quark matter 2002falk meissner, lbnl falk meissner lawrence berkeley national laboratory for the...
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Quark Matter 2002Falk Meissner, LBNL Exclusive Vector Meson Production A ’ VA Extrapolate p ’ Vp to A ’ VA with Glauber calculation Large cross sections: 350 mb at s NN 1/2 =130 GeV 590 mb at s NN 1/2 =200 GeV S.Klein, J.Nystrand, Phys. Rev C (1999), A. Baltz, S. Klein,J. Nystrand PRL 89, (2002) Factorize as function of impact parameter Nuclear breakup by single (1n1n) and multiple (xnxn )neutron emission single/multiple neutron emission selects different impact parameters Exclusive production AuAu AuAu 0 … with nuclear excitation AuAu Au*Au* 0TRANSCRIPT
Quark Matter 2002 Falk Meissner, LBNL
Falk Meissner Lawrence Berkeley National Laboratory
For the STAR Collaboration
Quark Matter 2002 19.07.02
Coherent Vector Meson Production in Coherent Vector Meson Production in Ultra-Peripheral Heavy Ion CollisionsUltra-Peripheral Heavy Ion Collisions
•Ultra Peripheral Collisions•Exclusive Meson Production•2000/2001 Data Sets and Analysis•Cross Sections•Photon-Photon Interactions•Summary
Quark Matter 2002 Falk Meissner, LBNL
Ultra-Peripheral CollisionsUltra-Peripheral Collisions
Au
Au
XPP
Nuclei ‘miss’ geometrically and interact via long range fields
Coupling strengthCoupling strengthlarge cross sections• Photon- Z2 Equivalent Photon Approximation (Weizsaecker-Williams, Fermi)
• Pomeron-P A4/3 (surface) to A 2 (volume)
Coherent coupling to extended charge of both nuclei• P> R_A Small transverse momentum: pT < h/2RA~ 90
MeV• Longitudinal component PL < h/2RA ~ 6 GeV• Quasi Real Photons
Quark Matter 2002 Falk Meissner, LBNL
Exclusive Vector Meson Production Exclusive Vector Meson Production AA’’VAVA
• Extrapolate p’Vp to A’VA with Glauber calculation
Large cross sections:350 mb at sNN
1/2=130 GeV 590 mb at sNN
1/2=200 GeVS.Klein, J.Nystrand, Phys. Rev C60 014903 (1999), A. Baltz, S. Klein,J. Nystrand PRL 89, 012301 (2002)
• Factorize as function of impact parameter
• Nuclear breakup by single (1n1n) and multiple (xnxn )neutron emission
• single/multiple neutron emission selects different impact parameters
Exclusive production AuAu AuAu0
)()( 022 bPbbPd GDR
… with nuclear excitation AuAu Au*Au*0
Quark Matter 2002 Falk Meissner, LBNL
Experimental Signature of UPCExperimental Signature of UPC• Two oppositely charged
tracks with vertex • Low total pT
• Back-to-back in transverse plane
ZDC ZDC
CTB-Topology
Challenge: Trigger !
