# Presentation: 700515

## LDRD DR on Jet Physics at the LHC

- Ivan Vitev, Nuclear Theory, T-16 , LANL
- Patrick McGaughey, P-25, LANL
- +
- Camelia Mironov, P-25, LANL
- Gerd Kunde, P-25, LANL

- P-25 Nuclear Physics, LANL, Los Alamos, NM

## Title and abstract

- The Large Hadron Collider (LHC) located in Geneva, Switzerland will begin commissioning in 2008, providing the highest energy colliding beams in the world. The LHC will enable a new frontier in nuclear and particle physics - the first measurement of jets in ultra high energy nuclear collisions and their use as a diagnostic for  ultra high energy nuclear collisions. We propose to study the modification of jet shapes and topologies as a signature and sensitive probe of the strong interaction dynamics at the new and unknown energy frontier. Measurements of jet energy loss will be performed via tagged decays of Z0 -> mu+mu- or direct photons.The first ever differential study of jet energy loss in the quark-gluon plasma (QGP) will be made, providing direct insight into the nature of jet interactions in matter and the response of the QGP to large deposited energies.

- Jet Tomography at the LHC

## * * *Plasma Radiography at the Large Hadron Collider * * * The largest and most complex scientific instrument ever developed is the Large Hardon Collider (LHC) at CERN/Geneva. It was conceived for the study of physics beyond the standard model, manly accessed ub Proton Proton collisions. However it is as well capable of producing plasmas comprised from quarks and gluons by colliding heavy ions with an unprecedented center of mass energy of 5.5 TeV. The creation of the quark gluon plasma as was established in collisions at the Relativistic Heavy Ion Collider at lower energies. At LHC the exceedingly high energy produces hard probes in an abundance that allow for a new type of plasma study – plasma radiography. In analogy to proton radiography or tomography (the analogous term in the medical field) we propose to study the plasma with a probe that through interaction with the medium delivers information about the properties of the plasma volume. The tool – jets - is ‘borrowed’ from high energy particle physics . Jets are collimated sprays of particles that originated from a fragmenting parton. The jet cross sections at the LHC are sufficient to study specific classes of jets, i.e. jets tagged by electromagnetically interacting particles or tagged by heavy quarks. The tagging makes radiography possible in that it defines either the initial hard scattering in measuring the energy of the scatter or by defining the type of propagating heavy quark. Thus we are able to connect theory, i.e. pQCD, and experiment in a much more precise manner than possible before and will be able to extract the properties of the strongly interacting plasma. 

## Goal: study of jet shapes in nuclear collisions 

** **Clearly large effects - significant
-   redistribution of the energy
-  Non-Gaussian shapes, actual depletion
-   near the center of the jet cone. As
-   opposed to assuming
-  The first experimental measurement
-     and shape study

**Goal: study of jet shapes in nuclear collisions **

- Vacuum

- Consistent approach to calculating jet shapes in nuclear collisions

- Medium - Induced

## Slide 5

## Z0 / Virtual Photon - tagged jets

- Calculations done by Camelia Mironov

-  A better way of tagging

- Although the rates are smaller, they are
- sufficient to pinpoint the jet interactions
- In matter

## HI@LANL – Next Era

**Unique Probes**** **
- of the
**Standard Model**** **
- in
** ****Heavy Ion Collisions**** **
- at the** **
**LHC**

- Camelia Mironov

## RHIC II vs LHC

- RHIC II
- higher luminosity
- longer running time
- flexibility for variation
-  of energy and colliding species
**LHC**
-  uniqueness due to higher sqrt(s)
**higher rates**: jets, heavy quarks
**new probes**: Z0
- excellent detection capabilities:
-  performant tracking
- 2π in azimuth (jets,..)
- Si-tracker |η|<2.5 (b-,c- physics, ...)
- good momentum resolution
- Granularity of the **Si-pixel layer+4T mag field**  ΔpT/pT < 1.5%
- For jet finding, calorimeters ση=0.028 σφ=0.032

## Need both!

**E. Shuryak: nucl-th/0609011**

- Ideea: need to tackle from both directions in order to map the QGP regimes and its properties.
- (maybe a better picture to illustrate this)

## Need both!

- pT

- pQCD

**Hydro**

- ~ 2

- ~ 6

**Soft**

- 0

**Intermediate**

- ~ 30

- GeV/c

**~250**

**Need both!**

## SO!

- Have a jet and a heavy-quarks machine, USE IT!

