# Presentation: 747404

## 
  HOT QUARKS'04

Taos, NM - July 24th, 2004

**  ****HOT QUARKS'04**
- Taos, NM - July 24th, 2004

**David d’Enterria**
**Nevis Labs, Columbia University, NY**

**Relevance of baseline****hard p+p spectra for A+A****and p+A physics at high p****T**

##  

   [ or ... how to bring (part of) the RHIC high pT excitement to SPS energies ]

   [ or ... how to make M.J.Tannenbaum happy ]

   [ or ... how not to make friends in BRAHMS (or CGC “community”) :-) ]

   [ or ... how to make life difficult to PHENIX “photoners” ]

-    [ or ... how to bring (part of) the RHIC high pT excitement to SPS energies ]
-    [ or ... how to make M.J.Tannenbaum happy ]
-    [ or ... how **not** to make friends in BRAHMS (or CGC “community”) :-) ]
-    [ or ... how to make life difficult to PHENIX “photoners” ]

**High p****T**** p+p baseline spectra: Overview**

-    _Case I_:  p+p → π+*X* at √s ≈ 20 GeV
-    Is high pT A+A hadroproduction at SPS enhanced or suppressed ?
-    _Case II_: p+p → π,h± +*X* at √s = 62.4 GeV
-    How accurate are our current ISR-averaged p+p references ?
-    _Case III_: p+p → h± +*X* at √s = 200 GeV at forward y vs pQCD:
-    Is there truly suppresssion in d+Au collisions at η=3.2 ?
-    _Case IV_: p+p → +*X* at √s = 200 GeV
-    Is there a way to disentangle suppressed prompt photons (from quenched
-     jet fragmentation) from enhanced (thermal) photons in Au+Au at RHIC ?

## Case I: p+p high pT reference at √s ≈ 20 GeV  

**Case I: ****p+p high p****T**** referen****ce at ****√s ≈ ****20 GeV  **

## Enhanced high pT production in Pb+Pb @ CERN-SPS ? 

**Enhanced h****igh p****T**** production in Pb+Pb ****@ ****CERN-SPS ? **

- NO p+p  π0 *X *baseline measurement at SPS Pb+Pb energy (√s = 17.3 GeV)
- RAA for central Pb+Pb constructed with 2 different parametrizations:

**WA98 Collab.**
**EPJ C23 (93)225 **
- Huge Cronin
- enhancement
**Wang&Wang**
**PRC 64 (01) 034901**
- Cronin
- enhancement

- But suppressed Rcp at
- the same   time (?!)

## p+p → π +X references @ √s ≈ 20 GeV

-  p+p  π0 *X *parametrizations confronted to data @ √s = 16 – 20 GeV:

- WA98 parametrization
- undershoots the data
- by up to a factor of ~3
- X.N.Wang parametriz.
- undershoots the data
- by up to a factor of ~2

## New p+p → π +X reference @ √s ≈ 20 GeV

**New ****p+p ****→**** ****π**** ****+*****X***** reference ****@**** ****√s ≈ ****20 GeV**

- Much better agreement
- in shape and magnitude
- (within exp. uncertainties)

- New parametrization [Blattnig00] versus p+p data √s = 16 – 20 GeV:
-       New WA98, WA80 & CERES nuclear modification factors:

- RAA at SPS are not
- enhanced but consistent
- with “collision scaling”.
- Agreement with parton
- energy loss calculations
- [I.Vitev nucl-th/0404052]
- in moderately dense
- system (dNg/dy ~ 400-600)

## Indications of high pT suppression @ SPS

**Indications of h****igh p****T**** suppression @ SPS**

- Centrality evolution of high pT π0 production at SPS:
- “Collision scaling” in 0-8% central collisions (RAA ~ 1).
- “Cronin” enhancement in peripheral ... and suppression in 1% most central
- Wish list (1): Run RHIC Au+Au, p+p @ √sNN≈ 20 – 30 GeV (onset of suppr.)

- 0-8% central

**Peripheral**
**1% top central**

**0-8% central**

## Case II:p+p high pT reference at √s = 62.4 GeV

**Case II:****p+p high p****T**** referen****ce at ****√s = 6****2.4 GeV**

## p+p high pT data @ 62.4 GeV

**p+p high p****T**** data ****@**** 62.4 GeV**

-   Au+Au @ 62.4 GeV measured at RHIC in Run-4. But no concurrent p+p ...
-   p+p @ 62–63 GeV measured at ISR: pions: π0 (8), π± (4); charged hadrons (1)

## How consistent are the p+p → π +X spectra @ 62.4 GeV ?

**How consistent are the ****p+p ****→**** ****π**** ****+*****X***** spectra @ 62.4 GeV ?**

-  Discrepancies as large as a
-  factor of ~3 between data sets ...

