# Presentation: 693491

**The STAR Heavy Flavor Tracker **
**and Intermediate Silicon Tracker **
**An Introduction and Brief Review of the Technical Design and Physics Goals at Mid-rapidity**
**Jim Thomas**
**Lawrence Berkeley National Laboratory**

## The STAR Detector at RHIC

## Participating Institutions for the HFT & IST

**Argonne National Laboratory**
**Brookhaven National Laboratory***
**IPHC, Strasbourg (R&D)***
**Lawrence Berkeley National Laboratory***
**Massachusetts Institute of Technology***
**Ohio State University**
**UC Irvine (R&D)**
**UC Los Angeles**
**+Individuals**

## The Heavy Flavor Tracker

**The Heavy Flavor Tracker**

**The HFT:  2 layers of Si at mid rapidity**

**The HFT is a new detector**
**30 ********m silicon pixels**
**	****to yield 10 ********m space point resolution**
**Direct Topological reconstruction of Charm**
**Detect charm decays with small c********, including  D****0**** ******** K ******
**	****New physics**
**Charm collectivity       and flow to test thermalization at RHIC**
**C & B  Energy Loss to test pQCD in a hot and dense medium at RHIC **
**The proposed Tracking Upgrades include**
**HFT   (2 layers)**
**IST    (2 layers)**
**SSD  (existing layer)**

**+ IST + SSD**

## Direct Topological Identification of Open Charm

- The STAR Inner Tracking Upgrade will identify daughters of the decay and do direct topological reconstruction of open charm hadrons.
- No Mixed events, no random background subtraction.

- Goal: Put a high precision detector near the IP to extend the TPC tracks to small radius

## “Heavy Flavor” is the Next Frontier 

**The QGP is the universally accepted hypothesis at RHIC**
**The next step in confirming this hypothesis is the proof of thermalization of the light quarks in RHIC collisions**
**The key element in proving this assertion is to observe the flow of charm ... because charm and beauty are unique in their mass structure**
**If heavy quarks flow**
**frequent interactions among all quarks**
**light quarks (u,d,s) likely to be thermalized**

- Current quark: a bare quark whose mass is due to electroweak symmetry breaking

- Constituent quark: a bare quark that has been dressed by fluctuations in the QCD sea

**Notes:**
An important example of such a vacuum condensate is the Higgs vacuum, which is introduced in the Standard Model of particle physics to generate the masses of quarks, leptons, and the gauge bosons of the weak interaction. The vacuum expectation value of the Higgs field, hφi = 246 GeV, is uniquely determined in the Standard Model; the quark and lepton masses differ from one another only due to the different strength of the coupling of each fermion to the Higgs field. The quark masses receive additional contributions from the quark and gluon condensates in the QCD vacuum, which have been measured
to be: h ̄qqi = (235MeV)3,
         hg2GμGμ i = (840MeV)4. (1)
In fact, the contribution of the QCD vacuum condensates to the masses for the three light quark flavours u, d, s considerably exceed the mass believed to be generated by the Higgs field see Fig. 1).

Electro weak symmetry breaking is responsible for the current quark masses.  Chiral symmetry breaking is responsible for the constituent quark masses.

A constituent quark is a current quark that is dressed by the QCD vacuum.  It includes contributions from fluctuations in the QCD sea.
At RHIC, the heavy quarks do not interact with the QCD vacuum because they are too heavy.  The light quarks are modified and can change inside a QGP.  The higgs scale is too high for electro-weak symmetry breaking to be affected at RHIC energies.  So Charm and Beauty masses are invariant at RHIC.

## Flow: Probing Thermalization of the Medium

**p****y**

## Scaling as a Function of  (mT – m0)

**The light quark sector scales beautifully with v****2****/n****q****  .vs.  (m****T**** – m****0****)/n****q**
**Note that p****T**** < 1 GeV always did scale !**
**The strange quark sector also scales   with <v****2****> and the scaling holds at all centralities**
**Even the ******** meson**
**See S. Blythe QM2006**

