Transcript STATUS TRD COOLING TRD STATUS MEETING FEBRUARY 2006

Exploring the LHC Medium with
Electromagnetic Probes
A. Marin (GSI)
A.Marin (GSI), Hard Probes 2008
7/17/2015
Heavy Ion collisions
Transition from hadronic to quark matter
Possible Chiral symmetry restoration
LHC
Observables:
Photons and di-electrons
Exit medium unscattered
Carry information on the
entire history of the
collision
P.Braun-Munzinger, J. Stachel
A.Marin (GSI), Hard Probes 2008
7/17/2015
LHC: Entering a new regime
SPS
RHIC
LHC
√sNN (GeV)
17
200
5500
dNch/dy
430
730
1000-4000
t0QGP (fm/c)
1
0.2
0.1
T/Tc
1.1
1.9
3.0-4.7
e (GeV/fm3)
3
5
15-60
tQGP (fm/c)
≤2
2-4
≥10
tf (fm/c)
~10
20-30
15-60
Vf(fm3)
few 103
few 104
few 105
Cross-sections of interesting probes expected to increase by factors
~ 10 ( cc ) to
~ 102 ( bb ) to
~ > 105 (very high pT jets) ; Hard probes of the medium accessible at LHC
Direct photons are abundantly produced at LHC
A.Marin (GSI), Hard Probes 2008
7/17/2015
Direct photon sources
q
g
q
γ
qg Compton Scattering
γ
g
q
g
q
γ
q
q
g
qq Annihilation
q
g
γ
q
Bremsstrahlung,
fragmentation
Thermal photons from QGP and hadron gas
Photons from Jet re-interaction in the medium
...in a large background from p0 and h decays
A.Marin (GSI), Hard Probes 2008
7/17/2015
How many direct photons?
10k/year
Large sample of direct LO g-jet for pT <
30 GeV/c in PHOS
and pT <200850 GeV/c in
A.Marin (GSI), Hard Probes
EMCal …and in central Barrel
… but g/p0 = 0,01-0,1 for pT > 20 GeV/c
We need a good g/p0 PID
7/17/2015
Photon Production: different sources
Turbide, Gale, Jeon, and Moore
PRC (2004) 014906
Photons are abundantly produced at LHC
Jet-photon conversion in the plasma dominates 8<pT<14 GeV
Prompt hard NN scattering dominant for p T>20GeV at LHC
A.Marin (GSI), Hard Probes 2008
7/17/2015
How can we distinguish different
photon sources?
 Prompt : RAA = 1, v2=0 ( azimuthal anisotropy)
 Fragmentation: RAA<1, v2>0
 Thermal, Bremsstrahlung, Jet Conversion: RAA>1, v2<0
RAA >1 and v2<0
unambiguous signature of
medium produced photons
W.Liu, R.J.Fries nu-th/0801.0453
A.Marin (GSI), Hard Probes 2008
7/17/2015
Why photon-tagged jets?

Medium effects redistribute (q
^ L ) the parton
energy, Ejet, inside the hadron jet
(multiplicity, jT).

Redistribution can be best measured with the
Fragmentation Function... If we know Ejet.

HI environment hinders precise
If we measure Eg ≈ Ejet
1/Njet dN/d
reconstruction of Ejet.
Borghini,Wiedemann, hep-ph/0506218
Quenching increases
low-pT particles
  ln(
E
p
Quenching reduces
high-pT particles
A.Marin (GSI), Hard Probes 2008
7/17/2015
)  ln(
1
z
)
First Physics at LHC : From pp to Pb–Pb
 first pp run (starting end of this summer)