## Unsubstracted π 0 “contaminations” at ISR (1)

**Unsubstracted**** ****π**** ****0**** “contaminations” at ISR (1)**

-        All but one measurement at ISR didn't substract the η and direct-

- “World average” η/π0 ~0.45 ratio at high pT in hadronic colls.
- 18% η contribution needs to be substracted from “unresolved” π0 spectra.

- BRη →  • Rη/π0 = 0.39 • 0.45 ≈ 0.18

## Unsubstracted π 0 “contaminations” at ISR (2)

-        All but one measurement at ISR didn't substract the η and direct-

- /π0 ratio at high pT in p+p at 62 GeV (data compared to NLO pQCD):
-    Prompt  are a significant source of e.m. clusters above pT ~6 GeV/c
-    that needs to be substracted too

## Final corrected p+p spectra @ 62.4 GeV

**Final corrected ****p+p spectra ****@**** 62.4 GeV**

- 2 data sets (outliers) excluded.
- Final corrected data consistent
- among each other within ±25%

## Uncertainties of final p+p high pT refs. @ √s = 62.4 GeV

-      Neutral pions:  ± 25%					     Charged hadrons:   ± 35%

## High pT suppression in Au+Au @ 62.4 GeV

**High p****T**** suppression in Au+Au @ 62.4 GeV**

-      Using p+p  π0 *X**  *parametrization
-      Using [p+p  h± *X *parametrization] / 1.6
- 				Parton energy loss calculations
- 				with dNg/dy = 650 – 800
- 				 I. Vitev nucl-th/0404052

-   Propagated uncertainties in the RAA for π0:
-    pT dependent, mimic physical (e.g. “Cronin”-like) effects
-  Wish list (2): Run RHIC p+p @ √sNN= 62.4 GeV (detailed quantitative
-                          study of √s-dependence of high pT suppression)

- PHENIX
- preliminary

- Ratio /h at high pT

## Case III:p+p high pT reference at √s = 200 GeVat forward rapidities

**Case III:****p+p high p****T**** referen****ce at ****√s = ****200 GeV****at forward rapidities**

## d+Au nuclear modification factor @ η = 3.2

**d+Au nuclear modification factor ****@**** ****η = 3.2**

- First time a large “shadowing” is seen at small-x and high pT in nuclear syst.
- So far unexplored(*) perturbative region of nuclear (x,Q2) plane.
- (*) Caveat: The “back-of-the-envelope” estimates (x~pTe-y)
-      of the small-x values probed at forw. rapidities
-      at RHIC provide usually too low values.
-      Effective <x2> values are at least ~10 times larger.

- Factor ~2 suppression
-    in hadron production:
-    pT = 1-3 GeV/c, η = 3.2
-    x2 ~ 10-4 in Au(*)

## High pT p+p reference spectra vs pQCD (mid-rapidity)

- Good agreement with NLO pQCD

**    ****η = 0****	****	****	****	****	****	****	****	****      η =  1**

- [calculations by W. Vogelsang]

## High pT p+p reference spectra vs pQCD (forward η)

-  Good agreement with NLO pQCD

**    ****η = 2.2****	****	****	**

**η =  3.8**

- [calculations by W. Vogelsang]

- STAR Collaboration
- PRL92 171801 (2004)

## High pT p+p reference spectrum vs pQCD (η=3.2)

- Two highest pT points (there where the RdAu “suppression” appears) are “enhanced” w.r.t. NLO (which describes all other rapidities, even y = 3.8 !).
- Let's be provocative ... Is there d+Au suppression or (“genuine” ?) 		p+p “enhancement” ?

**η =  3.2**

## Case IV:p+p high pT photon reference at √s = 200 GeV   

**Case IV:****p+p high p****T**** photon referen****ce at ****√s = ****200 GeV   **

## Thermal photon production in Au+Au @ √sNN = 200 GeV

-      Thermal (real&virtual)  are the most direct (the only ?) probe sensitive to
-      the thermodynamical state (EOS) of underlying matter.

