Transcript Document 7677832

2 Talks For 1 Time Slot
EM Cluster Detection in AA
Pablo P Yepes, Rice University
AA Ultra-Peripheral Collisions
Pablo P Yepes, Rice University
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
1
EM Cluster Detection in AA
MiniTalk I
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
2
Why EM Clusters
• Compact MUON Solenoid HI studies have
focused on Muons for Quarkonia.
• Electrons:
– Physics: Quarkonia (double stats and better
handle on systematics), Z  e+e-, b  e + b  m
– Current experiments:
• PHENIX design for e detection (RICH)
• STAR studies indicate that J/Y should be possible
with EMC, tracking and L3.
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
3
Why EM Clusters
• Photons:
 g-jet without jet reconstruction. Detect jet and look
at hadronic activity in cone opposite to it. (à la
X.N. Wang). Go down to low ET.
 p0
• Assume g/e look the same in calos. First step:
study g detection with calos only.
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
4
Analysis
• “Data” samples:
– 1000 photons ET=1-100 GeV
– 40 Hijing PbPb central events
• Pass “data” samples through full simulation
• Reconstruct EM clusters in EMC
– Look for crystals ET>ETSeed (2 GeV).
– Sum energy around a R=0.05 cone.
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
5
ET per Crystal in Barrel ECAL in PbPb
Remember CMS EMC has around 80K crystals
Minbias
Pablo Yepes, Rice U.
Central
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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EM Cluster Angular Resolution
Generated - Reconstructed Angles
Eff. Cut
Pablo Yepes, Rice U.
Eff. Cut
Eff. Cut
CMS Heavy Ion Workshop, MIT Feb
9, 2002
Eff. Cut
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Em Cluster Reco Efficiency
with Calorimetry only
Unmatched
reco’ed
EM Clusters
in one Central Event
For e tracking should add a significant rejection factor!!!
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
Pt(GeV)
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EM Cluster Reconstruction
Efficiency versus rapidity
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
9
EM Cluster Energy Resolution
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
10
Conclusions
• It is possible to reconstruct EM clusters very
well in the HI environment
• EM opens news possibilities: ee, em
• Calos alone cannot do the job.
• High Level Trigger would be needed to get
rid of large backgrounds.
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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End of First MiniTalk
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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Ultra-Peripheral Collisions in AA
MiniTalk II
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
13
Ultra-Peripheral Collisions (UPC)
gg, gP, PP, gA
Collider
b>R1+R2
Z
Z
• No direct nuclear interaction: b>2 R.
• Collision through EM or long range
strong forces: gg, gP.
• Only products of coherent interaction
seeing at |h|<<hbeam
• When Coherence exists:
pL < g h/RA ~ 100 GeV/c
pT < h/RA~ 50 MeV/c
Falk Meissner
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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gg Collider
Luminosities
dLgg/dM (GeV-1cm-2s-1)
(G. Baur et al.)
Ca LHC
p LHC
Pb LHC
ee LEP
gg NLC
1034
1032
1030
1028
1026
1024
50
100
150
200
Mgg(GeV/c2)
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
250 300
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UPC Physics
• UPC Workshop at CERN,
March 8-9, Hencken & PY &
HIF. Theory&Experiment
10-2
10-6
10-8
10-10
1010
p0 h h' f2
a2
f2' hcc
c0
cc2
H' h
b
h0b
h2b
Ca+Ca
events/year
10-4
sAA(barn)
• Great Variety of topics
• White Paper : “Hot Topics in
Ultra-Peripheral Ion Collisions”,
G. Baur et al (Erice Oct 2001).
– Gluon pdf in A
– Pomeron coupling to A
– Interferometry with short lived
particles.
108
106
104
104
10-12
1
HSM
10-14
0.1
1
10
100
M (GeV)
http://quasar.unibas.ch/upc
• Working group
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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LHC gA (gP) Production
• Cross sections larger
than gg
• Similar low total pT due
to coherence condition
• Heavy Ion Colliders
can be seen as vector
meson factories.
RHIC
Meson
Au
LHC
Pb
Ca

120

12
49
23000

7.9
46
15000
0.058
3.2
780
J/Y
520 230000
Particle rates (Hz) for nominal
Luminosities
(Klein and Nystrand, PRC 60, 014903)
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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Ultra-Peripheral Collisions at STAR
Proof of Principle
UPC in HI is possible
A Premiere
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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Ultra-Peripheral Collisions (UPC)
time
• Nuclei “miss” each other (b > 2RA)
– No hadronic interactions
• Ions are sources of fields
– Photons: ~
 very high fluxes
– Pomerons: A 2 (bulk)- A 4/3 (surface)
(Au Au,
200GeV/nucleon,
University of
Frankfurt)
Z2
Au
• Fields couple coherently to ions
– P < h/RA, ~30 MeV/c for heavy ions
– P|| < gh/RA ~ 3 GeV/c at RHIC
g, P, or meson
Au
Coupling ~ nuclear
form factor
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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Nuclear Excitation
In addition to UPC production, nuclei can exchange one or more
separate photons and become mutually excited.
Au*+n
Au
g
P
Process
g
Au+Au -> Au*+Au* + UPC
Au
Au*+n
•It is thought to factorize as function of impact parameter
•Decay yields neutrons at zero degrees wrt beam direction (ZDC)
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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A typical STAR event
sqrt(s)=200 GeV/A
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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 Analysis Selection
Minbias
•
•
•
•
2 +/- Primary Tracks
rvert< 15 cm, |zvert|<200 cm
Transverse Angle > 2.7 rad
Total pT<0.2 GeV
UPC Trigger
As Minbias plus anti-cosmic cut:
Opening Angle < 3 rad.
Pablo Yepes, Rice U.
Backgrounds:
– incoherent photonuclear interactions
– grazing nuclear collisions
– beam gas
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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‘Minimum Bias’ PT
0 PT
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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0 lineshape
STAR gAu --> (0 + p+p- )Au
ZEUS gp --> (0 + p+p- )p
Set =0 for STAR
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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First Glance at 2001 Data
• Around 10 times
more minbias events
Minbias
Pablo Yepes, Rice U.
• Dedicated trigger for
UPC running for
several weeks
Triggered
CMS Heavy Ion Workshop, MIT Feb
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• CMS triggers on energy
in the calorimeters.
• Monte Carlo study
requires: 2 particles
with energy > 1 GeV in
|h|<3
• Trigger Eff:
Efficiency
Can we trigger on those events?
 : ~20%
 : ~20%
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
Invariant Mass (GeV)
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Conclusions
• Active community in UPC, with lots of
physics topics.
• UPC seen at RHIC in the , ee channel.
• Large rates at LHC
• CMS large coverage will be ideal to look at
these events. Lower field would help.
• ZDC a must for UPC physics
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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ET per Crystal in Endcap ECAL
in PbPb
Central
Minbias
Pablo Yepes, Rice U.
CMS Heavy Ion Workshop, MIT Feb
9, 2002
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ET per Cell in HCAL in PbPb
Hijing, minbias 30k particles
Pablo Yepes, Rice U.
Hijing, central 70k particles.
CMS Heavy Ion Workshop, MIT Feb
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Max
50
processed
events
9, 2002