# Presentation: 624923

## p+p  J/ results from PHENIX Run-2

*Hiroki Sato, Kyoto University*
* **for the PHENIX collaboration*
- RBRC Workshop
- “Current and Future Directions at RHIC”
-  BNL, Upton, NY
- Aug. 15, 2002

## Heavy-flavor measurements with RHIC/PHENIX

- Open and bound-state heavy flavors are identified with PHENIX using their (semi-) leptonic decays
- J/ and 
- e+e-, +*-*
- Open charm and open bottom
- Single e(), ee, , e

- RHIC: s=200GeV

**Notes:**
Production of open and bound state heavy flavors have
Some theoretical interest since they include both perturbative and non-perturbative aspects of QCD.
Since PHENIX detector is good at lepton identifications, they are measured clearly 
Using their leptonic or semi-leptonic decay channels.
J/psi and upsilon are identified with electron and muon pairs and open charm and 
Bottom are identified with single leptons or lepton pairs.
This shows sensitive x and Q2 regions for our measurement of open charm through the single
Electrons and open bottom with the emu coincidence channel.
In this talk, I will present results of J/psi for both muon and electron channels.

## J/ production in p+p collisions at s = 200 GeV

- The highest energy measurement of the total cross section
- Discriminate theoretical models for the production mechanism
- Reference point for Au+Au data

- s dependence of the J/ total cross section with previous lower-energy experiments

**Notes:**
J/psi production at RHIC energy has not well studied yet.
Since PHENIX can measure even low pT J/psi, 
Total cross section can be obtained with 
The world highest energy measurement. 

## Theoretical models for the J/ production

- Color-Evaporation Model (CEM)
- “Ignore” color and other quantum numbers of a *cc* pair
- Certain fraction (free parameter) of all produced *cc* pairs form each charmonium
- Color-Single Model (CSM)
- Non-Relativistic (small *v**c*) QCD
- Only a *cc* pair with the color-singlet state and the same quantum numbers can form each charmonium   No free parameter
- Cross section disagrees with Tevatron data
- Color-Octet Model (COM)
- Different state of a *cc* pair (including color-octet states) can form a charmonium with (a) soft gluon emission(s).
-  Color-octet matrix elements are extracted from data  still in controversial
- Polarization of the high-*p**T* J/ disagrees with Tevatron data

## The PHENIX Detector in Run-2

- Central Arms to detect hadrons, electrons and photons
- || < 0.35
*p**T** *> 0.2GeV/*c*
- South Muon Arm to detect muons in the forward region
- 1.2 <  < 2.2
*p**tot** *> 2GeV/*c*
- Beam-Beam Counter (BBC) to trigger p+p interactions
- 3.0 < || < 3.9
- Trigger efficiency ~ 50% for p+p inelastic events

- Independent measurements of J/ using both e+e- channel and +- channel

**Notes:**
J/psi is measured using both electron and muon decay channels independently with PHENIX.
Electrons are measured using Central Arms which cover central rapidities.
Muons are measured using Muon Arms which cover forward rapidities.
In Run-2, both central Arms and one Muon Arm was operational.
To trigger pp interactions, Beam-beam counter was used which positioned here.

## RHIC Integrated p+p Luminosity

- RHIC delivered 700nb-1 to PHENIX
- After online vertex cuts, PHENIX recorded 150
- nb-1
- Present** **preliminary analysis used data from:
- 81 nb-1** **(1.7 x 109) +-
- 48 nb-1** **(1.0 x 109) e+e-

- 1/1/02

## The PHENIX Muon Arm

- Detect muons with *p**tot** *>2GeV/*c*, 1.2<*** *<2.2 (South Arm)
- Pre-hadron-rejection with Central Magnet steel (***int* ~5)
- Muon Tracking Chamber (MuTr)
- Measure momentum of muons with cathode-readout strip chambers at 3 stations inside Muon Magnet
- Muon Identifier (MuID)
- /μ separation with 5-layer sandwich of chambers (Iarocci tubes) and steel
- Trigger muons
- Successfully operated first time during Run-2

- MuID

- MuTr

- Muon Magnet

## Muon LVL-1 Trigger

- Coincidence of fired MuID planes of each “quadrant”
- One quadrant for “single-muon trigger” and more than one quadrant for “dimuon trigger”  used for this analysis
- Inefficiencies from hardware dead time is 1~2%

- ‘Quadrant’
- trigger

- μ

- MuID

- Quadrant

**Notes:**
MuID is divided into 4 quadrants and coincidence of all gaps
In each quadrant issues a quadrant trigger.
Number of quadrant trigger is counted and if it is one, single muon trigger is fired.
And if it is 2 or more, dimuon trigger is fired.
Inefficiencies of trigger hardware mainly from dead time is obtained to be small.

