# Presentation: 051924

## A measurement of                              

_**FNAL E866/NuSea**_

*ACU, ANL,  FNAL, GSU, IIT, LANL, LSU, NMSU, UNM, ORNL, TAMU, Valpo*

_**A measurement of                              **_

_**Anti-quark asymmetry in the Nucleon Sea**_

## From Draft NSAC Long Range Plan :

_**From Draft NSAC Long Range Plan :**_
_**“**__**The Structure of the Nuclear Building Blocks”**_

## Modification of parton momentum distributions of nucleons embedded in nuclei

-  e.g. shadowing – depletion of low-momentum partons. Process dependent?
**Nuclear effects on parton “dynamics”**
-  energy loss of partons as they propagate through nuclei
-  and (associated?) multiple scattering effects

_**Nuclear modification of parton level structure & dynamics**_

**Drell-Yan**

**E866 R(W/Be)**

**E772 R(W/D)**

**Ratio(W/Be)**

**1.0**

**0.9**

**0.8**

**0.7**

**NMC  DIS**

***Drell-Yan Process***

## Nuclear Dependence for heavy vector mesons, e.g. J/Ψ, Ψ ', 

-  production: color singlet or octet      (     ) and color neutralization timescale
-  hadronization time:
- Coherence length for cc fluctuations:
-  absorption on nucleons or co-movers
-  feed-down from higher mass resonances, e.g. χc

- E789

## NA50 -- Anomalous J/ suppression. Evidence for QGP??

- NA50 -- Anomalous J/ suppression. Evidence for QGP??

_**J/**__**Ψ**__** suppression – an effective signature of Quark-gluon plasma (QGP) formation?**_
-  **Color screening in a QGP would destroy        pairs before they can hadronize into charmonium**
** ****But ordinary nuclear effects also absorb or modify J/****Ψ’s**
**We need a comprehensive understanding of charmonium production in nuclei**
**Competing effects may be identified in p-A collisions by their strong kinematic dependencies, together with complementary studies**** of ****Drell-Yan scattering and open-charm production**** **

## E866/NuSea: 800 GeV p-A (Fermilab)

_**E866/NuSea: **_**800 GeV p-A (Fermilab)**
***PRL 84, 3256 (2000)***

-  J/Ψ and Ψ’ similar at large xF where they both correspond to a     traversing the nucleus
- but Ψ’ absorbed more strongly than J/Ψ  near mid-rapidity (xF ~ 0) where the resonances are beginning to be hadronized in nucleus.

**open charm: no A-dep**
**at mid-rapidity**

**Hadronized**
**J/******

_**P**__**T**__** Broadening at 800 GeV**_

- (pT) shape is independent of xF & same for NA3 at a lower energy

## PT Broadening in Drell-Yan and associated Radiative Energy Loss

**E866 – Preliminary**

***Baier et al. NP B484, 265 (1987)***

**or**

- So energy loss associated with observed pT broadening is tiny, e.g. for W:

_**P**__**T**__** Broadening in Drell-Yan and associated Radiative Energy Loss**_

## Quark energy loss in nuclear matter

**dE/dz = 2.32 ****±**** 0.52 ****±**** 0.5 GeV/fm**

- Charged hadron and 0 production at PHENIX versus pT for central collisions which, when compared to pQCD models that work well for peripheral collisions, suggests that jet-quenching or energy-loss may be present.

- dE/dx = 0

- dE/dx =0.25

***Johnson, Kopeliovich et al., PRL ***_***86***_***, 4483 (2001)***

**Shadowing**

**dE/dx & Shadowing**

_**Quark energy loss in nuclear matter**_

## Gluon Shadowing for J/Ψ’s – predictions?

_**Gluon Shadowing for J/**__**Ψ’s – predictions?**_

***Kopeliovich, Tarasov, & Hufner***
***hep-ph/0104256***

***Eskola, Kolhinen, Vogt hep-ph/0104124***

***J.C.Peng, LANL***

**E866/NuSea**

**PHENIX**
**μ****+****μ****-**

**e****+****e****-**

- PHENIX μ+μ-  (Au)

**In PHENIX ****μ acceptance**** for Au-Au collisions?**
***Eskola...***** : ~ 0.8**
***Kopeliovich...***** : ~ 0.4**
***Strikman...***** *****[hep-ph/9812322]***** : ~ 0.4**