important pp reference data for heavy ions
test of pQCD
minimum bias running
unique pp physics with ALICE (PID , tracking to very low p T )
 early heavy-ion run
 establish global event characteristics
 bulk properties (thermodynamics, hydrodynamics… )
 start of hard probe measurements
A.Marin (GSI), Hard Probes 2008
7/17/2015
ALICE
ATLAS
CMS
Experiments at the LHC
A.Marin (GSI), Hard Probes 2008
7/17/2015
ALICE: The dedicated HI Experiment
A.Marin (GSI), Hard Probes 2008
7/17/2015
ALICE: dedicated Heavy ion experiment at LHC
•excellent particle ID up to ~ 50 to 60 GeV/c
•Most (2p * 1.8 units h) of the hadrons (dE/dx + ToF), leptons (dE/dx, TOF, transition
radiation) and photons (high resolution EM calorimetry, conversions);
•Track and identify from very low (< 100 MeV/c) up to very high pt (>100GeV/c);
•Identify short lived particles (hyperons, D/B meson) through secondary vertex detection;
A.Marin (GSI), Hard Probes 2008
7/17/2015
The ATLAS Detector
•
•
•
Inner tracking, EM and Hadronic calorimeters, external muon spectrometers
Full azimuthal acceptance in all detectors
Large pseudorapidity coverage
A.Marin (GSI), Hard Probes 2008
7/17/2015
The CMS Detector
h = 10 for Calorimetry
h = 5 for Si tracker
2p
Capabilities
High-precision tracking over h < 2.5
Muon identification over h < 2.5
High resolution calorimetry over h < 5
Forward coverage
Large bandwidth: DAQ + Trigger
Very well suited for HI environment
J.Phys.G34:2307-2455,2007
A.Marin (GSI), Hard Probes 2008
 Large (mid-rapidity) acceptance
(tracker and calorimetry)
 DAQ+HLT will inspect
every single Pb+Pb event
 Large statistics for rare probes
Photon Detectors at LHC
Exp.
Name
Structure
Coverage
Granularity
h xf
Resolution
ATLAS
LAr Barrel
LArEndCap
Liquid Argon
0<|h|<1.4
2p
0.003x0.100
0.025x0.025
0.025x0.050
10%/√E 
0.5%
1.4<|h|<3.2
2p
0.025x0.100
0.025x0.025
0.025x0.050
10%/√E 
0.5%
A.Marin (GSI), Hard Probes 2008
CMS
ECAL(EB)
ECAL(EE)
PWO+APD
0<|h|<1.5
2p
1.5<|h|<3.
2p
0.017x0.017
0.017x0.017
to
0.05x0.05
2.7%/√E 
0.55%
5.7%/√E 
0.55%
ALICE
PHOS
EMCal
Barrel
PWO+APD
Pb+APD
TPC+ITS+
TRD+TOF
0<|h|<0.12
0.6p
0<|h|<0.7
0.6p
(0<|h|<0.9
2p)*
7% X/X0
0.014x0.014
3.10-4x 2.10-4
0.004x0.004
(resolution)
3.3%/√E 
1.1%
7%/√E 
1.5%
7/17/2015
2% low p T
5% high p T
Photon conversions in ALICE
 Identify photons converting in the
Beam Pipe, ITS and TPC
 Clean photon identification
 Provide directional information
Non vertex background (important source
of systematic errors in measurement of
direct photons) can be rejected.
TPC
ITS
 Good momentum resolution for
charged tracks at low pT
 Can be also use at high pT.
The use of L1 TRD trigger under investigation
Independent measurement of the same
quantities, with different systematics
compared to PHOS/EMCAL.
A.Marin (GSI), Hard Probes 2008
7/17/2015
p0 , h through conversions
6.3x10-4 p0 recons./event
p0
h
(not corrected for efficiency/accep.)
p0 reconstructed down to pT~0.4 GeV
Main systematic error is the material budget
p0 , h can be measured in first pp collisions
A.Marin (GSI), Hard Probes 2008
7/17/2015
First pp physics at 10/14TeV with PHOS
√s (TeV)
L (cm-2s-1)
T (s)
10TeV
0.5 ×1029
30 days
(effective run time is
30*(1/10))
h × f = 0.24 × 20°
1 PHOS module
A.Marin (GSI), Hard Probes 2008
eg = 0.9
7/17/2015
Identifying prompt g in ALICE (PHOS)
Y. Mao, Poster QM2008,
ALICE-INT-2007-021
 pp




