# Presentation: 676217

## Transverse dynamics at y=0 in BRAHMS

- Bjørn H. Samset
**Transverse dynamics**
**at RHIC, March 2003**

- A story of
- centrality dependent
- pt spectra of identified
- charged hadrons
- measured with the
**BRAHMS**
- experiment at
**RHIC**
- Data from AuAu collisions at

## Transverse dynamics at y=0 in BRAHMS

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- A story of
- centrality dependent
- pt spectra of identified
- charged hadrons
- measured with the
**BRAHMS**
- experiment at
**RHIC**

- Bjørn H. Samset
-  PhD student,
-  University of Oslo, Norway
-  Been with BRAHMS for 4 years...

## Transverse dynamics at y=0 in BRAHMS

**Transverse dynamics ****at y=0 in BRAHMS**

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- A story of
- centrality dependent
- pt spectra of identified
- charged hadrons
- measured with the
**BRAHMS**
- experiment at
**RHIC**

- Bjørn H. Samset
-  PhD student,
-  University of Oslo, Norway
-  Been with BRAHMS for 4 years...

**BRAHMS crater on Mercury,**
**formed by a high energy collision at low****centrality, plus some transverse flow.**

## Outline

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

-  The BRAHMS experiment at RHIC
-  The analysis - extracting particle yields from BRAHMS data
-  <pt> and centrality dep. of dNch/d at y=0
-  <pt> and centrality dep. of identified hadron pt spectra at y=0
-  Centrality dependence of like and unlike particle ratios    vs. pt at y=0
-  Conclusions and future visions

## The                      experiment                     at

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- The                      experiment                     at

## The BRAHMS collaboration

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

## The BRAHMS experimentSetup used for AuAu data in 2001

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

## BRAHMS coverage for theAuAu run of 2001

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**MRS**

**FS**

- 25 GeV/c

- 4o

- 2.3o (min)

- 90o

- Coverage of the
- y-pt plane is achieved
- by rotating the two
- spectrometer arms
- and changing
- magnetic fields.

- Angles covered in 2001: 90o, 60o, 45o, 40o, 35o, 20o, 12o, 8o, 4o, 3o

## Data analysis in

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- heading towards**Centrality dependence of charged particle production at midrapidity**

- Analysis mainly by E. J. Kim and J. H. Lee

## Particle identification in BRAHMS

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**Midrapidity performance:**
-  Time-of-flight resolution of~75 psec
- /K separation up to ~2.5 GeV/c
-  K/p separation up to ~4.0 GeV/c

**Forward spectrometer (example):**
-  RICH gives PID up to 25 GeV/c

- TOFW

- RICH

## Select data from y-pt plots

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- 90o

- 60o

- 40o

## Select data from y-pt plots

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- 90o

- 60o

- 40o

## Select data from y-pt plots

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- 90o

- 60o

- 40o

## Select data from y-pt plots

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- 90o

- 60o

- 40o

## A word on extracting a yield from a pt spectrum

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- We need to extrapolate to integrate the spectra, and here we have tomake an assumption about the spectral shape:

-  Boltzman?
-  pt exponential?
-  mt exponential?

- There is a 20% difference in theyields extracted via the differentfits - this goes into our systematicuncertainty.
**In the following we have used****m****t**** exponential fits unless **
**otherwise noted.**

## Centrality dependence of charged particle production at midrapidity

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**Analysis of total y~0 data set from Run-2 (Au-Au                        )**

- Approx. 30M events

## Centrality dependence of charged particle production at midrapidity

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**Analysis of total y~0 data set from Run-2 (Au-Au                        )**
**Events divided into centrality classes (0-10,10-20,20-40,40-60 %)**** as determined by Multiplicity detector (-2.2<********<2.2).**

## Centrality dependence of charged particle production at midrapidity

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**Analysis of total y~0 data set from Run-2 (Au-Au                        )**
**Divided into centrality classes (0-10,10-20,20-40,40-60 %)**** as determined by Multiplicity detector (-2.2<********<2.2).**
**PID by Time-Of-Flight, 3******** cut with respect to our momentum****and tof resolutions**

- Momentum

## Corrections applied to the data

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- We need to apply a number of corrections to our raw number ofparticles to get the correct yield. We've corrected for:
-  tracking efficiency, using a track embedding technique
-  efficiency in matching spectrometer tracks to hits in the time-of-flight systems
-  geometrical acceptance, using GEANT3.21
-  physics effects like multiple scattering, proton knockout from thebeampipe etc., also evaluated with GEANT3.21
- Caveats:
- The numbers I will show have not been corrected for  feed-down,
- and I will only show statistical errors.

## Corrections applied to the data

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- We need to apply a number of corrections to our raw number ofparticles to get the correct yield. We've corrected for:
-  tracking efficiency, using a track embedding technique
-  efficiency in matching spectrometer tracks to hits in the time-of-flight systems
-  geometrical acceptance, using GEANT3.21
-  physics effects like multiple scattering, proton knockout from thebeampipe etc., also evaluated with GEANT3.21
- Caveats:
- The numbers I will show have not been corrected for  feed-down,
- and I will only show statistical errors.

- Now for the data...

## Centrality dependence of charged hadron spectraat y=0

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

-  The charged hadron spectra havebeen fitted to a  power law formula:in the range 0.2 < pt < 4.0 GeV/c
-  dN/d and <pt> values are calc.from the fit parameters, with

**BRAHMS PRELIMINARY**

## dN/d at =0 from charged hadrons

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- dN/d per participant pair increasesfrom 3.0 for peripheral collisions to3.5 for central. This is consistent with what we showed in
- Phys.Rev.Lett.88:202301,2002

- <pt> rises from ~0.55 GeV/c forperipheral collisions to ~0.60 GeV/c
- for central.

**BRAHMS PRELIMINARY**

## Charged hadron yield per Ncoll,comparison between central and peripheral

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**BRAHMS PRELIMINARY**

- The ratio between the yield of
- charged hadrons from central
- and peripheral collisions
-  increases up to pt ~2.3
-  drops as pt increases beyond  this value

## Particle spectra from central AuAu collisions

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- Recap of

- Cent:0-10%

- Analysis byD. Ouerdane

## Charged hadron spectra:+, -

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**BRAHMS PRELIMINARY**

## Charged hadron spectra:K+, K-

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- 0-10%

**BRAHMS PRELIMINARY**

## Charged hadron spectra:p, p

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- 0-10%

**BRAHMS PRELIMINARY**

## Comparison: 0-10% vs. 40-60%

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**BRAHMS PRELIMINARY**

- We see no significant difference between the behaviors of pt spectrafor central and peripheral events.

## Inverse slope vs. mass and centrality

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

-  We see transverse flow at all rapidities, and all centralities at y=0
-  Inverse slope decreases with increasing rapidity
-  Inverse slope decreases somewhat for less central events

- y=0, 0.9

- y~3

**BRAHMS PRELIMINARY**

## <pt> for , K, p at y=0

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- The mean pt is evaluated from the exponential mt fits.
- <pt> for all particle species increases from peripheral to central events
- Values and centrality dependence is good agreement with preliminary Phenix data, except forthe pions. Ours are higher, likelybecause of the mt fit.

**BRAHMS PRELIMINARY**

## dN/dy per participant pair at y=0

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

-  The yield per participant pair increases with participant number for all particle species
-  K and p yields rise faster than 

- Statistical errors only. Dominant sources ofsystematic errors are Npart numbers andextraction of yields.

**BRAHMS PRELIMINARY**

## K/ ratio at y=0, 3

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- Recap of

-  Positive and negative ratios are identical aty=0.
-  At y=3 K-/- drops below the positives

- Analysis by
- D. Ouerdane

##  Centrality dependent-/+ ratios at y=0

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**The ********-****/********+**** ratio is flat over the range 0.5<pt<3.5GeV/c.**
**R(central) is equal within errors to R(peripheral)**

**BRAHMS PRELIMINARY**

##  Centrality dependentK-/K+ ratios at y=0

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**The K****-****/K****+**** ratios are almost flat over the range ****0.5<pt<3.5GeV/c. There may be a dip at low p****t**
**R(central) is again equal within errors to R(peripheral)**

**BRAHMS PRELIMINARY**

##  Centrality dependentp / p ratios at y=0

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**The p / p ratios for central events are flat over the range**** 0.5<pt<3.5GeV/c.**
**R(central) is equal within errors to R(peripheral)**

**BRAHMS PRELIMINARY**

## K /  ratios at y=0

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**K****-****/********-****, K****+****/********+**** ratios show an increase with p****t**
**There is no significant difference between central and****peripheral events.**

**BRAHMS PRELIMINARY**

## p /  ratios at y=0

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**p/********-****, p/********+**** ratios show an increase with centrality.**
**The ratios in central events reach 0.7~0.8 at 2GeV/c, ****while in peripheral events the ratios go up to 0.4~0.5.**