- Au+Au 200 GeV
- 0-10% central

- 2+1 hydro predictions:
- _Initial conditions_:
- 0 = 0.15 fm/c
- T0 = 580 MeV
- (reproduces bulk p dN/dpT)
- _EOS_:
- QGP (2.5 flavors) + hadron res. gas +
- 1st order phase transition (E=0.8 GeV)

- D. Peressounko, D.d'E.
- (in preparation)

- Thermal (QGP+HG) component
- NLO pQCD x TAB scaling

-      Thermal production (only)
-      apparent within
-      pT ≈ 1 – 2.5 GeV/c

## Medium effects in Au+Au→ + X @ √s = 200 GeV

**Medium effects in ****Au****+Au****→**** ********+ *****X***** ****@**** ****√s = 200**** GeV**

-      However, (part of the) prompt photons can be distorted by the dense
-      QCD medium (esp. in the region pT< 4 GeV/c).
-       Photon production in p+p @ 200 GeV:

- Below pT ≈ 4. GeV/c dominated by
-  from collinear q,g fragmentation

- NLO pQCD [W. Vogelsang]

**+**

- (                )

- (                )

- (             )

## “Nuclear modif. factor” Au+Au→ + X @ √s = 200 GeV

-      Back-of-the-envelope ansatz for  suppression: RAA( frag.) = RAA(q,g) ≈ 0.25
-      RAA ≈ Ratio of (tot – 0.75*frag)/(tot):
-      ~50% depleted prompt photon yield could mask the expected (enhanced)
-       thermal emission around pT = 2 GeV/c

- Fra

- NLO pQCD [W. Vogelsang]

- “RAA”~0.5			   			    “RAA”~0.8

- Results confirmed by more
- involved calculations:
- F.Arleo: hep-ph/0406291

- (No shadowing corrs.
-  included)

- 3 different scales

## Disentangling “thermal”  from quenched prompt 

-     Step 1: Measure p+p → (isolated) + *X*
-                 down to pT = 1 GeV/c
-                   with uncertainties ~10%
- Handle on from qg-Compton, qqbar annihilation
-     Step 2: Measure p+p → (total) + *X*
-                 down to pT = 1 GeV/c
-                    with uncertainties ~10%
-           Handle on fragmentation  production
-     Step 3: Measure Au+Au → (total) + *X*
-                   down to pT = 1 GeV/c
-                   with uncertainties ~10%
-     Step 4: (AuAu total) – TAB•(pp isolated)
-                   Upper limit on thermal spectrum.
-     Step 5:  (AuAu total) – TAB•(pp total)
-                    Lower limit on thermal spectrum.

## High pT p+p baseline spectra: Summary

-  _Case I_:  p+p → π+*X* at √s ≈ 20 GeV
-    Fact: High pT A+A hadroproduction @ SPS is (slightly) suppressed.
-    Wish: Measuring p+p, Au+Au at RHIC at √s = 20 – 30 GeV (Run-6 ?)
-  _Case II_: p+p → π,h± +*X* at √s = 62.4 GeV
-    Fact: Current ISR-averaged p+p refs. have uncertainties of order ~30%
-    precluding detailed quantitative study of √s-dependence of high pT A+A suppr.
-    Wish: Measuring p+p at RHIC at √s = 62.4 GeV (Run-5 ?)
-  _Case III_: p+p → h± +*X* at √s = 200 GeV at forward y
-    Fact: High pT spectra at η=0,1,2.2,(3.2),3.8 are (not) well reproduced by pQCD
-             putting (perhaps) into question the claimed d+Au suppression.
-    Wish: Independent confirmation of p+p h- spectrum at η=3.2
-  _Case IV_: p+p → +*X* at √s = 200 GeV
-    Fact: Depleted prompt  (from quenched jet fragmentation) can hide the           	 thermal photon signal in Au+Au at RHIC.
-    Wish: Measure isolated and non-isolated  in p+p at √s = 200 GeV

## hot quarks cooking guide (I)

- Nuclear modification factor with a incorrect depleted reference:

## hot quarks cooking guide (II)

- Nuclear modification factor with a correct baseline:

**=**

**p+p  = **

**A+A = **

- Enjoy the hot quarks !

- “because we can” © ...
-          *©**Richard Witt*

## backup slides ...

## BRAHMS Rcp vs RdAu

## Charged hadron over pion ratio at high pT

- .

## Thermal photons from other hydros

- .

## Final p+p → π +X reference @ √s = 62.4 GeV

- Parametrization:								   Good agreement with NLO:

- Calculations by
- Werner Vogelsang

## Nuclear modification factors below RHIC energies

- High pT π0 production in ~0 ─10% central A+A at SPS and ISR energies: