# Presentation: 517855

## dNch/dη and dET/dη                      at Mid-Rapidity                       from SIS to LHC

**dN****ch****/d****η**** and dE****T****/d****η****                      at Mid-Rapidity****                       from SIS to LHC**

***Alexander Milov***
***for the PHENIX collaboration***
***June 17, 2004***

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Outline.

** ****Apparatus,  Measurements & Errors:**
** ****PHENIX detector**
** ****dN****ch****/d****η**** and dE****T****/d****η**** measurement in PHENIX **
** ****Centrality & Trigger efficiency determination**
** ****Results:**
** ****PHENIX results**
** ****RHIC and lower energy results**
** ****Physics:**
** **** √****s****NN**** dependencies**
** ****Averaged <E****T****>/<N****ch****>**
** ****Centrality shape**
** ****Theoretical Models at Experimental Angle of View**
** ****Summary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Global observables: dNch/dη & dET/dη.

** ****Collision framework:**
** ****Particle and energy densities**
** ****Freeze-out conditions**
** ****Experimental environment**
** ****How does it change with:**
** ****Incident energy**
** ****Collision centrality**
** ****Relative behavior**
** ****Test for Theoretical Models.**
** ****Looking at the collision as global may reveal things hidden in details.**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

##  12 Countries;  58 Institutions;  480 Participants*

**             ****Brookhaven National Laboratory, Upton, NY **
**             ****University of California - Riverside, Riverside, CA**
**             ****University of Colorado, Boulder, CO**
**             ****Columbia University, Nevis Laboratories, Irvington, NY**
**             ****Florida State University, Tallahassee, FL**
**             ****Florida Technical University, Melbourne, FL**
**             ****Georgia State University, Atlanta, GA**
**             ****University of Illinois Urbana Champaign, Urbana-Champaign, IL**
**             ****Iowa State University and Ames Laboratory, Ames, IA**
**             ****Los Alamos National Laboratory, Los Alamos, NM**
**             ****Lawrence Livermore National Laboratory, Livermore, CA**
**             ****University of New Mexico, Albuquerque, NM **
**             ****New Mexico State University, Las Cruces, NM**
**             ****Dept. of Chemistry, Stony Brook Univ., Stony Brook, NY**
**             ****Dept. Phys. and Astronomy, Stony Brook Univ., Stony Brook, NY  **
**             ****Oak Ridge National Laboratory, Oak Ridge, TN**
**             ****University of Tennessee, Knoxville, TN  **
**             ****Vanderbilt University, Nashville, TN****	**

**Brazil        University of São Paulo, São Paulo**
**China        Academia Sinica, Taipei, Taiwan**
**                  ****China Institute of Atomic Energy, Beijing**
**                  ****Peking University, Beijing**
**France      LPC, University de Clermont-Ferrand, Clermont-Ferrand**
**                  ****Dapnia, CEA Saclay, Gif-sur-Yvette**
**                  ****IPN-Orsay, Universite Paris Sud, CNRS-IN2P3, Orsay          **
**                  ****LLR, Ecòle Polytechnique, CNRS-IN2P3, Palaiseau**
**                  ****SUBATECH, Ecòle des Mines at Nantes, Nantes**
**Germany  University of M****ü****nster, M****ü****nster**
**Hungary   Central Research Institute for Physics (KFKI), Budapest**
**                  ****Debrecen University, Debrecen**
**                  ****Eötvös Loránd University (ELTE), Budapest **
**India         Banaras Hindu University, Banaras**
**                  ****Bhabha Atomic Research Centre, Bombay**
**Israel        Weizmann Institute, Rehovot**
**Japan       Center for Nuclear Study, University of Tokyo, Tokyo**
**                  ****Hiroshima University, Higashi-Hiroshima **
**                  ****KEK, Institute for High Energy Physics, Tsukuba **
**                  ****Kyoto University, Kyoto**
**                  ****Nagasaki Institute of Applied Science, Nagasaki**
**                  ****RIKEN, Institute for Physical and Chemical Research, Wako**
**                                               ****RIKEN-BNL Research Center, Upton, NY              **
**	****     ****Rikkyo University, Tokyo, Japan             **
**                  ****Tokyo Institute of Technology, Tokyo**
**                  ****University of Tsukuba, Tsukuba **
**                  ****Waseda University, Tokyo                    **
**S. Korea   Cyclotron Application Laboratory, KAERI, Seoul**
**                  ****Kangnung National University, Kangnung**
**                  ****Korea University, Seoul **
**                  ****Myong Ji University, Yongin City **
**                  ****System Electronics Laboratory, Seoul Nat. University, Seoul**
**                  ****Yonsei University, Seoul**
**Russia      Institute of High Energy Physics, Protovino **
**                  ****Joint Institute for Nuclear Research, Dubna **
**                  ****Kurchatov Institute, Moscow**
**                  ****PNPI, St. Petersburg Nuclear Physics Institute, St. Petersburg**
**                  ****St. Petersburg State Technical University, St. Petersburg**
**Sweden    Lund University, Lund**