**BRAHMS PRELIMINARY**

## The BRAHMS experimentAdditions since 2001 

- The BRAHMS experimentAdditions since 2001

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- C4  - Cherenkov counter

- Spectrometer triggers for pp and dA

-  Extended pt coverage at midrap.
-  Better timing resolution
-  Allows triggering on events  w. tracks in spectrometer for inc.  data rate

- TOFWII second time-of-flightwall

## What to expect from BRAHMSin the near future

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**Existing AuAu data:**
** **Analysis is ongoing away from midrapidity
-  Our centrality dependent spectra will be extended out to y~3**pp and dAu data:**
-  pp data are being analyzed to serve as baseline for our AuAu data
-  dAu data are being taken and analyzed as we get them. Now we only   need the machine to deliver enough beam for a good high pt sample!**A future AuAu run at full RHIC energy:**
** **C4 and TOFWII extend our capabilities at midrapidity, allowing for  an even better comparison between mid and high rapidities
-  Our pt coverage at midrapidity will go increase, nicely complementing  the data we already have

## Conclusions

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- BRAHMS has measured the transverse dynamics of charged hadrons
- at midrapidity from AuAu collisions at
- In brief, we have shown that
-  for charged hadrons, <pt> increases as a function of centrality
-  this also applies to each particle species individually
-  the global behavior of identified particle spectra does not change with centrality
-  like-particle ratios are constant as a function of pt and centrality
-  the p/ ratio shows an increase for more central events

## Conclusions

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- BRAHMS has measured the transverse dynamics of charged hadrons
- at midrapidity from AuAu collisions at
- In brief, we have shown that
-  for charged hadrons, <pt> increases as a function of centrality
-  this also applies to each particle species individually
-  the global behavior of identified particle spectra does not change with centrality
-  like-particle ratios are constant as a function of pt and centrality
-  the p/ ratio shows an increase for more central events

- Thank you for listening

## Comparison: 0-10% vs. 40-60%mt-m0

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

## High pt, nuclear modification factor

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- Recap of

- Analysis by C. E. Jorgensen

**Numbers from**
**nucl-ex/0206011**

## Calculating <pt> from mt spectra

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- We've fit our spectra with an mt exponential to extract the inverse slope.Using the fit functions for pt:

- we can extract the mean pt by integrating:

## Analysis details 1:Track and event selection

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**All MRS 90 degree data set**
**    ****->  run4692 - run5983 **
**    ****->  BB, TPC, TOFW, BbVertex calibration**
**No specific Trigger selection**
**Centrality cut from latest calibration from DB **
**Select  Good MrsTracks **
**Magnet Fiducial cut : 1cm (x,y) from edge**
**Run-by-Run fitting**
**   ****- Diff(Vzdc-Vbb) : 4********cut**
**   ****- matching (Dang,Dy,Daly,Ty) : 3******** cut**

## Analysis details 2:Acceptance maps

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**Flat distributions :  p, ******
**    ****-> 10M at each setting**
**    ****-> -17.5cm < z <17.5cm, ********z = 5cm**
**New TPM2 geometry for 2001 data setting**
**Selection : same as used in data **
**   ****-> remove bad TOFW slats  **
**   ****-> Magnet Fiducial cut : 1cm (x,y)**
**y-mt, y-pt map for ********, K, p**
**   ****-> Acceptance values below 4.5(5.5) are**
**       ****applied to data.  (reduce edge effect)  **

## Analysis details 3:Corrections

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**Track-by-Track corrections**
**TPC efficiency : ~ 89%, 96%**
**    ****-> as a function of # of clusters**
**TOFW : remove bad slats**
**Corrections for particle species**
**    ****-> Multiple scattering : ********p**
**    ****-> Decay correction : ********, K**
**    ****-> Absorption : pbar**
**    ****-> as a function of momentum**

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

- @

- Cent:0-10%

## Centrality dependence of charged particle production at midrapidity

- Bjørn H. Samset
**Transverse dynamics****at RHIC, March 2003**

**Analysis of total y~0 data set from Run-2 (Au-Au                        )**
**Divided into centrality classes (0-10,10-20,20-40,40-60 %)**** as determined by Multiplicity detector (-2.2<********<2.2).**
**PID by Time-Of-Flight, 3******** cut with respect to our momentum****and tof resolutions**

-  Yields and <pt> from charged hadrons
-  Yields and <pt> from identified hadrons
-  Centrality and pt dependence of like and unlike particle ratios

- ...and now for the data: