pp and pA data as reference point and maybe more

1
pp and pA data as reference point(and maybe
more)

• Karel afarík, CERN
• htpp//home.cern.ch/karel/pppAcapetown.ppt
• Karel.Safarik_at_cern.ch

2
Outlook

• Examples why we needed pp and pA
• NA38, NA50 (NA60)
• J/? suppression
• NA45
• low dilepton mass enhancement
• WA97, NA57
• (anti-)hyperon enhancement
• Historical pA data from 80s
• what we learn ?
• system size dependence
• How it helps at RHIC
• initial vs. final state effect
• What we plan to do at LHC

3
J/? suppression

• NA38/50
• CERN

4
J/? suppression

• NA38/50
• CERN

5
? suppression

• NA38 CERN SPS

6
Low mass dielectrons
7
Strangeness enhancement

• WA97 CERN SPS

8
NA49 strangeness

• K/? ratio in pp and AA

• Energy scan (M.G. horn)

Will have to wait for FAIR (Facility for
Antiproton and Ion Research) confirmation
9
Strangeness in hh

• Data on K/p in hadron-hadron interactions show
  steady (slow) increase with energy

• with multiplicity
• (CERN SppS and FNAL Tevatron)
• Possible explanations
• experimental bias, due to high pt cut-off
• increasing role of gluons for particle
  production
• It is a physical effect
• does this mean deconfinement ?

10
pA data from 80s

• pA collisions (at that time high energies) were
  extensively studied at the beginning of 80s
• predictions for nuclear densities that may be
  achieved in head-on collisions of large nuclei
• A.S.Goldhaber, Nature 275 (1978) 114
• among other also strange particle yields was
  measured
• P.Skubic et al., Phys.Rev. D18 (1978) 3115
• D.Antreasyan et al., Phys.Rev. D19 (1979) 764
• D.S.Barton et al., Phys.Rev. D27 (1983) 2580
• M.G.Abreu et al., Z.Phys. C25 (1984) 115
• W.Busza, R.Ledoux, Ann.Rev.Nucl.Part.Sci. 38
  (1988) 119
• D.H.Bricket al., Phys.Rev. D39 (1989) 2484, 45
  (1992) 734
• C.De Marzo et al., Phys.Rev. D26 (1982) 1019
• I.Derado et al., Z.Phys. C50 (1991) 31 ...

11
Centrality measures

• In pA
• usually
• n A shp / shA (? A1/3)
• assumes that incident nucleon has constant
  x-section during re-scattering
• or just A
• In AA
• number of wounded nucleons (Nw n 1)
• number of participants Np
• sometimes identical with Nw
• sometimes includes nucleons kicked-out in
  secondary re-scattering

12
A-dependence (1/3)

• pion production in central region in pp and pA
• (fits by A.Jacholkowski)

13
A-dependence (2/3)

• kaon production in central region in pp and pA

14
A-dependence (3/3)

• K/p ratio in central region in pp and pA

15
pA versus pp

• all experiments found consistently an increase in
  yield of any secondaries between pp and
  back-extrapolation from pA
• this enhancement sets already at first measured
  nuclei (usually C but is there already for Be !)
• conclusions (from D.S.Barton et al.)
• the A dependence of the inclusive cross-sections
  in projectile fragmentation region exhibits a
  remarkable simplicity
• the A dependence is an universal, independent of
  the outgoing particle, its transverse momentum,
  and the incident energy

16
pA versus pp

• Ratio (strange) / (non-strange) in pA collisions
  independent on A
• however different (higher) than in pp
• Why then there have been claims on common smooth
  increase in enhancement pp ? pA ? AA ?