*** ******12 Countries;  58 Institutions;  480 Participants****

***as of January 2004**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## PHENIX Detector.

** ****Pad Chamber Detectors:**
** ****MWPC with binary pad readout**
** ****2.5m and 5.0m from the IP**
** ****|****η****|< 0.35 ****Δφ**** = 90****0**
** ****σ****φ****= 1.4mrad (3.5mm PC1)**
** ****σ****η****= 0.7×10****-3 **** (1.7mm PC1)**
** ****Double Hit Resolution ~4cm **

** ****Electromagnetic Calorimeter:**
** ****Lead+Scintillator 18 X****0**** **
** ****5.1m from the IP**
** ****|****η****|< 0.38 ****Δφ**** = 90****0**
** ****σ****E****= 8.1%/√E[GeV] ×2.1%**

** ****Beam-Beam Counters:**
** ****64 Cherenkov Counters**
** ****3.1<|****η****|< 3.9 ****Δφ**** = 360****0**
**  ****σ****vertex****= ~5mm (central)**
** ****σ****t****= ~100 ps**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Multiplicity analysis.

** ****Counting tracks on statistical basis:**
** ****Combine all hits in PC1 to hits in PC3**
** ****Project lines onto the plane through the beam pipe**
** ****Count tracks inside the acceptance **
** ****Subtract combinatorial background by event mixing.**
** ****Corrections:**
** ****Tracks outside acceptance and background subtraction****	****4.3%±1%**
** ****Inactive regions****	****	****15%±2.3%**
** ****Double hit resolution**
**Hit losses****	****	****2×7%**
**Background subtraction **
**	****	****	****3.6% of bkg**
**Uncertainty (in central)****	****±3.6%**
** ****Particle in-flow and out-flow**
**	****Low energy****	****	****10%±5.5%**
**	****Higher energy****	****	****1%  ±2%**

**No Field**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Transverse Energy analysis.

** ****E****T**** definition:**
** ****E****T**** = E×sin(****θ****)**
** ****E****T**** ≈ m****T**** at Mid-Rapidity in C.M.S.**
** ****E is full E for leptons and mesons**
** ****E is E±m for (anti) baryons**
** ****EMCal energy scale:**
** ****Measures full energy of e****±**** and ****γ**** (****π****0****)**
** ****Slow hadrons are fully absorbed.**
** ****Relativistic hadrons leave M.I.P. peak**
** ****EMCal measures >75% of energy**
** ****Systematic errors:**
** ****Energy response****	****	****3.9%-4.7%**
** ****Noise in central:****	****	****<0.5%**
**	****in peripheral:****	****3.5%-6.%**
** ****In-flow and out-flow****	****3.0%**

**AGS test**
**RHIC data**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Centrality and trigger analysis.

**N****p**** using**
**Glauber**

**N****ch**** using**
**Generator**

**N****hits**** using**
**Detector MC**

**Match to**
**the data**

**N****p****, N****c**
**ε****trigger**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Centrality and trigger using NBD.

**N****p**** using**
**Glauber**

**N****ch**** using**
**Generator**

**N****hits**** using**
**Detector MC**

**Match to**
**the data**

**N****p****, N****c**
**ε****trigger**

**Assumed**
**N****ch**** ~ N****p**

**Use N.B.**
**statistics**

_**Negative Binominal Distribution:**_** is the statistics describing distribution of number of trials (n) which are necessary to get a number of successes, if the probability of success (****μ****) is known:**
**	****P(n,********,k) = ********(n + k) / (********(k) n!) ******** (********/k)****n**** / (1 + ********/k)****n+k****	**
**where k is a N.B.D. parameter related to the width of the distribution ******** in a following way: **
**	****(********/********)****2**** = 1/k + 1/******

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## d-Au example.