Topology requirements in central trigger barrel (CTB)
Coincident signals from nucl. Breakupin zero degree calorimeters (ZDC)
Quark Matter 2002 Falk Meissner, LBNL
Transverse Momentum & Transverse Momentum & Invariant Mass SpectraInvariant Mass Spectra
• 2000: 130 GeV; 9hrs dedicated, 30k triggers
• 2001: 200 GeV; trigger mix 1.5M topology triggers• Peak at low pT coherent interaction• Background model from like-sign pairs
normalized to dataNo neutron signal in ZDC gold nuclei
remain in ground state
Signal region: pT<0.15 GeV
Topology Trigger AuAu AuAu0
200GeV
Preliminary
Quark Matter 2002 Falk Meissner, LBNL
Meson Production with Nuclear Meson Production with Nuclear Break-upBreak-up
Minimum Bias (ZDC) Trigger AuAu Au*Au*0
ZDC Response
Signal region: pT<0.15 GeV
•2000: ~400k triggers L~60/mb•2001: ~1.7M triggers L~250/mb
200GeV
Preliminary
Quark Matter 2002 Falk Meissner, LBNL
Mass FitMass Fit
• Acceptance corrected• Breit-Wigner+direct pion
pair production+ BG • Background contribution at
low mass from e+e- pairs • Amplitude ratio similar
to lepton nucleon scattering
130 GeV-
+
A+-A
Quark Matter 2002 Falk Meissner, LBNL
Cross Section Cross Section (AuAu (AuAuAuAu(*)(*)AuAu(*)(*)))130 GeV - nucl-ex/0206004, 200 GeV Preliminary Luminosity normalization from 7.2b hadronic AuAu cross sectionSystematic uncertainties ~20%
Theory: A. Baltz, S. Klein J. NystrandPreliminaryTotalNo Breakup
xn,xn
1n,1n
Quark Matter 2002 Falk Meissner, LBNL
• Compare to lepton-nucleon scattering
• A dependence of photo-nuclear cross section
• VM Production mechanism depends on scale - c.m.s. energy, pT, quark masses
• J/sensitive to gluon distribution in the nucleus
A-Scaling and Energy DependenceA-Scaling and Energy Dependence
Quark Matter 2002 Falk Meissner, LBNL
Two-Photon Interaction Two-Photon Interaction AuAuAu*Au*e+e-
Identified e+e - Pairs via dE/dx only at low momentum p<0.13 GeVNon-Identified coherent e+e- pairs - background for production; extrapolate identified e+e- to all momenta with MC
Coherent e+e- Pairs pT < h/b (<b>~40fm)
Physics Topics:Strong field QED Z ~ 0.6Large cross section Z44
Au
Au
e-
e+
200GeV, 0.25T Magnetic Field
Quark Matter 2002 Falk Meissner, LBNL
SummarySummaryFirst measurements for coherent meson production in ultra-First measurements for coherent meson production in ultra-
peripheral heavy ion collisions with and without nuclear peripheral heavy ion collisions with and without nuclear excitation excitation
Au + Au -> Au + Au + and Au + Au -> Au* + Au* + .• low pT= coherent coupling• Cross Sections agree with predictions =>Approximate factorization of rho-production and nuclear excitation =>Weizsaecker-Williams photon flux from large relativistic charges ok. => Glauber extrapolation of N to Au ok• This is just the beginning; Future analysis topics:
– Vector meson spectroscopy ,excited states (*,…)– Multiple VM production– Hard diffraction - higher mass states J/– Strong field QED - e+e- pairs– Interference of decaying particles
RHIC is a good place to study diffractive and electromagnetic processes in heavy ion collisions. Lots of data and physics topics.
Quark Matter 2002 Falk Meissner, LBNL
Quark Matter 2002 Falk Meissner, LBNL
RapidityRapidityExtrapolationExtrapolation
• Y-distribution differs for prod. with (xnxn,1n1n) and without
(0n0n) breakup
Nucl.Breakup
STAR Data•Acceptance is flat in pT and Mass•Analysis |y|<1•Extrapolate to 4pi with MC
Quark Matter 2002 Falk Meissner, LBNL
Compilation of VM cross Sections Compilation of VM cross Sections
Quark Matter 2002 Falk Meissner, LBNL
Entangled Nonlocal WavefunctionsEntangled Nonlocal Wavefunctions• VM are short lived (~10-23 s) decay before traveling distance b• Decay products interfere
• J/s many decays: e+ e-, +- +- , hadrons• At the decay time(s) neither amplitude can know
about the other (no overlap)Either independent decays --> little/no interferenceOR The wave function retains amplitudes for all possible
decays, long after the decay occurs The wave function only collapses when it interacts
with the detector Quantum mechanics predicts choice 2 Example of the Einstein-Podolsky-Rosen paradox
+
-
+
-
b
-
e+
e-
b
J/
J/
+0
???
Quark Matter 2002 Falk Meissner, LBNL
2-slit interferometer with separation of impact paramter b!
<b> ~ 40 fermi >>RA ~ 7 fmJ have negative parity JPC = 1- -
Amplitudes have opposite signs ~ |A1 - A2eip·b|2
destructive interference at pT=0 (maximal at y=0 when A1=A2)
Can’t differentiate between projectile and target
Expected Signal
No Interference
Interference
InterferenceInterference
S. Klein and J. Nystrand, Phys. Rev. Lett. 84(2000)2330