PHENIX plans for RHIC low energy run

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PHENIX plans forRHIC low energy run

• Takao Sakaguchi
• Brookhaven National Laboratory

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Phase transitions where?

• Deconfinement, chiral restoration

3
What is good and what is bad?

• Needs strong support from theoretical groups

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Signals

• Shoji Nagamiyas schematics on phase transition
• Most of them have been measured
• Havent found critical behavior in any of
  observables
• Whats missing were
• Prompt photon production
• Jet quenching
• di-hadron, ?-hadron correlations
• Mostly high pT business

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To begin with

• Low energy scan program is an important and
  integral part of the PHENIX Physics program
• No observables become more easily accessible
• S/B may become better, but the signal of interest
  would move toward the pT region where S/B is
  worse
• S/B may become better, but the measurement would
  become statistically starved
• Mid-pT at vs200GeV corresponds to high pT at
  vslt40GeV
• Almost no observables that manifest specifically
  at low energies
• And, lower luminosity below injection energy
  would even make cases difficult
• So, what would be observables?
• Fluctuations
• On ltpTgt, ltK/pgt, ltpbar/pgt, ltv2gt, ltNgt
• K/p and pbar/p provides the location off the
  system in phase diagram
• Correlations (See J. Mitchells talk in detail)
• Longitudinal density correlations, low-pT
  multi-particle correlations

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New but old, old but new..?
Going up and coming down in ?s made a job

• RAA excitation function energy loss
• p,K,p, electrons (decayed from heavy quarks)
• Also di-hadron correlation if statistics allows
• Quark number scaling of v2
• Temperature
• Thermal photons, di-electrons
• And, some baseline measurement
• Dont forget pp and pA
• 22GeV pp is needed to complete 22GeV CuCu
  program

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Issue for low energy measurement

• Trigger and its efficiency
• We have Beam-Beam Counter (BBC) located at
  3.1ltylt3.9
• Very low multiplicity at this high ? region in
  low vs
• 0.5Hz trigger rate at 9GeV, 3 of the recorded
  data were good collisions
• Expect Machine improvement
• Z vertex 120-150cm -gt 60cm with RF
• Electron cooling
• Centrality definition
• BBC will pick particles from fragmentation region
• Hard to correlate BBC signal with centrality of
  collisions

PHOBOS, PRL102, 142301(2009)
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PHENIX detector
HBD
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New trigger devices

• RXPN detector already installed (should be taken
  out when VTX comes in
• VTX detector can be used as a trigger device
  covering large region of ?
• Without VTX detector, we can not measure PID
  spectra below injection energy
• A simple trigger scintillator (?) that covers
  around beam pipe would also be useful

HBD
tracking
EMC
0 f coverage 2p
tracking
EMC
MPC, BBC
MPC, BBC
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-3 -2 -1
0 1 2
3 rapidity
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RXPN detector

• Covering 1ltylt2.8 for north and south sides
• Already installed and is in operation

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Silicon Vertex (VTX)
VTX barrel hlt1.2

• VTX silicon VerTeX barrel tracker
• Fine granularity, low occupancy
• 50mm425mm pixels for L1 and L2
• R12.5cm and R25cm
• Stripixel detector for L3 and L4
• 80mm1000mm pixel pitch
• R310cm and R414cm
• Large acceptance
• hlt1.2, almost 2p in f plane
• Standalone tracking

FVTX endcaps
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Physics possibility and rates

• 10-hour-days to accumulate 1M evts
• Minimum assume 100 purity, and a factor of 1.8
  improvement in luminosity

Events needed to do good physics
PHENIX also prefers to have 62GeV runs for
di-electron program
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Longitudinal density correlation

• Critical point exist at the Npart80?

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Hadron PID spectra, excitation function of RAA

• Interplay of Cronin effect (initial multiple
  scattering) and energy loss
• Comparing pA and AA data will manifest energy
  loss sector

Phys. Rev. Lett.101, 162301 (2008)
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Electro-magnetic probes?

• Thermal real (virtual) photons
• Past WA98 data can be either explained by
  kT-smearing or higher initial temperature
• No data saw pTgt4GeV, where pQCD photons dominate
• Recent data points at 100MeV available from
  WA98.
• By analysis of correlation strength in
  interferometry

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Hard photons baseline

• Measurement of hard photons is essential in
  determining thermal photon component
• Also, in case we can not measure spectra in pp,
  direct photons will be a good measure of the
  initial condition
• Rate can be estimated using xT scaling

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Scope to low pT virtual photons

• Always the pT region of interest where initial
  condition is reflected.
• New technique developed at RHIC is useful

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Hadron Blind Detector (HBD)
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• Windowless Cerenkov detector with CF4
  avalanche/radiator gas (2 cm pads)

• Designed for low-mass dileptons in AA
• Removes Dalitz and conversion pairs (small
  opening angle)
• Commissioned in Run-9 pp

CsI photocathode covering triple GEMs
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Di-electron measurement

• Both time development and probe selection can be
  done using di-electrons
• Selecting pT and mass region will manifest
  various contributions individually
• With the inclusion of the HBD, PHENIX could get a
  marginal measurement for energies as low as 17.2
  GeV w/ 50 M-evts
• Rate of collisions at this low energy makes the
  collection time for 50 Mevts impractical
• Practical di-electron measurements are at 62.4
  39 GeV.
• Marginal measurements available at 27 GeV.

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Conclusion

• PHENIX has plans to measure many observables that
  may be sensitive to CEP
• Conventional probes as well as new probes
  explored at RHIC
• Penetrating probe is especially useful for
  characterizing collisions at low energies
• A lower bound on initial temperature can be
  measured
• Energy loss of hard may provide info related to
  mB
• Detectors are already up for the plans
• Some trigger devices may strengthen our
  capability on looking at even lower energies

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Backup
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Single non-photonic electrons

• Non-photonic electrons are mostly decayed from
  charm/beauty
• Will contribute understanding energy loss at CP
• Statistics starved measurement

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Di-hadron, gamma-hadron correlation

• Golden channels to investigate opacity of the
  matter
• Idea (Direct ? pT) (away side jet pT)
• Momentum loss of jets can directly be measured
• Subtract p0-h, h-h from (incl g)-h

• Red points integrated RAA from single p0
  measurement (pTgt5GeV/c)
• Blue points Same from g-h measurement (Assoc.
  pTgt5GeV/c)

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Femtoscopy HBT

• Any drastic change in HBT parameters at CP?

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Some Physics perspective

• Fluctuation of particle ratio
• From Jeff Mitchells slide

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Pbar/p

• A prediction from theory. This type of prediction
  is useful from the point of view of experiment

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Low pT photons at RHIC

• PHENIX applied internal conversion technique
• Real photons can convert to virtual photons
• Inv. mass shapes for Dalitz decay of mesons are
  calculable using Kroll-Wada formula
• If MltltpT, the ratio of observed inv. mass to
  expected is proportional to direct photon excess
  ratio
• Take ratio where p0 contribution is small ? S/B
  increases

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Elliptic and hexadecapole flow

• Eta/s as a function of T, uB
• Utilizing an excellent scaling of particle v2,
  eta/s can be obtained

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Critical exponent
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VTX Progress
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Pixel Detector Ladder
Successful DOE review this week
Pixel read-out
Test Beam at FNAL
Installation in 2010
Strip read-out
Strip Detector Ladder
Users Meeting 2009
Stefan Bathe
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v4/v22 ratio
The statistical error and systematic error are
calculated in the same way
Hydro v4/v22 1?
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Application of the probe ?-jet correlation
Run4 g-h become mature, and will more be in Run7

• Idea (Direct ? pT) (away side jet pT)
• Momentum loss of jets can directly be measured
• PHENIX subtract p0-h, h-h from (incl g)-h
• STAR subtract p0-h from (enriched g)-h so that
  near-side associated yield become zero

• Red points integrated RAA from single p0
  measurement (pTgt5GeV/c)
• Blue points Same from g-h measurement (Assoc.
  pTgt5GeV/c)

J. Frantz, M Nguyen, M Conner, J. Chen,
A.Adare, W.Holzmann,B.Cole,J.Nagle, R. Seto
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Isospin effect in direct photon prod. in 200GeV
AuAu and test with 62GeV

• Direct photons suppressed at very high pT?
• Isospin effect is electric charge dependent,
  which affects to photons ?0 is color charge
  dependent

• A theory F. Arleo (JHEP 0609 (2006) 015)
• Isospin effect, in addition to jet-quenching(BDMPS
  ) and shadowing.
• Jet-photon conversion is not taken into account
• Low pT region is underestimated because of lack
  of jet-photon conversion?

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Future topics

• Comparing p0 or direct photons in mid-rapidity
  and forward rapidity would help determining time
  evolution scenario
• Landau expansion will make one order reduction
  at pT4GeV/c at y2 compared to y0 in direct
  photons.
• Direct measurement of CGC and structure function
  (in dAu or pAu)
• Forward calorimeter upgrade in PHENIX (MPC, NCC
  etc.)
• B. Meredith, K. Sedgwick

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What is expected from structure function?
gq -gt?q is main contribution
AuAu minimum bias
Eskola,Kolhinen,Ruuskanen Nucl. Phys.
B535(1998)351
Structure function ratios drop by 20 from x0.1
to 0.2?