## Jets! ... Reconstruction

- Jet finding algorithm – full jet reconstruction, event by event
- Efficient at high-pT

- 2-particle correlation – statistical jet reconstruction
- Good at low + high pT

## Jet Measurements

**Z****0****(****μμ****)**** ****+ jet**** **
_**real baseline measurement: p**__**T**__**Z0**__**~p**__**T**__**jet  **_Needed no mather what the jet measurement.
- measure in pp and AA
- the distribution of the hadrons associated with Z0, as a function of z
- jet ‘properties’: kT,jT,etc
- ‘calibrate’ the jet finder

## Jets Measurements (Ivan’s new ideas )

- Jet radiography : intra-jet surgery
-  R      = const – vary pTmin
-  pTmin = const – vary R
- Inter-jet surgery:
**Sigma_2jets/Sigma_3jets, **measure in pp and AA

- R      – jet cone radius
- pTmin – cutt-off for the
-              hadrons in the jet

**handle on angular and energy distrib of gluons **
**	******** ****start characterizing the medium-induced bremsstrahlung spectrum**

## b, c production

- c vs b energy loss in QGP

**STAR nucl-ex/0607012**

-  c  μ+ + anything   (B.R.: 9.6%)
-  D0μ++anything (B.R.: 6.87%)
-  Dμ +anything (B.R.: 17.2%)
- b  μ+ + anything     (B.R.: 10.9%)
-  Bμ+anything   (B.R.:10.2%)

## b,c-tagged jets

-  Address the underlying hard scattering   processes and open charm production  mechanisms

**I. Vitev hep-ph/0605200**

-  Look at hadron composition of the away side

## Bibliography

- RHIC II – Heavy Flavor Working Group:
- _[http://rhicii-science.bnl.gov/heavy/doc/whitepaper/rhic2_hf_wp_july17.pdf](http://rhicii-science.bnl.gov/heavy/doc/whitepaper/rhic2_hf_wp_july17.pdf)_
- CERN – Yellow Reports

## Wht this is all about

-  The opportunity that exists for a group of
- theorists and experimentalists at LANL to
- make a major contribution to fundamental
- high energy and high energy nuclear physics
- within the Standard model and beyond

-  Use the CMS experiment at the LHC as
- opposed to more “traditional” heavy ion
- experiments

## Outline of the Talk

- The physics case for the LHC
-  Discovery of the Higgs, supersymmetry, search for extra dimensions
-  New states of matter, quark-gluon plasma, jets in nuclear collisions
- Definition of jets and jet observables
-  Historical overview, jet algorithms and jet variables
-  Calculating jet cross sections in perturbative QCD
-  Calculating jet shapes and comparison to Tevatron data
- Jets in nuclear collisions
-  The contribution of medium induced bremsstrahlung
-  Strategy for combining the vacuum and the medium-induced radiation
-  Defining a sensitive observable for the jet interactions in matter (QGP tomography)
- Leading single inclusive particles as proxies to jets
-  Light particle quenching and limitations in sensitivity
-  Dissociation: new approach to D- and B-mesons suppression in the QGP
-  Discriminating  power of charm and beauty jets - including AdS/CFT conjectures
- Conclusions

## LHC

**LHC**

**And LHCb**

- p+p @
- p+A @
- A+A @

- ALICE

- CMS

- ATLAS

**What is LHC?**

- LHC is what SSC
- should have been

## LHC capabilities: hard probes

- Hard probes: high pT and ET, particles and jets, heavy quarks and quarkonia, vector mesons and the Higgs

**LHC capabilities: hard probes**

- For reference: in pp s1/2 = 14 TeV, L ~ 1034 cm-2s-1

**I.V. hep-ph/0212109**

- CMS estimates for 106s provided by Camelia Mironov

## Planned discovery of the Higgs

**Planned discovery of the Higgs**

**J. Hogan, Nature 445 (2007)**

- Higgs
-  The remaining scalar field after the
-    spontaneous
-  The only missing SM particle

**M.Spira, Fortsch. Phys. 46 (1998)**

## Golden channels (Higgs)

**Golden channels (Higgs)**

- Branching ratios

-  Detected via:

- Jet physics as the basis for Higgs searches

## Planned discovery of Supersymmetry

**Planned discovery of Supersymmetry**

- Theoretical appeal
-  Based on tried and true symmetry
-   principles
-  No new gauge couplings
-  Unification of the coupling constants
-  Excellent candidate for cold dark
-    matter

**P. Mercadante, Braz. J. Phys. 46 (2004)**

- “I would argue that the *first discovery* at the
- LHC will not be the Higgs but supersymmetry”
-                             J. Ellis, CERN colloquium

## Discovery channels (supersymetry)

**Discovery channels (supersymetry)**

- Rich spectroscopy

-  Detected via high jet multiplicity + missing energy ( since there is lightest
-   supersymmetric particle - stable neutralino                                                             )

- The decay chain of the gluino:

- Really high (>10) jet
- multiplicities
- Understanding jets,
- jet energy flow, and
- QCD backgrounds
- is critical for discovering
- physics beyond the
- standard model

## Jet definitions

**Jet definitions**

-  Jet variables

- Jets are collimated showers of energetic particles that carry a large fraction of the energy available in the collisions

-  Transverse energy
-  (Pseudo) Rapidity
-  Angle

- R

- Jet algorithms:

-  Kt algorithm: preferred (collinear and
-   infrared safe to all orders in PQCD)
-  Cone algorithm:

## Jets from factorized PQCD

**P****c**

**P****d**

**P****c ****/ z****c**

**P****d ****/ z****d**

- X

- X

**Jets from factorized PQCD**

-  Single and double inclusive hard production
-   in PQCD - applicable from photons to heavy
-   quarks

- For jets:

-  Jet cross sections are more inclusive and therefore more robust PQCD observables

- Caveat: parton-hadron duality

- CDF studies:

## The difficult path to jet physics

**The difficult path to jet physics**

-  Exponential spectrum

-  Energy spectrum consistent with exponential soft string breaking mechanism. No indication of hard scattering (power law)

-  Fixed target experiment

**C. DeMarzo et al., NA5 Phys.Lett.B 112 (1982)**

-  Most of the HEP community doubts the model
-   of hard scattering constituents in the proton
-   (partons) around 1980

## The discovery of jets 

**Paris 1982 ****– the beginning of ****modern jet physics**

**M. Banner et al., UA2 Phys.Lett.B 118 (1982)**

-  The highest energy jets measured at the
-   Tevatron are of ET > 600 GeV

## Jet cross sections: comparison to LO and NLO PQCD

**Jet cross sections: comparison to LO and NLO PQCD**

-  Good comparison to the shape at LO.
-   Meaningful K-factor

-  Even better comparison at NLO.

**W. Horowitz, I.V., S. Wicks, in preparation**

## Jet shape variables

**Jet shape variables**

-  Much more stringent tests of the underlying PQCD theory

- r

-  **Differential jet shape**:

-  Example at CDF

## Calculating the jet shape (I)

**Calculating the jet shape (I)**

-  Definition of a “+” distribution

-  LO splitting functions

**Kinoshita, T., 1962, J. Math. Phys. 3, 650**

**Lee, T.D., and M. Nuenberg, 1964, Phys. Rev. B133, 1549**

-  Infrared safety theorem

-  QCD kernel

- Note: Kinoshita, Lee, Nauenberg does
- not guarantee collinear safety

- Obtain:                        correct at r >> 0

## Calculating the jet shape (II)

**Calculating the jet shape (II)**

-  Sudakov resummation (the way to deal with the collinear divergence)

**M.H. Seymour, Nucl. Phys. B 531 (1998)**

-  Final expression: resummed, matched, and power corrected

- Obtain:                                                             correct at r -> 0  but not r >> 0

-  Matching: correct behavior at both small and large

- R

- r

-  Including power corrections

## Comparison to Tevatron data (I)

- Calculations done by Simon Wicks

**W.Horowitz, I.V., S.Wicks, in preparation**

- CDF collaboration    ( s1/2 = 1.96 TeV, improved cone algorithm, R = 0.7   )

- Rsep - min. separation to form 2 jets

- Sensitivity to Rsep (cone separation variable)

- Sensitivity to fq (quark jet fraction)

- Fq + Fg = 1 (Theoretically calculable)

## Comparison to Tevatron data (II)

**Comparison to Tevatron data (II)**

- Calculations done by Simon Wicks

**W.Horowitz, I.V., S.Wicks, in preparation**

- CDF collaboration    ( s1/2 = 1.96 TeV, improved cone algorithm, R = 0.7   )

- Sensitivity to Q0
- (non-perturbative effects and
-  power corrections)

- Good description of the differential Tevatron jet shape data
-  Reasonable Rsep
-  Reasonable Q0

## Medium-induced bremsstrahlung

- 2

- +

- +

- +

- +

- +

- +

- +

- +

- +  ...

- +

- +

- Organizing principle!

**M.Gyulassy, P.Levai, I.V., Nucl.Phys.B594 (2001); **
**Phys.Rev.Lett.85 (2000)**

## Angular distribution to Ist order in opacity

- Angular distribution to Ist order in opacity

**Naive picture**

**Solution to first order in the mean # of scatterings**

**I.V., Phys.Lett.B 630 (2005)**

- +2Re

## Gluon energy and angular distributions 

- Conditions: central Pb+Pb at the LHC

- First order in opacity

-  Angles range from
-   to

-  Gluon energies range
-    from

## Light hadrons as proxies to jets

**I.V., Phys.Lett.B 639 (2006)**

**Light hadrons as proxies to jets**

-  Very “special” jets: atypical, sensitive
-    to hadronization effects

- Significantly different values are
- indicative of theoretical inconsistency

** **

- Single inclusive pion suppression at the LHC** **

-  High pT  suppression at the LHC can be
-    comparable and smaller than at RHIC
-  LHC quenching follows the steepness
-    of the partonic spectra
-  Reduced sensitivity to medium properties

- Running

- Fixed

**S.Wicks et al., in progress**

## Direct photon at the LHC

-  Direct photons also have limited sensitivity: isospin effects,
-    cold nuclear matter e-loss

- Prompt photons

- Fragmentation photons

- +

-  Direct photon tagging:
-   can be compromised by
-   fragmentation photons

-  Better jet interaction
-    measures?

## Z0 / Virtual Photon - tagged jets

- Calculations done by Camelia Mironov

-  A better way of tagging

- Although the rates are smaller, they are
- sufficient to pinpoint the jet interactions
- In matter

## Non-Photonic Electron / Heavy Flavor Quenching

**S. Wicks et al., (2005)**

-  Diffusion coefficient D and eventually
-  Existence of heavy heavy
-   resonances near Tc in the QGP

