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Mark Strikman of Penn State University presented a notable proposal of a new sum rule. The workshop devoted a full day to contributions dealing with the physics of QCD at various extremes, such as at the lowest parton fractional momenta low-x QCD and at the highest densities achievable, e. Various other talks covered the latest experimental and theoretical developments in each of these two active research areas of the strong interaction, all with prospects at the LHC very much in mind.
Presentations on experimental developments highlighted the challenge of diffractive physics and the way that it relies on a particularly close symbiosis of measurement and theory. The impressive precision of the data reveals beautiful features that demonstrate the quark and gluon components of the t-channel i. Taking advantage of the presence of the unique breadth of expertise present at an EDS meeting, a panel discussion took place between representatives of theory and experiments, moderated by Karsten Eggert of Case Western Reserve University and CERN.
It provided the opportunity to exchange ideas about which measurements to carry out first at the LHC, how to create synergies between different experiments and about future upgrade possibilities for the forward proton detectors. Several new ideas for possible measurements at the LHC were proposed and discussed.
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Stay tuned for more. News News Topic: Experiments. In the heart of CMS Hidden inside several layers of subdetectors, the pixel detector surrounding the beam pipe is the core of the experiment, as it is the closest to the particle-collision point. Fast-forward to the future Some of the existing detectors would not perform well enough during the HL-LHC phase, as the number of proton—proton collisions produced in the HL-LHC will be ten times higher than that originally planned for the CMS experiment.
Related Articles. LS2 Report: the complex case of vacuums in th It should be emphasized that analyticity see Eq. Certainly, at the very high-energy end it violates unitarity.
We now see that it does not have the proper shape to satisfy analyticity at the lower-energy end. Clearly, this form requires substantial ad hoc structural changes to join on to the low-energy constraints. This is due to employing the low-energy analyticity constraints, as well as using a sifted data set. Using extensive air showers, cosmic ray experiments can measure the penetration in the atmosphere of these very high-energy protons—however, extracting proton—proton cross sections from cosmic ray observations is far from straightforward .
By a variety of experimental techniques, extensive air shower experiments map the atmospheric depth at which cosmic ray initiated showers develop.
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Brief description of extensive air shower measurements We now give a brief description of extensive air showers development. A high-energy particle proton, alpha particle, iron nucleus, etc. This encounter initiates a cascade of secondary particles—called an extensive air shower—which keeps growing in size until ionization losses exceed bremmstrahlung losses. The depth in the atmosphere at which this turnover in size takes place is called Xmax , the shower maximum.
From here on down into the atmosphere, the shower size diminishes until secondary particle energies are below particle production thresholds. Figure taken from Ref. Instead, what is measured is the Xmax distribution of extensive air showers. An example of his computer-generated Xmax distribution is shown in Fig. A computer-generated Xmax distribution. The latter effect is taken into account in Eq.
The departure of k from unity depends on the inclusive particle production cross sections for nucleon and meson interactions in the light nuclear targets of the atmosphere and their energy dependences. First, one calculates the p—air total cross section from the production cross section inferred in Eq. The subsequent N M. Also plotted in Fig. It is at this point important to recall Eq. The measured depth Xmax at which a shower reaches maximum development in the atmosphere, which is the basis of the cross section measurement in Ref. Its predicted values range from 1.
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The comparison between prediction and experiment in Fig. Using the calculations from Fig. The large dot on this curve is the c. These converted cosmic ray values are shown in Fig. Clearly, all of the cosmic ray data are too high, compared to accelerator predictions. Because the parametrization is both unitary and analytic, its high-energy predictions are effectively model-independent, if one requires that the proton asymptotically becomes a black disk.
In prod Fig. The solid line is pp and the dotted line is pp. A plot of the predicted total pp cross section, in mb vs. Letting k be a free parameter in M. The solid line is for pp and the dotted line is for pp. By combining the results of Figs. Since the cosmic ray spectrum varies very rapidly with energy, there must be allowance for systematic errors in k due to possible energy misassignments. The increase of the total cross section with energy to a black disk of soft partons is the shadow of increased particle production which is modeled in SYBILL by the production of mini -jets in QCD.
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The difference between the k values of 1. In most other codes QGSjet  , it is remedied by the use of an energy-dependent transverse momentum cut-off in the computation of the mini-jet production cross section. As demonstrated in Fig. The distribution in Xmax is the result of the convolution of the X1 distribution into the X distribution. As emphasized earlier, neither the X nor the X1 distribution can be measured in air shower experiments. However, the X distribution can be simulated using Monte Carlo data, utilizing various air shower and particle production models for some details about generating Monte Carlo extensive air showers, see Pryke .
HiRes X distribution. The X distribution, using Monte Carlo data. A computer-simulated X1 distribution, taken from Ref. Shown in Fig. The Monte Carlo data used for this exercise was taken from the shower library. The model sensitivity is p. The number of showers in a bin is plotted against the logarithm of proton primary energy, in eV. Finally, Fig.
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The energy distribution of the experimental extensive air showers in HiRes. Shown are the number of showers per bin vs. The solid line is a hybrid curve which requires some explanation. See the text for details.
The HiRes measurement is taken directly from Ref. Using the results of Fig.