**N****p**** using**
**Glauber**

**Match to**
**the data**

**N****p****, N****c**
**ε****trigger**

**Assumed**
**N****ch**** ~ N****p ****  &**
**uncorrelated **
**N****ch ****production**

**Use N.B.**
**statistics**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Other examples:

| Case | |η|<0.35 | 3<|η|<4 | Comment |
| --- | --- | --- | --- |
|   d-Au 200 GeV | No | Yes | Matches pp trigger and tagged spectrum |
| Au-Au 200 GeV | No | Yes | Np is the same as found using standard technique |
| Au-Au 130 GeV | No | N/A |  |
| Au-Au 62.4 GeV | Yes/No | No | Preliminary gives the same trigger efficiency as standard |
| Au-Au 19.6 GeV | Yes | No | Works well on central arm. |

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Results: The distributions.

**Results: The distributions.**

** ****Only part of the acceptance shown**
** “****Classical” Shape: Peak, Valley, Edge.**
** ****Centrality classes shown.**
** ****Edge might be modified due to acceptance limitation**

**PHENIX preliminary**

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Results: Centrality curves.

** ****Consistent behavior for E****T**** and N****ch**
** ****Both increase with energy**
** ****Both show steady rise from peripheral to central**

**PHENIX preliminary**

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Results: Systematic errors.

** ****Three types of errors**
** ****All plotted as 1 standard deviation**
** ****Statistical error:**
** ****Point-by-point error (<1%). In all points is smaller than the marker size.**
** ****Systematic errors:**
** ****Band**** (correlated) allow to tilt points within the limit of the band.**
**	****In peripheral (~20%) due to ****	****trigger uncertainty. **
**	****In central (~4%) are due to DHR ****	****of the detectors**
** ****Scaling (correlated) allow to shift curves up and down.**
** ****Total systematic error is a quadratic sum of two. It is shown with the ****bars.**

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Results: Ratios at different energies.

** ****R200/19.6 is larger for E****T**** than for N****ch**
** ****Both are flat within systematic errors **
** ****Both show steady rise with incident energy**

**PHENIX preliminary**

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Results: Ratios <ET>/<Nch>.

**Results: Ratios <E****T****>/<N****ch****>.**

** ****Ratio <E****T****>/<N****ch****> increases by ~20% from 19.6 GeV to 200 GeV and stays the same between 200 GeV and 130 GeV**
** ****Consistent with the average particle momentum increase between those two energies.**
** ****Ratio <E****T****>/<N****ch****> is independent of centrality**
** ****Still a puzzle.**
** ****Same freeze-out conditions?**
** ****Since trigger and centrality related uncertainties cancel out, the flatness of the curves is quite precise statement.**

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Comparison to other RHIC results.

**Comparison to other RHIC results.**

** ****Spectacular agreement between all 4 RHIC experiments:**
** ****All measurements are absolutely  independent (including human factor) besides similar approach of using Glauber model.**
** ****BRAHMS:****	****Si + Scintillators**
** ****PHENIX: ****	****PC at 2.5m and 5m**
** ****PHOBOS:  Si detectors**
** ****STAR:****	****Tracking in magnetic field.**
** ****Would allow to calculate averaged values and reduce systematic errors **

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Illustration only

**Recalculation between systems.**

** ****In C.M.S.: **
** ****At Mid-Rapidity: E****T****~m****T**
** ****dE****T****/dy ≈ 1.25 dE****T/****d****η**
** ****In Lab:**
** ****dm****T****/dy ≈ 1.25 dE****T****/dy**
** ****dE****T****/dy ≈ dE****T****/d****η**

** ****In C.M.S.: **
** ****dN****ch****/dy ≈ 1.25 dN****ch/****d****η**
** ****In Lab:**
** ****dN****ch****/dy ≈ 1.04 dN****ch****/d****η**

** ****Recalculation parameters are “rather” independent on energy**
** ****A systematic error of 5% is assigned to any recalculated value**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Comparison to other SPS results.

** ****Good agreement between PHENIX measurements at 19.6 GeV and SPS measurements at 17.2 GeV in both measured values.**
** ****SPS spread of the data is larger than RHIC, but the same averaging should be possible to reduce the systematic errors.**

**Comparison to other SPS results.**

**PHENIX preliminary**

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Comparison of SPS results.