**PHENIX ****μ**
**PHENIX ****e**
**E866 (mid-rapidity)**
**NA50**

- Expected statistical errors from a 2-week
- d-A run at PHENIX and measurements form E866/NuSea

## Theoretical Models for PT Broadening

_***Kopeliovich et al, hep-ph/0110221***_
- “Light Cone Dipole” approach

_**Theoretical Models for P**__**T**__** Broadening**_

**R(Au/H)**

*(full)*

*(longitudinal only)*

**RHIC**

**LHC**

**Predicts a different dominant mechanism for p****T**** broadening in DY at RHIC & LHC energies:**
**For lower energy fixed target measurements initial-state multiple scattering is most important**
**But at RHIC & LHC color filtering preserves small       dipole configurations which have high-p****T**** and therefore give larger p****T**** broadening**

_***DY as bremsstrahlung in the target rest frame***_

## J/Ψ Polarization

_**J/**__**Ψ**__** Polarization**_

***E866/NuSea***

**NRQCD based predictions (color octet model) necessary to explain CDF charm cross sections**
**E866 J/******** measurement not in agreement with NRQCD based predictions *****[Beneke & Rothstein, PRD ***_***54***_***, 2005 (1996)]***** which give**
**0.31 < ****λ < 0.63**
**Complicated by feedown (~40%) from higher mass states.**

**However ********(2S+3S), which should not suffer from feeddown, have maximal polarization consistent with the Octet model!**

***E866/NuSea – PRL ***_***86***_***, 2529 (2001).***

## e+e-

_**Charmonium at PHENIX - Coming soon!**_

**e****+****e****-**

******+********-**

**PHENIX: South Muon & Electrons taking first data now (Au-Au over; p-p in progress)**
**North Muon in 2003 (after shutdown)**
**d-A collisions: strong consensus building; hopefully coming soon.**

*** Min-bias/RHIC-year for ********= .92 (Nagle & Brooks)**
**** E866 nuclear dependence data only   *** Upsilons from E772**

- Simulated

- Simulated

##  Physics Program - High-pT Single ’s

**High-p****T**** single-********’s come from heavy mesons, i.e. D’s or B’s**
**These mesons are produced primarily through gluon fusion and thus are sensitive to the gluon structure functions.**
**In p-A collisions the shadowing of gluons can be studied**

**With polarized beams the gluon polarization, ********G, can be studied.**
**W****±****  ******** ********±**** ****ν******** can be identified by high-p****T**** single-********’s and W****+****/W****- ****can be used to measure the flavor asymmetry in the nucleon sea including its spin decomposition**

- Simulated

- Simulated

## From Draft NSAC Long Range Plan :

_**From Draft NSAC Long Range Plan :**_
_**“**__**The Structure of the Nuclear Building Blocks”**_

## The North- Arm

**North ******** arm**

**South ******** arm**

_**North-**__****__** arm advantages:**_
**Superior arm** with more kick, better momentum resolution & better mass resolution than South (for ’s: North= 190 MeV  compared to South = 240 MeV )
- While **J/********’s should melt in a QGP, ********’s are smaller and should not**, so a well separated  peak (separation of 1S & 2S is 563 MeV) is critical
-  mesons may be broadened, shifted in mass or even enhanced in a QGP. With its 10o (as opposed to 12o for South) minimum theta, the **North-******** arm has much larger acceptance for ********’s** which tend to decay into ’s are small angles.
- The ******ID is directly behind the tracking volume** (in contrast with the South- arm which has a large gap). This should help reduce backgrounds and improve matching between tracking and ID.

_**Two **__****__**-arms**_**:**
**Doubles the counting rate**
-  Allows measuring **forward and backward** ******+********-**** simultaneously**, i.e. negative & positive rapidity  at the same time. Important for the study of formation-time effects in p-A.
- Allows for **events with one ******** in each arm**, e.g. mid-rapidity ’s
**Required for ****W****±****  ******** ********±**** ****ν******** ****spin measurements** since the Z0 ****  +-  backgrounds can be determined only using two arms.

## PHENIX Silicon Vertex Upgrade

- Accurate projection to collision vertex
- => close, thin detector

- Matching tracklets in silicon to tracks in -arms
- Momentum measurement
- displaced vertex
- And also detect *h* in silicon

- LANL LDRD supporting
- R&D for us ($250K/yr)

- Gluon polarization in proton
- Nuclear dependence of open charm:
- Gluon shadowing
- Charm cross section
- To understand J/ in A-A collisions