A.Rybicki QM2004
17
Strangeness Enhancement pp ? pA

• Two alternative definitions
• mostly used
• (yield / Nw)pA E (yield / Nw)pp
• Nw in pA n 1 in pp 2
• yield pA E (Nw / 2) yieldpp E ? (n 1)
  (yieldpp / 2)
• or (H.-G.Fischer NP A715 118c) any produced
  particle is associated to projectile or target
  fragmentation and then put the enhancement factor
  only for projectile fragmentation
• yield pA (n F ? 1) (yieldpp / 2)
• (symbol F invented by F.Aninori, QM2004)

18
Strangeness Enhancement pp ? pA

• If we blame strangeness enhancement on some part
  of the pA event, the enhancement factor (F) has
  to be larger than if we assume enhancement for
  all event (E)
• F E (E 1) ? n
• and increases with n

F
n
19
Strangeness enhancement in pA
Enhancement in pPb / pp up to the factor 3 at xF
0.3 !
But at xF 0.3 pions are at rapidity 2.74 (near
to phase-space limit), kaons not (2.18),
therefore we progressively exhaust pions in more
central pPb pions !
Using xF is justified for studying
fragmentation, which is certainly not all
particle production Using xF for particles with
different masses has no justification !
20
Strangeness Enhancement pp ? pA

• Motivation to separate entire particle production
  into two fragmentation region
• NA49 analysis of various combinations (a, b)
• a p ? b(xF) X
• shows this factorization for net baryon-number
• (where naturally fragmentation at SPS is
  dominated mechanism)
• E910 (D.Cole et al.) reported at low energy a L
  enhancement increasing with n in p fragmentation
  (however, there is a large overlap of the two
  fragmentation regions)
• experiments at 200 GeV (D.H.Brick et al. and C.De
  Marzo et al.) contradict to this finding, they
  blame any increase in L production on nucleus
  fragmentation
• Problems with such separation
• how to do it, let say for anti-X ?
• how to justify it, let say for pA collisions at
  LHC energy ?

21
pp vs. pA enhancement

• trivial reason - difference in pp and pn
  collisions
• there is a difference in isospin which can affect
  yields
• an exercise (just for fun)
• PYTHIA pn versus pp at 100 GeV increses
• ? 1
• anti ? 2
• ? 28
• anti ? 14
• second reason - re-scattering
• increases yield of all produced particles again
  in different way and mostly in target
  fragmentation

22
Long Island
23
Centrality Dependence
Au Au Experiment
d Au Control Experiment
Preliminary Data
Final Data

• Dramatically different and opposite centrality
  evolution of AuAu experiment from dAu control.
• Jet Suppression is clearly a final state effect.

24
Back-to-back jets
25
BRAHMS results CGC ?
PRL 91 072305 (2003)
BRAHMS preliminary

• Qualitative agreement with CGC tendencies.
• Also qualitative agreement with shadowing.
• Look for quantitative results from all RHIC
  experiments.

26
Conclusion from past

• pp, and even more pA, data are indispensable for
  understanding heavy-ion collisions
• and maybe more than that

27
Future ALICE at LHC
28
Use different Ion species to vary the energy
density
central
minimum bias
and pA
29
Is pA possible at LHC ?

• Two independent accelerating cavities ?
• Two-in-one dipoles ?
• implies the same p/m for the two beams
• means in general different velocities
• problem to keep the IP in definite place
• However, we can bump the beam orbit
• how much we need for pPb ?
• cat on equator problem
• at the top energy little bit above 1mm ?
• but at injection above 3cm problem ?
• for dPb is not dramatically better
• needs a study

30
Motivation for pp study

• First insight in pp collisions in new energy
  domain (?s ? 14 TeV), study of evolution of soft
  hadronic physics
• Cosmic ray interactions show knee in 1015?1016
  eV region and ankle in 1018?1019 eV region
• ?s ? 14 TeV corresponds to 1017 eV in lab frame
• We can reach in pp collisions energy densities
  (under conditions of small volume) in excess of
  that in heavy-ion collisions at SPS and
  comparable to RHIC

31
Motivation (cont.)

• Contribution to knowledge of underlying minimum
  bias (background) pp events for other LHC physics
  programmes (Higgs search, B?physics, etc.)
• Provide pp data as a reference for study of other
  collision systems (p-A, A-A)
• Low multiplicity data to commission and calibrate
  various components of ALICE

32
Requirements

• ALICE is relatively slow detector, needs lower
  luminosity
• foreseen max ?? ? ?? m reduce luminosity by
  factor ? 100
• we will need additional factor of 10?30
• To be ready right at the start-up when LHC will
  run with protons at low luminosity
• ALICE should be an integral part of initial pp
  programme
• Have at that time largest possible geometrical
  acceptance both in pseudorapidity and azimuth
• only few secondaries in minimum bias pp collisions

