Low mass diffractive systems at LHC

1
Low mass diffractive systems at LHC

• ALICE detector
• Diffractive gap trigger in ALICE
• Signatures of Pomeron
• Signatures of Odderon
• Photoproduction of heavy quarks
• Conclusions, outlook

2
The ALICE experiment
Acceptance central barrel -0.9 lt h lt 0.9
HMPID
TRD
MUON SPEC.
ITS
TPC
Acceptance muon spectr. 2.5 lt h lt 4.
TOF
PHOS
3
ALICE diffractive gap trigger
g additional forward detectors (no
particle identification)
1 lt h lt 5
-4 lt h lt -1
g definition of gaps h , h_
Luminosity L 5x1030cm-2s-1
g one interaction/ 80 bunches
diffractive L0 trigger (hardware)
gap h 3 lt h lt 5 g Dh 0.5
gap h- -2 lt h lt -4 g Dh 0.5
high level trigger (software)
-3.7 lt h lt 5
4
ALICE forward calorimeter

• neutron calorimeter on each side
• Placed at 116 m from interaction region
• Measures neutral energy at 0o
• Diffractive events
• pp g ppX no energy in zero degree
  calorimeter
• pp g pNX energy in one calorimeter
• pp g NNX energy in both calorimeters

( no Roman pots for proton tagging )
5
Acceptance LHC experiments

• ALICE
• trigger central barrel tracks pT gt 500 MeV/c (
  gap trigger)
• Electron identification in TPC, TRD
• tracking inner detectors gt 50 MeV/c
• CMS
• calorimeter trigger gt 4 GeV
• muon trigger gt 3.5 GeV/c
• Tracking inner detector gt 0.3 GeV/c

ggood ALICE acceptance for f, J/Psi, Y by
electron decays
6
ALICE pseudorapidity acceptance

• ALICE acceptance matched to diffractive central
  exclusive production

central barrel
Dh 4
Dh 3
f
gap
had
gap
h
7
Pomeron signatures

• Compare pomeron-pomeron fusion events to min bias
  inelastic events
• 1) Enhanced production cross section of glueballs
  states study resonances in central region when
  two rapidity gaps are required
• 2) Slope pomeron traj. a 0.25GeV-2 in DL fit,
  a 0.1GeV-2 in vector meson production at HERA,
  t-slope triple pom-vertex lt 1GeV-2
• g mean kt in pomeron wave function a 1/kt2
  probably kt gt 1 GeV
• g ltpTgt secondaries in pomeron-pomeron gt
  ltpTgt secondaries min bias
• 3) kt gt 1 GeV implies large effective
  temperature
• g K/p, h/p, h/p ratios enhanced

8
The Odderon

• Consider processes a b g a b, amplitude
  Aab(s,t)
  a b g
  a b, amplitude Aab(s,t)
• Define A(s,t) ½ ( Aab(s,t) Aab(s,t))
• g Aab(s,t) A(s,t) A (s,t)
• Aab(s,t) A(s,t) A (s,t)
• A identical for both processes, positive
  C-parity Pomeron
• A changes sign, negative C-parity Odderon,
  (Photon)
• g mesonic reggeon contributes to A
• g Odderon is part of A which doesnt vanish
  rapidly with s

9
Signature Odderon cross section

• Look at exclusive processes with rapidity gaps
• Examples

diffractive pseudo scalar and tensor meson
production C 1 states
diffractive vector meson
production C -1 states
g measure cross sections
10
The hunt for the Odderon

• Production cross sections in pp at LHC energies
• diffractive production p0,h,hc(JPC0 ),
  f0(0), a2(2)
• g contributions from Photon-Photon,
  Photon-Odderon, Odderon-Odderon
• Look for diffractive J/Y production JPC 1
• g Photon-Pomeron, Odderon-Pomeron
  contributions
• g such an experimental effort is a continuation
  of physics programs carried out at LEP (gg) and
  HERA (g-Odderon)

11
Odderon experimental status

• Odderon searches at HERA
• gp g ppo published, no signal found
• gp g phc analysis ongoing ?
• Weak evidence for Odderon by comparing pp and pp
  scattering data at CERN-ISR at sqrt(s) 53 GeV
  in the dip region at t 1.5 GeV2
• LHC How large are cross sections ? Interference
  effect
• Donnachie, Dosch, Landshoff, Nachtmann Pom
  eron physics and QCD The continuing
  non-observation of the Odderon would have a
  major impact on our understanding of
  diffractive phenomena

12
Diffractive J/Y production in pp at LHC

• First estimates by Schäfer, Mankiewicz, Nachtmann
  1991
• pQCD estimate by Bzdak, Motyka, Szymanowski,
  Cudell
• Photon t-integrated 15 nb
  (2.4 - 27 nb)
• Odderon t-integrated 0.9 nb
  (0.3 - 4 nb)

ds
dy
y0
ds
dy
y0

• At L 5x1030 cm-2s-1
• 0.15 J/Y in ALICE central barrel in 1 s,
  150k in 106 s
• 9000 in ee- channel in 106 s

g identify Photon and Odderon contribution by
analysing
pT distribution ( Odderon harder pT spectrum )
13
Signature Odderon interference

• Cross sections contain squared Odderon
  amplitudes
• g Odderon-Pomeron interference !

ds Ag(AP AO) 2 dNq AP 2
2Re(APAO) AO 2

• look at final states which can be produced by
  Odderon or Pomeron exchange
• find signatures for interference of C-odd and
  C-even amplitude

14
Interference signal

• Interference effects (relative contribution C
  1)
• Asymmetries in pp and KK pairs (C 1) in
  continuum
• charge asymmetry relative to polar angle of p in
  dipion rest frame
• C-even Psum sum of transverse momenta of p,p
• C-odd Pdiff difference of transverse momenta
  of p,p
• look at distribution of angle a (Pdiff relative
  to Psum)
• C-transformation a g a p
• g signature in coefficients of Fourier series
  eina

15
Incl. heavy quark photoproduction in pp _at_ LHC

• Photoproduction of QQ
• photon fluctuates into QQ,
• Interacts as color dipole
• sdip(x,r) 2 d2b1-S(x,r,b)
• S matrix element S(x,r,b)exp(-r2
  )
• QQ-production cross section in pp-collisions
• s(pp gQQ pp) 2 sgpgQQ(Wgh)dw

geff
Qs2(x,b)
S0black disk S1color trans
4
dngp(w)
dw
Goncalves, Machado Phys. Rev. D (2005)
16
Diffractive Photoproduction of heavy quarks

• Advantage of diffractive photoproduction
• Clear final state defined by two rapidity gaps

Goncalves, Machado Phys. Rev. D75 (2007)
pPb mode L 1029 cm-2s-1 g R (cc) 5 Hz
Acceptance 10 , Efficiency 50
g R(cc)20k per day
Heavy quarks can also be produced by central
exclusive diffraction, ie two pomeron fusion g
harder spectrum of quarks, hence could be
disentagled in pT spectrum
17
Conclusions, outlook

• ALICE has unique opportunity to do diffractive
  physics
• Diffractive trigger defined by two rapidity gaps
• Neutron tagging at zero degree
• Phenomenology of Pomeron/Odderon
• Photon-Photon physics

18
Photoproduction of heavy quarks in pA/AA

• gp cross section is input to pA/AA coherent
  process
• s(pA gQQ pA) sgpgQQ(w)dw

dngA(w)
dw
pA _at_ LHC
Goncalves, Machado Phys. Rev. C (2006)
PbPb _at_ LHC
Goncalves, Machado EPJC 31 (2003)
19
Trigger rates

• pp _at_ 14 TeV L 5x1030 cm-2 s-1

TOF TOF MULT, NV0 V0A mult V0C mult
non-

diffractive

diffractive

S/B
PYTHIA
resonance
g different downscaling for NV00, NV00 topology
prod J/Y,Y
g need additional TRD L0 inputs to CTP