# Presentation: 680347

## Measurement of J/ -> e+e-  and C -> J/ +in dAu collisions at PHENIX/RHIC

- A. Lebedev, ISU                                                          1                                       Fall 2003 DNP Meeting

*Alexandre Lebedev, Iowa State University*
*          **for the PHENIX Collaboration*

- 1. Motivation
- 2. J/ measurement
- 3. C measurement

## Motivation

- A. Lebedev, ISU                                                          2                                       Fall 2003 DNP Meeting

- If quark- gluon plasma (QGP) is formed in relativistic heavy ion
- collisions, color screening will lead to suppression of
- charmonium production (*T. Matsui, H. Satz, Phys. Lett. B178(1986)416**)*.
- A promising signal of QGP formation.

- More recent studies predict increased J/ production at RHIC
- due to recombination (*R.L. Thews  et al, Phys. Rev. C63(2001)054905*).

- It is important to measure simulataneously several charmonium
- states, e.g. J/ and C to find out which models of charmonium
- production work best.
- dAu collisions, along with pp, provide a baseline for
- understanding J/ and C production in AuAu.

## The PHENIX Experiment

- A. Lebedev, ISU                                                          3                                       Fall 2003 DNP Meeting

- The PHENIX experiment at RHIC
- has the unique ability to measure
- both J/ and C in relativistic heavy ion
- collisions.
- Charged particle tracking and the
- momentum measurement by the
- Drift Chamber.
- Electron identification in Ring Imaging
- Cherenkov Detector and Electromagnetic
- Calorimeter (EMCal).
- Photon Identification in EMCal
- Muon tracking and identification in
- Muon Arms.

## J/ measurement in the PHENIX Central Arms

- A. Lebedev, ISU                                                          4                                       Fall 2003 DNP Meeting

- The plot shows e+e-  invariant mass
- distribution for 20%- 25% of all run3
- dAu data.
- Combinatorial background is subtracted
- The background was caculated using
- mixed events method (same sign
- background does not work in Phenix).
- Background is normalized using
- the number of same sign pairs.
- In all of run3 dAu we can expect to
- have 400- 500 J With looser
- vertex and electron ID cuts we can
- get as many as ~700 J

## Acceptance for  C ->+ J/ -> e+e-

- A. Lebedev, ISU                                                          5                                       Fall 2003 DNP Meeting

- To calculate C acceptance, a simulation
- using single C was done.
- If J/ is detected in the Phenix Central Arms,
- the probability to detect the photon is 11%
- Assuming that 40% of J/ come from C,
- we can expect few tens of reconstructed C
- in all run3 dAu data.

## Acceptance for  C ->+ J/ -> 

- A. Lebedev, ISU                                                          6                                       Fall 2003 DNP Meeting

- In case of J/Psi decaying to ,
- the probablility to detect the photon in
- Central Arms, while muons are
- detected in Muon Arms is 2.5%.
- Expected number of reconstruced J/
- in Muon Arms is ~1000 per arm, which
- makes the expected number of
- reconstructed C in this channel
- comparable to e+e-  channel.
- However, the photon energy is very low,
- which makes C measurement using
- Muon Arms practically impossible.

## Background estimate for  C -> J/ + 

- A. Lebedev, ISU                                                          7                                       Fall 2003 DNP Meeting

- The plot shows C -  J/  invariant
- mass distribution for 20%- 25% of all
- run3 dAu data. Several C are expected
- in this plot.
- Red histogram shows combinatorial
- background calculated using mixed
- events method.
- The width of C peak is expected to be
- ~55 MeV (from EMCal resolution and
- full scale simulations).
- Combinatorial background will be
- 100- 200 counts per 100 MeV bin.

## Full scale simulation

- A. Lebedev, ISU                                                          8                                       Fall 2003 DNP Meeting

- For a more realistic study, single
- J/ and C were merged with simulated
- dAu events, and complete data analysis
- was performed.
- 40% of events with merged C were
- added to 60% of events with merged
- J/
- Red histogram in the top plot shows
- combinatorial background calculated
- using mixed events method. Background
- was normalized at the tail of the
- distribution (mass>0.55 GeV).
- This plot corresponds to 5-6 times
- larger statistics than we expect in
- run3 dAu.

## Ways to reduce background

- A. Lebedev, ISU                                                          9                                       Fall 2003 DNP Meeting

- 1. Changing photon energy cut.. Lower
- cut will move the maximum of the
- background to lower masses.
- 2. Use angle between the photon
- and the JThe background is
- peaked at small angles.
- 3. Use correlation between the
- photon and electron momenta.
- Momentum of the electron in the same
- arm with the photon is correlated with
- the photon momentum.
- 4. Remove photon pairs which have
- pi- zero mass.

## Conclusions

- A. Lebedev, ISU                                                         10                                       Fall 2003 DNP Meeting

- The ongoing  J**/******** **->** **e**+**e**- ** and  ******C**** **->** **J**/******** **+****
-  analysis in dAu collisions was presented.
- ~500  J**/******are expected** **to be reconstructed in
- run3 dAu.
- Expected number of reconstructed Chi is few tens,
- while combinatorial background is expected to be
- 100- 200 counts per 100 MeV
- In Central Arms Chi measurement is difficult but
- feasible, while in Muon Arms it is impossible due to
- low photon energy.