R = 0.3, SpT < 2 GeV/c
Efficiency: 69%
Background rejection: 1/170
First year (10 pb-1)
 3000 g (Eg > 20 GeV)
 PbPb




R = 0.2, pTthresh = 2 GeV/c
Efficiency: 50%
Background rejection: 1/14
One month of running
 2000 g (Eg > 20 GeV)
5
signal
G. Conesa et al., NIM A 580(2007) 1446,
NIM A 585(2008) 28
A.Marin (GSI), Hard Probes 2008
7/17/2015
ALICE: Photon-Tag Jets Fragmentation
Function
Y. Mao, Poster QM2008,
ALICE-INT-2007-021
pp
Imbalance distribution
A.Marin (GSI), Hard Probes 2008
G. Conesa et al., NIM A 580(2007) 1446,
NIM A 585(2008) 28
PbPb
Isolated photons and
background subtracted
7/17/2015
ALICE: g-tagged FF RAA
Systematic errors due
to jet(p0)-jet background
Charged + EM
R AB 
dN
T AB
P
AB
 d  NN
P
C
G. Conesa et al., NIM A 580(2007) 1446,
NIM A 585(2008) 28
With error quenched p0
Sensitive to medium modifications at low z
if larger than ~5%.
A.Marin (GSI), Hard Probes 2008
7/17/2015
CMS: Photon identification performance
Photon ID: ECAL+HCAL+tracker
Working Point at 60% efficiency
96.5% background rejection
Quenched Pb+Pb
Before cuts:
S/B=0.3
After cuts:
S/B=4.5
WP=60% Seff
Photon isolation and shape cuts improve S/B by factor ~15
C. Loizides nucl-ex/0804.3679v1
A.Marin (GSI), Hard Probes 2008
CMS: Jet-fragmentation functions
reconstruction via g-jet
arXiv:0804.3679v1;nucl-ex
▪ Medium mod. FFs measurable for z<0.7 & 0.2 << 5 with high significance
▪ Syst. uncertainties dominated by (low) jet reconstruction effic. 30-70 GeV
A.Marin (GSI), Hard Probes 2008
7/17/2015
EM Layer 1 ET (GeV)
g+Jet in ATLAS
g
Δη×Δϕ = 0.003x0.1
One (of 64) rows
in barrel EM
calorimeter 1st
sampling layer
h
and p 0 separation for ET<70
GeV
Isolated photon gives clean signal
in EM first sampling layer
Even in central Pb+Pb !
g
A.Marin (GSI), Hard Probes 2008
7/17/2015
dN / d h  2700
N. Grau for the ATLAS Collaboration,
QM2008, Arxiv:0805.4656,nucl-ex
1/N dN/dpT

ATLAS: Direct Photon Spectrum
ATLAS simulation
Reconstructed spectra not corrected for
efficiency and energy resolution.
A.Marin (GSI), Hard Probes 2008
 Resulting spectrum from
combining shape and
isolation cuts
 e ~ 50-60%
 Assuming RAAh/RAAg = 1
 ~200,000 direct
photons/LHC year above
30 GeV with S/B>1
(factor 5 supression)
 Large rates because of ET
reach and h coverage
7/17/2015
ATLAS: Jet Fragmentation Function
N. Grau for the ATLAS Collaboration,
QM2008, Arxiv:0805.4656,nucl-ex
 Discriminate between energy-loss models
 Few hard vs. many soft gluons
ET > 70 GeV
ATLAS Simulation
A.Marin (GSI), Hard Probes 2008
ATLAS Simulation
7/17/2015
New Approach Di-Lepton Tagging
Srivastava, Gale, Awes - PRL C 67 (2003) 054904
 Tag with virtual photon that
decays into a dilepton !
q+q  g*+ Jet  l+l- +Jet
 Background: Drell-Yan and
Semileptonic Heavy Quarks