## J/  +- signal

-  Significant enhancement of unlike-sign pair in the J/ mass region
-   Peak (3156  74 MeV/*c*2) is consistent with J/ mass
-   Mass width (257  75 MeV/*c*2) is consistent with expectation  further improvement is expected
-  36 counts in 2.5<mass<3.7GeV/c assuming same count of unlike and like-sign pairs from background (confirmed with simulation)
-  Systematic error on the count ~10 % by changing mass cut

- 3.16+-0.26 GeV

**Notes:**
This is the dimuon mass distribution for both unlike-sign and like-sign muon pairs.
Number of J/psi is obtained to be 36 assuming the number of  background is same for unlike-sign and like-sign pairs
Which is confirmed with simulation.

## Normalizations for the muon channel

*N**J/***: Number of measured J/* *in* *1.2<y<2.2
*A**cc*: South Muon Arm Acceptance ×reconstruction efficiency for J/ (1.2<y<2.2)  μ+μ- with the ideal detector
***MuID*: Real MuID trigger and road efficiency
***MuTr*: Real MuTr track efficiency
***BBC**J/***: BBC efficiency for J/ events
*L*: Luminosity with good vertex cut (|z-vertex|<38cm)
***y*: rapidity coverage = 1.0

**Notes:**
To obtain cross section for the muon channel, various kinds of efficiencies as well as lumonisity are needed.

## MuID trigger and road efficiencies

- Realistic panel-by-panel efficiencies are used in simulation (obtained from minimum bias real data)
- Single muon trigger×road efficiency ~ 0.80
- Dimuon trigger×road efficiency ~ 0.62
- Systematic uncertainty (run dependence) ~ 11%
- Ratio (road efficiency)/(trigger ×road efficiency) is  consistent with real data (~0.9)

- Panel efficiency (%)

- Number of panels

## MuTr Track efficiency

- MuTr inefficiency is caused mainly due to dead HV and dead FEM during the run
- Efficiency for dimuons ~ 0.23
- MuTr efficiency obtained using MuID roads is consistent with simulation except Octant-5 and Octant-7
- 10% systematic error is assigned from this inconsistency
- Run dependence is <4%
- Better efficiency is expected in the next Run

- Azimuthal angle of roads (degree)

- MuTr efficiency  (number of roads with a track) / (number of roads)

- MuTr efficiency

## J/ Acceptance × reconstruction efficiency with real chamber efficiencies 

- J/ rapidity

- J/ *p**T* (GeV/c)

- <*A**cc****MuID****MuTr*>*1.2<y<2.2* = 0.0163

-  *p**T* dependence is small
-  Uncertainty from the unknown J/ polarization is assigned to be 10%

- AccMuIDMuTr

- AccMuIDMuTr

**Notes:**
J/psi acceptance times reconstruction efficiency with realistic chamber efficiencies and dead area for the muon channel 
Is obtained to be 
1.6 % in average with simulation.
This is rapidity dependence and this is pT dependence. pT dependence is relatively small.
Uncertainty from the unknown J/psi polarization is assigned to be 10% assuming polarization parameter 
Should be less than 0.3 for the absolute value which is consistent with other experiments.
Uncertainties from chamber efficiencies are estimated to be 11% for MuID and 10% for MuTr.

## BBC efficiency and luminosity

-  ***inela*: p+p inelastic cross section  (PYTHIA, s fit)
-  ***BBC**J/***: BBC efficiency for p+p  J/+X μ+μ- events
-  pT (J/) dependence is small
-  consistent with p+p  J/+X e+e- (0.75) and p+p  0 X (0.75)
* ****BBC**inela*: BBC efficiency for p+p inelastic events
-  *N**int*: Number of interaction triggers with vertex cut (|z|<38cm)

- simulation

- Real data

-   Analysis of ***BBC**inela****inela* is still in progress

- Assign conservative 20% error on it

**Notes:**
To properly normalize the cross section, two kinds of efficiencies for BBC which is the pp interaction
Trigger counter, need to be obtained. One is for events in which J/psi is produced and decay muons
Go to the Muon Arm acceptance. This number is consistent with the number for the electron channel
And other hard process, which is pi0 production.
BBC efficiency for the pp inelastic events are estimated to be 0.51 to get luminosity.

## Br d/dy|y=1.7 result and its uncertainties

|  | Center value | Uncertainty |
| --- | --- | --- |
| NJ/psi | 36 (2.5<mass<3.7GeV/c2) | 19% (statistical)
10% (cut dependence) |
| AccMuIDMuTr

 | 0.0163 (1.2<y<2.2)  | 10% (J/ pol. dep., ||<0.3)
11% (MuID efficiency)
10% (MuTr efficiency) |
| BBCJ/L | 60nb-1 | 20% (consistency with machine value)
<5% (Trigger counter efficiency) |

- Br(J/+-) dJ//dy|y=1.7*.*  = 37  7(stat.) 11(syst.)  nb

- PHENIX Preliminary

**Notes:**
This is the summary for the numbers to obtain the branching ratio times cross section for the muon channel
We obtained 37...