** ****At intermediate SPS energy the energy spread between points is relatively large.**
** ****Using weighted average and error scaling by S-factor (see PDG)**
** ****S=1 ****	****	****if ****χ****2****/n.d.f. < 1**
** ****S=√****χ****2****/n.d.f.****	****if ****χ****2****/n.d.f. > 1**
** ****At lower SPS energy the data spread is even larger, a higher quality data is highly desirable.**
** ****At AGS energy the Centrality curve is deduced from a combined data.**

**Comparison of SPS results.**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Comparison to other results.

** ****There is a continuous set of measurements from AGS to RHIC data.**
** ****Data quality: **
**	****The best we have, ****	****	****but not the best we want.**

**Comparison to other results.**

**using PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## √sNN dependence.

** ****PHENX suggested ln(s****NN****) at QM01 and it works ****	****well with better and larger data-set.**
** ****Both in E****T**** and in N****ch**** show log-scaling.**
** ****Works even better on N****ch**** for N****p**** = 350. **
**	****Band on the right is 2****σ**** error!**
** ****Extrapolation to LHC dN****ch****/dη = (6.1****±****0.13)****×****(0.5Np).**
** ****Extrapolation to lowest energy gives:**
** ****for E****T****: ****	****√s****0****NN**** = 2.35 ****±   ****0.2 GeV**
** ****for N****ch****: ****	****√s****0****NN**** = 1.48 ****± ****0.02 GeV**

**√****s****NN**** dependence****.**

**PHENIX preliminary**

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Low √sNN story

**-0.5 GeV                       +0.5 GeV**

** ****Energy conservation law.**

** ****What do ****√s****o****NN**** mean?**

** ****Now comes FOPI at <0.1 GeV kinetic energy!**

**Low √s****NN**** story**

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## What happens to <mT>?

**What happens to <m****T****>?**

** ****At low √s****NN****:**
** ****E****T**** is “produced” energy only.**
** ****N****ch**** can benefit from pre-existing particles (baryons).**
** ****At higher √s****NN****:**
** ****Critical temperature T****c****=0.17GeV.**
** ****Assuming: ****	****	****<E****kin****>=3/2T****c****	****≈ 0.26 GeV****	****	****<m****0****> ****	****	****≈ 0.25 GeV**
**	****<m****T****> = <E****kin****> + <m****0****>**
**	****	****	****≈ ****0.51 GeV**
**	****<E****T****>/<N****ch****> ≈ 1.6 <m****T****>**
**	****	****	****≈ ****0.82 GeV**
** ****Prediction for LHC: 0.93±0.04 GeV**

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## √sNN = 4-8GeV?

**√****s****NN**** = 4-8GeV?**

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Centrality shapes.

** ****Hard/Soft approach:**
** ****Might be deceiving: e.g. strangeness turn on.**
** ****Negatively correlated errors are huge.**
** ****N****p****α**** parameterizations:**
** ****assumes a power law**
** ****what does ****α**** mean?**
** ****Still large errors**
** ****PHOBOS as of June 2,2004 ****	****	****nucl-ex/0405027:**
** ****Bottom line: inconclusive!**

**Centrality shapes.**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Centrality shapes: basic approach

**Centrality shapes: basic approach**

**PHENIX preliminary**

** ****So can be done with othe centralities, we use N****p****=100**

** ****Instead of peripheral events, where data is absent or has large errors, one can use pp data. N****p****=2**

** ****To make more sense about the shapes let’s look at the difference for different centralities.**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Centrality shapes: basic approach

**Centrality shapes: basic approach**

**PHENIX preliminary**

** ****Quality of the data still needs to be improved!**
** ****Isn’t this familiar?**
** ****Almost flat at RHIC energies**
** ****Rising behavior at SPS and below.**
** ****No room for saturation!?**
** ****Centrality curve doesn’t tend to become flat**
**What happens above?**
** ****pp data tend to approach ln(s****NN****) line.**
** ****Would the A-A data stay the same or deviate from ln(s****NN****)?**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Bjorken energy.