33
Luminosity in pp

• Physics programme requires ? 109 minimum bias pp
  events, readout rate 500 Hz can gives up to 5109
  events per year (107 s)
• Luminosity of ? 1028 cm-2 s-1 and loose
  interaction trigger will do
• Upper limit - no threshold effect, rather
  progressive deterioration of performance
• up to ? 2?1029 cm-2 s-1 ideal situation - one
  event in TPC
• above non-useful (junk) data volume growth
• at about 3?1030 cm-2 s-1 (20 events piled-up in
  TPC) start to pile-up in silicon drift
• (well) above 1031 cm-2 s-1 difficult to handle
  (we reach silicon strip and HMPID integration
  time)

34
Event rate vs. luminosity

• ? ? ?? mb , dNch/d? ? ?

Further we assume L 3?1030 cm-2 s-1
35
Detector Acceptance

• Full ALICE central part (TPC tracking ? ????,
  multiplicity ? ?1.5)
• Forward detectors (FMD from ? 1.7 up to 3.54.7)

36
Comparison ATLAS and CMS

• pt cut-off
• Magnetic field (but this could be lowered)
• Material thickness (hard to change)
• Particle identification (TOF and HMPID)
• ATLAS and CMS have better ? coverage

37
Strangeness production (cont.)

• Statistics for hyperons with same fiducial cuts
  as for heavy-ion collisions
• probably we can do better
• With 109 pp events we may detect few hundreds of
  open charm decays in ?K mode (again using same
  cuts as for heavy-ions)

38
Who carry baryon number

• Standard point of view
• quarks have baryon charge 1/3
• gluons have zero baryon charge
• Baryon number is carried by quarks, not by gluons
• It is not obvious
  (B.Kopeliovich)
• baryon number can be transferred by specific
  configuration of gluon field

39
How baryon number flows ?

• When original baryon change its colour
  configuration (by gluon exchange) it can transfer
  its baryon number to low x without valence quarks

Heavy-ion collision
40
Exchange in t-channel

• Exchange of spin 1/2 (quark)
• ? exp (-1/2 ?y) ( s-1/2)
• strong damping with rapidity interval (i.e. for
  annihilation with energy)
• Exchange of spin 1 (gluon)
• ? const.
• no damping at all
• Q what is actually exchanged ?

q
q
41
Central region at LHC
Asymmetry AB 2 (B anti-B) / (B anti-B)
H1 (HERA) ?? 7
in
9.61(8.63) ? ?
at LHC
(B. Kopeliovich)
42
B-aB absorption in detector

• Asymmetry in cross-section between proton and
  antiproton at few 100 MeV creates the problem
• Lint in front of TPC 5 (and for antiprotons
  10)
• We expect to correct for this effect till 10
  level (using our sophisticated simulation)
• residual systematic 0.5

43
Protons from secondary interactions

• Dangerous beam pipe first layer of tracker
• 1 lint
• For pions this gives 10 increase of protons
  (very low energy)
• To remove it
• impact parameter cut (miss primary vertex)
• cut on pt (protons we anyway detect only from 300
  MeV)
• residual systematic lt 1

44
Asymmetry systematic

• Total systematic
• beam gas
• antiproton absorption
• secondary protons
• S less than 2

45
Statistics needed

• For proton antiproton one needs precision 1
• the effect is about 7, compare to 3 in
  normal case
• using ALICE acceptance, efficiency etc. this
  needs few times 104 minimum bias pp events, i.e.
  something like first 100 sec of running
• Larger effect expected for strange particle,
  Lambda anti-Lambda about 15
• for this few times 105 events will do
• For Omega anti-Omega a huge effect is expected
  (under some assumptions even 100)
• 100 Omegas would be enough for that order of
  107 events
• a good day of running will do it all

46
Conclusions

• ALICE detector has large potential to study
  minimum bias pp physics which will dominate at
  the initial LHC stage
• Minimum bias pp physics is important for both
• its intrinsic interest
• reference for comparison with p-A and A-A
  collisions
• Complete ALICE detector has considerable
  advantages compared to other LHC detectors at low
  luminosity stage
• low momentum threshold
• good momentum and angle resolution
• unique particle identification capability
• ALICE should not miss this opportunity and should
  be ready right at LHC start-up

47
Summary
Looking forward to fill the empty space