# Presentation: 836516

## Unturned Stones for Electromagnetic Probes of Hot and Dense Matter

**Kevin L. Haglin**

**St. Cloud State University, Minnesota, USA**

**Hot Quarks 2006, May 15-20, 2006, Villasimius, Sardinia, Italy**

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## What’s under those stones?

**Photons**
**	****a) thermometry**
**	****b) flow**
**2)  Dileptons**
**	****c) vector meson spectroscopy**
**	****d) collective many-body effects**
**3)  Diphotons**
**	****e) thermal production - thermometry**
**	****f)  scalar and tensor meson spectral functions**
**	****g) hadron spectroscopy**
**4)  *****J*****/******** & ********c**

******, ********* [e****+****e****-****, ********+********-****], ******

***J*****/********, ********c**

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## 3) Diphotons

**It turns out that studies of photon pair production have a fairly long history....**
**  ****R. Yoshida, T. Miyazaki, M. Kadoya, PRD **_**35**_**, 388 (1987).**
**  ****K. Redlich, PRD **_**36**_**, 3378 (1987).**
**  ****J. Letessier and A. Tounsi, PRD **_**40**_**, 2914 (1989).**
**  ****R. Baier, H. Nakkagawa, A. Niegawa, K. Redlich, PRD **_**45**_**, 4323 (1992).**
**  ****M. Hentschel, B. Kampfer, O.P. Pavlenko, K. Redlich, G. Soff, Z. Fur**
**   ****Phys. C, 333 (1997).**

**+ crossed + contact**

**+ crossed diagram**

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## Motivation:  That is, suggestions at the time (1990) were....

**                                       ****at fixed temperature**
** ****ratio of ***dN**** ***/** *dydM*** to **(*dN**ch ***/***dydM*)2** should exhibit a more abrupt change in slope when the phase boundary is crossed as compared to ordinary hadronic matter**

**Difficulties:**
**Fold the rates to predict yields, and the “effect” diminishes owing to the long lifetime of the hadron phase**
**b)  Drell-Yan “like” photon pairs dominates at some point**

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##                        New idea...       let’s use the diphoton signal to do

**Thermometry**
**	****	****rate is proportional to ****exp**(*- ****M******  ***/*** ****T***)** times a function of *****T***
**2)  Spectroscopy**
**tensor mesons couple to 2********[f****2****(1270), a****2****(1320), f****2****’****(1525), ...]**
**f****1****************f************************1.3 MeV******
**scalar, pseudoscalar mesons couple to 2********’********f****0****, a****0******
**3)  Heavy quark physics**
**	****	********c********2********with rate 7.4 keV (full width is 17.3 MeV)**
**	****	********c0********2******** with rate 2.6 keV (full width is 10.1 MeV)**

**What are the major background contributions?**

**do spectroscopy!**

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## Hadron processes

**QCD processes**

**Meson spectral functions**

**Singles masquerading as doubles**

**charmonium**

**                              ****Inventory**

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## Hadron annihilation processes

**M. Hentschel, B. Kampfer, O.P. Pavlenko, K. Redlich, G. Soff, Z. Fur Phys. C, 333 (1997).**

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## QCD annihilation processes [screened, net (resummed) rate]

**where *****c***** is approximately 0.42.    The range of validity is *****M > T*****.**

****

**q**

**q**

**R. Baier, H. Nakkagawa, A. Niegawa, K. Redlich, PRD **_**45**_**, 4323 (1992).**

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## Hadron phenomenology

****

****

****

****

****

****

****

****

****

****

****

****

**,*****K ***

**,*****K ***

**,*****K ***

**,*****K ***

**,*****K ***

**,*****K ***

**Vertex form factors:**

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## More phenomenology...

****

****

****

****

****

**Chiral Lagrangian from KH,  C. Gale, PRC 63, 065201 (2001).**

****

****

****

****

****

****

****

**,*****K* ***

**,*****K* ***

**,*****K* ***

**,*****K* ***

**,*****K****

**,*****K* ***

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## Comments:

**Comments:**
**Quark rate comes from re-summed (HTL) thermal field theory**
**Pion and kaon results are diagrammatic calculations w/o form factors**
***V***** +*****V *****- ******** ********use chiral Lagrangian to identify the interactions**
********** ******** ****use Wess-Zumino interaction**

**KLH, to be published.**

**The QCD rate seems to be  quite similar to the HG rate!**

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## Hadron thermal decay into photon pairs

**=**

****

****

****

****

****

****

**+ others**

**a**

****

****

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## Results:

**KLH, to be published.**

**Results:**
**Diphoton rate from QGP vs. HG seems roughly the same at fixed temperature. **
**     ****This is the same conclusion one had with single photons.**
**A temperature can be extracted – thermometry**
**Meson spectral properties at finite temperature can be probed – spectroscopy, in-medium physics**
**Chiral restoration ******** f****1**** spectral function should approach equivalence with ******

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## Singles “looking like doubles”

**And we take **

**where**

**Parameterization from ****J. Kapusta, P. Lichard, D. Seibert, PRD **_**44**_**, 2774 (1991)****.**

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## Two comments:

**Two comments:**
**HG and QGP can now be compared directly on this figure---they are very similar.**
**The singles’ corruption of the double is negligible.**

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## Next, let’s establish the relative importance of form factors.

**Next, let’s establish the relative importance of form factors.**
**Of course, at high mass off-shell behavior will become more important.**
**Results of monopole form factors:**
**Low mass pairs are reduced by a factor of 2**
**High mass pairs suffer an order of magnitude suppression.**

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## 4) Charmonium:   “suppression of c as QGP indicator”!

**The same idea for *****J*****/******** suppression carries over to ********c****.**
**Full width for ********c ****is 17.3 MeV.  It should stand “tall and proud” unless it is disturbed by the QGP!!**
**The other charmonium states represent additional tools---it’s all good.**

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## Summary

**Bursts of electromagnetic energy cleanly probe the full space-time extent of the strongly-interacting system.**

**Further studies underway...**

**More complete hadron description, i.e. form factors**
**b)  space-time evolution for yields; add DY-like pairs**

**2)  Photons allow thermometry**

**3)  Dileptons provide spectroscopic information on vector mesons at finite energy density**

**4)  ****Diphotons open the door for both thermometry and spectroscopy**

**5)  Charmonium (eta-charm) suppression could be a very useful QGP diagnostic (if experimental resolution is sufficient).**

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## That’s all folks...

**Research supported in part by the National Science Foundation under grant number PHY-0555521.**

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