Interesting Physics beyond the QGP discovery phase Heavy flavor production Flavor dependence of QCD...
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Transcript of Interesting Physics beyond the QGP discovery phase Heavy flavor production Flavor dependence of QCD...
Interesting Physics beyond the QGP discovery phase
Heavy flavor production Flavor dependence of QCD energy loss Jet studies and gluon-jet correlations in 4 Chiral Symmetry Restoration Onium Physics
R. Bellwied, February 2002R. Bellwied, February 2002
Interesting physics in the SPS dilepton spectrum
Dilepton Measurements: open charm production (D) charmonia suppression (J/) light mesons in dense matter
() thermal dimuons from QGP
Charm is a heavy flavor that is abundantly produced at RHIC
so These measurements provide the closest link to
pQCD, together with jet production at RHIC
No enhancement in pp and pA collisions
Strong enhancement of low-mass e+e- pairs in A-A collisions (compared to expected yield from known sources)
Enhancement factor (.25 <m<.7GeV/c2) : 2.6 ± 0.5 (stat) ± 0.6 (syst)
Low Mass Electron Pairs:
Chiral Symmetry Restoration ? (measure leptonic and hadronic decay channels)
The Intermediate Mass Region (IMR) excess: evidence from SPS (NA38/NA50)
pA: AA:
NA38+NA50
Properly described byDrell-Yan and D meson decays
and with a Total charm cross-
section consistent with previous direct measurements
IMR yield is higher than thesum of DY and D meson decays
in particular A factor 2 higher in
central Pb-Pb
Possible explanation for
IMR excess
Thermal radiation ?
Very good fit to databut
is a factor 3 charm enhancement conceivable ?
Good account for the IMR excesswhen added to expected sources
assuming QGP phase with Ti = 192 MeVMeasure Charm Enhancement at RHIC direct via hadronic decay channels
A high precision vertex detectorwill allow a clean separation of charm and bottom decays
m c eX GeV m %
D0 1865 125 6.75D± 1869 317 17.2
B0 5279 464 5.3B± 5279 496 5.2
Need secondary vertex resolution ~ 30 - 50 mm
We need a direct measurement
of heavy flavor production
m c GeV m prime decay channel
D0 1865 125 K- + anything (54%), K-+ (4%)D± 1869 317 K-++ (9%),K0+ (3%)
B0 5279 464 K* J/B± 5279 496 K+ J/
CDF (Phys. Rev. D58 (1998) 072001) very successful in direct B-meson reconstruction using new defined isolation cut.
Decay channels for direct
measurement
D’s are relatively abundant (higher yield in STAR detector than1D/unit y))Even B-mesons be in our acceptance ~ once every ~100 events
Study flavor dependence of jet quenching (tag with identified high pT particle)
Important to extend spectra of identified charged particles out to as high pT as possible
Enhanced High pT
Physics
pt-dependence of ratios in STAR (based on year-1 data)
Need high pt !! (will get a little more from statistics in years-2+(based on existing RICH for p and topology analysis for )
How to measure a high pt spectrum
For the primaries you need PID out to large pt (see next slide)
For the secondaries you can use the topology method out to large pt without PID (to some extent). E.g. the spectrum in STAR will reach out to about 5 GeV/c.
You need precision tracking for D-meson and B-meson reconstruction.
Extended PID with Aerogel
Aerogel together with TOF can extend the PID capability up to ~ 10 GeV/c
5 - 91 - 5 n=1.007Aerogel
17 -5 - 17 n=1.004RICH
0 - 50 - 2.5 ~100 ps
TOF
Kaon-Protonseparation
Pion-Kaonseparation
0 4 8
0 4 8
0 4 8 0 4 8
0 4 8
0 4 8
Y. Miake
Forward Physics in STAR
Charged hadron and lepton (?) spectra (pt and rapidity) between h = 2.5-4.0 for AA and pA collisions.
Separate peripheral collision program Important jet physics program in pp and pA. V0 reconstruction (without PID) Possibly better phase space for D-meson mass
reconstruction through charged hadron channel
Bellwied, RHIC workshopBellwied, RHIC workshop
More Forward Physics Goals
Measurements in the baryon-dense regime In central collisions the forward region will be baryon-
rich (high baryochemical potential). Exotic phenomena, e.g. centauro-like events and strangelets, are preferably produced in such an environment..
production of light nuclei and antinuclei carries information of baryochemical potential and of production mechanism in baryon-rich region compared to baryon-poor mid-rapidity region.
anti-proton suppression due to increased annihilation ?
Bellwied, RHIC workshopBellwied, RHIC workshop
Precision Measurements: Tagged Jet quenching
Direct -tagged events: E~Ejet
Compare AA to pp Need to measure pT spectrum
of particles opposite high ET or 0 ?
Need to do this vs Species/Energy to find energy
loss How big? Proportional to mean free
path? Gluon/quark difference
PT
Reaction Plane
jet
Collision axis
Large back to back coverage:EMCAL and tracking & high pt pid in 4
would be ideal
Tomography? (penetrating probes)(from Richard Seto’s talk)
Do as a function of “position” I.e. many bins of centrality, pt, y, reaction plane E.g
Jet energy loss Mass shift Other? (J/ Suppresssion/charm enhancement)
Requires Very High statistics
E.g. 10 bin in pt, 5 bins in y,5 bins in centrality, 8 bins in reaction plane
400 points per centrality; 2000 points Good geometry measurements
Reaction plane/centrality – event by event
Summary There is interesting physics in the heavy flavor production (s, c, b)
that is not achievable with the present STAR detector. In particular the D- and B-meson cross section and the pt-spectrum
of strange, charm and bottom particles ( flavor dependence of QCD energy loss)
Jet studies and gluon-jet correlations will benefit from 4coverage In terms of continuation of original measurements:
Measure lepton and hadron decay channels of vector mesons in parallel (chiral symmetry restoration)
-> Tomography of the QGP source
Detectors we need
High pt PID in 4 RICH, Aerogel and TRD detectors
High precision vertexing at central rapidity Active pixel or CDD layers
High precision tracking in 4 Forward tracking with straw-tubes or Silicon
-> See Howard’s Talk
• Separation of charm/bottom decays by measuring displaced secondary vertex improve measurement accuracy of c and b cross sections to < 10% separate c and b contribution in each pT bin (flavor dependence of QCD energy loss)
• Direct measurement of D mesons combined with particle id, can measure D -> Kp modes => pT spectrum of D’s (flavor dependence of QCD energy loss)
• Improved momentum resolution for Upsilon spectroscopy
• Enhanced capabilities for spin physics wider acceptance (g-jet & jet-jet studies, c,b-tagging, etc)
• Enhanced physics capabilities for charm and bottom in pA
Enhanced Physics Capabilities with
a
High Precision Vertex Tracker