**Non-Photonic Electron / Heavy Flavor Quenching**

-   Langevin simulation of heavy quark
-   diffusion

**N. Armesto et al., (2006)**

**H. van Hees, R. Rapp, (2005)**

**G. Moore, D.Teaney (2005)**

- Radiative and collisional energy loss

-  Ratio:
-  Opacity           of the QGP

## Conceptually Different Approach to D / B

**Conceptually Different Approach to D / B**

** **Fragmentation and dissociation of hadrons from heavy quarks  inside the QGP

-  Problem: treated in the same way  as light quarks

-  Lowest order lightcone Fock component

## Heavy Meson Dissociation at RHIC and LHC

- Coupled rate equations_x0003_

-  The asymptotic solution in the QGP -
-   sensitive to t0~0.6 fm and expansion
-   dynamics
-  Features of energy loss
-  B-mesons as suppressed as D-mesons
-   at pT~ 15-20 GeV at the LHC

- Unique feature

## Quenching of Non-Photonic Electrons 

**Quenching of Non-Photonic Electrons **

-  B-mesons are included. They give a
-   major contribution to (e++e-)

-  Similar to light       , however, different
-   physics mechanism

-  Full semi-leptonic decays of C- and B-
-   mesons and baryons included. PDG
-   branching fractions and kinematics.
-   PYTHIA event generator

- Note on applicability

- (e++e-) to 25 GeV

- D-, B-mesons to

## The Path Forward 

-  An interesting idea       valid physics explanation

**A.Adil, I.Vitev, Phys. Lett. B (2006)**

**W.Horowitz, M. Gyulassy, (2007)**

-  To understand heavy flavor modification in the QGP we need direct and
-    separate measurements of D- and B-mesons, excellent statistics

- Measurable at RHIC

- Measurable at the LHC

- Meson
- dissociation

- String theory
- AdS/CFT

- PQCD,
- Transport

- PT [GeV]

- 10-15

- 50-100

- Never

## Conclusions

- The physics case for major involvement at LHC via CMS
-  Outstanding jet physics capabilities
-  Modern ‘new physics’ experiment
- The first measurement of jets in nuclear collisions
-  Bridging the gap between high energy and nuclear physics
-  First real measurement of the QGP-induced modification of jet properties
-  Rich phenomenology of topological jet observables
-  Significantly larger discriminating power for theoretical models
-  Solution to heavy quark puzzles from RHIC
- Jets in pp collisions
-  Higgs discovery
-  Supersymmetry discovery
-  Precision perturbative QCD
- Opportunity for LANL leadership

## Heavy Flavor Elliptic Flow and Suppression

-    Understand the structure of mesons
-    light cone wave functionsc

**A. Adil, I. Vitev, Phys.Lett.B (2007)**

-    Sensitive to the opacity of the QGP
-    and its formation time

**D. Molnar (2004)**

-    Test coalescence model fits  to the v2 of
-    light hadrons via heavy flavor

## Jet cross sections

- Calculations done by Simon Wicks

## Jet cross sections

## RHIC

** **Small probability not to radiate

- Medium properties

- LHC

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- Derivative

- Fundamental

## Hard Probes from Factorized PQCD

**P****c**

**P****d**

**P****c ****/ z****c**

**P****d ****/ z****d**

- X

- X

**Hard Probes from Factorized PQCD**

-  Single and double inclusive hard production
-   in PQCD - applicable from photons to heavy
-   quarks

-  Single and double inclusive hard production
-   in PQCD - applicable from photons to heavy
-   quarks

- Power laws:

- Quenching factor

## Cold Nuclear Matter Effects

-  Effect of cold nuclear matter energy
-    loss is equal to the doubling of the
-    parton rapidity density

-  Initial-state E-loss

- Energy scale

## Direct Photon Production at RHIC and the LHC

**Direct Photon Production at RHIC and the LHC**

** **Direct photon production calculated in
-   the  QCD factorization approach

- Prompt photons

- Fragmentation photons

- Suppressed

** **Same ratio in NLO, Wogelsang

- Determines the final-state interactions

## Cold Nuclear Matter Effects for 0 and Direct 

-  Where it starts from

-  Dynamical shadowing (coherent final
-   state scattering)
-  Cronin effect (initial state transverse
-   momentum diffusion)
-  Initial state energy loss (final state at
-   these energies - negligible)