DIRECT ENERGY LOSS MEASUREMENT
 Tag gives the pT of the hard scatter
A.Marin (GSI), Hard Probes 2008
7/17/2015
CMS: g, g* and Z tagging of jet production
dimuon trigger
away
side
g
g*
Heavy quark dimuon (dominant) background can be
rejected by a secondary vertex cut.
Resolutions: 50 mm in radius and 20 mm in f
associated
hadrons
Z0+jet
A.Marin (GSI), Hard Probes 2008
7/17/2015
CMS: Z0 tagged jets
 Z0 tags look very promising
 Signal to background ratio
is good above 20 GeV/c
A.Marin (GSI), Hard Probes 2008
7/17/2015
Why very low mass dileptons?
p
 Start from Dalitz decay
 Calculate invariant mass distribution of Dalitz
2
2
pairs 1 dN
4m
2m
2
1
N g dm ee

3p
invariant mass of
Dalitz pair
1
e
2
mee
(1 
e
2
ee
m
invariant mass of
virtual photon
qq
0
R. H. Dalitz 1951 ;Proc. Phys. Soc. A 64, 667-669
ee
g
Compton
Compton
)
mee
g
*
g
p
0
g*
g
gg
2
F (m ) (1 
form factor
2
ee
qq
eg+
e-
e+
e-
2
mee
M
2
)
3
phase space factor
 Now direct photons
 Any source of real g
produces virtual g with very
low mass
 Rate and mass distribution
given by same formula
 No phase space factor
for mee<< pT photon
A.Marin (GSI), Hard Probes 2008
7/17/2015
In Practice
÷
÷
÷
200-300 MeV
140-200
90-140
0-30
Rdata
 Material conversion
pairs removed by
analysis cut
 Combinatorics
removed by mixed
events
 Calculate ratios of various Minv bins to lowest one: Rdata
 If no direct photons: ratios correspond to Dalitz decays
 If excess: direct photons
A.Marin (GSI), Hard Probes 2008
7/17/2015
Direct photons in AuAu at √sNN=200GeV
nucl-ex:0804.4168v1
•pp consistent with
NLO pQCD calculations
•AuAu larger than calculation
for pT<3.5GeV/c
A.Marin (GSI), Hard Probes 2008
Excess exponential in pT
T=221± 23(stat)±18(sys) MeV
7/17/2015
ALICE: Virtual photon spectrum
Uses Central Barrel: (ITS,TPC, TRD,TOF)
pp
PbPb
(Analysis performed in 0.2<mee<0.6 GeV)
Expected rates for 1 year statistics
Access to low pT photons
A.Marin (GSI), Hard Probes 2008
7/17/2015
Conclusions and Outlook
 The LHC experiments are finally a reality. First pp beams in
summer, PbPb in 2009
 With LHC we enter in a new era:
 The energies reached at LHC will be ~30 times larger than RHIC
 The Quark Gluon plasma formed will be hotter, larger and live longer
 Cross sections for electromagnetic probes are large.
 They will provide the medium characteristics: fragmentation function
using g tagged jets, energy loss mechanisms
 The very low mass dileptons extend the direct photons measurement to
very low pT .
 ALICE, ATLAS and CMS will provide independent results,
complement each other.
Essential to understand the new system
Thanks to my ALICE colleagues
and to CMS and ATLAS for providing material for this talk
A.Marin (GSI), Hard Probes 2008
7/17/2015
Backup
slides
A.Marin (GSI), Hard Probes 2008
7/17/2015
g and p0 predictions for p+p at LHC
Start up scenario : 2 PHOS modules (f=40, y=0.25)
L=1030 cm-2s-1 ;T=10 days=8.6105 s; LT= 8.6 108 mb-1
3·108 events/GeV at 1-2 GeV/c
8 events/GeV at 35 GeV/c; 38 events/GeV at 50 GeV/c
de+e- /(dpt dy)~=Ce+e- dg /(dptdy)
P. Aurenche et al.
75 counts
15 counts
35
A.Marin (GSI), Hard Probes 2008
50
7/17/2015
Available data on direct (isolated) photon
production in p+p and p+p