** ****ε****BJ****=(S****τ****)****-1****dE****T****/dy**
** ****200 GeV 5.4±0.6GeV/(fm****2****c) 5%**
** ****What about “****τ****”?**
** ****Limiting: ****	****	****	****1/(2R****γ****) ≈ 0.15 fm/c**
** ****Formation: ****	****	****	****h/m****T ****≈ 0.6E****T****/N****ch ****≈ 0.3 fm/c**
** ****Centrality is measured and can be used to compare to other effects in HI collisions.**
** ****STAR (nucl-ex/03011017) uses another approach taking for overlap area S ~N****p****3/2****.**
** ****area of the nuclei**
** ****area of the nucleons**
** ****different at low N****p**

**PHENIX preliminary**

** ****Two curves agree within errors, but the slope at STAR is smaller.**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Models: experimentalist’s view

** ****Global observables can constrain (give input to) some models, but cannot prove them to be right.**
** ****What can experimentalists do with the models?**
** ****Theoretical model is particularly hard to kill               even with the data!**
** ****How well defined is a model within its own assumptions?**
** ****How should one compare models to data?**
** ****Model vs. Generator:**
** ****Do you know why we are such in love with HIJING?**
** ****IMHO: Model is a precursor to the Generator.**
** ****Major difference besides completeness and ease of use**
**	****	****Generator does partial probabilities!**
** ****Thanks to all authors who sent us their data!**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Models I

**Models I**

**LUCIFER****	****Hadronic cascade model, input fixed from lower energy.**
**	****D.E.Kahana & S.H.Kahana, nucl-th/0208063.**
**Minijet ****	****Multiphase transport model, includes both initial partonic and final hadronic interactions. **
**	****S. Lee and X.N. Wang, Phys Lett B527, 85 (2002) **
**EKRT ****	****K.J. Eskola, et al., Nucl. Phys. B570, 379 (2000), Phys Lett B497, 39 (2001). **
**SSHM ****	****Saturation for Semi-Hard Minijetis. pQCD-based for semi-hard partonic interaction**
**	****WNM for soft particle production. ****A.Accardi, Phys Rev C64, 064905 (2001). **
**KLN****	****D. Kharzeev and M. Nardi, Phys Lett B507, 121(2001), D. Kharzeev and E. Levin, Phys Lett B523, 79 (2001). ****	**

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Models II

**Models II**

**DSM: ****	****Dual String Model, Dual Parton Model + strings. **
**	****R. Ugoccioni, Phys Lett B49, 253 (2000). A. Capella et al, Phys Lett C236, 225 (1994). **
**HIJING: ****	****pQCD for initial minijet production and the Lund string model for jet fragmentation **
**	****and hadronization, +jet quenching +nuclear shadowing. ****X.N. Wang et al. PRC 68, 054902 (2003).**
**LEXUS:****	****Linear EXtrapolation of UltraRrelativsitic nucleon-nucleon scattering data to nucleus-****	****nucleus collisions. ****S. Jeon and J. Kapusta, Phys Rew C63, 011901 (2001)**
**AMPT:****	****multiphase transport model +initial partonic and final hadronic interactions. **
**	****Z. Lin et al. Phys Rew. C64, 011902 (2001). **
**SFM:****	****String Fusion Model  string model, includes hard collisions, collectivity in the ****	****initial state (string fusion), and final state. ****N. Armesto Perez et al., Phys Lett B527, 92 (2002) **

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Models III

**Models III**

**PHENIX preliminary**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Summary

**Ravioli**

- What is inside?

**Cheese?**

**Meet?**

**Potato?**

**Spinach?**

**Nothing?**

**Mushrooms?**

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004

## Summary

**Ravioli**

** ****Global observables “phase transition”:**
** ****Quantity ******** Quality**
** ****Measurement ******** Systematization ******** Understanding.**
** ****Intriguing and exciting:**
** ****<E****T****>/<N****ch****> vs. centrality is flat!**
** ****<E****T****>/<N****ch****> vs. √s****NN ****is consistent with freeze-out temperature and has two distinct regions.**
** ****Both dE****T**** /d****η**** and dN****ch****/d****η**** at mid-rapidity scale with ln(s****NN****) over all measured √s****NN**** (factor of 100 for N****ch****) landing SIS and RHIC on the same line!**
** ****What do √s****0****NN**** mean?**
** ****Centrality shape of dN****ch****/d****η**** looks to be independent of √s****NN**** at RHIC energies and flattens out at lower.**
** ****Something is going on at lower SPS energy!**
** ****LHC predictions are on the desk! Let’s see what data says! **

- Sasha Milov      Focus on Multiplicity     Bari      June 17, 2004