# Presentation: 102179

## Rapidity gaps in Heavy IonsCollisions at RHIC and the LHC

- Rapidity gaps in Heavy IonsCollisions at RHIC and the LHC

- Features of Heavy Ion collisions
- forward detectors at RHIC and LHC
- Ultra-Peripheral Collisions
- ATLAS plans

- S**.White 9/19/03**

## Models

- H

- H

- QCD inclusive, factorized

- QCD inclusive, non factorized

- QCD exclusive

- QED exclusive

- H

- H

- A)

- C)

- D)

- B)

- p

- p

- p

- p

- p,A

- p,A

- p

- p

- (Boonekamp& Kucs)

## 10-20% Tag probability in Heavy Ion Peripheral  events

_**10-20% Tag probability in Heavy Ion Peripheral  events**_

**STAR- fraction as expected from factorization (cp.**
**RHIC MCD paper)**

**Beam fragmentation **
**un-correlated in tags from**
**Coulomb interactions**

## Orientation of reaction plane and Centrality are key observables in 

**z**

**Spectator neutrons**
**measure centrality,**
**Min_min_bias trigger**

- _Orientation of reaction plane and Centrality are key observables in _
- _Recent papers from RHIC_

- Beam-Beam Counter Mult/1000

- b direction from BBC
- (3<<4 hodoscope array)

**(Calorimeter@********<2mr.)**

## Evidence for Jet Suppression at RHIC(PHENIX)

## ... and disappearance of “away side” jet(STAR)

- ... and disappearance of “away side” jet(STAR)

## dn/d ~ 1 + 2 v2 cos (2 )

- Scaling of elliptic flow (meson vs. baryon)

## AA  cross-normalization with pp

- From pp comparison data
- Error from AA &pp Luminosity uncertainties  and ncollision
- From central/peripheral
- Error from determination of centrality classes

- <-*   Klaus Reygers,*
*PHENIX internal note 7/01*

## Fixed Target Heavy Ion Experiments (ie WA98)

**Fixed Target Heavy Ion Experiments (ie WA98)**
** ****found net pt (v1) in reaction plane of spectator nucleons**
- should be observable in ZDC

- 20-30 Mev pt
- 100 GeV/n
- ->4-6 mm displacement@ZDC

## PHENIX forward cals in ‘03

- 18 meters

- DX

- DX

- ZDC

- FCAL

- grey protons

- grey neutrons

- black protons/neutrons

*fcal acceptance*

- DX magnet and layout similar to TAN
- Z-->(2.7Tev/0.1 TeV)*Z
- X,Y -->(~1)*X,Y

- ZDC in all experiments since day-1
- PHENIX has ZDC shower max@2*I
-     “	    “      FCAL for d-Au run

## Slide 11

## FCAL complements ZCAL centrality measurement

- single proton in FCAL (n-Au events)

- single neutron in ZDC (p-Au events)

- N-tagged events used by STAR and
- PHENIX ->clean sample of peripheral
- p-A collisions

- Run 3, d-Au data

## Calculated cross sections for PbPb@LHC

*A.J.Baltz, C.Chasman and SNW NIM A417(1998)p.1*

| 1n,1n | 0.537 barns |
| --- | --- |
| 1n,xn | 1.897 |
| xn,xn | 14.75 |
| xn | 227.3 |

_**(Absolute Luminosity in Heavy Ion mode to <5%)**_

## The Machine connection

- Van derMeer scans to
- measure *
- (PHENIX with proton beams)

## ...and Shower Max Detector ->independent measurement of displacement and crossing angle

- ...and Shower Max Detector ->independent measurement of displacement and crossing angle

## Implementation in ATLAS

- LARP proposed luminometer
- 4 quadrant High Pressure ionization
- Chamber , occupies ~15 cm of TAN
- Absorber slot

- Beam position (cms)

- Asymmetries used to
- Measure beam steering

_**Implementation in ATLAS**_

## IP1&IP5 absorbers

- TAN@140m

- _Exploded view_

##     Electromagnetic Interactions of Heavy Ions:

-     _**Electromagnetic Interactions of Heavy Ions:**_
**(‘24)-E.Fermi develops Equivalent ******** approx**
** ****	****for int of e****-**** and ********’s with atoms**
**(‘33) -Weiszacker and Williams**
**(50’s) demonstration of EPA with interactions**
** ****	****of ~500 MeV e****-**** with Nuclei- **
**      ****(Wilson, Panofsky et al. @ Stanford)**
**(80-90’s) -first measurement of EM interaction **
**using ion beams @Bevalac SPS and AGS**
**(‘03->)- “rapidity gap” physics w. Heavy**
**Ions @ RHIC & LHC**

##  Luminosities based on LHC design parameters

-  Luminosities based on LHC design parameters
- E.Papageorgiu hep-ph/9503372

- Low mass Higgs production
-  cross section=flux*(->H0)

##  and DPE exchange roles in pp and PbPb

-  and DPE exchange roles in pp and PbPb
-  ***Z******2******(or Z******4******) vs. A******0.3****** *B******0.3***

- 

- “Pomeron”

- p-p

- Pb-Pb

## Fixed target  beam w. E->100TeV

- Fixed target  beam w. E->100TeV

## Heavy Ion Physics ca. 2008

- Heavy Ion Physics= Opportunities with a tool that we are just learning
- to exploit
-  (c.f. e+e- physics)

- LHC energy (Pb)
-       2.7 TeV/n
- ATLAS measures
- jet to +/- 4.7

## summary

- Beam tagging is a feature of the RHIC Heavy Ion program
- Similar Instrumentation will be available at LHC
- Increase in energy at LHC significant
- Hard processes in peripheral events
- Will complement the pp forward physics program

## Extra Slides

## SMD based polarimetry at PHENIX

- Spin Rotators OFF

**Blue**

**Yellow**

- Spin Rotators ON, Current Reversed

**Yellow**

**Blue**

**Blue**

**Yellow**

- Spin Rotators ON, Correct!

- PB=35.5%

- PB=37%

**Run-03**

- Left-right asymmetry measures
- (vertical) proton polarization

## Slide 26