A.Marin (GSI), Hard Probes 2008
7/17/2015
LHC: entering a new regime
Hard processes contribute significantly to
the total
AA cross-section (σhard/σtot = 98%):
Bulk properties dominated by hard
processes;
Very hard probes are abundantly
produced.
Weakly interacting probes become
accessible (g, Z0 , W±).
A.Marin (GSI), Hard Probes 2008
7/17/2015
Momentum/ angular resolution
A.Marin (GSI), Hard Probes 2008
7/17/2015
ALICE compared to other LHC detectors
Relatively low magnetic field
Low momentum cut-off
20
30
CMS pTmin ~0.2
A.Marin (GSI), Hard Probes 2008
7/17/2015
Event rate estimation
(L.Benhabib)
√s (TeV)
10TeV
0.5 ×1029
L (cm-2s-1)
30 days
(effective run time is 30*(1/10))
T (s)
h × f = 0.24 × 20°
1 PHOS module
eg = 0.9 (assuming there is NO material
in front of PHOS!)
A p0(pt)
dN
dp t
 L int 
d
dp t
 Ag , p 0  e
Calculated with INCNLO program
7/17/2015
10 GeV/c < pt < 100 GeV/c
pt < 10 GeV/c
A.Marin (GSI), Hard Probes 2008
(p0 + p1 pt)(1- e-(pt- p2)/ p3 ) )
p0 = 0.042
p1 = 0.0013 c/GeV
p2 = 0.55 GeV/c
p3 =1.25 GeV/c
p0 = 0.064
p1 = 0.0012 c/GeV
p2 = 14 GeV/c
p3 =12 GeV/c
7/17/2015
41
Photon Detection in ALICE
 PHOS (1000 x 0.24 in h)
 high resolution (energy and spatial)
 small coverage
 EMCal
 larger coverage: 120O x 1.4 in η
 coarser spatial resolution than PHOS
 gZ→ e+e- Conversions (Central Barrel)
 large coverage: 360O x 1.8 in h
 low conversion probability (8-12%)
A.Marin (GSI), Hard Probes 2008
Expected direct photon excess over decay
photons
NLO pQCD+Hydro, hep-ph/0311131
A.Marin (GSI), Hard Probes 2008
7/17/2015
g and p0 predictions for Pb+Pb at LHC
Start up scenario : 2 PHOS modules (f=40, y=0.25)
L=1026 cm-2s-1;T=10 days=8.6105 s; LT= 8.6 104 mb-1
7·107 events/GeV at 1-2 GeV/c;
50 events/GeV at 35 GeV/c; 40 events/GeV at 50 GeV/c
50 counts
40 counts
35
A.Marin (GSI), Hard Probes 2008
50
7/17/2015
45
PHOS: Feasibility,Statistics/Systematics
 One warm (not-cold) PHOS module
 Capable to measure p0
 Estimate of the statistics.
500kp0/109events
@14TeV(by Hisa)
• Systematic error estimation
• Extrapolation from PHENIX
• Largest ones are from raw p0 yield
extraction and energy scale
A.Marin (GSI), Hard Probes 2008
Extrapolate from
PHENIX (by Dmitry)
7/17/2015
Tagging jet with photon
ALICE-INT-2005-014
 Strategy (event by event):


Search identified prompt photon
largest pT (E g > 20 GeV).
Search leading particle :



(PHOS)
with

R
fg-fleading180º
Eleading > 0.1 Eg
leading
Particles around the leading with pT > 0.5 GeV/c,
inside a cone of R = 0.3.
2 configurations: charged and neutral hadrons
(TPC+EMCAL) and charged only (TPC).
A.Marin (GSI), Hard Probes 2008
fmax
EMCal
Reconstruct the jet:

fmin
TPC
7/17/2015
IP
g
PHOS
Fragmentation function
Yaxian M. poster QM2008
pp
A.Marin (GSI), Hard Probes 2008
PbPb
7/17/2015
CMS Photon ID: Isolation and cluster
shape cuts
*
 Identification
 10 cluster shape
variables
 based on ECAL
 10 isolation variables
 based on ECAL/HCAL
 Track-based cut
Prompt
photon
ECAL
p0
ECAL
 Selection
 Total of 21 variables
grouped into 3 sets
 Linear discriminant
analysis (Fisher) and
cut optimization using
TMVA
HCAL
HCAL
TMVA: http://tmva.sourceforge.net
A.Marin (GSI), Hard Probes 2008
*) Maximum set to 10
CMS Studies - Gamma*