**Does it work in the Charm Sector? **
**A strong test of the theory**

- Yuting Bai, QM 2006 for the STAR Collaboration

- STAR Preliminary work by Yan Lu

## Heavy Flavor Energy Loss ... RAA for Charm

**Heavy Flavor Energy Loss ... R****AA**** for Charm**

**Heavy Flavor energy loss is an unsolved problem**
**Gluon density            ~ 1000 expected from light quark data**
**Better agreement with the addition of inelastic E loss**
**Good agreement only if they ignore Beauty ...**
**Beauty dominates single electron spectra above 5 GeV**
**We can separate the Charm and Beauty by the direct topological identification of Charm**

- Theory from Wicks et al. nucl-th/0512076v2

**Where is the contribution from Beauty?**

**Notes:**
Figure 9: Non-photonic electron RAA in central Au+Au collisions from STAR (open-symbols, top 5%) and PHENIX (filled-symbols,  top 10%) from Refs. [58,59,60].  Theoretical predictions for charmed-hadron and charm and beauty-hadron decayed electrons are shown as blue- and yellow-bands, respectively. In these calculations, the initial gluon density was assumed to be unrealistically large: ~3500,  see Ref [63] .
Figure 9 shows RAA for non-photonic electrons[i],[ii],[iii] from STAR and PHENIX.  The data extend up to pT ~ 10 GeV/c.  The figure shows that the suppression factor for single electron spectra is in the range of 0.2-0.3 which is almost exactly the same as the suppression factor observed for charged hadrons and pions[iv],[v] (i.e. light quarks).  Using an unrealistically large initial gluon density of dNg/dy = 3500, Djordjevic, Gyulassy, Vogt and Wicks have done a pQCD calculation[vi], including gluon radiative energy-loss, which can barely reproduce the electron RAA (see the blue-line in Figure 9).  The model ignores the contributions from beauty-hadrons, and when beauty is added to the model, the resulting prediction for RAA cannot describe the data at all (see the yellow band in Figure 9 ); the model with beauty over-predicts the data by a factor of 2-3.   Note that for light-quark hadrons, like pions, a gluon density of ~1000 has been used to  reproduce the observed RAA[jt1].  These results raise a serious challenge to our understanding of both the mechanism for heavy-quark production and the mechanism for energy-loss in a hot and dense medium. In order to resolve these important issues, we have to do direct topological reconstruction of open charm.  It is experimentally and theoretically too difficult to make definite conclusions from the single-electron measurements due to the complications from the mixing of the electrons from D-meson decay and electrons from bottom hadron decay as well as the smearing of the decay kinematics. 

## A Rich Physics Program	

**There is a rich physics program when all of the STAR physics detectors are working together**
**Flow in the Charm sector**
**dE/dx in the Charm and Beauty sector**
**Recombination and R****AA**** in the Charm and Beauty sector**
**Vector Mesons**
**Charm Angular Correlations**
**now accessible due to STAR’s large acceptance**
**non-photonic electrons**
**...**

## The Methodology: Surround the Vertex with Si

**The Methodology: Surround the Vertex with Si**

- The HFT is a thin detector using 50 m Si
- to finesse the limitations imposed by MCS

- The IST and SSD form the ingredients of an Inner Tracking Upgrade

## Double sided Si wafers 300 m thick with 95 m x 4.2 cm strips

Crossed at 35 mrad  –	effectively 30 m x 900 m

One layer at 23 cm radius

20 ladders, 67 cm long

air cooled

 < 1.2

1 % radiation length @  = 0

**Double sided Si wafers 300 ********m thick with 95 ********m x 4.2 cm strips**
**Crossed at 35 mrad  –****	****effectively 30 ********m x 900 ********m**
**One layer at 23 cm radius**
**20 ladders, 67 cm long**
**air cooled**
****** ****< 1.2**
**1 % radiation length @ ******** = 0**

**The SSD – An Existing Si Detector**

## The IST – A New Detector Using Si Strips

**Singled sided Si wafers 300 ********m thick with 60 ********m x 4.0 cm strips @ 17 cm**
**Si strips with 60 ********m x 2.0 cm strips @ 12 cm radius**
**27 ladders,  52 cm long**
**19 ladders,  40 cm long**
**air cooled**
****** ****< 1.2**
**1.5 %  per layer @ ******** = 0**