## Direct Photon Quenching at the LHC

- Reminder: isospin and
- Initial-state energy loss
- effects

- Nuclear modification RAA()
- follows the ratio:

- Correction to the energy
- in photon-tagged jets

## Heavy Quark Production and Correlations

-  Possibility for novel studies of heavy
-    quark-triggered  (D and B) jets: hadron
-    composition of associated yields

-  Fast convergence of the perturbative
-   series

## Conceptually Different Approach to D / B

**Conceptually Different Approach to D / B**

** **Fragmentation and dissociation of hadrons from heavy quarks  inside the QGP

-  Problem: treated in the same way  as light quarks

-  Lowest order lightcone Fock component

## Heavy Meson Dissociation at RHIC and LHC

- Coupled rate equations_x0003_

-  The asymptotic solution in the QGP -
-   sensitive to t0~0.6 fm and expansion
-   dynamics
-  Features of energy loss
-  B-mesons as suppressed as D-mesons
-   at pT~ 15-20 GeV at the LHC

- Unique feature

## Quenching of Non-Photonic Electrons 

**Quenching of Non-Photonic Electrons **

-  B-mesons are included. They give a
-   major contribution to (e++e-)

-  Similar to light       , however, different
-   physics mechanism

-  Full semi-leptonic decays of C- and B-
-   mesons and baryons included. PDG
-   branching fractions and kinematics.
-   PYTHIA event generator

- Note on applicability

- (e++e-) to 25 GeV

- D-, B-mesons to

## References to the Four Contributions, Collabs.

- Light hadrons

- Energy loss

- Direct photons

- Heavy flavor

## Conclusions

- Looking forward to
- jet physics at the LHC

## Scales in Thermalized QGP (GP) 

** ****Experimental: Bjorken expansion**

** ****Theoretical: Gluon dominated plasma**

** ****Energy density**

** ****Transport coefficients (****not a good**** measure for expanding medium)**

** ****Define the average for Bjorken**

## E-loss in Back-to-Back Di-jets and Correlations 

**E-loss in Back-to-Back Di-jets and Correlations**

- Tag

- I.Vitev, Phys.Lett.B630 (2005)

-  Multi-particle modification

-  Angular gluon distribution

- Two particle suppression / enhancement in A+A reactions

- See talk by M. Brooks

## When One ≠ One

**When One ****≠**** One**

-  Theoretical results: cancellation between factor of 4 Cronin enhancement and 2- to 3-fold quenching

***N*****coll,Pb+Pb**** = 807 ****±**** 81**** **

-  Experimental findings:

**S.Bathe., LANL seminar**

**I.V., Phys.Lett.B  632 (2005) **

-   With any multiple scattering effect  there is no reason to expect

-   If one understands this in A+A collisions one should also accept this is
-    p+A collisions

## Langevin Simulation of Heavy Quark Diffusion

- Radiative energy loss is dominant except for b-quarks and very small systems

- Input in a Langevin simulation of heavy quark diffusion

**H. van Hees, I.V., R. Rapp, in preparation**

-  Drag coefficient:

-  Diffusion coefficient:

- Equilibration is imposed by Einstein’s
- fluctuation-dissipation relation:

## Transport + Quenching Approach

-  The suppression and v2 are large when e-loss and q-resonance interactions are
-   combined
-  Normal hierarchy: c quarks are significantly more suppressed than b-quarks

- Numerical results for heavy quark diffusion

**H. van Hees, I.V., R. Rapp, in preparation**

- Results are preliminary

## Wicks et al. 

**Wicks et al. **

**How do you build                      **
**from T =  400 MeV**

**LHC: from T =  1 GeV**
** **

**Wang**