Signal and heavy quark background
 At LHC the gamma* tags are difficult
 (unless there is strong heavy quark suppression)
A.Marin (GSI), Hard Probes 2008
7/17/2015
Results at RHIC energies
A.Marin (GSI), Hard Probes 2008
7/17/2015
5
Dileptons in Heavy Ion Collisions
Time
time
g
p f Jet p K g p
e L cc m
freeze-out
Expected sources

Light hadron decays



Dalitz decays p0, h
Direct decays r/w and f
Hard processes


Charm (beauty) production
Much larger at RHIC than at SPS
hadronization
formation and
thermalization
of quark-gluon
matter?
hard parton scattering
Space
Au

Photons and dileptons: radiation from the media




Au
direct probes of any collision stages (no final-state interactions)
large emission rates in hot and dense matter
according to the VMD their production is mediated in the hadronic phase
by the light neutral vector mesons (ρ, ω, and φ) which have short life-time
Changes in position and width: signals of the chiral transition?
A.Marin (GSI), Hard Probes 2008
7/17/2015
Dileptons from jet-thermal interactions
•Jet-thermal as large as
DY/heavy quark decay
(RHIC)
•Jet-thermal still as large as
DY. S/B could improve with
harder pT cut.
•At RHIC, there is a
contribution to the IM region
•In-medium jet
bremsstrahlung will also add
to the signal
•No heavy quark energy loss
•Signal as large as it is for
photons
A.Marin (GSI), Hard Probes 2008
Turbide, Gale, Srivastava, Fries, PRC (2006)
7/17/2015
CMS: Photon identification performance




Photon ID:
ECAL+HCAL+tracker
Set working point
to 60% signal
efficiency
WP
p+p
Pb+Pb
Leads to 96.5%
background
rejection
Training is done on
unquenched
samples only
A.Marin (GSI), Hard Probes 2008
11-Dec-2007
CMS: Jet-fragmentation functions
reconstruction via gamma-jet
Unquenched
Quenched
 Major contributions to systematic uncertainty (added in quadrature)
–
Photon selection and background contamination (15%)
–
Track finding efficiency correction (10%)
–
Wrong/fake jet matches (10%)
–
Jet finder bias (largest contribution in quenched case)
A.Marin (GSI), Hard Probes 2008
No or small 
dependence
CMS: Fragmentation function ratio
Reco quenched Pb+Pb / MC unquenched p+p
ETg >70GeV
ETg >100GeV
 Medium modification of fragmentation functions can be
measured
 High significance for 0.2 < ξ < 5 for both, ETg >70GeV and ETg >100GeV
A.Marin (GSI), Hard Probes 2008
ATLAS: Identified Photon S/B
ATLAS simulation
ATLAS simulation
 Recall from NLO pQCD S/B = 1/20-1/10
 If RAAh/RAAg~0.2, S/B>1 for ET>30 GeV
A.Marin (GSI), Hard Probes 2008
7/17/2015
ALICE: Z0 reconstruction
R. Bailhache, Poster QM2008
Z0 +jet also under study in ALICE
(P. Constantin)
A.Marin (GSI), Hard Probes 2008
7/17/2015
Dileptons from jet-thermal
interactions
•Dilepton from jet-medium interactions will be more important at LHC
than at previous lower energies
•New way to access information about the temperature and partonic nature
of fireball
nucl-th:0707.0261v1
A.Marin (GSI), Hard Probes 2008
7/17/2015