## J/ pT distribution

- 1.2<y<2.2

*p**T* distribution (shape) is consistent with PYTHIA (color-singlet model) prediction

**Notes:**
This is pT distribution of the cross section with the muon channel.
Which is consistent with PYTHIA with large error bars.

## Electron Measurement with the Central Arms

- Charged tracks are identified with Drift Chambers (DC) and Pad Chambers (PC1/2/3)
- Ring Imaging CHerenkov detector (RICH) and Electro-Magnetic Calorimeter (EMCal, i.e. PbSc/PbGl) are used to identify electrons
- EMCal is also used for electron/photon Trigger

**Notes:**
Next I will talk about the electron channel.
This is the cross section of the Central Arms. Beam axis runs this way and
Detectors are aligned radially.

## Electron LVL-1 Trigger and its Efficiency

- EMCal 2x2 towers non-overlapping sum (threshold=0.8GeV)  single electron/photon trigger
- Trigger efficiency for J/ is expected to 0.90 + 0.06 - 0.07
- Use Monte-Carlo tuned to describe single-photon efficiencies with real data well

*e*+-

- 1 PMT (Tower)

- 2x2

- EMCal

**11cm**

## J/e+e- Signal 

*N**J/*** = 24  6 (stat.)   4 (syst.)

## J/e+e- Acceptance and Reconstruction Efficiency

***acc ****eff*  = 0.0163  0.0020
- Flat rapidity distribution in |y|<0.5 is assumed
- Uncertainties from unknown *p**T* distribution is estimated to be 7%

## Br d/dy|y = 0 result

- .
*N**J/***= 24  6(stat.)  4(syst.)
***acc****eff* = 0.0163  0.0020
***run-run* = 0.87  0.09   additional Run-by-Run correction factor
_**__*trig*_ = 0.90 + 0.06 – 0.07
***BBC**J/*** = 0.75  0.11
*L* = 48  10 nb-1
***y* = 1.0
-  Br(J/e+e-)* *d/dy|y = 0 =52  13 (stat.)  18 (syst.)  nb

- PHENIX Preliminary

## J/ Rapidity distribution and Total cross section

- Rapidity distribution is consistent with PYTHIA
- A global fit gives

- μ+μ-

- e+e-

- Br(J/*l*+*l*-) (total) = 226  36 (stat.)  79 (syst.) nb
- (total) = 3.8  0.6 (stat.)  1.3 (syst.) μb

- PHENIX Preliminary

## Total Cross section compared with the Color-Evaporation Model prediction

- CEM Parameters are fixed by fitting low energy data
- Our result agrees with the CEM prediction at s=200GeV

- Fixed target experiments

- Phys. Lett. B390,323(1997)

## Color-Singlet Model prediction

|  | (J/) in b |
| --- | --- |
| Direct J/ | 0.28 |
| c2 decay | 0.31 |
| c1 decay | 0.06 |
| Total | 0.65 |

- Other contributions will be small (’, *b*-quark)
- Disagrees with our result by factor ~6

- PYTHIA
- p+p s=200GeV
- GRV94LO
- Gluon fusion only

## Color-Octet Model prediction

- Work in progress
- Large uncertainties from extraction of color-octet matrix elements, charm-quark mass, PDF, and so on.
- Needs theorists’ help to predict
- Total cross section
- Polarization
*p**T* distribution

## In Run-3 and later

- Much higher statistics (>10 times) leads to
- Measurement of the J/ polarization (spin alignment)   critical test to separate CEM and COM
- More precise measurement of the *p**T* slope
- Longitudinally polarized proton-proton collisions
- Double-longitudinal spin asymmetry (*A**LL*) of the J/ production  polarized gluon density

## Summary

- Cross section of inclusive J/ production was measured with PHENIX using both e+e- decay channel (|y|<0.35) and +- decay channel (1.2<y<2.2) in Run-2 p+p collisions at s = 200GeV
- Br(J/+-) dJ//dy|y=1.7 = 37    7(stat.)  11(syst.) nb
- Br(J/e+e-) dJ//dy|y=0    = 52  13(stat.)  18(syst.) nb
- Rapidity fit including both results gives
-     J/(total) = 3.8  0.6(stat.)  1.3(syst.) μb
- The result agrees with the Color-Evaporation model prediction and disagrees with the Color-Singlet Model prediction
- In Run-3, measurement of the J/ polarization and *A**LL* is expected

## J/ polarization dependence of acceptance

- There is J/ polarization dependence of acceptance because of intrinsic momentum cut (~2GeV/c) of the Muon Arm
- But there is no indication from previous experiment (both Fixed target energy and Tevatron)  || is larger than 0.3.
- Assign 10% systematic error assuming || < 0.3.

- cos*(Gottfried-Jackson frame)

- cos* dependence of J/ acceptance
- (with real chamber efficiencies)

- 

- =0

- Due to momentum cut (P~2GeV/c)

- Quick Monte-Carlo

-  (J/ polarization) dependence of J/ acceptance

- AccMuIDMuTr

- Acc