**The IST – A New Detector Using Si Strips**

## The HFT – A New Detector with Active Pixels

**Active Pixel Sensors, thinned to 50 ********m thickness**
**30 ********m x 30 ********m pixels**
**Two layers at 7 & 2.5 cm radius**
**24 ladders, 19.2 cm long**
**  ****9 ladders, 19.2 cm long**
**air cooled**
****** ****< 1.2**
**0.28 % radiation length @ ******** = 0**

**The HFT – A New Detector with Active Pixels**

## Summary of Si Detectors Inside the TPC

**TPC – SSD – IST – HFT ****(single track pointing, without a vertex constraint)**
**TPC pointing resolution at the SSD is  ~ 1 mm**
**SSD pointing at the IST   is  ~ 300 ********m **
**IST pointing at the HFT  is  ~ 250 ********m **
**HFT pointing at the VTX   is  ~ 40 ********m**

**Summary of Si Detectors Inside the TPC**

## Charm-hadron Simulation Results 

- _Detector radii:_
- 	TOF
- 	TPC (50cm)
- 	SSD (23cm)
- 	IST2 (17cm)
- 	IST1 (12cm)
- 	HFT2(6.9cm)
- 	HFT1 (2.5cm)

**The Monte Carlo reconstructed yield of D****0 ****is very good**
**A complex p****T**** dependence ... however efficiency vs p****T**** is the FOM**
**D****0 ****decay length is ~ 125 ********m as compared to the change from 22 to 35 ********m**
**HFT-1 is now further back from the vertex and see’s a lower hit density **
**IST helps reduce search radius on HFT and thus reduces ghost track inefficiencies as well as allows more relaxed kinematic cuts on the data**
**Kinematic cuts in the software are the dominant contributor to efficiency**

##  Rates Estimation - v2

**dN/dp****T**** distributions for D-mesons.**
-       Scaled by <Nbin > = 290, corresponds to the minimum bias Au + Au collisions at RHIC.
**(b) Assumed v****2**** distributions for D-mesons.**
-                  ---- PLB 595, 202 (2004)
-        Error bars shown are from 15% systematic errors** **
**(c) D****0**** meson v****2**** rates from minimum bias Au + Au collisions at 200 GeV.**
-       The small and large error bars are for 15% and 30% systematic errors, respectively.  For the v2 analysis, 12 bins in  are used.

| pT(GeV/c) | ∆pT(GeV/c) | # events
qC = qu,d,s | # events
qC = 0 |
| --- | --- | --- | --- |
| 0.6 | 0.2 | 260x106 | 525x106 |
| 1.0 | 0.5 | 70x106 | 140x106 |
| 2.0 | 0.5 | 53x106 | 125x106 |
| 3.0 | 1.0 | 390x106 | 270x106 |
| 5.0 | 1.0 | 520x106 | 880x106 |

- 500 M Events is achievable with DAQ1000

## Good Physics needs Good Technology 

**Technologies to explore**
**Silicon Chips for the HFT**
**Further refinement of on-chip electronics**
**Readout Electronics for the HFT and IST**
**speed, heat dissipation, compatibility with STAR DAQ**
**The Mechanical Arms to insert the HFT and allow it to be replaced quickly**
**Alignment and stability**
**Calibration, Tracking & Software**
**New levels of precision**
**IST**
**Optimize the strip geometry at each layer **
**The R&D profile allows us to complete the development of the MimoSTAR chips**
**Mount them in STAR – explore the background environment**
**Use the real beam pipe – detectors at 2.5 cm from the vertex**
**Use the real mechanical insertion device – explore calibration and alignment**
**The Construction Profile allows us to complete the development of the UltraSTAR chips with 200 ********sec frame rate readout by the end of FY11**

## R&D in Run 7

**A Three Layer Telescope with MimoSTAR II Chips.**
**A full system test from pixel to DAQ using an extension of one TPC sector trigger line.**

## Summary

**The HFT, IST & SSD will explore the Charm and Beauty sectors**
**We will do **_**direct**_** topological reconstruction of Charm**
**Our measurements will be unique at RHIC**
**The key measurements include**
**V****2**
**Energy Loss **
**Charm Spectra, R****AA  ****& R****cp**
**Vector mesons**
**Angular Correlations**
**The technology is available on an appropriate schedule**