# Presentation: 907895

## Low pT Φ reconstruction in PHOBOS 2004

- _Based on:_
- Analysis of data from simulation of 40mln low pT (<0.5GeV) Φ
- Corey presentation
- _Papers:_
- Star - Φ production in Au+Au at 130 GeV, Phys. Rev. C65 (2002)
- Star - Φ production in Au+Au at 200 GeV, nucl-ex/030601
- Phenix - Φ production in Au+Au at 200 GeV, nucl-ex/0209028
- Presentations of preliminary results by Phenix and Star

**Andrzej Olszewski**

## Statistics Needed

-  Rate measurements:
-  inclusive > 100 Φ’s
-  in bins of centrality > 50 Φ’s in most central bin
-    means > 1000 Φ’s in inclusive sample
-  in bins of transverse momentum > 100 Φ’s in lowest and the highest pT bins  means also 1000’s of Φ’s needed
-  Shape measurements:
- Both mass peak position and width (shape) require more than 5000 Φ’s for a single point

## AuAu 200 GeV Φ’s / event

-  Phenix 200 GeV inclusive: dN/dη(Φ) = 2.01
-  STAR 130 GeV 10% central: dN/dη(Φ) = 5.7
-  STAR 200 GeV 10% central: dN/dη(Φ) = 6 – 6.5
-  Φ rates in 200 GeV Au+Au, over full rapidity:
-  45 per 10% central event
-  38 per 25% central event
-  14 per inclusive event

## Low pT Φ’s / event

-  STAR 130 GeV mT slope:
-   0.378 MeV (10% central)
-   and statement of increasing  slope with energy
-  STAR 200 GeV mT slope:  ~0.340 MeV on average
-  Phenix 200 GeV: using   0.320 MeV in simulations
-  What’s the difference?
- pT < 0.5  GeV: 20 - 24%
- pT < 0.15 GeV: 2  - 2.5%

## Low pT Φ  -  geometrical acceptance

-  Properties of simulated Φ’s
-  Exponential mT with T = 378 MeV, pT = (0, 0.5)
-  Corey – 20·106 experimental VZ = [-20, 20]
-  Andrzej – 40·106 flat VZ = [-40, 0]
-  Geometrical acceptance depends on the Track Quality criteria:(for pairs of Kaon tracks from ΦK+K- decays)
-  ‘Trackable1’: > 6 spectrometer layers hit    1872 / 40 · 106
-  ‘Trackable2’: > all curved track layers hit   1150 / 40 · 106
-  ‘Trackable3’: all possible layers with hits      435 / 40 ·106
-  ‘AccHough’: matching Hough tracking             1 / 40 ·106

## Estimation of usefull statistics - events

-  Written:
-  120 mln events on tape
-  Triggering on collision efficiency:
-  60% collision events
-  Triggering on vertex:
-  80% in usefull vertex range (-40,10)
-  Vertexing efficiency
-  80% RMSSelVertex
-  This makes 46 mln usefull events and 644 mln Φ’s total

## Estimation of usefull statistics - Φ’s

-  After geometrical acceptance cuts we are left with:
-  pT < 0.5 GeV
-  6000 Φ’s decaying to ‘trackable1’ Kaons
-  1400 Φ’s decaying to ‘trackable3’ Kaons
-  pT < 0.15 GeV
-  600 Φ’s decaying to ’trackable1’ Kaons
-  150 Φ’s decaying to ‘trackable3’ Kaons
-  If we can reconstruct and identify ‘trackable3’ Kaons efficiently we are already close to measure production rates of even the lowest pT Φ’s

## Kaon identification efficiency

- Even with Kaon tracks found Φ may be not reconstructed if the particle is not identified. Fortunately for these low pT Φ’s most Kaon decay products have momenta lower then 0.7 GeV

## Tracking low pT Φ’s

-  Hough tracking
-  after strong ‘AccHough’ geometrical cut efficiencies of reconstruction higher pT (>0.5GeV) Φ’s close to 80%.
-  lower pT Φ’s not reconstructed so far
-  Banana tracking
-  just started looking at this tracking
-  found it as easy to use as Hough tracking, and fast!
-  not ready to reconstruct Φ’s, missing templates
-  first results indicate possible capability of reconstruction of low pT Φ’s, efficiency unknown.

## First results on Banana efficiency 

- Efficiency of tracking on all findable tracks in MC event
- vertex Z (-1,0), single arm SpecN

## First results on Banana efficiency 

- This is best performance.  Vertex Z (-1,0), single arm SpecN
- I have seen lower efficiency at large negative vertex Z!

## How much more statistics do we need?

-  Uncertainty in tracking efficiency prevents from giving a good estimate of how much more events we need.
-  To be safe we would need to increase statistics by a factor of 10 or more. With good tracking efficiency this would make possible more precise measurements and with worse tracking this would enable us at least to estimate rates at low pT end.
-  With the increase by a factor of 2-3 the rate measurement is still kept only possible.

## How could we increase statistics?

-  _By using centrality trigger_
-  but in this way we loose some physics goals
-  by going to 25% central the rate of Φ’s is increased only by a factor of 2.5 since it scales with the number of produced particles

-  _By moving vertex Z range_ and making it more narrow around Z = -30cm value. Gives maximum factor of 2 gain.
-  This is not true for ‘good’ tracks with hits in all spectrometer layers.
-  Possible to use only if tracking very good in finding those difficult tracks.

- Geometrical acceptance

## Summary

- If we want to make high statistics Φ measurements at low pT we need both a very efficient tracking of partially registered Kaons from Φ decays and we would have to make an extra effort to increase statistics in every possible way. This would be risky.
- With reasonable tracking which seems possible we should be able to measure rate of Φ production at low pT and some high statistics measurements at higher pT. This however leaves only option of doing central triggering in order to increase statistics.

## Backup

- BACKUP SLIDES

## Banana tracking on Data

## Geometrical acceptance for „good” decays 

## Acceptance 

## Acceptance

## Summary

- Results are limited only to yields, the mass peak position and width are only „compatible” with PDG values
- dN/dy of scales linearly with number of charged particles but the ratio grows with increasing energy of the collision
- dN/dy of  scaling with both number of charged particles and collision energy follows closely Kaon production scaling
- dN/dy and inverse slope measurement shows boost invariance for  within |y|<1.0
- The slope of  transverse mass distribution increases for AA collisions with energy
- In AuAu collisions, within the measured centrality range, the shape of the transverse momentum distribution weakly depends on the centrality – absence of significant hadronic re-scatterings for ?

## dN/dy vs. nCharge

- STAR preliminary

-  dN/dy increases
- linearly with  nCharge;
- • Statistical errors only.

## Mt Spectra

-            130 GeV				   200 GeV

**PRELIMINARY**

- PRC, 65 041901(R) (2002)

- ----- Mt exponential Fits

## <pT> Centrality Dependence

**1)** , K, p mean transverse
- momentum <pT> increase
- in more central collisions;
**2)** Heavier mass particle
- <pT> increase faster than
- lighter ones as expected
- from hydro type collective
- flow;

- Star preliminary

**1)** , K, p mean transverse
- momentum <pT> increase
- in more central collisions;
**2)** Heavier mass particle
- <pT> increase faster than
- lighter ones as expected
- from hydro type collective
- flow;
**3)** -meson seems flow
- differently.