measurement of charged antiparticle to particle ratios by the phobos experiment at rhic
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Measurement Of Charged Antiparticle To Particle Ratios by the PHOBOS Experiment at RHIC. C o nor Henderson Massachusetts Institute of Technology. For the PHOBOS collaboration. PHOBOS Collaboration. ARGONNE NATIONAL LABORATORY Birger Back, Nigel George, Alan Wuosmaa - PowerPoint PPT PresentationTRANSCRIPT
Conor Henderson, MIT APS April 2001
Measurement Of Charged Antiparticle To Particle Ratios by the
PHOBOS Experiment at RHIC
Conor Henderson
Massachusetts Institute of Technology
For the PHOBOS collaboration
Conor Henderson, MIT APS April 2001
PHOBOS CollaborationARGONNE NATIONAL LABORATORY
Birger Back, Nigel George, Alan Wuosmaa
BROOKHAVEN NATIONAL LABORATORY
Mark Baker, Donald Barton, Alan Carroll, Stephen Gushue, George Heintzelman, Robert Pak, Louis Remsberg, Peter Steinberg, Andrei Sukhanov
INSTITUTE OF NUCLEAR PHYSICS, KRAKOW
Andrzej Budzanowski, Roman Holynski, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki , Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
Wit Busza* , Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane , Judith Katzy, Piotr Kulinich, Johannes Muelmenstaedt, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep Sarin, Stephen Steadman, George Stephans, Gerrit van Nieuwenhuizen, Carla Vale, Robin Verdier, Bernard Wadsworth, Bolek Wyslouch
NATIONAL CENTRAL UNIVERSITY, TAIWAN
Willis Lin, JawLuen Tang
UNIVERSITY OF ROCHESTER
Joshua Hamblen , Erik Johnson, Nazim Khan, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs
UNIVERSITY OF ILLINOIS AT CHICAGO
Russell Betts, Clive Halliwell, David Hofman, Burt Holzman, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter
UNIVERSITY OF MARYLAND
Richard Bindel, Edmundo Garcia-Solis, Alice Mignerey
* Spokesperson
Conor Henderson, MIT APS April 2001
Why Measure Antiparticle/Particle Ratios?
• Microscopic viewpoint:– Antiproton/proton ratio determined by:
• Baryon stopping;
• Pair production;
• Absorption in nuclear medium
• Thermodynamic viewpoint:– Particle ratios can be used to estimate hadro-chemical
potentials
Conor Henderson, MIT APS April 2001
The PHOBOS Detector
Ring Counters
Paddle Trigger Counter
Spectrometer
TOF
Octagon+Vertex
GeVS NN130
Au+Au collisions
68,359 events
12% most central
Conor Henderson, MIT APS April 2001
The PHOBOS Spectrometer
• One arm with 16 layers of Si sensors
• Outer layers situated in 2T magnetic field
• Coverage near mid-rapidity
Conor Henderson, MIT APS April 2001
B-field inverted to obtain antiparticle/particle ratios:e.g. Antiparticles for B+/ Particles for B-
Particle Tracking In Spectrometer
x 10 cm
1
2
By 1. Road-following algorithm
finds straight tracks in field-
free region
2. Curved tracks in B-field found
by clusters in (1/p, ) space
3. Match pieces by ,
consistency in dE/dx and fit in
yz-plane
z
Conor Henderson, MIT APS April 2001
Particle Identification
• dE/dx in Si sensors depends only on velocity
• dE/dx vs. p therefore allows identification of particle
• Ratios stable w.r.t. cut variation
p
K
Conor Henderson, MIT APS April 2001
Corrections to the Raw Numbers
• Secondary particles (+2%)– Little material between interaction point and
sensitive volume
• Antiproton absorption in detector (+8%)– From GEANT simulations
• Feed-down from weak decays (-2%)– Reduced by tracking within 10cm of vertex– Further limit by distance-of-closest-approach cut
on tracks
Conor Henderson, MIT APS April 2001
The Results
.)(06.0.)(04.060.0
.)(06.0.)(07.091.0
.)(02.0.)(01.000.1
syststatp
p
syststatK
K
syststat
•No strong pt dependence observed
For pt < ~1 GeV, near mid-rapidity:
(Submitted to PRL; preprint hep-ex/0104032)
Conor Henderson, MIT APS April 2001
Comparison To Lower Energies and Models
• K-/K+ and pbar/p
significantly higher
than at AGS or SPS
• HIJING over-predicts
our data, RQMD
under-predicts it.
Conor Henderson, MIT APS April 2001
Estimation Of Baryo-chemical Potential
• Statistical model of
Redlich et al. (QM ’01)
• Assume freeze-out
temperature 160–170
MeV
• Obtain B = 455 MeV
• SPS, B = 240-270 MeV
Conor Henderson, MIT APS April 2001
Summary
• Antiparticle/particle ratios measured near mid-rapidity by PHOBOS silicon spectrometer
• K-/K+ and pbar/p higher than at AGS or SPS B=45 MeV is lower .)(06.0.)(04.060.0
.)(06.0.)(07.091.0
.)(02.0.)(01.000.1
syststatp
p
syststatK
K
syststat
Conor Henderson, MIT APS April 2001
Spectrometer Acceptance
Averaged over vertex range and azimuthal angle
Conor Henderson, MIT APS April 2001
HIJING & RQMD Comparison : Baryon Stopping
Net
Bary
on
Nu
mb
er
y