## Cold nuclear matter effects from dAu

- Central arm shows little change in open heavy flavor in dAu w.r.t pp, but this does not access x region where gluon saturation would be expected to play a role
- Muon arm shows some forward/backward asymmetry, but precision limited for same reasons as stated previously

## FVTX Contributions—Reduction of Decay Background

- Cutting on DCA<DCAmax allows long-lived ,K decays to be separated from heavy quark decays AND cleaner sample of ,K at forward rapidity
- Especially necessary to access low pT spectra

## FVTX Contributions—Reduction of Punch-Throughs

- Cutting on DCA > DCAmin allows ,K punch-throughs (prompt) to be separated from open heavy flavor decays
- Especially necessary to access high pT spectra

## FVTX Contributions—Adding forward rapidity coverage

- Forward rapidity critical to map out gluon polarization function over broad x range
- Small asymmetries expect (~few percent)limit to high pT and/or more precise measurement at low pT

- Forward rapidity critical to map out saturation or not of gluons in cold nuclear matter, over broad x range

- c->eX

- B->J/

## FVTX Contributions—Separation of Charm and Beauty

- _Charm/beauty separation still difficult, but a few possibilities:_
- Natural separation at high pT (doesn’t depend on FVTX)
- Take advantage of somewhat longer decay length for b compared to c
- Measure BJ/ events and infer beauty differential cross section:  cut at 1 mm 10-4 rejection of prompt J/s, 40% acceptance of BJ/)
- Like-sign dimuons (under study)
-  Measurement improved (under study)

- Note: Prompt J/s scaled down by 100

## Physics Cont’d: Backgrounds can also be signals

- _Pion/Kaon production at forward rapidity:_
- With FVTX, can have clean pion, kaon identification as well as separation from open charm and prompt muons
- Can also probe gluon contribution to proton spin
- Cold nuclear matter effects at small, large x
- Modification in heavy ion collisions at forward rapidity

## Potential to improve W measurement

- W measurement in polarized pp collisions to get at sea quark contributions to proton spin:
- Isolation cut with FVTX detector could be used to suppress hadron background w.r.t. W signal
- Better tagging of in-flight decays (under study)

- Hadron contamination?

## Dimuon measurements at forward rapidity

- J/ measurements of interest to:
- Get information about gluon contribution to proton spin
- Combined with open charm production can disentangle initial-state and final-state modifications to onium production in cold nuclear matter
- Addition of ’ and  measurements will further understanding
- In heavy ion collisions, charm plus J/ production can yield:  modification of charm production, effect of medium on hadronization, contributions of prompt and recombination to J/ production.
- Critical to get precision measurements versus centrality, rapidity, pT

## J/ Centrality and Rapidity Dependence and Errors in AuAu

- Most difficult dimuons measurements are in AuAu because of combinatorial background
- Precision on all measurements in AuAu events limited by signal:background

## FVTX Contributions—Removal of Backgrounds

- Signal:Background in central south arm events ~1:20
- Combinatorial background from 3 possible combinations of hadron decay muon and punch-through

- Mass (GeV)

- Two combinations which include a decay can potentially be separated from prompt J/s:  ~60% at J/ mass

## FVTX Contributions—Improved Mass Resolution

- In addition, mass resolution at J/ is dominated by effects of multiple scattering and energy straggling in the absorber material
- Precision angular measurement before the absorber removes the first issue, thus reducing the mass resolution
- This further reduces signal:background as background window will be reduced, and allows for better separation of J/ and ’

## Additional dimuon measurements

- Drell-Yan
- Sea quark contribution to proton spin
- More information to separate initial-state, final-state effects in cold and hot nuclear matter
- ’, 
- Improved mass resolution allows cleaner separation of  from ’
- Reduced background improves possibility of  at central rapidity

## FVTX Bonuses:

- Reaction Plane Improvement
- Future measurements at up to y=3 that can no longer be done by Phobos/Brahms
- Provides e/ separation capabilities for nosecone calorimeter
- Can provide data to Lvl-1 trigger (which is likely critical in future runs)

## Physics Signal Rates

| Observable | Counts per RHIC p+p Run 10 | Counts per RHIC Au+Au Run 10? |
| --- | --- | --- |
|  | ~4x108  | ~1x108 |
|  | ~400 k  | ~100 k |
|  | ~2000  | ~600 |

**Physics Signal Rates**

- Assumptions:
- 50 pb-1
- Acceptance only, no efficiency cuts
- p > 2.5 GeV
- You can trigger

| pT bin | Fraction of accepted |
| --- | --- |
| 0-1 | 0.63 |
| 1-2 | 0.35 |
| 2-3 | 0.01 |
| 3-4 | 6E-4 |

- D->X

## Detector Design and Performance

## Detector Design and Performance

- 4 layers of tracking: to allow at least 3 hits/track
- Radial extents:  to allow at least 3 hits/track as much as possible in area of muon coverage, constrained by the detector envelope
- Strips are 50 m (r segmentation) x 2-13.5 mm (phi segmentation): to allow good DCA measurement in boost direction, limited by multiple scattering rather than detector resolution,  and reduce occupancy in AuAu

## Detector design – Strip width

- DCA versus strip width and momentum
- Strip width is chosen to be 50 m as you start to reach diminishing returns because of multiple scattering contributions

## Detector acceptance

- Number of Forward Silicon, Barrel Pixel, and Barrel Strips
-  hit versus theta and z vertex position

## Detector occupancy in Central AuAu

- Hits/cm2

- At inner radii, strip size is 0.05 x 2 cm = 0.1 cm2
- 0.7% occupancy in highest occupancy areas
- Generally quote 1.5% maximum occupancy to take into account simulation uncertainty
- Low enough to expect track finding to be very doable

## Expected future simulation work:

- Continue background rejection studies
- Detailed study of matching to MuTr
- Incorporating silicon hits, MuTr, MuID and other upgrade detector hits all together into one track fit to determine performance of integrated systems:  background rejections, improvement in momentum resolutions...
- Forward + Barrel silicon performance to be studied
- Explore performance with different strip orientations?
- More complete study of rates with efficiency hits taken into account
- Take into account resolution of, efficiency of  finding primary vertex
- Full estimates for physics quantities (RAA, flow...)

## Summary

- Physics Program Improvements in areas of:
- Open heavy flavor – charm and beauty
- /K measurements at forward rapidity, including PID
- W
- Vector mesons
- Drell-Yan
- via reduction of backgrounds and improvements in mass resolution
- Detector Performance:
- Geometrical layout gives ≥3 hits per track most of the time
- Occupancies 1.5%
- Simulations with expected material retain good DCA resolution
- 50 m strips give good DCA resolution and desired segregation of prompt tracks, short lived decays, and long-lived decays

## Backups

## Backups– Simulation Details

- PISA simulation with beam pipe, barrel silicon, etc.
- 1% of a radiation length/silicon layer

## FVTX Improvements—Reaction Plane?

- Improved S/B yield extraction error

- Improved reaction plane measurement would improve measurements w.r.t. reaction plane

## Backups